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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 | . Presumably there were points in chemical evolution where choice of pathway also occurred, for example, where the rate of one reaction caused it to predominate over a thermodynamically more probable one5
; but it would seem even more difficult to estimate the number. Assuming one thousand such choices, however, we 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 | I am greatly indebted to Dr. Roger S. Pinkham for kindly criticism throughout the development of these thoughts.
中文
(206
, 131-132; 1965)
H. F. Blum: National Cancer Institute, National Institutes of Health, Department of Health, Education and Welfare, Bethesda, Maryland, and Department of Biology, Princeton Univer... | 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
我们可以用下式来表示日地系统中的变化:
S
为熵,N
为涉及的分子数量;k为玻尔兹曼常数;ln表示自然对数;W
是该系统的微观性质排列的数量;而P
是该状态下的可能性。微观性质,即分子中电子的能量水平、分子中原子的振动和分子的速度等排列的数量越大,有序性越低,可能性越高。因此,根据热力学第二定律,W
2
>W
1
,P
2
>P
1
,我们不能去度量W
或P
,但是在一个给定的系统中,只要该系统可表示成可以用N
和k定义的维数,我们就可以用各种方法估计这些变量的相对变化,即ΔS
。
英文
为了试着将生物圈中有序性的增加与日地系统中的相反变化联系起来,我们首先模拟一台数字计算机,并对它不断提出问... | 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 | 假定该过程中可能发生的变化与选择的成功突变的总数成反比,根据公式(3),我们估计生物进化达到当前水平的可能性是10–9
。假定在文化进化的过程中引入了一百万个创新(这看来也是保守的),把该选择数目的可能性乘以生物进化的相应数字,则人类生物学与文化进化的总可能性就降到了10–15
。假设在化学进化的过程中也存在着一些路径选择的节点,例如,其中一个反应的比率导致它优于在热力学上更可能的另一个反应[5]
;不过看来估计出这些数字更加困难。然而,假设有1,000个这样的选择,我们就会得出人类能够达到今天这样的进化程度的总可能性为10–18
。该估计看上去是保守的,不过可以反映出宇宙中其他“适宜”星球上存在类人生物的可能性。
英文... | 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 | U.T. in the basin of the Podkanemaia Tunguska River, Siberia (60°55′ N, 101°57′ E), some 500 miles to the north of Lake Baykal1
. It was seen in a sunlit cloudless sky over an area of about 1,500 km in diameter and was described as the flight and explosion of a blindingly bright bolide which “made even the light 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 | Before reporting the present work it may be of interest to repeat some of the accounts of the effects of the Tunguska meteor. The general area of the fall is composed of taiga with peat bogs and forest and is (fortunately) very sparsely populated. One eye-witness, S. B. Semenov, a farmer at Vanovara some 60 km away, 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 | burnt in Vassili Ilich's storage including his clothing. His silverware and samovars (tin?) were molten. Only some large buckets were left intact.
中文
According to Krinov1
the dazzling fireball moved within a few seconds from the south-east to north-west leaving a trail of dust. Flames and a cloud of smoke were seen... | 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 Tunguska meteor also caused a definite disturbance of the Earth's magnetic field as registered at the Irkutsk Observatory and others around the world. The disturbances were similar to those recorded following nuclear explosions in the atmosphere.
中文
After the fall of the meteor, the nights were exceptionally b... | 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 effects of the meteor, such as burning the area, etc.
中文
The Cometary Hypothesis
This hypothesis was proposed by A. S. Astapovich and independently by F. J. W. Whipple in 1930 (ref. 6). The evidence in favour of a cometary nature of the meteor is the motion of the meteorite opposite to that of the Earth and 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 | It appears unusual, however, that such a comet was not observed on its collision course with the Earth, as it should have been seen unless it approached from a direction with very small angular distance from the Sun. Fesenkov estimated the size of the cometary nucleus as about several hundred metres5
, which is perhap... | 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 17-18 km from the epicenter, Zolotov found trees which had been subjected to a thermal flash and had started to burn. A natural forest fire was ruled out for the area. In order to start a fire in a living tree, about 60-100 cal/cm2
of incident thermal radiation is required. By calculation the radiant energy 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 | While the dissipation of kinetic energy in the Tunguska explosion probably accounts for the major portion of energy released, the reaction with air of vast amounts of chemical high-energy species such as the radicals observed on comets can be an additional source of energy. For high meteor velocities, the relative cont... | 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 | compression seems equally unlikely, for this must be a result of the mechanical forces generated by penetration into the atmosphere.
中文
To obtain the effects from a fusion reaction, a sufficient amount of deuterium, and possibly tritium, must be contained in a compressed state and heated to several million deg. C. I... | 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 | , or about 3×1030
, and the yield of energy would be of the order 1027
ergs, rather than 1023
as observed. The fact that the bolide did not reach the surface of the Earth is ignored in this estimate, and is off-set by the additional distance due to the inclined trajectory of the object. The discrepancy factor is, ne... | 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 | We have, of course, no information concerning the state or the chemical composition of the supposed anti-matter comprising the bolide. Assuming it to be molecular compounds similar to those of ordinary meteorites, we ignore annihilation of the electrons, for these would produce a small fraction of the yield and would f... | 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 | neutron emission at the time of absorption and 100 MeV is then lost by boiling-off of neutrons and charged particles in an evaporative process. Taking the mean energy16
of the prompt neutrons as 12 MeV and their binding energy as 8 MeV, the mean number of prompt neutrons is 2. Assuming that the probability for then bo... | 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 making this estimate, we have taken the radiocarbon to be uniformly distributed in the atmosphere after both vertical mixing and mixing between the northern and southern hemispheres, and have neglected absorption in the ocean and biosphere. Thus the result is approximate.
