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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 | 但是据我们预测,也正如丹戎所言,这些变化应该有更重要的意义,因为它们紧随强太阳耀斑活动发生。我们确信,这种效应是真实存在的,并且突变确实是由与1972年8月初的太阳活动相关的事件所引起。 英文
图2. 1972年5~10月AT–UT2的变化情况。强太阳活动后斜率发生变化,而随后又回归至耀斑发生前的斜率,这充分说明了该事件的重要性。
英文
我们不难想出一个模型来解释为何耀斑活动开始到日长的突变发生之间有5天的滞后效应。在本文中我们不会讨论详细的机制问题,仅指出地球大气层的大尺度环流会受太阳活动的影响。例如,当到达地球的太阳宇宙射线水平较高时,高纬度地区环流模式中的低压槽就会加深[10,11]。同沙茨曼[6]一样,我们认为日长的突... | 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 | use. 中文
Soon after the first noble gas compounds had been discovered8-12, Pomeroy13 suggested that chemical methods might be useful for trapping krypton and xenon isotopes. Slivnik14 has studied reactions of krypton-xenon mixtures with fluorine for waste-gas treatment and has demonstrated that xenon can be separated fr... | 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 | Flow experiments were carried out with O2SbF6 powder and samples of air (0.33-0.76 l. at STP) which had been artificially contaminated with 222Rn and 133Xe. In each experiment, a rare gas/air mixture was passed through a glass U-tube packed with the powder, then through a trap cooled with liquid nitrogen to condense an... | 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 | Mixtures of approximately three parts O2SbF6 and one part antimony pentafluoride by volume (grey powders, prepared in a dry box) react with radon but not with xenon. Dilution with antimony pentafluoride therefore lowers the free energy of O2SbF6 below the threshold for zenon oxidation but not below that for radon oxida... | 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 | Because it has negligible vapour pressure at 25°C, and because oxygen is the gaseous product, the dioxygenyl compound appears to be a very “clean” reagent for air-purification purposes. It is less corrosive than such complex fluorides as ClF2SbF6, BrF2SbF6, and BrF2BiF6, and may be stored in glass or fluorinated plasti... | 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 research may disclose oxidants that can be used to collect krypton as well as radon and xenon. Krypton forms a simple fluoride, KrF2, which is stable only at low temperatures, and a complex fluoride, KrF2.2SbF5, which is stable at 25°C (refs. 21, 22). (The latter is probably an ionic compound, , analogous 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 | Grosse, A. V., Kirshenbaum, A. D., Streng, A. G., and Streng, L. V., Science, 139, 1047 (1963).
Pomeroy, J. H., in Noble Gas Compounds (edit. by Hyman, H. H.), 123 (University of Chicago Press, Chicago, 1963).
Slivnik, J., in Proc. of Symp. on Treatment of Airborne Radioactive Wastes, 315 (Int. At. Energy Agency, Vienn... | 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485~700 mm压强、23~150°C温度范围内,没有观测到氪的反应。 英文
用O2SbF6粉末与人为污染222Rn和133Xe的空气样品(标准状态下0.33~0.76l)进行了流动实验。每个实验中,稀有气体/空气混合物先经过一个填满该粉末的玻璃U形管,接着再经过一个液氮冷阱,冷凝未反应的放射性同位素。随后通过测定U形管和冷阱中的γ发射来确定放射性同位素的分布。(即刻确定133Xe的分布;3小时后确定222Rn的分布,已知此时222Rn与其γ发射子体214Pb和214Bi处于放射性平衡中。)在用氡同位素和长5.0 cm、直径6.3 mm的粉末床进行的3次实验中,所有的氡都被吸收了。在用氙同位素和长6.5 cm、直径5.5 mm... | 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
感谢马尔姆提供的关于六氟合锑酸(V)双氧盐的制备信息,以及恩格尔克迈尔提供的混合气体质谱分析的信息。本研究得到了美国原子能委员会的赞助。 英文
(王耀杨 翻译;安俊岭 审稿)
Cores of the Terrestrial Planets
K. E. Bullen
Editor’s Note
In the early 1970s we were just beginning to understand the properties of the planets of the Solar System, as the first unmanned space missions sent back data. In parti... | 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 an early attempt at reconciliation, Ramsey4 and myself5 independently advanced a “phase-transition theory” which treated the Earth’s outer core as a high-pressure modification of the lower mantle material. This theory agreed with a common overall composition for the three planets and fitted well the then available o... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | As a possible alternative, I propose a theory which avoids the principal difficulties of the phase-transition theory while retaining the important feature that the pressure pc at N is critically involved in the changes of property at N. The theory incorporates a suggestion of O. G. Sorokhtin (personal communication) 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 | The second property secures a common overall composition for the family. The masses of Y and Fe in any planet are such as would combine precisely to form Fe2O when p ≥ pc, and the ratio of the total mass of Fe, Fe2O and Y to M is the same for the whole family. 中文
The family has three subsets—H, J, K, say (Fig. 1). 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 | I have started from a simplified Earth model, taken to be a member of the subset J, in which the mean densities of the mantle, outer and inner cores are 4.5, 11 and 13 g cm–3, respectively. I have provisionally neglected variations of density inside planetary zones and taken the ratio of the mean densities of X and Y 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 | The postulates also determine the ratio of the mass of the inner core to the mass M of any H planet as approximately 0.15. For a particular H planet of assigned mass, a first approximation to R is then formally yielded if values are available for the mean densities, ρ1 and ρ2 say, of the core and mantle. For Mars, M=0.... | 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 | Ironically, after the phase-transition theory had been shown to fit closely the then assumed observational estimate R=3,390 km for Mars, several investigators were disposed to reject that theory by insisting on observational values of 3,350 km or less17. A value of 3,350 km would fit the Fe2O theory extremely well. 中文
... | 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 | References:
Jeffreys, H., Mon. Not. Roy. Astron. Soc., Geophys. Suppl., 4, 62 (1937).
