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   493629篇
  免费   55400篇
  国内免费   778篇
  549807篇
  2021年   4391篇
  2018年   5242篇
  2017年   4978篇
  2016年   7214篇
  2015年   10376篇
  2014年   11703篇
  2013年   15596篇
  2012年   18393篇
  2011年   18595篇
  2010年   12204篇
  2009年   11196篇
  2008年   15924篇
  2007年   16329篇
  2006年   15297篇
  2005年   14954篇
  2004年   14982篇
  2003年   13818篇
  2002年   13046篇
  2001年   20048篇
  2000年   19953篇
  1999年   16031篇
  1998年   6105篇
  1997年   6066篇
  1996年   5848篇
  1995年   5537篇
  1994年   5243篇
  1993年   5225篇
  1992年   13201篇
  1991年   13081篇
  1990年   12788篇
  1989年   12251篇
  1988年   11428篇
  1987年   10743篇
  1986年   10237篇
  1985年   10001篇
  1984年   8338篇
  1983年   7189篇
  1982年   5431篇
  1981年   4907篇
  1980年   4577篇
  1979年   7705篇
  1978年   6273篇
  1977年   5529篇
  1976年   5167篇
  1975年   6018篇
  1974年   6551篇
  1973年   6362篇
  1972年   5638篇
  1971年   5230篇
  1970年   4392篇
排序方式: 共有10000条查询结果,搜索用时 0 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.
Reactivity of histidine residues in equine growth hormone to ethoxyformic anhydride was studied. The existence of two kinetically different sets was demonstrated: one of them including only the slow reacting histidine 169 (k = 0.164 min-1) and the other containing fast reacting histidines 19 and 21 (k = 0.892 min-1). A correlation between the decrease in the capacity to compete with 125I-labeled hormone for rat liver binding sites and the degree of ethoxyformylation of the fast group was found. Circular dichroism studies indicated no significant conformational changes in the protein with all three residues modified. These results fully agree with those obtained for bovine growth hormone which is further evidence supporting the vinculation of histidines 19 and/or 21 with the binding site of these hormones to their specific receptors.  相似文献   
83.
84.
85.
86.
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   
87.
88.
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   
89.
90.
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   
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