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C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | pairs of (+) mutants which straddle barrier b6. The presence of the barrier is obligatory because, if it is removed by mutation, the (++) doubles are unable to grow at all on E. coli K12. The minutes are clearly due to a phase error of one sort of another and the phase error is dependent on the barrier b6 which we now ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | It thus seems unlikely that UGA codes for any amino-acid, and in particular it does not appear to code for either cysteine (UGU and UGC) or tryptophan (UGG). The wobble theory of codon-anticodon interaction developed by one of us8 makes the prediction that because of a wobble in the recognition mechanism at the third p... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | For the structure of the genetic code and the evidence for nonsense triplets see the papers in the Cold Spring Harbor Symposium XXXI on “The Genetic Code”, 1966 (in the press).
Weigert, M. G., Lanka, E., and Garen, A., J. Mol. Biol., 23, 391 (1967).
Sarabhai, A., and Brenner, S., in preparation.
Barnett, L., Brenner, S... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 因此,DNA中的这个三联密码子或者不含G–C碱基对,或者只含有一个G–C碱基对,而且这个碱基对是通过G–C到A–T的转换连接到另一个不可接受的三联密码子上的。 英文
表1.X655及其衍生物的抑制特性
将噬菌体液加到下面这些菌株[9]中:su–,CA244;,CA266;,CA180;,CA265;,CA165;,CA167;,CA248。 英文
表2.X655的回复性质
和以前描述过的方法一样,X655都是用2–氨基嘌呤和羟胺处理的[4,5]。总噬菌体在大肠杆菌B中进行实验,而r+回复子在CA244(su–)菌株中进行。赭石回复子在CA248菌株中进行选择,并通过在CA248和CA244菌株中挑选300个噬菌斑和r+回复子进行... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 如果B蛋白已经含有一个对其功能有重要影响的半胱氨酸,那么UGA在其他位置处的功能也许就是在UGA插入的半胱氨酸和(假定存在的)基本半胱氨酸之间形成一个S–S键,以便使蛋白质失活。尽管如此,我们还是可以举出两方面的理由来驳斥这一点,一方面是基因上的,另一方面是化学上的。 英文
在基因上的证据与由B顺反子中某些(++)重组产生的反常菌斑有关[4]。在B顺反子第一部分的某些区域中,两个(+)相位移动突变体的重组子能够在限制性宿主大肠杆菌K12中生长到一定程度。但产生的菌斑非常小,这说明野生表型还远远没有得到完全恢复。在对其中一组重组子进行深入研究后发现:只有跨过障碍物b6的(+)突变体对才能生成菌斑。这种障碍物的存在是必不可少的。因为,如... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Specific Binding of the λ Phage Repressor to λ DNA
M. Ptashne
Editor’s Note
In 1961, French biologists François Jacob and Jacques Monod described a negative form of gene regulation whereby so-called repressor proteins switch off target genes. But the underlying molecular mechanism was unclear. Here molecular biologist ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The Genetic System
The protein made by the C1 gene of phage λ, called the λ phage repressor, is used in these experiments. This repressor blocks the expression of the other phage genes, keeping the phage chromosome dormant within its host, E. coli. Only a very short segment of the phage genome is involved in this contr... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The binding experiments to be described were performed mainly with the repressor made by the mutant phage λind-. The ind- mutation renders the repressor insensitive in vivo to many conditions which inactivate the wild type repressor6. For example, a small dose of ultra-violet light delivered to a λ-lysogen will inactiv... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Fig. 2. Specific binding of the λind- repressor to λ DNA. A portion of 14C-labelled λind- repressor, pooled and concentrated from the peak fractions of a DEAE column run, was mixed with 100 μg of λ or λimm434 DNA. The DNA was preheated at 70°C for 15 min. to minimize aggregation. The solutions were made 0.01 M EDTA, 0.... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | shows that about half the 14C label but none of the 3H label sedimented with the DNA. 中文
Fig. 3. Selective binding of the λ C1 product to λ DNA. 14C-labelled λind- repressor was isolated on a DEAE column from an extract which also contained the 3H-labelled gene products of the phage λC1sus34. This mixture was then tes... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | In order of binding to have been detected under the experimental conditions used, the repressor must bind very tightly to DNA. A close examination of Figs. 2 and 3 shows that some of the bound repressor washes off the DNA as it sediments. This suggests that the dissociation constant is of the same order of magnitude as... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | I thank Nancy Hopkins for technical assistance, and also Drs. W. Gilbert, J. D. Watson and S. E. Luria for help. The work was supported by grants from the U.S. National Science Foundation and the U.S. National Institutes of Health. 中文
(214, 232-234; 1967)
Mark Ptashne: Department of Biology, Harvard University.
