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   226013篇
  免费   15224篇
  国内免费   50篇
  241287篇
  2021年   1834篇
  2018年   3232篇
  2017年   3144篇
  2016年   3773篇
  2015年   3313篇
  2014年   4562篇
  2013年   6556篇
  2012年   7787篇
  2011年   8293篇
  2010年   5922篇
  2009年   4989篇
  2008年   7270篇
  2007年   7516篇
  2006年   7217篇
  2005年   6722篇
  2004年   6869篇
  2003年   6581篇
  2002年   6530篇
  2001年   9287篇
  2000年   8963篇
  1999年   6995篇
  1998年   2131篇
  1997年   1959篇
  1996年   1826篇
  1992年   5478篇
  1991年   5682篇
  1990年   5654篇
  1989年   5626篇
  1988年   5218篇
  1987年   4867篇
  1986年   4447篇
  1985年   4680篇
  1984年   3703篇
  1983年   3026篇
  1982年   2018篇
  1981年   1725篇
  1980年   1728篇
  1979年   3338篇
  1978年   2581篇
  1977年   2381篇
  1976年   2336篇
  1975年   2827篇
  1974年   3119篇
  1973年   3093篇
  1972年   2750篇
  1971年   2606篇
  1970年   2213篇
  1969年   2160篇
  1968年   2032篇
  1967年   1801篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A quantitative electron microscopical investigation of the sinus node of the atrioventricular His' bundle and of the perinodal working myocardium in intact rats and 7, 15 and 30 days after right-sided vagotomy has revealed variable character of changes in the neural elements of the zones mentioned. Certain ultrastructural rearrangements in the neural apparatus are described; they reflect a combination of destructive and regenerative processes in the heart under vagotomy. Thirty days after the operation, regeneration of the neural elements in the sinoauricular area is of restorative and in the atrioventricular area--of excess character. The data are presented on dynamics of changes in the diameter of the amyelinated neural fibers in the cardiac areas investigated. Participation of both nervi vagi in innervation of the main and additional pacemakers of the organ is discussed.  相似文献   
992.
993.
994.
995.
The alkaloid composition of mycelium and culture liquid filtrate of the fungus Penicillium roqueforti IBPM-F-141 was studied. The new metabolite--3,12-dihydroroquefortine, a derivative of roquefortine, the main component of the alkaloid fraction of this culture, has been isolated for the first time. The structure of 3,12-dihydroroquefortine was determined by chemical and physico-chemical methods. In addition to roquefortine and 3,12-dihydroroquefortine, representatives of a new alkaloid group, the clavine alkaloids, e. g. isofumigaclavine A, isofumigaclavine B and festuclavine, were also isolated and identified. The data on the content of these compounds in mycelium and culture medium are presented.  相似文献   
996.
Supplementary effect of high temperature (37 degrees C) an hour after the treatment of mature sperms of Drosophila with ethylene imine resulted in an increased level of the inactivation (the frequency of dominant lethal mutation). The frequency of complete mutations (recessive sex-linked lethal mutations) increased by the supplementary effect of high temperature at low doses of E1, and it did not change under a comparatively high dose of the mutagen. The frequency of mosaic mutations decreased under the effect of high temperature at both doses of E1. No effect of high temperature was observed in 4 and 24 h after the E1 treatment. The results obtained are discussed in connection with the proportion of inactivation and mutagenesis under the effect of chemical mutagens on Drosophila germ cells.  相似文献   
997.
A selective uptake of ethanol by presenting its 5% solution as the only source of fluid was elaborated in rats for 2 months. It was found that lithium chloride injected intravenously in a dose of 35 mg/kg twice per 24 hours for 14 days depressed the ethanol preference causing a motivation inversion whose mechanism was associated with the changes in the activity of the hypothalamic centres of the neuroendocrine regulation. A possibility of lithium salts in the therapy of chronic alcoholism is discussed.  相似文献   
998.
A parallel histological and electron microscopic study of the capillary network of interalveolar septa has shown that in this microstructure there is only one two-dimensional capillary network, common for adjacent alveoles. In septal spaces of interalveolar septa the collagenic fibrils form an even thin network and additional collagenic bundles. The latter are mainly found in intercapillary septal spaces. The elastic fibres in interalveolar septa are found rarely, no interstitial cells being found at all.  相似文献   
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