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   450902篇
  免费   55960篇
  国内免费   283篇
  507145篇
  2018年   3841篇
  2017年   3521篇
  2016年   5489篇
  2015年   8233篇
  2014年   9208篇
  2013年   12972篇
  2012年   14935篇
  2011年   15042篇
  2010年   9920篇
  2009年   9191篇
  2008年   13134篇
  2007年   13597篇
  2006年   12321篇
  2005年   12110篇
  2004年   11871篇
  2003年   11319篇
  2002年   10826篇
  2001年   21671篇
  2000年   21791篇
  1999年   17431篇
  1998年   6245篇
  1997年   6492篇
  1996年   6317篇
  1995年   5715篇
  1994年   5772篇
  1993年   5594篇
  1992年   13679篇
  1991年   12986篇
  1990年   12665篇
  1989年   12525篇
  1988年   11189篇
  1987年   10810篇
  1986年   9897篇
  1985年   9679篇
  1984年   8215篇
  1983年   7089篇
  1982年   5535篇
  1981年   5016篇
  1980年   4680篇
  1979年   7709篇
  1978年   5939篇
  1977年   5438篇
  1976年   5090篇
  1975年   5385篇
  1974年   5832篇
  1973年   5678篇
  1972年   5124篇
  1971年   4747篇
  1970年   3940篇
  1969年   3867篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The biochemical pathways involved in acetyl-L-carnitine utilization were investigated in conscious, freely moving rats by 13C NMR spectroscopy. Following 4-h [(1,2-13C2)acetyl]-L-carnitine infusion in fasted animals, the free carnitine levels in serum were increased, and an efflux of unlabelled acetyl-L-carnitine from tissues was observed. [(1,2-13C2)Acetyl]-L-carnitine was found to enter biosynthetic pathways in liver, and the acetyl moiety was incorporated into both cholesterol and 3-hydroxybutyrate carbon skeleton. In accord with the entry of [(1,2-13C2)acetyl]-L-carnitine in the mitochondrial acetylCoA pool associated with tricarboxylic acid cycle, the 13C label was also found in liver glutamate, glutamine, and glutathione. The analysis of the 13C-labelling pattern in 3-hydroxybutyrate and cholesterol carbon skeleton provided evidence that the acetyl-L-carnitine-derived acetylCoA pool used for ketone bodies synthesis in mitochondria was homogeneous, whereas cholesterol was synthesized from two different acetylCoA pools located in the extra- and intramitochondrial compartment, respectively. Furthermore, cholesterol molecules were shown to be preferentially synthesized by the metabolic route involving the direct channelling of CoA-activated mitochondria-derived ketone bodies into 3-hydroxy-3-methylglutarylCoA pathway, prior to equilibration of their acyl groups with extramitochondrial acetylCoA pool via acetoacetylCoA thiolase.  相似文献   
992.
Aims of this study were to analyze the long-term effects of postovulatory aging of mouse oocytes on 1) reproductive traits of parental (F(0)) and first (F(1))-generation females (pregnancy rate, gestation length, litter size, perinatal death, and sex ratio of offspring) and 2) developmental and behavioral variables of F(1) and second-generation (F(2)) offspring (birth weight and weight gain during preweaning development, postnatal day of attainment of immediate righting, spontaneous motor activity, and passive and active conditioned learning ability). Hybrid (C57BL/6JIco x CBA/JIco) females were artificially inseminated at 13 h (control group) or 22 h (oocyte-aged group) after GnRH injection. Experimental (oocyte-aged group) F(0) females exhibited lower pregnancy rate, shortened gestation length, decreased litter size, higher perinatal death of their pups, and increased percentage of male offspring compared to control F(0) females. Postovulatory aging of oocytes was also associated with increased number of growth-retarded pups, delayed development of the righting reflex, and higher spontaneous motor activity and emotionality of F(1) offspring. Postovulatory aging of F(0) oocytes did not affect birth weight, weight gain during preweaning development, passive and active conditioned learning ability of F(1) offspring, or reproductive traits of F(1) females or developmental and behavior variables of F(2) offspring.  相似文献   
993.
994.
995.
996.
997.
998.
999.
1000.
By means of analytical and electroantennogram methods, cis-11-and trans-11-tetradecenyl acetate have been isolated and identified as the sex pheromones of the fruit tree tortrix moth, Archips podana. In contrast to the single compounds, mixtures in a ratio of about 1 : 1 are highly attractive to male moths in field experiments.  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