Receive... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 该阻遏物能够阻断其他噬菌体基因的表达,使噬菌体的染色体在它的宿主大肠杆菌内只能处于休眠状态。在噬菌体的基因组中只有一个非常短的DNA片段参与了这一调控过程[4,5],该区域包括C1基因和若干能决定噬菌体对阻遏物敏感程度的位点。仅在这个片段上有所不同的两种噬菌体是λ噬菌体和λimm434噬菌体(见参考文献4)。λimm434噬菌体含有λ噬菌体中几乎所有的其他已知基因,唯一的不同就在于它只能合成434噬菌体阻遏物并只对434噬菌体阻遏物敏感。因此,对于阻遏物特异性来说,决定性的检验标准就是:分离出来的λ阻遏物应该与λ DNA结合,而不是与λimm434 DNA结合。 英文
λ噬菌体阻遏物的特性
对λ噬菌体阻遏物的分离可以通过用紫外光破坏... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 为了保证与DNA一起沉降的标记在阻遏物中而不是在杂质中,我们进行了一次双标结合实验。利用DEAE柱,我们从含有λC1sus34噬菌体侵染细胞的3H标记产物的混合提取物中分离出了14C标记的λind–阻遏物。λC1sus34噬菌体的C1基因发生了sus34琥珀突变,这一突变可以阻断该噬菌体中阻遏物的产生[7]。因此,3H将能够标记除阻遏物之外的所有蛋白。从图3中可以看出:与DNA一起沉降的有大约一半的14C标记,但没有3H标记。 英文
图3.λ C1产物与λ DNA的选择性结合。利用DEAE柱从同时含有3H标记的λC1sus34噬菌体基因产物的抽提物中分离出14C标记的λind–阻遏物。然后按照图2中所描述的方法检测所得混合物与λ ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 英文
(吕静 翻译;陈新文 陈继征 审稿)
The North Pacific: An Example of Tectonics on a Sphere
D. P. McKenzie and R. L. Parker
Editor’s Note
Although the discovery of seafloor spreading by Fred Vine and Drummond Matthews in 1963 confirmed the theory of plate tectonics—the idea that the Earth’s crust consists of rigid plates moving on a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | are lines of pure slip. They are always parallel, therefore, to the relative velocity vector between two plates—a most useful property. We have tested this paving stone theory of world tectonics in the North Pacific, where it works well. Less detailed studies of other regions also support the theory. 中文
The movement of... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | on the surface of a sphere. 中文
There are several points on the surface of the Earth where three plates meet. At such points the relative motion of the plates is not completely arbitrary, because, given any two velocity vectors, the third can be determined. The method is easier to understand on a plane than on a sphere,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The sign convention takes a rotation which is clockwise when looked at from the centre of the sphere to be a positive vector which is pointing outward along the rotation axis. By adding more terms, equation (2) can be extended to circuits crossing more than three plates and applies to all possible circuits on the surfa... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Fig. 2. Mechanism diagrams for four circum-pacific earthquakes. The lower half of the focal sphere is projected stereographically on to a horizontal surface, and the rare-fraction quadrants are shaded. The horizontal projection of the slip vector in plane 1 is marked with a double arrow. (a) June 28, 1966, Parkfield15,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | relative rotation. The two which are used here are the strike of the San Andreas between Parkfield and San Francisco, and the average slip vector of all the aftershocks in the Kodiak Island region16 of the 1964 Alaskan earthquake. A pole position of 50°N., 85°W. was obtained by construction on a sphere. If the paving s... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Fig. 3. A Mercator projection of the Pacific with a pole at 50°N., 85°W. The arrows show the direction of motion of the Pacific plate relative to that containing North America and Kamchatka. If both plates are rigid all slip vectors must be parallel with each other and with the upper and lower boundaries of the figure.... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | the direction of slip remains the same along the entire Aleutian arc, the change in strike changes the fault plane solutions from overthrusting in the east to strike slip in the west (Fig. 2c). A sharp bend occurs between the Aleutians and Kamchatka (Fig. 3). Here the fault plane solutions change back to overthrust (Fi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | corrections which possess a large azimuthal variation23 also suggest that there is a high velocity region extending deep into the mantle similar to that in the Tonga–Kermadec24 region. These complications disappear when the ridge and trench structures join again and become the Queen Charlotte Islands fault. 中文
Fig. 5.... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The two ends of the North Pacific belt may also be discussed with the help of vector circuits. The end in Central Japan gives the trivial result that two trenches can join to give a third. The other end at the entrance to the Gulf of California is the circuit in Fig. 1, and shows how the East Pacific rise and the Middl... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | America and the main Pacific plate joined to that which still exists to the west of Chile. This piece of ocean floor has since been consumed, and therefore the direction of spreading in the Pacific appears to have changed in the north but not in the south. This explanation requires changes in the shape of the plates bu... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Stauder, W., and Bollinger, G. A., J. Geophys. Res., 71, 5283 (1966).
Stauder, W., and Bollinger, G. A., Bull. Seism. Soc. Amer., 56, 1363 (1966).
Tocher, D., Bull. Seism. Soc. Amer., 50, 267 (1960).
Hill, M. L., and Dibblee, jun., T. W., Bull. Geol. Soc. Amer., 64, 443 (1953).
