path stringclasses 189
values | ext stringclasses 1
value | size_bytes int64 569k 327M | mtime stringdate 2025-09-26 17:48:05 2025-09-26 19:10:03 | text stringlengths 40 2k | source stringclasses 1
value |
|---|---|---|---|---|---|
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Since the proposal of the neutrino hypothesis by Pauli and its success in Fermi's theory of nuclear beta decay, the particle has been called upon to play similar parts in the observed decay of a number of different mesons22
. The question arises as to the identity of these neutrino-like particles with the neutrino of ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | physics of today.
中文
The known properties of the neutrino are summarized below.
Properties of the Neutrino
中文
Our work and that of our associates reported in this paper were supported by the United States Atomic Energy Commission.
中文
(178
, 446-449; 1956)
Frederick Reines and Clyde L. Cowan, jun.: Universit... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 最简单的β衰变过程就是自由中子的衰变[9]
,可用下式说明:
n
0
→p
+
+ β–
+ v
_
(1)
因中子、质子和β粒子都带有半整数的自旋,为了式(1)中的角动量平衡(式中三个产物粒子中的任何两个必须自旋反平行),必须赋予中微子一个量子数为1/2的自旋。因为式(1)中四个粒子全都是费米子,所以应遵从自旋为1/2的粒子的狄拉克相对论波动方程。每个粒子都可能存在相应的反粒子,但只有反电子(或称为正电子)和反质子已被确认。式(1)的中微子相应的反粒子可以通过把这几项重排而获得:
p
+
→n
0
+ β+
+ v
+
(2)
这个过程是在丰质子放射性核素的正电子衰变中观测到的,其中质子和中子都是核子的组成成... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 束缚在核内的质子的阈值会随着靶与子核之间的能量差的增加而增高。有趣的是,我们注意到由式(8)可知,低能(E
<α+1)的中微子对物质的穿透力无限大,仅有几兆电子伏的中微子的穿透力都很大,测得的吸收平均自由程可与宇宙的半径相比。
英文
式(6)可以应用到如下实验:大量的氢原子作为强中微子流的靶,并用一个能够记录同时产生的正电子和中子的探测器进行监测。多兆瓦反应堆中的裂变碎片的高β衰变速率的可用性,以及通过使用液体闪烁器而带来的检测技术的改进,最终使得这类直接实验得以实施。对来自大反应堆的中微子流的估计表明,反应堆附近放置的50升水中每小时有几个质子发生反应(6)。问题是如何排除反应堆中的中子和γ射线、天然放射性和宇宙射线的背景... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | (4)这对脉冲中的第二个脉冲是由与正电子同时产生的中子经延迟后在镉中俘获产生的,这可由其俘获时间分布与中子源的计算和观测结果相比较来确定。第二个脉冲的谱与镉俘获γ射线谱一致,移除镉将导致反应堆的信号也随之消失。
(5)对于与反应堆有关的辐射,例如中子和γ射线,有两类实验可将它们排除在信号来源之外。在第一类实验中,在检测器保护箱外放置一个强镅–铍中子源,我们发现它不仅在产生可接收的延迟符合方面效率很低,而且它产生的第一个脉冲谱并不像要求的信号那样随着能量的增高单调下降。在第二类实验中,一个附加的保护箱为反应堆的中子和γ射线提供了一个至少为10的衰减因子,观测发现除了影响到式(1)统计涨落外,它并不引起反应堆的信号变化。
英文
因... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
(沈乃澂 翻译;尚仁成 审稿)
A Test of a New Type of Stellar Interferometer on Sirius
R. Hanbury-Brown and R. Q. Twiss
Editor's Note
Robert Hanbury-Brown and Richard Twiss had recently demonstrated that photons in two separate but coherent beams of light tend to arrive together at two distinct detectors. Here they show how t... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 1
, M
2
, which focused light on to the cathodes of the photomultipliers P
1
, P
2
and which were guided manually on to the star by means of an optical sight mounted on a remote-control column. The intensity fluctuations in the anode currents of the photomultipliers were amplified over the band 5-45 Mc./s., which e... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | There is no necessity in an “intensity” interferometer to form a good optical image of the star. It is essential only that the mirrors should focus the light from the star on to a small area, so that the photocathodes may be stopped down by diaphragms to the point where the background light from the night sky is relati... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | In order to ensure that any correlation observed was not due to internal drifts in the equipment, or to coupling between the photomultipliers or amplifier systems, dummy runs of several hours duration were made before and after every observation; for these runs the photomultiplier in each mirror was illuminated by a sm... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | , a series of observations was made with the mirrors close together and exposed to the night sky alone. No significant correlation was observed over a period of several hours.
