全文获取类型
收费全文 | 101936篇 |
免费 | 1348篇 |
国内免费 | 813篇 |
出版年
2022年 | 90篇 |
2021年 | 218篇 |
2020年 | 115篇 |
2019年 | 128篇 |
2018年 | 11980篇 |
2017年 | 10794篇 |
2016年 | 7651篇 |
2015年 | 970篇 |
2014年 | 744篇 |
2013年 | 762篇 |
2012年 | 4833篇 |
2011年 | 13335篇 |
2010年 | 12337篇 |
2009年 | 8539篇 |
2008年 | 10235篇 |
2007年 | 11769篇 |
2006年 | 700篇 |
2005年 | 929篇 |
2004年 | 1349篇 |
2003年 | 1349篇 |
2002年 | 1145篇 |
2001年 | 487篇 |
2000年 | 333篇 |
1999年 | 182篇 |
1998年 | 104篇 |
1997年 | 112篇 |
1996年 | 89篇 |
1995年 | 73篇 |
1994年 | 76篇 |
1993年 | 103篇 |
1992年 | 161篇 |
1991年 | 172篇 |
1990年 | 131篇 |
1989年 | 115篇 |
1988年 | 110篇 |
1987年 | 115篇 |
1986年 | 72篇 |
1985年 | 70篇 |
1984年 | 81篇 |
1983年 | 86篇 |
1982年 | 68篇 |
1981年 | 43篇 |
1980年 | 41篇 |
1979年 | 70篇 |
1977年 | 52篇 |
1976年 | 41篇 |
1975年 | 64篇 |
1973年 | 46篇 |
1972年 | 296篇 |
1971年 | 305篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
361.
WHEN chromosomes pair at meiosis the bivalents so formed do not normally interlock. Heat-treatments can, however, induce bivalent interlocking in the locust Locusta migratoria. Only the longest bivalents interlock and usually only two are found per cell; two “rod” bivalents, with single chiasmata, two “ring” bivalents, each with two or three chiasmata, or one “rod” and one “ring” bivalent (Fig. 1a, b and c). The nature of this interlocking and the metaphase orientational and congressional properties of interlocked bivalents are analysed in detail elsewhere1. 相似文献
362.
The kinetic properties of pyruvate kinase (ATP:pyruvate-phosphotransferase, EC 2.7.1.40) from Streptococcus lactis have been investigated. Positive homotropic kinetics were observed with phosphoenolpyruvate and adenosine 5′-diphosphate, resulting in a sigmoid relationship between reaction velocity and substrate concentrations. This relationship was abolished with an excess of the heterotropic effector fructose-1,6-diphosphate, giving a typical Michaelis-Menten relationship. Increasing the concentration of fructose-1,6-diphosphate increased the apparent Vmax values and decreased the Km values for both substrates. Catalysis by pyruvate kinase proceeded optimally at pH 6.9 to 7.5 and was markedly inhibited by inorganic phosphate and sulfate ions. Under certain conditions adenosine 5′-triphosphate also caused inhibition. The Km values for phosphoenolpyruvate and adenosine 5′-diphosphate in the presence of 2 mM fructose-1,6-diphosphate were 0.17 mM and 1 mM, respectively. The concentration of fructose-1,6-diphosphate giving one-half maximal velocity with 2 mM phosphoenolpyruvate and 5 mM adenosine 5′-diphosphate was 0.07 mM. The intracellular concentrations of these metabolites (0.8 mM phosphoenolpyruvate, 2.4 mM adenosine 5′-diphosphate, and 18 mM fructose-1,6-diphosphate) suggest that the pyruvate kinase in S. lactis approaches maximal activity in exponentially growing cells. The role of pyruvate kinase in the regulation of the glycolytic pathway in lactic streptococci is discussed. 相似文献
363.
LSD was found to induce chromosomal aberrations in root tip cells of Allium cepa, Hordeum vulgare and Secale cereale. Aberrations occurred in the form of chromatid and isochromatid breaks with most of these breaks failing to rejoin. The distribution of chromosome breaks was not uniform over the length of chromosomes, and a majority of the breaks were localized at the centromeric regions. For a given dose of LSD (30 g/ml), onion appeared to be more susceptible than barley or rye. The diploid and tetraploid rye used in the study showed no appreciable difference in sensitivity to LSD treatment. — A preliminary study on meiotic chromosomes in LSD-treated diploid rye revealed the presence of univalents, chromosome breaks and fragments, suggesting that LSD can induce meiotic abnormalities in plant material.Contribution from the Department of Agronomy, University of Kentucky. The investigation reported in this paper (73-3-75) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. 相似文献
364.
365.
Y(pyruvate) was 17.3, similar to Y(arginine), for Streptococcus faecalis 6783 grown statically in a complex medium in 1 atm of air. 相似文献
366.
367.
368.
369.
370.