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C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | To estimate the past accumulation rate we adopt a procedure based on the observation that the present precipitation rate on the Antarctic plateau is strongly correlated with surface temperature. Robin25 has suggested that this correlation exists because precipitation is governed by the amount of water vapour in the atm... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | ice origin is determined. Then, the thinning function is calculated and the ice redated all along the core. The process is repeated using the new dates as the initial conditions until the initial and final datings converge. 中文
Fig. 2. Surface and bedrock topography along the Ridge B–Vostok axis (lower curve) and the t... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | This accumulation value, although uncertain given the very short period (<10 yr) over which this parameter was determined, seems to be a reasonable average over the Holocene period. Our dating puts the end of the last climatic transition at around 10 kyr BP which compares well with the same event recorded in the Dome C... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | linear (correlation coefficient, r = 0.989 for the –20 to –55 °C interval) and its slope can be correctly explained on a theoretical basis applying a recently developed kinetic isotopic model26. Second, the ice thickness has probably undergone only minor fluctuations and the ice origin can be reliably reconstructed. In... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Concerning the transition between the last glacial maximum (around 18 kyr BP) and the Holocene periods (B–A in our terminology), the present results confirm the excellent agreement between the two East Antarctic sites, with a δ18O shift, before corrections, of 5.4‰ at Dome C7 and of ~5‰ at Vostok, and to a lesser degre... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | It is now widely accepted that δ18O in benthic foraminifera primarily reflects ice-volume changes3,45,46. Although the relationship can be distorted by many factors, the CLIMAP project members concluded that there is no compelling evidence to reject the first-order assumptions of isotope synchroneity or fidelity to the... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | uncertainties (probably of ~10 kyr at this level) prevent a detailed discussion of this possible lag. On the other hand, the fact that ice stage G probably lasted longer than stage 5e is a key element for understanding the last interglacial climate and the initiation of the last ice age. A detailed interpretation is be... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Beyond this reconstruction of the East Antarctic climate, we now discuss some current important aspects of the mechanisms which have probably controlled this climate and how the East Antarctic climate is related to the global climate. We will examine the possible role of changes in insolation, atmospheric CO2 content a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | The particular importance of the obliquity cycle, previously suggested from some high-latitude oceanic cores54, would indicate that orbital forcing acts at a local scale. At 80° S, the maximum change of annual insolation is ~7% (ref. 59) which, from the radiative equilibrium equation, corresponds to a direct temperatur... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Shackleton et al.66 have used the idea that the difference in carbon isotope ratios in surface and deep oceanic waters varies with CO2 levels67 to develop an indirect approach which extends the atmospheric CO2 record further back in time. They estimate this parameter from the δ13C difference between planktonic and bent... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | There are several other features of the CO2–climate relationship. CO2 measurements at Dome C indicate that the increase in CO2 concentration associated with the end of the last ice age began before, or simultaneously with, the climatic change at high southern latitudes65. On the other hand, from the 340-kyr reconstruct... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Ice-volume feedbacks. Although many assumptions are involved, the above discussion suggests that local insolation and possibly the atmospheric CO2 have played a part in determining the Antarctic climate over the past 150 kyr. The two factors alone, however, would not explain all the climatic variability seen in the δ18... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | compared with the Northern Hemisphere ice volume can be solved as suggested by Budd61. 中文
Conclusions
We have obtained the first complete and unambiguous isotope description from a deep-ice core of the last climatic cycle. The 2,083-m Vostok record covers the past 150 kyr extending into the end of the previous glacial ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 中文
The presence of a roughly 40-kyr cycle in the Vostok record strongly supports the role of orbital forcing in determining climatic changes. This record is approximately in phase with the annual insolation at 80° S suggesting that this forcing operates at a local scale. There are also some common features between the ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | We are very grateful to all Soviet and French participants in drilling, field work and ice sampling which was prepared, in particular, by K. V. Blinov. We thank G. Mondet for isotopic determinations. We also thank W. F. Budd, R. Sadourny, N. J. Shackleton for helpful discussions. The presentation of the work has largel... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Lorius, C., Raynaud, D., Petit, J. R., Jouzel, J. & Merlivat, L. Annls Glaciol. 5, 88-94 (1984).
Paterson, N. S. B. Nature 266, 508-511 (1977).
Young, N. W., Pourchet, M., Kotlyakov, V. M., Korolev, P. A., & Dyugerov, M. B. Annls Glaciol. 3, 333-338 (1982).
Lorius, C. et al. IAHS Publ. 86, 3-15 (1970).
Barkov, N. I. An... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Robin, G. de Q. The Climatic Record in Polar Ice Sheets, (ed. de Q. Robin G.) 180-189 (Cambridge University Press, 1983).
Jouzel, J., Merlivat, L., Petit, J. R. & Lorius, C. J. Geophys. Res. 88, 2693-2703 (1983).
Joussaume, S., Jouzel, J. & Sadourny, R. Nature 311, 24-29 (1984).
Lorius, C. & Merlivat, L. IAHS Publ. 118... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Stauffer, B., Hofer, H., Oeschger, H., Schwander, J. & Siegenthaler, U. Annls Glaciol. 5, 160-164 (1984).
Raynaud, D. & Barnola, J. M. Annls Glaciol. 5, 224 (1984).
Shackleton, N. J., Hall, M. A., Line, J. & Cang Shuxi Nature 306, 319-323 (1983).
Broecker, W. S. Progr. Oceanogr. 11, 151-197 (1982).
