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   206451篇
  免费   4894篇
  国内免费   854篇
耳鼻咽喉   2922篇
儿科学   7827篇
妇产科学   6045篇
基础医学   26584篇
口腔科学   6044篇
临床医学   16366篇
内科学   37301篇
皮肤病学   4903篇
神经病学   12482篇
特种医学   10996篇
外国民族医学   99篇
外科学   30275篇
综合类   2156篇
一般理论   3篇
预防医学   17266篇
眼科学   4739篇
药学   14465篇
  8篇
中国医学   497篇
肿瘤学   11221篇
  2021年   673篇
  2018年   4028篇
  2017年   4238篇
  2016年   3486篇
  2015年   5220篇
  2014年   4780篇
  2013年   4009篇
  2012年   10682篇
  2011年   5688篇
  2010年   2776篇
  2009年   4261篇
  2008年   2699篇
  2007年   3417篇
  2006年   3565篇
  2005年   11715篇
  2004年   13146篇
  2003年   8717篇
  2002年   3898篇
  2001年   4730篇
  2000年   2156篇
  1999年   6114篇
  1998年   652篇
  1992年   6906篇
  1991年   7139篇
  1990年   7386篇
  1989年   6987篇
  1988年   6498篇
  1987年   6274篇
  1986年   5972篇
  1985年   5260篇
  1984年   3599篇
  1983年   2917篇
  1982年   1012篇
  1981年   773篇
  1980年   842篇
  1979年   3834篇
  1978年   2366篇
  1977年   1787篇
  1976年   1563篇
  1975年   2480篇
  1974年   3106篇
  1973年   2739篇
  1972年   2758篇
  1971年   2744篇
  1970年   2556篇
  1969年   2464篇
  1968年   2239篇
  1967年   2163篇
  1966年   1898篇
  1965年   1135篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We studied prospectively the occurrence of hip fractures among the over 49-year-old urban populations (n = 88,206) in the cities Tampere, Jyv?skyl? and Kotka in 1989 and compared the results with a parallel Scandinavian multicentre study. During 1989, there were 266 inhabitants who were treated for a hip fracture, 213 of them were women. Women had in 132 cases a femoral neck fracture and in 81 cases a trochanteric fracture, and the corresponding numbers for men were 22 and 31. Among women, the total hip fracture incidence in Jyv?skyl? (n = 22) was the lowest when compared with the ones in Tampere (n = 47) and Kotka (n = 36). These incidences were on average lower than in the other Scandinavian cities studied in parallel. The all over ratio of femoral neck/trochanteric fractures was 1.1 in Tampere, 3.0 in Jyv?skyl? and 2.2 in Kotka and in Tampere, women had 9.3 times more femoral neck fractures than men. Our study showed that in Finland in three major cities the hip fracture incidence was lower than what has been similarly registered in corresponding urban populations in other Scandinavian countries. We also point out that the relative part of trochanteric fractures appears to be increasing.  相似文献   
992.
Lipase activity in homogenates of guinea-pig adrenals was studied under conditions which exclude the hormone-sensitive lipase/cholesterol ester hydrolase. Antibody inhibition and chromatography on heparin-Sepharose showed that most of the activity was due to lipoprotein lipase (LPL), and that there was only a small amount of hepatic lipase activity. Northern blot analysis of total RNA demonstrated the same three adrenal LPL mRNA species (1.8, 3.1 and 3.5 kb) as were found in adipose tissue and heart. Hence, at least part of the LPL activity in adrenals is due to enzyme synthesized within the tissue. Immunolocalization showed that LPL was associated with the endothelium of blood vessels throughout the gland. In addition, there was cytoplasmic immunoreaction, suggesting that lipase was synthesized in a subpopulation of cells in the transitional zone between the fasciculata and reticularis layer of the cortex, particularly over lipid-filled cells. There was also intense immunofluorescence over scattered cells in the adrenal medulla. Treatment with an ACTH analogue depot (20 IU, i.m.) for 11 days induced a 12-fold increase in serum cortisol and increased adrenal weight 2.2-fold. The treatment induced increases in LPL mRNA (about twofold), LPL activity and in the number of cells in the adrenal cortex which gave an immunoreaction for LPL.  相似文献   
993.
