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C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 2. Isolation of an anti-SRBC antibody-secreting cell clone. Activity was revealed by a halo of haemolysed SRBC. Direct plaques given by: a, 6,000 hybrid cells Sp-1; b, clones grown in soft agar from an inoculum of 2,000 Sp-1 cells; c, recloning of one of the positive clones Sp-1/7; d, higher magnification of a pos... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 3. Autoradiograph of labelled components secreted by anti-SRBC specific hybrid lines. Fractionation before (B) and after (A) reduction was by IEF. pH gradient was 5.0 (bottom) to 9.0 (top) in the presence of 6 M urea. Other conditions as in Fig. 1. Supernatants from: a, hybrid clone Sp-1/7-2; b, hybrid clone Sp-2/... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The uncloned population of P3-spleen hybrid cells seems quite heterogeneous. Using suitable detection procedures it should be possible to isolate tissue culture cell lines making different classes of antibody. To facilitate our studies we have used a myeloma parental line which itself produced an Ig. Variants in which ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Received May 14; accepted June 26, 1975.
References:
Potter, M., Physiol. Rev., 52, 631-719 (1972).
Horibata, K., and Harris, A. W., Expl Cell Res., 60, 61-70 (1970).
Milstein, C., and Munro, A. J., in Defence and Recognition (edit. by Porter, R. R.), 199-228 (MTP Int. Rev. Sci., Butterworth, London, 1973).
Cotton, R... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 这些实验结果最初来自于由大鼠细胞和小鼠细胞组成的异源系统,现在已经在来源于同一个小鼠品系的两个骨髓瘤融合细胞系中得到证实。这些结果也为了解分泌抗体的杂交系的来源提供了基础,因为该杂交系亲本细胞之一是可分泌抗体的脾细胞。 英文
在实验中我们使用了两个BALB/c小鼠来源的骨髓瘤细胞系。P1Bul细胞具有5-溴-2′-脱氧尿嘧啶抗性[4],在选择性培养基(HAT,参考文献6)中不生长,并且可以分泌一种骨髓瘤蛋白——Adj PC5,属于IgG2A(κ)亚型(参考文献1)。这种蛋白的轻、重链合成并不是均衡的,也可以检测到分泌的游离免疫球蛋白轻链。另一个细胞系P3-X63Ag8来自于P3细胞[2],可以耐受20 μg·ml–1的8-氮鸟嘌呤,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 另一方面,两个亲本的重链属于不同的亚型,因此我们预测可以通过等电聚焦实验来确定是否发生了VH–CH的错误连接。在我们研究的克隆中,并没有检测到这种错误连接的发生,即使错误连接确实发生,其概率也是非常低的。我们的结论是,在同源性细胞杂交实验中(不同物种间的细胞杂交也是一样的),V–C的整合并不是发生在细胞质中的事件的结果,而是在转录的过程中DNA发生易位或者重排导致的。整合mRNA分子的发现[11],以及在已经定型的细胞中V片段或C片段缺失的重链(存在功能缺陷)的发现[12]都支持了这一结论。 英文
上述P3-X63Ag8细胞系在HAT培养基中不能存活。从免疫后的小鼠中获得的脾细胞也会在生长培养基中死去。当这两种细胞在仙台病毒的作用下... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 图4也进一步证明了这一点:特异性抗IgM的抗体可以抑制绵羊红细胞的裂解。等电聚焦实验通常不能分辨19S的IgM分子。因此,在非还原的样品a中(图3B)IgM应该没有显现出来,不过在还原之后μ链应该会显示在图中(样品a,图3A)。 英文
图4. 杂交细胞克隆Sp-1/7-2分泌的抗体抑制红细胞溶解。反应在9 cm培养皿中进行。在5 ml 0.6%的琼脂糖(溶解在PBS中)中按1/80(体积比)加入了绵羊红细胞。中间的孔中含有2.5 μl 20倍浓缩的Sp-1/7-2培养上清和2.5 μl小鼠血清。a,绵羊抗小鼠巨球蛋白(MOPC 104E,范斯坦博士);b,绵羊抗MOPC 21(P3)IgG1与Adj PC-5结合;c,绵羊抗Adj... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The International Afar Research Expedition has now recovered remains of twelve hominid individuals from geological deposits estimated to be ~3.0 Myr in Hadar, Ethiopia. A partial skeleton represents the most complete hominid known from this period. The collection suggests that Homo and Australopithecus coexisted as ear... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | All hominid fossils (Table 1), and most of the vertebrate material, were surface finds, although some small scale excavation and sieving operations were undertaken. A painted marker was placed at each palaeontological locality, each located on a map and the geological section carefully examined to determine the horizon... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Both proximal femora lack heads and necks. The left is best preserved with the shaft broken ~ 38.0 mm below the lesser trochanter. From the remaining portions of the femora it is clear that the neck is flattened anteroposteriorly and that its cross section is oval. There is an indication of trochanteric flare, the troc... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | A heavily eroded temporal fragment (AL 166‒9) constitutes the only other hominid discovery from the 1973 field season. The specimen derives from a sandstone horizon a few metres stratigraphically above the level of the postcranial material. The temporal has been extensively eroded, with most of the petrous portion brok... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | somewhat deeper posteriorly. 中文
In lateral view this specimen exhibits pronounced alveolar prognathism. The zygomatic root is situated above the first molar, the maxillary sinuses are large and the lower nasal margin is guttered. 中文
The right half maxilla is smaller in size and is less complete, with C‒M3, as well as b... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | A right mandibular fragment (AL 188‒1) containing M2‒M3 and roots of P3‒M1, was collected from a sandstone horizon immediately below KHT. The molars are heavily worn. The mandible exhibits some wind abrasion, but it is possible to estimate a thickness of 20.7 mm and a depth of ~32.0 mm in the region of M1. 中文
AL 277‒1,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | During screening operations, three additional teeth were located at this locality: a right I2 (AL 198‒18), a left I2 (AL 198‒17a) and a left I1 (AL 198‒17b). The interproximal facets on the upper incisors match perfectly, suggesting that they are from the same individual. Because of the close association of these teeth... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | the recovery of all bone fragments from the site. Laboratory preparation and analysis has only just begun, and in this report it is possible to mention only a few salient points. 中文
