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   258266篇
  免费   21237篇
  国内免费   214篇
  279717篇
  2018年   2823篇
  2017年   2715篇
  2016年   3724篇
  2015年   4319篇
  2014年   5352篇
  2013年   7415篇
  2012年   8601篇
  2011年   8920篇
  2010年   5990篇
  2009年   5115篇
  2008年   7888篇
  2007年   8187篇
  2006年   7823篇
  2005年   7369篇
  2004年   7455篇
  2003年   7218篇
  2002年   7195篇
  2001年   11316篇
  2000年   11504篇
  1999年   8664篇
  1998年   2872篇
  1997年   2810篇
  1996年   2580篇
  1995年   2389篇
  1994年   2311篇
  1993年   2384篇
  1992年   6870篇
  1991年   7038篇
  1990年   6756篇
  1989年   6672篇
  1988年   6168篇
  1987年   5806篇
  1986年   5287篇
  1985年   5389篇
  1984年   4362篇
  1983年   3757篇
  1982年   2610篇
  1981年   2397篇
  1979年   4167篇
  1978年   3278篇
  1977年   2926篇
  1976年   2626篇
  1975年   3290篇
  1974年   3649篇
  1973年   3507篇
  1972年   3346篇
  1971年   2997篇
  1970年   2595篇
  1969年   2514篇
  1968年   2404篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
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   
182.
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   
183.
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   
184.
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   
185.
186.
187.
188.
It has been shown that at late periods after immobilization stress there is an essential reduction in the cytostatic activity of CBA mice splenocytes detected by inhibition of mastocytoma P 815 cell proliferation in the test with 3H-uridine incorporation. The cytostatic activity returns to normal 5 to 14 days after stress. The changes in the cytolytic and cytostatic activity of mouse splenocytes following stress are correlated and a possible biological value of changes in the immunoassays for the host are discussed.  相似文献   
189.
The processes of the cultivation of N. meningitidis, serogroups A, B and C, in a liquid synthetic culture medium have been studied. Strictly group-specific biomass has been obtained. The maximum productivity at all stages of the batch cultivation of N. meningitidis strains 125 and 133 in this medium does not differ from that at similar stages of cultivation in modified Cohen-Wheller semisynthetic medium. In the serotype antigen preparations obtained from N. meningitidis strain 125 grown in the above-mentioned liquid synthetic culture medium basic polypeptides with a molecular weight of 33000, 36000 and 41000 D have been detected. Their presence in N. meningitidis cells is linked with the growth phase of the population.  相似文献   
190.
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