中文
The results have been used to derive an experimental value for the apparent angular diameter of Sirius. The four measured values of C
(d
... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 中文
A detailed comparison of the absolute values of the observed correlation with those expected theoretically has also been made, and the results are given in Table 1 and in Fig. 2. In making this comparison, it is convenient to define a normalized correlation coefficient Г2
(d
), which is independent of observing t... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | than the value given in the previous paper, which refers to an alternative electronic technique). The most important quantities in this calculation are the gains and output currents of the photomultipliers and the band-widths of the amplifiers; but it is also necessary to make a small correction for the combined spectr... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | ) are shown together with their probable errors, and may be compared with the broken curve, which gives the theoretical values for a uniform disk of 0.0063′′. It can be seen that both the relative and absolute values of Г2
(d
) are in reasonable agreement with theory, and that within the rather wide limits of this pr... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | photomultipliers and the electronic apparatus could be increased, or if photocathodes with higher quantum efficiencies become available. It must also be noted that the technique of using two mirrors, as described here, would probably be restricted to stars of spectral type earlier than G
, since cooler stars of adequa... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Keenan, P. C., and Morgan, W. W., “Astrophysics”, edit. J. A. Hynek (McGraw-Hill, New York, 1951).
Hanbury Brown, R., and Twiss, R. Q., Phil. Mag
., 45
, 663 (1954).
Twiss, R. Q., and Hanbury Brown, R. (in preparation).
Hanbury Brown, R., Jennison, R. C., and Das Gupta, M. K., Nature
, 170
, 1061 (1952).
Jennison, ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 运行时,通过光电阴极上方活盖内的一个小灯照射每个反射镜的光电倍增管。在任何情况下都没有观测到任何显著的相关性。
英文
在该实验初期阶段,我们试图在1955年的11月及12月的上弦月和下弦月的每个夜晚都进行观测。满月那段时间没有观测,因为夜空背景光过亮。在这两个月里观测时间总计达5小时45分,由于探照灯控制系统的失灵而浪费的观测时间与其大致相同。观测结束后综合相关系数C
(d
)的实验值列在表1的第3行中。C
(d
)是相关电机的计数器读数与该读数的均方根不确定性之间的比值。
英文
表1.理论相关系数和观测得到的相关系数之间的比较
英文
在该实验的第二阶段,增加两面反射镜之间的间距,在东西向基线为5.6米、... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 然而,由于这些数据和在每一基线处不同的观测时间值和光通量值有关,所以更为方便的是用相对应的值C
(o
)对观测值C
(d
)进行归一化,以便得到表1第7行给出的归一化相关系数Г2
(d
)。在图2中,给出了Г2
(d
)的实验值及其各自的可能误差,并可以和角直径为0.0063′′均匀圆盘理论值的虚线进行比较。我们可以看出,Г2
(d
)的相对值及绝对值都与理论吻合,而且在这种初步的测试的较宽限制下,理论预测和观测分别得到的相关系数并没有显著差异。
英文
在评估本文所描述的这种技术的潜能时,值得我们注意的是尽管该测量工作耗费了5个月的时间才完成,但能见度太低以至于总观测时间只有18小时,同时在这一有限的时期内... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | out of reach.
中文
Introduction
T
HE basic conditions which must be established before a thermonuclear reactor is possible are, first, the containment of a high-temperature gas so that it is isolated from the walls of the surrounding vessel, and second, the attainment of temperatures sufficiently high for nuclear re... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | The preliminary results reported in this article show that relatively long-time stability can be achieved in a toroidal metal-walled tube. The neutron yield and the kinetic ion temperatures have been measured over a limited range of conditions. The nuclear reaction-rates observed are not inconsistent with those expecte... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | short-circuited.
中文
Fig. 2 Oscillograph recordings of the voltage per turn of the transformer, and the secondary current I
s
. The lower trace shows the pulses produced by proton recoil in a scintillation neutron counter. Conditions: gas, deuterium +5 percent nitrogen + 10 percent oxygen; pressure, 0.13×10–3
mm. m... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | The centre of the current channel is displaced towards the outer wall due to the tendency of the ring current to expand. This expansion is opposed by eddy currents in the metal walls, which are of 1-in. thick aluminium. Measurements of the internal magnetic fields in the plasma are reproducible and show that the axial ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | The third column of Table 1 gives the temperatures required to produce the observed neutron yields assuming a thermonuclear process. In calculating these figures, it has been assumed that the current channel is 20 cm. in diameter, emits neutrons uniformly for a period of 1 msec. and all the deuterium initially present ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Fig. 5. The two lower traces are photomultiplier records of the intensity variation of two selected spark lines during the current pulse
中文
The Doppler broadening of spark lines emitted in a radial direction is used for estimating the kinetic ion temperature of deuterium and neon discharges. Small quantities of oxy... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | =160 gauss. The temperature of the deuterium gas, estimated from the observed neutron yield, is shown for comparison
中文
Conclusion
These preliminary results demonstrate that it is possible to produce a stable highly ionized plasma isolated from the walls of a toroidal tube. Hydrogen gas has been maintained in a sta... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 他们试图通过强大的电流爆发加热等离子体使其温度接近太阳的温度。这个小组描述了令人振奋的初步结果,但不久发现大量的等离子体的不稳定性阻碍了课题的最终成功。五十多年后的今天,多种等离子体的不稳定性仍然阻碍着聚变能的应用。
英文
引言
在成功建立热核反应堆前必须具备的基本条件是:第一,约束高温气体,确保将其与周围的容器壁隔离开;第二,达到足够高的温度,使轻元素间能发生核反应。这两个条件是相互依存的。不好的约束条件会使能量损失太大,以致气体温度难以达到远大于106
K的温度。
英文
设计的实验装置通过与气体中电流相关的磁场来研究电离氢(或氘)的约束情况,该装置能达到可以用氘检测是否发生核反应所需的足够高的温度。这台在哈威尔原子... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
高能辐射
在氘的气体电流超过84千安时观测D-D反应产生的中子发射,发现发射集中在峰值电流附近,时间约为1毫秒。
英文
表1显示了在峰值电流增高时每个脉冲发射的平均中子数。
英文
表1
条件:气体D2
+5% N2
;气压:0.12×10–3
毫米汞柱;Bz
=160高斯
英文
图4为在电流脉冲周期内中子发射的平均速率的直方图。
英文
图4.电流脉冲周期内不同时间的中子计数的直方图
英文
表1的第三列给出了假定的热核过程产生观测到的中子数所需的温度。在计算这些值时假定,电流通道的直径是20厘米,在1毫秒期间内均匀地发射中子,并且所有最初存在的氘均在电流通道内。由于反应速率是一个对温度... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
(沈乃澂 翻译;尚仁成 审稿)