中文
An alternative basis for an estimate 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 | carbon-14 atoms. Therefore, if the Tunguska explosion had been due to anti-matter, it should have behaved like 35 MT of fission or fusion fired at the same latitude (say the U.S.S.R. test site at Novaya Zemlya, 74°N, 150°E) and, using our experience with bomb test carbon-14 as a basis of comparison, we can estimate 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 | Additional tree-ring samples were measured from an oak tree (samples provided by L. Wood, Inst. Geophysics, Univ. Calif., Los Angeles) cut in 1964 near Los Angeles (in the Simi Valley, 34°12′N, 118°48′W). They are given as UCLA-776, 778, 779.
中文
Table 1. Radiocarbon Content of Tree-Rings around 190822
中文
The res... | 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 are A.D. 1687 (+2.65 percent), 1297 B.C. (+2.23 percent), and 1925 B.C. (+2.34 percent), where the deviations are taken with respect to the average values obtained from 39 oak samples ranging in age from 110 to 203 years prior to 1960. When compared with the deviation of the oxalic acid standard, however, which ... | 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
为了解释由大流星、小彗星或核爆炸引起的规模巨大的现象,人们已提出了各种假设。无论是支持意见还是反对意见都很有说服力。通过之前提到的扰动记录以及基于对陨石坠落地带爆炸和热破坏的推论,所得到的对产生总能量的估计是相互符合的,且产量超过1023
尔格,可能约为1024
尔格。如果这是某种核爆炸的结果,则爆炸产生的中子进入大气后,会与大气中的氮形成碳-14,能在当时生长的植物物质中分析检测得到。因此,作这种分析看来是具有价值的,并为此选择树木年轮来进行分析。
英文
陨石坠落现象
在陈述现阶段的工作之前,可以先来回顾一下有关通古斯陨石造成的影响的报告。陨石坠落的位置一般是泥炭沼泽地和森林,(值得庆幸的是)这里人迹罕至。住在距... | 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 | 由于没有发现任何一个陨石坑痕迹,所以人们猜想有可能是在永久冻土层中曾经存在陨石坑,但很快就变形了,因此在第一个夏天之后就不能再辨认。
英文
在费先科夫[5]
的分析中,所有的证据都表明存在一个与黄道夹角很大、逆向围绕太阳公转的轨道。这是来源于小行星解体后的陨石的非典型轨道。关于陨石运动的另一种解释是以较低的速度相对于地球平行方向运动,但这种相对速度必须非常小。考虑到释放出的巨大能量,较高相对速度的逆行轨道的解释要优于低速轨道的解释,因为后者很难与陨石产生的一些影响相一致,比如烧焦的地区等。
英文
彗星假设
1930年阿斯塔波维奇和惠普尔独立地提出了这个假设(参考文献6)。支持陨石是彗星的证据是,陨石是对着地球运动的,并... | 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
陨石的大规模化学基爆炸将会解释许多观察到的现象。我们对彗星上自由基的实际浓度及其准确的性质和自由基反应机制不够了解,使采用这种模型对释放能量作定量计算还相当困难,尤其是考虑到通古斯陨石轨道的不确定性[13]
。
英文
反物质假设
除了这些完全的自然现象之外,很难再建立出能产生已观测效果的裂变或聚变链式反应模型。对裂变反应而言,可以假定根据其中原有的已接近临界的大量裂变物质在进入大气层时被急剧填实。然而,这种填实是指在极短的时间内要使裂变物质密度急速上升到远大于临界值,以防止它爆裂飞散而导致能量释放过低。考虑人们熟知的这种情况下核爆炸效率极低,要获得所观测到的几百万吨量级的爆炸能量,对于通常的铀密度,发生这种情况将需要... | 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 | 考虑到该估计中的各种不确定性,我们将假定所有的负的π介子都是在静止时被核吸收的。通过测量核乳胶负的π介子吸收产生的星状径迹,得到的简化过程是:原子核得到的π介子的140兆电子伏静止能,在吸收时由于快中子发射损失40兆电子伏,而蒸发中子和带电粒子损失100兆电子伏。取瞬发中子的平均能量[16]
为12兆电子伏,其结合能为8兆电子伏,则瞬发中子的平均数为2。假定随后蒸发放射1个中子的概率与放射1个质子的概率相同,并且通过相应的计数方式可以得到概率的加权,我们发现从轻核中会多产生2个中子。因此,每吸收1个π介子产生4个中子,或每湮灭1对核子产生8个中子。由于估计中有很大的不确定性,我们取的数为8±4。因此,由核子–反核子湮灭产生的总能量... | 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
表1.1908年左右树木–年轮的放射性碳的含量[22]
英文
第V列和第VI列中的结果分别在图1和图2中绘出。
英文
图1
英文
图2
英文
每个样品约测量90,000个计数,每个数值的标准偏差为该值的0.005量级。经验表明,仪器是足够稳定的,所以主要因素是统计数据的不确定度。
英文
讨论
观察表1数据可以发现以下有趣的特点:在第III和第V列的所有数中,仅1909年的数值超出参考标准水平。在第V列中,另两个值也超出了标准,但只超出了很小的量。当对1909年前后的40年进行平均值计算时发现,后者约超出了这个平均值1%。
英文
第二点值得注意的是,在1893年和1928年附近数据出现... | 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 | HE nucleotide sequence of messenger RNA is a code determining the amino-acid sequences of proteins. Although the biochemical apparatus which translates the code is elaborate, it is likely that the code itself is simple and consists of non-overlapping nucleotide triplets. In general, each amino-acid has more than one tr... | 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 many of the amber
mutants of bacteriophage T
4 (ref. 4). These mutants have been isolated in various ways and the permissive (su
+
) and non-permissive (su
–
) strains used have been different. When isogenic bacterial strains, differing only in the su
locus, are constructed, it can be shown that all these mu... | 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 the completed chain contains a serine at a position occupied by a glutamine in the wild type6
as shown in Fig. 1.