Allen, C. R., Phil. Trans. Roy. Soc., A, ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 极点位置本身并不重要,它仅仅是一个构造点。上述讨论将威尔逊[8]提出的转换断层概念扩展到了在球体上的运动,其重要的补充设想是把单个无震区作为在球体表面上运动的刚性板块。 英文
地球表面存在数个三个板块的交界点。在这些点上,板块的相对运动不是完全任意的,因为如果已知任意两个速度矢量,就可以确定第三个。在一个平面上理解这种方法比在一个球面上更容易,该方法可从图1的平面环路中推导出来。从板块A上的一个点x出发沿顺时针运动,则在矢量图上,板块B的相对速度AυB将沿AB方向。同样,相对速度BυC和CυA将分别沿BC和CA方向。矢量图必须是封闭的,因为环形路线会返回到x点。因此:
AυB+ BυC+ CυA=0
(1)
建立此类三角形的一般法则... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 由此,我们在球体上得到了一个位于北纬50度西经85度的极点。如果应用铺石板理论,那么所有滑移向量都应该与相对于该极点所画的纬线平行。虽然上述预测可以通过把与观测结果不一致的地方列成表格来检验,但一个更简单和更直观的检测方法是:采用墨卡托投影法将滑移向量投射到世界地图上,并把投影极点作为旋转轴(图3)。采用墨卡托投影有两个优点:其一,它是正形投影,这就意味着角度在局部保持不变,滑移向量可以直接画出;其二,所有以投影极点为中心的小圆都是平行的。因为图3的上边界和下边界本身就是小圆,所以该理论要求所有滑移向量不仅要相互平行,而且还要平行于图的顶边和底边。1957年以来,该预测已得到80个已发表的[6,11-17]浅源地震断层面解的验证。其... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 该区在1964年地震之后发生了局部的隆升,说明那里存在多个活动断层[16],因此如果没有更多的断层面解资料,将无法了解其构造特征。 英文
第三个地区位于千岛群岛,在那里有两个断层面解(图6a和b)证明曾发生过倾滑断裂和地壳伸展。这种运动完全不同于该区域内的绝大多数与北太平洋其他地区一致的断层面解。两次地震均发生于岛弧一侧的千岛海沟的陡壁下,并且与进入海沟的重力滑坡体一致。由这些滑动体形成的阶地具有与日本海沟和阿留申海沟相同的特征[25,26]。虽然地壳的缩短与区域变形类型一致,但仍然有一个可以推断出太平洋应该逆冲于千岛群岛之上的断层面解(图6c)。 英文
图6.图2所示的千岛群岛三次地震的机制图。(a)1962年9月15日(参考文... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | generating the beams is still controversial. For this discovery, in 1974 Hewish became the first astronomer to be awarded the Nobel Prize in physics. 中文
I N July 1967, a large radio telescope operating at a frequency of 81.5 MHz was brought into use at the Mullard Radio Astronomy Observatory. This instrument was design... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | already revealed the presence of three others having remarkably similar properties which suggests that this type of source may be relatively common at a low flux density. A tentative explanation of these unusual sources in terms of the stable oscillations of white dwarf or neutron stars is proposed. 中文
Position and Flu... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | A record obtained when the pulsating source was unusually strong is shown in Fig. 1a. This clearly displays the regular periodicity and also the characteristic irregular variation of pulse amplitude. On this occasion the largest pulses approached a peak flux density (averaged over the 1 MHz pass band) of 20×10–26 W m–2... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | was obtained on August 13, 1967. This and all subsequent measurements agree within the error limits. The position in declination is not so well determined and relies on the relative amplitudes of the signals obtained when the reception pattern is centred on declinations of 20°, 23° and 26°. Combining the measurements y... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | In this analysis the daily value plotted is the peak flux density of the greatest pulse. Again the variation from day to day is irregular and no systematic changes are clearly evident, although there is a suggestion that the source was significantly weaker during October to November. It therefore appears that, despite ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | phase shifting device in order to prevent severe attenuation of the output signal by the time constant of the receiver. The rate of change of signal frequency has been deduced from the additional phase shift required and is dv/dt =–4.9±0.5 MHz s–1. The direction of the frequency drift can be obtained from the phase of ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | in T if care was taken to add or subtract one period where necessary. The observations, however, show a marked curvature in the sense of a steadily increasing frequency. If we assume a Doppler shift due to the Earth alone, then the number of pulses received per day is given by
where N0 is the number of pulses emitted ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | It is also interesting to note the possibility of detecting a variable Doppler shift caused by the motion of the source itself. Such an effect might arise if the source formed one component of a binary system, or if the signals were associated with a planet in orbit about some parent star. For the present, the systemat... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The positional accuracy so far obtained does not permit any serious attempt at optical identification. The search area, which lies close to the galactic plane, includes two twelfth magnitude stars and a large number of weaker objects. In the absence of further data, only the most tentative suggestion to account for the... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | s. 中文
If the radiation is to be associated with the radial pulsation of a white dwarf or neutron star there seem to be several mechanisms which could account for the radio emission. It has been suggested that radial pulsation would generate hydromagnetic shock fronts at the stellar surface which might be accompanied by... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | medium. 中文