Shackleton, N. J. & ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 这一方面是因为理想的冰芯钻探点位于南极和格陵兰的中部,而后勤保障存在问题;另一方面,深孔钻取也存在技术上的难题。 英文
第四纪期间经历了连续的冰期和间冰期气候波动[1-3]。在格陵兰西北部的世纪营地进行初次钻探以来[4],又陆续在南极洲的伯德站[5]、沃斯托克站[6]、冰穹C[7]以及格陵兰的Dye 3[8]钻取了直达末次冰期的五根深冰芯。人们对这些冰芯中的氧–18含量(相对于标准平均大洋水(SMOW),表示为δ18O)和化学杂质进行了广泛研究,为地球的古气候和古环境研究提供了宝贵信息(见参考文献9和10)。 英文
在这些冰芯中,世纪营地冰芯可延伸至末次间冰期。因为冰层沉降入冰盖时会减薄,所以当冰芯到达基岩时,末次间冰期的冰只限于冰... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 剖面的显著特征是存在四个非常明显的冷期(即δ18O的低值),分别位于425米、975米、1,525米和2,050米处,其δ18O值均为–62‰左右。这使得对图1中各连续时期的界定相对直观起来。从上部开始,暖期(阴影区)用A、C、E和G标注,而冷期用B、D、F和H标注。阶段A和G的同位素值最高,分别约为–57‰和–55‰。从图1中的实曲线可以看出,在G阶段1,790米处,有一同位素的跃变(约2‰)。E和C阶段是相对温暖的间冰阶,是介于全冰期和间冰期之间的一种气候状况。 英文
图1的顶部标出了各连续阶段的年代(所使用的定年方法会在下面说明)。阶段A与现在的全新世相对应,阶段B~F则覆盖了整个末次冰期,阶段G包含了末次间冰期的最大值,而H... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 距今约1.3万年至2.6万年之间(参考文献32)的微粒含量峰值也为冰芯第一部分的定年提供了间接的支持,这一时期澳大利亚处于干旱期[33]。其他的定年误差可能来源于对积累量变化的估算,减薄函数也会有些影响。因此,冰芯底部的定年误差可能会大于1万年至1.5万年。 英文
古气候信息
极地雪的同位素含量主要受控于TF,同时也依赖[9,10,34,35]于其他几个参数,如气团的源地及运动历史,以及降雪形成的微物理过程。要重建一个完整的大气水汽及降水中同位素含量的时空变化,需要将同位素循环纳入大气环流模式(GCM)[36]。 英文
在新方法全面开发出来之前,我们现在只能通过现代降水和(或)同位素模型中观测到的δ18O–温度的关系来重建冰芯中的气... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 英文
图4.时间变化:a,80° S处冬季、夏季和全年的太阳辐射(参考文献59);b,沃斯托克冰芯的δ18O值(本文);c,V 19~30深海岩芯的Δδ13C[68]值,以及右侧的CO2值;d,65°N处夏季太阳辐射(参考文献59);e,刺葡萄虫V 19~30深海岩的芯的δ18O值[68],上面标注了连续的气候变化阶段。 英文
采用沃斯托克定年,深海氧同位素阶段1~4和沃斯托克A~D阶段之间是很一致的。阶段E包含了5a~5c,阶段F则对应于5d。然而,在深海岩芯和冰芯记录中分别代表末次间冰期的5e和G阶段并不完全对应(图4)。这两个阶段的持续时间差别较大,5e为1.1万年而G为2.4万年。在沃斯托克冰芯中末次间冰期的峰值距今约1... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 格陵兰和南极冰芯包裹的气泡测量表明,CO2浓度的变化与气候变化相关。对过去4万年以来冰芯CO2浓度的直接测定已完成(参考文献62~65)。结果是从末次冰盛期到工业革命前的全新世,CO2浓度增加了约40%。这些测量结果表明,CO2及其温室效应也参与了控制冰期的周期性变化[21],以及南北半球气候的同步性变化[42,60]。 英文
沙克尔顿等人[66]发展了一种间接方法进一步延伸了大气CO2记录的尺度,该方法基于这样一个认识,即海洋表层水与深层水的碳同位素比率随CO2水平的变化而变化[67]。他们从浮游有孔虫和底栖有孔虫之间的δ13C差异(Δδ13C)估计该参数。因估算的CO2值与在相同年代(过去的4万年)的极地记录是一致的[66],这... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 长度为2,083米的沃斯托克冰芯记录涵盖了过去15万年的气候记录,时间尺度延伸至倒数第二次冰期的结束期。通过结合两种方法对该冰芯进行定年,建立时间序列。一种方法是利用适宜的冰川学模型(该冰芯只代表了冰盖的上半部分)。第二种方法是通过冰芯稳定同位素的记录估算过去冰川积累率的变化。虽然这种结合法仍存在局限性,但其优点是它完全独立于其他古气候指标或气候强迫因子的时间序列。 英文
沃斯托克冰芯的δ18O记录可以解释为从根本上反映了南极洲东部的温度变化。这一解释的理论基础是观测到的现代降水中δ18O–温度梯度以及简单的动力学同位素模型。虽然我们也意识到利用GCM模型更为详细地模拟大气δ18O循环是十分必要的,但我们对于该冰芯δ18O解释温度变... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | atoms—60 of them—in the form of a truncated icosahedron, a figure made up of 12 pentagons and 20 hexagons. This was a design used by the American architect Richard Buckminster Fuller to construct what are known as geodesic domes, whence the name buckminsterfullerene for the molecule. Kroto and his colleagues, Robert Cu... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | opened first and then the vaporization laser was fired after a precisely controlled delay. Carbon species were vaporized into the helium stream, cooled and partially equilibrated in the expansion, and travelled in the resulting molecular beam to the ionization region. The clusters were ionized by direct one-photon exci... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Figure 3 shows a series of cluster distributions resulting from variations in the vaporization conditions evolving from a cluster distribution similar to that observed in ref. 3, to one in which C60 is totally dominant. In Fig. 3c, where the firing of the vaporization laser was delayed until most of the He pulse had pa... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | these cluster thermalization and cluster-cluster reactions in the “integration cup” shown in Fig. 2. The concentration of cluster species in the especially stable C60 form is the prime experimental observation of this study. 中文
Our rationalization of these results is that in the laser vaporization, fragments are torn ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Assuming that our somewhat speculative structure is correct, there are a number of important ramifications arising from the existence of such a species. Because of its stability when formed under the most violent conditions, it may be widely distributed in the Universe. For example, it may be a major constituent of cir... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | consensus. 中文
We thank Frank Tittel, Y. Liu and Q. Zhang for helpful discussions, encouragement and technical support. This research was supported by the Army Research Office and the Robert A. Welch Foundation, and used a laser and molecular beam apparatus supported by the NSF and the US Department of Energy. H.W.K. ac... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 将上述结构中的每个顶点放置一个碳原子,就可以形成一个C60分子,为符合碳原子的价态,其中所有原子均为两个单键和一个双键,该分子具有多重共轭结构,属于芳香族化合物。 英文
图1.得克萨斯草坪上的一个足球(在美国称为英式足球)。本文中描述的C60分子让人想起截角二十面体结构,就是将图示足球中接线上的每个顶点用一个碳原子代替形成的结构。 英文
