全文获取类型
收费全文 | 4434篇 |
免费 | 469篇 |
出版年
2021年 | 66篇 |
2020年 | 37篇 |
2019年 | 37篇 |
2018年 | 60篇 |
2017年 | 45篇 |
2016年 | 104篇 |
2015年 | 236篇 |
2014年 | 296篇 |
2013年 | 341篇 |
2012年 | 207篇 |
2011年 | 173篇 |
2010年 | 191篇 |
2009年 | 214篇 |
2008年 | 152篇 |
2007年 | 151篇 |
2006年 | 150篇 |
2005年 | 150篇 |
2004年 | 142篇 |
2003年 | 117篇 |
2002年 | 111篇 |
2001年 | 75篇 |
2000年 | 71篇 |
1999年 | 90篇 |
1998年 | 95篇 |
1997年 | 63篇 |
1996年 | 64篇 |
1995年 | 51篇 |
1994年 | 49篇 |
1993年 | 64篇 |
1992年 | 72篇 |
1991年 | 46篇 |
1990年 | 57篇 |
1989年 | 61篇 |
1988年 | 64篇 |
1987年 | 52篇 |
1986年 | 43篇 |
1985年 | 39篇 |
1984年 | 50篇 |
1983年 | 50篇 |
1982年 | 60篇 |
1981年 | 43篇 |
1980年 | 55篇 |
1979年 | 42篇 |
1978年 | 51篇 |
1977年 | 37篇 |
1976年 | 31篇 |
1974年 | 35篇 |
1973年 | 45篇 |
1972年 | 27篇 |
1971年 | 35篇 |
排序方式: 共有4903条查询结果,搜索用时 15 毫秒
41.
John A. Secrist III 《Nucleosides, nucleotides & nucleic acids》2013,32(1-2):73-83
Abstract Analogues of S-adenosylmethionine with modifications in the 5′-group were prepared as potential inhibitors of S-adenosylmethionine decarboxylase (AdoMet-DC). These new analogues contained carbonyl-reactive end groups in the 5′-side chain, designed to interact favorably with the pyruvate prosthetic group of AdoMet-DC. Several of the analogues proved to be outstanding inhibitors of the enzyme. The analogues were also evaluated for their activity against human cytomegalovirus in vitro. 相似文献
42.
David F. Gilmore Walter Godchaux III Edward R. Leadbetter 《Archives of microbiology》1989,152(4):387-392
We have studied the regulation of sulfate assimilation by the gliding bacterium Cytophaga johnsonae in which 20% of the total sulfur is in the sulfornate moiety of sulfonolipid. Added cystine inhibited sulfate uptake and growth with cystine as sulfur source resulted in a repression of sulfate uptake. However, low concentrations of cystine preferentially repressed the terminal reactions of sulfate assimilation responsible for cysteine synthesis while allowing the transport and activation of sulfate for sulfonolipid synthesis. The significance of this novel pattern of regulation in bacteria is discussed. 相似文献
43.
Vitali I. Betaneli Michael V. Ovchinnikov Leon V. Backinowsky Nikolay K. Kochetkov 《Carbohydrate research》1982,107(2):285-291
N.m.r., enzymic, and chemical techniques have been used to characterise the d-galactose-containing tri- and tetra-saccharides produced on hydrolysis of carob and L. leucocephalad-galacto-d-mannans by Driselase β-d-mannanase. These oligosaccharides were shown to be exclusively 61-α-d-galactosyl-β-d-mannobiose and 61-α-d-galactosyl-β-d-mannotriose. Furthermore, these were the only d-galactose-containing tri- and tetra-saccharides produced on hydrolysis of carob d-galacto-d-mannan by β-d-mannanases from other sources, including Bacillus subtilis, Aspergillus niger, Helix pomatia gut solution, and germinated legumes. Acid hydrolysis of lucerne galactomannan yielded 61-α-d-galactosyl-β-d-mannobiose and 62-α-d-galactosyl-β-d-mannobiose. 相似文献
44.
45.
46.
Dopamine and prostaglandin A1 were infused intravenously in 4 patients with the hepatorenal syndrome, in 1 patient with acute tubular necrosis, and 1 patient with cortical necrosis. Large doses of prostaglandin A1 decreased arterial blood pressure preventing increase in dosage; in contrast, high doses of dopamine elevated blood pressure. When the two drugs were administered conjointly, much larger doses of each agent could be administered without change in arterial blood pressure. Significant improvement of renal function was not observed in any of these critically ill patients during or within 24 hours after dopamine and prostaglandin A1 administration. This study demonstrated that extremely large doses of these vasodilating agents can be safely administered conjointly. 相似文献
47.
48.
Summary The ciliary crown and the relationship of the ciliary crown to the underlying axoneme were studied by electron microscopy in cilia from hamster and rat trachea and bronchioles, and rabbit trachea. The ciliary crown is a cluster of 4 to 6 fibrils 35 nm long protruding beyond the plasma membrane at the tips of the cilia. The fibrils are well preserved after tannic acidglutaraldehyde-osmium tetroxide fixation and have high contrast with a periodic density of 4.5 nm. They stain relatively weakly with phosphotungstic acid. The surface of the fibrils stains with ruthenium red.The microtubules of the axoneme end in a plate of electron dense amorphous material. A five layered disc occupies the space between the membrane and the amorphous plate at the tip of the axoneme. The plasma membrane can be dissolved with the detergent triton X-100 without loss of the ciliary crown. This indicates that the ciliary crown is composed of transmembranous filaments which are bound to the disc at the tip of the axoneme.Supported by U.S.P.H.S. Research Grant number HL-12650 相似文献
49.
50.
Unfertilized eggs and early embryos up to the 2-day (16-cell) cleavage stage of development in the rabbit contain predominantly the most cathodal lactate dehydrogenase isoenzyme made up of A-type subunits. Following early cleavage there is a progressing increase in total LDH activity in the embryo as development proceeds through 4- and 6-day blastocyst stages. This is accompanied by an increase in the amount of B-type subunits and a concomitant shift in the lactate dehydrogenase isoenzyme electrophoretic pattern toward the anodal isoenzyme types. 相似文献