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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 | right direction); but it is diagnostic of a very specific structural interaction and of a very specific shape of the attached molecule. It has been found in many cases, as I will describe, that proteins which may be involved in non-muscular motility can form complexes of virtually identical structure. 中文
A final featur... | 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 | absence of free calcium, but allows it to take place in its presence, possibly by a steric blocking mechanism dependent on changes in position of tropomyosin. In molluscan muscles, however (including the striated muscle of Pecten), regulation is effected by changes in the myosin molecules to which calcium ions become 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 | In the past few years, however, several groups of workers have shown that the form of the myosin component in vertebrate smooth muscles is very dependent on the physical and chemical environment of the muscle; and Lowy et al.15,16 have found that with appropriate conditions before and during fixation, prominent and ple... | 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 | Before I consider how some of the other motile systems might function mechanically, it will be helpful to review briefly some of the more recent findings on their protein components. This account cannot do justice to many of the pioneers, but very often technical advances have now made it possible to characterize these... | 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 | Next consider the slime mould Physarum polycephalum, which shows very active cytoplasmic streaming. It has been shown by Hatano et al.22–24 that an actin-like protein can be extracted from this organism, which shows the same double helical structure as muscle actin in the electron microscope. As in muscle actin, the mo... | 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 | Further examples could be given, but I think cases mentioned are sufficient to show decisively that in a number of widely different cells exhibiting different forms of motile activity, a protein closely similar to muscle actin by rather strict criteria is present in significant amounts. And in many cases, the protein c... | 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 the case of blood platelets, Bettex-Gallard et al.41 and Booyse et al.42 have shown that the other component of thrombosthenin is a myosin-like protein, having calcium and magnesium-activated ATPase activity and a molecular weight of approximately 540,000. Adelstein et al.28 have shown that this molecule contains la... | 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 | Indeed, one can take this argument a stage further and suggest that the actin filament-myosin head interaction was developed as a motile mechanism very early in evolution, and that cells have been using it ever since, with a high degree of conservation of the essential protein interactions involved. As multicellular or... | 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 location of the actin and myosin assemblies could be interchanged. 中文
Cell organelles could be moved more directly by means of attached actin filaments, which could interact with myosin in large or even very small assemblies and propel themselves along in a manner which I suggested some years ago4, or by the intera... | 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 character of encounters with other cells would depend on whether the external attachment sites on the two interacting cells could attach to each other, or only to a third, freely movable site on the opposing membrane. In the latter case, the attachment sites between cells would be drawn to their edge, sustained ove... | 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 | et al.56 showed that a ring of filaments, just below the surface of the cleavage furrow at the newt egg, would bind HMM to give arrowhead complexes. This ring of filaments has been described by several workers on jellyfish eggs57,58, and also on the eggs of a polychaete worm58 and on the ciliate Nassula59 as a contract... | 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 | Kendrick-Jones, J., Lehman, W., and Szent-Gyorgyi, A. G., J. Mol. Biol., 54, 313 (1970).
Lehman, W., Kendrick-Jones, J., and Szent-Gyorgyi, A. G., Cold Spring Harbor Symp. Quant. Biol., 37, 319 (1972).
Lowy, J., and Hanson, J., Physiol. Rev., 42, Suppl. 5, 34 (1962).
Hanson, J., and Huxley, H. E., Symp. Soc. Exp. Biol.... | 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 | Hatano, S., and Ohnuma, J., Biochim. Biophys. Acta, 205, 110 (1970).
Hatano, S., and Takahashi, K., J. Mechanochem. Cell. Motility, 1, 7 (1971).
