全文获取类型
收费全文 | 94292篇 |
免费 | 365篇 |
国内免费 | 812篇 |
出版年
2023年 | 5篇 |
2022年 | 34篇 |
2021年 | 55篇 |
2020年 | 32篇 |
2019年 | 31篇 |
2018年 | 11880篇 |
2017年 | 10689篇 |
2016年 | 7497篇 |
2015年 | 663篇 |
2014年 | 347篇 |
2013年 | 369篇 |
2012年 | 4288篇 |
2011年 | 12898篇 |
2010年 | 12058篇 |
2009年 | 8262篇 |
2008年 | 9845篇 |
2007年 | 11437篇 |
2006年 | 324篇 |
2005年 | 566篇 |
2004年 | 1015篇 |
2003年 | 1071篇 |
2002年 | 810篇 |
2001年 | 257篇 |
2000年 | 164篇 |
1999年 | 33篇 |
1998年 | 17篇 |
1997年 | 25篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 31篇 |
1992年 | 22篇 |
1991年 | 39篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1984年 | 8篇 |
1983年 | 17篇 |
1980年 | 2篇 |
1975年 | 5篇 |
1973年 | 2篇 |
1972年 | 246篇 |
1971年 | 275篇 |
1970年 | 5篇 |
1965年 | 13篇 |
1962年 | 24篇 |
1956年 | 5篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
241.
Kimball and Wilson1 reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen2 observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators3 had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore4 reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler5 has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore. 相似文献
242.
ALINA TAYLOR 《Nature: New biology》1971,234(48):144-145
JACOB and Fuerst1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ3 which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli2 and one would therefore expect its substrate to be murein. 相似文献
243.
WHEN chromosomes pair at meiosis the bivalents so formed do not normally interlock. Heat-treatments can, however, induce bivalent interlocking in the locust Locusta migratoria. Only the longest bivalents interlock and usually only two are found per cell; two “rod” bivalents, with single chiasmata, two “ring” bivalents, each with two or three chiasmata, or one “rod” and one “ring” bivalent (Fig. 1a, b and c). The nature of this interlocking and the metaphase orientational and congressional properties of interlocked bivalents are analysed in detail elsewhere1. 相似文献
244.
245.
246.
E S Bulygina V F Galchenko N I Govorukhina A I Netrusov D I Nikitin Y A Trotsenko K M Chumakov 《Journal of general microbiology》1990,136(3):441-446
Nucleotide sequences of 5S ribosomal RNA (rRNA) isolated from 19 strains of Gram-negative methylotrophic bacteria were determined. Comparison of these sequences allowed construction of a tentative phylogenetic tree and showed that the bacteria analysed belong to the Proteobacteria and fell into several clusters, including obligate methanotrophs, obligate methylotrophs and several groups of facultative methylotrophs. Taxonomic relations between methylotrophic and non-methylotrophic bacteria are discussed, and the polyphyletic nature of methylotrophy as a taxonomic feature is highlighted. 相似文献
247.
The effect of algae on the production of musty-smelling compounds by actinomycetes was studied. Streptomyces spp., causing intensive musty odor, were isolated from hypertrophic Lake Kasumigaura and cultured in association with algae from the same lake. Isolate E and I effectively utilized the cyanobacteria, Microcystis aeruginosa and Anabaena spiroides, and the diatom, Synedra acus, as a carbon source and produced a musty-smelling 2-methylisoborneol in the shaken sediment cultures. High populations of algae and actinomycetes, and aerobic condition in the sediment seem responsible for the occurrence of musty odor in Lake Kasumigaura. 相似文献
248.
249.
Maxim K. Elias 《Pal?ontologische Zeitschrift》1962,36(1):29-37
The type specimen ofGonioloboceras goniolobum (Meek), rediscovered by Spath in the British Museum, is the foundation for a more accurate comparative study of this and other species ofGonioloboceras.Gonioloboceras described asG. goniolobum byElias in 1938 is differentiated asGonioloboceras schmidti, new species. Suture sets (new term) for several growth stages inG. goniolobum (Meek),G. welleriSmith,G. schmidtiElias, G.eliasiMiller &Owen, andG. asiaticumLibrovitch are assembled and used for differentiation of the species.The Kazakhstan goniatite faunule containingG. asiaticum is considered of very late Pennsylvanian age. 相似文献
250.
R. Schoysman B. Lejeune E. Van Roosendaal L. Segal P. Vanderzwalmen M. Nijs B. Vandamme G. Bertin 《Andrologie》1996,6(4):432-439
The authors report their experience with the use of spermatids in TESE programs where mature spermatozoa could not be isolated from testicular biopsies. The details of the indications for spermatid insemination, the technicity of the procedure and the results are exposed. 相似文献