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   5255篇
  免费   567篇
  5822篇
  2021年   64篇
  2019年   58篇
  2018年   75篇
  2017年   49篇
  2016年   95篇
  2015年   141篇
  2014年   172篇
  2013年   237篇
  2012年   267篇
  2011年   240篇
  2010年   161篇
  2009年   144篇
  2008年   188篇
  2007年   209篇
  2006年   206篇
  2005年   205篇
  2004年   207篇
  2003年   220篇
  2002年   192篇
  2001年   169篇
  2000年   151篇
  1999年   130篇
  1998年   74篇
  1997年   63篇
  1996年   53篇
  1994年   54篇
  1993年   41篇
  1992年   91篇
  1991年   87篇
  1990年   91篇
  1989年   74篇
  1988年   68篇
  1987年   63篇
  1986年   70篇
  1985年   62篇
  1984年   84篇
  1983年   55篇
  1982年   46篇
  1981年   41篇
  1980年   50篇
  1979年   48篇
  1978年   52篇
  1977年   56篇
  1976年   46篇
  1975年   62篇
  1974年   49篇
  1973年   80篇
  1972年   56篇
  1971年   43篇
  1970年   38篇
排序方式: 共有5822条查询结果,搜索用时 0 毫秒
1.
2.
3.
Amphiphilic cationic peptides mediate cell adhesion to plastic surfaces   总被引:2,自引:0,他引:2  
Four amphiphilic peptides, each with net charges of +2 or more at neutrality and molecular weights under 4 kilodaltons, were found to mediate the adhesion of normal rat kidney fibroblasts to polystyrene surfaces. Two of these peptides, a model for calcitonin (peptide 1, MCT) and melittin (peptide 2, MEL), form amphiphilic alpha-helical structures at aqueous/nonpolar interfaces. The other two, a luteinizing hormone-releasing hormone model (peptide 3, LHM) and a platelet factor model (peptide 4, MPF) form beta-strand structures in amphiphilic environments. Although it contains only 10 residues, LHM mediated adhesion to surfaces coated with solutions containing as little as 10 pmoles/ml of peptide. All four of these peptides were capable of forming monolayers at air-buffer interfaces with collapse pressures greater than 20 dynes/cm. None of these four peptides contains the tetrapeptide sequence Arg-Gly-Asp-Ser, which has been associated with fibronectin-mediated cell adhesion. Ten polypeptides that also lacked the sequence Arg-Gly-Asp-Ser but were nonamphiphilic and/or had net charges less than +2 at neutrality were all incapable of mediating cell adhesion (Pierschbacher and Ruoslahti, 1984). The morphologies of NRK cells spread on polystyrene coated with peptide LHM resemble the morphologies on fibronectin-coated surfaces, whereas cells spread on surfaces coated with MCT or MEL exhibit strikingly different morphologies. The adhesiveness of MCT, MEL, LHM, and MPF implies that many amphiphilic cationic peptides could prove useful as well defined adhesive substrata for cell culture and for studies of the mechanism of cell adhesion.  相似文献   
4.
Clinical interest in the lipoproteins stems mainly from the association between serum cholesterol concentrations and coronary heart disease. Investigations of lipoproteins should be performed in patients with premature coronary heart disease, with a strong family history of coronary heart disease, or with certain cutaneous stigmata of hyperlipoproteinaemia and when fasting serum samples are seen to be lipaemic. Family studies should be performed in appropriate cases to identify relatives at increased risk of developing coronary heart disease. Patients with conditions known to cause secondary hyperlipoproteinaemia should be investigated if they fall into one of these categories but only after treatment of the underlying condition. Non-specialist laboratories should be able to measure total cholesterol and triglyceride concentrations and high density lipoprotein cholesterol concentrations. Lipoprotein electrophoresis has a limited role in such laboratories and is not necessary as a routine procedure. Specialist laboratories should in addition be able to measure individual lipoproteins and identify apolipoprotein E phenotypes.  相似文献   
5.
Sickness and Healing: An Anthropological Perspective. Robert A. Hahn. New Haven, CT: Yale University Press, 1995 (cloth and paper), viii. 327 pp.  相似文献   
6.
7.
8.
9.
The healthcare of people with HIV is transitioning from specialty care to the primary healthcare (PHC) system. However, many of the performance indicators used to measure the quality of HIV care pre-date this transition. The goal of this work was to examine how existing HIV care performance indicators measure the comprehensive and longitudinal care offered in a PHC setting. A scoping review consisting of peer-reviewed and grey literature searches was performed. Two reviewers evaluated study eligibility and indicators in documents meeting inclusion criteria were extracted into a database. Indicators were matched to a PHC performance measurement framework to determine their applicability for evaluating quality of care in the PHC setting. The literature search identified 221 publications, of which 47 met inclusion criteria. 1184 indicators were extracted and removal of duplicates left 558 unique indicators. A majority of the 558 indicators fell under the ‘secondary prevention’ (12%) and ‘care of chronic conditions’ (33%) domains when indicators were matched to the PHC performance framework. Despite the imbalance, nearly all performance domains in the PHC framework were populated by at least one indicator with significant concentrations in domains such as patient-provider relationship, patient satisfaction, population and community characteristics, and access to care. Existing performance frameworks for the care of people with HIV provide a comprehensive set of indicators that align well with a PHC performance framework. Nonetheless, some important elements of care, such as patient-reported outcomes, are poorly covered by existing indicators. Advancing our understanding of how the experience of care for people with HIV is impacted by changes in health services delivery, specifically more care within the PHC system, will require performance indicators to capture this aspect of HIV care.  相似文献   
10.
The location of the B-glucosidase activity in a whole culture broth of the thermophilic organism Thermoactinomyces has been studied. Little beta-glucosidase activity was found in the culture filtrate, while the culture solids contained the major part of the activity of the whole culture broth. The activity does not appear to be adsorbed to the culture solids; rather there is evidence that it is an intracellular soluble enzyme(s). The pH and temperature optima for a crude beta-glucosidase preparation were determined to be pH 6.5 and 50--55 degrees C. Enzyme activity studies indicate that the same enzyme(s) accounts for the beta-glucosidase and the cellobiase activities. The validity of using the filter paper activity of culture filtrates from Thermoactinomyces to predict the total saccharification of cellulosic materials to glucose is discussed.  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