Co-operative Phenomena in Hot Plasmas
L. Spitzer, jun.
Editor's Note
The new experiments producing high-temperature plasmas in the ZETA device at Harwell not only shed light on the potential for controlled fusion energy, but also provided an opportunity for studying plasma physics in extreme cond... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | , may be used to set an upper limit to the rate at which positive ions are heated by electron-ion collisions. In this method the rate of heating is made a maximum by setting the electron temperature equal to three times the ion temperature, T
i
, and setting the electron density equal to a constant, n
e
, correspondi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | at the higher current is the temperature obtained from the Doppler width of the O V triplet, as shown in Fig. 6 of the Harwell article. The ion temperature obtained from the neutron yield under this condition is about 50 percent greater, but no information is available on the time at which the neutrons appear in this c... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | observed; since this current produces only a minor perturbation in the magnetic field, there was no pinching of the discharge. Time-resolved spectroscopic profiles of the He II line, λ 4,686, indicated that the kinetic temperature of these ions increased to 1.2×106
degrees K. in 1.5×10–4
sec., as compared to a theore... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
索恩曼及其同事们在先前的文章中阐述了一个很有意思的结果,这个结果不仅说明我们在热核能量的可控释放中迈出了重要的一步,而且还提出了一个极具挑战性的有关完全电离的气体(即等离子体)的动力学问题。光谱线剖面和中子数提供了与正离子加速相矛盾的证据。然而,理论显示仅靠电子–离子碰撞并不足以解释观测到的升温速率,其中应该包含某些未知的机制。
英文
在之前的一篇文章[1]
中,我曾提到正离子温度升高的速率是由电子–离子碰撞导致的。然而在英国和美国都有人提出,这个碰撞过程不足以解释正离子在释放电荷后获得能量的速率。斯蒂克斯[2]
提出了一个相对简单的过程,可以用来确定电子–离子碰撞所导致的正离子升温的速率上限。在这种方法中,将电子... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
(沈乃澂 翻译;尚仁成 审稿)
A Three-Dimensional Model of the Myoglobin Molecule Obtained by X-Ray Analysis
J. C. Kendrew et al.
Editor's Note
Although X-ray diffraction had been used since the beginning of the twentieth century to analyse the structure of crystalline materials such as common salt, it had not yielded much in... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | In describing a protein it is now common to distinguish the primary, secondary and tertiary structures. The primary structure
is simply the order, or sequence, of the amino-acid residues along the polypeptide chains. This was first determined by Sanger using chemical techniques for the protein insulin1
, and has sinc... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | of X-ray analysis (not counting hydrogens, myoglobin contains 1,200 atoms, whereas the most complicated molecule the structure of which has been completely determined by X-rays, vitamin B12
, contains 93). Until five years ago, no one knew how, in practice, the complete structure of a crystalline protein might be foun... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | . It was clear that further progress could only be made if the analysis were extended to three dimensions. As we shall see, this involves the collection of many more observations and the production of three or four different isomorphous replacements of the same unit cell, a requirement which presents great technical di... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | -iodo-phenylhydroxylamine. Each group of ligands combined specifically at a particular site, five distinct sites being found in all. The substituted phenylhydroxylamine is a specific reagent for the iron atom of the haem group6
, and may be assumed to combine with that group; in none of the other ligands have we any c... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | -co-ordinates of all the heavy atoms with some precision. This was the starting point for the three-dimensional analysis now to be described.
