全文获取类型
收费全文 | 3368篇 |
免费 | 192篇 |
国内免费 | 1篇 |
出版年
2022年 | 33篇 |
2021年 | 60篇 |
2020年 | 32篇 |
2019年 | 48篇 |
2018年 | 52篇 |
2017年 | 63篇 |
2016年 | 78篇 |
2015年 | 112篇 |
2014年 | 129篇 |
2013年 | 157篇 |
2012年 | 219篇 |
2011年 | 192篇 |
2010年 | 125篇 |
2009年 | 106篇 |
2008年 | 150篇 |
2007年 | 125篇 |
2006年 | 113篇 |
2005年 | 110篇 |
2004年 | 100篇 |
2003年 | 72篇 |
2002年 | 81篇 |
2001年 | 90篇 |
2000年 | 64篇 |
1999年 | 70篇 |
1998年 | 31篇 |
1997年 | 30篇 |
1996年 | 25篇 |
1995年 | 25篇 |
1992年 | 50篇 |
1991年 | 61篇 |
1990年 | 45篇 |
1989年 | 55篇 |
1988年 | 39篇 |
1987年 | 48篇 |
1986年 | 31篇 |
1985年 | 73篇 |
1984年 | 46篇 |
1983年 | 52篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 41篇 |
1979年 | 53篇 |
1978年 | 33篇 |
1976年 | 25篇 |
1975年 | 27篇 |
1974年 | 32篇 |
1973年 | 28篇 |
1971年 | 34篇 |
1970年 | 29篇 |
1969年 | 33篇 |
排序方式: 共有3561条查询结果,搜索用时 15 毫秒
981.
The artifactual nature of fluoride inhibition of reverse transcriptase and associated ribonuclease H
S K Srivastava E Gillerman M J Modak 《Biochemical and biophysical research communications》1981,101(1):183-188
Surprisingly, the -1 configuration of 1-0-hexadecyl-2-acetyl-glycerylphosphorylcholine showed significant activity, 3.22 × 10?9 M, when compared to the -3 enantiomer, 2.92 × 10?10 M and a racemic mixture with a value of 7.2 × 10?10 M. A methoxy substitution at the C-1 or C-2 position of octadecyl glycerylphosphorylcholine gave a derivative with high biological activity for stimulating serotonin release from rabbit platelets. A 1-0-dodecyl-2-methoxy analogue showed very low activity; also, a comparable series of 0-benzyl derivatives were inactive. Examination of 1-0-hexadecyl, 1-0-octadecyl- or 1-0-dodecyl-2-acetyl--glyceryl-3-phosphorylcholine showed that the hexadecyl compound had three times the biological activity of the octadecyl and five times that of the dodecyl. 相似文献
982.
Antibody to purified terminal deoxynucleotidyl transferase (nucleosidetriphosphate : DNA deoxy-nucleotidylexotransferase, E.C. 2.7.7.31) from calf thymus was prepared in rabbits using terminal deoxynucleotidyl transferase crosslinked to bovine serum albumin. These antibodies, partially purified by 60% ammonium sulfate precipitation and Sephadex G-200 column chromatography, produced one precipitation band with calf thymus terminal deoxynucleotidyl transferase on immunodiffusion. This antibody preparation also inhibited the in vitro activity of terminal deoxynucleotidyl transferase from calf thymus, acute leukemic lymphoblasts and Molt-4 cells but not that of DNA polymerases alpha, beta and psi from these cells 相似文献
983.
Brahm S. Srivastava 《Molecular & general genetics : MGG》1976,143(3):327-332
Summary The isolation and properties of a new radiation sensitive mutant of Escherichia coli K-12 are described which shows a correlation between radiation sensitivity and replication of irradiated DNA. The mutation, called rer, is located between argB and purD loci. The mutant, when grown in tryptone broth after irradiation, is sensitive to UV and -rays and incorporates little or no 3H-thymidine but in minimal glucose-salts medium both the radiation sensitivity and incorporation of 3H-thymidine remain identical to that of the parent strain. Studies with a temperature sensitive double mutant rer dnaC show that 1 hr incubation of irradiated cells at 42° C before their transfer to 30° C results in higher survival as compared to their incubation at 30° C only. It is suggested that rer controls the replication of irradiated DNA and thus regulates the coordination between replication and repair of DNA. 相似文献
984.
