全文获取类型
收费全文 | 73315篇 |
免费 | 6044篇 |
国内免费 | 38篇 |
专业分类
79397篇 |
出版年
2022年 | 645篇 |
2021年 | 1203篇 |
2020年 | 914篇 |
2019年 | 965篇 |
2018年 | 1507篇 |
2017年 | 1286篇 |
2016年 | 2110篇 |
2015年 | 3151篇 |
2014年 | 3059篇 |
2013年 | 3978篇 |
2012年 | 4731篇 |
2011年 | 4421篇 |
2010年 | 2660篇 |
2009年 | 2468篇 |
2008年 | 3414篇 |
2007年 | 3350篇 |
2006年 | 3128篇 |
2005年 | 3386篇 |
2004年 | 3270篇 |
2003年 | 2830篇 |
2002年 | 2392篇 |
2001年 | 1852篇 |
2000年 | 1791篇 |
1999年 | 1586篇 |
1998年 | 724篇 |
1997年 | 677篇 |
1996年 | 703篇 |
1995年 | 592篇 |
1994年 | 578篇 |
1993年 | 526篇 |
1992年 | 1144篇 |
1991年 | 1048篇 |
1990年 | 956篇 |
1989年 | 916篇 |
1988年 | 919篇 |
1987年 | 828篇 |
1986年 | 779篇 |
1985年 | 740篇 |
1984年 | 697篇 |
1983年 | 532篇 |
1982年 | 418篇 |
1981年 | 438篇 |
1980年 | 395篇 |
1979年 | 542篇 |
1978年 | 467篇 |
1977年 | 378篇 |
1976年 | 342篇 |
1975年 | 376篇 |
1974年 | 398篇 |
1973年 | 368篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
The stoichiometric palmitoyllysophosphatidylcholine (lysoPC)/gramicidin (4:1, mol/mol) lamellar complex (Killian, J.A., De Kruijff, B., Van Echteld, C.J.A., Verkleij, A.J., Leunissen-Bijvelt, J. and De Gier, J. (1983) Biochim. Biophys. Acta 728, 141-144) is a useful model system to investigate the various aspects of lipid protein interactions. To study the effect of gramicidin on local order and motion of 1-palmitoyl-sn-glycero-3-phosphocholine (lysoPC) we employed 31P and 2H nuclear magnetic resonance (NMR) using selectively deuterated lysoPC's and we compared the results to those obtained for lysoPC in bilayers with cholesterol (1:1, mol/mol) and dipalmitoylphosphatidylcholine (DPPC) (1:4, mol/mol). 2H-NMR experiments on acyl chain deuterated lysoPC showed similar quadrupole splittings in the liquid crystalline state for the lysoPC/DPPC and the lysoPC/gramicidin samples. In the lysoPC/cholesterol sample an increase of the quadrupole splitting was found. T1 measurements showed that gramicidin decreases the lysoPC acyl chain motion, especially at the C12 position. In the lysoPC/cholesterol sample an increase of motion was observed as compared to lysoPC in fluid bilayers of DPPC. 31P-NMR and 2-H-NMR measurements of lysoPC, deuterated at the alpha- and beta-position of the choline moiety, indicated an increase in headgroup flexibility in all samples as compared to the parent compound DPPC. In addition, a change in headgroup conformation was observed. The alpha- and beta-segments in all samples exhibited concerted motion. It was found that also in the polar headgroup gramicidin induces a decrease of the rate of motion. 相似文献
62.
Jeroen M. G. Stevens Hilde Vervaecke Han de Vries Linda van Elsacker 《International journal of primatology》2007,28(6):1417-1430
Bonobos have a reputation as a female-dominated and egalitarian species. We examined the 2 aspects of dominance in 6 captive
bonobo groups. Females do not consistently evoke submission from all males in all contexts. Though females occupy the highest-ranking
positions in the dominance hierarchy, there are in each group males that obtain rather high ranks and are able to dominate
≥1 female. Thus female dominance is not complete and hierarchies can be better described as nonexclusive female dominance.
We studied egalitarianism by measuring linearity and steepness of dominance hierarchies. The hierarchies of all groups are
highly linear. Hierarchies among males are steeper than among females. On average, male bonobos are more despotic than females,
but females too can have despotic relations, both with other females and with males. Hence one can call bonobos in captivity
semidespotic rather than egalitarian. 相似文献
63.
Martin T. R. Kuiper Marijke Holtrop Hans de Vries 《Molecular & general genetics : MGG》1988,213(2-3):519-528
64.
65.
I. Albesa P. Bogdanov A. Eraso N.R. Sperandeo M.M. de Bertorello 《Journal of applied microbiology》1995,78(4):373-377
I. ALBESA, P. BOGDANOV, A. ERASO, N.R. SPERANDEO AND M.M. DE BERTORELLO. 1995. The antibiotic activity of new synthetic isoxazolylnaphthoquinone imines was studied. Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922 were resistant to the four compounds studied (MIC > 128 µg ml−1 ), but Staphylococcus aureus ATCC 25923, ATCC 29213 and 30 clinical isolates of Staph. aureus were inhibited by 2-hydroxy- N -(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (I). This compound diminished bloodstream infection of mice injected i.m. with Staph. aureus; septicaemia decayed significantly when I was applied at the beginning of the infection while when I was given 3 d after bacterial challenge, a significant protection was afforded. Bactericidal activity in serum increased during the 5 h after I was administered i.p.
The acetyl derivative of I had a high MIC but when inoculated orally in mice decreased the Staph. aureus counts in circulation. This protection occurred only when the schedule of administration started close to the bacterial challenge. Antibiotic activity in vivo may be associated with in vitro effects. 相似文献
The acetyl derivative of I had a high MIC but when inoculated orally in mice decreased the Staph. aureus counts in circulation. This protection occurred only when the schedule of administration started close to the bacterial challenge. Antibiotic activity in vivo may be associated with in vitro effects. 相似文献
66.
67.
68.
69.
Biological screening for hereditary thrombophilia must be performed with constant concern for quality of the results and the interpretation. Different guidelines are available common to most laboratory tests, common to hemostasis tests, thrombophilia screening or specific for each test. These different steps are discussed in this paper with a special focus on the diagnosis of antithrombin, protein C and protein S deficiencies. 相似文献
70.
Methyl 3-azido-2-O-benzoyl-3,4-dideoxy-β-dl-erythro-pentopyranoside (6) was synthesized through two routes in five steps from methyl 2,3-anhydro-4-deoxy-β-dl-erythro-pentopyranoside (1). The first route proceeded via selective azide displacement of the 3-tosyloxy group of methyl 4-deoxy-2,3-di-O-tosyl-α-dl-threo-pentopyranoside, followed by detosylation and benzoylation. The second route consisted, with a better overall yield, in the azide displacement of the mesyloxy group of methyl O-benzoyl-4-deoxy-3-O-methylsulfonyl-α-dl-threo-pentopyranoside (10), obtained by benzylate opening of 1, followed by benzoylation, debenzylation, and mesylation. Compound 6 was transformed into its glycosyl chloride, further treated by 6-chloropurine to give the nucleoside 9-(3-azido-2-O-benzoyl-3,4-dideoxy-β-dl-erythro-pentopyranosyl)-6-chloropurine (13). When treated with propanolic ammonia, 13 yielded 9-(3-azido-3,4-dideoxy-β-dl-erythro-pentopyranosyl)adenine. 相似文献