中文
In three dimensions the procedure is much more lengthy because all the general reflexions hkl
must be included in the synthesis, and more complicated because these reflexi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | structure. If the α-helix, or something like it, forms the basis of the structure, we need only work to a resolution sufficient to show up a helical chain as a rod of high electron density. For this purpose we require only reflexions with spacings greater than about 6 A. ; in all there are some 400 of these, of which a... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | A first glance at the synthesis shows that it contains a number of prominent rods of high electron density; these usually run fairly straight for distances of 20, 30 or 40 A., though there are some curved ones as well. Their cross-section is generally nearly circular, their diameter about 5 A., and they tend to lie at ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | -projection, the position of the iodine atom is near that of our group; this is what we should expect, since this reagent specifically combines with the haem group; (iv) the orientation of the disk corresponds, as closely as the limited resolution of the map allows one to determine it, with the orientation of the haem ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | example, its mean density would drop to near the average for the cell and the chain would fade out at this resolution. Similarly, side-chains should, in general, scarcely show up, so that the polypeptide rods in the model must be imagined as clothed in an invisible integument of side-chains, so thick that neighbouring ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | and it is precisely at corners that the chain must lose the tightly packed configuration which alone makes it visible at this resolution (an α-helix, for example, cannot turn corners without its helical configuration being disrupted). Also, there are several apparent bridges between neighbouring chains, perhaps due to ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Perhaps the most remarkable features of the molecule are its complexity and its lack of symmetry. The arrangement seems to be almost totally lacking in the kind of regularities which one instinctively anticipates, and it is more complicated than has been predicated by any theory of protein structure. Though the detaile... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | , 287 (1954).
Bragg, W. L., and Perutz, M. F., Proc. Roy. Soc.
, A, 225
, 315 (1954).
Dintzis, H. M., Cullis, A. F., and Perutz, M. F. (in the press).
Kendrew, J. C., and Parrish, R. G., Proc. Roy. Soc.
, A, 238
, 305 (1956).
Jung, F., Naturwiss.
, 28
, 264 (1940). Keilin, D., and Hartree, E. F., Nature
, 151
,... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 这一领域的进展缓慢,是由于球状蛋白分子比X射线分析的一般对象——有机分子结构复杂很多(不考虑氢原子,肌红蛋白中还有1,200个原子,而采用X射线方法完全确定结构的最复杂的分子——维生素B12
仅有93个原子)。五年前还没有人知道如何实际利用X射线方法来获得结晶蛋白的完整结构,而当时蛋白质晶体学家常用的方法最多只能对分子结构给出极为粗略的描述。佩鲁茨及其同事[2]
的发现改变了这种情况。他们发现,重原子可以结合到蛋白质分子中特定的位置上,所得到的复合物给出了明显不同于普通蛋白质的衍射图案,这使得我们可以用一种名为“同晶置换方法”的经典结构分析方法确定其相对相位。这一方法可以很容易地用于二维分析,给出晶胞沿着某一轴向的投影图。佩鲁茨... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 一旦确定了一般反射线的相位,就可以进行三维傅里叶综合分析,获得结果代表了晶胞内每一点的电子密度。
英文
不过,在开始进行这些处理之前,必须先确定需要达到的分辨率。所需反射线的数量以及与此对应的工作量正比于分辨率的立方。要分辨出每个原子,必须至少包含所有间距大于1.5Å的反射线,总共约有20,000个。另外我们还必须记得对每一种
同晶衍生物测定其全部反射线的强度。除此之外,重金属元素的引入还可能导致晶格的轻微变形。随着分辨率的提高,这种变形将对相位确定的精确性产生越来越严重的影响。对于现阶段的分析工作而言,最紧迫的任务是得到一张足以显示出分子的一般轮廓(即分子的三级结构)的电子密度图。如果构成分子结构的基础是α螺旋或者类似的结... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
肌红蛋白分子
现在我们可以开始研究与其邻近分子隔开的单个肌红蛋白分子的三级结构。图2给出了三维分子模型的不同视角,这一模型显示了单个分子中的高电子密度区域。有几点是必须要注意的。首先,模型显示的只是高电子密度区域的大致分布。那些螺旋形多肽链的核心应该是这样的区域,但是如果多肽链伸展开,例如转变为β构型,那它们的平均电子密度将降低到晶胞电子密度的平均值附近,此时这些多肽链在该分辨率下就看不到了。与此类似,侧链基本上很难显示出来,因此要将模型中的多肽链想象成被一层不可见的侧链外壳所覆盖,这一外壳非常厚以至于邻近的链实际上是彼此接触的。第三,除多肽链之外的其他部分也可能对某些高密度区域有贡献,例如吸附盐分形成的斑点。第四,所选取的... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
(王耀杨 翻译;吕扬 审稿)
Sexually Mature Individuals of Xenopus laevis
from the Transplantation of Single Somatic Nuclei
Gurdon et al.
Editor's Note
Here British developmental biologist John Gurdon and colleagues describe the production of the first sexually mature cloned animals, specifically frogs. Gurdon transferred n... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | , and are excluded from our results. The marker is introduced by taking donor nuclei from a stock of mutant individuals having only one nucleolus in all cells, as opposed to wild-type individuals in which all cells contain potentially two nucleoli. Large series of observations and measurements show no differences in th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Table 1 gives the numbers of metamorphosed frogs that have been obtained from different germ-layers and developmental stages of donor embryos. When transplanting endoderm nuclei from post-neurula stages care has been taken to avoid using nuclei from the region of the presumptive germ-cells.
