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   545933篇
  免费   49228篇
  国内免费   1061篇
  596222篇
  2018年   16990篇
  2017年   15822篇
  2016年   13716篇
  2015年   7913篇
  2014年   8868篇
  2013年   12145篇
  2012年   18432篇
  2011年   28579篇
  2010年   23109篇
  2009年   18829篇
  2008年   24142篇
  2007年   26682篇
  2006年   12817篇
  2005年   13276篇
  2004年   13322篇
  2003年   12895篇
  2002年   12427篇
  2001年   17891篇
  2000年   17784篇
  1999年   14081篇
  1998年   5230篇
  1997年   5457篇
  1996年   5032篇
  1995年   4727篇
  1994年   4608篇
  1993年   4716篇
  1992年   11743篇
  1991年   11704篇
  1990年   11404篇
  1989年   11002篇
  1988年   10600篇
  1987年   10185篇
  1986年   9448篇
  1985年   9352篇
  1984年   7857篇
  1983年   6828篇
  1982年   5298篇
  1981年   4739篇
  1980年   4568篇
  1979年   7493篇
  1978年   5948篇
  1977年   5482篇
  1976年   5275篇
  1975年   5666篇
  1974年   6396篇
  1973年   6246篇
  1972年   6399篇
  1971年   5819篇
  1970年   4672篇
  1969年   4601篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Book reviews     
Environmental Biology of Fishes -  相似文献   
993.
994.
A 14-days' training of rats designed to adapt the animals to the procedure of blood-pressure measurement caused in the myocardium a decrease, in serum an increase in noradrenaline ( NA) content. The latter remained unchanged following 3 days of treatment with 2.5 mg depot angiotensin II (AII) but decreased by more than one-half in the myocardium of untreated animals, and increased in serum. Despite the considerable difference in myocardial NA content and blood-pressure behaviour, both trained and untrained rats showed the same morphological reactions following administration of A II. These myocardial alterations which largely correspond to the so-called epinephrine myocarditis should not therefore be due solely to NA action; rather, the involvement of A II should be considered also.  相似文献   
995.
Combined patch-clamp and fura-2 measurements were performed to study the calcium release properties of Chinese hamster ovary (CHO) cells transfected with the rabbit skeletal muscle ryanodine receptor cDNA carried by an expression vector. Both caffeine (1-50 mM) and ryanodine (100 microM) induced release of calcium from intracellular stores of transformed CHO cells but not from control (non-transfected) CHO cells. The calcium responses to caffeine and ryanodine closely resembled those commonly observed in skeletal muscle. Repetitive applications of caffeine produced characteristic all-or-none rises in intracellular calcium. Inositol 1,4,5-trisphosphate (IP3) neither activated the ryanodine receptor channel nor interfered with the caffeine-elicited calcium release. These results indicate that functional calcium release channels are formed by expression of the ryanodine receptor cDNA.  相似文献   
996.
997.
998.
Staphylococcus and Micrococcus populations were collected from the healthy skin of 10 infant subjects. Infants were sampled from 1 day to 32 weeks of age. Species were characterized by approximately 30 different morphological, physiological, and biochemical characters. Staphylococci were the predominant inhabitants of normal skin, whereas micrococci were found only occasionally in this environment. Staphylococcus epidermidid, S. haemolyticus, and S. hominis were the predominant and persistent staphylococci. These species constituted a high percentage of the total aerobic bacterial flora of infant skin. Micrococcus luteus and M. kristinae were the prevalent micrococci found on infant skin. Only limited correlation between Staphyloccus and Micrococcus populations and infant age or body area sampled was indicated by this study.  相似文献   
999.
J. E. Devitt 《CMAJ》1979,120(11):1370-1372
Most reports advocating mammography have been written by radiologists rather than by clinicians who are frequently confronted by women with breast complaints. The value of mammography in managing patients with breast problems was studied by reviewing its role in 1026 breast consultations; there were 129 patients with cancer. Mammography was performed in 95 patients. The procedure hastened the diagnosis of one comedocarcinoma, and in another patient was suspicious 3 years before she presented with a locally advanced lesion. It missed six cancers. In seven patients it recognized clinically obvious cancers, though in one of these it had given negative results 10 months before the patient presented with a lesion 15 cm in diameter. It also falsely suggested the possibility of cancer in 28 women. In the other 52 patients the clinical diagnosis of a benign condition was usually fairly evident. The morbidity caused by mammography does not seem to have been widely appreciated, no doubt because of the hope that clinically unrecognized cancers would be found by it. Most breast problems can be diagnosed without mammography.  相似文献   
1000.
The effects of ionic strength, urea, calcium and fluorine ions, ouabain and cholinesterase inhibitors on the changes in the ionization equilibrium of an erythrocyte suspension under heating were studied. Proton release by erythrocytes was compared to a release of potassium ions and hemoglobin from the cells. The proton release under heating is mainly determined by the physico--chemical properties of superficial structures of erythrocytes and does not depend on the activity of cholinesterase, ATPase and glycolytic processes.  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