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   250779篇
  免费   23074篇
  国内免费   311篇
  2018年   2815篇
  2017年   2765篇
  2016年   3656篇
  2015年   4055篇
  2014年   4964篇
  2013年   7043篇
  2012年   7778篇
  2011年   8427篇
  2010年   5759篇
  2009年   5121篇
  2008年   7260篇
  2007年   7424篇
  2006年   7015篇
  2005年   6673篇
  2004年   6591篇
  2003年   6348篇
  2002年   6221篇
  2001年   12071篇
  2000年   12003篇
  1999年   9190篇
  1998年   2712篇
  1997年   2786篇
  1996年   2727篇
  1995年   2510篇
  1994年   2455篇
  1993年   2353篇
  1992年   7199篇
  1991年   7005篇
  1990年   7085篇
  1989年   6867篇
  1988年   6374篇
  1987年   6025篇
  1986年   5366篇
  1985年   5683篇
  1984年   4488篇
  1983年   3878篇
  1982年   2694篇
  1981年   2509篇
  1980年   2318篇
  1979年   4120篇
  1978年   3145篇
  1977年   2890篇
  1976年   2837篇
  1975年   3279篇
  1974年   3502篇
  1973年   3527篇
  1972年   3060篇
  1971年   2847篇
  1970年   2531篇
  1969年   2302篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Morphofunctional indices of pyracryl (phosphate poly-2-pyridylethylmethacrilate) effecting reproduction system of Wistar rats have been studied. It has been shown that monthly administration of pyracryl in doses 1 mg/kg and 5 mg/kg lead to infiltration of mast cells and their pronounced degranulation and impairment of blood and lymph microcirculation. As far as gonadotropic effect is concerned, its parametres depend on the administration of pyracryl. Pyracryl in doses of 1 mg/kg stimulates folliculogenesis in ovaries, a dose of 5 mg/kg may cause expressed atresia of growing follicules and changes of oestrous cycle. It is suggested that biologically active substances of mast cells in female reproduction system play an important role in realization of gonadotropic effects of pyracryl.  相似文献   
992.
Five popular but iron-inefficient cultivars were crossed with three efficient genotypes and both parents and F1s were evaluated for iron-efficiency in potted calcareous and noncalcareous soil. The iron-efficient genotypes were dark green or green in both noncalcareous and calcareous soils whereas inefficient types were light green to yellow in calcareous soil. The chlorophyll and active iron (Fe2+) concentration of leaves was less in iron-efficient genotypes compared to efficient types in calcareous soil and reduction of both the parameters from noncalcareous to calcareous soil was considerably high in iron-inefficient lines. There was significant correlation between visual scores, chlorophyll and active iron content. There were no differences among F1s for iron chlorosis and they were all iron-inefficient. The frequency of iron-inefficient plants was higher than the efficient plants in all F2 populations. But most of the productive plants came from iron-efficient segregants indicating strong association between iron-efficiency and productivity. Based on the results selection for iron-efficiency in early generations and extensive evaluation for productivity in advanced generations is suggested for developing varieties for cultivation in calcareous soils.  相似文献   
993.
Fedorov  D. A.  Frolova  M. Yu.  Krasovskaya  I. E.  Kuleva  N. V. 《Biophysics》2019,64(5):808-811
Biophysics - Abstract—The goal of the present study was to investigate the molecular mechanisms that underlie heart and skeletal muscle damage in male Wistar rats weighing 200–250 g in...  相似文献   
994.
995.
Aptamers constitute a potential class of therapeutic molecules typically selected from a large pool of oligonucleotides against a specific target. With a scope of developing unique shorter aptamers with very high biostability and affinity, locked nucleic acid (LNA) nucleotides have been investigated as a substrate for various polymerases. Various reports showed that some thermophilic B-family DNA polymerases, particularly KOD and Phusion DNA polymerases, accepted LNA-nucleoside 5′-triphosphates as substrates. In this study, we investigated the docking of LNA nucleotides in the active sites of RB69 and KOD DNA polymerases by molecular docking simulations. The study revealed that the incoming LNA-TTP is bound in the active site of the RB69 and KOD DNA polymerases in a manner similar to that seen in the case of dTTP, and with LNA structure, there is no other option than the locked C3′-endo conformation which in fact helps better orienting within the active site.  相似文献   
996.
The amino acid composition of cell walls and surface proteins, isolated from virulent (M+) and avirulent (M-) streptococcal strains (group A, type 29) has been determined by the method of E. H. Beachey et al. The kinetics of the lysis and proteolysis of streptococcal cell walls with muramidase and protease obtained from Actinomyces levoris and streptolysin has been studied. The constants describing the progress rates of these processes has been determined; their values in case of both lysis and proteolysis are higher in virulent strains than in avirulent ones.  相似文献   
997.
Protein I (PI) is the most abundant protein on the gonococcal cell surface and besides its porin function it may have important properties contributing to pathogenicity. By allelic exchange using cloned PI genes from FA19 (PIA) and MS11 (PIB) and a selectable marker introduced closely downstream of these genes, we constructed sets of isogenic gonococcal strains that differ only in their PI gene. Analysis revealed that PI has a major effect on stable resistance to normal human serum, and a slight effect on low-level resistance to antibiotics. All PIA/B hybrids were hypersusceptible to serum, suggesting a possible explanation for why such hybrids do not occur in nature.  相似文献   
998.
999.
Custom prefabrication of free flaps provides an unlimited variety of applications, since flaps can be created with expendable tissues and without restriction to naturally occurring vascular territories. These principles also can be used to customize flaps that could not be completed by conventional means. We report a case of scalp reconstruction using a random-pattern abdominal flap in which a radial artery fascial flap was induced to serve as the vascular carrier. In addition to providing durable scalp coverage, the prefabricated free flap enabled salvage of an abdominal flap that would otherwise have been aborted after intermediate transfer to the forearm.  相似文献   
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