J Fernandes U C Hegde S Srivastava R S Phadke G Govil 《Physiological chemistry and physics and medical NMR》1992,24(1):63-69
The ability of spermatozoa to reduce nitroxide spin--TEMPO has been used as a parameter to understand maturation, capacitation and calcium uptake of sperm obtained from Holstman strain rats. The rate of spin label reduction by sperm follows the trend--caput greater than cauda greater than corpus. With the increase in age, the electron donating capability shows first a gradual increase, for 60- to 85-day-old rats, peaking at 85 days (corresponding to puberty) and leveling off after 92 days. Calcium uptake takes place in two phases which corresponds to accumulation of and activation by calcium. The presence of polyclonal antibody which is known to cause agglutination, does not adversely affect the sperm activity. 相似文献
985.
986.
The 3'-, 4'-, and 6'-deoxy analogs of UDP-GlcpNAc have been synthesized chemically and found to act as donor-substrates for N-acetylglucosaminyltransferase-I (GnT-I) from human milk. Incubation of UDP-GlcpNAc and these deoxy analogs with GnT-I in the presence of alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -O(CH2)8COOMe gave beta-D-GlcpNAc-(1----2)-alpha-D-Manp-(1----3)-[alpha-D-Manp- (1----6)]- beta-D-Manp-O(CH2)8COOMe (6), and the deoxy analogs 12-14 where HO-3, HO-4, and HO-6, respectively, of the beta-D-GlcNAc residue were replaced by hydrogen. The tetrasaccharide glycosides 6 and 12-14 were characterized by 1H-n.m.r. spectroscopy and evaluated as acceptors for GnT-II, the next enzyme in the pathway of biosynthesis of Asn-linked oligosaccharides. Deoxygenation of the 3-position of the beta-D-GlcNAc residue of 6 completely abolished its acceptor activity, whereas removal of HO-4 or HO-6 caused only modest decreases in activity. 相似文献
987.
Phenolic compounds at low concentrations decrease pea diamine oxidase activity without affecting growth, but they have no effect on barley polyamine oxidase in spite of a decrease in growth. 相似文献
988.
An attempt has been made to determine the correlation between liver damage and the virulence of mildly pathogenicMycobacterium avium in thioacetamide treated rabbits. Liver damage increased the susceptibility of rabbits to infection even with a moderately
virulent organism. 相似文献
989.
R. C. Srivastava Bandana Bose R. D. Tripathi D. Mukerji S. N. Mathur 《Biologia Plantarum》1982,24(3):183-187
Chloramphenicol has been found to inhibit nitrate reductase activity in black-gram leaves. It inhibitsin vivo nitrate reductase activity up to 50–67%, and the catalytic property of the enzyme up to a maximum of 70–98%. Modulators,
such as KNO3, NADH and HCO3 could not protect enzyme inhibition by chloramphenicol. It is suggested that the chloramphenicol inhibition is mainly through
its effect on the catalytic process of the enzyme. 相似文献
990.
Isolation of rabbit testicular cathepsin D and its role in the activation of proacrosin 总被引:1,自引:0,他引:1
Cathepsin D was purified 900-fold with 30% recovery from rabbit testes using pepstatin bound Sepharose affinity chromatography. The enzyme is homogeneous as observed by acrylamide gel electrophoresis. The heat stable enzyme exhibits an apparent molecular weight of 42,000 with identical subunits of 20,000. Purified cathepsin D catalyses the conversion of proacrosin to acrosin. 相似文献