用来产生并检测这种不同寻常的分子的技术包括:利用聚焦的脉冲激光使含碳物质从固体石墨盘表面气化,进入高密度的氦气流。气化激光是Q开关Nd : YAG(钕钇铝石榴石)激光器产生的二次谐波,脉冲能量约为30 mJ。生成的碳簇在超声分子束中膨胀,经准分子激光器光电离后,利用飞行时间质谱进行检测。图2中所... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 这种C60分子的直径约为7 Å,提供了一个有可能容纳各种原子的内部空腔[8]。 英文
假设我们推测的结构是正确的,那么这类化合物的存在就会衍生出许多重要分支。它是在最剧烈的条件下形成的,由于它的稳定性,该分子有可能广泛存在于宇宙之中。例如,它可能是含有大量碳的星周壳中的主要成分。它有可能是星际尘埃的组成成分,并可能是导致星际分子形成的表面催化化学过程中的主要位点。甚至可以进一步猜测,C60或者其某一衍生物,可能是弥散星际线的携带者[9]。 英文
如果能找到一种大规模合成C60这类化合物的方法,也许就能证明它具有极高的化学研究和实际应用价值。人们可以很容易地设想出多种C60的衍生物,诸如C60Fe等C60与过渡金属形成的化合物,以及像... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Specimens of Australopithecus boisei have been found in 2.5-Myr-old sediments west of Lake Turkana, Kenya. The primitive morphology of these early A. boisei suggests that robust and hyper-robust Australopithecus developed many of their common features in parallel and further that A. africanus is unlikely to have been a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Prospecting was carried out in 1985 in Pliocene sediments to the west of Lake Turkana, Kenya. It led to the recovery of two A. boisei specimens. A cranium and a partial mandible were discovered at two separate localities: sediments in the Lomekwi and Kangatukuseo drainages (see Fig. 1) at approximately 3°45′ N, 35°45′ ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | within strata correlative with submember C9 of the Shungura Formation. Based on the K/Ar chronology of the Shungura Formation and scaling on the basis of constant sedimentation rates there, the cranium is estimated to be 2.55 Myr old. Using palaeomagnetic polarity boundaries as the basis of chronological placement, the... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | The interval of section from which the australopithecine specimens were collected has also yielded over 200 fossils representing more than 40 other mammalian species (Table 1), including the skeleton of a ground-dwelling colobine and a relatively complete camel mandible. Bovids are the most common elements of the fauna... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | KNM-WT 17000 is an adult cranium with the following parts missing: all of the tooth crowns except a half molar and the right P3; some facial bone fragments which have spalled off the infilled maxillary sinus; most of the frontal processes and temporal plates of the zygomatics; the zygomatic arches themselves; a large p... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | hominid. Further, the sagittal crest joins completely to compound temporal-nuchal crests with no intervening bare area18. The foramen magnum position is far forward as in other robust Australopithecus specimens19. 中文
The one complete tooth crown, right P3, is 11.5 mesiodistally by 16.2 buccolingually. This is bigger me... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | refs therein) as well as the condition found in KNM-WT 17000. For most features the new specimen resembles A. boisei. 中文
Table 2. Compilation of features of Australopithecus species
中文
There are some features of KNM-WT 17000 that differ from all other “hyper-robust” specimens as well as from robust ones. The most ob... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Although future finds may show that KNM-WT 17000 is well within the range of variation of A. boisei, it is also possible that the differences will prove sufficient to warrant specific distinction. If the latter proves to be the case we suggest that some specimens from the same time period and from the same sedimentary ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Therefore, this new specimen shows that A. robustus is a related, smaller species that was either derived from ancestral forms earlier than 2.5 Myr and/or has evolved independently in southern Africa, perhaps from A. africanus. It has been suggested before that A. robustus was derived from A. africanus4, but by those w... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Other primitive features found in KNM-WT 17000, but not known or much discussed for A. afarensis, are: very small cranial capacity; low posterior profile of the calvaria; nasals extended far above the frontomaxillary suture and well onto an uninflated glabella; low calvaria with receding frontal squama; and extremely c... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | We thank the Government of Kenya and the Governors of the National Museums of Kenya. This research is funded by the National Geographic Society, Washington, D.C., the Garland Foundation and the National Museums of Kenya. F.H.B. was funded for analyses by NSF grant BNS 8406737. We thank Bw. Kamoya Kimeu and his team for... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Johanson, D. C. & White, T. D. Science 203, 321-330 (1979).