Nachmias, V. T., and Ingram, W. C., Science, 170, 743 (1970).
Nachmias, V. T., J. Cell Biol., 52, 648 (1972).
Nachmias, V. T., Proc. US Nat. Acad. Sci., 69, 2011 (1972).
Bette... | 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 | 我们因此提出疑问,这些系统是否都有着共同的基本机制?如果是的话,目前在某些方面对于横纹肌收缩机理已经相当详尽的研究能否为那些了解相对较少的其他运动机制的研究带来一些启示呢? 英文
在这篇文章中,我首先对肌肉机制的某些方面进行了介绍,尤其是肌肉的结构——我认为这与运动的普遍性问题特别相关。接着,我回顾了近来的很多研究,结果都非常明确地证明,人们所关注的蛋白质之间的相似性与肌肉运动机制中最基本的性质和相互作用有关。最后,我认为这些观点提示了特定种类细胞运动的明确机制。虽然这个普遍性的机制(“主动剪切”)在以前也曾被其他人提到过[1–3](尽管有时表述地不够明确),但似乎尚未得到广泛认可。 英文
根据肌肉收缩的肌丝滑动模型,横纹肌由一系列... | 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
如果这幅图所描述的机制是正确的话,那么由此我们可以得出肌肉收缩的基本原理就是通过细肌丝与结合在它上面的肌球蛋白头部形成具有相互作用的复合物来实现的。同样的,我们还可以得出,如果要维持纤维适当的极性,肌球蛋白分子组装成肌丝纤维的精确模型可能存在某些可变之处。即使都是横纹肌,不同的无脊椎动物物种之间肌球蛋白的组装模式也有所不同,并且很有可能在某些情况下,肌球蛋白可通过一种完全不同的形式组装而仍保持原有的肌球蛋白头部–肌动蛋白的相互作用。 英文
横纹肌肌丝滑动模型的第三个特点是肌球蛋白头部与肌动蛋白纤维之间精确的结合方式。目前,还没有一种办法可以捕捉到横桥的摆动过程,也不能在ATP存在的情况下阻止随后横桥与细肌丝的解离。然而,当没有... | 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
我们很容易便可以找出一些平滑肌的例子,比如双壳类动物的内收肌和牵缩肌。这些肌肉中也含有丰富的粗肌丝和细肌丝[13],却没有横纹。在琼·汉森和我[14]看来,缺乏横纹的原因很简单,主要由于这些肌丝没有像在横纹肌中那样高度有序地排列。最近的研究表明,研究脊椎动物平滑肌的难度大得多。多年来,虽然生化实验的结果表明其中显然同时含有肌动蛋白和肌球蛋白,但是人们通过电子显微镜只能观察到其中的细肌丝,通过X射线衍射实验也只能检测到肌动蛋白的反射信号。 英文
然而,最近几年,多个研究组的研究结果表明,脊椎动物平滑肌中的肌球蛋白的存在形式高度依赖于肌肉所处的物理和化学环境。洛伊等人[15,16]发现在固定前和固定过程中保持适当的条件,便可以观察... | 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 | 这种蛋白质可以与重酶解肌球蛋白结合形成典型的“箭头”结构,并且在双向电泳图谱中显示出与肌肉肌动蛋白具有非常高的化学相似性——在十四个甲硫氨酸标记的肽链中有十个与肌肉肌动蛋白一致,显示其与肌动蛋白具有很高的同源性,不过完全的一致性是不必要的。 英文
类似的例子还可以举出很多,不过我想上面提到的这些例子已经有力地证明了在各种具有不同运动能力的细胞中,都在严格标准下存在相当数量的与肌肉肌动蛋白高度相似的蛋白质。在许多例子中,人们发现这种蛋白质能在细胞中被原位鉴定出,它们是具有适当直径的束状纤维,可以被重酶解肌球蛋白“修饰”,且这些蛋白质通常可能分布在与运动相关的位置[32–34]。 英文
除了肌动蛋白,在许多具有运动能力的非肌细胞中还发现... | 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 | 这些肌动蛋白纤维可以与或大或小的肌球蛋白聚集体相互作用,从而通过某种方式驱动它们移动(我在几年前便提出了这种方式[4]),或者通过上文所述的相互作用方式运动。 英文
当细胞在某种基质上运动时(例如在组织培养物中),可以肯定的是,细胞中的其中一部分必须锚定在基质支持物上,而另一部分必定对这些附着位点做相对移动,并形成自己新的附着位点。由于在细胞上和细胞间的附着位点上经常可以观察到来自它们的拖尾的纤维,我们很自然的认为这些纤维是剪切系统中的某种组分,比如肌动蛋白,而另一个组分(此处指肌球蛋白,译者注)则因存在于细胞质中而得以向前流动越过附着的纤维。这些纤维的附着位点,可能与肌节中的Z线相似,会穿过细胞膜并锚定在基质上。当细胞的前端被胞质... | 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 growth of the nuclear industry from the 1950s onwards, generalized radioactive contamination became a matter of general concern. There are, however, particular problems of an unexpected character. This paper draws attention to the possibility that photographic emulsions, and in particular those used for taking... | 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 film we describe will have about 3.5×108 grains cm–2. With 10–4 μCi g–1 silver one will have a radioactive decay in 2.7×105 grains cm–2 yr–1. Thus about one per thousand of the grains will be directly involved in each year. If every radioactive decay involved one grain only, there would be no serious fogging, but t... | 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 | and with the data given we obtain photon fluxes of 5.3 s–1 cm–2 (0.67 MeV); 6.8 s–1 cm–2 (0.88 MeV); and 2.3 s–1 cm–2 (1.4 MeV) to give dose rates of 7×10–6 R h–1 (0.67 MeV); 12×10–6 R h–1 (0.88 MeV); and 6×10–6 R h–1 (1.4 MeV). Adding these fluxes gives a dose rate of 210 mR yr–1. This result is obtained without takin... | 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 | 这种物质的放射性是每立方厘米0.43 d.p.s.,并导致Sv为0.56 s–1·cm–3 (0.67 MeV)、0.61 s–1·cm–3 (0.88 MeV)和0.167 s–1·cm–3 (1.4 MeV)的光子发射。位于放射性均匀分布的无限平面源中心的光子流量为:
φ=BSv[1–E2(μsd)]/μs
其中B为累积因子,E2(μsd)是二阶指数积分,平板厚度为2d。当d在15 cm左右时,将有μsd>1;因E2(μsd)~0.1,故而[1–E2(μsd)]可以忽略。暂时忽略累积因子,就可得到:
φ ~ Sv/μs
我们还可以利用给定的数据求得光子流量分别为:5.3 s–1·cm–2 (0.67 MeV)、6.8 s–1·c... | 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 | however, is less fully documented. Here we describe the effect of chronic lithium chloride treatment on dopamine synthesis in striatal brain slices. 中文
Male albino Sprague-Dawley rats (180 to 200 g) were housed four per cage in a regime of 12 h light and 12 h darkness and fed lab chow and water ad lib. Lithium chloride... | 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 | lithium concentrations were determined by atomic absorption spectrometry. 中文
Acute injections of lithium chloride in doses of 2 to 4 mequiv kg–1 did not affect endogenous dopamine nor the synthesis of 3H-dopamine in striatal slices (Table 1). Daily administration of lithium chloride, 1 and 2 mequiv kg–1 for 14 days, 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 | Corrodi et al.14 also found a slight but significant decrease in whole brain dopamine turnover in rats treated with lithium for 3 weeks, judged on the basis of the rate of dopamine decline observed after injection of α-methyl-p-tyrosine. They have further found, using the histochemical fluorescence method, an increase ... | 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 | McIlwain, H., Biochem. J., 78, 213 (1961).
