全文获取类型
收费全文 | 16719篇 |
免费 | 1902篇 |
国内免费 | 1篇 |
出版年
2021年 | 217篇 |
2019年 | 149篇 |
2018年 | 184篇 |
2017年 | 163篇 |
2016年 | 336篇 |
2015年 | 485篇 |
2014年 | 514篇 |
2013年 | 650篇 |
2012年 | 825篇 |
2011年 | 760篇 |
2010年 | 577篇 |
2009年 | 525篇 |
2008年 | 701篇 |
2007年 | 748篇 |
2006年 | 612篇 |
2005年 | 627篇 |
2004年 | 584篇 |
2003年 | 578篇 |
2002年 | 484篇 |
2001年 | 427篇 |
2000年 | 434篇 |
1999年 | 383篇 |
1998年 | 180篇 |
1997年 | 187篇 |
1996年 | 172篇 |
1995年 | 147篇 |
1994年 | 179篇 |
1993年 | 142篇 |
1992年 | 352篇 |
1991年 | 339篇 |
1990年 | 341篇 |
1989年 | 295篇 |
1988年 | 296篇 |
1987年 | 268篇 |
1986年 | 251篇 |
1985年 | 271篇 |
1984年 | 258篇 |
1983年 | 261篇 |
1982年 | 207篇 |
1981年 | 154篇 |
1980年 | 167篇 |
1979年 | 232篇 |
1978年 | 201篇 |
1977年 | 183篇 |
1976年 | 179篇 |
1975年 | 174篇 |
1974年 | 182篇 |
1973年 | 177篇 |
1972年 | 160篇 |
1971年 | 143篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
David G. Reid David M. Doddrell Dudley H. Williams Keith R. Fox 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,798(1):111-114
Uniformly 15N-labelled triostin A and echinomycin have been prepared by growing the producing organisms on enriched media and their 15N nuclear magnetic resonance spectra partially assigned by a combination of nuclear Overhauser effect and scalar coupling constant measurements. Selective feeding experiments using unlabelled L-tryptophan-supplemented media have shown that N-1 and N-4 of the quinoxaline rings have their origins in the indole and amino groups of tryptophan, respectively. 相似文献
36.
The role of duplication in the expression of a variable surface glycoprotein gene of Trypanosoma brucei 总被引:1,自引:0,他引:1
The variable surface glycoprotein (VSG) genes of Trypanosoma brucei have been classified into two groups depending upon whether or not duplication of the genes is observed when they are expressed. We report here the observation of duplication apparently linked to expression of the ILTaT 1.3 gene in the ETaR 1 trypanosome stock. In the ILTaR 1 stock, expression of the ILTaT 1.3 VSG did not involve a new duplication, but instead activation of a preexisting gene copy that had been apparently generated earlier by a duplication event analogous to that directly observed in the ETaR 1 trypanosomes. The results suggest that the well-characterised gene duplications found with other VSG genes are common to all VSG genes but are not directly responsible for controlling expression. All currently available data can be accommodated by a model that assumes that gene duplication and replacement occurs independently of antigenic switching. 相似文献
37.
Spleen cells from rats given experimental pyelonephritis using Escherichia coli and Proteus mirabilis as infecting organisms were evaluated for their ability to respond to the mitogen Concanavalin A. Results indicate an 80% reduction in the response of animals with gross suppuration in the kidney, but no inhibition is observed in animals with kidney infection, but not renal abscesses. The inhibition is not, apparently, due to serum factors. 相似文献
38.
J M Phang S J Downing G C Yeh R J Smith J A Williams 《Biochemical and biophysical research communications》1979,87(2):363-370
L-pyrroline-5-carboxylic acid, an intermediate in the interconversions of glutamic acid, ornithine and proline, is a potent stimulator of the hexose-monophosphate pentose pathway in cultured human fibroblasts. These studies suggest that pyrroline-5-carboxylate reductase, which catalyzes the conversion of pyrroline-5-carboxylate to proline coupled with the oxidation of NADPH, provides the NADP for the observed activation of the hexose-monophosphate pentose pathway. 相似文献
39.
40.
Peter W. Wilson Katie E. Osterday Aaron F. Heneghan Anthony D. J. Haymet 《The Journal of biological chemistry》2010,285(45):34741-34745
In this study, we examined the effects that antifreeze proteins have on the supercooling and ice-nucleating abilities of aqueous solutions. Very little information on such nucleation currently exists. Using an automated lag time apparatus and a new analysis, we show several dilution series of Type I antifreeze proteins. Our results indicate that, above a concentration of ∼8 mg/ml, ice nucleation is enhanced rather than hindered. We discuss this unexpected result and present a new hypothesis outlining three components of polar fish blood that we believe affect its solution properties in certain situations. 相似文献