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   445581篇
  免费   51510篇
  国内免费   738篇
  497829篇
  2018年   4163篇
  2017年   4009篇
  2016年   5714篇
  2015年   8253篇
  2014年   9607篇
  2013年   12946篇
  2012年   15347篇
  2011年   15801篇
  2010年   10462篇
  2009年   9497篇
  2008年   13851篇
  2007年   14296篇
  2006年   13432篇
  2005年   12816篇
  2004年   12867篇
  2003年   12012篇
  2002年   11663篇
  2001年   18919篇
  2000年   18854篇
  1999年   15074篇
  1998年   5625篇
  1997年   5631篇
  1996年   5361篇
  1995年   5150篇
  1994年   4851篇
  1993年   4857篇
  1992年   12476篇
  1991年   12439篇
  1990年   12194篇
  1989年   11663篇
  1988年   10836篇
  1987年   10205篇
  1986年   9735篇
  1985年   9502篇
  1984年   7879篇
  1983年   6829篇
  1982年   5136篇
  1981年   4626篇
  1980年   4312篇
  1979年   7349篇
  1978年   5969篇
  1977年   5291篇
  1976年   4967篇
  1975年   5771篇
  1974年   6302篇
  1973年   6122篇
  1972年   5462篇
  1971年   5076篇
  1970年   4274篇
  1969年   4204篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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   
82.
83.
84.
85.
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   
86.
87.
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   
88.
89.
D-2 dopamine receptors in the frontal cortex of rat and human   总被引:2,自引:0,他引:2  
D R Liskowsky  L T Potter 《Life sciences》1985,36(16):1551-1559
D-2 dopamine receptors and serotonin receptors in the frontal cortex of rat and human were labelled with 3H-spiroperidol. The D-2 receptors were then distinguished in 4 ways. Dissociation of spiroperidol was biphasic, indicating two populations of sites. Cinanserin in competition with 3H-spiroperidol exhibited high (75%) and low (25%) affinity sites. Dopamine and LY 141865 in competition with 1.25 nM 3H-spiroperidol exhibited high (20-25%) and low (80-75%) affinity sites in the absence of cinanserin, while in the presence of 300 nM cinanserin only the high affinity sites remained. Lesioning of the dopaminergic meso-cortical pathway increased the number of cinanserin-resistant sites by 26%. Thus 3H-spiroperidol binding in the presence of cinanserin can be used to selectively label D-2 receptors in the frontal cortex.  相似文献   
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