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   846383篇
  免费   94392篇
  国内免费   480篇
  941255篇
  2018年   7785篇
  2017年   7617篇
  2016年   10476篇
  2015年   13573篇
  2014年   16043篇
  2013年   23575篇
  2012年   26199篇
  2011年   26695篇
  2010年   17959篇
  2009年   16605篇
  2008年   23628篇
  2007年   24332篇
  2006年   22937篇
  2005年   21928篇
  2004年   21771篇
  2003年   20712篇
  2002年   20247篇
  2001年   40966篇
  2000年   40967篇
  1999年   32506篇
  1998年   10911篇
  1997年   11563篇
  1996年   10894篇
  1995年   10012篇
  1994年   9916篇
  1993年   9780篇
  1992年   26473篇
  1991年   25350篇
  1990年   24870篇
  1989年   24373篇
  1988年   22403篇
  1987年   21109篇
  1986年   19645篇
  1985年   19588篇
  1984年   15956篇
  1983年   13678篇
  1982年   10361篇
  1981年   9212篇
  1980年   8852篇
  1979年   15106篇
  1978年   11703篇
  1977年   10639篇
  1976年   9895篇
  1975年   10846篇
  1974年   11569篇
  1973年   11334篇
  1972年   10381篇
  1971年   9326篇
  1970年   8137篇
  1969年   7580篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Slash pine needles and cortex oleoresin have been found to contain a new major diterpene constituent, imbricataloic acid. The closely related imbricatoloic acid, previously reported only in Araucaria imbricata, was found to be present in small amounts in slash pine needle extract. Spectral data are given for an unidentified diterpene alcohol isolated from the cortex oleoresin.  相似文献   
992.
Chromosomal RNA: an artifact of preparation?   总被引:2,自引:0,他引:2  
  相似文献   
993.
994.
995.
996.
Significant adverse correlation of the fetus mass and the degree of its hydration was noted at term in rats with placental insufficiency induced by ligation of about 40% of preplacental vessels on the 16th day of gestation. Disorders revealed in transplacental water-salt metabolism are apparently of some importance for the pathogenesis of fetal growth retardation. Even moderate retardation alters fetal respiratory activity in anoxia, which is associated with the changes in the function of respiratory centres and neuromuscular abnormalities.  相似文献   
997.
The authors analyze the results of comparative studies on 15 paired sera from children with suspected measles, of 32 sera from children and adolescents aged 1.5 to 16 immunized against measles, and of 21 sera from adults aged 19 to 86 with a history of the disease. EIA proved to be more sensitive than HAIT: the detection rate of positive sera was higher, as were the titers of antibodies detected by it, in examinations of the sera from vaccinated children and the adults. Analysis of the distribution of sera with different titers of antibody to measles virus in EIA and HAIT has revealed a correlation between the titers in the sera with high antibody levels. In the cases with low antihemagglutinin titers, no correlation between the titers determined in the two tests has been observed.  相似文献   
998.
Endogenous inhibitors for calcium-activated neutral protease (CANP) were purified from rabbit erythrocytes and liver. The purified inhibitors showed single bands but with significantly different mobilities on sodium dodecylsulfate-polyacrylamide gel electrophoresis. Peptide mapping and sequencing analyses have revealed that the erythrocyte inhibitor (429 residues) retains the C-terminal three repetitive units of the liver inhibitor (639 residues), which contains four potential repetitive units for inhibition of CANP. The erythrocyte and liver inhibitors inhibited 3 and 4 moles of CANP on the basis of the molecular weights of 46,000 and 68,000, respectively.  相似文献   
999.
1000.
The main condition of completing the process of adaptation of the body to the effect of an external factor is the return of the homeostatic system parameters to their initial levels or their stabilization at a new level. The article considers the state of incomplete adaptation (IA) based on the process of the stabilization of systemic reactions (respiration and blood circulation) on repeated exposure to extreme environmental factors (hypoxia and cold) associated with the excitation of the central regulatory mechanisms of the respiratory center system performing a compensatory–protective function. It is postulated that a change in the afferent information flows (the thresholds of excitation and reactivity of the peripheral receptor systems) forms the basis of IA. The IA state is supposed to persist for an indefinitely long period of time due to insufficient functional reserves and to be the cause of psychosomatic pathology.  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