Bullen, K. E., Rept. Austral. NZ Assoc. Adv. Sci., 23, 25 (1937).
Cook, A. H., Proc. Roy. Soc., A, 328, 301 (1972).
Ramsey, W. H., Mon. Not. Roy. Astron. Soc., 108, 406 (1948).
Bullen, K. E., Mon. Not. Roy. Astron. Soc., 109, 457 (19... | 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 | 然而这两个原初的地球模型被指出必须进行修正(参考文献10,11):(其中)要允许地球中心密度的估算值[12]从大约18 g·cm–3降到13 g·cm–3,同时允许地球转动惯量系数的估算值[13]从0.3336降到0.3309。这两个修正都对金星和火星的拟合造成了轻微的不良影响。 英文
地球化学家在协调所提出的相变理论与地球核幔边界(如N处)大的密度跳跃(比值为0.7或更大)时遇到了困难,困难主要在于氧原子在下地幔物质中的填充问题。 英文
在实验室进行的高压下瞬变激波实验中,并未提供足以支持在N处发生相变的正面证据。 英文
替代模型
针对实验解释存在的各种问题和不确定性,我认为像一些研究学者们那样作以下断言——这些困难“反驳”了这个... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 对于这个质量的J类行星,简化的Fe2O理论得出R=6,010 km、Rc=2,710 km和Ri=2,110 km。由于体积小的金星不如地球致密,模型中忽略了压缩率的不同,考虑压缩率的修正后将增加R的估算值。因此Fe2O理论和金星观测半径(约6,050 km)符合得和预计的一样好。 英文
假设金星外核为液体,同样有趣的是,我们得到其外核的厚度值T为600 km。这可能与相变理论得到的超过900 km的值(参考文献7)以及假设主要由铁构成外核的理论得出的大很多的值不同。通过估算T的最小值,Fe2O理论能很好地解释为何没能观测到明显的围绕金星的磁场;而由地球磁场数据推测(地球外核)的厚度为2,200 km。 英文
这些假设也确定了任意H... | 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 | consideration of the possible crystalline forms of iron in the inner core (and their melting points), along with the presence of impurities such as nickel, might eliminate the “stable stratification” that would inhibit convection. Today it is believed that Jacobs was right, although the detailed structure and compositi... | 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 | Fe particles suspended in a Fe-rich liquid. There is, however, a critical limit to the solid grain sizes in order that they do not precipitate out faster than the core can stir them up. Malkus6 has estimated that critical size is 1 μm for a convection-driven dynamo and 10 μm for a precession-driven dynamo. Such small g... | 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 | Also, the core is not pure Fe but contains ~15% of some light alloying element. This not only modifies the phase relationships but also considerably lowers the melting temperature of the core. Hall and Murthy13 have estimated that if the lighter alloying element is sulphur, at core pressures the melting temperature 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 | I have re-estimated17 the adiabatic gradient in the core by a different method18—assuming that there is a linear relationship between 1/α and pressure in analogy with Bullen’s compressibility-pressure hypothesis19. There is no real reason to suppose that the use of such an empirical relationship is superior to any of 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 | Elsasser, W. M., Core-Mantle Interface Conf. (NASA, 1972).
Kraut, E. A., and Kennedy, G. C., Phys. Rev., 151, 668 (1966).
Birch, F., Geophys. J., 29, 373 (1972).
McLachlan, D., and Ehlers, E. G., J. Geophys. Res., 76, 2780 (1971).
Verhoogen, J., Core-Mantle Interface Conf. (NASA, 1972).
