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   18046篇
  免费   57篇
  国内免费   94篇
系统科学   91篇
丛书文集   122篇
教育与普及   51篇
理论与方法论   48篇
现状及发展   7518篇
研究方法   899篇
综合类   9236篇
自然研究   232篇
  2013年   159篇
  2012年   292篇
  2011年   509篇
  2010年   124篇
  2008年   371篇
  2007年   409篇
  2006年   414篇
  2005年   405篇
  2004年   365篇
  2003年   374篇
  2002年   338篇
  2001年   690篇
  2000年   673篇
  1999年   415篇
  1994年   314篇
  1992年   389篇
  1991年   273篇
  1990年   332篇
  1989年   295篇
  1988年   256篇
  1987年   313篇
  1986年   318篇
  1985年   389篇
  1984年   282篇
  1983年   266篇
  1982年   248篇
  1981年   227篇
  1980年   218篇
  1979年   597篇
  1978年   436篇
  1977年   402篇
  1976年   352篇
  1975年   360篇
  1974年   433篇
  1973年   395篇
  1972年   354篇
  1971年   415篇
  1970年   576篇
  1969年   434篇
  1968年   449篇
  1967年   412篇
  1966年   384篇
  1965年   288篇
  1959年   145篇
  1958年   242篇
  1957年   155篇
  1956年   154篇
  1955年   138篇
  1954年   140篇
  1948年   124篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
Summary Electrophoretic experiments have shown that there are marked differences in the composition of the soluble lens proteins of mammels on the one hand and of fishes on the other hand.  相似文献   
997.
Archive for History of Exact Sciences - From Antiquity through the early modern period, the apparent motion of the Sun in longitude was simulated by the eccentric model set forth in Ptolemy’s...  相似文献   
998.
Viruses are obligate intracellular pathogens that are dependent on cellular machineries for their replication. Recent technological breakthroughs have facilitated reliable identification of host factors required for viral infections and better characterization of the virus–host interplay. While these studies have revealed cellular machineries that are uniquely required by individual viruses, accumulating data also indicate the presence of broadly required mechanisms. Among these overlapping cellular functions are components of intracellular membrane trafficking pathways. Here, we review recent discoveries focused on how viruses exploit intracellular membrane trafficking pathways to promote various stages of their life cycle, with an emphasis on cellular factors that are usurped by a broad range of viruses. We describe broadly required components of the endocytic and secretory pathways, the Endosomal Sorting Complexes Required for Transport pathway, and the autophagy pathway. Identification of such overlapping host functions offers new opportunities to develop broad-spectrum host-targeted antiviral strategies.  相似文献   
999.
Areas of the Knysna estuarine bay in the Western Cape are dominated by three endemic South African truncatelloid microgastropods, temporarily known as ‘Hydrobiaknysnaensis (Krauss), ‘Assimineacapensis (Sowerby) and ‘Assimineaglobulus Connolly. Although first described 80–170 years ago and present in abundance (up to 100,000 m?2), they remain surrounded by confusion and still await taxonomic assignment, largely because they appear most atypical members of their groups by virtue of anatomy and/or biogeography and/or habitat. This study contributes in-life perspectives to morphological and phylogenetic analyses known to be on-going. At Knysna, they are syntopic: at least two occurring in >85% and all three in >40% of individual 0.0026 m2 samples from their region of dominance. Nevertheless, they tend to greater abundance in divergent microhabitats; ‘A.’ globulus dominating higher tidal levels, and ‘A.’ capensis and ‘Hydrobia’ lower ones; the former especially unvegetated sediment, the latter, if anything, seagrass. Interspecific feeding interactions appear unlikely to be responsible for these patterns, other evidence suggesting that all are maintained below carrying capacity. Field biology of ‘H.’ knysnaensis generally appears equivalent to that of northern-hemisphere intertidal hydrobiids and that of ‘A.’ globulus is typically assimineid, albeit at atypically low shore height. Unlike assimineids, however, ‘A.’ capensis is truly aquatic. The success of these truncatelloids in unusual circumstances may be consequent on the absence from South Africa of other microgastropod groups that fill their niches elsewhere in the southern hemisphere.  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