The mandible is not heavily built; it is 30.0 mm deep and 19.0 mm thick in the region of M1. The M3s are fully erupted and occlusal wear f... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | A complete left femur is associated with the innominate. But the distal portion is badly crushed. Its total length has been estimated at 280 mm but may be slightly revised when the distal end is reconstructed. The femur has minimal trochanteric flare, the neck is anteroposteriorly flattened, an intertrochanteric line i... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Sterkfontein. 中文
Previously the 1973 postcranial material has not been assigned to a taxon. It is now clear that it should probably be included in the same category as the AL 288 specimen because of the striking similarity of the proximal tibial fragments in size and morphology as well as the preserved femoral fragment... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | the genus Homo10,12. It must be recognized that other aspects of the AL 200 maxilla are “primitive”, such as the guttered nasal margin and the alveolar prognathism. 中文
The AL 266‒1 and AL 277‒1 mandibles resemble, in details of the dentition and mandibular morphology, other specimens assigned to Homo, such as OH 7 (ref... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Johanson, D. C., Taieb, M., and Coppens, Y., in African Hominidae of the Plio-Pleistocene (edit. by Jolly, C. L.,) (Duckworth, London, in the press).
Clark, J., Beerbower, J. R., and Kietzke, K. K., Fieldiana, Geol. Mem., 5, 1-158 (1957).
Kern, H. M., and Straus, W. L., Am. J. Phys. Anthrop., 7(1), 53-66 (1949).
Heiple... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
1973年人科动物的发现
1973年10月30日在哈达尔地区首次发现了人科动物化石,当时从一处泥岩层采集到了四个相关联的腿骨残段(AL 128和AL 129)。这些标本包括残断的左右股骨近端以及与其相关的右侧胫骨近端及股骨远端。它们彼此都很靠近,且股骨近端的形态和尺寸都很相似,这强有力地说明它们来自同一个体。该标本提供了一个完整的膝关节,这将大大增加我们对早期人科动物的这一重要关节的生物力学认识(见图3)。 英文
图3. AL 129–1a和1c的前面观。
英文
两块股骨近端都缺少头部和颈部。左股骨近端保存最好,在小转子下约38.0 mm的骨干处有断裂。从股骨的其余部分看,股骨颈在前后方向上很明显是扁平的,其横截面呈椭圆... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 下颌骨显示出某种程度的风化,但是可以估计出在M1处的厚度为20.7 mm,深度约为32.0 mm。 英文
AL 277–1是一块带有C~M2和I1~I2牙槽的残破不全的左下颌骨,它们是从砂岩层挖掘出来的。在中线右侧及M2之后发生了断裂。咬合面磨损严重,犬齿已经磨平。前部断裂让人感觉下颌骨深,P3远端深约41.0 mm。突出的门齿后平面保存下来,还有一个明显的下颌圆枕。联合部的下表面变平,具有明显的颏棘。下颌骨显示出轻微的外翻现象。 英文
在泥岩中发现并复原了一块有趣的左半部分下颌骨(AL 198–1),其位置在地层上与AL 199和AL 200相当。该标本在接近中线处断裂,I1牙槽和I2牙根保存下来。C~P4和M1~M2也保存下来,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 确切地说,骨盆的尺寸以及在某种程度上的形态与Sts14颇为相似。但是,较浅的髋臼和相对高的髂骨表明其与斯泰克方丹标本有一定差异,并且AL 288标本可能反映了一种更为原始的状态。属于同一个体的V形下颌骨值得我们注意。利基[10]引起了我们对下颌骨形状的注意,并且提出KNM–ER 1482(肯尼亚国家博物馆,鲁道夫湖以东)和Omo 18应该被归为原始人类标本,因为他们也具有V形的下颌。如果证明这是一种具有判别性的特征,那么AL 288有可能保留了比南方古猿非洲种更加原始的特征,这些特征正是从斯泰克方丹的标本中辨认出来的。 英文
在此之前,1973年得到的颅后材料没有被划入到任何分类单元中。现在很明显,它们很可能被划入与AL 288标本... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | clamp is a means of maintaining a fixed voltage across the membrane of the cells being studied. The authors Bert Sakmann and Erwin Neher were awarded the Nobel Prize for Medicine in 1991. 中文
THE ionic channel associated with the acetylcholine (ACh) receptor at the neuromuscular junction of skeletal muscle fibres is pro... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | cholinergic agonist at micromolar concentrations. Its interior is connected to the input of a virtual-ground circuit, which clamps the potential inside the pipette to ground and at the same time measures current flowing through the pipette, that is, through the patch of membrane covered by the pipette opening. The inte... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | pipette and membrane. To minimize the leakage conductance, the muscle was treated with collagenase and protease9. This enzyme treatment digested connective tissue and the basement membrane, thereby enabling closer contact between glass and membrane. At the same time, however, it made the membrane fragile and more sensi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | with the degree of hypersensitivity of the muscle membrane; an amplitude dependent on membrane potential as predicted by noise analysis; a mean length or channel open time, which should depend on voltage in a characteristic manner2; pharmacological specificity with different mean open times for different cholinergic ag... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | delivered from a pipette filled with 1 M SubCh (40 MΩ pipette resistance, 10 nA bucking current, sensitivity measured at resting potential). Pooled data from eight experiments. Broken line represents linear regression. c, Amplitude histogram of membrane current. Current traces were digitalised and baselines fitted by e... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | arise if not all of the channels are located ideally in the central region of the pipette opening. Current contributions from peripherally located channels would only partially be picked up by the pipette. This source of error is also likely to lead to an underestimate of channel size if the pipette seal is not optimal... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The results obtained so far, especially the pharmacological specificity, lead us to conclude that the observed conductance changes are indeed recordings of single-channel currents. They are consistent with the conclusions drawn from statistical analysis of endplate current fluctuations, and show that current contributi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Neher, E., and Lux, H. D., Pflügers Arch. ges. Physiol., 311, 272-277 (1969).