Tobias, P. V. Palaeont. afr. 23, 1-17 (1980).
Olson, T. R. in Aspects of Human Evolution (ed. Stringer, C. B.) 99-128 (Taylor & Francis, London, 1981).
Harris, J. M. & Brown, F. H. National Geographic Res. 1, 289-297 (1985).
Brown, F. H., McDougall, L., Davies... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 英文
越来越多的人认同,东非和南非标本与其他地区标本的不同之处足以将他们划分到不同的物种中[1-4]。南方古猿鲍氏种的模式标本是奥杜威人科5号[7,8]。 英文
有些学者将这两个粗壮种物种归入傍人属中[9]。尽管有些人认识到这两种已知的标本在时间上有重叠,但他们还是主张是南方古猿粗壮种衍生出了南方古猿鲍氏种,二者具有祖裔关系。可能最近对于后一个观点的最有说服力的证据就是拉克对南方古猿面部结构和功能的典型研究[4]。他所遵循的演化图解中,粗壮种分支起源于南方古猿非洲种,因此不能把粗壮种看作是人类祖先[10]。这种方案还没有得到普遍认同[11,12]。 英文
地点
1985年,研究人员在肯尼亚图尔卡纳湖西侧的上新世沉积物中进行了勘查工作... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 英文
表1.图尔卡纳湖西侧南方古猿新遗址出土的哺乳动物化石
英文
标本
KNM-WT 17000是一件成人颅骨,它的如下部分丢失了:除了半颗臼齿和右P3外的所有齿冠;一些从已被填充的上颌窦剥落的面骨碎片;大部分额突和颧骨的颞板;颧弓自身;额骨的大部分和顶骨上部(但是在顶骨前部的一块矢状嵴保存了下来);两侧翼状区下部与上颌骨后部的部分骨骼及右侧腭骨;枕骨颈区的下部。此颅骨双侧对称,所有骨质接触部位都很清晰。没有证据表明存在任何的塑性变形,因此该脑颅保留下了其球形形状(图2)。 英文
图2.颅骨KNM-WT 17000的前、后、左侧、上、下视图。标尺单位为厘米。 英文
这是一件厚重的颅骨,具有很大的面部骨骼、腭骨和大的颅底,但是... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 英文
尽管将来的发现可能会显示KNM-WT 17000正好处于南方古猿鲍氏种的变异范围之内,但是也有可能这些差异足以成为物种差异的根据。如果事实证明是后者的话,那么我们主张,有些来自同一时间段、同一沉积盆地的标本(例如,来自尚古拉组的奥莫1967-18)可被归入同一物种中。奥莫1967-18是由阿朗堡和科庞[24]命名的埃塞俄比亚副猿的模式标本。那么在我们看来,其适当的名字应该是南方古猿埃塞俄比亚种。 英文
结论
这些新标本表明南方古猿鲍氏种谱系是在至少250万年前建立起来的,并且在粗壮性和牙齿大小方面,至少早期种群的一些成员与后来的成员是一样大的。尽管有位权威人士认为,粗壮种南方古猿的颅骨和牙齿会随着时间变小[25],但是大部分... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 布朗的研究受到了美国国家科学基金会BNS 8406737项拨款的资助。我们感谢卡莫亚·基梅乌及其团队提供的宝贵协助。许多同事,尤其是利基和希普曼都以不同方式提供了帮助。 英文
(刘皓芳 翻译;董为 审稿)
Forty Years of Genetic Recombination in Bacteria: A Fortieth Anniversary Reminiscence
Joshua Lederberg
Editor’s Note
In 1944, Canadian-born researcher Oswald Avery and colleagues demonstrated that DNA was the molecul... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | IN September 1941, when I started as an undergraduate at Columbia University, the genetics of bacteria was still a no-man’s-land between the disciplines of genetics and (medical) bacteriology. The question whether “bacteria have genes, like all other organisms” was still unanswered, indeed rarely asked. My own thoughts... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | bacteria). In October 1944, I was reassigned to begin my studies at Columbia Medical School; but I continued working with Ryan at the Morningside Heights campus. 中文
Discovery
The important biological discovery of that year, by Avery, MacLeod and McCarty, was the identification of DNA as the substance responsible for th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | At once, I thought of attempting similar transformations by DNA in Neurospora. This organism had a well understood lifecycle and genetic structure. The biochemical mutants opened up by Beadle and Tatum also allowed the efficient detection of nutritionally self-sufficient (prototrophic) forms, even if these were vanishi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Dubos5 cited many unclear, and two clear-cut negative results7,8 for sexuality in bacteria using genetic exchange methodology. But these two studies had no selective method for the detection of recombination and so would have overlooked the process had it occurred less often than perhaps once per thousand cells. With t... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | that I arrive in New Haven in late March, to give him time to set up his laboratory. He hinted that he had some similar ideas of his own, but never elaborated them. The arrangement suited him by leaving him free to complete his work on the biochemistry of Neurospora, perform the heavy administrative duties of his new p... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | under the microscope. These subsequent observations did quiet remaining concerns of the group that Lwoff had assembled at the Pasteur Institute, including Jacques Monod, Francois Jacob and Elie Wollman, who were to make the most extraordinary contributions to the further development of the field. The single cell method... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | single, and then double mutants in E. coli9. In 1946, I was very much aware of strain specificities and was speculating about mating types (as in Neurospora). I have no way to say how many other strains would have been tried, or in how many combinations, had the June 1946 experiments not been successful. 中文