Leppaluoto, D. A., Phys. Earth P... | 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
而且,地核并不是纯铁,而是包含了大约15%的其他轻合金元素。这不仅改变了相态关系,也大大降低了地核的熔点温度。霍尔和穆尔蒂[13]推测,如果更轻的合金元素是硫,在地核压力下,铁–硫化铁共晶的熔点温度大约比纯铁的熔点温度低1,600°C,如果硫的添加仅仅局限于外核,并且内核主要包含铁–镍和极少量更轻的元素,那么仍然有其他方法来解释这个地核悖论[14]。外核中的硫可能降低了它的液相线,使其低于铁的液相线,以至于希金斯和肯尼迪通过内核/外核边界的绝热线没有与之相交。 英文
绝热温度梯度公式如下:
dT/dr=–αgT/cp
(1)
其中r是地球半径,α是热膨胀系数,g是重力产生的加速度,cp是定压比热。希金斯和肯尼迪通过两种方法来估... | 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 | Core formation has often been regarded as a slow process which may not yet be complete4-9. Oversby and Ringwood challenge this10, concluding, from a study of isotope ratios, that core formation must have been completed within 5×108 yr, and probably 108 yr, of the Earth’s formation. Further, the oldest known rocks, 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 | infall theories that the mantle viscosity is too high. 中文
The response time for the Earth to reach thermal equilibrium, at about 0.4 times the melting point, is a few times 108 yr. This is very different from that expected on conduction theory and implies that the present thermal state is virtually decoupled both 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 | The time scale of core formation may be estimated using Stokes’s law, V0=2a2g(ρ–σ)/9η. I assume ρ–σ=4, and neglect any effect arising from the fact that core material would be descending all around the Earth and any cooperative motion between the various pieces. For a sphere to traverse the mantle of viscosity 1020 poi... | 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 | Convection will affect the infall process and be affected by it. Continental drift indicates the velocity of present-day convective motion is about 1 cm yr-1. If mantle-wide convection is assumed during core formation and due allowance is made for the rapid release of gravitational energy in the region through which 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 | There is no reason to assume heat transport by this convection is less efficient than by steady convection, but, if it is, the viscosity could be lowered giving more rapid convective movements and core formation. There would still be some viscosity effectively maintained by the convection itself. 中文
When core formation... | 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 | Munk, W. H., and Davies, D., in Isotope and Cosmic Chemistry, chapter 22 (edit. by Craig, H., Miller, S., and Wasserberg, G.) (North-Holland, Amsterdam, 1964).
Runcorn, S. K., Nature, 193, 311 (1962).
Runcorn, S. K., in Continental Drift, chapter 1 (Academic Press, 1962).
Runcorn, S. K., Nature, 195, 1248 (1962).
Runco... | 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 | 它们下沉速度的不同导致各片段的汇集和凝聚速度越来越快。尽管早期的凝聚得益于固体块的结合,但是向地心流入的地核物质极有可能是液态。本文提出的模型与前人模型[12]的不同之处在于,我们考虑了地核形成期间对流的作用以及沉降和对流过程之间的相互影响。 英文
该理论所依据的热演化史以及地幔流变观点与托泽的观点[13-15]类似,他的模型是以流变学为基础建立的,在这种流变状态中没有绝对的固态和液态之分。相反,该模型考虑了不同物质对小的非静水压力的响应,一般认为这会导致物质发生永久变形,尽管其速率随温度的变化非常大。在与静压平衡状态偏离较小的情况下,流变性可用牛顿黏度表示。对流体中进行的对流过程本身将黏度值限制在了一个很窄的范围内。倘若对流区厚达... | 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 | 所以,地核形成期间对流的形式只能是间歇性的,表现上类似于湍流,或者是受对流区域内的下沉物质运动的控制。 英文
没有理由假设通过这种对流进行热量传输的效率低于稳定的对流,但是,如果确实存在这种情况,要想使对流及地核形成得更快,那么地幔的黏度应当降低。另外,对流本身也会有效地维持一部分黏度。 英文
地核完全形成后将形成一个稳定的对流,用几亿年的时间使地球达到热平衡状态。在此期间,地核与地幔将作为两个系统分别发生对流,并且很快在百分之几的精度内达到现今的温度。假定整个地幔范围内的对流可能分解为多个不同区域,而其中仅有部分区域处于对流状态。 英文
托泽提出的对流模型预测了存在随着温度的升高和黏度的降低,高黏性耗散的有限区域[15]。这些区域... | 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 1 shows the extensional moduli of two selected samples (sample 1: =6,180, =101,450; sample 2: =13,350, =67,800) as a function of the natural draw ratio. The extensional moduli were calculated from the 10 s isochronal stress-strain curves obtained from the creep response in a dead loading creep experiment at room... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 2. Melting curves for two samples. Upper curve, sample 2; lower curve, sample 1.
中文
It therefore seems from the results of the thermal analysis that extended chain crystallites can be produced by cold drawing, provided that polymers of suitable molecular weight and molecular weight distribution are chosen. It 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 | 在最高拉伸比处,拉伸模量是迄今为止所报道的这种聚合物数据中最大的(约7×1010 N·m–2),而且几乎接近完全伸展的聚乙烯链的理论模量范围(2.4×1011 N·m–2,见参考文献2)。而且似乎直到拉伸比为30时,样品的分子量与分子量分布对模量的影响都很小。 英文
图1. 两种样品的拉伸模量。●—●,=6,180,=101,450;○---○,=13,350,=67,800。
英文
但是,分子量及其分布的差异确实导致了样品之间的结构差异,它们的熔融行为揭示了这一点。熔融曲线是在杜邦热分析仪的差示扫描量热(DSC)单元上采用DSC加热模式测得的。所得结果如图2所示。样品1的熔融峰大约位于137°C,这是迄今为止所研究过的较低拉... | 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 | MANY important functions in molecular biology are determined by antiparallel double helical nucleic acids with complementary base pairing between the two strands, as first described by Watson and Crick1. Although considerable work has been carried out on the structures of double helical nucleic acids2-8, the fine detai... | 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, subsequent analysis revealed that the sodium salt had crystallized rather than the bromoamine. A crystal measuring 0.2 mm×0.15 mm×0.05 mm was mounted on the tip of a glass fibre for X-ray analysis. The crystal was found to be monoclinic, space group P21, with cell dimensions a=18.025 Å, b=17.501 Å, c=9.677 Å, ... | 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 | functions or N-atom symmetry minimum functions, are compared. These two Pattersons are (1) the standard F 2 Patterson, calculated using all the diffraction data, and (2) a Patterson calculated only from the higher-order reflexions whose Fs should contain a larger contribution from the heavier atoms sought as they are 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 | Fourteen cycles of Fourier refinement using the corrected Es as Fourier amplitudes revealed the two molecules of ApU, the sodium ions and four water molecules. The other water molecules were located in a series of difference syntheses. The structure has been refined using isotropic thermal parameters and only the 1 Å o... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 1. View of the crystal structure perpendicular to the base planes showing hydrogen bonding (dashed lines) as well as the base stacking interactions. The darkest portions of the figure are those nearest the viewer. The rotational relationship is easily seen by comparing the front (black) and rear (white) glycosidic... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | Fig. 3. Perspective view of the structure as seen from the minor groove showing the numbering scheme and the coordination of the sodium ions. Both sodium ions (●) have distorted octahedral coordination involving water molecules and other oxygens. The central sodium ion is 2.36 Å from the uracil O2 atoms.
