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   597440篇
  免费   54035篇
  国内免费   997篇
  2018年   16523篇
  2017年   15206篇
  2016年   14782篇
  2015年   12082篇
  2014年   12922篇
  2013年   18367篇
  2012年   24579篇
  2011年   31623篇
  2010年   23978篇
  2009年   18947篇
  2008年   26238篇
  2007年   27747篇
  2006年   17080篇
  2005年   16213篇
  2004年   16186篇
  2003年   15546篇
  2002年   14699篇
  2001年   20769篇
  2000年   20767篇
  1999年   16922篇
  1998年   6217篇
  1997年   6377篇
  1996年   6110篇
  1995年   5590篇
  1994年   5692篇
  1993年   5490篇
  1992年   13925篇
  1991年   13251篇
  1990年   13079篇
  1989年   12959篇
  1988年   11853篇
  1987年   11204篇
  1986年   10350篇
  1985年   10505篇
  1984年   8566篇
  1983年   7434篇
  1982年   5693篇
  1981年   5070篇
  1980年   4875篇
  1979年   8154篇
  1978年   6303篇
  1977年   5636篇
  1976年   5452篇
  1975年   5895篇
  1974年   6138篇
  1973年   6077篇
  1972年   5646篇
  1971年   5097篇
  1970年   4274篇
  1969年   3964篇
排序方式: 共有10000条查询结果,搜索用时 594 毫秒
991.
Rats were trained to run spontaneously, without stress, in running wheels. The running activity increased gradually and could reach a plateau of 7 km/night after 3–4 weeks. During the first hour of running in the dark phase the squeak threshold increased significantly and remained high in the morning. The degree of increased threshold was correlated to the amount of running activity. The squeak threshold declined during the following 6 hours of inactivity. A rapid decrease in threshold occurred after naloxone (1–2 mg/kg i.p.). It is suggested that long-lasting muscle exercise (e.g. jogging), acupuncture, and low frequency electrical stimulation of afferent nerve fibres produce discharges in muscle afferents which influence central endorphin mechanics giving analgetic effects.  相似文献   
992.
993.
Spin-echo NMR spectroscopy was shown to be a reliable technique for the monitoring of the in situ cleavage of gamma-Glu-Ala by gamma-glutamyl-amino acid cyclotransferase in whole erythrocytes and hemolysates. Of particular importance was the difference in chemical shifts between peptide resonances and those of the constituent amino acids. Using lysates of varying dilution, it was shown that the specific activity of the enzyme was not concentration-dependent, thus suggesting a lack of cytosolic low-molecular-weight-effectors or enzyme dissociation. Furthermore, the initial velocities of the reaction as a function of substrate concentration obeyed Michaelis-Menten kinetics with a Km = 2.0 +/- 0.3 mmol/l and Vmax = 137 +/- 7 mmol/h/l of cell water in 1H2O medium. Similar analysis in 2H2O medium revealed a solvent kinetic isotope effect of 1.9 +/- 0.4 at low substrate concentrations. The implications of this observation for the mechanism of the reaction are discussed. Cleavage of the peptide by a suspension of intact erythrocytes was at a rate 300 times less than the corresponding lysate flux, thus indicating the rate limitation by transport in the coupled system.  相似文献   
994.
995.
996.
997.
C. P. W. Warren  K. S. Tse 《CMAJ》1974,110(4):425-427,429
Using a solid-phase radioimmunoassay, serum IgE level was determined in 46 normal subjects, 53 patients with bronchial asthma, 44 patients with chronic bronchitis and / or emphysema, and 19 patients with restrictive lung disease. Sputum IgE was measured simultaneously in 51 of the subjects. The range of serum IgE concentration in the normal subjects was wide. It varied between 15 and 750 ng/ml with a mean of 135 ng. Asthmatic patients had significantly higher levels of serum IgE with a mean of 579 ng/ml, but only 30% fell outside the normal 95% confidence limits. Patients with chronic bronchitis, emphysema and restrictive lung diseases had normal IgE levels. There was a significant correlation between serum and sputum IgE levels.  相似文献   
998.
999.
1000.
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