Fishman, H. M., Proc. Natl. Acad. Sci. U.S.A., 70, 876-879 (1973).
Takeuchi, A., and Takeuchi, N., J. Neurophysiol., 22, 395-411 (1959).
Betz, W., and Sakmann, B., J. Physiol., Lond., 230, 673-688 (1973).
Neher, E., and Sakmann, B., Pflügers ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 只有当管和膜接触后管内和室间的电导率降低到1/4或更多时,才能分辨出不连续的电导率变化。为了将泄漏电导率降到最低,肌肉都经过了胶原酶和蛋白酶的处理[9],结缔组织和基膜中的胶原得以消化,从而使玻璃和膜之间可以更加紧密的接触。然而,与此同时,这样的处理也使得膜变得易碎,且对插进的管造成的破坏更敏感。但是,这并没有改变纤维对ACh的敏感性,也没有改变ACh诱导的电导率出现波动的特性(内尔和萨克曼未发表数据)。 英文
所有实验都在去神经后的超敏肌纤维的突触外区域进行。在这些区域都表现出对ACh的一致敏感性,这大大提高了所研究的膜片上能发生激动剂诱导的电导率变化的可能性。突触外的去神经肌肉纤维ACh通道的平均开放时间比终板通道的开放时期长约... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
对于记录的电流值的时间分析,一部分来自于对单个通道长度的测定,其值为40~50次测量结果的平均值,另一部分来源于对记录的电流的能谱分析。在后种情况下,可以通过洛伦兹谱的截止频率ƒ0估算平均开放时间τ(或脉冲时长),其关系式为τ=1/(2πƒ0)。两种方法所得的平均开放时间值在±30%的误差范围以内是一致的。用SubCh作为激动剂,温度为8°C时,-120 mV下,开放时间为45±3 ms(n=11);-80 mV下,开放时间是28±3 ms(n=14)。这些值大约是由噪音分析所得到的终板通道平均开放时间的3倍[15]。但是值得注意的是,已经通过常规的噪音分析法独立地测定了关于终板值,在额外的连接点处,通道开放期被延长了3~5倍... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | First-order difference equations arise in many contexts in the biological, economic and social sciences. Such equations, even though simple and deterministic, can exhibit a surprising array of dynamical behaviour, from stable points, to a bifurcating hierarchy of stable cycles, to apparently random fluctuations. There ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Second, I indicate some of the interesting mathematical questions which do not seem to be fully resolved. Some of these problems are of a practical kind, to do with providing a probabilistic description for trajectories which seem random, even though their underlying structure is deterministic. Other problems are of in... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | One of the simplest systems an ecologist can study is a seasonally breeding population in which generations do not overlap1-4. Many natural populations, particularly among temperate zone insects (including many economically important crop and orchard pests), are of this kind. In this situation, the observational data w... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | In many of these contexts, and for biological populations in particular, there is a tendency for the variable X to increase from one generation to the next when it is small, and for it to decrease when it is large. That is, the nonlinear function F(X) often has the following properties: F(0)=0; F(X) increases monotonic... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | becomes extinct. 中文
Fig. 1. A typical form for the relationship between Xt+1 and Xt described by equation (1). The curves are for equation (3), with a=2.707 (a); and a=3.414 (b). The dashed lines indicate the slope at the “fixed points” where F(X) intersects the 45° line: for the case a this slope is less steep than –... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | An equivalent graphical method is to find the points where the curve F(X) that maps Xt into Xt+1 intersects the 45° line, Xt+1=Xt , which corresponds to the ideal nirvana of zero population growth; see Fig. 1. For the single-hump curves discussed above, and exemplified by equations (3) and (4), there are two such point... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 2. The map relating Xt+2 to Xt , obtained by two iterations of equation (3). This figure is for the case (a) of Fig.1, a=2.707: the basic fixed point is stable, and it is the only point at which F(2)(X) intersects the 45° line (where its slope, shown by the dashed line, is less steep than 45°).