中文
The helic... | 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 | discrepancies between adenine and uracil torsion angles are caused by the differences between the 3′ and 5′ ends of the molecule as the same pattern was obtained with respect to the 3′ and 5′ ends in that molecule which had the opposite base sequence. 中文
In the protonated structure UpA, it was noted that there were sho... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | The crystal structure can be visualized as a rod-like entity. The central portions of these rods contain the stacked base pairs. These are flanked by the ribose phosphate backbones, both of which in turn are surrounded by the solvent structure. The large amount of water allows the crystal structure to assume a conforma... | 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 of more general occurrence in other crystals containing A–U sequences, it is possible that this type of coordination may be of importance in polynucleotide structure and function. 中文
As noted above, one of the most significant features of the organization of the crystal structure of ApU is that the two independent 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 | This research was supported by grants from the National Institutes of Health, the National Science Foundation and the American Cancer Society. N. C. S. is a postdoctorate fellow of the Damon Runyon Foundation, J. M. R. is a predoctoral trainee of the National Institutes of Health, F. L. S. is a postdoctoral fellow of 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 | Karle, J., and Hauptman, H., Acta Cryst., 17, 392 (1964).
Voet, D., and Rich, A., Prog. Nucl. Acid. Res. Mol. Biol., 10, 183 (1970).
Sunderalingam, M., Biopolymers, 7, 821 (1969).
Donahue, J., and Trueblood, K. N., J. Mol. Biol., 2, 363 (1960).
Sussman, J. L., Seeman, N. C., Kim, S.-H., and Berman, H. M., J. Mol. 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 | 英文
结构解析
尽管晶格中没有晶体学二次轴,在帕特森函数的哈克截面上出现了约为初始高度40%的峰值,这提示在该结构中存在非晶体学二次轴。由此我们推断出了ApU的双螺旋本质。我们认为这一峰值包含了一个ApU分子中的每一原子到另一独立分子中相应原子的所有矢量,而且这些矢量是相关对称的。根据以前针对质子化尿苷–3′,5′–腺苷磷酸[14](UpA)这种二核苷磷酸的研究,人们已经知道,在辨别一个大的结构中源自两个第二排(编者注:应指元素周期表第三周期)原子的矢量时,分辨率差异帕特森技术是有效的。(分辨率差异帕特森技术是指将两种帕特森或叠加函数(如多个最小值函数或N原子对称最小函数)进行比较。这两种帕特森函数是:(1)标准F2帕特森函数,采用... | 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
图2. ApU(上方)和RNA 11(下方)的结构比较。观察角度大致垂直于竖直虚线所示的螺旋轴。
英文
图3. 从(DNA双螺旋的)小沟上观察到的透视结构图,显示了核苷酸中原子的编号和钠离子形成的配位结构。两个钠离子(●)均参与形成扭曲的八面体配位,参与成键的原子还有水分子和其他氧原子。位于中心的那个钠离子距离尿嘧啶的O2原子的距离是2.36 Å。
英文
从图1中可以看到这些分子的螺旋形态,在此图中,读者的观察方向与碱基对平面垂直。图中前方和后方的碱基对的糖苷键(C1′到腺嘌呤N9或C1′到尿嘧啶N1)之间存在明显的旋转关系。图2则显示了从平行于以氢键连接的堆积碱基的方向观察到的结构。通过观察核糖磷酸链上的相邻核糖... | 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 | 不过,关于这一点,我们最近发现与之密切相关的二核苷磷酸,鸟苷–3′,5′–胞苷磷酸在晶体状态下确实形成了右手反向平行双螺旋,且形成的是晶体学二次轴(戴、西曼、罗森堡和里奇的未发表成果)。此前我们强调了伪二次轴对该晶体结构的重要性,这一近期结果支持了我们的结论。 英文
我们通过分析双螺旋片段所得到的重要结果有,确定多聚核苷链构象的重要详细参数,特别是关于磷酸基团几何结构的部分。核糖磷酸链的结构对于理解多聚核苷酸链的物理性质和行为都至关重要[23]。对于解释多聚核苷酸双螺旋以及形式更为复杂的RNA中的(如在tRNA中观察到的)分子结构细节,这些信息将会非常有价值[24]。 英文
此研究得到了国立卫生研究院、国家科学基金会和美国癌症协会的... | 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 | unaltered. 中文
To estimate the evolutionary distances (number of mutant substitutions) among 5S rRNA sequences, we made the alignment shown in Fig.1, using published data1–3 on human, yeast and bacterial (Escherichia coli and Pseudomonas fluorescens) sequences. To arrive at this alignment, previous attempts1,3 involving... | 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 average mutational distance between the eukaryotes (man, yeast) and the prokaryotes (E. coli, P. fluorescens) turned out to be
Keu–pro=0.817±0.158
where the standard error was obtained from four observations (comparisons). On the other hand, the corresponding quantity between the human and yeast was
Kh–y=0.561±0.09... | 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 | higher than Keu–pro/Kh–y=1.46. It is possible that the difference is due to sampling error, with the true value lying somewhere between these two. At any rate we should take these estimates as tentative (including the problem that might arise because of the multiplicity of ribosomal genes). There is some reason to 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 | forthcoming (for example, ref. 12) we hope that the studies of molecular evolution will soon supply a more accurate date. 中文