2. An equal... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 编者按
1944年加拿大裔研究者奥斯瓦尔德·埃弗里和他的同事证明DNA分子对遗传起作用。美国分子生物学家乔舒亚·莱德伯格受这一结论的启发,开始研究他自己提出的假说,即细菌有时可以进行有性生殖,在此过程中基因信息重组和融合,而不是通过无性生殖来传递精确拷贝的过程。在本文中,他回顾了证明细菌可交配并交换基因的实验,这项工作为莱德伯格和同事爱德华·塔特姆赢得了1958年的诺贝尔奖。当这些挑战传统法则的结果在1946年冷泉港学术研讨会上被提出时,引起了热烈讨论,而不久之后,细菌遗传重组理论就被纳入教科书和主流的分子生物学研究中。 英文
从1946年4月到6月,乔舒亚·莱德伯格和爱德华·塔特姆开展的一系列实验证实了细菌可以通过有性杂交交换其... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 但是,细菌真的是无性生殖么?勒内·杜博斯的专论——《细菌细胞》[5]中明确指出,任何支持或否定细菌细胞间存在性连接的形态学表现都无明确的结论。 英文
我在1945年7月8日详细记录了用于寻找念珠菌(一种医学上十分重要的类似酵母的真菌)中的交配以及细菌中的遗传重组(所采取的实验方案后来证明是成功的)的假设性实验。这些记录与我在医学细菌学课程一开始的内容一致。它们挑战了传统教科书认为细菌是裂殖类、属于无性生殖的原始植物的观点,并且赞同索尔·施皮格尔曼和哈丽雅特·泰勒主张酵母存在性别差异[6]的观点,这是两人在哥伦比亚研究生时期的研究工作。 英文
杜博斯[5]引用了很多利用遗传交换方法研究细菌有性生殖的阴性结果[7,8],其中很多结果尚不... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 英文
实验的运气
我们已经知道[12]选取大肠杆菌K-12菌株做实验材料本身就是一件非常幸运的事:根据我们的实验方案在随机挑选的20个大肠杆菌菌株中,只有大约1株可以在实验中得到阳性结果。尤其是B菌株,它成为了噬菌体研究的标准实验材料,并且该菌株是高度不育的。塔特姆从斯坦福大学微生物系的常规培养物库存中得到了K-12,那时他打算寻找一个大肠杆菌菌株作为脉胞菌色氨酸合成研究[13]中色氨酸酶的来源。当他开始构建大肠杆菌的单突变体以及之后的双突变体[9]时,很快就得到了相同的菌株。1946年,我对菌株的特异性非常了解,并开始推断交配的方式(就像在脉胞菌中一样)。如果1946年6月的实验不成功的话,我不知道还要尝试多少其他的菌株,也不知道... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | MOLECULAR biology is now a major source of quantitative and objective information about the evolutionary history of the human species. It has provided new insights into our genetic divergence from apes1-8 and into the way in which humans are related to one another genetically9-14. Our picture of genetic evolution withi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | MtDNA was highly purified from 145 placentas and two cell lines, HeLa and GM 3043, derived from a Black American and an aboriginal South African (!Kung), respectively. Most placentas (98) were obtained from US hospitals, the remainder coming from Australia and New Guinea. In the sample, there were representatives of 5 ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | average of 370 restriction sites per individual were surveyed, representing about 9% of the 16,569 base-pair human mtDNA genome. 中文
Map Comparisons
The 147 mtDNAs mapped were divisible into 133 distinct types. Seven of these types were found in more than one individual; no individual contained more than one type. None ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | where δx is the mean pairwise divergence (in percent) between individuals within a single population (X), δy is the corresponding value for another population (Y), δxy is the mean pairwise divergence between individuals belonging to two different populations (X and Y), and δ is a measure of the interpopulation divergen... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Figure 2 shows the sequence divergence (δx) calculated for each population across seven functionally distinct regions of the mtDNA genome. As has been found before24,27,28, the most variable region is the displacement loop , the major noncoding portion of the mtDNA molecule, and the least variable region is the 16S rib... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Fig. 3. a, Genealogical tree for 134 types of human mtDNA (133 restriction maps plus reference sequence); b, comprehensive list of polymorphic restriction sites used. The tree accounts for the site differences observed between restriction maps of these mtDNAs with 398 mutations. No other order of branching tested is mo... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | noncoding regions and genes for transfer RNA, ribosomal RNA and proteins (ND, NADH dehydrogenase; CO, cytochrome oxidase; ATP, adenosine triphosphatase; CYT b, cytochrome b). For example, 8j indicates a MboI site beginning at nucleotide position 8 in the D loop that was not found in mtDNA type 1 but was present in type... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | population-specific tree, while the latter tree required fewer changes at four sites; both trees require the same number of changes at the remaining 67 sites. The minimum-length tree is thus favoured by a score of 22 to 4. The hypothesis that the two trees are equally compatible with the data is statistically rejected,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | * For clusters represented by two or more individuals (and calculated for individuals, not for mtDNA types) in Fig. 3.
