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   799897篇
  免费   82765篇
  国内免费   253篇
  882915篇
  2018年   8005篇
  2017年   7644篇
  2016年   10751篇
  2015年   13651篇
  2014年   16236篇
  2013年   23385篇
  2012年   26283篇
  2011年   27050篇
  2010年   18460篇
  2009年   17052篇
  2008年   24149篇
  2007年   25094篇
  2006年   23468篇
  2005年   22555篇
  2004年   22327篇
  2003年   21440篇
  2002年   20937篇
  2001年   34754篇
  2000年   34210篇
  1999年   27599篇
  1998年   10200篇
  1997年   10277篇
  1996年   9858篇
  1995年   9068篇
  1994年   8727篇
  1993年   8758篇
  1992年   22344篇
  1991年   21925篇
  1990年   21378篇
  1989年   20821篇
  1988年   19094篇
  1987年   18325篇
  1986年   17096篇
  1985年   16959篇
  1984年   13942篇
  1983年   12189篇
  1982年   9243篇
  1981年   8360篇
  1980年   7755篇
  1979年   12946篇
  1978年   10205篇
  1977年   9194篇
  1976年   8805篇
  1975年   9821篇
  1974年   10490篇
  1973年   10354篇
  1972年   9478篇
  1971年   8461篇
  1970年   7384篇
  1969年   7259篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Nine pairs of polymerase chain reaction (PCR) primers that amplify polymorphic microsatellite loci in the desert locust, Schistocerca gregaria (Forskal), were developed using a magnetic bead‐based enrichment protocol. A sample of 48 locusts collected during the 1993 and 1995 upsurge periods in Eritrea, East Africa, were genotyped. The number of alleles per locus ranged from six to 20; the average was 12.67. Allelic distributions were significantly different between samples from different localities.  相似文献   
993.
The morphology of dissociated single cerebellar Purkinje cells obtained from wild-type P1 CD1 mice was assessed in the absence and in the presence of glia. A dedicated noninvasive technique based on optical microscopy was developed. Image processing algorithms were implemented to extract metrical features characterizing cell structure and dendritic arborization. The morphological features were analyzed in order to identify quantitative differences in Purkinje cell morphology due to interactions with astrocytes.  相似文献   
994.
Hafnia alvei, a Gram negative bacillus related to the Enterobacteriaceae family, is considered an opportunistic pathogen of several animal species and humans. In this communication, we describe fimbrial-like structures from different strains of H. alvei that cannot be easily ascribed to any of the previously reported fimbrial types in this species (type I or type III). Polymerase chain reaction (PCR) and immunofluorescence assays were carried out to study fimbriae and flagella in H. alvei strains isolated from different sources. No correlation between the results obtained by PCR and those obtained by phenotypic methods were found, and the antibodies used gave cross or different recognition patterns of the surface structures present in these strains. We report as well that strain and growth temperature influence fimbriation and expression of flagella in human and animal isolates of H. alvei. This study also indicates that the absence of fimbriae have a significant positive influence on the initial adhesion of H. alvei to human epithelial cells.  相似文献   
995.
Arundo donax L. (Poaceae) is native to Mediterranean Europe and invasive in the Rio Grande Basin of North America. Rhizomes from nine sites in France and Spain infested with a candidate control agent, the armoured scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) weighed 50% less than those from nine sites without scale.  相似文献   
996.
997.
998.
999.
Fourteen fresh run salmon Satmo salar L. with early extant lesions of ulcerative dermal necrosis (UDN) were kept in separate tanks and treated with zinc free malachite green. Ten of the fish were held at 10° C and 4 at 2° C. The treatment precluded infection with Saprolegnia fungus and allowed natural resolution of the lesions. There was a marked difference in rate of healing between warm and cold water conditions.
Histological examination of healing lesions at different stages showed that there was a primary invasion of cuboidal epithelium over the collagen scar followed by a phase of disorganized proliferation which eventually organized itself into normal epithelium. Melanocytes were very obvious in the dermis of healing lesions.  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