Neff, N. H., Spano, P. F., Groppetti, A., Wang, C. T., and Costa, E., J. Pharmacol. Exp. Ther., 170, 701 (1971).
Laverty, R., and Taylor, K. M., Anal. Biochem., 22, 269 (1968).
Udenfriend, S., Molecular Biology Series (edit. by Kaplan, N. O., and Scheraga, H. A.), 129 (Academi... | 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 | 在培养液中加入4~18 mEq/L锂离子,或者是用等量的锂取代培养液中的钠,孵育经生理盐水处理的大鼠纹状体切片,不会影响多巴胺的合成(表2)。 英文
表1. LiCl对纹状体切片中多巴胺合成的影响
* 动物数量,每只提供两份相同的纹状体样品。
† P < 0.005
‡ P < 0.001
英文
表2. LiCl或以锂离子取代钠离子对离体纹状体多巴胺合成的影响
* 动物数量,每只提供两份相同的纹状体样品。
英文
由此看来,通过锂离子对多巴胺合成进行抑制似乎需要长期治疗。由急性注射或者体外加入锂离子所产生的高锂浓度,不足以抑制其合成。这些结论与临床观察相关:锂离子的抗躁狂作用,需要每天服药一至两周才能实现。我们的结果与所观察到... | 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 | Human or rat brains were dissected and stored on dry ice as previously described6. Human material was obtained at autopsy from either control (no known neurological disorder) or Parkinsonian patients. Nine Parkinsonian patients received L-dopa until they died; two others did not receive L-dopa therapy. The patient grou... | 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 GAD activity in the striatum and substantia nigra of the non-dopa treated Parkinsonian patients was less than 50% of the control mean (Table 1), in agreement with a previous report1. In other brain regions GAD activity was within the range of the control values. In the brains of patients who received L-dopa for 8 m... | 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 the rats treated chronically with oral L-dopa, after administration of L-dopa for 37 and 38 days the striatal GAD activity was not different from control (Table 2). After 109 days, however, striatal GAD activity was significantly greater than in either those rats which had received lower doses of L-dopa for a shorte... | 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 | highest GAD activities were treated for longer (1 year or longer) and received, as a group, a higher dose of L-dopa (Table 1). It has also been shown that the striatal dopamine concentration of chronically L-dopa treated patients is markedly higher than in non-dopa treated patients5,12,13. Correspondingly, the more chr... | 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 alternative hypothesis is an enhanced synthesis of GAD apoenzyme in compensation for decreased cofactor availability as a result of Schiff base formation with L-dopa15,16. Such an in vivo formation of Schiff base would not be reflected in vitro where an optimal concentration of pyridoxal phosphate is added. Signs of... | 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 | Perkinson, E. N., and DaVanzo, J. P., Biochem. Pharmacol., 17, 2498 (1968).
McGeer, E. G., McGeer, P. L., Wada, J. A., and Jung, E., Brain Res., 32, 425 (1971).
McGeer, P. L., McGeer, E. G., and Wada, J. A., Neurology, 21, 1000 (1971).
Kim, J. S., Bak, I. J., Hassler, R., and Okada, Y., Exp. Brain Res., 14, 95 (1971).
... | 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 | 在接受L–多巴治疗等于或少于8个月的患者脑中,GAD活性明显低于对照组(参见表1)。对于连续接受L–多巴治疗1年及以上的患者,其尾状核、壳核、黑质和苍白球中GAD活性处于对照组的活性范围之内,显著高于接受治疗时间较短的患者。接受更长时间L–多巴治疗的患者其他脑区GAD活性只是略高一点而已。 英文
表1. 对照患者与帕金森氏症患者不同脑区中L–谷氨酸脱羧酶的活性
不同治疗周期的患者的L–多巴日口服剂量为2~6 g。酶活性(平均值±标准差)以每2小时100 mg蛋白质产生的二氧化碳纳摩尔数表示(括号中为案例数)。脑组织在冰冷的等渗葡萄糖溶液中匀浆,在含有磷酸盐缓冲液(pH 7.0)和0.6 mM磷酸吡哆醛的溶液中孵育20分钟(37°C... | 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
在L–多巴长期治疗期间,纹状体GAD活性增加可能与临床有重要的关联,因为它与L–多巴明显改善帕金森氏症患者颤抖呈现显著的平行关系(这可能要花上几个星期至几个月的时间[17])。目前为止,L–多巴的抗震颤作用与任何已知的神经化学物质都不相关;我们的观察表明这一过程可能会涉及含γ–氨基丁酸(GABA)的神经元系统。基于这一说法,最近报道了一种新的GABA样化合物,其对帕金森氏症患者具有特异性的抗震颤作用[18]。 英文
p–溴–m–羟基苯甲氧基羟胺由纽约珀尔里弗莱德利实验室的小史密斯博士所提供。这项研究由纽约诺威奇克拉克精神病研究所和伊顿实验室提供支持。 英文
(王耀杨 翻译;李素霞 审稿)
Neutral Mutations
... | 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 | Kimura and Ohta believe that most nucleotide substitutions in evolution are due to the random fixation of selectively neutral alleles, and that protein polymorphisms revealed by electrophoresis merely represent a transient phase of this molecular evolution. Most of the mathematical results described in this book have 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 | Now the rate of neutral mutation for the whole genome can be estimated by multiplying the rate per nucleotide site by the total number of sites in the genome, calculated from the DNA content of sperm. For man, Kimura and Ohta estimate that between sixty and seventy-five neutral mutations occur per genome per generation... | 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 | 尽管在20世纪70年代中期这是一个很有争议的观点,但是实验显示它在多数情况下都是正确的。 英文
《群体遗传学理论》*是一本极好的图书,每一个对群体遗传学感兴趣的读者都应该阅读它。这本书的作者是世界上两位杰出的理论遗传学家,这本书主要讲述了他们过去五年里在这个领域所做出的贡献。本书内容非常清晰、精炼,大多数的数学证据都降低了难度,使数学手段成为附属工具,从而迎合了非数学思维模式。第1章处理了突变基因的固定的问题;第2章对进化速率观测结果的阐释进行讨论,这用到了第1章的内容,其中进化速率是根据蛋白质序列数据测得的。接下来的章节阐述了有效群体大小的概念、遗传负荷理论、双基因座问题、群体多样性的维护以及性别的适应意义。 英文