More observational evidence is clearly needed in order to gain a better understanding of this strange new class of radio source. If the suggested origin of the radiation is confirmed further study may be expected to throw valuable light on the behaviour of compact stars and also on the properties of matter a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 被记录信号的脉冲特性是由一个信号的周期部分产生的,该信号的频率在接收机的整个1 MHz通带内递减。 英文
最开始,研究人员认为这些信号的不寻常特性源自于一些人造的信号传输装置,比如或许源自深空探测器、行星雷达或者从月球上反射回来的地球信号。但这些解释都不能为人们所接受,因为:没有视差足以说明信号源远在太阳系之外。在对更多的脉动源进行初步探测之后,研究人员发现还有三个源也具有非常类似的性质。这表明此类低流量密度的源在宇宙中可能还是比较常见的。本文提出了一个尝试性的解释,即认为这些不寻常的信号源来自于白矮星或者中子星的稳定振荡。 英文
位置和流量密度
天线中包含着一个由2,048个全波段偶极子组成的矩形阵列,这些偶极子排成16行,每行1... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 在图2a中绘出了时长30min内10个连续脉冲的峰值脉冲幅度的平均值。这张图说明有可能存在持续几分钟的周期,但是从相关分析中并没有得到有价值的结论。如果这些信号是线偏振的,则电离层中的法拉第旋转就会产生随机的变化,但是该曲线的形状似乎与这种机制并不相符。该脉动源在首次被发现后的每日变化情况示于图2b。在这张分析图中,每天的数据都是以最大脉冲的峰值流量密度来表示的。另外,虽然该源在10月到11月期间有明显变弱的迹象,但每天的变化仍是不规则的,而且也没有明显的证据表明存在系统性的变化。因此,尽管这些脉冲的出现是规则的,但是其发射能量的大小在或长或短的时间段内都表现出了一定的波动性。 英文
图2.a. 平滑了(10个脉冲)的脉冲幅度随时... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 如果N0真的是一个常数,那么对该脉动源赤纬的估计值就可以达到±1’的精度,这一结果是不会受到电离层折射影响的。 英文
另一件值得一提的事是:我们可能会观测到由源自身运动所造成的多普勒频移的变化,这一效应在以下两种情况下或许有出现的可能性:或者脉动源是双星系统中的一个成员,或者该信号与在围绕某颗母恒星的轨道上运行的行星有关。就目前了解的情况而言,N的系统性增长通常为量级,所以可以证明:其他的轨道运动所造成的影响都无法与地球的轨道运动相比。 英文
射电源的性质
观测视差不大于2′说明源与地球的距离超过了103个天文单位。如果该源的辐射是各向同性的,那么它在一个脉冲间隔内释放的能量——在频率为81.5 MHz处的1 MHz带宽内进行积分—... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 正如上文所提到的,一种可能性更大的情况是脉冲辐射在穿过星际介质时被色散。 英文
为了更好地理解这种奇特的新型射电源,显然还需要更多的观测证据。如果能够证明这种辐射的起源与本文中所设想的完全一致,那么经过进一步的研究人们或许可以了解到一些有关致密恒星行为以及高密度物质性质的重要线索。 英文
我们要感谢马丁·赖尔爵士教授、鲍德温博士、朔伊尔博士和谢克沙夫特博士为此提出了有价值的意见,还要感谢科学研究理事会为此项研究提供了经费。我们中的一位作者(贝尔)要感谢北爱尔兰教育部,另一位作者(柯林斯)要感谢科学研究理事会提供了维持费用;皮尔金顿要感谢帝国化学工业公司提供研究基金。 英文
(冯翀 翻译;蒋世仰 审稿)
Rotating Neutr... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | can, after all, not be much larger than the distance light travels in the few milliseconds that represent the lengths of the individual pulses. No such concentrations of energy can be visualized except in the presence of an intense gravitational field. 中文
The great precision of the constancy of the intrinsic period als... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | overlaid by a different Faraday-rotating medium. A single pulsating region, on the other hand, could scarcely generate a repetitive fine structure in polarization as seems to have been observed now8. 中文
There are as yet not really enough clues to identify the mechanism of radio emission. It could be a process deriving ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The evidence so far shows that pulses occupy about 1/30 of the time of each repetition period. This limits the region responsible to dimensions of the order of 1/30 of the circumference of the “velocity of light circle”. In the radial direction equally, dimensions must be small; one would suspect small enough to make t... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The observed distribution of amplitudes of pulses makes it very unlikely that a modulation mechanism can be responsible for the variability (unpublished results of P. A. G. Scheuer and observations made at Cornell’s Arecibo Ionospheric Observatory) but rather the effect has to be understood in a variability of the emis... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Pilkington, J. D. H., Hewish, A., Bell, S. J., and Cole, T. W., Nature, 218, 126 (1968).
Drake, F. D., Gundermann, E. J., Jauncey, D. L., Comella, J. M., Zeissig, G. A., and Craft, jun., H. D., Science, 160, 503 (1968).
Drake, F. D., Science (in the press).
Drake, F. D., and Craft, jun., H. D., Science, 160, 758 (1968)... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 照现在的情况来看,等离子体与电磁辐射场的耦合可能是磁层动力学行为的主要根源。 英文
从目前的证据来看,脉冲在每个重复周期内占大约1/30的时间。这使电磁辐射区域大小的数量级被限制在“光速圆周”周长的1/30左右。同样,在径向方向上尺寸也一定很小。我们可以认为要小到足以使脉冲上升时间等于或大于光穿过辐射区的时间。这意味着,产生辐射的等离子体的运动速度小于光速的1%。对于有这样速度的区域,预计其辐射效应在任何情况下都会变得很重要。 英文
这里暗含的轴向不对称性有待进一步讨论。一颗半径为10 km的中子星的表面磁场很可能会达到1012高斯。对应于已观测到周期的“光速圆周”,其周长在4×1010 cm至0.75×1010 cm之间。在上述“... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | RHODOPSIN, the photosensitive pigment of vertebrate rods and of a number of invertebrate photoreceptors, consists of a colourless protein (opsin), which carries the 11-cis isomer of retinal (retinaldehyde, vitamin A aldehyde) as chromophore. Bownds1 showed that in cattle rhodopsin the chromophore is bound in Schiff bas... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | A direct experimental test of this hypothesis will have to wait until more is known about the amino-acid sequence and the three-dimensional structure of rhodopsin. Indirect support comes, however, from the observation that the absorption maxima of all the visual pigments that are known to have 11-cis retinal as chromop... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | of incubation before the addition of 11-cis retinal differ for the three denaturants. The comparison therefore is only qualitative. The denaturation of rhodopsin was measured as irreversible bleaching in the dark. This involved only the measurement of the absorption spectrum in the presence of 0.07 M hydroxylamine, and... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Fig. 4. Position of the absorption maximum (λmax) of native and altered rhodopsin as a function of the Gu-HC1 concentration.
