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   465433篇
  免费   51406篇
  国内免费   191篇
  2018年   4468篇
  2016年   6130篇
  2015年   8300篇
  2014年   9683篇
  2013年   13328篇
  2012年   15359篇
  2011年   15872篇
  2010年   10836篇
  2009年   9967篇
  2008年   14276篇
  2007年   14928篇
  2006年   14043篇
  2005年   13459篇
  2004年   13423篇
  2003年   12552篇
  2002年   12318篇
  2001年   17844篇
  2000年   17785篇
  1999年   14397篇
  1998年   5618篇
  1997年   5703篇
  1996年   5296篇
  1995年   4965篇
  1994年   4825篇
  1993年   4921篇
  1992年   11996篇
  1991年   11863篇
  1990年   11611篇
  1989年   11242篇
  1988年   10798篇
  1987年   10342篇
  1986年   9660篇
  1985年   9543篇
  1984年   8108篇
  1983年   7017篇
  1982年   5567篇
  1981年   5033篇
  1980年   4787篇
  1979年   7679篇
  1978年   6136篇
  1977年   5636篇
  1976年   5471篇
  1975年   5780篇
  1974年   6525篇
  1973年   6396篇
  1972年   5927篇
  1971年   5354篇
  1970年   4748篇
  1969年   4696篇
  1968年   4541篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
41.
42.
43.
Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the ‘Titanic’ wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there.  相似文献   
44.
Reconstruction of bony structures of the face is always a problem as big as the defect and the function that must be replaced. Everything from simple grafts to sophisticated distant bone flaps has been used. Based on the studies of Cutting et al., Psillakis et al., and Casanova et al., we have developed the full-thickness galeoparietal bone flap, initially for mandibular reconstruction, but of great use for all maxillofacial reconstructions. From July of 1987 to December of 1988, 14 patients have been operated on. The experience with this flap is shown in four patients as follows: primary reconstruction of a mandible as a result of ameloblastoma, secondary reconstruction of a mandible with associated old fractures and malalignment of segments, bilateral malar reconstruction in a patient with Treacher Collins syndrome, and severe sequelae of an already treated Romberg case. Small variations could be made to best accommodate the technique used to the defect we were treating. Some technical details, the experience, the results, and possible sequelae or complications are also discussed.  相似文献   
45.
46.
47.
48.
49.
50.
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results.  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