中文
Fig. 1. Amino-acid sequences of the relevant region of the head protein in wild-type T
4D
and in the amber
mutant H
36 on su
–
and su
+
I
strains
中文
In addition to the amber
mutants,... | 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 | If we accept that both types of nonsense mutants result in termination of the polypeptide chain, we have to ask: at which level of information transfer is this effect exerted? We have recently shown that it is likely that chain termination occurs as part of protein synthesis, since both types of mutants vanish when 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 | strand; it carries the genetic information proper and contains a nucleotide sequence which is the inverse complement of the sequence of the messenger RNA. The other strand, the antisense
strand, has the same sequence as the messenger. In a phage, treated with hydroxylamine, the altered base, U′, could be on either 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 | mutants are not induced to revert by hydroxylamine, and we conclude that in neither mutant, does the triplet in the DNA contain G–C pairs, or, if a G–C pair is present, that triplet is connected by a G–C→A–T transition to another nonsense codon. In other words, subject to the last important reservation, we can conclude... | 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 | triplets differ from each other by only one nucleotide base, and must have the other two bases in common. 2-Aminopurine is a base analogue mutagen inducing the transition
in both directions13
. This tells us that one of the triplets has a G–C pair in the DNA. The experiment reported in Table 4 shows that ochre
muta... | 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 | triplet has two A–T base pairs, and which also establishes the orientation of the pairs with respect to the two strands of DNA. Let us suppose that the amber
triplet in the messenger RNA contains a U. This corresponds to an A in the sense strand of DNA of the amber
mutant, implying that the wild-type DNA contains a G... | 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 | 164, mutants occur with approximately equal frequency in both sets. The first class fulfils the expectation for a C→U change on the sense strand, while the second class must arise by C→U changes on the antisense strand. This shows that the amber
triplet in the messenger contains both an A and a U. The same should be 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 | triplet is connected by mutation. In particular, we note that it should be connected to two and only two amino-acid codons by transitions, corresponding, in fact, to the two types of origin of the mutants described here. The third codon to which it is connected by a transition is the ochre
triplet. As mentioned earlie... | 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 shown that poly AC does not code for tryptophan, but does for glutamine. However, they find that the triplet for glutamine clearly has the composition (CAA) and is definitely not (CAC). Since this latter triplet corresponds neither to glutamine nor to tryptophan we can eliminate the first alternative. We note 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 | mutant to either lysine or arginine. This may be the final transversion expected since AAG is a codeword for lysine20
.
中文
It should be noted that in the foregoing discussion it has been tacitly assumed that the amber
and ochre
signals are triplets. Examination of revertants of amber
mutants has supported this 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 | RNA carrying an amino-acid. Mechanisms of suppression can be classified according to which s
RNA carries the amino-acid to the nonsense codon.
