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   152539篇
  免费   5364篇
  国内免费   5760篇
  163663篇
  2024年   154篇
  2023年   845篇
  2022年   2006篇
  2021年   3247篇
  2020年   2244篇
  2019年   2712篇
  2018年   13731篇
  2017年   12056篇
  2016年   9791篇
  2015年   4442篇
  2014年   5005篇
  2013年   5068篇
  2012年   9738篇
  2011年   17496篇
  2010年   14720篇
  2009年   10806篇
  2008年   12796篇
  2007年   13996篇
  2006年   2771篇
  2005年   2590篇
  2004年   2672篇
  2003年   2597篇
  2002年   2018篇
  2001年   1258篇
  2000年   1133篇
  1999年   918篇
  1998年   575篇
  1997年   544篇
  1996年   528篇
  1995年   454篇
  1994年   445篇
  1993年   375篇
  1992年   509篇
  1991年   393篇
  1990年   311篇
  1989年   285篇
  1988年   238篇
  1987年   225篇
  1986年   180篇
  1985年   166篇
  1984年   134篇
  1983年   142篇
  1982年   85篇
  1981年   50篇
  1980年   58篇
  1979年   69篇
  1974年   58篇
  1973年   48篇
  1972年   301篇
  1971年   303篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
The purpose of this review is to provide a global perspective on Oncorhynchus salmonine introductions and put-and-take fisheries based on modern stocking programs, with special emphasis on freshwater ecosystems. We survey the global introductions of nine selected salmonines of the genus Oncorhynchus: golden trout, cutthroat trout, pink salmon, chum salmon, coho salmon, masu/cherry salmon, rainbow trout/steelhead, sockeye salmon/kokanee, and chinook salmon. The information is organized on a geographical basis by continent, and then by species and chronology. Two different objectives and associated definitions of ‘success’ for introductions are distinguished: (a) seed introduction: release of individuals with the purpose of creating a wild-reproducing, self-sustaining population; and (b) put-and-take introduction: release of individuals with the purpose of maintaining some level of wild population abundance, regardless of wild reproduction. We identify four major phenomena regarding global salmonine introductions: (1) general inadequacy of documentation regarding introductions; (2) a fundamental disconnect between management actions and ecological consequences of introductions; (3) the importance of global climate change on success of previous and future introductions; and (4) the significance of aquaculture as a key uncertainty in accidental introductions. We conclude this review with a recognition of the need to terminate ongoing stocking programs for introduced salmonines worldwide.  相似文献   
62.
63.
One of the major properties of the semi-synthetic minimal cell, as a model for early living cells, is the ability to self-reproduce itself, and the reproduction of the boundary layer or vesicle compartment is part of this process. A minimal bio-molecular mechanism based on the activity of one single enzyme, the FAS-B (Fatty Acid Synthase) Type I enzyme from Brevibacterium ammoniagenes, is encapsulated in 1-palmitoyl-2oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes to control lipid synthesis. Consequently molecules of palmitic acid released from the FAS catalysis, within the internal lumen, move toward the membrane compartment and become incorporated into the phospholipid bilayer. As a result the vesicle membranes change in lipid composition and liposome growth can be monitored. Here we report the first experiments showing vesicles growth by catalysis of one enzyme only that produces cell boundary from within. This is the prototype of the simplest autopoietic minimal cell.  相似文献   
64.

Background  

Identifying essential genes in bacteria supports to identify potential drug targets and an understanding of minimal requirements for a synthetic cell. However, experimentally assaying the essentiality of their coding genes is resource intensive and not feasible for all bacterial organisms, in particular if they are infective.  相似文献   
65.

Background  

Phylogenies capture the evolutionary ancestry linking extant species. Correlations and similarities among a set of species are mediated by and need to be understood in terms of the phylogenic tree. In a similar way it has been argued that biological networks also induce correlations among sets of interacting genes or their protein products.  相似文献   
66.
67.
68.
69.
70.
γ-Butyrolactone derivative molecules in Streptomyces play a crucial role in cell density control, secondary metabolism, and cell differentiation. As their synthesis level in the cell is very low compared to those of similar N-acyl homoserine lactone molecules from gram-negative bacteria, it is very hard to analyze them even with several hundredfold concentration of the culture broth. We have developed a very quick and easy detection method using an affinity capture technique with His-tagged receptor proteins and electrospray tandem mass spectrometry. Using Streptomyces coelicolor as a model system, SCB1 was detected from only 100 ml of the culture broth after solvent extraction. This method can be further applied to detection and quantitative analysis of butanolides and inhibitor screening of the receptor molecules.  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