We have recently shown that synoviocytes and extracellular matrices exhibit distinct patterns of carbohydrate expression. Their biological relevance is however not known. The purpose of the present study was to find out whether human synovial tissue would also show a specific receptor pattern for complex sugar molecules. Endogenous lectins were displayed by means of biotinylated neoglycoproteins and sulfated polysaccharides in paraffin-embedded material or cryosections. In addition to certain carbohydrate components that are known to be constituents of the carbohydrate part of cellular glycoconjugates, our panel included heparin and fucoidan, a sulfated fucose. Binding sites were shown using the avidin-peroxidase technique for light microscopy. The results were compared with immunohistochemical methods and enzyme histochemistry. Our study demonstrates that human synovial tissue contains a complex pattern of endogenous lectins depending on the different types of synovitis. The staining method we used in the investigation allows for precise localization of saccharide binding receptors and is therefore believed to be a reliable technique for further phenotypic characterization of synovial cells.  相似文献   
994.
995.
The lateral mobility of cell membrane glycoproteins is often restricted by dynamic barriers. These barriers have been detected by measurements of fluorescence photobleaching and recovery (FPR) and barrier-free path (BFP). To define the location and properties of the barriers, we compared the lateral mobility, measured by FPR and BFP, of wild-type class I major histocompatibility complex (MHC) membrane glycoproteins with the lateral mobility of mutant class I MHC glycoproteins truncated in their cytoplasmic domains. Mutants with 0 or 4 residues in the cytoplasmic domain were as mobile as lipid-anchored class I MHC molecules, molecules whose lateral mobility is relatively unrestricted by barriers. In contrast, mobility of class I MHC molecules with 7-residue cytoplasmic domains was as restricted as mobility of class I molecules with full-length, 31-residue cytoplasmic domains. Though some of the difference between the mobilities of mutants with 4- or 0-residue domains and the other class I molecules may be due to differences in the net charge of the cytoplasmic domain, FPR measurements of the mobility of molecules with 7-residue domains show that length of the cytoplasmic domain has an important influence on the lateral mobility. Model calculations suggest that the barriers to lateral mobility are 2-3 nm below the membrane bilayer.  相似文献   
996.
The possible immunoregulatory role of the tonsils was studied by determining immunoglobulins IgG, A, M, E and factors C'3, C'4 and PFB of the complement system before and after tonsillectomy. The synthesis in vitro of IgG and IgM by lymphocytes stimulated with pokeweed mitogen was also measured. There were statistically significant differences between pre and post-operative levels of serum IgG, IgA and IgM, which decreased after surgery. Practically no change in the mean values of IgE and no significant differences in the levels of serum C'3, C'4, and PFB, were found. The in-vitro synthesis of both immunoglobulins (IgG, IgM) by lymphocytes increased significantly after tonsillectomy. Our results suggest that not only does tonsillectomy have no counterproductive effect on the immune system, but that, on the contrary, it seems to improve the immune response, since it appears to unblock the suppression to which the immune system was subject.  相似文献   
997.
998.
999.
At two scientific conferences in 1985, one in Copenhagen sponsored by the Nordic Council of Ministers and the World Health Organization (WHO), the other in Raleigh, NC, it was concluded that chronic toxic encephalopathy may develop following long-term occupational exposure to organic solvents (1,2). The terms organic affective syndrome, mild and severe chronic toxic encephalopathy were suggested for this condition describing increasing severity. In May 1990, a conference on organic solvents and the nervous system was held in Copenhagen sponsored by the Commission of the European Communities and the Danish Ministry of the Environment (3). Scientists and representatives from the governments, industries, and labour organisations from the EEC and US participated.  相似文献   
1000.
Has smoking changed the epidemiology of ulcerative colitis?   总被引:3,自引:0,他引:3  
The influence of smoking on the risk of developing ulcerative colitis is well documented. Compared with lifetime non-smokers, the risk is reduced in smokers and increased in ex-smokers. During the past 50 years general smoking habits have changed considerably. The proportions of smokers and ex-smokers among men and women have undergone significant changes and, consequently, probably also their risk of ulcerative colitis. A review of 56 earlier epidemiologic studies of ulcerative colitis from 1930 to 1990 showed that the sex distribution in ulcerative colitis has changed from an earlier female predominance that has now been replaced by a male predominance. In contemporary pediatric studies no such changes were seen. We propose that these changes in adults are not related to the disease per se but to an extrinsic factor affecting adults but not children--namely smoking.  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