† Average age in thousands of years based on the assumption that mtDNA divergence occurs at the rate of 2–4% per million years15,30.
‡ Assuming that Africa is the source, there is only one African clus... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | As Fig. 3 shows, the common ancestral mtDNA (type a) links mtDNA types that have diverged by an average of nearly 0.57%. Assuming a rate of 2–4% per million years, this implies that the common ancestor of all surviving mtDNA types existed 140,000–290,000 years ago. Similarly, ancestral types b–j may have existed 62,000... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Greenberg et al.28 sequenced the large noncoding region, which includes the displacement loop (D loop), from four Caucasians and three Black Americans. A parsimony tree for these seven D loop sequences, rooted by the midpoint method, appears in Fig. 4. This tree indicates (1) a high evolutionary rate for the D loop (at... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Our tentative interpretation of the tree (Fig. 3) and the associated time scale (Table 3) fits with one view of the fossil record: that the transformation of archaic to anatomically modern forms of Homo sapiens occurred first in Africa43-45, about 100,000–140,000 years ago, and that all present-day humans are descendan... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | that Asian erectus was ancestral to Homo sapiens50–52. Perhaps the non-African erectus population was replaced by sapiens migrants from Africa; incomplete fossils indicating the possible presence of early modern humans in western Asia at Zuttiyeh (75,000–150,000 years ago) and Qafzeh (50,000–70,000 years ago) might ref... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | our species arose. 中文
We thank the Foundation for Research into the Origin of Man, the National Science Foundation and the NIH for support. We also thank P. Andrews, K. Bhatia, F. C. Howell, W. W. Howells, R. L. Kirk, E. Mayr, E. M. Prager, V. M. Sarich, C. Stringer and T. White for discussion and help in obtaining pla... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Hauswirth, W. W. & Laipis, P. J. in Achievements and Perspectives in Mitochondrial Research, Vol. 2 Biogenesis (eds E. Quagliariello, E. C. Slater, F. Palmieri, C. Saccone & A. M. Kroon) 49-60 (Elsevier, New York, 1986).
Johnson, M. J. et al. J. Molec. Evol. 19, 255-271 (1983).
Cann, R. L. Ph. D. Thesis, Univ. Californ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Chapman, B. S., Vincent, K. A. & Wilson, A. C. Genetics 112, 79-92 (1986).
Chakravarti, A. et al. Proc. Natl. Acad. Sci. U.S.A. 81, 6085-6089 (1984).
Chakravarti, A. et al. Am. J. Hum. Genet. 36, 1239-1258 (1984).
Rightmire, G. P. in Origins of Modern Humans: A World Survey of the Fossil Evidence (eds Smith, F. H. & Sp... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 此外,核基因遗传自父母双方并在每一代中混合。这种混合模糊了个体的遗传背景,两亲本基因组之间可以发生遗传重组。如果不研究那些紧密连锁的位点,遗传重组会使得特定DNA片段的遗传历史难以追踪。 英文
在全世界范围内对线粒体DNA(mtDNA)的调查研究在以下三个方面加强了我们对人类基因库历史的认识:第一,因为mtDNA的突变积累速度比核基因快好几倍[15],这使我们更容易观察到人类基因库中的遗传多样性;第二,mtDNA是母系遗传,不会发生遗传重组[16],从而能够将个体之间关联起来;第三,人体中约有1016个mtDNA分子,它们的DNA序列通常是完全相同的[17-19]。由于每个卵母细胞中mtDNA分子遗传上有效群体大小的瓶颈效应[20]... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 实际上,非洲人群内部的变异程度与非洲人群和其他群体之间的分化程度(δxy=0.40~0.45)一样大。亚洲人群内分化程度(δx=0.35)也近似于群体之间的分化程度。澳大利亚人群、高加索人群和新几内亚人群的群体内的变异程度近似相等(δx=0.23~0.25),群体之间的分化程度稍稍大于群体内的变异程度。 英文
表1.五个群体内和群体间的mtDNA分化程度
通过已发表文献中的方法计算了分化程度[26]。对角线为群体内不同个体之间的平均成对分化值(δx)。对角线之下的为两个不同群体X和Y的个体之间的平均成对分化值(δxy)。对角线之上为群体之间的平均成对分化值(δ),该值已由等式(1)进行群体内变异的校正。. 英文
群体间的分化程度(... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 由于参照序列(110型mtDNA)中并没有此位点,8位起始位置其实是一个半位点,不同于1位的MboI识别序列(参见参考文献23中确定这些位点位置的方法)。并不是所有的酶切位点在所有个体中都能找到,如在1、31、59、63、68型mtDNA和所有新几内亚人的mtDNA中没有找到8j、1484e和7750c的位点;114和121型mtDNA中没有RsaI位点。一些位点的位置与之前报道的结果[23,24]不同,一些位点出现的个体也与之前报道的结果不同;所做的这些修正是通过对所研究的mtDNA的复查得到的。 英文
从数据中可以得到很多最小长度或者接近最小长度的进化树,从图3中可以看出所有这些进化树有以下共同的特点:(1)两个一级分支中,一... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 因此我们所估算的2%~4%的速率值对人类来说是一个相对合理的值,即使仍需要进一步的比较来做更准确的校正。 英文
如图3所示,共同mtDNA祖先(a型)与平均分化程度为0.57%的mtDNA类型相联系。假如进化速率为每一百万年2%~4%,那么所有存留下来的mtDNA类型的共同祖先出现在14万年至29万年以前。同样推算,祖先类型b~j可能出现在6.2万年至22.5万年前(表3)。 英文
从非洲向外迁移是什么时候开始的呢?最古老的不含非洲人群mtDNA的mtDNA类型簇起源于祖先c,包括了11~29类型(图3)。此类型mtDNA的表观年龄达9万年至18万年(计算值见表3),其祖先可能在这个时间已经离开了非洲。然而,大批迁移同样有可能发生在... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 也许非洲以外的直立人被来自非洲的智人移民替换了,不完整的化石记录显示在西亚的祖提耶(7.5万年至15万年以前)和卡夫泽(5万年至7万年前)可能出现了最初的现代人群,这也许反映了这些最初的移民[45,53]。 英文
