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   398419篇
  免费   43155篇
  国内免费   215篇
  2018年   4434篇
  2017年   4052篇
  2016年   6088篇
  2015年   9063篇
  2014年   9859篇
  2013年   13650篇
  2012年   15915篇
  2011年   15367篇
  2010年   10157篇
  2009年   8630篇
  2008年   13311篇
  2007年   13448篇
  2006年   12498篇
  2005年   12136篇
  2004年   11641篇
  2003年   11339篇
  2002年   10618篇
  2001年   13225篇
  2000年   13263篇
  1999年   11012篇
  1998年   4355篇
  1997年   4337篇
  1996年   4262篇
  1995年   4013篇
  1994年   4004篇
  1993年   3854篇
  1992年   9375篇
  1991年   9086篇
  1990年   8761篇
  1989年   8626篇
  1988年   8112篇
  1987年   7949篇
  1986年   7352篇
  1985年   7585篇
  1984年   6368篇
  1983年   5675篇
  1982年   4532篇
  1981年   4371篇
  1980年   3942篇
  1979年   6507篇
  1978年   5103篇
  1977年   4841篇
  1976年   4623篇
  1975年   5015篇
  1974年   5499篇
  1973年   5389篇
  1972年   4920篇
  1971年   4496篇
  1970年   3960篇
  1969年   3976篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
951.
952.
Coagulation and fibrinolysis were measured in the portal and peripheral circulation in 15 rabbits after ligation of the superior mesenteric artery. It was found that the local coagulation syndrome in the mesenteric region can be recognized by tests in blood samples taken from the peripheral circulation area.  相似文献   
953.
954.
M R Joffres  P Hamet  S W Rabkin  D Gelskey  K Hogan  G Fodor 《CMAJ》1992,146(11):1997-2005
OBJECTIVE: To estimate the prevalence and distribution of elevated blood pressure (BP) among Canadian adults and to determine the level of control, treatment, awareness and prevalence of other risk factors among adults with high BP. DESIGN: Population-based cross-sectional surveys. SETTING: Nine Canadian provinces, from 1986 to 1990. PARTICIPANTS: A probability sample of 26,293 men and women aged 18 to 74 years was selected from the health insurance registers in each province. For 20,582 subjects, BP was measured at least twice. Nurses administered a standard questionnaire and recorded two BP measurements using a standardized technique. Two further BP readings, anthropometric measurements and a blood specimen for lipid analysis were obtained from those subjects who attended a clinic. OUTCOME MEASURES: Mean values of systolic and diastolic BP, prevalence of elevated BP using different criteria, and prevalence of smoking, elevated blood cholesterol, body mass index, physical activity and presence of diabetes by high BP status are reported. MAIN RESULTS: Sixteen percent of men and 13% of women had diastolic BP of 90 mm Hg or greater or were on treatment (or both). About 26% of these subjects were unaware of their hypertension, 42% were being treated and their condition controlled, 16% were treated and not controlled, and 16% were neither treated nor controlled. Use of non-pharmacologic treatment of high BP with or without medication was low (22%). Hypertensive subjects showed a higher prevalence of elevated total cholesterol, high body mass index, diabetes and sedentary lifestyle than normotensive subjects. Most people with elevated BP were in the 90 to 95 mm Hg range for diastolic pressure and 140 to 160 mm Hg range for systolic pressure. Prevalence of high isolated systolic BP sharply increased in men (40%) and women (49%) 65 to 74 years old. CONCLUSIONS: The relatively low level of control of elevated BP calls for population and individual strategies, stressing a non-pharmacologic approach and addressing isolated systolic hypertension in the elderly.  相似文献   
955.
A microspectrofluorimetric study is made of the influence of dimethylnitrosamine on NADP reduction, following sequential microinjections into the same L cell, of two substrates: (1) isocitrate, with activity of isocitrate dehydrogenase both in the extramitochondrial and intramitochondrial compartments, (2) 6-phosphogluconate, with activity of the dehydrogenase in the extramitochondrial compartment. In control L cells a two-step reduction of NAD(P) is obtained followed by relatively slow reoxidation. In the minutes which follow addition of carcinogen, e.g., dimethylnitrosamine, to the cell medium the isocitrate and 6-phosphogluconate-induced transient NADP reoxidation is decreased in magnitude compared to control, while the rate constant of NADPH reoxidation is considerably accelerated, possibly due to requirements at the level of the microsomal metabolizing system. Observations within the first hour of carcinogen addition suggest an interesting system for evaluating the immediate actions of carcinogens at extranuclear sites: i.e., a comparative study of NADP reduction-reoxidation rate constants via injection of substrates for extra- vs. intramitochondrial pathways.  相似文献   
956.
957.
958.
959.
960.
Fraction F1 with a MW of 5.10(3)-5.10(4), which had been isolated from the blood serum of blood donors as controls and patients at the terminal stage of chronic kidney insufficiency, specifically inhibited the erythropoiesis of test animals at the stage sensitive to erythropoietin and morphologically distinguishable cells of the bone-marrow. In uremia, protein concentration was twice higher in comparison to the normal one. The inhibiting effect of fraction F1 from the serum of patients is caused by the enlargement of level of physiological inhibitors and unspecific toxins of the cell proliferation. Those data characterising the factor detected in the fraction F1 of normal serum together with the erythrocytic chalon are 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