中文
Table 1. Metamorphosed... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Elsdale, T. R., Fischberg, M., and Smith, S., Exp. Cell Res.
(in the press).
Nieuwkoop, P. D., and Faber, J., “Normal Table of Xenopus laevis
” (1956).
源于单个体细胞核移植的非洲爪蟾性成熟个体
格登等
编者按
本文中,英国发育生物学家约翰·格登和他的同事们描述了第一批性成熟克隆动物——特别是成蛙的产生。格登将处于胚胎时期的蝌蚪细胞的细胞核移植到未受精的蛙卵中,该蛙卵能继续正常发育。数年后,他用成体细胞获得了克隆蛙,这无可辩驳地证明了来自成熟的、已发生分化的细胞的细胞核可以重... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
(苏慧 翻译;刘京国 审稿)
A New Fossil Skull from Olduvai
L. S. B. Leakey
Editor's Note
Louis Leakey almost single-handedly made Africa the site of choice for palaeontological exploration from the 1930s to the present. He was born in Kenya, educated at Cambridge, England, and appointed director of the Coryndon Museum in Na... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | antelope bones, jaws and teeth.
中文
It is of special importance to note that whereas the bones of the larger animals have all been broken and scattered. The hominid skull was found as a single unit within the space of approximately one square foot by about six inches deep. Even fragile bones like the nasals are prese... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | The Olduvai skull is patently a member of the sub-family Australopithecinae, and in certain respects it recalls the genus Paranthropus
. In particular, this is the case in respect of the presence of the sagittal crest, the great reduction in the size of the canines and the incisors, the relatively straight line of the... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | I, Olduvai.
中文
A new genus of the Hominidae, sub-family Australopithecinae, which exhibits the following major differences from the genera Australopithecus
and Paranthropus
:
中文
(a
) in males a nuchal crest is developed as a continuous ridge across the occipital bone;
中文
(b
) the inion, despite the great e... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | ) the very prominent and keeled anterior margin of the crests on the frontal bone for the anterior segment of the temporal muscles in the region of the post-orbital constriction (even the most muscular male Paranthropus
exhibits nothing comparable);
中文
(n
) the very unusual position of the nasion, which is on the ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | this buttress is wholly absent and the form of architecture of this region is that which is found in Homo
;
中文
(s
) the very great area of muscle attachment on the inferior margin of the malars;
中文
(t
) the relatively greater reduction of the canines in comparison with the molar-premolar series than is seen ev... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | II have shown that there is a constant and well-marked break between the top of Bed I and the base of Bed II. It is incidentally on this clearly defined land surface that Chellean Stage I living sites are found.
中文
There has also been found a great deal of new faunal evidence, and it is now clear that the fauna of O... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
7月17日,在坦噶尼喀地区奥杜威峡谷的FLK
遗址中第I层上界之下深约22英尺的地方,我的妻子发现了一件人科化石的头骨。在斜坡上的头骨正处于被侵蚀出来的过程之中,正是因为受到了侵蚀令标本有一部分已经被暴露出来,使得发现它成为可能。次日我们便开始对这个遗址进行挖掘,并一直持续到8月6日。结果我们发现了一件近乎完整的人科的头骨。发现该头骨与奥杜威文化(前舍利–阿舍利文化)的一个清晰可辨的生活面具有紧密的联系。
英文
在这个生活面中,除了奥杜威文化的工具及废弃的破片之外,还有已石化的破碎的或裂成破片的动物的骨。这些动物是这个最为原始的石器时代文化创造者们的部分食物。现在还不可能对在这个生活面上发现的动物群进行研究;但可以说... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 这比正常类型的乳突上脊要明显得多;
英文
(f
)乳突的大小与形状都更类似于现在的人类所呈现的乳突;
英文
(g
)在外耳道上方,颞骨颧突后面出现了强而宽阔的猿板;
英文
(h
)不论是从侧面看还是从底部看,鼓板的形态与形状都与远东爪哇猿人属相似;
英文
(i
)颞骨的整个乳突区气窦很大,甚至侵入鳞部;
英文
(j
)相对于颞骨的总体尺寸,颞骨颧突很硕壮;
英文
(k
)在颞骨的鳞部之后,顶骨几乎是垂直升起,之后弯曲形成一个圆顶;
英文
(l
)与枕骨及颞骨相比,顶骨相对较薄;
英文
(m
)眶后缩狭区供颞肌前段附着的额骨上的脊的前缘十分突出,呈龙骨状突起(甚至肌肉最强... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
英文
(田晓阳 翻译;吴新智 胡荣 审稿)
The Affinities of the New Olduvai Australopithecine
Editor's Note
The shift of focus from southern to eastern Africa in the search for human origins was so abrupt that it can be dated precisely—to 15 August 1959, when Nature
published Louis Leakey's discovery of a super-robust australop... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | The description consists largely of a list of twenty “major” differences between the new specimen and the two previously known genera. Some of these points cannot be dealt with as they are briefly stated in terms which are not useful by themselves for comparison. Others, for example, continuous nuchal crest, enlargemen... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Fig. 1. Variation of the tympanic bone at the lateral end of the external auditory meatus in Paranthropus
from Swartkrans (SK
48, SK
52 and SK
848). The Olduvai specimen resembles in this feature the condition illustrated in the middle diagram
中文
