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   181333篇
  免费   14334篇
  国内免费   50篇
  195717篇
  2018年   1807篇
  2017年   1758篇
  2016年   2248篇
  2015年   2137篇
  2014年   2936篇
  2013年   4188篇
  2012年   4802篇
  2011年   5306篇
  2010年   3716篇
  2009年   3352篇
  2008年   4854篇
  2007年   5129篇
  2006年   4823篇
  2005年   4538篇
  2004年   4690篇
  2003年   4595篇
  2002年   4573篇
  2001年   8383篇
  2000年   8577篇
  1999年   6310篇
  1998年   1989篇
  1997年   2036篇
  1996年   1801篇
  1995年   1674篇
  1992年   5200篇
  1991年   5366篇
  1990年   5139篇
  1989年   5121篇
  1988年   4732篇
  1987年   4487篇
  1986年   4076篇
  1985年   4235篇
  1984年   3408篇
  1983年   2911篇
  1982年   1929篇
  1981年   1728篇
  1980年   1718篇
  1979年   3212篇
  1978年   2547篇
  1977年   2279篇
  1976年   2082篇
  1975年   2546篇
  1974年   2884篇
  1973年   2804篇
  1972年   2652篇
  1971年   2415篇
  1970年   2117篇
  1969年   2022篇
  1968年   1906篇
  1967年   1743篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
In this study we explore the relationships between intelligence test score, educational level, and degree of body fatness. We collected data on intelligence test score, educational level, height, and weight from a sample of 26,274 young Danish men and computed body mass index (weight/height2) as a measure of fatness. Both intelligence test score and educational level had maximum values below the median for body mass index and declined monotonically thereafter. The decline was equal for test score and educational level and above 32 kg/m2 corresponded to almost half a standard deviation. These results are not readily explained by stigmatization of frank obesity, and other mechanisms, possibly genetic, may be responsible.  相似文献   
996.
997.
998.
999.
Abstract. Lysosomal inhibitors (amino acid methyl esters) and platelet-derived growth factor stimulate resting NIH 3T3 cells to enter the S period. Incubation of cells in medium containing lysosomal inhibitors causes an increase in protein accumulation and does not disrupt lysosomes. The results indicate that proliferative homeostasis depends partially on the metabolic status of the cell and that catabolic processes activated in resting cells negatively influence prereplicative reactions.  相似文献   
1000.
Abstract. Haemagglutination activity was studied in last larval instars, pupae and adults of both sexes of the Culex pipiens mosquito complex. In females of Culex pipiens quinquefasciatus Say, an anautogenous member of C. pipiens complex, activity was detected in the homogenate of the head‐thorax complex, gut and remaining abdomen (after removing the gut), before and after sucking water, glucose solution or blood. Similar investigations were made in females of autogenous Culex pipiens molestus Forskal, a member of the same mosquito complex. The results were compared with data obtained for males of these subspecies, plus the larvae and pupae. The results show that haemagglutination activity in adult females depends not on the sucking of blood, but on the age of the females. In newly emerged females, the level of activity was very low, but after 24 h or 48 h of activity was highly enhanced, even in females that had no possibility to suck water or other liquids including blood. Furthermore, in C. p. molestus, the haemagglutination activity does not change in hungry or engorged females, and a high level of activity was found in the gut of last larval instars, a developmental stage that never takes blood. Treatment with methoprene reduces haemagglutination activity in both sexes, but 20‐hydroxycdysone application decreased activity in the gut of females. It is suggested that haemagglutination activity may be regulated indirectly by the endocrine system. The possibility that haemagglutination activity may depend on some aspect of the digestive system that has no direct connection to blood uptake is discussed. In addition, the activity may be important not only for the elimination of infections, but also for the processing of food and the utilization and transport of nutrients.  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