中文
Alteration in the recognition of the chain-terminating s
RNA might allow the attachment of an amino-acid to this s
RNA. This could be brought about either by modifying ... | 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 | , but suppression of amber
and ochre
mutants cannot be readily explained by this theory. It is scarcely likely that such a mechanism could be specific for only one or two triplets, and for this reason it might be expected to give us suppression of mutants which are not nonsense, but missense, and this has not been fo... | 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 | 这些RNA分子将核DNA信息转运到细胞器中,在细胞器中合成蛋白质。基本原理是DNA中的核苷酸三联体(密码子)用RNA中相应的三联体表示,一般而言在各个蛋白质中,每一个密码子确定一个特定的氨基酸。本文中,剑桥大学的辛迪·布伦纳及其同事们以大肠杆菌为材料,通过实验探索了遗传密码的本质。布伦纳于2002年获得了诺贝尔奖。
英文
信使RNA中的核苷酸序列是编码蛋白质氨基酸序列的密码。尽管翻译该密码的生化结构很复杂,但是很可能密码本身很简单并且是由不重叠的核苷酸三联体构成的。一般而言,每个氨基酸都对应着不止一种三联体,但是目前尚不清楚64个三联体中有多少用来编码20种氨基酸。“无义”三联体泛指不编码氨基酸的核苷酸三联体。但目前尚不清楚这... | 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
表1.大肠杆菌Hfr H
(λ
)的su
+
菌株对r
II突变体的抑制作用
英文
与某些琥珀抑制基因不同,所有赭石抑制基因的抑制作用都比较弱[7,8]
。这令我们无法分离到头部蛋白的赭石突变体。因此我们无法知道赭石突变体的分子机理,但是我们可以假定它们与琥珀突变体一样也导致了多肽链终止。
英文
如果这两种类型的无义突变体都导致了多肽链终止的话,那么我们不得不问这个作用是发生在信息传递的哪个阶段?最近我们发现链终止可能是在蛋白质合成的某些阶段发生的,因为当遗传信息的读取阶段发生变化时,两种类型的突变体都消失了[9]
。由此我们得出以下结论:琥珀突变体和赭石突变体产生了不同的三联体,这些三联体在正确的... | 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 | 我们研究了26个r
II赭石突变体,其中25个被转变成了琥珀突变体。表3给出了结果中的一个样本,表明该突变被2–氨基嘌呤强烈诱导而成,其突变频率与赭石突变体回复为野生型的频率相当。其他实验(本文未报道)表明5–溴尿嘧啶也可以诱导赭石突变体转变为琥珀突变体或者回复为野生型,但是突变频率比2–氨基嘌呤要低。这些结果表明琥珀三联体和赭石三联体只有一个核苷酸碱基的差异,另外两个碱基相同。2–氨基嘌呤是一种碱基类似物诱变剂,
两个方向的转换都可以由它诱导发生[13]
。这告诉我们DNA中的一个三联体有一对G–C碱基对。表4报道的实验结果表明羟胺不能诱导赭石突变体突变为琥珀突变体,甚至羟胺处理的噬菌体已在大肠杆菌B
中生长。这表明具有G... | 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 | 每组中的r
突变体用少于2毫升来分离,保证各组中筛选的突变是彼此独立的事件。剔除r
I突变体和渗漏突变体之后,将挑选出来的这些突变体导入B菌株和K菌株。然后在菌株su
+
III
和su
+
B
上筛选r
II突变体作为选择出来的琥珀突变体和赭石突变体,进一步通过遗传图谱定位。
英文
幸运的是,我们可以通过突变来确定琥珀三联体与何种氨基酸相对应,从而解决这个问题。特别是我们注意到它应该与通过转换形成的两种(仅此两种)氨基酸密码子有关,实际上这两种密码子对应本文描述的两种突变体。通过转换与第三个密码子相关的就是赭石三联体。正如早期提到的,头部蛋白琥珀突变体H
36是由羟胺诱导谷氨酰胺突变产生的(图1)。另外,我们有证... | 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 | 关于该机制,我们可以用许多可能的方式来详细叙述,但是它们都只是推导出来的,所以在这里不赘述了。这一假说的本质特征是要使链终止的过程与链延伸的过程完全一致。
英文
在抑制菌株中,存在着一种可与链终止竞争的机制。该过程很容易被视为识别无义密码子的两种方式,一种是通过链终止s
RNA,另一种是通过携带一个氨基酸的s
RNA。可以根据哪个s
RNA将氨基酸携带至无义密码子而对抑制机制进行分类。
英文
链终止s
RNA识别的不确定性可能允许将一种氨基酸与该s
RNA联系起来。而这个过程可以通过修饰正常的激活酶进而扩大酶的专一性来实现,也可以通过改变链终止s
RNA以使它可以被激活酶识别来实现。
英文
还有一种可能... | 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 | URING the recent inferior conjunction of the planet Mercury in April, 1965, radar observations were obtained by the Arecibo Ionospheric Observatory in Puerto Rico (operated by Cornell University with the support of the Advanced Research Projects Agency under a Research Contract with the Air Force Office of Scientific R... | 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 | comparison a degree of confidence could be established, and an estimate obtained of the measurement error.
