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   1087184篇
  免费   116308篇
  国内免费   712篇
  2018年   9832篇
  2016年   13251篇
  2015年   18137篇
  2014年   21263篇
  2013年   30834篇
  2012年   33986篇
  2011年   34672篇
  2010年   23575篇
  2009年   21602篇
  2008年   30796篇
  2007年   31748篇
  2006年   29994篇
  2005年   28833篇
  2004年   28772篇
  2003年   27710篇
  2002年   26910篇
  2001年   47644篇
  2000年   48010篇
  1999年   38356篇
  1998年   13833篇
  1997年   14431篇
  1996年   13462篇
  1995年   12760篇
  1994年   12449篇
  1993年   12288篇
  1992年   32038篇
  1991年   31206篇
  1990年   30603篇
  1989年   29974篇
  1988年   27909篇
  1987年   26292篇
  1986年   24527篇
  1985年   24723篇
  1984年   20504篇
  1983年   17448篇
  1982年   13415篇
  1981年   11997篇
  1980年   11242篇
  1979年   19158篇
  1978年   14962篇
  1977年   13795篇
  1976年   12716篇
  1975年   14070篇
  1974年   15058篇
  1973年   14929篇
  1972年   13591篇
  1971年   12418篇
  1970年   10714篇
  1969年   10487篇
  1968年   9573篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
901.
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   
902.
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   
903.
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   
904.
Compound 26 is more potent against Escherichia coli. and 24 is more active against Staphylococcus aureus, β-Heamolytic streptococcus, Vibreo cholerae, Salmonella typhii, and Shigella flexneri than the standard drug ciprofloxacin. Moreover, of all the compounds tested, 26 is more effective against Aspergillus flavus and Mucor, than the standard drug fluconazole.  相似文献   
905.
906.
The effect of pergolide mesylate was studied in two previously untreated men with large prolactinomas and exceptionally high prolactin concentrations. The study was designed to determine whether pergolide would be effective in alleviating symptoms, correcting hormonal abnormalities and shrinking the tumour. Starting with 50 micrograms daily the dose of pergolide was slowly increased over 10 weeks to 1 mg once daily, when repeat assessment was performed. Both patients reported complete relief of symptoms, with no side effects. Serum prolactin concentration was suppressed to normal in both subjects, and evidence to suggest tumour shrinkage was observed. Pergolide appears to be effective treatment for men with large prolactinomas.  相似文献   
907.
908.
909.
S L Wardlaw  P J Wang  A G Frantz 《Life sciences》1985,37(20):1941-1947
The effect of estradiol on the brain concentration of immunoreactive beta-endorphin (beta-EP) and C-terminal ACTH (CLIP) was studied in ovariectomized rats. Dopamine, a known inhibitor of pituitary intermediate lobe pro-opiomelanocortin (POMC), was examined as a possible mediator of the estradiol induced changes in brain POMC. Animals were treated for 1 or 3 weeks with either 1) saline; 2) silastic estradiol implants; or 3) estradiol implants plus haloperidol 1 mg/kg/day. After one week of treatment no significant change in hypothalamic beta-EP content was noted in any group compared to the control level of 4.13 +/- .33 (SEM) pmoles although in the neurointermediate lobe beta-EP increased from 566 +/- 72 to 942 +/- 73 pmoles after haloperidol (p less than .005). After 3 weeks, however, hypothalamic beta-EP decreased from 3.96 +/- .28 to 2.74 +/- .19 pmoles (p less than .005) and C-terminal ACTH decreased from 3.78 +/- .33 to 2.82 +/- .18 pmoles (p less than .02) in the estradiol treated rats. This estradiol induced decrease in the hypothalamic content of beta-EP and C-terminal ACTH was not blocked by haloperidol. We conclude that estradiol lowers the hypothalamic content of beta-EP and CLIP and that this effect does not appear to be mediated by dopamine.  相似文献   
910.
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