中文
Fig. 3. As fo... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | period 2 appear, as illustrated in Fig. 3. 中文
In short, as the nonlinear function F(X) in equation (1) becomes more steeply humped, the basic fixed point X* may become unstable. At exactly the stage when this occurs, there are born two new and initially stable fixed points of period 2, between which the system alternat... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 4. This figure illustrates some of the stable (——) and unstable (- - - -) fixed points of various periods that can arise by bifurcation processes in equation (1) in general, and equation (3) in particular. To the left, the basic stable fixed point becomes unstable and gives rise by a succession of pitchfork bifurc... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | As the parameter increases beyond the critical value, at first all these cycles have even periods, with Xt alternating up and down between values above, and values below, the fixed point X*. Although these cycles may in fact be very complicated (having a non-degenerate period of, say, 5,726 points before repeating), th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | As is made clear by Tables 3 and 4 below, any one particular stable cycle is likely to occupy an extraordinarily narrow window of parameter values. This fact, coupled with the long time it is likely to take for transients associated with the initial conditions to damp out, means that in practice the unique cycle is unl... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The general process is illustrated in Fig. 5, which shows how period 3 cycles originate. By an obvious extension of the notation introduced in equation (8), populations three generations apart are related by
Xt+3=F(3)(Xt)
(11)
If the hump in F(X) is sufficiently steep, the threefold iteration will produce a function F(... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | There are, therefore, two basic kinds of bifurcation processes1,4 for first order difference equations. Truly new cycles of period k arise in pairs (one stable, one unstable) as the hills and valleys of higher iterates of F(X) move, respectively, up and down to intercept the 45° line, as typified by Fig. 5. Such cycles... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | each value of the parameter in F(X). The entire range of parameter values (1<a<4 in equation (3), 0<r in equation (4)) may thus be regarded as made up of infinitely many windows of parameter values—some large, some unimaginably small—each corresponding to a single one of these basic dynamical units. Tables 3 and 4, bel... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | non-degenerate points of basic period k, as listed in the second row of Table 2. More sophisticated ways of arriving at this result are given elsewhere13,14,16,22,30,31. 中文
Table 2. Catalogue of the number of periodic points, and of the various cycles (with periods k=1 up to 12), arising from equation (1) with a singl... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Returning to the example of period 6, we have already noted the five degenerate cycles whose periods are submultiples of 6. The remaining 54 points are parcelled out into one cycle of period 6 which arises as the harmonic of the only stable three-point cycle, and four distinct pairs of period 6 cycles (that is, four in... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Such catalogues of the total number of fixed points, and of their order of appearance, are relatively easy to construct. For any particular function F(X), the numerical task of finding the windows of parameter values wherein any one cycle or its harmonics is stable is, in contrast, relatively tedious and inelegant. Bef... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 中文
For each basic cycle of period k (as catalogued in the last row of Table 2), it is more interesting to know the parameter values at which: (1) the cycle first appears (by tangent bifurcation); (2) the basic cycle becomes unstable (giving rise by successive pitchfork bifurcations to a cascade of harmonics of periods ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | a fairly large period, and moreover it will typically take many thousands of generations before the transients associated with the initial conditions are damped out: thus the density plot produced by numerical simulations usually looks like a sample of points taken from some continuous distribution. 中文
An especially in... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Such an effectively stochastic description of the dynamical properties of equation (4) for large r has been provided28, albeit by tactical tricks peculiar to that equation rather than by any general method. As r increases beyond about 3, the trajectories generated by this equation are, to an increasingly good approxima... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Non-analytical functions F(X) in which the hump is in fact a spike provide an interesting special case. Here we may imagine spikey hills and valleys moving to intercept the 45°line in Fig. 5, and it may be that both the cycles born by tangent bifurcation are unstable from the outset (one having λ(k)>1, the other λ(k)<–... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | a=3.67.. (compare the first column in Table 1). 中文
These eccentricities of behaviour manifested by non-analytical functions may be of interest for exploring formal questions in ergodic theory. I think, however, that they have no relevance to models in the biological and social sciences, where functions such as F(X) sho... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | deterministic population growth relationship such as equation (1). This point is discussed more fully and carefully elsewhere1. 中文
Alternatively, it may be observed that in the chaotic regime arbitrarily close initial conditions can lead to trajectories which, after a sufficiently long time, diverge widely. This means ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | A more down-to-earth application is possible in the use of equation (1) to fit data1,2,3,38,39,43 on biological populations with discrete, non-overlapping generations, as is the case for many temperate zone arthropods. Figure 6 shows the parameter values λ and β that are estimated39 for 24 natural populations and 4 lab... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Pairs of coupled, first-order difference equations (equivalent to a single second-order equation) have been investigated in several contexts4,44-46, particularly in the study of temperate zone arthropod prey—predator systems2-4,23,47. In these two-dimensional systems, the complications in the dynamical behaviour are fu... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | for equation (1). 中文
An explicit and rather surprising example of a system which has recently been studied from this viewpoint is the ordinary differential equations used in ecology to describe competing species. For one or two species these systems are very tame: dynamic trajectories will converge on some stable equil... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | I would therefore urge that people be introduced to, say, equation (3) early in their mathematical education. This equation can be studied phenomenologically by iterating it on a calculator, or even by hand. Its study does not involve as much conceptual sophistication as does elementary calculus. Such study would great... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Chaundy, T. W., and Phillips, E., Q. J. Math. Oxford, 7, 74-80 (1936).