如果亚洲古代居民与非洲出现的解剖学意义上的现代人发生交配,我们应该能在当今亚洲人的mtDNA类型里找到一些极端分化的类型,其分化程度要比在非洲发现的mtDNA类型分化程度更高。但对亚洲人的研究中[21,54-56]没有任何这种mtDNA类型存在的证据。尽管这些古老的mtDNA类型可能在种群之间的杂交过程中会丢失,但是mtDNA血统在一个膨胀的种群中灭绝的可能性是很低的[57]。因此我们推测亚洲的直立人被入侵的非洲智人取代了... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | THE presence of a shallow crustal magma chamber at active spreading centres is an important element of current geological models for the formation of ocean crust1-3. However, the shape, longevity and along-strike variability of ridge-crest magma chambers remain the subject of considerably controversy4,5. The feasibilit... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | where evidence for a large crustal magma chamber is generally lacking19,20. 中文
Fig. 1. Map showing the East Pacific Rise (EPR) and the track coverage obtained during our 1985 multi-channel seismic experiment. Labelled profiles (thick solid lines) are shown in Figs 2 and 3 or interpreted in Fig. 5. Dashed lines show th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Two representative CDP reflection profiles across and along the EPR are shown in Figs 2 and 3. A large amplitude reflection is present about 0.6 s below the sea floor on both profiles. On the cross-ridge profile, this high-amplitude event is centred beneath the rise axis and is less than 3 km in width, although a weak ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Fig. 3. Time section of a 100-km-long segment of CDP line 556 along the EPR south of the 11°45′N OSC illustrating the alongstrike continuity of the magma chamber reflection. Lower panel shows a 20-m Sea Beam map of this portion of the EPR crest and the location of the MCS profile (dashed line). The reflection data have... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 13°10′ N), sonobuoys collected elsewhere along the rise axis also frequently display this same strong attenuation of refracted energy beyond 10–12 km range. 中文
Fig. 4. Record sections for three ESPs shot along and parallel to the EPR near 13° N. ESP 9 (top) was shot along the rise axis, ESP 11 (middle) and ESP 13 (bot... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | that an event such as this has been seen in marine reflection profiles. 中文
In the 13° N area, a magma chamber reflection is observed on only a few profiles crossing the ridge, and Moho reflections are generally not seen, possibly due to somewhat rougher ridge-flank topography. Where magma chamber reflections are observ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Depth of the magma chamber. The depth of the top of the magma chamber is also well-constrained in our experiment by the ESPs shot along the rise axis and the two-way travel time between the sea floor and the AMC reflection. Along the portion of the EPR we have surveyed, the roof of the magma chamber varies in depth bet... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | interpretive section, where the AMC event becomes weak and somewhat discontinuous. However, in each instance we believe this was caused by the vessel sliding off the axial high rather than a physical discontinuity in the magma chamber. Several other small gaps in the AMC reflection (for example, 11° N, 11°29′ N, 11°40′... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | The largest gap in the AMC reflection (~77 km) occurs north of the Clipperton transform. This ridge segment is deep (>2,700 m) and relatively narrow (<4 km wide), plunging over 200 m toward the Clipperton ridge–transform intersection (Fig. 5). The absence of an AMC reflection along this part of the EPR indicates that a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | ridge axis discontinuities located between OSCs, including seven of the ten Devals identified along this portion of the EPR (Fig. 5). It may be significant that several Devals (9°17′ N, 9°53′ N, 11°08′ N, 12°28′ N) are located near or close to prominent dips in the AMC reflection, although in these areas it is difficul... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 中文
Fig. 6. Schematic drawing of the shape and dimensions of the AMC at the EPR based on the multi-channel seismic results presented in this paper. Location of ESPs shown in Fig. 4 is indicated for comparison. See text for discussion. 中文
There is a good correlation between some of the geochemical and petrological vari... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | we can trace the AMC reflection laterally for distances of at least 40–50 km along strike. We believe a physically continuous magma chamber must exist at this scale along at least portions of the EPR. South of Clipperton transform, where morphological9, petrological11 and seismic evidence all indicate a large, robust m... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | We thank the officers and crew of the RVs Conrad and Washington and the members of the scientific parties on both ships for their help at sea. Jeff Fox and Ken MacDonald provided us with large-scale versions of their Sea Beam maps prior to our cruise which were essential in planning and carrying out this experiment. We... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | Hekinian, R. et al. Mar. Geophys. Res. 7, 359-377 (1985).