木村和太田认为... | 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 | reconstruct hotspot motions over the past 180 million years, and conclude that while in general they don’t retain their relative positions, some small groups do so. Hotspot motions offer clues about the patterns of mantle convection, which are still debated today. 中文
Although not all hot spots are fixed with respect to... | 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 | hot spot at any time in the past is marked by the point of that age on its trace. 中文
Misfit
Figure. 1 is a reconstruction of the Atlantic ocean and its surrounding continents about 120 m.y. ago7, and five selected Atlantic hot spots which possess comparatively well defined traces are plotted on it at the positions that... | 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 | hot spots between 120 m.y. ago and the present relative to Colorado Seamount hot spot. Palaeoequator is around average pole at 69° N 180° W with respect to North America.
中文
Data used to plot the hot spot positions on Fig. 1, and for subsequent parts of this paper, are listed in Table 1. The positions of the two nort... | 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 | axis of the spreading ridge, and is justified because hot spot traces extend away on both sides of the spreading ridge. Data are given in Table 3 and the change in great circle distance with time is shown in Fig. 2. Although the shape of the curve showing the relative motion is crudely exponential, we do not attach sig... | 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 | Ideally, palaeomagnetic data can be used to establish how the relative motion between the hot spots has been distributed with respect to the magnetic field and by inference to the spin axis. We have estimated average palaeomagnetic poles for various plates at particular times from data contained in a recent compilation... | 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 | Seventeen poles for the Eurasian plate 60 m.y. ago are almost all closely grouped, but the average pole they define is not compatible with an average pole for North America5 when the appropriate North Atlantic motion8 is removed (Table 4, in brackets). Three poles in the Eurasian group plot 20° away from the main group... | 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 | m.y. ago can be interpreted as indicating a large northward motion of the Iceland hot spot (about 20°) since this time. In view of the uncertainty in the palaeomagnetic data, we would suggest that although relative northward motion of this hot spot is probable, the amount of motion may be more modest. We estimate from ... | 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 | be moving in a similar manner. 中文
McElhinny5 showed that the apparent motion of the Iceland hot spot with respect to the magnetic field3 is more likely to be due to relative motion between hot spots than to a rotation of the mantle containing fixed plumes with respect to the lithosphere as a whole3,22. Our conclusion t... | 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 | We think that the idea that deep mantle plumes2,24 underlie hot spots is at present the only satisfactory hypothesis available to account for hot spots, especially to explain their persistence as discrete localized anomalies, in some cases for 180 m.y. This is particularly the case for those hot spots which are on the ... | 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 groups of hot spots that we have shown to remain essentially fixed internally have an approximate maximum horizontal dimension of 2,000 km. This is of the same order as the large swells that occur in East Africa and the Red Sea area, which are about 1,500 km across. We interpret the pattern of alkaline volcanism on... | 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 | hot spots become available. If it is accepted that deep mantle plumes2,24 underlie hot spots, then information relating to processes at the core-mantle boundary, and perhaps in the core, might eventually be extracted from the distribution and relative motion of hot spots. Our observations of the motion of some hot spot... | 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 | Le Pichon, X., and Fox, P. J., J. Geophys. Res., 76, 6294 (1971).
Bullard, E. C., Everett, J. E., and Smith, A. G., Phil. Trans. R. Soc., A258, 41 (1965).
Piper, J. D. A., and Richardson, A., Geophys. J. R. astr. Soc., 29, 147 (1972).
Phillips, J. D., and Forsyth, D., Geol. Soc. Am. Bull., 83, 1579 (1972).