We tentatively conclude that the eukaryotes diverged from prokaryotes nearly 2×109 yr ago, thus opening up the way toward “higher organisms”. 中文
We thank Dr. K. Miura and Mr. H. Komiya for callin... | 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 | 我们在估计中使用的原则是,只要分子的结构和功能保持不变,那么对于每个信息大分子而言,在进化过程中,每年每个位点的核苷酸替代率是恒定的。 英文
为了估计5S rRNA序列的进化距离(突变替代的数量),我们用已发表的人类、酵母和细菌(大肠杆菌和荧光假单胞菌)的数据[1-3]进行了序列比对,如图1所示。为了获得这个比对,之前涉及两到三个序列比对的尝试[1,3]是有帮助的。这个比对是按照将两个序列间匹配的数量最大化同时又使插入的间隙数尽可能少的原则建立的。这是一个试错的过程,移动各个区域,记录两个序列之间一致的核苷酸数量,接下来计算当前结果的概率或随机出现的更好的一致性的概率。图1明确显示了(正如其他人已经注意到的)该分子显著的保守性,事实... | 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 | 结合将来更多的相关数据(例如参考文献12),我们希望不久后分子进化的研究将提供一个更加准确的日期。 英文
我们暂且推断大约2×109年前真核生物从原核生物分离,从此走上了通向“高等生物”的道路。 英文
感谢三浦博士和小宫先生引起我们对5S rRNA序列相关文章的关注,感谢丸山博士、武村博士和绀户博士的宝贵讨论。 英文
(邓铭瑞 翻译;陈新文 陈继征 审稿)
Isolation and Genetic Localization of Three φX174 Promoter Regions
C. Chen et al.
Editor’s Note
Four years before the φX174 bacteriophage 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 | protected by RNA polymerase. As most of the restriction fragments have been ordered with respect to the φX174 genetic map (manuscript in preparation), this localizes the protected sequences within the map as well. 中文
Two procedures were used to identify DNA fragments bearing sequences protected by RNA polymerase. In 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 | † A blank filter background of 0.35% has been subtracted.
Hybridization of RNA-polymerase-protected 3H-labelled φX174 RF DNA to specific 32P-labelled, endonuclease R and Z fragments. The preparation of 32P-RFI, endonuclease R and Z digestions, electrophoresis and autoradiography have been described previously5,6. The 3... | 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 | bound was calculated as the fraction of input counts bound minus the percentage of counts bound to a blank filter. The counts were determined from 100 min counts and were reproducible in four different experiments.
中文
The second procedure used to identify DNA fragments bearing RNA-polymerase-protected sequences was 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 | mm. The integrated counts in the various bands were plotted (log scale) against mobilities (band position in mm). Band R6 has been shown to contain three unresolved fragments of about the same size5 and so has three times (n=3) the number of counts as those bands containing a single fragment (n=1). Band R7 as those ban... | 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 | electrophoresis of an endonuclease R digest of phage S13 RF gives the normal φX174 pattern of fragments except that r4, r3 and r5 (gene B) are missing and are replaced by a single large fragment.) Band R6 has been shown to contain three fragments5 (named r6.1, r6.2 and r6.3) which have been partially resolved on prolon... | 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 is clear that RNA polymerase when reacted with DNA in this way protects specific sequences from nuclease digestion. It seems likely to us that these sequences contain the start sites10 within the promoter regions. RNA polymerase in the presence of ATP and GTP presumably becomes associated with the DNA at entry sites... | 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 | Table 2. Hybridization of 3H-labelled E. coli DNA Sequences Protected by RNA Polymerase to Specific 32P-labelled Endonuclease R and Z Fragments
* A blank filter background of 0.21% has been subtracted.
† A blank filter background of 0.18% has been subtracted. See legend to Table 1 for the procedures used.
中文
The hybri... | 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 | Hutchison, C. A., III, and Edgell, M. H., J. Virol., 8, 181 (1970).
Smith, H. O., and Wilcox, K. W., J. Mol. Biol., 51, 379 (1970).
Jones, O. W., and Berg, P., J. Mol. Biol., 22, 199 (1966)
Blattner, F. R., Dahlberg, J. E., Boetliger, J. K., Fiandt, M., and Szybalski, W., Nature New Biology, 237, 232 (1972).
