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   67453篇
  免费   18315篇
  国内免费   792篇
  86560篇
  2024年   99篇
  2023年   404篇
  2022年   576篇
  2021年   1096篇
  2020年   3334篇
  2019年   4960篇
  2018年   5251篇
  2017年   4944篇
  2016年   4688篇
  2015年   4627篇
  2014年   5238篇
  2013年   6142篇
  2012年   4734篇
  2011年   5242篇
  2010年   4296篇
  2009年   3320篇
  2008年   3557篇
  2007年   3021篇
  2006年   2880篇
  2005年   2529篇
  2004年   2109篇
  2003年   2076篇
  2002年   1773篇
  2001年   1317篇
  2000年   810篇
  1999年   704篇
  1998年   408篇
  1997年   374篇
  1996年   374篇
  1995年   404篇
  1994年   352篇
  1993年   335篇
  1992年   324篇
  1991年   278篇
  1990年   250篇
  1989年   252篇
  1988年   218篇
  1987年   221篇
  1986年   186篇
  1985年   292篇
  1984年   392篇
  1983年   263篇
  1982年   335篇
  1981年   280篇
  1980年   230篇
  1979年   211篇
  1978年   188篇
  1977年   161篇
  1976年   147篇
  1975年   110篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
The effect of 6-aminonicotinamide (6AN) treatment on the activities of alternative pathways of glucose metabolism in 20-day-old rat brain was evaluated by measurements of yields of 14CO2 from glucose labeled with 14C on carbons 1, 2, 3 + 4, or 6 and uniformly labeled glucose, and from the incorporation of 14C from specifically labeled glucose into lipids by brain slices from cerebral hemispheres and cerebellum. At the highest dose of 6AN used (35 mg/kg body weight) there was a significant decrease in the 14CO2 yields via the pentose phosphate pathway, the glycolytic route, tricarboxylic acid (TCA) cycle, and via the glutamate-gamma-aminobutyric acid pathway. Giving a graded series of doses (20-35 mg 6AN/kg body weight) revealed a hierarchy of responses in which the pentose phosphate pathway, lactate, glyceride-glycerol, and fatty acid formation were most sensitive, followed, in sequence, by the pyruvate dehydrogenase reaction, the glutamate-gamma-aminobutyrate route and, finally, the TCA cycle. The nature of the blocks in the various pathways was examined by the use of metabolite profiles.  相似文献   
54.
Two separate human liver aldehyde dehydrogenases exist which show differences in substrate specificity, cation inhibition or activation, and molecular weight. In this paper we report a common absence of enzyme 2 in Chinese which may be taken to indicate a gene deletion coding for this enzyme. The possible implication of this gene deletion among Chinese is discussed.  相似文献   
55.
Variation at the -glycerophosphate dehydrogenase (-Gpdh; EC 1.1.1.8) locus was surveyed in 11 species of waterstriders (Gerridae: Hemiptera) and five other species of aquatic Hemiptera. Species of waterstriders exhibited considerable inter- and intraspecific variation in degree of winglessness. Average heterozygosity (0.401±0.090) and average number of observed electromorphs (5.36±0.96) for the 11 gerrid species were well above values reported for nearly all other insect species surveyed to date. Wing-monomorphic and wing-polymorphic species did not differ in average -Gpdh heterozygosity. Of the three wing-polymorphic species surveyed geographically, two species exhibited marked variation in wing-morph frequencies but homogeneous -Gpdh allele frequencies. The third species exhibited geographically homogeneous -Gpdh and wing-morph frequencies, but no significant association between -Gpdh phenotype and wing morph was observed in any surveyed population. These results are consistent with hypotheses evoking either relaxed purifying selection at the -Gpdh locus in species of Gerridae due to the apparent reduced importance of flight, or selective maintenance of common -Gpdh electromorphs.This work was supported by NSF Grant DEB 76-20967 to Alan H. Brush, funds from the Research Foundation of the University of Connecticut to Carl W. Schaefer, and USPHS Grant GM 21133 to Richard K. Koehn.  相似文献   
56.
57.
The LDH isozymes were surveyed in bacterized cultures of syngens 1, 3, 12, and 13 of Paramecium caudatum by polyacrylamide gel electrophoresis. All the examined stocks of different syngens except one stock in syngen 3 had a single common LDH isozyme, and intra- and intersyngenic variation was not observed except for the one stock in syngen 3. Breeding data using the exceptional stock indicated that the LDH isozymes of P. caudatum are controlled by two codominant alleles at a single locus whose products aggregate randomly, forming a dimer.  相似文献   
58.
The locus for sorbitol dehydrogenase (SORD, E.C. 1.1.1.14) has been shown to segregate with hexosaminidase A and mannose phosphate isomerase in a series of human-Chinese hamster somatic cell hybrids. Cytogenetic analysis supports the assignment to chromosome 15 and further defines the gene locus to the region 15pterq21.This research was supported by the Medical Research Council of Canada (MT 4061), the Children's Hospital of Winnipeg Research Foundation, Inc., and the Department of Health, Province of Manitoba (H.S.W.).  相似文献   
59.
60.
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