中文
Either interpretation presupposes that Gu-HC1 shifts the absorption spectrum of rhodopsin by altering the conformation of opsin. Gu-HC1, however, carries a positive charge, localized primari... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Fig. 5. Analysis of the irreversible denaturation of rhodopsin by Gu-HC1. Upper left (I), successive absorption spectra (A to G) recorded with a Cary model 14 spectrophotometer, after adding a small volume of a concentrated rhodopsin solution in 2 percent aqueous digitonin to buffered 6.2 M Gu-HC1. Upper right (II), th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | is, curves IIIA minus template IIIA, IIIB minus template IIIB, etc.). (IV) Also shows the absorption spectrum of 11-cis retinal at the initial rhodopsin concentration in this solvent system. It has λmax at 400 nm, a surprisingly long wavelength, and a specific absorbance at λmax about 0.6 that of the Schiff base and of... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | This raises the question as to why the protonated Schiff base has not been seen as an intermediate in other types of denaturation of rhodopsin7,8 except, of course, by strong acid3. The answer probably lies in the extraordinary stability of the unprotonated Schiff base in concentrated Gu-HC1. Fig. 5, I, II and IV, show... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 鲍恩兹[1]指出:在牛的视紫红质中,生色团被限于与视蛋白内一个赖氨酸残基的ε–氨基相连的席夫碱中。 英文
柯林斯[2]以及莫顿、皮特及其同事[3]首先证明,视黄醛与视蛋白上的一个脂肪族氨基形成了一种席夫碱[3]。这引出了下面的问题,即这种类型的连接如何使视紫红质具有吸收性质,因为在水溶液中11–顺式视网膜醛的λmax位于380 nm处,席夫碱的λmax位于363 nm附近,而视紫红质的λmax则位于接近500 nm处。(不同动物视紫红质λmax的准确位置会略有差异,也许是因为视蛋白的种类有所不同吧。) 英文
为了解释这些吸收特性,克罗普夫与哈伯德[4]从由鲍尔等人[5]最先进行的观测入手,即尽管视网膜醛与脂肪胺可以生成一种席夫碱:
... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 英文
两种解释都需要预先假定Gu-HCl是通过改变视蛋白的构象而使视紫红质的吸收光谱发生位移的。但是,Gu-HCl所带的一个正电荷主要定域在对称胍离子的中心碳原子上。当高浓度的Gu-HCl影响到视紫红质的吸收光谱时,在带电胍离子与视黄基生色团分子轨道之间有可能会存在着一种直接的相互作用。但视紫红质λmax随Gu-HCl浓度增加而发生突然性变化的现象(图4)说明并非来自非特异性溶剂对生色团的影响,而倾向于视蛋白构象发生了变化。 英文
视紫红质在Gu-HCl作用下发生不可逆变性的速度是比较慢的。它的第一个产物是λmax为445 nm的色素(图5,III),这种色素会慢慢地转化成另一种λmax为362.5 nm的色素(图5,III和IV)... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 可以这样讲,Gu-HCl的作用是将视蛋白与生色团剥离,因而表现为质子化席夫碱吸收光谱未出现增强的现象。 英文
这样就引出了以下这个问题,即为什么在其他类型视紫红质的变性过程中从未看到过质子化席夫碱作为中间产物出现[7,8],当然,在强酸条件下[3]除外。答案可能就在于未质子化席夫碱在高浓度Gu-HCl中的超常稳定性。图5中的I、II、IV表明,未质子化亚胺在362.5 nm的λmax始终没有发生变化(即在23°C下长达75 min的时间内),但视网膜醛席夫碱在这个pH值下通常会在约15 min之内水解,证据是λmax位移到了自由视黄醛的位置[3]。因此我们必须假定,高浓度的Gu-HCl显著降低了水的活性,以至于浓度为6 M的溶液就像... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | recognition. It seemed probable that the polarization characteristics of the pulse were also being smeared by the passband. Observations of the pulsar were therefore repeated on the nights of December 11, 12, 13 and 20 at 1,720 MHz with narrower bandwidths. The fast rise and short duration of the pulse as recorded by a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The position angle at 1,720 MHz of the mean plane of linear polarization over the pulse was measured on the four nights of observation at this frequency and found to be the same. The internal agreement was considerably better than the error of 5 percent quoted in Table 1 for the absolute value of the position angle. Th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | field lines responsible for the polarization must vary smoothly over a similar range, for the amplitude of the radiation builds up from zero to a maximum and then falls off again. Detailed measurements across the pulse were not possible with the 2,700 MHz receiver because of the wide bandwidth as mentioned earlier. The... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | It seems reasonable to assume that the polarization of the radiation from pulsars reflects the magnetic field in the region of generation. A very highly linearly polarized pulse must then imply that all of the radiation in the pulse was generated in, or modified in, passage through a small region where the field was es... