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   244783篇
  免费   22536篇
  国内免费   244篇
  2018年   2644篇
  2017年   2584篇
  2016年   3436篇
  2015年   3688篇
  2014年   4597篇
  2013年   6580篇
  2012年   7237篇
  2011年   7926篇
  2010年   5411篇
  2009年   4806篇
  2008年   6899篇
  2007年   7113篇
  2006年   6747篇
  2005年   6438篇
  2004年   6345篇
  2003年   6172篇
  2002年   6030篇
  2001年   12024篇
  2000年   11979篇
  1999年   9158篇
  1998年   2686篇
  1997年   2748篇
  1996年   2614篇
  1995年   2478篇
  1994年   2422篇
  1993年   2317篇
  1992年   7181篇
  1991年   6987篇
  1990年   7063篇
  1989年   6845篇
  1988年   6360篇
  1987年   6014篇
  1986年   5358篇
  1985年   5659篇
  1984年   4466篇
  1983年   3865篇
  1982年   2671篇
  1981年   2494篇
  1980年   2303篇
  1979年   4111篇
  1978年   3141篇
  1977年   2879篇
  1976年   2828篇
  1975年   3268篇
  1974年   3499篇
  1973年   3528篇
  1972年   3057篇
  1971年   2841篇
  1970年   2528篇
  1969年   2299篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Protein I (PI) is the most abundant protein on the gonococcal cell surface and besides its porin function it may have important properties contributing to pathogenicity. By allelic exchange using cloned PI genes from FA19 (PIA) and MS11 (PIB) and a selectable marker introduced closely downstream of these genes, we constructed sets of isogenic gonococcal strains that differ only in their PI gene. Analysis revealed that PI has a major effect on stable resistance to normal human serum, and a slight effect on low-level resistance to antibiotics. All PIA/B hybrids were hypersusceptible to serum, suggesting a possible explanation for why such hybrids do not occur in nature.  相似文献   
992.
993.
Custom prefabrication of free flaps provides an unlimited variety of applications, since flaps can be created with expendable tissues and without restriction to naturally occurring vascular territories. These principles also can be used to customize flaps that could not be completed by conventional means. We report a case of scalp reconstruction using a random-pattern abdominal flap in which a radial artery fascial flap was induced to serve as the vascular carrier. In addition to providing durable scalp coverage, the prefabricated free flap enabled salvage of an abdominal flap that would otherwise have been aborted after intermediate transfer to the forearm.  相似文献   
994.
995.
996.
Journal of Ichthyology - The paper considers the effect of the Sea of Azov salinization on the food supply to anchovy Engraulis encrasicolus maeoticus as the level of salinity was rising from 12.7...  相似文献   
997.
Relationships between the strongyloid nematodesRugopharynx delta, R. zeta, R. omega, R. longibursaris, R. mawsonae andR. sigma, all from macropodid marsupials, were investigated using allozyme data. The phylogenetic trees derived from the electrophoretic data set were congruent with those of the hosts and were consistent with the hypothesis that the species complex originated in pademelons of the genusThylogale and diversified in rock-wallabies (Petrogale spp.) and scrub wallabies of the subgenusNotamacropus. Host switching is evident only between closely related macropodid taxa.  相似文献   
998.
999.
The effect of intranasal substance P injection on parkinsonian syndrome and the generator of pathologically enhanced excitation (GPEE) in caudate nuclei (CN) was investigated. MPTP or reserpine administration in old rats induced oligokinesia, rigidity and tremor followed by the high amplitude slow and rapid waves in both CN. The bilateral intranasal injection of substance P (25 micrograms/kg) resulted in an increase in motor activity and almost completely abolished the rigidity and tremor. The reduction of extrapyramidal symptoms was considered as a result of the inhibition of GPEE in CN. The possibility of substance P entry from nasal cavity into the brain was discussed. The changes of the substance P balance in nigrostriatal system was suggested to be on of the pathogenetic links of parkinsonian syndrome.  相似文献   
1000.
At the level of DNA organization into chromatin, there are mechanisms that define gene expression profiles in specialized cell types. Genes within chromatin regions that are located at the nuclear periphery are generally expressed at lower levels; however, the nature of this phenomenon remains unclear. These parts of chromatin interact with nuclear lamina proteins like Lamin B1 and, therefore, can be identified in a given cell type by chromatin profiling of these proteins. In this study, we created and tested a Dam Identification (DamID) system induced by Cre recombinase using Lamin B1 and mouse embryonic fibroblasts. This inducible system will help to generate genome-wide profiles of chromatin proteins in given cell types and tissues with no need to dissect tissues from organs or separate cells from tissues, which is achieved by using specific regulatory DNA elements and due to the high sensitivity of the method.  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