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   436264篇
  免费   42752篇
  国内免费   301篇
  2016年   5059篇
  2015年   6164篇
  2014年   7463篇
  2013年   11059篇
  2012年   12184篇
  2011年   12885篇
  2010年   8713篇
  2009年   7983篇
  2008年   11684篇
  2007年   12064篇
  2006年   11421篇
  2005年   10969篇
  2004年   10980篇
  2003年   10693篇
  2002年   10460篇
  2001年   18918篇
  2000年   19203篇
  1999年   14738篇
  1998年   5127篇
  1997年   5396篇
  1996年   5070篇
  1995年   4597篇
  1994年   4510篇
  1993年   4581篇
  1992年   12436篇
  1991年   12526篇
  1990年   12040篇
  1989年   11989篇
  1988年   11049篇
  1987年   10576篇
  1986年   9684篇
  1985年   9955篇
  1984年   8186篇
  1983年   6975篇
  1982年   5104篇
  1981年   4650篇
  1980年   4437篇
  1979年   7858篇
  1978年   6119篇
  1977年   5785篇
  1976年   5303篇
  1975年   6089篇
  1974年   6780篇
  1973年   6626篇
  1972年   6056篇
  1971年   5645篇
  1970年   5023篇
  1969年   4829篇
  1968年   4504篇
  1967年   3979篇
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
91.
International Journal of Primatology - The selection of sleeping sites and sleeping trees in nonhuman primates is related to social and ecological factors. We investigate the role of body...  相似文献   
92.

Background  

Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation.  相似文献   
93.
Systematic analysis of the long-chain components of Eubacterium lentum   总被引:1,自引:0,他引:1  
The cellular long-chain component patterns of 33 strains of Eubacterium lentum were determined by gas chromatography. Two main types of long-chain component patterns were distinguished. The first (26 strains) was characterized by saturated branched-chain fatty acids (br14:0, br15:0, br16:0 and br17:0). The second (7 strains) did not contain branched-chain fatty acids and was characterized by saturated straight-chain fatty acids (11:0, 12:0, 14:0 and 16:0). Both types contained fatty aldehydes and their respective dimethyl acetals (14ald and 14dma, 16ald and 16dma). br16dma was only found in the first type. The G + C content of the DNA (Tm) of the 33 strains varied between 63.7 and 69.1 mol %. Canonical correlation analysis distinguished three subtypes within the first main type.  相似文献   
94.
Experiments on frogs were performed to examine the effect of the M-cholinomimetic pilocarpine on the heart. It was discovered that at concentrations of 10(-15)--10(-5) g/ml pilocarpine exerted only an adverse chronotropic effect on the perfused heart. When applied at a concentration of 10(-4) g/ml the drug produced a negative as well as a positive chronotropic effect. The latter occurred spasmodically (without progressive rise in the heart rate) in association with a slow heart rate. In some experiments such effects were preceded by a certain deceleration of the heart. In experiments with positive chronotropic effects, arrhythmias and sinoatrial dissociation were observed sometimes. Experiments with recording of the electrograms of the sinuses and lower parts showed that such effects were caused not by pacemaker acceleration but by the removal of the blockade of conduction, between the pacemaker and the atria. As far as the pacemaker is concerned, pilocarpine exerted only a negative chronotropic effect.  相似文献   
95.
96.
Effect of B. pertussis lymphocytosis-promoting factor (LPF) on the lympho-hematopoietic system of mice was studied. The injection of LPF was shown to sharply enhance endogenous colony formation and to induce a severe depletion of thymus cells, reaching its maximum of day 4. Thymocytes obtained on day 2 or 3 after the injection of LPF produced a suppressive effect on endogenous colony formation. The proliferative activity of hematopoietic stem cells sharply increased under the influence of LPF, though it had no radioprotective action. On the following day after the injection of LPF a steep rise in the number of hematopoietic stem cells was observed in the blood of mice: their content increased 20-fold in comparison with the control level. These data may be important for the evaluation of the side effects of pertussis vaccine on the lympho-hematopoietic system.  相似文献   
97.
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   
98.
99.
100.
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