Clague, D. 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 | 虽然亚速尔群岛热点确实位于1.2亿年前它所在的相对位置上,但南大西洋的其他三个热点则均落在了当时位置之外约20°的地方。这说明在过去的1.2亿年中,它们与北部两个热点之间发生了相对运动,平均速率为1.8厘米/年,其方向大致与板块相对运动的总体方向垂直。 英文
图1. 1.2亿年前大西洋板块轮廓的示意图。其中给出了大致的板块边界示意图(据参考文献7),参照系相对于北美洲固定。●,代表根据其迹线得到的该时期5个热点的位置;,表示北部两个热点的早期部分迹线;,为插入的一条较老的迹线(见正文);○,代表当前南部热点相对于科罗拉多海山热点的位置,其中科罗拉多海山热点相对于北美洲的位置与1.2亿年前保持一致。A,亚速尔群岛;CS,科罗拉多海山... | 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
根据1.8亿年前的古地磁极平均位置以及其他古地磁极平均位置得到的古纬度所存在的误差,可能比我们利用所选定的分布在各重要地区的数据资料所测定的值误差还要大,达15°~20°。但是,1.8亿年前和1.2亿年前的古地磁极平均位置被选定以后,我们又对其作了适当的旋转,使之与后来这些相关板块发生的总体运动可以协调起来,因此,相对于根据各个分散板块上的古地磁极平均位置所得到的值来说,由此得到的古纬度值可能更可靠一些,因为在消除了后来的板块运动影响之后,各板块的古地磁极平均位置并不相符。表4给出的古地磁极平均位置应该看成现今估测值,并且仅限于所给定的年龄范围内。根据过去2,500万年的古地磁数据,非洲板块相对于磁偶极场未作任何运动(参考文献... | 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 | 各热点相对于磁场和自转轴作不同的运动,而对于我们所研究的几个热点来说,似乎主要是向极运动,不过并不是所有的热点都向其所在半球的极点运动。向极运动也可能是间歇性的,有时甚至会反向运动。其他热点的有关资料也非常值得研究,然而遗憾的是,虽然热点有很多[23],但具有清晰的迹线且年龄确定,同时又与中大西洋和南大西洋热点同时期的、能够观测到的却少之又少(如果有的话)。 英文
符合要求的假说
我们认为,深层地幔柱[2,24]位于热点之下的观点是当前唯一符合要求的、能够解释热点的假说,尤其是可以解释为什么作为分散的、小范围的异常体,它们能够延续至今,要知道它们中有的已有1.8亿年的历史了。而扩张脊脊轴上的热点尤其如此,并且它们长久以来一直处于这种... | 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 | It was realized more than two hundred years ago that there is a critical mass and radius beyond which light cannot escape the gravitational field of an object—such an object becomes a “black hole”. This idea was rigorously validated by the theory of general relativity. Here Stephen Hawking shows that black holes have 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 | order of 1071 (M⊙/M)–3 s. For a black hole of solar mass this is much longer than the age of the Universe. There might, however, be much smaller black holes which were formed by fluctuations in the early Universe2. Any such black hole of mass less than 1015 g would have evaporated by now. Near the end of its life the 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 | fi and the :
The βij will not be zero because the time dependence of the metric during the collapse will cause a certain amount of mixing of positive and negative frequencies. Equating the two expressions for φ, one finds that the bi, which are the annihilation operators for outgoing scalar particles, can be expressed... | 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 | αωω' ≈ C exp [i(ω–ω')υ0](ω'/ω)1/2 · Γ(1–iω/κ) [–i(ω–ω')]–1+iω/κ
βωω' ≈ C exp [i(ω+ω')υ0](ω'/ω)1/2 · Γ(1–iω/κ) [–i(ω+ω')]–1+iω/κ
The total number of outgoing particles created in the frequency range ω→ω+dω is . From the above expression it can be seen that this is infinite. By considering outgoing wave packets which are... | 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 | symmetry which merely simplifies the calculation. 中文
Beckenstein6 suggested on thermodynamic grounds that some multiple of κ should be regarded as the temperature of a black hole. He did not, however, suggest that a black hole could emit particles as well as absorb them. For this reason Bardeen, Carter and I considered... | 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 | 虽然量子效应在局部很小,然而它们仍然可能在宇宙的寿命≈1017s内积累产生重大的影响,这个时间远长于普朗克时间≈10–43 s。这篇快报的目的是说明,似乎任何黑洞都将以预期的速率产生和发射粒子,如中微子或光子,正如同黑洞是一个温度为(κ/2π)(ћ/2k)≈10–6(M⊙/M)K的物体所表现的那样,其中κ是黑洞的表面引力[1]。当黑洞发射这类热辐射时,我们预期它将损失质量。这本身将增大它的表面引力,因而增大其发射速率。从此,黑洞将具有1071(M⊙/M)–3 s量级的有限寿命。对于太阳质量的黑洞,这将比宇宙年龄更长。然而,可能存在许多较小的黑洞,它们是由早期宇宙中的涨落形成的[2]。任何这类质量小于1015 g的黑洞到现在都应该蒸发... | 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 | 这意味着对于大的ω':
|αωω'|=exp (πω/κ)|βωω'|
由此可得,这个波包模式中发射的粒子数是从I–入射到黑洞上的类似波包中已被吸收的粒子数的[exp(2πω/κ)–1]–1倍,但这正是根据几何单位下温度为κ/2π的物体所预期的吸收和发射截面之间的关系。类似结果对任何整数自旋的无质量场也同样成立。对半整数自旋,正如我们对费米子的热辐射所预期的那样,也能得到类似结果,只是发射截面是吸收截面的[exp(2πω/κ)+1]–1倍,这些结果似乎并不依赖于只是为了简化计算而采取的精确球对称性假设。 英文
贝肯斯坦[6]在热力学基础上提出,κ的某个倍数应该被看作黑洞的温度。然而,他并未提出,黑洞可以像吸收粒子一样发射粒子。因此,... | 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 | of Koobi Fora was begun in 1972 and continued in 1973. No hominids have yet been found in the limited exposures of the Kubi Algi Formation. A notice of two specimens—KNM-ER 1510 and 1590—that were previously1 mentioned only by number, is included in this report. The 1973 hominids are not here attributed to genera as 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 | I. Findlater extended mapping of tuffaceous horizons to the south of Koobi Fora and collected samples for isotope dating. A series of dates has been obtained from material collected during 1972 (unpublished work at Miller, Findlater, Fitch and Watkins). Palaeomagnetic studies complement those of 1972 and there are suff... | 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 | of a slight inferior mandibular torus and the distinct eversion of the mandibular body when viewed from below. 中文
Fig. 1. Mandible, KNM-ER 1802. a, Superior view; b, inferior view; c, right lateral view.