中文
The data were used to compute a most likely value of intrinsic planetary rotation with a procedure developed by Dr. Irwin Shapiro of the Lincoln Laboratory, Massachusetts Institute of Technology. Fig. 1 show... | 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
在1965年4月水星最近一次的下合期间,位于波多黎各的阿雷西博电离层天文台(它由康奈尔大学在高等研究计划局的支持下,在空军科学研究办公室的一个研究合同框架下运行)对其进行了雷达观测。该系统的工作频率为430兆周/秒,天线增益为56分贝,发射功率为2兆瓦。该系统的灵敏程度不仅可以接收到来自紧靠行星盘最近部分的显著回波信号,还能把观测区扩大到行星半径的0.06倍处。利用时长为500微秒的短发射脉冲,可以分离出更远区域的回波功率,并利用傅里叶分析研究其频谱组成。
英文
由于延迟回波的反射源与行星表面已知区域的关系相当可靠,故行星视自转速率的大小可以通过一个简单的几何关系从测得的光谱色散中得到。视自转是行星本身的自转与观测者和... | 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 | OLAR tidal friction must be an intense effect for Mercury, and it must be expected that the planet's spin would have relaxed from any original value to one that is under the control of this effect in a time short compared with the age of the solar system. The retarding torque exerted by the Sun on a planet is proportio... | 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 | quantitative description of the dissipation properties of the planet, but involving certain assumptions. The tidal phase lag has to be assumed to be a small angle only, and one may make the calculation with Q
being dependent on amplitude and frequency in a variety of ways (1/Q
is the specific dissipation function1
)... | 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 | 但即使现在我们对水星也知之甚少。用来对水星进行研究的信使号于2004年发射,在三次飞掠过水星之后它将在2011年3月进入环绕水星的轨道。
英文
太阳的潮汐摩擦作用对水星产生强烈的影响,并且可以预期在与太阳系年龄相比更短的时间内,水星自转速率已经在潮汐作用下从某个初始值减少到了现在的数值。太阳作用于行星的黏滞力矩正比于1/r
6
(r
是太阳和行星间的距离),对水星来说该系数比地球的差不多大了300倍。位于圆轨道上的行星,其最终的状态就是类似月球相对于地球的同步绕转。水星绕太阳转动一圈需要88天,并且由于同步绕转,其恒星周期也应该是88天。但观测到的59±5天的结果与该值明显不符(见前一篇报道)。
英文
然而对于轨道偏... | 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 suggested that we should distinguish between two essentially different ways in which energy can be degraded or dissipated: “Dissipation in the form of increasing disorder (entropy increase) is one of them, and dissipation by expansion without increase of disorder is the other. For an increase of disorder, walls of so... | 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 terminology here introduced makes it possible to clarify a number of points in connexion with the second law of thermodynamics which seem in urgent need of clarification.
中文
Again following Prigogine3
, we can split the change of entropy dS
X
in any system X
into two parts: dS
Xe
, or the flow of entropy due... | 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 | Yet, so far as our knowledge of the Universe goes, the precise opposite appears to be the case. With very few and short-lived exceptions, the entropy in almost all known regions (of sufficient size) of our universe either remains constant or decreases, although energy is dissipated (by escaping from the system in quest... | 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 being by far the most frequent and important cases: in almost all sufficiently large systems known to us, entropy production seems to be equalled, or even exceeded, by entropy loss through heat radiation.
中文
This may be explained by the conjecture that every entropy-producing region is open towards some large (... | 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 | . For during the incubation of birds' eggs entropy rather than neg-entropy is supplied to them, though they are in a period of increasing organization; and while in an organism dying of heat or of fever entropy may increase, if it dies of cold—say, by deep-freezing—its entropy certainly decreases.
中文
(207
, 233-234... | 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
再次按照普里高津的观点[3]
,我们可将任何系统X
熵值的变化dS
X
分成两部分:由于与系统X
的外界相互作用引起的熵的流动dS
Xe
,以及由于系统X
内部的变化引起的熵的变化dS
Xi
。由此,我们可得:
dS
X
= dS
Xe
+ dS
Xi
(1)
我们可用下式表示第二定律:
dS
Xi
≥ 0
(2)
英文
对于能量封闭的(或“孤立的”)系统X
,我们通过定义可知dS
Xe
= 0,式(2)变成了经典表述:熵永不减少。但是,如果系统X
对更冷的外界开放,则有:
dS
Xe
< 0
(3)
那么总熵是增加还是减少便自然取决于增加的熵dS
Xi
和减少的熵dS
Xe
分别有多... | 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;张元仲 审稿)
Experimental Evidence of a Twinkling Layer in the Earth's Atmosphere
C. C. Hudson
Editor's Note
The idea that stars in the sky twinkle when observed with the human eye is commonly remarked upon, but the reasons for this behaviour are far from clear. This paper from Craig C. Hudson at the Sandia 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 | apertures, the modulation (fluctuation relative to mean light level) can exceed 100 percent even at the zenith, while for large apertures 10-20 percent is more typical. Twinkling also depends on the source size; the larger planets, for example, showing very little effect. Finally, twinkling depends on meteorological co... | 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 uncertain by orders of magnitude. The primary variables in the theory of scintillation, therefore, are the thickness of the turbulent layer and the intensity of its turbulence. Keller's parameter study is partially reproduced in Table 1. In each case, the experimental data are satisfied by a different set of parame... | 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 idea of the experiment was to allow a point source light beacon to fall through the twinkling region, observing it continuously with a telescope fitted with a recording photometer. The beacon was carried to 65,000 ft. as the pay-load of a 6-in. Apache
rocket motor. To restrain the free fall somewhat, to keep the l... | 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 addition to observations of the falling beacon, scintillation measurements were also made on ground lights at various distances, on a number of stars and planets, and on the satellite Echo I
. The purpose of these measurements was mainly to check and calibrate an untried system, but also to make available a more co... | 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 | From Fig. 3 one gets the impression that the twinkling layer is not associated either with the wind speed structure or with the tropopause; but since it seems typically to occur in that neighbourhood, a re-check of the wind vectors was made to see if strong shears or wind gradients could be found in the layer; but 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 | will be determined at the frequency that seems to be most prominent, and this frequency (corrected for the rocket's motion) will also establish the scale of turbulence. As a precaution, microphones will also be used to determine the level of pressure fluctuations, and the instruments are so mounted that correlations be... | 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 | 在1周/秒~10周/秒频率范围内信标灯的闪烁幅度比恒星的小50%~75%,而在147周/秒~153周/秒频率范围内其闪烁幅度则比恒星的要小两倍以上。
英文
他们也将闪光作为一个双星光脉冲的相关函数来研究。在1周/秒~10周/秒频率范围内闪烁出现在海拔为10万英尺或更高的地方。而在更高的频率,大约150周/秒,闪烁则出现在3万英尺附近。为了解释这种高海拔低频率的变化,他们提出:这些高度上的大气密度变化较大,大气相对于地球而言基本上是静止的,随着地球自转,观察恒星的视线会扫过这些密度变化的区域。
英文
目前正在进行一些新的实验,这些实验可能会更清楚地揭示大气的结构和恒星闪烁的原因,这里给出其中第一个实验的情况。
英文
... | 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 | 我们将确定最为突出的频率下的温度变化的均方差δ2
T
,这个频率(根据火箭运行而进行修正)也将确立扰动的尺度。为防万一,也将采用扩音器来确定波动水平,并安装仪器来观测气压与温度波动间的关系。
英文
这项工作得到了美国原子能委员会的支持。
英文
(蔡则怡 翻译;沈志侠 审稿)
Opening Electrical Contact: Boiling Metal or High-Density Plasma?
