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   100340篇
  免费   1011篇
  国内免费   815篇
  2022年   48篇
  2021年   140篇
  2020年   107篇
  2019年   145篇
  2018年   11975篇
  2017年   10791篇
  2016年   7704篇
  2015年   1027篇
  2014年   786篇
  2013年   800篇
  2012年   4789篇
  2011年   13337篇
  2010年   12364篇
  2009年   8538篇
  2008年   10199篇
  2007年   11752篇
  2006年   602篇
  2005年   868篇
  2004年   1314篇
  2003年   1314篇
  2002年   1007篇
  2001年   368篇
  2000年   265篇
  1999年   132篇
  1998年   74篇
  1997年   63篇
  1996年   48篇
  1995年   31篇
  1994年   28篇
  1993年   54篇
  1992年   74篇
  1991年   88篇
  1990年   46篇
  1989年   48篇
  1988年   56篇
  1987年   50篇
  1986年   28篇
  1985年   47篇
  1984年   38篇
  1983年   43篇
  1982年   34篇
  1981年   26篇
  1979年   25篇
  1973年   23篇
  1972年   258篇
  1971年   293篇
  1970年   25篇
  1968年   23篇
  1965年   23篇
  1962年   24篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
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   
53.

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   
54.

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   
55.
56.
57.
58.
59.
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   
60.
Cecropin XJ, as a heat stable antimicrobial peptide (AMP), displayed broad bacteriostatic activities, effectively inhibited proliferation of cancer cells and induced cell apoptosis in vitro. However, it exhibited little hemolytic activity and very low cytotoxicity to erythrocytes and normal cells. Although exerts multiple remarkable bioactivities, the refined molecular conformation of native Cecropin XJ remains unsolved. The aim of the present study is to comprehensively investigate the physicochemical characteristics and structure-function relationship of this antimicrobial peptide by using a series of bioinformatics and experimental approaches. In this study, we revealed that the mature Cecropin XJ consists of 41 amino acids, containing two α-helical structures from Lys7 to Lys25 and from Ala29 to Ile39. The phylogenetic tree indicated that Cecropin XJ belongs to the Class I AMPs of cecropin family. Hydrophobic analysis showed Cecropin XJ is a typical amphiphilic molecule. The surface of Cecropin XJ was found to have a much wide range of electrostatic potential from ?83.243 to +83.243. The amphipathicity and surface potential of Cecropin XJ partially supported the AMP pore-forming hypothesis. Scanning electron microscopy experimentally confirmed the damages of Cecropin XJ to microbial membrane. Four predicted docking sites respectively for magnesium ion (Mg2+), adenosine diphosphate (ADP), bacteriopheophytin (BPH), and guanosine triphosphate (GTP) were found on the surface of Cecropin XJ. Thereinto, Mg2+ was experimentally proved to suppress the antibacterial activity of Cecropin XJ; both GTP and ADP enhanced the bactericidal activities to varying degrees. The present study provides a foundation for further investigation of molecular evolution, structural modification, and functional mechanisms of Cecropin XJ.  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