Klitgord, K. D. & Mammerickx, J. J. Geophys. Res. 87, 6725-6750 (1982).
Orcutt, J. A., Kennett, B., Dorman, L. & Prothero, W. Nature 256, 475-476 (1975).
Rosendahl, B. R. et al. J. Geophys. Res. 81, 5244-5304 (1976).
McClain, J. S., Orcutt, J. & Burnett, M. J. G... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 然而,洋脊顶部岩浆房的形态、寿命及其沿走向的变化性仍然是一个极具争议的课题[4,5]。十年前在9° N附近获得了三条24道横穿东太平洋海隆(EPR)的反射地震剖面[6,7],这表明利用现代多道地震技术对洋脊顶部岩浆房进行成像是可行的。1985年5~6月期间,我们重返该地区,在EPR 8°50′ N至13°30′ N的范围内,进行了更为广泛的双船多道地震调查。这项调查试图为轴部岩浆房的形状和大小提供新的信息,并研究沿海隆轴向几十到几百公里距离内岩浆房的变化情况。 英文
在Sea Beam型多波束测深仪和Sea MARC I型侧扫系统的调查中[8-10],沿隆起轴[11,12]进行了广泛的拖网,并用海底摄像和载人潜水器[13]进行了高分... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 英文
图3.OSC 11°45′ N 以南沿EPR的 CDP测线556上一段长100 km的时间剖面,它展示了岩浆房反射沿走向的连续性。下图显示了EPR顶部这部分20 m的Sea Beam型多波束测深图以及MCS剖面(虚线)的位置。反射数据已经经过5~40 Hz的带通滤波,球面扩散校正,预测反褶积(滤波器长度为750 ms;预测距离为40 ms)以及6~20 Hz滤波的再次处理。数据显示方式与图2中的一样。Deval的位置是根据兰米尔等[11]确定的;五角星代表已报道的热液活动区域[24]。 英文
地壳岩浆房存在的证据。数条测线的证据表明在这些记录上观测到的位于洋脊轴部的浅层同相轴是来自地壳中一个低速带顶部的反射。该反射在单道记... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 我们发现的窄岩浆房(宽度最大为4~6 km,一般小于3~4 km)与基于蛇绿岩模型得到的大型(大于10~20 km)漏斗状岩浆房不一致[3,26],但是与最近在EPR获得的折射实验结果相一致[17-19]。 英文
岩浆房的深度。在我们的实验中,沿着隆起轴部对ESP放炮的实验以及海底与AMC反射波之间的双程走时都为岩浆房顶部深度的确定提供了良好的约束。沿着我们所调查的EPR部分,岩浆房顶部的深度在海床以下1.2~2.4 km之间变化,这一结果与先前在EPR基于地震折射的研究结果一致[15-18]。在此项研究中最有意思的新发现是岩浆房深度(也就是岩浆房之上地壳盖层的厚度)与隆起轴的深度之间存在相关性。尽管EPR的深度沿着我们所调查的长5... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 然而,在横穿过许多位于OSC之间的较小洋脊轴间断面,包括沿EPR这一区域识别出的十个Deval中的七个(图5),AMC反射面一般是连续的。几个Deval(9°17′ N、9°53′ N、11°08′ N、12°28′ N)位于AMC反射显著倾斜的部位附近,这可能有重要意义,尽管在这些地方很难将船精确地定位于轴部高地的顶部。 英文
讨论
我们尚不能对岩浆房的侧壁或顶部进行成像,但是我们的数据能为岩浆房形态的某些方面提供约束。图6展示了一个与我们观察结果相一致的模型。岩浆房被模拟成一个带有2~3 km宽顶盖的顶部平坦物体。我们在岩浆房的顶部引入了一个薄的熔融流体区域,以解释AMC反射层的高振幅及其极性倒转。然而,这两种观测都只需要大的负... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | 杰夫·福克斯和肯·麦克唐纳在我们航次开始前提供了他们的大尺度SeaBean型多波束测深图,这对于我们在计划和执行这项实验的过程中起了十分重要的作用。我们也感谢乔·卡恩、杰夫·福克斯、阿利斯泰尔·哈丁、查利·兰米尔、肯·麦克唐纳和珍妮特·莫顿的意见或评论。这项工作由美国国家科学基金会项目OCE-8314653(罗得岛大学)、OCE-8315466(拉蒙特–多尔蒂地质观测中心)、OCE-8316549(斯克里普斯海洋研究所)和OCE-8409509(美国伍兹霍尔海洋研究所)资助。 英文
(陈林 张新彦 翻译;张忠杰 审稿)
Transmission Dynamics of HIV Infection
R. M. May and R. ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | timescales, which is to say many years. In the absence of such information, mathematical models of the transmission dynamics of HIV cannot be used at present to make accurate predictions of future trends in the incidence of AIDS, but they can facilitate the indirect assessment of certain epidemiological parameters, cla... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0305. 《自然》百年科学经典(英汉对照版)(第七卷)(1985-1992).epub | .epub | 41,865,664 | 2025-09-26T19:07:39.767346 | The characteristics of most STDs cause their epidemiology to differ from that of common childhood viral infections11,14,15. Unlike infections caused by airborne transmission, the rate at which new infections are produced is not dependent on the density of the host. Second, the carrier phenomenon in which certain indivi... | 400套付费套装书 |
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