F. Llewellyn Jones and M. J. Price
Editor's Note
The opening of an electrical contact may not appear to hi... | 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 | where ψ = a generalized potential equal to the electrical potential in the absence of thermo-electric effects, θ = temperature, λ = thermal conductivity and κ = electrical conductivity. Thus, on gradual separation of the electrodes the constriction resistance increases and the temperature rises up to and past the melti... | 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 | will be negative, and experiment has established that the final stable shape is usually the nodoid. The ψ, θ theorem shows that the hottest region of the microscopic molten metal bridge between like electrodes will probably be the narrow neck and, at first sight, it might appear that this is the region at which the bri... | 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 | up to the boiling point can, in certain circumstances, take place. Measurements of the contact current, potential difference and maximum temperature, and its location, enable a determination to be made of the transport properties of metals such as their thermal and electrical conductivities and Thomson coefficients 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 | course, could have serious practical effects.
中文
Thus, the precise processes of the actual opening of the circuit are a matter of considerable practical and theoretical importance, and these phenomena have been under investigation at Swansea for some time. The relationships of the size of the molten metal bridge 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 | . Consequently, in recent years effort has been directed to finding direct evidence for the existence of such a plasma. It will be appreciated that, owing to the speed of events in the final stages of the development of the molten metal bridge, extensive expansion of the plasma to a size which can readily be seen may 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 | ), the low luminosity for metals other than platinum and tungsten, and the difficulty associated with the synchronization of the camera and the phenomenon to be photographed. A certain degree of elusiveness of the bridge at all stages of its life also made photography difficult. However, an optical system incorporating... | 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. 3. Material, iron; atmosphere, vacuum; current, 60 amp; circuit E.M.F., 6 V; polarity, top electrode positive; magnification, ×19.5; framing rate, 7,000 f.p.s.
中文
Fig. 2 illustrates a less stable condition in which the degree of oxidation was such that the surface tension could not be maintained constant over ... | 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 | We thank Mr. Ieuan Maddock of the Atomic Weapons Research Establishment, U.K. Atomic Energy Authority, Aldermaston, for the loan of a high-speed camera and for advice. One of us (M. J. P.) is also grateful for the award of a Department of Scientific and Industrial Research postgraduate research studentship. Thanks are ... | 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
低压下(约为4伏特)电接触断开的过程有重要的基础物理学意义,同时对电子工程学和通信工程领域也有重要的实用价值。众所周知[1]
,初始状态是两个电极紧压在一起处于完全导通的状态,断开过程中会导致电流线的收缩,这会导致在最后的微观接触区域产生很强的局部加热和熔化。在接触区的最高温度与电势差有关,可以通过ψ,θ定理表示,如下式:
式中ψ为广义势(在没有热电效应情况下就等于电势),θ为温度,λ为热导率,κ为电导率。因此,随着电极的逐渐分离,收缩电阻增大,温度升高并超过了金属的熔点。继续分离,熔化的体积随之增加,这种熔融金属逐渐被拉成连接着两个固体电极的微观桥;电接触最终会断开,但只有这个微观的桥断开时整个电路才会断开。然而,这个... | 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 | 人们已发现在许多金属中,特别是铂[1,6-9]
中,局部电感(尤其是在10–6
亨~10–8
亨之间)有很快的变化。并且,通过对由桥断裂形成的坑状结构进行的光学检测发现,在一些金属中,整个熔融金属桥的体积都参与了转移。这个微观桥的形态和大小取决于各个电极断裂后熔融等温线的几何形状。
英文
这些情况很难与由熔融金属桥分解时产生的微滴机械喷溅而导致的物质转移图像相吻合。相反,这些情况与如下观点更为一致,即这种物质的转移是呈离子态的,而这种离子的运动取决于熔融金属桥断裂后在电极间振荡的电场。由于上述原因,人们提出了另一种基于微等离子体产物的观点,这一微等离子体很有可能最初形成于熔融金属桥的断裂颈上[11]
。因此,近年来我们... | 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
我们感谢位于奥尔德马斯顿的英国原子能管理局原子武器研究中心的爱恩·马多克先生借给我们一台高速照相机并提供了一些建议;感谢科学及工业研究署颁发给我们之间的一员(普赖斯)的研究生研究奖学金,也同样感谢皇家学会同意为给我们购买一些贵金属。
英文
(沈乃澂 翻译;赵见高 审稿)
Abnormal Haemoglobins and the Genetic Code
D. Beale and H. Lehmann
Editor's Note