(4) The very unusual position of the nasin—almost coinciding with... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | (7) The shape and arrangement of the zygomatic process of the maxilla: The Olduvai specimen has a relatively poorly developed zygomatic process, the lower border of which passes almost horizontally from the zygo-maxillary suture to the main body of the maxilla. In some specimens of Paranthropus
the process passes from... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | , as an omnivore eating at least a moderate amount of flesh, has a dental apparatus very similar to that of the older hominines. The relative sizes of the teeth along the tooth row are closely similar, as is the arrangement of the dental arcades. The anterior teeth, especially the canines, are well developed, but the p... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | the Australopithecus
and hominine pattern. The areas of origin and insertion of these muscles are sturdy; hence the large surface area of the mandibular ramus, the massive zygomatic arch—which also is widely spaced from the brain-case to allow for the very large temporal muscle—large medial and lateral pterygoid plate... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | pattern as here outlined very accurately—the differences being almost entirely of the sort shown to be variable within a single population by the sample of nearly 200 specimens of Paranthropus
now in the collections of the Transvaal Museum. The chief feature of the Olduvai form which does not fall within the observed ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | It is hard enough to reach agreement among zoologists on the taxonomic status of living primates, under conditions in which we possess the skull, skeleton, skin and viscera for study, and it will always be much more difficult to do so when we have only fossils to guide us. I can only say that the very considerable addi... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | figures with mine for Zinjanthropus
.
中文
As to the morphology of the palate, I do not know upon what evidence Robinson is basing his statement, since I have published no measurements of the palatal depth in Zinjanthropus
. I must repeat, however, quite categorically, that the morphology of the Zinjanthropus
palat... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | In any event, the ratio between the canine and the premolar alone cannot have any bearing upon the relation of the canine size to the total molar-premolar series, unless the premolar bears a constant relation to the total post canine series.
中文
I therefore repeat my statement that in Zinjanthropus
there is a relati... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 奥杜威标本的头盖骨类型与傍人的一样。
英文
(3)鼓板的形态不同:利基博士利用标本清楚地论述了这一观点。这一特征在南方古猿中是变化的,且存在与奥杜威标本非常类似的情况。所观察到的变化范围如图1所示。就因为存在这样的变化,在任何情况下,这个特征在种系发生上的价值都不高。
英文
图1.源于斯瓦特克朗斯的傍人外耳道侧端耳鼓骨处的差异(SK
48、SK
52和SK
848),奥杜威标本的特征与本图中间所示的情形类似。
英文
(4)鼻根点的位置几乎与眉间点一致,这点非常罕见:傍人的情况就是如此,至少有些南方古猿也是如此。像奥杜威标本一样,傍人的鼻骨在鼻根点附近相对很宽。
英文
(5)眶间区的绝对宽度和相对宽度都... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
傍人头骨具有奇特而典型的特征,与一些大猩猩头骨非常相近但与南方古猿头骨明显不同。通过与所有其他已知的人科成员相比发现,这些特征在功能上是密切相关的,并且主要是由其特定的食性决定的。这些功能上与结构上的不同清晰地表明了两种类型之间的适应性差异,因此在进化方向上也是有差异的。在现代分类学上,适应性演化差异和特性具有属一级的分类意义。
英文
奥杜威标本的形态符合傍人属的特征,此处概括得已非常准确——即奥杜威标本所反映的形态差异基本没有超出德兰士瓦博物馆现有藏品中约200个傍人标本所体现的形态变异范围。奥杜威标本明显超出藏品所观测的变异范围的特征是它的大小。若进行大小的比较,就必须是一个男性标本,并且该标本的牙齿从第三上前臼齿... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 很显然,一个个体可能具有一枚长16毫米、宽6毫米的犬齿(模数等于11)以及一枚长9毫米、宽7毫米的前臼齿(模数等于8),然而别的标本可能具有长11毫米、宽11毫米的犬齿以及一枚仅仅长5毫米、宽11毫米的前臼齿,尽管这两套牙齿的模数比值相同,但完全没有意义。
英文
无论如何,对犬齿大小与全部臼齿-前臼齿齿系的关系来说,单个的犬齿和前臼齿间的比值并不具备任何意义,除非前臼齿与全部的后犬齿齿系间具有某种恒定的关系。
英文
因此,我重申一下我的观点,就全部臼齿-前臼齿齿系的比较而言,在东非人中犬齿的退化比在傍人中看到的退化相对来说幅度更大,并且我认为鲁滨逊无法反驳我的这一观点。
英文
鲁滨逊认为,我们需要依据其食性和生活方... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | state and then quickly lose some of their excitation energy through non-radiative transitions to the 2
E
state4
. This state then slowly decays by spontaneously emitting a sharp doublet the components of which at 300°K. are at 6,943 Å. and 6,929 Å.(Fig. 2a
). Under very intense excitation the population of this meta... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
肖洛和汤斯[1]
提出了一种以碱金属蒸气作为工作介质产生单色性极高的红外光辐射的技术。贾范[2]
和桑德斯[3]
也讨论了在电子激发气体中产生这种辐射的若干方案。在本实验室中,我们已经成功地将光泵浦技术用于固体荧光材料中,并以此获得了负温度及波长为6,943 埃的受激光辐射,其中所用的工作介质是红宝石(含铬的刚玉)。
英文
图1给出的是该晶体中三价铬离子的能级结构简图。当我们用波长约为5,500埃的能量照射此材料时,铬离子被激发到4
F
2
态,然后通过非辐射跃迁迅速损失部分激发能而跃迁到2
E
态[4]
。随后这个能态通过自发辐射而缓慢衰变,辐射产生了明锐的双线,它们在温度为300 K时的波长分别是6,9... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | C
(ref. 4). We wish to report the results of chemical studies on four adult haemoglobin components5
found in a single individual, D. K. P.; her haemoglobins turned out to be normal in both peptide chains, abnormal in one or other chain and abnormal in both chains, respectively. Apart from their genetic interest, thes... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | in the same buffer. The relative amounts (percent) recovered were: A, 35; G, 27; C, 23; X, 15.
