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   252441篇
  免费   23257篇
  国内免费   264篇
  275962篇
  2018年   2713篇
  2017年   2633篇
  2016年   3555篇
  2015年   3865篇
  2014年   4814篇
  2013年   6879篇
  2012年   7617篇
  2011年   8284篇
  2010年   5672篇
  2009年   5053篇
  2008年   7312篇
  2007年   7527篇
  2006年   7104篇
  2005年   6814篇
  2004年   6723篇
  2003年   6579篇
  2002年   6372篇
  2001年   12133篇
  2000年   12057篇
  1999年   9250篇
  1998年   2787篇
  1997年   2818篇
  1996年   2781篇
  1995年   2552篇
  1994年   2513篇
  1993年   2405篇
  1992年   7267篇
  1991年   7062篇
  1990年   7136篇
  1989年   6917篇
  1988年   6423篇
  1987年   6083篇
  1986年   5439篇
  1985年   5755篇
  1984年   4556篇
  1983年   3947篇
  1982年   2757篇
  1981年   2569篇
  1980年   2378篇
  1979年   4182篇
  1978年   3195篇
  1977年   2944篇
  1976年   2879篇
  1975年   3319篇
  1974年   3562篇
  1973年   3574篇
  1972年   3098篇
  1971年   2863篇
  1970年   2571篇
  1969年   2320篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Evidence is presented for the assignment of seven fox genes on the basis of the segregation data for chromosomes and enzymes of fox x Chinese hamster somatic cell hybrids. The chromosomal loci of the following enzyme genes were determined: ME1, VFU1; ADK and PP, VFU4; PEPA, VFU5; GSR, VFU7; and MPI and GOT1, VFU15. The localization of these genes now extends the fox genetic map to 22 mapped genes. Based on comparative analysis of mammalian genetic maps, karyotype evolution in Carnivora is discussed.  相似文献   
912.
Rearrangement of Fusarium oxysporum retro- transposon skippy was induced by growth in the presence of potassium chlorate. Three fungal strains, one sensitive to chlorate (Co60) and two resistant to chlorate and deficient for nitrate reductase (Co65 and Co94), were studied by Southern analysis of their genomic DNA. Polymorphism was detected in their hybridization banding pattern, relative to the wild type grown in the absence of chlorate, using various enzymes with or without restriction sites within the retrotransposon. Results were consistent with the assumption that three different events had occurred in strain Co60: genomic amplification of skippy yielding tandem arrays of the element, generation of new skippy sequences, and deletion of skippy sequences. Amplification of Co60 genomic DNA using the polymerase chain reaction and divergent primers derived from the retrotransposon generated a new band, corresponding to one long terminal repeat plus flanking sequences, that was not present in the wild-type strain. Molecular analysis of nitrate reductase-deficient mutants showed that generation and deletion of skippy sequences, but not genomic amplification in tandem repeats, had occurred in their genomes.  相似文献   
913.
914.
In experiments on Wistar rats the cytotoxic activity of NK on the 1, 2, 10 days after partial hepatectomy (PH) and the application of Rodiola extract (RE) was studied. After 5 injections of RE the NK activity in gut increased by 112%, and after 12 ones (towards the end of experiment) by 222% in the spleen. The decreasing of this index in a first day after PH in lung, liver and gut was shown to restore in these tissues to the end of experiment. The absence of NK cytotoxicity diminishing just after PH in all the tissues was shown in operated animals, receiving RE and the decreasing of this index was found only in the lungs (by 335%).  相似文献   
915.
916.
The tissue polarity genes control the polarity of hairs, bristles and ommatidia in the adult epidermis of Drosophila. We report here the identification of a new tissue polarity gene named starry night (stan). Mutations in this essential gene alter the polarity of cuticular structures in all regions of the adult body. The detailed polarity phenotype of stan on the wing suggested that it is most likely a component of the frizzled (fz) pathway. Consistent with this hypothesis, stan appears to be downstream of and required for fz function. We molecularly cloned stan and found that it encodes a huge protocadherin containing nine cadherin motifs, four EGF-like motifs, two laminin G motifs, and seven transmembrane domains. This suggests that Stan functions in signal reception, perhaps together with Fz.  相似文献   
917.
The macrozoobenthos taxonomic composition in small karst lakes of Vladimir oblast is studied for the first time. In the structure of bottom communities, 149 taxa one rank below the genus have been found. Chironomid larvae and other amphibiotic animals, as well as oligochaetes, prevail. Most of them are species widely distributed in the surface waters of European Russia. The highest macrozoobenthos species diversity was recorded in neutral lakes, and the lowest diversity was in lakes with weakly acidic waters.  相似文献   
918.
For the entire territory of West Siberia, including its plain and mountainous parts, two maps were constructed for populations of amphibians together with reptiles, and of birds. Communities of these classes of vertebrates differ from one another in their spatial differentiation. The differences are demonstrated for the plain and mountainous territories considered jointly and separately.  相似文献   
919.
920.
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