Here biologists D. Beale and Hermann Lehman from Cambridge University describe how the degene... | 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 | or G or C or U. Table 1 gives the codons for amino-acids involved in substitutions of human haemoglobin; those surmised because A and G, and C and U, respectively, are alternatives in the third position, are in italics. Table 2 summarizes the amino-acid substitutions which have been reported in human haemoglobin. They ... | 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 electrophoretic mobility suggests a double charge change from an acidic to a basic residue. The peptide involved (αTp
XII) contains both, one Glu (α116) and one Asp (α126), but as Glu→Arg, Asp→Arg, and Asp→Lys would require a double mutation the likely formula is α2
116Glu→Lys
β2
. By similar reasoning one can... | 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 seems remarkable that of eleven glutamic acid residues, nine and possibly ten have been involved in mutations, three of them twice, yet of seventeen aspartic acid residues only one30
, or possibly two29
, have been subject to substitutions. On the other hand, changes to Asp and Glu occur with similar frequency, 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 | V peptides have the same electrophoretic mobility (horizontal) as the abnormal peptides from haemoglobin I, but they are well separated by chromatography (vertical)
中文
The new peptide was purified by electrophoresis at p
H 6.4 followed by chromatography in isoamyl alcohol:pyridine:water (30:30:35) and its amino-ac... | 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 | leucine amino peptidase whereby glycine, glutamic acid and valine, but no glutamine, were quickly released.
中文
This biochemical finding arising from a suggestion made by Dr. F. H. C. Crick is of interest because it is probably the first time that the genetic code has been used as an aid in the analysis of a protein,... | 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,腺嘌呤;C,胞嘧啶;G,鸟嘌呤;U,尿嘧啶
英文
表2.人血红蛋白中的氨基酸替换
英文
图1说明了表2列出的氨基酸中可能发生的一步突变。除了一个例外,这个图涵盖了所有可能发生的替换。正如克里克博士指出,血红蛋白I α16处Lys→Asp不是单点突变的结果,而是需要某一密码子内双突变。鉴于这一点具有相当重要的理论意义,我们再一次对血红蛋白I展开研究,发现实际上α16处的替换是Lys→Glu。因此,目前发现的人血红蛋白中所有的氨基酸替换都是单点突变的结果。我们必须假设密码子具有简并性,因为编码甘氨酸的密码子的最后一个碱基与突变Glu→Gly[15]
和Gly→Asp[24-28]
不可能相同;类似地,编码精氨酸... | 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 | 与αTp
III和αTp
IV的类似分析相比较,这一分析结果(表3)显示可能在α链的第16个氨基酸的位置上,一个赖氨酸残基被一个谷氨酸或者谷氨酰胺取代(在水解过程中谷氨酰胺可以转变为谷氨酸)。
英文
表3.来自血红蛋白I的异常多肽与来自血红蛋白A的αTp
III和αTp
IV多肽的氨基酸分析
* 借助埃利希试剂进行多肽的测定。推测阳性反应可能是由于存在一个色氨酸残基。
英文
与血红蛋白A相比,血红蛋白的电泳迁移率显示每条α链都发生了双电荷改变,从而支持是Lys→Glu而不是Lys→Gln。为了证实这一点,用胰凝乳蛋白酶消化新肽,将酶解后的多肽片段在pH 6.4的条件下通过纸电泳分离。用这种方法分离出胰蛋白酶酶解... | 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 article suggests that these features are not isolated, that few come to dead ends, but that they are connected into a continuous network of mobile belts about the Earth which divide the surface into several large rigid plates (Fig. 1). Any feature at its apparent termination may be transformed into another feature... | 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 | when he proposed that the Pyrenees Mountains were compressed because of the rifting open of the Bay of Biscay (presumably by the formation of a mid-ocean ridge along its axis). The types illustrated are all dextral, but equivalent sinistral types exist.
中文
In this article the term “ridge” will be used to mean mid-oc... | 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 distinctions between types might appear trivial until the variation in the habits of growth of the different types is considered as is shown in Fig. 4. These distinctions are that ridges expand to produce new crust, thus leaving residual inactive traces in the topography of their former positions. On the other hand... | 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 their edges.
中文
The data on which the ensuing accounts are based have largely been taken from papers in two recent symposia4,5
and in several recent books3,6,7
in which many additional references may be found.
中文
North Atlantic ridge termination.