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | That the two most rapidly pulsating sources have shown an increase in period with time as predicted on Gold’s model adds further support to the rotation hypothesis. Goldreich3 has developed a simple axisymmetric version and shown that relativistic particles must be carried out along the field lines which extend beyond ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | If pulsars have satellites, and the satellites influence the activity of the pulsar in the manner of Io’s influence on Jupiter13, the radiation would exhibit many of the characteristics that are found at low frequencies. In spite of Jupiter’s proximity and the time over which the low frequency radiation had been studie... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 本文的作者拉达克里希南曾在印度和澳大利亚接受过射电天文学的培训;他是诺贝尔奖获得者著名科学家拉曼的儿子,后来他继承父业成为班加罗尔物理实验室的负责人。 英文
我们用帕克斯210英尺反射望远镜在2,700 MHz和1,720 MHz频率下对莫隆格勒射电天文台发现的脉冲星PSR 0833–45[1]——现在暂时被证认为船帆座-X的超新星遗迹——进行了观测。我们发现这颗脉冲星具有脉冲宽度窄、强度高且稳定、完全线偏振和周期变动等值得注意的特征。我们对该天体的观测结果似乎排除了径向脉动是射电辐射起源的可能性,而支持由戈尔德提出[2]并被戈德赖希讨论过[3]的旋转模型。 英文
最初的观测是在12月8日、9日和10日用工作于2,700 MHz的宽... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 英文
图4.表示在PSR 0833–45的脉冲中存在偏振面摆动的示意图。
英文
米尔斯[11]报道了他在阿雷西博观测到的蟹状星云脉冲星,他发现其周期在以每年1 / 2,400的速率加长。他进一步指出:由于PSR 0833–45具有目前已知的次短周期,或许它也会呈现出相同的特性。受其观点启示,我们又对PSR 0833–45的周期进行了几次观测,观测结果示于图5中。 英文
图5.PSR 0833–45的周期在12天观测期内显示出的变化。斜率所对应的周期增长为每天10 ns或1 / 107。
英文
PSR 0833–45的周期在以每天10 ns的速率增加,即每年1 / 24,000。假设该脉冲星位于拉奇等人[6]所给出的位置,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 英文
(王耀杨 翻译;邓祖淦 审稿)
Detection of Water in Interstellar Regions by Its Microwave Radiation
A. C. Cheung et al.
Editor’s Note
As radio receivers became capable of observations at ever shorter wavelengths, new molecules were detected in space. A. C. Cheung and colleagues here report the discovery of radio emission from wa... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Fig. 1 shows the spectral intensity near the H2O resonance in the approximate direction of Sgr B2, the antenna being pointed at the position α1950 =17 h 44 m 23 s. δ1950 = –28°25′. The observed antenna temperature is plotted as a function of Doppler velocity. The mean Doppler velocity of about 70 km s–1 for the spectra... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Doppler velocities near 20 km s–1 and 7 km s–1 (ref. 2); the latter coincides more closely with the H2O velocity. 中文
Fig. 2. Observed spectral intensity of 616→523 H2O rotational transition in the direction of the Orion Nebula. The position of peak emission is α1950.0 = 5 h 32 m 57 s ± 4 s, δ1950.0 = –5° 25.5′ ±1.0′.
... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The Orion and W49 sources were not large enough in angular size noticeably to broaden the beam width of 8.8′ in drift scans across the sources. Thus we conclude that these radiating sources are not larger in angular diameter than 3′. 中文
The radiation found is attributed to H2O because its frequency coincides very close... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | In the case of Sgr B2, the situation is more complex. Rather strong NH3 radiation was, in fact, observed from the same (or nearly the same) direction as the H2O radiation. The (1,1), (2,2), (3,3) and (4,4) inversion transitions of NH3 were all found with antenna temperatures between 0.5° K and 1.5° K (unpublished work ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | There is, of course, H2O in the Earth’s atmosphere. One might wonder if it could produce the observed radiation. It can be eliminated as a possible source for several reasons. One is that the antenna beam is switched from one part of the sky to a neighbouring part, so that only radiation which varies very rapidly with ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | In Orion, the actual microwave brightness temperature of the source would have to be at least as high as a few hundred degrees, and in W49 at least as great as about one thousand degrees. The actual temperatures may be much higher if these sources are smaller than the upper limit of 3’ of arc given, or if they are opti... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 因此,这些观测结果表明水分子是在不断地被激发。后来人们发现是氢分子的碰撞引发了这种激发过程——但当时人们还没有发现在星际空间中存在氢分子。 英文
