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   443325篇
  免费   51463篇
  国内免费   719篇
  2018年   4166篇
  2017年   4009篇
  2016年   5720篇
  2015年   8260篇
  2014年   9609篇
  2013年   12950篇
  2012年   15346篇
  2011年   15801篇
  2010年   10464篇
  2009年   9499篇
  2008年   13851篇
  2007年   14300篇
  2006年   13432篇
  2005年   12814篇
  2004年   12867篇
  2003年   12011篇
  2002年   11660篇
  2001年   18897篇
  2000年   18836篇
  1999年   14947篇
  1998年   5423篇
  1997年   5412篇
  1996年   5136篇
  1995年   5143篇
  1994年   4850篇
  1993年   4849篇
  1992年   12473篇
  1991年   12432篇
  1990年   12189篇
  1989年   11661篇
  1988年   10825篇
  1987年   10202篇
  1986年   9729篇
  1985年   9501篇
  1984年   7876篇
  1983年   6824篇
  1982年   5139篇
  1981年   4623篇
  1980年   4311篇
  1979年   7346篇
  1978年   5962篇
  1977年   5289篇
  1976年   4958篇
  1975年   5770篇
  1974年   6301篇
  1973年   6115篇
  1972年   5457篇
  1971年   5074篇
  1970年   4273篇
  1969年   4200篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
993.
The influence of diet on the excretion of catecholamines, some of their metabolites, and pHPG, an octopamine metabolite, was examined. Two groups of rats were fed either a cereal-containing standard laboratory Purina rat chow or a cereal-free casein diet. Use of the standard chow resulted in significant increases in the urinary values for total MHPG, pHPG, DHPE, MHPE, and free and total DOPAC by the seventh day in comparison to the casein diet. No changes were noted in the excretion of free and total NE, DA, and HVA. The data indicate that it is necessary to place the animals on the casein diet several days before determining the excretion of the aforementioned metabolites.  相似文献   
994.
995.
The purification procedure of 6,6′-diesters of trehalose from Corynebacterium diphtheriae was modified and the isolated substance was analysed by mass spectrometry as its permethylated derivative. The fatty acid moiety released from the glycolipid after alkaline hydrolysis was studied by mass spectral analysis of the O-methylated and O-acetylated methyl ester derivatives. By argentation thin-layer chromatography, three species of O-acetylated methyl esters were recognized, corresponding to saturated, mono-unsaturated and di-unsaturated α-branched-β-hydroxylated fatty acids. The double bond was located by ozonolysis of the O-acetylated methyl ester derivatives, by gas chromatography of the reaction product and mass spectrometry of the effluent from the gas chromatograph. The main components of each species of α-branched-β-hydroxylated fatty acids found in the gly colipid fraction of C. diphtheriae were 2-tetradecyl-3-hydroxyoctadecanoic acid (C32H64O3, corynomycolic acid), 2-tetradecyl-3-hydroxy-11-octadecenoic acid (C32H62O3, corynomycolenic acid), 2-tetradec-7′-enyl-3-hydroxy octadecanoic acid (C32H62O3) and 2-tetradec-7′-enyl-3-hydroxy-11-octadecenoic acid (C32H60O3, corynomycoldienic acid). The glycolipid fraction from C. diphtheriae is obviously a complex mixture of 6,6′-diesters of trehalose.  相似文献   
996.
The biological and immunological activities of Staphylococcal enterotoxin B are stable in pH 2.0 approximately 11.0, and also resistant to proteolytic enzyme (trypsin, pepsin) digestion for 3 approximate 4 hours. Therefore, the toxin could be purified with trypsin digest and then absorbed on kaolin and Kieselgel, followed by eluting the different pH buffer solutions. Further purifications was chromatographied on CM-Sephadex column.  相似文献   
997.
998.
999.
Although the use of hypochlorite to disinfect seeds is widespread, the effects on tissues isolated from them have been largely ignored. Disinfection of barley ( Hordeum vulgare L. cv. Himalaya) half-seeds with hypochlorite solutions of ≥1.0% (w/v) available chlorine caused the pericarp to separate from the underlying tissues. Aleurone layers isolated from these grains had lower rates of oxygen consumption and released significantly less protein, PO43− Mg2+, K+ and amylase (EC 3.2.1.1) into the medium in response to gibberellic acid (GA3) than layers isolated from grains disinfected with a 0.1% hypochlorite solution. Disinfection with 1.0% hypochlorite also quantitatively altered the spectrum of proteins released into the incubation medium by the layers in response to GA3.  相似文献   
1000.
A study was made of the chronic effect of pesticides, within a wide range of doses, combined with whole-body gamma-irradiation, on the content of carbohydrate-containing proteins of rat liver. The extent to which disturbances in the carbohydrate-containing protein metabolism were manifest was shown to depend upon dose and time of action of the damaging factors. As determined by certain parameters, the combined effect of pesticides and gamma-radiation at the biochemical level was additive, and it was more than additive as estimated by a number of other tests.  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