If Europe and North America have moved apart, an explanation ... | 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. 6. Diagram illustrating three stages in the rifting of a continent into two parts (for example, South America and Africa). There will be seismic activity along the heavy lines only
中文
The dextral transform faults (ridge-ridge type) such as AA′
which would result from such a period of rifting can be seen to ha... | 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 | .) showing how the Mid-Atlantic ridge is offset to the left by active transform faults which have dextral motions if the rift is expanding (see Fig. 4a
). ||, Mid-ocean ridge; —, active fault; - - -, inactive fault trace; ..., hypothetical extension of fault
中文
It seems possible that the old fault in Pennsylvania ... | 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 terminates by joining a large thrust fault in south-eastern Turkey (Z. Ternek, private communication). The East African rift valleys are a still later extension formed in Upper Miocene time according to B. H. Baker (private communication).
中文
The many offsets in the Gulf of Aden described by Laughton20
provide ... | 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 the relations between them and those off the coast he writes: “If the two systems represent one consistent system, some interesting possibilities arise. One that the San Andreas and Alaska Complex is a gigantic tear fault, along which the Pacific Basin is being slid, relatively speaking under the Alaska Mainland, ... | 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 similar in that their seismicity is confined to the offset parts between ridges. An extension of this suggests that the offsets in the magnetic displacements observed in the aseismic facture zones off California may not be fault displacements as has usually been supposed, but that they reflect the shape of a contem... | 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 article began by suggesting that some aspects of faulting well known to be anomalous according to traditional concepts of transcurrent faults could be explained by defining a new class of transform faults of which twelve varieties were shown to be possible.
中文
The demonstration by a few examples that at least s... | 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 | 在发生转换的地方,沿断层发生的水平剪切运动会突然终止,并转变为洋脊或裂谷的扩张运动,地震活动也随之发生变化。
英文
一种构造转变为另一种构造的交汇处在这里被称为转换。上述这种类型以及图2中的b
和c
所示的其他两种类型也可以称为半剪切(这一名称由贝尔纳教授在一次交谈中提出)。因为山脉是不对称的,而洋脊是两边对称的,所以山脉半剪切类型是洋脊半剪切类型的两倍。这种大规模水平剪切运动的突然终止方式可以用来解释大型断层的一些长期令人费解的现象,如圣安德烈亚斯断层。
英文
图1.现今地球活动带网的示意图,包括处于挤压状态的主要活动山脉和岛弧(实线)、处于水平剪切作用下的活动转换断层(细虚线)以及处于拉张环境的活动大洋中脊(粗虚... | 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 | 希森和尤因[10]
认为大西洋中脊向西伯利亚海盆方向延伸,而威尔逊[11]
则提出大西洋中脊以新西伯利亚群岛为支点发生了旋转,并转换为上扬斯克山脉。与图4a
所预测的一致,如图5所示,地震沿整个德海尔断层线分布,而沿虚线所示的挪威、熊岛和格陵兰岛北部之间的老痕迹则没有地震发生。巴芬湾中脊和魏格纳断层如今都是静止的。哈兰德[10]
与加拿大地质学家就斯匹次卑尔根岛和埃尔斯米尔岛的相似性曾做过评论。
英文
赤道大西洋破碎带
如果一个内部存在断层或薄弱带的大陆分裂为两部分(图6),那么新的伸展断裂就会沿着已经存在的断层发育,并受其影响。
英文
图6.大陆分裂为两部分所经历的三个阶段(例如,南美洲与非洲)。仅仅沿粗线部... | 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
图9.北美洲西海岸简图,图中示出了沿阿留申海沟的一个海底逆冲断层、迪纳利断层(据圣阿芒)、圣安德烈亚斯断层以及另一个大型转换断层(据贝尼奥夫)、部分东太平洋海隆和另外一个大洋中脊(据梅纳德)的大概位置。
英文
圣阿芒[21]
描述了几个位于阿拉斯加的大断层。关于它们与岸外断层之间的关系,他写道:“如果两个体系代表的是一个统一的体系,那么将会出现一些有趣的可能性。一种可能性是,圣安德烈亚斯断层和阿拉斯加的复合体是一个巨大的横推断层,太平洋海盆沿该断层滑动,或者更确切地说,是在阿拉斯加大陆和白令海之下滑动。另一种可能性是,如果整个体系是具有右行错位的走滑断层,那么,整个北太平洋海盆的西部肯定正在发生旋转。”
英文
... | 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
(齐红艳 翻译;孟庆任 审稿)
A Physical Basis for Life Detection Experiments
J. E. Lovelock
Editor's Note
James Lovelock is best known for his Gaia hypothesis, which postulates that the Earth regulates its climate with feedback processes much like the homeostatic mechanisms that maintain constant conditions in living organis... | 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 the object of this article to show that we are not necessarily limited to experiments based on the recognition of a specific life-form, either Earth-like or alien. Also, that it is possible, by accepting a limited phenomenological definition of life, to design simple experiments from the general recognition of li... | 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 | reach an agreed classification as follows: “Life is one member of the class of phenomena which are open or continuous reaction systems able to decrease their entropy at the expense of substances or energy taken in from the environment and subsequently rejected in a degraded form”. This classification is broad and inclu... | 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) Order in chemical structures and sequences of structure. A simple gas chromatograph or a combined gas chromatograph-mass spectrometer instrument would seek ordered molecular sequences as well as chemical identities.
(2) Order in molecular weight distributions. Polymers of biological origin have sharply defined mole... | 400套付费套装书 |
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