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   418637篇
  免费   35645篇
  国内免费   295篇
  2018年   4877篇
  2017年   4667篇
  2016年   6090篇
  2015年   6359篇
  2014年   8134篇
  2013年   11604篇
  2012年   13173篇
  2011年   14106篇
  2010年   9706篇
  2009年   8590篇
  2008年   12427篇
  2007年   12840篇
  2006年   12263篇
  2005年   11576篇
  2004年   11468篇
  2003年   11123篇
  2002年   10977篇
  2001年   18988篇
  2000年   18845篇
  1999年   14580篇
  1998年   4462篇
  1997年   4460篇
  1996年   4288篇
  1995年   3910篇
  1994年   3814篇
  1992年   11405篇
  1991年   11319篇
  1990年   11308篇
  1989年   11097篇
  1988年   10316篇
  1987年   9704篇
  1986年   8745篇
  1985年   9267篇
  1984年   7341篇
  1983年   6225篇
  1982年   4341篇
  1981年   3912篇
  1980年   3728篇
  1979年   6792篇
  1978年   5174篇
  1977年   4781篇
  1976年   4664篇
  1975年   5475篇
  1974年   5949篇
  1973年   5965篇
  1972年   5278篇
  1971年   4966篇
  1970年   4306篇
  1969年   4092篇
  1968年   3865篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
942.
A fluorescent probe was used to study hydrocortisone (10 microM) action on mitogen-stimulated free cytoplasmic calcium level in lymphocytes of patients with bronchial asthma. The patients were divided into two groups according to their sensitivity to glucocorticoid therapy. Hydrocortisone-specific calcium-blocking effect was absent in hormone-resistant patients. Lymphocytes of hormone-sensitive patients responded to hydrocortisone administration by a decline of mitogen-induced calcium level.  相似文献   
943.
Formaldehyde fixation of cells is routinely used to study DNA-protein interactions in vivo. In these studies, DNA is often analyzed using a polymerase chain reaction technique. Although it is known that formaldehyde can damage DNA, no studies have been performed so far to compare the efficiency of DNA amplification between normal and fixed cells. Here we show that formaldehyde fixation results in a 15% to 20% reduction in the ability to amplify cellular DNA. The loss of amplifiability is independent of the length of the amplification region and the degree to which DNA is compacted on packaging into chromatin.  相似文献   
944.
Dynamic Light Regulation of Photosynthesis (A Review)   总被引:9,自引:7,他引:2  
Regulatory reactions providing the photosynthetic apparatus with the ability to respond to variations of irradiance by changes in activities of the light and the dark stages of photosynthesis within a time range of seconds and minutes are considered in the review. At the light stage, such reactions are related to the changes in both distribution of light energy between two photosystems and probability of nonphotochemical dissipation of absorbed quanta in PSI and PSII. These regulatory reactions operate in a negative feedback mode, thus avoiding overreduction of electron transport chain and minimizing the probability of generation of reactive oxygen species. The crucial role in preventing the generation of reactive oxygen species belongs to dynamic regulation of electron transport activity despite the presence of complex system of their detoxification in chloroplasts. In dark reactions of Calvin cycle, the regulatory responses involve a positive feedback principle being related to redox regulation of activities of several enzymes, which is sensitive to the reduction status of PSI acceptor side. The complex of regulatory reactions based on negative and positive feedback principles provides prolonged functioning of a chloroplast and high stability of photosynthetic activity under various light conditions.  相似文献   
945.
The influence of ionizing radiation (gamma-rays 60Co) on aggregation activity of the vascular wall and functional (aggregation) platelet activity was studied in the course of the development of acute radiation sickness. The decrease in the aggregation properties of the vascular wall and high functional activity of platelets were inversely proportional, correlating with the periods of acute radiation sickness development and depending on the radiation dose. It is suggested that the changes detected may play a role in the pathogenesis of the development of the postirradiation thrombohemorrhagic syndrome.  相似文献   
946.
947.
948.
Seventy-one human x mouse hybrid cell lines were used to map the locus of a human alpha-3-fucosyltransferase to 11q. The enzyme transfers fucose onto H type 2 more efficiently than onto sialyl-N-acetyllactosamine, suggesting that it is the myeloid type of alpha-3-fucosyltransferase (Mollicone et al., 1990), which makes the 3-fucosyllactosamine epitope on polymorphonuclear cells and monocytes. This epitope is also known as CD15 (Tetteroo et al., 1987).  相似文献   
949.
I. ALBESA, P. BOGDANOV, A. ERASO, N.R. SPERANDEO AND M.M. DE BERTORELLO. 1995. The antibiotic activity of new synthetic isoxazolylnaphthoquinone imines was studied. Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922 were resistant to the four compounds studied (MIC > 128 µg ml−1), but Staphylococcus aureus ATCC 25923, ATCC 29213 and 30 clinical isolates of Staph. aureus were inhibited by 2-hydroxy- N -(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (I). This compound diminished bloodstream infection of mice injected i.m. with Staph. aureus; septicaemia decayed significantly when I was applied at the beginning of the infection while when I was given 3 d after bacterial challenge, a significant protection was afforded. Bactericidal activity in serum increased during the 5 h after I was administered i.p.
The acetyl derivative of I had a high MIC but when inoculated orally in mice decreased the Staph. aureus counts in circulation. This protection occurred only when the schedule of administration started close to the bacterial challenge. Antibiotic activity in vivo may be associated with in vitro effects.  相似文献   
950.
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