Myrberg, P. J., Ann. Akad. Sc. Fennicae, A, I, No. 336/3 (1963).
Myrberg, P. J., Ann. Akad. Sc. Fennicae, A, I, No. 259 (1958).
Lorenz, E. N., J. Atmos. Sci., 20, 130-141 (1963); Tellus, 16, 1-11 (1964).
Metropolis, N., Stein, M. L., and Stein, P. R... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Landau, L. D., and Lifshitz, E. M., Fluid Mechanics (Pergamon, London, 1959).
Martin, P. C., Proc, Int. Conf. On Statistical Physics, 1975, Budapest (Hungarian Acad. Sci., Budapest, in the press).
Southwood, T. R. E., in Insects, Science and Society (edit. by Pimentel, D.), 151-199 (Academic, New York, 1975).
Metropoli... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 这些应用包括从抽象的隐喻(如用从一个稳定点到“混沌”的转变来类比流体中湍流的出现)到生物学种群的动力学行为模型(人们可以设法利用野外数据或实验数据来估计差分方程中的参数值)。 英文
第四,本文还包括了对上述一系列动力学行为——稳定点、稳定循环、混沌——可以在二阶或更高阶差分方程(也就是说,二维或更高维,两个或者多个相互作用的物种)中出现的文献的一个极为简略的综述。在这些情况下,混沌的出现通常不需要那么严格的非线性性质。为此,我还对微分方程进行了探讨。看起来,处理混沌行为需要的是一个三维的一阶常微分方程组。 英文
这篇综述性文章以一个热忱的呼吁作为结束,即将这些差分方程引入到初等数学课程中,以便让学生看到简单的非线性方程会呈现复杂的问... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 对于单一物种种群在高密度时受一种流行病影响的情况,该模型看起来是合理的[28]。方程(4)中的函数F(X)比方程(3)中的稍微复杂一些,但作为补偿,其优势在于,对于所有X>0的范围内,局域稳定即意味着全局稳定[1]。 英文
(3)和(4)两种形式绝不是能够从生态学文献中精选出来的形如方程(1)的单峰函数F(X)的全部可能。梅和奥斯特[1]给出了这样一个相当完整的目录,并且都附有参考文献。梅特罗波利斯等人[16]给出了其他类似的数学函数。至于F(X)的其他形式,将会在“数学方面的好奇心”这一标题下探讨。 英文
方程(1)的动力学性质
利用代数方法,令Xt+1=Xt=X*,即可求出方程(1)中X的可能的常数解,即平衡值(或“不动点”),... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | (两点处的斜率很明显是相同的[1,20],更一般地,对于周期为k的循环,所有k个点处的斜率都是相同的。)不仅如此,通过想象图2与图3之间的过渡阶段可以知道,这个确定稳定性的斜率在2点循环刚产生时的值是λ=+1,继而随着F(X)的峰逐渐变陡,经由零逐渐减少到λ=-1。超过该点之后,周期为2的各点将会依次变得不稳定,并且产生分岔而形成周期为4的初始稳定循环。照此方式,依次可以产生周期为8的循环,进而产生一个周期为16, 32, 64, ..., 2n的稳定循环的分岔谱系。在各种情况下,周期为k的稳定循环逐渐变得不稳定,同时产生分岔而形成周期为2k的新初始稳定循环,其方式基本上与对k=1的情况所概括的过程相类似。目前,参考文献1包含了更为... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 这些性质可以通过图像方法而定性地理解,并且对于方程(1)中任何行为良好的函数F(X)都是普遍适用的。 英文
现在我们要对解析函数就混沌区域中的数学结构进行更为详细的探讨,继而对上面涉及的实际问题加以讨论,并对非解析函数(如表1右侧两列中的函数)所呈现出的行为特性加以考察。 英文
表1. 对方程(1)中各种“单峰”函数F(X)在混沌区域的行为方式的总结,区分出一般性的动力学性质与非一般性的动力学性质
* 在这个a值以下,X=0是稳定的。
† 当a值超过此值后,所有的解都被吸引到–∞。
‡ 事实上,当r或b变得足够大时,X将会变得非常小以致等价于0,从而导致生物学种群模型中的灭绝。
英文
混沌区域的精细结构
我们已经看到初始不动点X... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
这些各式各样的循环在相关参数值的区间中是如何分布的呢?就我所知,至少有6组人曾经独立地回答过这个问题,他们曾经在组合论[18,30]、数值分析[13,14]、种群生物学[1]以及(广义的)动力系统理论[22,31]等不同背景下审视过这个问题。 英文
一种简单的方法(优点是不需要技术性工具,缺点是过于粗略)是,首先要回答下面的问题:可以有多少个周期为k的点?也就是说,方程
可以有多少个不同的解?如果函数F(X)具有充分陡峭的峰,正如当参数值充分大时它将会呈现出的那样,每次相继的迭代都会使峰的数目加倍,因此,F(k)(X)有2k–1个峰。对于足够大的参数值,所有这些峰和谷都会与45°线相交,产生2k个周期为k的不动点。它们被列于... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 第一个奇数周期的循环当α值满足以下方程时出现[21,31]:
X*(α)=F(2)(Xmax(α))
(13)
英文
如同前面已经提到的,另一个临界值是周期为3的循环首次出现的位置。这个参数值可以从方程(1)三次迭代的解中通过数值方法得到。对于方程(3),它就是[14]。 英文
迈尔伯格[13](对于全部k≤10)和梅特罗波利斯等[16](对于全部k≤7)给出了关于方程(3)中稳定循环的数值信息。他们没有给出参数值窗口,而是给出了使得一个给定循环最大程度稳定的单独值。也就是说,使得确定稳定性的F(k)(X)斜率为0(λ(k)=0)的a的值。由于k次迭代映射F(k)的斜率在周期为k的循环上的任意一点处都恰好等于在该循环上每个点处F(... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 前者对于大的r几乎是周期性的“爆发”,将很多个代分隔开;后者当a→4时与伯努利抛币序列没有什么区别。 英文
