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   613418篇
  免费   66972篇
  国内免费   1050篇
  681440篇
  2018年   15272篇
  2017年   13706篇
  2016年   12540篇
  2015年   8415篇
  2014年   9675篇
  2013年   13576篇
  2012年   18753篇
  2011年   26948篇
  2010年   21040篇
  2009年   16960篇
  2008年   22400篇
  2007年   24534篇
  2006年   13276篇
  2005年   13128篇
  2004年   13465篇
  2003年   13109篇
  2002年   12414篇
  2001年   22910篇
  2000年   23340篇
  1999年   18623篇
  1998年   6660篇
  1997年   7064篇
  1996年   6850篇
  1995年   6573篇
  1994年   6555篇
  1993年   6493篇
  1992年   16252篇
  1991年   16154篇
  1990年   15804篇
  1989年   15374篇
  1988年   14373篇
  1987年   13820篇
  1986年   12920篇
  1985年   13064篇
  1984年   10971篇
  1983年   9703篇
  1982年   7471篇
  1981年   7011篇
  1980年   6588篇
  1979年   10960篇
  1978年   8520篇
  1977年   7849篇
  1976年   7458篇
  1975年   8265篇
  1974年   8559篇
  1973年   8403篇
  1972年   8180篇
  1971年   7167篇
  1970年   6055篇
  1969年   5713篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
Cryptococcosis is an often fatal opportunistic fungal infection. Despite efforts to elucidate the role of immunity in host defense against the disease, much remains to be learned. The purpose of this brief review is to provide the reader with an overview of the history of research concerned with host immunity in cryptococcosis. Both humoral and cell-mediated studies are included. An effort has been made to present the reader with a comprehensive list of references in the hope of encouraging additional reading and research in this important area.  相似文献   
132.
133.
A chronic implant for recording of cochlear potentials in primates   总被引:1,自引:0,他引:1  
A new technique for the continuous recording of peripheral bioelectrical activity in the auditory system of primates is described. Because of basic differences in the anatomy of the temporal bone, the approach to the round window of the cochlea is more difficult in most primates than in lower animals. A relatively simple surgical approach, which made possible the placement of an electrode into the perilymph of the inner ear via the well-demarcated horizontal semicircular canal was therefore developed and is described in detail. The bared tip of a Teflon-coated wire was cemented into the canal opening with carboxylate cement, and the wire attached to a permanent electrical connector on the skull. Cochlear microphonic and action potentials of 50 to 100 μV amplitude were thus recorded on a continuing basis at the same time that behavioral studies of primate auditory acuity were conducted.  相似文献   
134.
135.
—A resolution of the enhancement of protein synthesis in the visual cortex of rats during first exposure to light (Richardson and Rose , 1972) was achieved by polyacrylamide gel electrophoresis using a double-labelling technique. Differential incorporation of lysine was established between exposed and control animals in two fractions of the soluble proteins and seven fractions of the insoluble proteins. This suggests that exposure to a new experience of this type involves a specific effect on protein synthesis, rather than a general stimulation across all fractions.  相似文献   
136.
137.
138.
139.
A new gas-liquid chromatographic method was developed for the determination of diethylether in whole blood. Ether was quantitated by peak area ratio analysis with n-propanol as the internal standard using a flame ionization detector. Blood ether concentrations were determined in cats undergoing inhalational anesthesia by ether in oxygen. In normal spontaneously breathing cats, anesthesia began at ether concentrations of about 0.6 g/l, and respiratory arrest occurred at 2.4 g/l and above. Mean arterial blood pressure was well maintained throughout the entire anesthetic range. In spinal artificially respired animals, mean arterial blood pressure correlated inversely with blood ether concentration. The data suggest that decline in blood pressure may be a useful sign of ether toxicity in spinal cats.  相似文献   
140.
ABSTRACT   The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship.  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