中文
A weathered mandible, KNM-ER 1801, bears some resemblances to KNM-ER 1802, but its worn dentition and loss of ... | 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 large mandible, KNM-ER 1806, was discovered by Meave Leakey at the same site and horizon as was KNM-ER 1805. There are no tooth crowns preserved and the ascending rami are missing in this otherwise complete specimen. The mandible is typical of the large East Rudolf hominid that I have previously attributed to Austral... | 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 | Other specimens recovered during 1973 are listed in Table 1 and will be described in detail after studies are completed. 中文
Significance of the 1973 Collection
In previous reports1,4-7, the East Rudolf hominids were assigned to Australopithecus, Homo or indeterminate (the last category included both very fragmentary sp... | 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, KNM-ER 1813, may prove to be quite distinct from the robust australopithecines and from Homo, as represented by KNM-ER 1470. The dentition is ‘hominine’, yet the cranial capacity appears small. The cranium has some of the features seen in the gracile, small brained, hominid Australopithecus africanus Dart,... | 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 | morphological dichotomy. 中文
I suggest the following as a basis of nomenclature for Plio-Pleistocene hominids. One genus would include much of the material currently referred to Australopithecus robustus and A. boisei. A second genus would incorporate many of the gracile specimens from Sterkfontein presently referred to... | 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 those who made important discoveries. I would also express thanks to my wife Meave who, as always, provided invaluable assistance both at the museum and in the field. 中文
(248, 653-656; 1974)
R. E. F. Leakey
National Museums of Kenya, PO Box 40658, Nairobi
Received January 9, 1974.
References:
Leakey, R. E. F., N... | 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 | 鲍恩指导了对130区和131区的上下段地层的研究,包括对产出KNM–ER 1470头骨的地层关系的确认。由约翰逊带领,来自新罕布什尔州达特茅斯学院的研究小组对102区出露完好的库比福勒组的地层剖面进行了研究。贝伦斯迈耶对人科动物化石地点做了初步地质调查,并记录了沉积环境和可能伴生的动物群;进一步的研究已做好了安排。 英文
芬勒特将对凝灰岩层的绘图工作扩展到了库比福勒以南,并且采集了同位素测年样品。从1972年间采集到的材料中已经获得了一系列年代数据(米勒、芬勒特、菲奇和沃特金斯未发表的工作)。古地磁学研究补充了1972年的研究数据,现在已经有足够多数据来相互印证[3]。 英文
人科动物标本
此前报道过的KNM–ER 1590号标本[... | 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 | 上颌骨的两侧可以拼接到一起,从而可看出齿弓的形状。右上颌骨残片包括颧骨部及与右眼眶侧边相连的部分。 英文
图2. 颅骨,KNM–ER 1813。a,右侧面视;b,上面视;c,左上颌嚼面视。
英文
1973年间挖掘的其他标本都在表1中列出,并将在相关研究完成以后再做详细描述。 英文
1973年所采集标本的意义
在之前的报道中[1,4-7],鲁道夫湖以东的人科动物化石被归入到了南方古猿、人属或分类未定(后者既包括破碎的标本,也有分类位置不明的标本)。 英文
鲁道夫湖以东发现的标本被归入南方古猿,其分布时间在距今300万到100万年,期间几乎未曾发生显著形态变化。这类南方古猿与南方古猿鲍氏种[8]相同;同时也显示了与南非的南方古猿粗... | 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
我想对国家地理学会、国家科学基金会、唐纳基金会和其他组织提供的经济资助表示感谢。感谢肯尼亚国家博物馆和肯尼亚政府提供的支持与鼓励使我们的研究得以顺利进行。由于鲁道夫湖以东研究项目组的成员太多,无法一一致谢,但是我得说所有人都在成功的野外发掘工作中起了相当重要的作用,并同时感谢获得重要发现的人员。我还要感谢我的妻子米芙一如既往地在博物馆和野外工作方面所提供的宝贵帮助。 英文
(刘皓芳 翻译;同号文 审稿)
Stratospheric Sink for Chlorofluoromethanes: Chlorine Atom-Catalysed Destruction of Ozone
M. J. Molina and F. S.... | 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 | chemical inertness and high volatility which make these materials suitable for technological use also mean that they remain in the atmosphere for a long time. There are no obvious rapid sinks for their removal, and they may be useful as inert tracers of atmospheric motions4-6. We have attempted to calculate the probabl... | 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 | wavelengths is complicated by the intense narrow band structure in the Schumann–Runge region, and the effective rates of vertical diffusion of molecules at these altitudes are also subject to substantial uncertainties. Vertical mixing is frequently modelled through the use of “eddy” diffusion coefficients10,15-18, whic... | 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 | chlorofluoromethane at higher altitudes and the concentrations should be very low above 50 km. The peak rate of destruction, and formation of Cl atoms, occurs at 25-35 km, in the region of high ozone concentration. The rates of formation of Cl atoms at different altitudes, and the chlorofluoromethane atmospheric lifeti... | 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 | Possible terminations involving the Cl series with itself (for example, Cl + ClO → Cl2O) or with one of the others (for example, Cl + NO → NOCl) normally lead to molecules with appreciable absorption coefficients at longer wavelengths, which are very rapidly dissociated again by the much more intense solar fluxes avail... | 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 | atom. Thus, each molecule of CFCl3 initially photolysed probably leads to between two and three Cl atom chains, and CF2Cl2 probably produces two Cl atom chains when it is photolysed. Initial calculations suggest that F atom chains will be much shorter than Cl atom chains because the reaction of abstraction from CH4 is ... | 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 | Photolysis of these chlorofluoromethanes does not occur in the troposphere because the molecules are transparent to wavelengths longer than 2,900 Å. In fact the measured absorption coefficients for CFCl3 and CF2Cl2 are falling rapidly at wavelengths longer than 2,000 Å (ref. 14). The reaction between OH and CH4 is beli... | 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 with most NOx calculations, our calculations have been based entirely on reactions in the gas phase, and essentially nothing is known of possible heterogeneous reactions of Cl atoms with particulate matter in the stratosphere. One important corollary of these calculations is that the full impact of the photodissocia... | 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 | McElroy, M. B., Wofsy, S. C., Penner, J. E., and McConnell, J. C., J. Atmos. Sci., 31, 287 (1974).