数学方面的好奇心
如同前面已讨论的,贯穿混沌区域的稳定循环序列存在的本质的原因是,当每次通过切分岔而新生成一对循环时(见图5),其中一个开始时是稳定的,由光滑的峰和谷与45°线相交而产生。对于解析函数F(X),仅有的能够使密度图或“不变测度”为连续并且真正遍历的参数值都位于谐振的累加点处,这些累加点将一个稳定循环与后一个循环分隔开。这些例外的参数值已经找到了用途,如当a=4时,使用方程(3)作为随机数生成器[34,35]:在区间0<X<1中,它具有与成正比的连续密度函数。 英文
其峰实际上是一个尖峰的非解析函数F(X),提供了... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
流体的湍流提供了一个经典实例,将一系列确定方程(纳维-斯托克斯方程组)中的一个参数(雷诺数)加以调节,流体运动就能够从某种稳定状态(如层流)发生突变而进入一个显然随机的、混沌的区域。作为对这一过程的数学隐喻,已经提出了很多种基于纳维-斯托克斯微分方程组的模型[15,40,41]。在最近一份关于湍流理论的综述中,马丁[42]注意到一维差分方程(1)对于这个问题可能是有帮助的。与早先的模型[15,40,41]相比,它的不足在于其数学隐喻意义更为抽象,而其优势则是提供了一份动力学行为谱系,虽然更为复杂,但更适合于分析研究。 英文
一个更为实际的应用是,有可能利用方程(1)来处理具有离散和非重叠世代的生物学种群数据[1,2,3,38,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 这个方程可以通过计算器,甚至手算的方式,迭代进行唯象研究。对它的研究不像初等微积分那样涉及很多概念意义上的细微精妙。这样的学习将会大大丰富学生对于非线性系统的直觉。 英文
不仅在研究中,而且在政治和经济领域的日常生活中,如果有更多的人认识到简单的非线性系统并不一定具有简单的动力学性质,那么我们就会生活得更加舒适。 英文
霍彭施泰特、于佩尔、米斯、普雷斯顿、斯梅尔、约克,特别是奥斯特,给了我很大的帮助。本研究部分得到了美国国家科学基金会的支持。 英文
(王耀杨 翻译;李典谟 审稿)
Australopithecus, Homo erectus and the Single Species Hypothesis
R. E. F. Le... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Among the variety of hypotheses put forward to accommodate the evidence in an evolutionary framework, the most explicit and directly simple is the single species hypothesis2. This hypothesis rests on the assumption that dependence upon tools was the primary hominid adaptation that enabled expansion into open country en... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The cranium is large (glabella to inion/opisthocranion is 183 mm) with large projecting supraorbital tori and little postorbital constriction (minimum postorbital breadth 91 mm). There is a marked postglabellar sulcus and the frontal squama rises steeply from behind it to reach vertex at bregma. The skull decreases in ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | KNM-ER 729 (ref. 1) was excavated in 1971 from the base of the Middle Tuff and KNM-ER 3230 (ref. 6) from the upper part of the BBS complex. Other, more incomplete, specimens of robust Australopithecus mandibles have come from the higher levels of the Formation between the Karari/Chari and Koobi Fora/BBS tuffs. The radi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | morphologies over long periods of time. 中文
We thank the Museum Trustees of Kenya and the National Museums of Kenya for access to material and facilities and the National Geographic Society for support. The NSF supported A.C.W. We also thank colleagues who helped with suggestions and observations on this paper. 中文
(261,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 该假说的一个很好的阐释[3]是,对文化更多更有效的依赖促使早期人科动物的一些基本特征发生了改变,包括直立行走、减小的犬齿尺寸以及生理成熟的推迟。这个基本的早期人科动物文化适应的假设与竞争排他原理[4,5]联系在一起,推导出以下结论,两种或更多种人科动物不可能有重叠的生活分布区。而在这里我们将提供确切证据表明在库比福勒地区同时生活着两个人科动物物种。 英文
在库比福勒组上段的地层中就地发现了一个成年颅骨,编号KNM-ER 3733(参考文献6)[7]。地层位置上,沉积物位于KBS与库比福勒/BBS凝灰岩之间。颅骨包括齐全的头盖骨与大量面部骨骼(包括鼻骨与颧骨)。几乎完整的前部牙齿齿槽,前臼齿和臼齿的样本也都保存了下来。第三臼齿在石化前... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
(田晓阳 翻译;刘武 邢松 审稿)