中文
Fig. 1. Starch-gel electrophoresis of D. K. P.'s haemoglobin at p
H 8.6 in 0.05 M
veronal buffer
中文
Each haemoglobin was digested with trypsin and fingerprinted11
. Haemoglobin A appeared to be completely normal ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | The following relationship for these five peptides was established by means of quantitative amino-acid analyses of the isolated peptides with the Spinco model Moore and Stein automatic analyser, by endgroup determinations with the dinitrophenol procedures12
, by stepwise degradation with the Edman-Sjøquist procedure13... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | . It is clear from the results (Figs. 2 and 3) that haemoglobin X contains the abnormal peptides characteristic of both haemoglobin C and G. Peptide A-4 (β chain) is replaced by the two haemoglobin C peptides C-4a
and C-4b
. Peptides A-3 and A-9 (α chain) are replaced by the three haemoglobin G peptides G-3a
, G-9a
... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | It is important to realize the random nature of this final step in the assembly of the molecule, in contrast to the previous dimerization step, which is specific. The fact that the four haemoglobins occur in roughly equal amounts, with A predominating, implies that at least in this patient the rate of manufacture of th... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Hunt, J. A., and Ingram, V. M., CIBA Found. Symp. Biochem. Human Genetics (Naples), 114 (1959).
Hill, R. L., and Schwartz, H. C., Nature
, 184
, 642 (1959).
Hunt, J. A., and Ingram, V. M., Nature
, 181
, 1062 (1958).
Atwater, J., Schwartz, I. R., and Tocantins, L. M., Blood
, 15
, 901 (1960).
Edington, G. M., and... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
费城的托坎廷斯医生和阿特沃特小姐慷慨地为我们提供了患者D. K. P.的血液样本,他们叙述了该患者的临床表现,并指出该患者血液样本中存在着四种几乎等量的血红蛋白[5]
。由于这四种血红蛋白在pH值为8.6时电泳迁移率不同,它们分别被命名为血红蛋白A、G、C和X[5]
,字母表示蛋白迁移顺序,A表示迁移速度最快的蛋白组分。其中,前三种血红蛋白是根据与各自迁移率相同的标准蛋白样本来命名的,而X组分是一个未知的血红蛋白,在目前已知的所有血红蛋白中迁移最慢。他们还发现[5]
血红蛋白G的性质与施奈德医生所研究的G样本是一致的。因此,它很可能与莱曼和埃丁顿[6]
描述的血红蛋白G以及舒特等人[7]
最近描述的血红蛋白GIb
... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
(2)肽段G-3b
刚好包含甲硫氨酸,在指纹印迹过程中,甲硫氨酸残基会一定程度地被氧化为亚砜,由此产生的“G-3b
ox”可以通过层析法进行分离与鉴定。肽段A-3和A-9(以及A-25)也存在着同样的氧化现象。
英文
血红蛋白X也被消化并进行指纹印迹分析[11]
,从实验结果(图2和图3)可以很明显地看出血红蛋白X含有异常肽段,其特征与血红蛋白C和血红蛋白G的异常肽段相似。其肽段A-4(β链)被血红蛋白C的两个肽段C-4a
和C-4b
所取代,肽段A-3和A-9(α链)被血红蛋白G的三个肽段G-3a
、G-9a
和G-3b
所取代。因此,血红蛋白X是自然产生的α链和β链均异常的成人血红蛋白。板野和鲁滨逊... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | -chromosomes can be of maternal or paternal origin in different cells of the same animal, and that they are genetically inactive. This could, she explained, account for the mottled appearance of female mice heterozygous for coat colour genes. The Lyon hypothesis, now widely accepted, states that in female mammals, one ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | . They have been thought to be allelic with one another, but since no fertile males can be obtained from any except, in rare cases, brindled, direct tests of allelism have usually not been possible. In addition, a similar phenotype, described as “variegated”, is seen in females heterozygous for coat colour mutants tran... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | normal and mutant cells varies, leading to incomplete penetrance in heterozygotes. The gene bent-tail, Bn
10
, may fit into this category, having 95 percent penetrance and variable expression in heterozygotes. Jimpy, jp
, is recessive, suggesting that the presence of some normal cells is enough to ensure a normal phe... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | ., 51
, 217 (1953).