Rüger, W.,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 首先,让大肠杆菌RNA聚合酶与3H标记的φХ174RFI(共价闭合环状DNA)结合。经过胰DNA酶的充分消化后,RNA聚合酶保护的DNA片段就被分离出来了。受保护的3H–DNA随后与固定在硝酸纤维素滤膜上的32P标记的纯化φХ174RF限制性片段进行杂交。留在滤膜上的DNA的3H计数表明与特定的限制性片段的同源序列的存在。 英文
受RNA聚合酶保护而免于被DNA酶消化的φХ174RFI大约有1.9%。形成的DNA–RNA聚合酶复合物非常稳定,因为消化过程中过量的冷RF也改变不了被标记的受保护DNA的比例。受RNA聚合酶保护的位点已经达到饱和,将RNA聚合酶与DNA的比例增加到超过4 μg聚合酶比0.02 μg DNA(我们的标准条件... | 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 | 剩余的100 μl RF的内切酶R的限制性消化产物也按如上步骤处理,只是不加入RNA聚合酶。电泳后,将凝胶放在一张滤纸上干燥,切成1 mm的片段后用闪烁计数器计数。示踪染料迁移了142 mm。将不同条带上计数值的整数(取对数值)对迁移率(条带位置,单位mm)作图。条带R6含有三种大小几乎相同的不能分解的片段[5],因此它们的计数是那些都含有单一的片段(n=1)条带的三倍(n=3)。条带R7含有两个不能分解的片段(n=2)。●没有RNA聚合酶;○加入RNA聚合酶。
英文
这些实验获得的数据与φХ174的限制性片段图谱一致。也就是说,每个含有RNA聚合酶保护序列的r片段与同样显示含有这些序列的z片段有重叠(图2)。 英文
图2. ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 显然大肠杆菌DNA的某些启动子区含有与φХ174RFDNA类似的起始位点。 英文
表2. 受RNA聚合酶保护的3H标记大肠杆菌DNA序列与特异32P标记的核酸内切酶R和Z片段的杂交
* 减去了0.21%的空白滤膜本底。
† 减去了0.18%的空白滤膜本底。使用的方法见表1注。
英文
两张表格中的杂交数据表明,不同的限制性片段存在不同程度的杂交。这些差异都是可重复的。这提示φХ174的启动子区域不是完全相同的。用这些技术有可能将启动子区分成不同种类。含有受RNA聚合酶保护序列的r6.3和z3之间的重叠少于100个核苷酸对。这个重叠的片段已经从同时被核酸内切酶R和Z消化的φХ174RF中分离出来了,并且经证实在靠近顺反子D的起始处含... | 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 | objections to the use of a calibrated time scale in prehistoric archaeology. 中文
THREE radiocarbon laboratories, at La Jolla, Philadelphia and Tucson1-3, have obtained radiocarbon dates over the past decade for specimens of bristlecone pine already dated dendrochronologically4, thereby allowing the “correction” of 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 | Any calibration curve based on tree rings is derived ultimately from the analysis of a series of tree-ring-dated wood samples, where each sample has both a tree-ring date (generally assumed to establish a date in calendar years with a probable error of less than two or three years), and a radiocarbon date with its atte... | 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 | important advantage of enabling several possible such functions to be easily compared. 中文
Earlier workers have approached this problem by fitting a smoothing function g to the bristlecone pine data alone, and then matching the observations from individual Egyptian samples against that curve. This can be done in two way... | 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 | Recent workers12,14 using method (a) have not correctly allowed for the standard error of a calibrated radiocarbon date. Such a standard error depends not only on that of the radiocarbon date itself, but also on the nature and precision of the smoothing function near the point of calibration. An important disadvantage ... | 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 bounded continuous first derivative, while the smoothing function g need not necessarily be constrained to have this property. For the present purpose, a discontinuous function, such as a series of unconnected straight lines, may be statistically convenient and quite valid, even if it would not be satisfactory as a 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 | The standard error of 45.5 yr assigned to the La Jolla radiocarbon dates is at least partially verified by the estimated error variance, namely 2,263 on eleven degrees of freedom, obtained by Clark and Renfrew17 by considering the differences23 between replicate radiocarbon determinations carried out by the La Jolla 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 | Some impression may be gained of the reliability of the ascription to the samples of a historical context by the Egyptologists concerned, together with the variation in the age of the samples when buried, by comparing the measured radiocarbon dates of samples from different archaeological contexts reported as approxima... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | These results imply (i) that some of measurement errors are greater than indicated by the laboratories, or (ii) that certain groups of samples are not in fact contemporaneous (which was assumed in these tests), or (iii) there are gross errors in some of the radiocarbon dates. If the measurement errors were increased by... | 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 | These discrepancies make the Egyptian data less suitable for a check on the bristlecone pine calibration than might be hoped. Both Berger20 and McKerrell16, however, have based comments on the calibration upon an examination of these Egyptian data, and it is important to consider such claims. In what follows analyses 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 | possible underestimation by all three laboratories of their overall measurement error. As has been noted elsewhere29,30, the reported standard error refers only to “counting error”, which is only part of the overall measurement error. The preceding analysis of paired differences indicates that such underestimation of 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 | Amongst the Egyptian data, in most cases there was more than one radiocarbon date corresponding to each of the eighteen distinct historical dates. For the purposes of curve-fitting, each group of radiocarbon dates corresponding to each historical date could be replaced by a weighted mean radiocarbon date. The residual ... | 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 Table 3, comparison of items d and f with e, using the appropriate F-tests, shows that a straight line is in fact an adequate fit over the time range to both the Egyptian and bristlecone pine data separately. Moreover, comparison of items g and e, yielding the low F-value of 1.08, indicates that a single straight li... | 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 | precision of these dates is thus necessary for any analysis, and our assumption facilitates the comparison of several smoothing functions. The remaining assumptions are likely to be at least approximately correct and, in any case, the analysis would be only marginally affected by small departures from them. 中文
Validity... | 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 | same way over this range, so as to yield closely comparable yet erroneous calibration functions. 中文
Our analysis thus lends support to the general validity of both the radiocarbon calibration and the Egyptian historical chronology. Further accurate work on Egyptian material is still required to reduce the level of erro... | 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 | Clark, R. M., and Renfrew, C., Archaeometry, 14, 5 (1972).
