首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1301篇
  免费   126篇
  2022年   12篇
  2021年   20篇
  2020年   17篇
  2019年   16篇
  2018年   19篇
  2017年   21篇
  2016年   41篇
  2015年   60篇
  2014年   77篇
  2013年   78篇
  2012年   93篇
  2011年   96篇
  2010年   62篇
  2009年   60篇
  2008年   67篇
  2007年   70篇
  2006年   69篇
  2005年   68篇
  2004年   56篇
  2003年   52篇
  2002年   45篇
  2001年   12篇
  2000年   9篇
  1999年   7篇
  1998年   15篇
  1997年   11篇
  1996年   10篇
  1995年   6篇
  1994年   9篇
  1993年   8篇
  1992年   11篇
  1991年   8篇
  1989年   6篇
  1988年   6篇
  1987年   8篇
  1986年   6篇
  1985年   6篇
  1984年   13篇
  1983年   12篇
  1982年   14篇
  1981年   15篇
  1980年   11篇
  1979年   12篇
  1978年   8篇
  1977年   5篇
  1976年   7篇
  1975年   6篇
  1974年   7篇
  1961年   5篇
  1945年   5篇
排序方式: 共有1427条查询结果,搜索用时 31 毫秒
31.
Karyotypically XY individuals of the C57BL/6J-YPOS mouse stock develop as females or hermaphrodites, but never as normal males. The aberrant sexual development results from the interaction of the C57BL/6J genetic background with the M. poschiavinus-derived Y chromosome. XY females from this stock were assayed for H-Y antigen. By the criteria of skin-grafting, the cell-mediated lympholysis test, and the popliteal lymph node assay, these XY females are antigenically indistinguishable from normal C57BL/6 males. Implications for the hypothesis that H-Y antigen induces formation of the mammalian testis are discussed.  相似文献   
32.
The condensing component of chicken liver fatty acid synthetase is inhibited by a sulfhydryl reagent, iodoacetamide, with a second-order rate constant of 0.23 M–1 sec–1 at pH 7.0 and 0. Complete inactivation requires the modification of approximately 8-SH groups per dimer of the enzyme. Quantitation of the extent of inactivation in the presence of i mM acetyl CoA (which completely protects the enzyme against inactivation) and in its absence shows that complete inactivation results from the binding of approximately 1.1 tool of carboxamidomethyl residues per dimer. These data are consistent with the proposed functional asymmetry of the enzyme.  相似文献   
33.
Impurities in 5(6)-carboxyfluorescein can affect phospholipid vesicle stability and apparent rates of carboxyfluorescein transfer into cells. Thorough purification and characterization of the dye are thus important to many applications with vesicles and/or cells. The dye can be purified by adsorption chromatography on a hydrophobic gel, following treatment with activated charcoal and precipitation from ethanol-water. The 5- and 6-carboxy-isomers can be separated from each other (though for most purposes it is not necessary to do so) by synthesis, crystallization, and hydrolysis of the diacetate derivatives. Purification is monitored by thin-layer and high pressure chromatography.  相似文献   
34.
35.
The metabolic rates of laboratory mice were compared in three conditions: isolated mice, mice paired together over six days (stable groups), and mice paired with strange partners daily (unstable groups). Stable pairs had 15% lower metabolic rates than either isolated or unstable pairs. In other experiments when two mice were placed in separate metabolic chambers and connected together via an air flow, the metabolic rate of the recipient in the series was 35% lower than the donor. The data suggest that a ‘factor’ produced by the donor mouse was passed via the air supply into the recipient's chamber.  相似文献   
36.
Imaginal discs of Drosophila melanogaster undergo transdetermination when cultured in vivo in the abdominal cavity of adult female hosts. We report here that leg discs cultured in vitro, in a recently developed system, also undergo transdetermination. Whether cultured in vivo or in vitro, leg discs produce a similar range of specific transdetermined structures. Moreover, in comparison to discs cultured in vivo, the discs cultured in vitro exhibit a similar correlation between the amount of growth and the total frequency of transdetermination.  相似文献   
37.
After fertilization, the development of a zygote depends upon both gene products synthesized by its maternal parent and gene products synthesized by the zygote itself. To analyze genetically the relative contributions of these two sources of gene products, several laboratories have been isolating two classes of mutants of Drosophila melanogaster: maternal-effect lethals and zygotic lethals. This report concerns the analysis of two temperature-sensitive mutants, OX736hs and PC025hs, which were isolated as alleles of a small-disc mutant, l(3)1902. These alleles are not only zygotic lethals, but also maternal-effect lethals. They have temperature-sensitive periods during larval life and during oogenesis. Mutant larvae exposed continuously to restrictive temperature have small discs. One-or two-day exposures to the restrictive temperature administered during the third larval instar lead to a homeotic transformation of the midlegs and hindlegs to the pattern characteristic of the forelegs. Mutant females exposed to the restrictive temperature during oogenesis produce eggs that can develop until gastrulation, but do not hatch.--The existence of these mutants, and one that was recently described by another group, implies that there may be a class of genes, heretofore unrecognized, whose products are synthesized during oogenesis, are essential for embryogenesis and are also synthesized during larval stages within imaginal disc cells.  相似文献   
38.
39.
40.
In an institution for the mentally retarded, an uncontrolled study was made on the effects of d-amphetamine, d-amphetamine followed by trifluoperazine, and of combined d-amphetamine and trifluoperazine on stuttering. Of 28 patients to whom d-amphetamine was given, 14 showed improvement after one month''s treatment. Eight more showed improvement when trifluoperazine was given for one month to those who did not improve on d-amphetamine. In many cases, improvement was sustained at least six months after treatment was discontinued.Treatment with d-amphetamine was apparently more effective in patients with functional than with organic retardation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号