全文获取类型
收费全文 | 50356篇 |
免费 | 5338篇 |
国内免费 | 13篇 |
出版年
2021年 | 694篇 |
2020年 | 446篇 |
2019年 | 605篇 |
2018年 | 758篇 |
2017年 | 700篇 |
2016年 | 1175篇 |
2015年 | 2035篇 |
2014年 | 2085篇 |
2013年 | 2680篇 |
2012年 | 3040篇 |
2011年 | 2735篇 |
2010年 | 1879篇 |
2009年 | 1677篇 |
2008年 | 2321篇 |
2007年 | 2263篇 |
2006年 | 2035篇 |
2005年 | 1989篇 |
2004年 | 1887篇 |
2003年 | 1652篇 |
2002年 | 1628篇 |
2001年 | 1448篇 |
2000年 | 1431篇 |
1999年 | 1279篇 |
1998年 | 703篇 |
1997年 | 647篇 |
1996年 | 649篇 |
1995年 | 618篇 |
1994年 | 575篇 |
1993年 | 599篇 |
1992年 | 1156篇 |
1991年 | 909篇 |
1990年 | 908篇 |
1989年 | 890篇 |
1988年 | 796篇 |
1987年 | 725篇 |
1986年 | 710篇 |
1985年 | 825篇 |
1984年 | 621篇 |
1983年 | 502篇 |
1982年 | 408篇 |
1981年 | 381篇 |
1980年 | 324篇 |
1979年 | 463篇 |
1978年 | 394篇 |
1977年 | 302篇 |
1976年 | 282篇 |
1975年 | 263篇 |
1974年 | 351篇 |
1973年 | 313篇 |
1972年 | 230篇 |
排序方式: 共有10000条查询结果,搜索用时 42 毫秒
51.
52.
53.
Two cases of right lower lobe oedema are presented as a supposedly very rare sign of left heart failure after myocardial infarction in the presence of acute mitral regurgitation. Causes of unilateral oedema and its clinical relevance in the diagnostic and therapeutic perspectives are discussed, and a review of the literature on this topic is presented. 相似文献
54.
55.
56.
57.
58.
A method is described for the histochemical detection of horseradish peroxidase in Paraplast Plus embedded brain sections. The procedure uses 150-micron-thick Vibratome-cut slices of glutaraldehyde-paraformaldehyde-fixed brain tissue. Tetramethylbenzidine stabilized by diaminobenzidine/cobalt/H2O2 is used as chromogen. The Vibratome-cut slices are dehydrated through a graded series of acetone, cleared in toluol and flat-embedded in Paraplast Plus embedding medium. Serial sections can be cut as thin as 5-7 micron. The method is universal in its application and permits optimal visualization of labeled neurons with great morphological detail at the light-microscopic level. 相似文献
59.
Blue Dextran has been coupled covalently to Sepharose-4B to purify the enzymatic complex NAD(P)H-nitrate reductase (EC 1.6.6.2) from the green alga Ankistrodesmus braunii by affinity chromatography. The optimum conditions for the accomplishment of the chromatographic process have been determined. The adsorption of nitrate reductase on Blue Dextran Sepharose is optimum when a phosphate buffer of low ionic strength and pH 6.5-7.0 is used. Once the enzyme has been bound to Blue Dextran Sepharose, it can be specifically eluted by addition of NADH and FAD to the washing buffer. However, none of the nucleotides added separately is able to promote the elution of the enzyme from the column. The elution can be also achieved, but not specifically, by increasing the ionic strength of the buffer with KCl. These results have made possible a procedure for the purification of A. braunii nitrate reductase which led to electrophoretic homogeneity, with an overall yield of 70% and a specific activity of 49 units/mg of protein. 相似文献
60.
M. A. P. J. Hacking F. van Rantwijk R. A. Sheldon 《Journal of Molecular Catalysis .B, Enzymatic》2000,9(4-6):201-208
Symmetrical dialkyl carbonates and dibenzyl carbonates reacted with various nucleophiles in the presence of Candida antarctica lipase B in organic solvents. For example, reaction of dibutyl and dibenzyl carbonate with an alcohol gave a mixture of the mono- and disubstituted products. Aminolysis, however, afforded only the carbamates, without subsequent reaction to the ureum derivatives. The reaction rates were rather low compared with carboxylic esters; the reactivity increased in the order dimethyl相似文献