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   98325篇
  免费   6868篇
  国内免费   26篇
  105219篇
  2023年   540篇
  2022年   719篇
  2021年   1404篇
  2020年   1211篇
  2019年   1385篇
  2018年   2422篇
  2017年   2118篇
  2016年   3164篇
  2015年   4373篇
  2014年   4534篇
  2013年   5971篇
  2012年   7320篇
  2011年   6888篇
  2010年   4206篇
  2009年   3562篇
  2008年   5439篇
  2007年   5248篇
  2006年   5116篇
  2005年   4412篇
  2004年   4353篇
  2003年   3989篇
  2002年   3692篇
  2001年   2407篇
  2000年   2424篇
  1999年   1772篇
  1998年   920篇
  1997年   641篇
  1996年   640篇
  1995年   656篇
  1994年   545篇
  1993年   498篇
  1992年   934篇
  1991年   846篇
  1990年   782篇
  1989年   773篇
  1988年   659篇
  1987年   654篇
  1986年   592篇
  1985年   584篇
  1984年   551篇
  1983年   446篇
  1982年   383篇
  1981年   311篇
  1980年   305篇
  1979年   459篇
  1978年   313篇
  1975年   308篇
  1974年   361篇
  1973年   347篇
  1972年   302篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
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   
83.
Acid-catalysed condensation of methyl β-d-glycero-l-manno-heptopyranoside with cyclohexanone yielded an approximately 3:1 mixture of the 2,3:6,7- and 2,3:4,7-di-O-cyclohexylideneheptosides (1 and 2), which could be separated either as their benzoates (3 and 4) or as their methyl ethers (5 and 6). The latter compounds afforded the 4- and 6-methyl ethers (7 and 8) of d-glycero-l-manno-heptitol.  相似文献   
84.
From the roots of Ferula loscosii the coumarins umbelliprenin, coladin and coladonin and the new natural isovaleryl derivative of the latter have been isolated. A study which confirms the structure of coladonin and its difference from farnesiferol A is also given.  相似文献   
85.
86.
87.
Summary This study is concerned with electron-microscopic observations on endocrine or paracrine cells in the fundic gastric mucosa of the bullfrog. Also, an attempt was made to identify the histamine-releasing cells involved in the secretagogue response. At least three distinct endocrine-like cell types were found. The classification is based on the appearance of secretory granules and other organelles, and the relationship of endocrine-like cells with other cells in the tissue. The amphibian endocrine-like cells resemble the ECL, D and EC cells of mammals. Type-I (ECL) cells showed degranulation after repeated stimulation with tetragastrin (TG), acetylcholine (ACh) and K+ depolarizing solution, all of which release histamine.  相似文献   
88.
89.
90.
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