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   3730篇
  免费   319篇
  国内免费   3篇
  2021年   37篇
  2020年   26篇
  2019年   35篇
  2018年   42篇
  2017年   47篇
  2016年   60篇
  2015年   115篇
  2014年   120篇
  2013年   143篇
  2012年   215篇
  2011年   187篇
  2010年   131篇
  2009年   109篇
  2008年   169篇
  2007年   190篇
  2006年   203篇
  2005年   145篇
  2004年   152篇
  2003年   133篇
  2002年   149篇
  2001年   72篇
  2000年   52篇
  1999年   53篇
  1998年   53篇
  1997年   38篇
  1996年   45篇
  1995年   37篇
  1994年   39篇
  1993年   39篇
  1992年   45篇
  1991年   54篇
  1990年   37篇
  1989年   44篇
  1988年   36篇
  1987年   42篇
  1986年   32篇
  1985年   22篇
  1984年   33篇
  1983年   30篇
  1982年   27篇
  1981年   23篇
  1979年   30篇
  1977年   23篇
  1976年   28篇
  1975年   27篇
  1973年   20篇
  1972年   22篇
  1971年   21篇
  1970年   21篇
  1968年   23篇
排序方式: 共有4052条查询结果,搜索用时 156 毫秒
1.
2.
Behaviour traits of cattle have been reported to affect important production traits, such as meat quality and milk performance as well as reproduction and health. Genetic predisposition is, together with environmental stimuli, undoubtedly involved in the development of behaviour phenotypes. Underlying molecular mechanisms affecting behaviour in general and behaviour and productions traits in particular still have to be studied in detail. Therefore, we performed a genome‐wide association study in an F2 Charolais × German Holstein cross‐breed population to identify genetic variants that affect behaviour‐related traits assessed in an open‐field and novel‐object test and analysed their putative impact on milk performance. Of 37 201 tested single nucleotide polymorphism (SNPs), four showed a genome‐wide and 37 a chromosome‐wide significant association with behaviour traits assessed in both tests. Nine of the SNPs that were associated with behaviour traits likewise showed a nominal significant association with milk performance traits. On chromosomes 14 and 29, six SNPs were identified to be associated with exploratory behaviour and inactivity during the novel‐object test as well as with milk yield traits. Least squares means for behaviour and milk performance traits for these SNPs revealed that genotypes associated with higher inactivity and less exploratory behaviour promote higher milk yields. Whether these results are due to molecular mechanisms simultaneously affecting behaviour and milk performance or due to a behaviour predisposition, which causes indirect effects on milk performance by influencing individual reactivity, needs further investigation.  相似文献   
3.
Media, and particularly TV media, have a great impact on the general public. In recent years, spatial patterns of information and the relevance of intangible geographies have become increasingly important. Gatekeeping plays a critical role in the selection of information that is transformed into media. Therefore, gatekeeping, through national media, also co-forms the generation of mental maps. In this paper, correspondence analysis (a statistical method) combined with cloud lines (a new visual analytics technique) is used to analyze how individual major regional events in one of the post-communist countries, the Czech Republic, penetrate into the media on a national scale. Although national news should minimize distortions about regions, this assumption has not been verified by our research. Impressions presented by the media of selected regions that were markedly influenced by one or several events in those regions demonstrate that gatekeepers, especially news reporters, functioned as a filter by selecting only a few specific, and in many cases, unusual events for dissemination.  相似文献   
4.
Owing to the exceptional intracellular distribution and the heterogeneous expression pattern during transformation and metastasis in various tumors, the EF-hand calcium-binding protein S100A2 attracts increasing attention. Unlike the majority of S100 proteins, S100A2 expression is downregulated in many cancers and the loss in nuclear expression has been associated with poor prognosis. On the other hand, S100A2 is upregulated in some cancers. This mini review highlights the general characteristics of S100A2 and discusses recent findings on its putative functional implication as a suppressor or promoter in cancerogenesis.  相似文献   
5.
6.
7.
8.
9.
10.
Lysostaphin is an extracellular glycylglycine endopep-tidase produced by Staphylococcus simulans biovar staphylolyticus ATCC1362 that lyses staphylococcal cells by hydrolysing the polyglycine interpeptide bridges of the peptidoglycan. Renewed analysis of the sequence of the lysostaphin gene (Iss), and the sequencing of the amino-terminus of purified prolysostaphin and of mature lysostaphin revealed that lysostaphin is organized as a preproprotein of 493 amino acids (aa), with a signal peptide consisting of 36 aa, a propeptide of 211 aa from which 195 aa are organized in 15 tandem repeats of 13 aa length, and a mature protein of 246 aa. Prolysostaphin is processed in the culture supernatant of S. simulans biovar staphylolyticus by an extracellular cysteine protease. Although prolysostaphin was staphylolytically active, the mature lysostaphin was about 4.5-fold more active. The controlled expression in Staphylococcus carnosus of Iss and Iss with deletions in the prepropeptide region indicated that the tandem repeats of the propeptide are not necessary for protein export or activation of Lss, but keep Lss in a less active state. Intracellular expressed pro- and mature lysostaphin exert staphy-lolytic activity in cell-free extracts, but do not affect growth of the corresponding clones. We characterized a lysostaphin immunity factor gene (lif) which is located in the opposite direction to Iss. The expression of lif in S. carnosus led to an increase in the serine/glycine ratio of the interpeptide bridges of peptidoglycan from 2 to 35%, suggesting that lysostaphin immunity depends on serine incorporation into the interpeptide bridge. If, in addition to lif, Iss is co-expressed the serine/glycine ratio is further increased to 58%, suggesting that Lss selects for optimal serine incorporation. Lif shows similarity to FemA and FemB  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