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   79422篇
  免费   5234篇
  国内免费   10篇
  2023年   589篇
  2022年   536篇
  2021年   1204篇
  2020年   1057篇
  2019年   1063篇
  2018年   2442篇
  2017年   2289篇
  2016年   2881篇
  2015年   3670篇
  2014年   3734篇
  2013年   5093篇
  2012年   6323篇
  2011年   5933篇
  2010年   3526篇
  2009年   2707篇
  2008年   4662篇
  2007年   4461篇
  2006年   4181篇
  2005年   3654篇
  2004年   3500篇
  2003年   3162篇
  2002年   2865篇
  2001年   1613篇
  2000年   1681篇
  1999年   1239篇
  1998年   556篇
  1997年   399篇
  1996年   413篇
  1995年   393篇
  1994年   327篇
  1993年   299篇
  1992年   635篇
  1991年   536篇
  1990年   469篇
  1989年   447篇
  1988年   441篇
  1987年   400篇
  1986年   364篇
  1985年   381篇
  1984年   400篇
  1983年   268篇
  1982年   266篇
  1981年   206篇
  1980年   222篇
  1979年   244篇
  1978年   242篇
  1975年   232篇
  1974年   245篇
  1973年   242篇
  1972年   197篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Eine nèue foliikole Flechte (Pleurotrema epiphylla sp. n.) aus Zaïre (Zentral-Afrika) wird beschrieben. Die systematischen Beziehungen der neuen Art zu den anderenPleurotrema-Arten und die Stellung der GattungPleurotrema innerhalb der FamilieParatheliaceae wird kurz diskutiert.  相似文献   
992.
993.
994.
Peanut agglutinin (PNA), a lectin specific for terminal d-galactosyl residues, was found to react with embryonal carcinoma cells, but not with their differentiated derivatives. Receptors for PNA were detectable at the surface of all cells of the quasinullipotent F9 line and on only 50% of the multipotent PCC3/A/1 line. The fraction of the PCC3/A/1 population which expresses the F9 antigen was found to be included in the subpopulation carrying the PNA receptors. PNA+ and PNA? subpopulations of PCC3/A/1 were separated by a PNA-mediated reversible agglutination of PNA+ cells with rabbit erythrocytes. These subpopulations were essentially F9+ and F9?, respectively.  相似文献   
995.
996.
The effect of ten derivatives of carbonylcyanide phenylhydrazone on growth of bacteria, yeast and different species of filamentous fungi was investigated. In yeast and mitochondria isolated from rat liver the effect of these derivatives on the respiratory activity was also followed. The relative efficiency of the individual derivatives of earbonylcyanide phenylhydrazone was determined on the basis of the results obtained. It was shown that derivatives, in which the substituent on the benzene ring causes simultaneously an increase of acidity and lipophilicity of the derivative as compared with the non-substituted carbonylcyanide phenylhydrazone (4-trifluoromethoxy-, 3-chloro-, 4-chloro and 3,4-dichloroderivatives) were most effective.  相似文献   
997.
Proteins of a crude enzyme preparation obtained from the cultivation medium of the basidiomycetePhellinus abietis were separated by gel filtration and ion-exchange chromatography. The preparation contained a minimum of three enzymes capable of splitting α-d-mannosidic bonds: α-mannosidase, exomannanase, and endomannanase, which were separated. Some properties of the mannanase complex of the crude enzyme preparation, and of a partially purified α-mannosidase were examined. The mannanase complex exhibited two pH optima, its temperature optimum being at 46 °C The pH optimum of purified α-mannosidase was at pH 5.0, the temperature optimum was at 60 °C; the enzyme had a relatively high heat stability. The Km of α-mannosidase forp-nitrophenyl α-d-mannopyranoside was 1.5 x 10−5 M. Pure α-mannosidase did not split mannan.  相似文献   
998.
The discovery of Foraminifera and Ostracodesin the dark green, sandy-glauconitic marl clay in the Joux Valley (in the Vaudois Jura) suggests to date these sediments Middle and Upper Albian. The Ostracode associations are similar to those found in the Paris Basin, but different from those which characterize the subalpine region.  相似文献   
999.
1000.
Crystal-containing organelles in cells of virus infected plants lying at chloroplasts and mitochondria are identical with single membrane-bound microbodies containing crystals of catalase described in healthy plants. Massive complex inclusions caused by turnip mosaic virus very frequently contain the same microbodies with crystal inclusions; that phenomenon may be related to some pathophysiological changes of virus infected plants. Comparable proteinaceous crystals, but not lying within microbodies limited by a membrane, may also be found in cytoplasm of infected cells. These crystals are sometimes surrounded by a substance resembling the microbody matrix. Disintegrated cytoplasm of virus infected cells may also contain the same crystals lying free in “empty spaces”. Cytopathological effects responsible for this phenomenon and possible artifacts as well are discussed.  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