Bemand, P. P., Clyne, M. A. A., and Watson, R. J., J. Chem. Soc., Faraday I, 69, 1356 (1973).
Hampson, R., et al., Chemical Kinetics Data Survey VI, National Bureau of Standard Interim Report 73-207 (1973).
Stolarski, 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 | 这些自由基会与平流层臭氧发生反应,使之发生破坏,而臭氧层恰恰担当着保护地球表面免受有害紫外线照射的部分屏障作用。这个预言在11年后被证实,并且引领了一场逐步淘汰氯氟烃的全球化变革。这项研究也使得莫利纳和罗兰获得1995年的诺贝尔化学奖。 英文
氟氯甲烷正以稳定增长的量被排放到环境中。这些化合物具有化学惰性,可以在大气中停留40~150年,预计其浓度能够达到目前水平的10~30倍。平流层中氟氯甲烷的光解可以产生大量氯原子,并会导致大气中臭氧的破坏。 英文
在过去的几十年中,卤代脂肪烃的应用日益广泛,主要是作为喷雾推进剂和制冷剂,并以稳定增长的数量被排放到自然环境中[1,2]。目前已检测到两种氟氯甲烷(CF2Cl2和CFCl3)分布在整... | 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 | 在大部分高度,将Cl–ClO奇电子链转换到一种含氯偶电子物质的第一个反应都是从CH4中抽提H,从而将奇电子性质转移给CH3自由基:
Cl+CH4 → HCl+CH3
(3)
在平流层温度下,对于反应(3)而言Cl原子[22]速率常数约为反应(1)的10–3,而O3/CH4浓度比可以使反应(3)的速率降至(1)的10–4。Cl原子链可以通过OH与HCl的反应恢复(参考文献23):
OH+HCl → H2O+Cl
(4)
通过吸收1,750~2,200 Å波长范围的光而产生的紫外离解反应也能在较高海拔处发生。反应(4)在平流层中的速率取决于只是大概知道的OH浓度。在我们的估计中,Cl–ClO链的终止是由于链中寿命更长的种类(ClO和HC... | 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 | 关于这些分子在环境中的生物学相互作用的了解还远远不够,因为自然条件下这种作用不会发生(仅有的例外是在来自火山喷发物的微量产物中)[29],不过看来不大可能有快速的生物学清除方法。在水中的相对不溶性以及它们的化学稳定性(尤其是对于水解反应来说)[30]意味着这些分子不会通过溶于海洋中而被快速清除,目前为止为数不多的观测指出海面与空气之间存在平衡,因而不能断定存在一种重要的海洋转换过程[3]。 英文
看来十分清楚的是,大气对于平流层产生的Cl原子只有有限的吸收能力,而这可能导致重要的结果。即使是对目前氟氯甲烷的排放速率来说,这一吸收能力可能也不足以保持稳态。为了确定这一环境问题可能爆发的程度,需要在不久的将来对这种吸收能力进行更为精确的... | 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 | which repeats every 200 base pairs, the best value currently being 205±15 base pairs5. 中文
The most cogent model for chromatin has been put forward by Kornberg6 who suggested that the basic structure consists of a string of beads each containing two each of the four major histones, each bead being associated with about ... | 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 | No doubt other types of kink could be built, but we have concentrated on one special type which we consider to be rather plausible. We have assumed that all the base pairs of the double helix are left intact (so that no energy is lost by unpairing them), that the straight parts of the DNA on each side of the kink remai... | 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 | To our surprise the configuration of the backbone at the kink can be made similar to that of the normal backbone of the B form except that the conformation at the C4′–C5′ bond in the sugar is rotated 120° about this bond, going from one of the possible staggered configurations to another one as shown in Fig. 3. (We hav... | 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 | helix, per unit length, to increase at least as fast as κ2. For a kinked helix, on the other hand, this energy increases only as κ. In this case κ is the mean “curvature” of the segmented double helix which is proportional to the number of kinks per unit length. Thus, as is intuitively obvious, at small κ the double he... | 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 | To introduce our fourth point we must first consider the relationship between three successive straight portions; that is, two kinks in succession. We assume that every kink is exactly the same. The structure formed will depend on the precise number of base pairs between the kinks. (It should be remembered that the B 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 | The exact dihedral angle associated with three successive straight stretches depends somewhat on the precise details of the kink but is typically about (m.36°–θ) where m is the number of base pairs between the two kinks and θ, the dihedral correction angle, is not far from 15-20°. A very small rotational deformation of... | 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 idea that the fold of DNA in chromatin was based on a unit of 10 base pairs was originally suggested to us by experimental evidence discovered by our colleague, Dr. Markus Noll. Noll15 has shown that the digestion of native chromatin with the nuclease DNase I produces nicks in the DNA which tend to be spaced multip... | 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 | kinks (see Fig. 5). In this position, being near a kink, they are more exposed than they would be in a stretch of unkinked DNA. 中文
Fig. 5. The minimal base sequence of the lac operon, taken from Gilbert and Maxam18. The dotted line marks the pseudodyad in the base sequence. The two sets of consecutive base pairs, rela... | 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 the present we have no compelling evidence which shows that DNA in chromatin is kinked rather than bent nor that kinks exist in DNA in other contexts. Nevertheless our model seems to us sufficiently attractive to be worth presenting now for consideration by other workers in the field. Kinks, if they occur, have at 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 | Van Holde, K. E., Sahasrabuddhe, B., and Shaw, R., Nucleic Acid Res., 1, 1579-1586 (1974).
