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   323750篇
  免费   21376篇
  国内免费   174篇
  345300篇
  2021年   3028篇
  2020年   2416篇
  2019年   2809篇
  2018年   5537篇
  2017年   5124篇
  2016年   6600篇
  2015年   7222篇
  2014年   8649篇
  2013年   11953篇
  2012年   13952篇
  2011年   13770篇
  2010年   9598篇
  2009年   7862篇
  2008年   11866篇
  2007年   11880篇
  2006年   11553篇
  2005年   10409篇
  2004年   10609篇
  2003年   9960篇
  2002年   9790篇
  2001年   11898篇
  2000年   11381篇
  1999年   8935篇
  1998年   3067篇
  1997年   2720篇
  1996年   2561篇
  1995年   2347篇
  1992年   6742篇
  1991年   6851篇
  1990年   6765篇
  1989年   6733篇
  1988年   6144篇
  1987年   5804篇
  1986年   5326篇
  1985年   5638篇
  1984年   4552篇
  1983年   3774篇
  1982年   2620篇
  1979年   4173篇
  1978年   3203篇
  1977年   3056篇
  1976年   2970篇
  1975年   3549篇
  1974年   3895篇
  1973年   3831篇
  1972年   3409篇
  1971年   3203篇
  1970年   2838篇
  1969年   2834篇
  1968年   2707篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
721.
The acarological+ study of dust samples from the homes of allergic patients and normal persons in Moscow mite antigens were detected, respectively, in 66.7% and 38.1% of homes. The indirect mast cell degranulation test and the brain gliacyte volume change test in white rats gave similar results. The occurrence of Dermatophagoides pteronyssinus was approximately twice as great of D. farinae, and the numerical prevalence of the former species over the latter one was 1.3-fold. Dermatophagoides mites occurred in the homes of allergic patients 1.8-2.3 times as frequently as in the homes of normal persons.  相似文献   
722.
The production of virus-neutralizing antibodies in high titers has been found to occur in persons immunized with tissue-culture rabies vaccines, concentrated and non concentrated, intramuscularly in a dose of 1 ml in accordance with reduced immunization schedules.  相似文献   
723.
Human and animal blood smear staining with PAPh has revealed mononuclear leukocyte-erythrocyte aggregates. Administration of retinoic acid increased concentration and dimensions of these aggregates and was followed by preferential accumulation of PAPh-negative osmotically unstable erythrocytes. Similar changes were detected in the blood samples of women engaged in the production of retinoic acid. Aggregate concentration showed positive correlation with erythrocyte sedimentation rate and no correlation with prothrombin time.  相似文献   
724.
Experiments on E. coli used as a model have revealed that fatty-acid composition is one of the characteristics which determine the viability of bacteria in the air. The viability of microbial cells in the air has been shown to increase with the increase of the pool of cyclopropane acids and the palmitic acid/palmitoleic acid ratio in the cells, irrespective of their genotype and the phase of their growth.  相似文献   
725.
726.
727.
The stimulating influence of glucose-containing muramyldipeptide (GMDP) on the nonspecific resistance of mice was shown to depend on the features of the pathogenesis of the infection. Thus, the intraperitoneal injection of GMDP increased the survival rate of mice infected with Escherichia coli, but had no stimulating effect on the resistance of the animals to Salmonella typhimurium natural infection in whose pathogenesis macrophages played an essential role. Experiments demonstrated that GMDP was capable of enhancing the ingestive function of macrophages, but did not increase their bactericidal activity with respect to this infection.  相似文献   
728.
Reversible inactivation of soluble liver guanylate cyclase by disulfides   总被引:1,自引:0,他引:1  
A new amino acid was isolated from the cuticle collagen of Ascaris lumbricoides and characterized by ultraviolet, mass and nmr spectroscopies and chemical degradation. The results indicate that the compound is an isomer of trityrosine, having an ether linkage. The name “isotrityrosine” is proposed. Its structure suggests that it serves as a crosslink and plays a role in the organization of the collagen structure.  相似文献   
729.
The authors studied the effect of dithiothreitol (DTT), carotenoids and protease inhibitors on stabilization and protection of the enzyme catalysing the conversion of beta-carotene into retinal during the enzyme isolation from the rabbit small intestine. The addition of 1 mM DTT into the homogenization mixture increased the activity of the enzyme 5 times compared with control. The additional introduction of 0.7 mg/ml soybean trypsin inhibitor or 2.10(-4) M phenylmethylsulfonyl fluoride increased the enzyme activity 2.1 and 1.2 times, respectively. Lutein, beta-carotene and lycopene at a concentration of 10 mg/ml increased the enzyme activity 2.1, 1.9 and 1.6 times respectively. The effects of DTT, lutein and the protease inhibitor depended on their concentrations and was of an independent additive character. The maximum activity of the isolated enzyme exceeded the control without DTT 15 times.  相似文献   
730.
A preliminary survey of the few units of the small-scale glass bangle industry in Firozabad, Agra District, Uttar Pradesh, indicated that the workers were exposed to severe degrees of heat stress during various operations in the manufacturing processes. A more detailed study in eight glass bangle units was therefore undertaken to make quantitative estimates of heat stress on exposed workers in the summer season. The thermal data collected confirmed that the heat stress on the workers was severe but measurement of certain physiological indicators revealed relatively low levels of strain amongst the exposed workers. The findings could be attributable to high degrees of acclimatization, but further observations in the field supplemented by studies on simulated exposures of volunteers in a climatic chamber seem to be warranted.  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