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   1148389篇
  免费   121827篇
  国内免费   546篇
  2018年   10993篇
  2017年   10485篇
  2016年   14862篇
  2015年   19309篇
  2014年   22954篇
  2013年   33178篇
  2012年   36982篇
  2011年   37799篇
  2010年   25908篇
  2009年   24049篇
  2008年   33675篇
  2007年   35034篇
  2006年   32695篇
  2005年   31538篇
  2004年   31158篇
  2003年   29994篇
  2002年   29151篇
  2001年   51593篇
  2000年   51176篇
  1999年   40796篇
  1998年   14565篇
  1997年   15076篇
  1996年   14217篇
  1995年   13172篇
  1994年   12686篇
  1993年   12735篇
  1992年   33305篇
  1991年   32329篇
  1990年   31406篇
  1989年   30702篇
  1988年   28153篇
  1987年   26818篇
  1986年   24974篇
  1985年   24946篇
  1984年   20574篇
  1983年   17714篇
  1982年   13397篇
  1981年   12232篇
  1980年   11417篇
  1979年   19289篇
  1978年   15133篇
  1977年   13706篇
  1976年   12899篇
  1975年   14310篇
  1974年   15438篇
  1973年   15155篇
  1972年   13854篇
  1971年   12502篇
  1970年   10931篇
  1969年   10581篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
931.
The inflammation markers alpha-1-antitrypsin (AAT), Clara cell protein (CC-16), soluble interleukin-2-receptor (IL-R) and the soluble adhesion molecule E-selectin, the intercellular adhesion molecule (ICAM-1) and the vascular adhesion molecule (VCAM-1) were determined in the serum of 195 salt-exposed miners to analyse dose-response relationships between markers and potash dust. Alpha-1-antitrypsin, Clara-cell protein, IL2-R, E-selectin and VCAM-1 were not changed by salt exposure, however the ICAM-1 level in the serum fell slightly as the salt exposure increased. This effect was strongest in the group of smokers, still visible in the group of ex-smokers, no effect was seen in non-smokers. Markers, with the exception of VCAM-1, were influenced by tobacco exposure. Since markers were not elevated in relation to salt dust exposure, the results do not support an inflammatory effect of potash dust on the respiratory system.  相似文献   
932.
Human bleomycin hydrolase (hBH) is a neutral cysteine protease genetically associated with increased risk for Alzheimer disease. We show here that ectopic expression of hBH in 293APPwt and CHOAPPsw cells altered the processing of amyloid precursor protein (APP) and increased significantly the release of its proteolytic fragment, beta amyloid (Abeta). We also found that hBH interacted and colocalized with APP as determined by subcellular fractionation, in vitro binding assay, and confocal immunolocalization. Metabolic labeling and pulse-chase experiments showed that ectopic hBH expression increased secretion of soluble APPalpha/beta products without changing the half-life of cellular APP. We also observed that this increased Abeta secretion was independent of hBH isoforms. Our findings suggest a regulatory role for hBH in APP processing pathways.  相似文献   
933.
Various plasmids carrying transposon Tn5 were used to generate insertion mutants synthesizing batumin, a unique antibiotic with a selective antistaphylococcal effect. One of the plasmids used provided a sufficient yield of the clones in question. An analysis of over 7000 clones allowed us to select the mutant clones with increased and decreased levels of batumin synthesis and the mutants that lost the ability to synthesize this antibiotic.  相似文献   
934.
935.
The psbQ gene encoding a 16-kDa polypeptide of the oxygen-evolving complex of photosystem II has been isolated from Arabidopsis thaliana and characterized. The gene consists of a 28 nucleotide long leader sequence, two introns and three exons encoding a 223-amino-acid precursor polypeptide. The first 75 amino acids act as a transit peptide for the translocation of the polypeptide into the thylakoid lumen. Expression studies show that the gene is light-inducible and expresses only in green tissues with high steady-state mRNA levels in leaves. Using this gene as a probe, restriction fragment length polymorphism between two ecotypes, Columbia and Estland, has also been detected.  相似文献   
936.
937.
938.
We present a time‐calibrated phylogeny of the charismatic green lacewings (Neuroptera: Chrysopidae). Previous phylogenetic studies on the family using DNA sequences have suffered from sparse taxon sampling and/or limited amounts of data. Here we combine all available previously published DNA sequence data and add to it new DNA sequences generated for this study. We analysed these data in a supermatrix using Bayesian and maximum likelihood methods and provide a phylogenetic hypothesis for the family that recovers strong support for the monophyly of all subfamilies and resolves relationships among a large proportion of chrysopine genera. Chrysopinae tribes Leucochrysini and Belonopterygini were recovered as monophyletic sister clades, while the species‐rich tribe Chrysopini was rendered paraphyletic by Ankylopterygini. Relationships among the subfamilies were resolved, although with relatively low statistical support, and the topology varied based on the method of analysis. Greatest support was found for Apochrysinae as sister to Nothochrysinae and Chrysopinae, which is in contrast to traditional concepts that place Nothochrysinae as sister to the rest of the family. Divergence estimates suggest that the stem groups to the various subfamilies diverged during the Triassic‐Jurassic, and that stem groups of the chrysopine tribes diverged during the Cretaceous.  相似文献   
939.
It has been experimentally and clinically established that the determination of leucine-aminotransferase activity in the blood serum and abdominal exudate may serve as a marker for the early determination of pancreonecrosis and edematous (serous) pancreatitis.  相似文献   
940.
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