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   499290篇
  免费   55783篇
  国内免费   775篇
  555848篇
  2018年   4901篇
  2017年   4685篇
  2016年   6901篇
  2015年   10346篇
  2014年   11789篇
  2013年   15903篇
  2012年   19043篇
  2011年   19456篇
  2010年   12906篇
  2009年   11648篇
  2008年   16963篇
  2007年   17459篇
  2006年   16394篇
  2005年   15797篇
  2004年   15839篇
  2003年   14810篇
  2002年   14453篇
  2001年   19585篇
  2000年   19334篇
  1999年   15729篇
  1998年   6394篇
  1997年   6188篇
  1996年   5895篇
  1995年   5702篇
  1994年   5372篇
  1993年   5391篇
  1992年   12979篇
  1991年   12878篇
  1990年   12564篇
  1989年   12035篇
  1988年   11217篇
  1987年   10520篇
  1986年   10060篇
  1985年   9873篇
  1984年   8293篇
  1983年   7166篇
  1982年   5570篇
  1981年   5004篇
  1980年   4641篇
  1979年   7584篇
  1978年   6246篇
  1977年   5553篇
  1976年   5185篇
  1975年   5980篇
  1974年   6520篇
  1973年   6321篇
  1972年   5577篇
  1971年   5196篇
  1970年   4401篇
  1969年   4312篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
71.
Antibodies to calcitonin, parathyroid hormone and cortisol are detected in acute stage of infection-caused bronchial asthma. The appearance of antibodies is paralleled by marked hypercalcaemia. The antibodies may bind excessive hormones in the blood, preventing further hormonal imbalance. Ten-day treatment with glucocorticoids decreased the amount of antibodies possibly due to normalization of hormonal secretion and restoration of their balance. As a result, calcium blood levels returned to normal.  相似文献   
72.
73.
74.
75.
76.
A random sample of schoolchildren, 119 boys and 153 girls, was tested in the fall of 1983. The data presented here are anthropometric data (height, weight, fat % and vital capacity) and oxygen uptake directly measured on a bicycle ergometer. The mean height and weight for boys were 179.1 cm and 67.7 kg, and those for girls were 168.0 cm and 59.6 kg. The mean fat content was 9.1% for boys and 19.1% for girls, and their mean vital capacities were 4.91 and 3.61 respectively. The boys had a high maximal oxygen uptake (51.7 ml X kg-1 X min-1) showing no reduction over the age span studied. The girls' maximal oxygen uptake was lower (overall mean 40.0 ml X kg-1 X min-1) with a small reduction from 16 to 19 years of age. When comparing maximal oxygen uptake per kg lean body mass in the two sexes, the boys had 18.4% higher values than the girls, indicating that girls of this age have the lower fitness level. The results of maximal aerobic power measurement in the boys compare well with findings from other investigations using direct measurements, indicating that the fitness of teenage boys is kept at a high level. Comparable data from various countries for girls show different pictures, but it appears that in general they have a low fitness level.  相似文献   
77.
78.
79.
The nicotinic acid hydroxylase from Clostridium barkeri is a selenoenzyme, as evidenced by the copurification of selenium with enzyme activity. This conclusion is supported by data showing a 23-fold increase in nicotinic acid hydroxylase activity when C. barkeri was cultured in media supplemented with selenium. A labile, selenium-containing compound was released from the native protein by treatment with either chaotropic agents and heat or by heating alone. A stable selenium compound was formed when the enzyme was alkylated prior to denaturation. This compound had the same chromatographic properties as dialykyl selenide in a number of systems. The formation of dialkyl selenide upon alkylation is not consistent with the selenium moiety being selenocysteine. Thus, nicotinic acid hydroxylase represents a new type of selenoenzyme.  相似文献   
80.
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