在人马座B2、猎户座星云和W49源的方向上观测到了由水分子616→523转动跃迁产生的微波辐射。这种波长为1.35 cm的射电辐射是在哈特克里克天文台用20英尺的射电望远镜观测到的,采用的技术与早先探测氨分子光谱的方法[1]相同。尽管有理由相信这两种分子之间并不存在密切的联系,但在人马座B2方向上,水分子的辐射和以前发现的大量氨分子的辐射(Cheung等人尚未发表的研究结果)都来自同一个方向。从猎户座星云(在其中并未探测到氨分子)中观测到水分子强辐射产生的天线温度为14 K;而从W49方向... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 对水分子来说,10 km/s的速度对应于0.75 MHz的频移,所以这些图中显示的多普勒位移与水分子在实验室中的频率22,235.22 MHz有小小的偏差。除位于22,234.53 MHz的氨分子(3,1)反演跃迁以外,在星际空间中再也没有其他简单分子能产生与这个频率相差几十兆赫之内的谱线了。虽然氨的这种跃迁很微弱,但仔细检查观测到的辐射是否有可能来自于氨分子仍然很重要。因此需要搜索氨分子的其他一些较强的跃迁。当激发温度高于50 K时,(3,3)跃迁比(3,1)跃迁大致强一个量级以上;而在激发温度低于50 K时,(1,1)跃迁同样会更强。即使在激发温度远高于50 K时,(1,1)跃迁的发生概率也常常是(3,1)跃迁的两倍以上。我们在... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 如果确实达到了热平衡,那么根据水分子的强微波辐射和存在于射电波段的强氘化水(HDO)跃迁就可以使我们进行一次关于氢–氘丰度比的有趣测量。 英文
在此感谢哈罗德·韦弗教授为我们提供了人马座天区羟基云的具体位置并和我们进行讨论,还要感谢保罗·罗德为我们提供了观测上的帮助。美国国家航空航天局、美国海军研究办公室和美国国家科学基金会为这项工作提供了一定的支持。 英文
(冯翀 翻译;沈志侠 审稿)
Early Stages of Fertilization in vitro of Human Oocytes Matured in vitro
R. G. Edwards et al.
Editor’s Note
Robert Edwards ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | We have adapted the conditions found successful in the hamster for work on the human oocyte. The preliminary results reported in this article indicate that human eggs can be fertilized in conditions similar to those found most suitable for the fertilization of hamster eggs in vitro. 中文
Maturation of Eggs and Inseminati... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | acetic-saline (20 percent acetic acid in normal saline solution) or acetic-alcohol (1:3), stained with aceto-orcein, and re-examined. In one-celled eggs, the occurrence of penetration was inferred from the presence of spermatozoa in the zona pellucida or in the perivitelline space; the presence in the vitellus of pronu... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Fig. 2. Spermatozoa in the perivitelline space of human eggs. In a, the sperm head is lying in the vitellus, the mid-piece is still embedded in the zona pellucida, and the main piece lies outside the zona. This egg was examined 13 h after insemination; the spermatozoon was still active. (× 1,650.) In b, the whole of th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | on staining, a mass of coarser chromatin was observed in one pronucleus in a region where the two pronuclei were apposed. 中文
Fig. 4. In a, a small body resembling a sperm mid-piece was found in a stained egg which contained three pronuclei and at least one polar body. (× 3,300.) In b, a spermatozoon present in the per... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | these effects. In some of the present experiments, however, we pre-incubated spermatozoa in follicular fluid before adding them to the eggs. Our impression is that this pre-incubation led to the attachment of more spermatozoa to the zona pellucida, and to a higher incidence of penetrated and pronucleate eggs. 中文
The fa... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | vitro; small amounts of RNA are synthesized by Xenopus oocytes in response to luteinizing hormone (LH) during the final period of maturation13. When maturation of rabbit oocytes was started in vivo by injecting gonadotrophins into the mother, and completed in the oviduct or in vitro, full term rabbit foetuses were obta... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The clinical use of human embryos will require the development of operative techniques for the recovery of follicular oocytes and for the transfer of eggs into human oviducts and uteri. Preliminary work using laparoscopy has shown that oocytes can be recovered from ovaries by puncturing ripening follicles in vivo, and ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Davidson, E., Allfrey, V. G., and Mirsky, A. E., Proc. US Nat. Acad. Sci., 52, 501 (1964).
Edwards, R. G., Nature, 208, 349 (1965).
Jagiello, G., Karnicki, J., and Ryan, R. J., Lancet, i, 178 (1968).
Henderson, S. A., and Edwards, R. G., Nature, 218, 22 (1968).