Lyon, M. F., J. Hered.
, 51
, 116 (1960).
Dickie, M. M., J. Hered.
, 45
, 158 (1954).
Phillips, R. J. S., Genet. Res
. (in the press).
Russell, L. B., and Bangham, J. W., Genetics
, 44
, 532 (1959).
Russell, L. B., and Bangham, J. W., Genetics
, 45
, 1008 (1960).
Falconer, D. S., Z. indukt... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 英文
因此,这一假说预示着所有性连锁基因小鼠的表型是由局部基因作用决定的,相应的杂合子都呈现嵌合体表型;并且当常染色体基因易位到X染色体上时,将会产生类似的效应;当表型不是由局部基因作用决定时,有可能产生各种类型的结果。除非在失活时这种基因作用被限制在具有非常少量细胞的后代中,否则除了极个别的特例外,这些原始细胞将包括两种类型。所以个体表型可能会介于正常型和半合子型之间,或者只要存在任何正常细胞就能够表现出正常的表型,或者可能由于正常细胞和突变细胞的比例不同从而该基因在不同细胞中表达水平不同而导致杂合子表现出不完全的外显率。弯尾基因Bn
[10]
可能就属于这种类型,其杂合子有95%的外显率和各种水平的基因表达。吉皮基因(jp
... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | ) A group of three bases (or, less likely, a multiple of three bases) codes one amino-acid.
(b
) The code is not of the overlapping type (see Fig. 1).
Fig. 1. To show the difference between an overlapping code and a non-overlapping code. The short vertical lines represent the bases of the nucleic acid. The case illus... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | show only single amino-acid changes. The newer experimental results essentially rule out all simple codes of the overlapping type.
中文
If the code is not overlapping, then there must be some arrangement to show how to select the correct triplets (or quadruplets, or whatever it may be) along the continuous sequence of... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | have previously argued that acridines such as proflavin act as mutagens because they add or delete a base or bases. The most striking evidence in favour of this is that mutants produced by acridines are seldom “leaky”; they are almost always completely lacking in the function of the gene. Since our note was published, ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | . It will be seen that they all fall in the B
1 segment of the gene, though not all of them are very close to FC
0. They scatter over a region about, say, one-tenth the size of the B
cistron. Not all are at different sites. We have found eight sites in all, but most of them fall into or near two close clusters of si... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | mutants.
中文
The double mutants (which contain a mutation plus its suppressor) which plate on K
have a variety of plaque types on B
. Some are indistinguishable from wild, some can be distinguished from wild with difficulty, while others are easily distinguishable and produce plaques rather like r
.
中文
We have ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | (0+1), then although the reading of triplets between FC
0 and FC
1 will be altered, the original reading will be restored to the rest of the gene. This could explain why such double mutants do not always have a true wild phenotype but are often pseudo-wild, since on our theory a small length of their amino-acid seque... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | whether the “reading frame” is shifted one place to the right or one place to the left.
中文
If we symbolize a shift, by one place, of the reading frame in one direction by → and in the opposite direction by ←, then we can establish the convention that our + is always at the head of the arrow, and our - at the tail. T... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 1 group, there must be one or more unacceptable triplets when a ← shift is made; similarly for the region to the right of the FC
21 cluster. Thus we predict that a combination of a + with a - will be wild or pseudo-wild if it involves a → shift, but that such pairs involving a ← shift will be phenotypically r
if the ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | is any integral number of bases, positive or negative.
中文
It can also be seen that our choice of reading direction is arbitrary, and that the same results (to a first approximation) would be obtained in whichever direction the genetic material was read, that is, whether the starting point is on the right or the left... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | Our ability to find the coding ratio thus depends on the fact that, in at least one of our composite mutants which are “wild”, at least one amino-acid must have been added to or deleted from the polypeptide chain without disturbing the function of the gene-product too greatly.
中文
This is a very fortunate situation. ... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | cistron (be it a deletion, an acridine mutant, or any other mutant) does not prevent the expression of the B
cistron. Conversely, no alteration within the B
cistron prevents the function of the A
cistron. This implies that there may be a region between the two cistrons which separates them and allows their functions... | 400套付费套装书 |
C:\Users\yuan\Documents\400套付费套装书\04-100套\epub\0306. 《自然》百年科学经典(英汉对照版)(第四卷)(1946-1965).epub | .epub | 35,511,682 | 2025-09-26T19:07:57.651603 | 中文
Is the Coding Ratio 3 or 6?
It remains to show that the coding ratio is probably 3, rather than a multiple of 3. Previous rather rough extimates10,14
of the coding ratio (which are admittedly very unreliable) might suggest that the coding ratio is not far from 6. This would imply, on our theory, that the alteratio... | 400套付费套装书 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.