Fossil Hominids from the Laetolil Beds
M. D. Leakey et al.
Editor’s Note
The Laetolil Beds are deposits of volcanic rocks and ash-falls 30 miles south of Olduvai. Fossils had been gathered there since the 1930s—the Leakeys had collected there on three occasions—but the absolute ages of the fossils... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | carried out on samples of biotite obtained during the 1975 field season. In 1974, however, lava flows which unconformably overlie the Laetolil Beds had been dated by G. H. C. at 2.4 Myr. 中文
We now report evidence that fossiliferous deposits of several different ages exist in the Laetolil area and that specimens found o... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Interest in the area was renewed in 1974 after the discovery by George Dove of fossil equid and bovid teeth in the bed of the Gagjingero river, which drains into Lake Masek at the head of Olduvai Gorge. These fossils were found to be eroding from relatively recent deposits, probably the beds named Ngaloba by Kent4. Exp... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Kent studied this area as a member of L. S. B. Leakey’s 1934–35 expedition, and his short paper is the only published description of the stratigraphy. He recognised three main subdivisions of the stratigraphic sequence, which overlies the metamorphic complex of Precambrian age. The lower unit he named the Laetolil Beds... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The lavas and agglomerates noted by Kent overlie an irregular surface deeply eroded into the Laetolil Beds. The lavas were erupted from numerous small vents to the south, south-west and west of Lemagrut volcano. Although designated as nephelinite by Kent, the flows proved to be vogesite, a highly mafic lava with inters... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Additional fossiliferous deposits, of mineralogical affinity to the Laetolil Beds and 10–15 m thick, lie between tuff d and the bed I (?) tuffs at several places. They are locally separated from tuff d and the underlying aeolian tuffs of the Laetolil Beds by an erosional surface with a relief of 8 m. These sediments co... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Tuff c is the uppermost of the dated horizons, lying near the top of the fossiliferous deposits. It is a widespread crystal-lithic air-fall tuff cemented with calcite and generally 10–15 cm thick. Abundant biotite crystals 1–2 cm in diameter occur in the upper part of the tuff, which is composed of nepheline and mileli... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Two dates were obtained from a biotite-bearing crystal-lithic tuff 60 cm thick lying approximately 50 m below tuff c near the middle of the thickest section of the Laetolil Beds at location B (Fig. 2). The tuff is of nephelinite composition, containing abundant augite and altered nepheline and 2–3% of biotite, some cry... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Equus, Theropithecus, Phacochoerus and Tragelaphus, formerly included in the Laetolil fauna, with the exception of Hippopotamus. 中文
The fossil material from the Laetolil Beds is dispersed and fragmentary and it is not possible to assess the number of individuals represented. In this article, “numbers of fossils” refer ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Proboscidea include Deinotherium and Loxodonta sp. (M. Beden, personal communication). There is no evidence that the equid material (other than that derived from later deposits) includes any genus except Hipparion. The suids consist only of two genera, Potamachoerus and Notochoerus (J. Harris, personal communication). ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The hominid specimens are listed in Table 3. Provisional stratigraphic correlation and dating have placed the hominid remains as shown in Fig. 3. With the exception of Laetolil hominids (LH) 7 and 8, all specimens retain the matrix characteristic of the Laetolil Beds from which they have been weathered or excavated. Th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Second molars (LH 2, 3, 6) Upper and lower deciduous second molars take the basic form of the analogous permanent first molars but are smaller in overall size. The dM2 of LH 2 is the only lower molar in the Laetolil sample bearing any indication of a tuberculum sextum. 中文
Permanent Dentition
Incisors (LH 2, 3, 5, 6, 14... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | apressed anteriorly between hypoconid and entoconid and no trace of a tuberculum sextum. The Y-5 pattern of primary fissuration is constant. 中文
Mandibles
Juvenile mandible (LH 2) This specimen (Figs 5 and 6) is incompletely fused at the midline, and the developing crowns of the permanent canines and premolars are expos... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | are weak to moderate superior and inferior transverse tori, the latter bearing strong mental spines. 中文
Fig. 7. Adult mandible from the Laetolil Beds (LH 2), occlusal view.
中文
The anterior root of the ramus is broken at its origin, lateral to M2. Occlusal and basal margins diverge strongly anteriorly, resulting in a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Laetolil permanent premolars show none of the molarisation seen in the latter specimens and bear particularly strong resemblances to South and East African material (STS 51, 52, 55; OH 7, 16, 24; KNM ER 808, 992) (refs 10–12, 14). 中文
The Laetolil permanent molars are consistent in aligning with the South African “graci... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Much of the recently discovered comparable fossil hominid material from the Hadar region of Ethiopia shows strong similarity to the Laetolil specimens23, and further collection combined with detailed comparative analysis of material from both localities is essential for the further understanding of human origins. The L... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Leakey, R. E. F., and Wood, B. A., Am. J. Phys. Anthrop., 39, 355 (1973).
Leakey, R. E. F., and Wood, B. A., Am. J. Phys. Anthrop., 39, 355 (1974).
Leakey, R. E. F., Nature, 242, 170 (1972).
Leakey, L. S. B., Nature, 188, 1050 (1960).
Leakey, L. S. B., and Leakey, M. D., Nature, 202, 3 (1964).