体外成熟后的人类卵母细胞体外受精的早期阶段
爱德华兹等
编者按
罗伯特·爱德华兹的绝大部分职业生涯是在剑桥大学度过... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 我们在另外5枚卵子的卵周隙中发现了精子(图2),而且其中4枚卵子中的精子仍能移动。在对这5枚卵子进行固定和染色后发现:其中4枚卵子正处于中期–II阶段,另外1枚卵子有一个小细胞核。 英文
图1.人工授精24 h后处于存活人卵透明带中的精子。(a,放大675倍;b,放大1,200倍)
英文
图2.处于人卵卵周隙中的精子。a,精子的头部位于卵黄中,中部仍嵌在透明带里,而主要部分则在透明带之外。这是在人工授精13h后观察到的卵子的情况;其中的精子仍可移动(放大1,650倍)。b,整个精子都位于卵周隙中,不过我们只能在图里看到精子的头部。这个精子仍能移动(放大750倍)。
英文
有7枚卵子已经很好地形成了原核。其中2枚卵子各有2... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | 当兔子和其他动物的卵母细胞在体外成熟而在体内受精时,它们看起来都能正常地发育到原核阶段,但是许多由此得到的胚胎在形成卵裂球时出现了亚核,并且几乎所有这样的胚胎在分裂早期就会死亡(参考文献12和爱德华兹尚未发表的研究结果)。胚胎发育异常或许是因为当把将要在体外培养成熟的卵母细胞从卵泡中取出时,RNA的合成还没有全部完成;处于成熟最后阶段的爪蟾卵母细胞会在促黄体生成激素(LH)的作用下合成一小部分RNA[13]。如果我们通过给雌兔注射促性腺激素来促发兔卵母细胞在体内的成熟过程,那么不管后续的成熟过程是在输卵管中完成还是在体外完成,都能够得到足月的胎兔(参考文献12和爱德华兹尚未发表的研究结果)。胚胎发育中的另一个问题是:一些在成熟过程中... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | RYLE gives good evidence1 that quasars evolve into powerful radio sources with two well separated radio components, one on each side of the dead or dying quasar. The energies involved in the total radio outbursts are calculated to be of the order of 1061 erg, and the optical variability of some quasars indicates that t... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Mpc. From these statistics it seems probable that a dead quasar-like object inhabits the local group of galaxies and we must expect many nearer than the Virgo cluster and M87. If we restrict ourselves to old quasars bright at radio wavelengths, then Sandage reduces his estimate by a factor of 200 so the average distanc... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | As Schwarzschild throats are considerable centres of gravitation, we expect to find matter concentrated toward them. We therefore expect that the throats are to be found at the centres of massive aggregates of stars, and the centres of the nuclei of galaxies are the obvious choice. My first prediction is that when the ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Numerical values are: Vc = 200 (M7/r)1/2 km s–1 at r pc. 12m diameter of Schwarzschild mouth = 1.6×1013 M7 cm ≃ M7, AU. Roche limit for a star of density ρ* g cm–3 (R) = 4.1×1013 (M7/ρ*)1/3 cm = 2.8 (M7/ρ*)1/3 AU. Greatest swallowable angular momentum per unit mass h0=4mc=0.5 M7 pc km s–1. Once the initial very low ang... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | sensible model of the swallowing rate we must estimate the magnetic friction and investigate what happens to the energy acquired by the magnetic field. Before doing this let us assume a conservative swallowing rate of 10–3 M⊙ per year and work out the power available through magnetic friction. We assume that this mass ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | between the gravity of the central mass and the non-magnetic pressure, GMr–3zρ = – cs2 ∂ρ/∂z, which gives
ρ = ρ0 exp [–z2/2b2] where b2 = r3cs2/GM
(7)
The local shear rate is given by Oort’s constant A
Hence
Here ∑ is the surface density of matter in the disk, . 中文
On multiplication by b3, equation (9) tells us that ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | highly conducting medium, however. In free space re-alignment of the magnets involves reconnexion of magnetic field lines through neutral points. This cannot happen in a force-free, strictly perfect, conductor. Rather one may show that neutral sheets develop with large sheet currents flowing through them. This situatio... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | nuclei ought to be radio sources because such cosmic rays will clearly radiate by the synchrotron mechanism in the magnetic field. In summary, we expect from a shear 2A the generation of a magnetic field given by equation (2), a shearing force given by equation (3), and a power p per unit area dissipated into cosmic ra... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | Apart from the trickle of angular momentum into the singularity g must be balanced in a steady state by the inward flux of angular momentum carried by the material. Thus, using equations (3) and (5)
that is
g ≃ F (GM r)1/2
(15)
Because g∝r1/2 we see from equation (13) that ∑∝r –3/2cs–2 ∝r–3/2 Vc–2 ∝r–1/2 and that the ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | From equation (7) b/r = 0.05x. ρ0 = (2π)–1/2∑/b=4.6×10–19 r0–3/2x–3F–3M7–1/2 =1.4×10–9 m0–3/2x–3F–3M7–2 g cm–3 (m0 ≫ 6). From equation (13), B = 3×10–3 r0–5/4 x–1/2 F–31/2M71/4 = 2.7×105 m0–5/4 x–1/2 F–31/2M7–1 G (m0 ≫ 6). From equation (18), p(r) ≃ 0.22r0–3F–3M7 ergs cm–2 s–1(r ≫ 6m). Notice that the power is strongly... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | The maximum temperature is at m0 = 7.05 and is T1 = 6.6×104 F–31/4 M7–1/2 K. The medium will be optically thick for ∑ = 90 x–2 F–3 M7–1 g cm–2. The disk is in danger of becoming optically thin around ∑= 1, but there the temperature has fallen to T2 ~ 700 K so dust will take over as a source of opacity (this may not hap... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0307. 《自然》百年科学经典(英汉对照版)(第五卷)(1966-1972).epub | .epub | 16,876,645 | 2025-09-26T19:07:54.356078 | K come from regions r0≃10–3 where the circular velocities are Vc≃6×103 km s–1. These emission lines should therefore be very broad. We may expect that the real disk is not steady, although exact periodicity due to a source in orbit is unlikely. Rather, we should expect variations on a time scale given by 2r/Vr at m = 2... | 400套付费套装书 |
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