Baldwin, J. P., Boseley, P. G., Bradbury, E. M., and Ibel, K., Nature, 253, 245-249 (1975).
Arnott, S., and Hukins, D. W. L., Nature, 224, 886-888 (1969).
Sundaralingam, M., Biopolymers, 7, 821-869 (1969).
Gourévitch, M., et al.,... | 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 | 因此我们曾经自问:这种折叠的DNA是否可能由相对笔直的舒展部分通过很大的扭结连接形成。本文描述了某一特定类型的扭结,这种扭结恰好可以完美构建,并具有令人感兴趣的性质。 英文
一个扭结的立体化学
尽管其他类型的扭结无疑也可以构建形成,但我们只关注一个特殊的类型,因为我们认为它比较合理。我们假设:DNA双螺旋中所有的碱基对都保持完好无损(即没有未配对碱基的能量损失),在扭结每一侧DNA的笔直部分都保持正常的B型,但是在扭结处,一个碱基对与相邻碱基对完全不是相互堆积的。因此,在每个扭结处,就损失了把一个碱基对堆积到另一个碱基对上的能量。当然,所有的键长和键角(包括二面角)都必须是立体化学上能接受的。 英文
我们发现,根据这些假设,可以令人... | 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 | (3)如果我们把扭结位点定义为扭结两侧的两个局部双螺旋两轴间的交点(或者,如果它们不相交,则把扭结位点定义为两个螺旋轴之间最短直线的中点),那么从扭结位点到最近碱基对所在平面的距离D就是可以估算的,其典型数值在7~8 Å这个区间内。 英文
为了介绍我们的第四点,我们首先要考虑三段连续直线部分之间的关系;也就是说,两个连续的扭结。我们假定每个扭结都是完全相同的。所形成的结构依赖于扭结之间碱基对的精确数目。(应该记住的是,B型DNA在10个碱基对以后有完全相同的重复片段)。例如,如果在两个扭结之间存在10(或者10的倍数)个碱基对,那么这个结构会粗略的弯曲环绕成正方形的三个边。如果在两个扭结之间存在5(或者5的奇数倍数)个碱基对,那么这... | 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 | 例如,可以设想一个有四个扭结的漂亮锯齿状模型,每个扭结之间相隔大约5个碱基对。该模型将两条序列通过二重轴相联系,每条序列具有六个连续的碱基对,分别安插在第一个和最后一个扭结的两侧(参见图5)。在这个位置上,由于靠近扭结,它们比在一段无扭结的DNA上更加的暴露。 英文
图5. 乳糖操纵子的最小碱基序列,来自吉尔伯特和马克萨姆的文章[18]。虚线标记的是碱基序列中的假二重轴。方框标记由二重轴联系的两组连续的碱基对。箭头表示扭结可能发生的位置。
英文
从本质上说,扭结也许是一种不用消耗太多能量就可以暴露一小组碱基对的方式。正常情况下这些碱基对被暴露的一侧位于大沟中。大沟的两侧通常是由磷酸–糖骨架构成的,扭结使其中一个骨架发生移位。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 | Medicine (with Niels K. Jerne) in 1984. 中文
THE manufacture of predefined specific antibodies by means of permanent tissue culture cell lines is of general interest. There are at present a considerable number of permanent cultures of myeloma cells1,2 and screening procedures have been used to reveal antibody activity 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 | Two myeloma cell lines of BALB/c origin were used. PlBul is resistant to 5-bromo-2′-deoxyuridine4, does not grow in selective medium (HAT, ref. 6) and secretes a myeloma protein, Adj PC5, which is an IgG2A(κ), (ref. 1). Synthesis is not balanced and free light chains are also secreted. The second cell line, P3-X63Ag8, ... | 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 | individual cells must therefore be able to express both isotypes. This result shows that in hybrid cells the expression of one isotype and idiotype does not exclude the expression of another: both heavy chain isotypes (γ1 and γ2a) and both VH and both VL regions (idiotypes) are expressed. There are no allotypic markers... | 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 | Figure 1A shows that clones derived from different hybridisation experiments and from subclones of one line are indistinguishable. This has also been observed in other experiments (data not shown). Variants were, however, found in a survey of 100 subclones. The difference is often associated with changes in the ratios ... | 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 | cells by a plaque assay technique13 (Fig. 2a). The hybrid cells were cloned in soft agar14 and clones producing antibody were easily detected by an overlay of SRBC and complement (Fig. 2b). Individual clones were isolated and shown to retain their phenotype as almost all the clones of the derived purified line are capa... | 400套付费套装书 |
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