Houtermans, J. C., thesis, Univ. Berne (1971).
Wendland, W. M., and Donley, D. L., Earth Planet. Sci. Lett., 11, 135 (1971).
Berger, R., Phil. Trans. Roy. Soc., A269, 23 (1970).
Edwards, I. E. S., Phil. Trans. Roy. Soc., A269, 11 (1970).
Barker, H., Burleigh, 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 | 一名研究者明确主张通过只参考埃及年代而不考虑刺果松来校正考古样本的放射性年代[8,16]。 英文
有足够的数据允许我们在考虑放射性碳定年过程中的实验误差的同时,在统计学上研究以上的问题。本研究选择的时间段涵盖了从埃及历史年表的开始(约公元前3100年)到第一次确切的并通过天文学考证的埃及历史年代(公元前1872年)这一时间段。 英文
校正函数
任何基于树轮的校正曲线最终都是从分析一系列标明树轮年代的树木样本中得出的,每个样本都有一个树轮年代(一般假定在日历年中确定一个概差小于两年或三年的年代),和一个主要由计数问题产生标准误差的放射性碳年代。同样,用于树轮校正检验的历史数据也来自一系列样本,这些样本除具有放射性碳年代(带标准误差)外... | 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
数据的评价
我们用于分析的数据包括52个埃及样本的给定历史年代和相应带有标准误差的放射性碳年代,这52个样本与公元前3100年到公元前1800年(日历年龄)时间段有关,包含51个由伯杰[20]和爱德华兹[21]给出的放射性碳年代及随后标记的校正[22],还有一特殊样本(BM 236)发现与UCLA 1208一致(参考文献22)。我们也使用了从豪特曼斯[18]始创的列表中,与这个时期相关的57个刺果松样本的树轮年代和放射性碳年代。这些样本由美国亚利桑那州大学树木年轮研究实验室进行树木年轮断代,样本的放射性碳年代是由苏斯在拉霍亚实验室测定的。关于这些放射性碳测量的标准误差,豪特曼斯[18]只是描述它们的范围在千分之四到千分之七,因... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | 英文
这些结果清楚地表明试图用埃及历史学年代为基础“校正”放射性碳年表,即完全独立于刺果松树木年轮断代法[16],不是很有依据。 英文
这些差异使埃及年表的数据远未像期望的那样适合检验刺果松的年龄校正结果。然而,伯杰[20]和麦克雷尔[16]把对校正的评价建立在埃及数据的检验上,而对这些论断进行思考是很重要的。因此,下文中的分析是基于以下临时假设进行的,即埃及样本指定的历史学年代没有错误,观察到的差异只是简单的放射性碳年代测量的高误差的结果。尽管,正如前面提到的那样,这个假设没有严格的根据,但这一假设不会对结论产生影响,除非历史学年代有严重的误差,因为表2中的F值并不接近临界值。 英文
表2. 埃及、刺果松和综合数据的各种平滑函数... | 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 | 但是,由于计算出的F值远离临界值,如果这些年代不存在非常严重的错误,我们的结论是相同的。因为没有对这些估计年代准确性的客观估量,所以利用既定数据对这一假设进行完全的客观统计检验是不可能的。虽然通过利用只基于刺果松观测的校正曲线对埃及放射性碳年代进行了校正,方法(a)似乎克服了这一问题,但没有客观方法来实现校正年龄和给定历史年代的对比。因此,关于这些年代的准确性的一些假设对任何分析都是必要的,我们的假设有助于几个平滑函数的比较。其余的假设可能至少近似正确,不管怎样,分析只受小偏差的轻微影响。 英文
时间尺度的有效性
埃及数据的详细分析显示,如果不考虑主要实验误差,要么是与放射性碳定年有关的标准误差被严重低估,要么是基于地层证据给定的一... | 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 finding chart for OQ172 is given by Véron4, who notes that it is a “blue stellar object”. From our inspection of the Palomar Sky Survey plates we agree with Véron’s assessment of the colour of OQ172, although Gent et al.3 list it as stellar, that is an object with neutral colours. Radio fluxes for OQ172 are available... | 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 | would also suggest a large redshift, say z2. We therefore conclude that the emission line redshift is near 3.53. The position of several features assuming a redshift of 3.53 have been marked on Fig. 1. 中文
Fig. 1. Image tube scanner spectrum of OQ172. Units of Fv are erg cm–2 s-1 Hz-1.