Day, M. H., and Leakey, R... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
莱托利尔层和奥杜威层的层序关系已经讨论了数年,但是1969年海提出莱托利尔层下伏于侧峡谷的克罗吉岛山的I层之下,因此确定了它们早于奥杜威层序。当I层与凝灰岩可以对比,以及发现更早的含化石的凝灰岩系不整合地覆盖在莱托利尔层之上时,这一点就得到了进一步的证实。 英文
1974年,当乔治·达夫在伽津格罗河的河床里发现了马科动物和牛科动物的牙齿后,人们对这一区域的兴趣被再度点燃。伽津格罗河在奥杜威峡谷的源头处流入马赛科湖。这些化石是由于相对更新的堆积物遭遇侵蚀而出露的,这些堆积物很可能是肯特命名的恩加洛巴层[4]。玛丽·利基迄今还没看到过莱托利尔层的出露,出露地层位于伽津格罗河的东部,在加鲁西河和奥杜威侧峡谷(科尔–拉森称之为马拉姆布... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 广泛分布的霓霞岩和熔岩(大部分是霞岩)捕虏体层处于该剖面的含化石部分的不同层面上,有利于相互对照。在某些霓霞岩中,黑云母是很常见的。 英文
其他与莱托利尔层具有矿物学相似性的10~15米厚的含化石堆积物在好几处地点都存在于凝灰岩d和I层(?)的凝灰岩之间。它们就地被一个起伏幅度达8米的侵蚀面所分隔而与凝灰岩d和下伏的莱托利尔层风成凝灰岩分开。这些沉积物由水成凝灰岩、风成凝灰岩、风成来源的黏土颗粒聚集物和石灰岩构成。火山喷发碎屑的成分是响岩和霞岩。目前还没搞清楚这些沉积物是否应该被看作是莱托利尔层的一部分。 英文
I层和II层以在地层上位于熔岩和恩加洛巴层之间的沉积物为代表。II层堆积物的局部含有化石和人工制品。 英文
图3. 显示... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
这些地点中有十八个在加鲁西河河谷,一个位于奥杜威侧峡谷的源头河谷处,一个在伽津格罗河河谷,五个在加鲁西河南部的一个河谷,还有一个在西部的一个孤立的位置(图2)。 英文
在露头看到的可鉴定化石或者被采集并记录,或者在遗址上标注出来。莱托利尔层的化石都是特殊的乳白色或者白色,并且有时呈白垩的质地,但是从地表采集到的材料也有褐色、灰色或黑色的标本,这些颜色经常是包在标本外面的。本项研究的标本排除了地表采集的标本,同时排除了那些附着有与莱托利尔层凝灰岩明显不同的围岩的化石。这些标本都是河马属、马属、狮尾狒属、疣猪属和林羚属的化石,除了河马属以外,其他原本就包括在莱托利尔动物群中。 英文
莱托利尔层中的化石标本分散而残破不全,因而不可能... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | LH 2的dM2是莱托利尔标本中唯一一枚有第六小尖迹象的下臼齿。 英文
恒齿系
门齿(LH 2、3、5、6、14):唯一的上中门齿非常大,而且具有明显的舌面突起。上侧门齿较小,舌面突起因不同个体而异。下门齿狭窄而高,突起很小。 英文
犬齿(LH 2、3、4、5、6、14):发育不充分的上犬齿LH 3很大、结实而尖锐,具有明显的舌面突起。LH 6稍微小一点,具有较少的舌面突起和一个高而尖的牙冠。LH 5在远中侧咬合边缘具有一个延长的牙本质暴露区,但是没有在磨损的状态下突出于咬合列之外。下犬齿与上犬齿在大尺寸、高度和舌面突起方面都很相似。 英文
前臼齿(LH 1、2、3、4、5、6、14):上前臼齿趋于沿颊舌向延伸并呈双尖型,舌侧主尖位... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 莱托利尔恒前臼齿完全没有在后来的标本中所见到的臼齿化现象,并且与南非和东非标本(STS 51、52、55;OH 7、16、24;KNM ER 808、992)(参考文献10~12、14)非常相似。 英文
莱托利尔恒臼齿与南非“纤细型”南方古猿和东非人属标本在大小和形态学上都具有一致性。这些臼齿没有表现出在南非和东非“粗壮型”南方古猿(SK 6、13、48、52;TM 1517;佩宁伊;KNM CH 1;KNM ER 729、801、802)(参考文献10、17~20)中高频出现的尺寸增大、出现额外的牙尖或突起、单个牙尖扩展的、“肿胀的”发育情况等。成年下颌骨与某些东非标本(如KNM ER 1802)具有相像之处,它们具有相似的下颌体... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | A DNA sequence for the genome of bacteriophage ΦX174 of approximately 5,375 nucleotides has been determined using the rapid and simple “plus and minus” method. The sequence identifies many of the features responsible for the production of the proteins of the nine known genes of the organism, including initiation and te... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 1. A provisional nucleotide sequence for the DNA of bacteriophage ΦX174 am3 cs70. Solid underlining indicates sequences that are fully confirmed; sequences with no underlining probably do not contain more than one mistake per 50 residues. Broken underlining indicates more uncertain sequences. Restriction enzyme re... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | At this stage sequencing techniques using primed synthesis with DNA polymerase were being developed16 and Schott17 synthesised a decanucleotide with a sequence complementary to part of the ribosome binding site. This was used to prime into the intercistronic region between the F and G genes, using DNA polymerase and 32... | 400套付费套装书 |
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