全文获取类型
收费全文 | 1274704篇 |
免费 | 109503篇 |
国内免费 | 1481篇 |
专业分类
1385688篇 |
出版年
2021年 | 17728篇 |
2020年 | 12572篇 |
2019年 | 16126篇 |
2018年 | 17236篇 |
2017年 | 16005篇 |
2016年 | 27717篇 |
2015年 | 42143篇 |
2014年 | 50159篇 |
2013年 | 76356篇 |
2012年 | 33998篇 |
2011年 | 21823篇 |
2010年 | 42389篇 |
2009年 | 44158篇 |
2008年 | 21373篇 |
2007年 | 18866篇 |
2006年 | 24798篇 |
2005年 | 25824篇 |
2004年 | 25156篇 |
2003年 | 22835篇 |
2002年 | 20994篇 |
2001年 | 29020篇 |
2000年 | 26093篇 |
1999年 | 27361篇 |
1998年 | 24833篇 |
1997年 | 24678篇 |
1996年 | 24316篇 |
1995年 | 22336篇 |
1994年 | 22284篇 |
1993年 | 21282篇 |
1992年 | 24227篇 |
1991年 | 22815篇 |
1990年 | 21392篇 |
1989年 | 22543篇 |
1988年 | 20539篇 |
1987年 | 19547篇 |
1986年 | 18576篇 |
1985年 | 20616篇 |
1984年 | 20891篇 |
1983年 | 18509篇 |
1982年 | 19639篇 |
1981年 | 19059篇 |
1980年 | 17747篇 |
1979年 | 17036篇 |
1978年 | 16403篇 |
1977年 | 16061篇 |
1976年 | 15274篇 |
1975年 | 14581篇 |
1974年 | 15024篇 |
1973年 | 15382篇 |
1972年 | 12886篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
The production of L-lysine fromDL-α-amino-ε-caprolactam (DL-ACL) by new strains producingL-α-amino-ε-caprolactamase and aminocaprolactam racemase is described. Optimal conditions for hydrolysis ofL-ACL byCryptococcus sp. and for racemization of ACL by cells of a strain isolated in nature and identified asPseudomonas sp. were determined. Synthesis ofL-α-amino-ε-caprolactamase is induced byDL-ACL orL-lysine with the same effectivity. A positive effect of phosphates (potassium salts) on reduction of the induction lag was
detected, the synthesis of this enzyme was found to be repressed by glucose and some possibilities of the reversion of this
repressive effect were demonstrated. Under conditions optimal for the production of both enzymes a quantitative theoretical
conversion of 10 % aqueousDL-ACL toL-lysine by a mixture of native cells in a mass ratio of 1: 2 (producer of ACL-hydrolase to producer of ACL-racemase) occurred
in 8 h at 40 °C and pH 8.0 相似文献
952.
Inflammatory reaction to ocular trauma is known to be related to prostaglandins. To further evaluate this phenomenon in human, PGE1 and E2 were measured by R.I.A. after silicic acid chromatography in aqueous humour of 26 patients before and 3 days after surgery for unilateral senile cataract (posterior chamber implant after extracapsular surgery). 13 out of these patients were treated with indomethacin by enteral route and 13 were not treated.PGE2 levels increased in all non-treated patients from : m < 214 pg/ml before surgery, to 2666 ± 869 pg/ml (range : 257 - 8728) p < 0.001 after surgery. PGE2 levels did not increase in indomethacin-treated patients. PGE1 levels did not increase significantly in non-treated as in treated patients.1) Intra-ocular surgery is followed in human by a constant increase of the only PGE2 in the aqueous humour. 2) Indomethacin inhibits this increase. 3) The post-surgical increase in the permeability of blood-aqueous barrier appears to be related to a release of PGE2. 相似文献
953.
954.
A.S. Tsaftaris J.C. Sorenson J.G. Scandalios 《Biochemical and biophysical research communications》1980,92(3):889-895
A protein isolated from maize scutella which inhibits catalase in vitro has been shown to contain 12% carbohydrate in the form of galactose. This corresponds to four galactose molecules per inhibitor subunit. Removal of the carbohydrate with β-galactosidase or blockage with a galactose-specific lectin abolished activity of the inhibitor. 相似文献
955.
W.M.F. Jongen P.H.M. Lohman M.J. Kottenhagen G.M. Alink F. Berends J.H. Koeman 《Mutation research》1981,81(2):203-213
Several short-term mammalian test systems were used for mutagenicity testing of the organic solvent dichloromethane. The compound was negative in the forward mutation test on the HGPRT locus in Chinese hamster cells and the unscheduled DNA synthesis test in both human and hamster cells. In the test on DNA synthesis inhibition, dichloromethane caused an aspecific inhibition in both human and hamster cells, but in this test the effect did not indicate a DNA-damaging action. A weak positive effect was found in the test on sister-chromatid exchanges in hamster cells. 相似文献
956.
957.
Regulation of G(1) cell-cycle progression by oncogenes and tumor suppressor genes. 总被引:13,自引:0,他引:13
Progression of resting quiescent G(0) cells into early G(1) and transition across the restriction point are highly regulated processes. Mutation of proto-oncogenes and tumor suppressor genes regulating these transitions are targeted during oncogenesis. Recent work has underscored the importance of the G(0) to early G(1) transition and metabolism to neoplastic cells. 相似文献
958.
C. Sanderson 《BMJ (Clinical research ed.)》1974,1(5901):245-246
959.
960.