中文
It is common for large redsh... | 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 | OQ172 is very bright. It was estimated by Véron4 to be magnitude 17.5. Our calibrated spectra, which should be accurate to ±20%, indicate that the V magnitude of the continuum is about 17.9. The strong continuum level, extending well into the ultraviolet, is in agreement with the blue classification given to OQ172 by V... | 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 | 尽管金特等人[3]将它列为恒星,但是根据我们在帕洛玛巡天底片中查阅的结果,我们赞同韦龙对OQ172颜色的评估,即它是一个具有中性颜色的天体。参考文献5中给出了OQ172的射电流量,并给出178 MHz和1,400 MHz之间的谱指数为–0.09。1,400 MHz、2,695 MHz和5,009 MHz处的流量分别为2.42、1.96和1.22流量单位[5],因此射电频谱非常平坦并延伸到高频段。 英文
图1显示了使用利克天文台的卡塞格林ITS系统获得的OQ172的光谱[6]。这条光谱是由不同夜晚得到的光谱数据叠加而成的,因此光谱中的信噪比是波长的函数。在6,000~6,500 Å光谱区,由于信噪比特别糟糕,我们只有一条光谱。在λ72... | 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 | Zürich, Switzerland, show that this cannot be so for antifreeze proteins from two types of Antarctic fishes. They conclude that these proteins must be exerting more specific effects, perhaps by altering the way ice crystals grow. Modern research now focuses on how antifreeze proteins’ surface structure affects ice nucl... | 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 DTA experiments were carried out in aluminium vessels in a Mettler vacuum thermal analyser. Controls of water or solutions of 1% chicken ovomucoid15 (a glycoprotein containing approximately 25% carbohydrate) in water and the solutions containing 1% AFGP froze at the same temperatures and had similar freezing and me... | 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 | Water and antifreeze glycoprotein solution was initially frozen at –3°C and then allowed to melt at +0.1°C until 5-10% of solution remained as ice crystals. The temperature was then adjusted to 0.0°C and periodically lowered and then raised as indicated. The times at each temperature intermediate between freezing and 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 | nucleation from the DTA experiments on kinetic effects. There are, therefore, no unusual “supercooling effects” as are commonly found in solutions in which initiation of freezing is very slow in the absence of crystals. The data indicate that there is no significant kinetic effect involved in the overall freezing mecha... | 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 | De Vries, A. L., and Wohlschlag, D. E., Science, 163, 1073 (1969).
Komatsu, S. K., thesis, Univ. California, Davis (1969).
DeVries, A. L., Komatsu, S. K., and Feeney, R. E., J. Biol. Chem., 245, 2901 (1970).
Komatsu, S. K., DeVries, A. L., and Feeney, R. E., J. Biol. Chem., 245, 2909 (1970).
DeVries, A. L., Vandenheede... | 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 | 通常情况下,小体积(10λ)的这种溶液在–15°C至–20°C时发生凝固,这取决于水的纯度以及实验时温度降低的速率。一般认为这种情况下的凝固温度与成核速率有关,而与冰水均衡态的凝固温度无关。因此,这些实验并没有揭示出抗冻糖蛋白对成核的抑制作用,也就是对最初结晶点形成的抑制。 英文
通过配备照相机和电视显示屏的蔡司全能偏光显微镜(放大倍数为90倍),我们可以在严格控温的条件下直接观察到大约50 λ的体积中的融化与凝固过程。显微镜载片是一个双室的结构,在中心分隔物的两侧分别有一个小室。整个载片是通过缓慢施加的冷氮气流进行冷却的,并通过载片分隔物上带有的加热元件对载片中心部位进行加热以维持温度。载片中心处的热电偶为Pt–PtRh。此仪器是... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0304. 《自然》百年科学经典(英汉对照版)(第六卷)(1973-1984).epub | .epub | 45,637,976 | 2025-09-26T19:07:36.672222 | One of the early triumphs of molecular biology was the working out of the mechanism of muscular contraction. Much of the work was done by Hugh Huxley at the Medical Research Council Laboratory of Molecular Biology at Cambridge. This paper describes Huxley’s views on muscular contraction (which are still regarded as ess... | 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 | According to the sliding filament model of muscle contraction striated muscles consist of overlapping arrays of actin and myosin filaments which can slide past each other when the muscle changes length. The individual filaments, and the arrays which they form because of their in-register arrangement, remain virtually 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 | myosin cross-bridge require that the interacting groups on the two molecules always have the appropriate mutual orientation. Thus actin filaments which interact with opposite ends of a myosin filament must contain actin monomers with opposite polarity. In practice, it is found that all the actin monomers along a given ... | 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 | S1 head generated at the link to the S2 part of the molecule. The arguments supporting this view, which I believe are very powerful are somewhat involved, and the original papers should be consulted4,6,7. In essence, they derive mainly from X-ray diffraction and electron microscope evidence that the attachment of the h... | 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 third feature of the sliding filament mechanism in striated muscle is concerned with the exact mode of attachment of the myosin head to the actin filaments. At present, no means are available to arrest the working stroke of the cross-bridge, or to prevent subsequent dissociation in the presence of ATP. In the absence... | 400套付费套装书 |
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