全文获取类型
收费全文 | 314563篇 |
免费 | 36641篇 |
国内免费 | 168篇 |
出版年
2018年 | 2634篇 |
2016年 | 3436篇 |
2015年 | 4644篇 |
2014年 | 5536篇 |
2013年 | 7657篇 |
2012年 | 8709篇 |
2011年 | 8952篇 |
2010年 | 5987篇 |
2009年 | 5656篇 |
2008年 | 7923篇 |
2007年 | 8127篇 |
2006年 | 7977篇 |
2005年 | 7673篇 |
2004年 | 7628篇 |
2003年 | 7423篇 |
2002年 | 7219篇 |
2001年 | 17834篇 |
2000年 | 18014篇 |
1999年 | 13851篇 |
1998年 | 4159篇 |
1997年 | 4433篇 |
1996年 | 4155篇 |
1995年 | 3765篇 |
1994年 | 3683篇 |
1993年 | 3785篇 |
1992年 | 10909篇 |
1991年 | 10759篇 |
1990年 | 10278篇 |
1989年 | 10082篇 |
1988年 | 9376篇 |
1987年 | 8740篇 |
1986年 | 7890篇 |
1985年 | 7753篇 |
1984年 | 6189篇 |
1983年 | 5359篇 |
1982年 | 3874篇 |
1981年 | 3429篇 |
1980年 | 3258篇 |
1979年 | 5653篇 |
1978年 | 4360篇 |
1977年 | 4008篇 |
1976年 | 3495篇 |
1975年 | 3994篇 |
1974年 | 4177篇 |
1973年 | 4088篇 |
1972年 | 3566篇 |
1971年 | 3353篇 |
1970年 | 2931篇 |
1969年 | 2862篇 |
1968年 | 2502篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
65.
66.
The ability of human uterine endometrium to aromatize androstenedione to estrogens was investigated using 10 normal and neoplastic tissues. Normal and neoplastic endometrial homogenates were incubated with [6,7-3H]androstenedione (A) and NADPH. Estrone (E1) and estradiol (E2) were subsequently isolated in amounts ranging from 0-17600 fmol/h/g and 0-377 fmol/h/g, respectively, from the incubates after purifications by using Bio-Rad AG1-X2 column, thin layer chromatographies and co-crystallization. The conversion of A to E1 and E2 was significantly higher in neoplastic tissues. 相似文献
67.
Properties of purified colchicine-binding protein from a cultured carrot cell extract 总被引:1,自引:0,他引:1
Colchicine-binding protein (CBP) was purified from a cultured carrot cell extract by DEAE-Sephacel, phosphocellulose and Sephadex G200 column chromatographies. The purified CBP separated into three bands on SDS-polyacrylamide gel electrophoresis. One of them reacted with a monoclonal antibody against chick brain alpha-tubulin and the other two with that against beta-tubulin. Colchicine-binding activity of the purified protein was enhanced by tartrate and inhibited little by an excess of podophyllotoxin. It decayed following first order kinetics, but was more stable than the CBP in the crude extract. The binding constant of the purified CBP for colchicine was 0.57 microM-1 and the number of binding sites of colchicine per mg protein was about 2 nmol. This binding constant is about ten times lower than that of porcine brain tubulin under identical conditions. 相似文献
68.
D-2 dopamine receptors in the frontal cortex of rat and human 总被引:2,自引:0,他引:2
D-2 dopamine receptors and serotonin receptors in the frontal cortex of rat and human were labelled with 3H-spiroperidol. The D-2 receptors were then distinguished in 4 ways. Dissociation of spiroperidol was biphasic, indicating two populations of sites. Cinanserin in competition with 3H-spiroperidol exhibited high (75%) and low (25%) affinity sites. Dopamine and LY 141865 in competition with 1.25 nM 3H-spiroperidol exhibited high (20-25%) and low (80-75%) affinity sites in the absence of cinanserin, while in the presence of 300 nM cinanserin only the high affinity sites remained. Lesioning of the dopaminergic meso-cortical pathway increased the number of cinanserin-resistant sites by 26%. Thus 3H-spiroperidol binding in the presence of cinanserin can be used to selectively label D-2 receptors in the frontal cortex. 相似文献
69.
70.
The effects on a cloned DNA fragment carrying an actinomycin resistance determinant on physiological processes in strains of streptomycetes with various potencies in producing this antibiotic, their inactive mutants, and the model strain ofStreptomyces lividans66 were studied. This fragment was shown to modulate bacterial resistance to actinomycin and biosynthesis of antibiotics. 相似文献