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   852200篇
  免费   97590篇
  国内免费   355篇
  950145篇
  2016年   9186篇
  2015年   12645篇
  2014年   15056篇
  2013年   21861篇
  2012年   23961篇
  2011年   24461篇
  2010年   16438篇
  2009年   15360篇
  2008年   21855篇
  2007年   23088篇
  2006年   21596篇
  2005年   20814篇
  2004年   20807篇
  2003年   20202篇
  2002年   19700篇
  2001年   34936篇
  2000年   35459篇
  1999年   28446篇
  1998年   10406篇
  1997年   10939篇
  1996年   10497篇
  1995年   10031篇
  1994年   9943篇
  1993年   9862篇
  1992年   24979篇
  1991年   24748篇
  1990年   24534篇
  1989年   24004篇
  1988年   22422篇
  1987年   21480篇
  1986年   20126篇
  1985年   20646篇
  1984年   17218篇
  1983年   15053篇
  1982年   11678篇
  1981年   10778篇
  1980年   10083篇
  1979年   16929篇
  1978年   13291篇
  1977年   12399篇
  1976年   11790篇
  1975年   12961篇
  1974年   13796篇
  1973年   13548篇
  1972年   12767篇
  1971年   11283篇
  1970年   9865篇
  1969年   9516篇
  1968年   8822篇
  1967年   7676篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
981.
An in vivo/in vitro evaluation of teratogenic action   总被引:1,自引:0,他引:1  
Several compounds were administered to pregnant Wistar-derived rats either 24 or four hours prior to the recovery of day 10 embryos for in vitro culture in Waymouth's medium and fetal calf serum. The compounds tested were 2-amino-1,3,4-thiadiazole (thiadiazole), cadmium sulfate, 1,2-dibromo-2,2-dichloroethyl dimethyl phosphate (dibrom), 2-(sec-Butyl)-4,6-dinitrophenol (dinoseb), led nitrate, polybrominated biphenyls (PBB), sodium arsenate, and trypan blue. After 24 hours in culture, two thirds of the embryos were recovered for examination. The remaining one third were continued in culture until 42 hours. Recovered embryos were examined for rotation of the embryonic axis, heart rate, establishment of the visceral yolk sac circulation, somite number, growth of the limb buds, closure of the neural tube, and development of the allantois and amnion. All tested compounds inhibited the rate of development in vitro.  相似文献   
982.
Idiopathic calcinosis of the scrotum is a rare disease that may cause massive deformation of the scrotal wall. The first patient we present was also known to have neurofibromatosis. In the second patient we describe, nodules of idiopathic calcinosis of the scrotum were seen with walls that evidenced no epithelial lining, as well as calcification in epithelial cysts. At present, the only possible treatment is excision, and we excised the afflicted skin without problems in primary wound closure.  相似文献   
983.
Three acetotrophicMethanosarcina species, which included marine, nonmarine, and thermophilic strains, were grown on acetate in a 10-liter pH auxostat. Specific growth rates and molar growth yields were constant throughout growth. Cell yields were up to 18-fold greater than previously reported. These properties of the pH auxostat indicate that it is a preferred culture method for the biochemical study of methanogenesis from acetate.  相似文献   
984.
A test system permitting the detection of influenza virus protein M at a concentration of 0.1-0.5 ng/ml in ELISA has been developed. The use of this system made it possible to detect influenza viruses A and B directly in crude virus-containing material and clinical samples obtained from influenza patients. During the outbreak of influenza in the spring of 1983 ELISA was successfully used for the rapid diagnosis of influenza, and some of its advantages in comparison with the conventional immunofluorescence test were thus demonstrated. To overcome difficulties arising from the low immunogenic potency of protein M, in the process of obtaining diagnostic sera and ascitic fluids the animals were immunized with the conjugate of protein M and polyelectrolite, which ensured considerable activation of humoral immune response.  相似文献   
985.
Addition of ethanol to rat brain homogenate containing opiate receptors inhibits at a concentration of 50 mM the stereospecific binding of 3H-naloxone at 37 degrees C but not at 0 degree C, with the ID50 being 462 mM under these conditions. The temperature-dependent inhibition of the ligand binding suggests that ethanol does not compete with naloxone for specific binding sites of opiate receptors and changes the structure of lipids in biological membranes. Scatchard's analysis has demonstrated that apart from a decrease in the number of highly affinity binding sites of 3H-naloxone, the total amount of the binding sites remains unchanged both in the presence and absence of ethanol and constitutes 453 and 549 fmol/mg protein. It is assumed that ethanol might interconvert highly and low-affinity binding sites. Analysis of the effect of ethanol on 3H-naloxone binding with opiate receptors contained by synaptic membranes obtained from animals with varying predisposition to voluntary alcoholization has shown that ethanol inhibits to a greater degree ligand binding with membranes obtained from rats predisposed to alcoholization. The possibility of the involvement of receptors in the biochemical mechanisms by which the initial alcoholic motivation is effected is under discussion.  相似文献   
986.
Home range, dispersal and the clan system of impala   总被引:1,自引:0,他引:1  
  相似文献   
987.
The regenerating scale and tissues comprising the scale pocket of Fundulus olivaceus were examined microscopically at specific intervals. Scale removal resulted in a thickening of the epidermis which persisted through the early stages of regeneration. This thickening was due in part to the appearance of columnar basal cells which divided producing cells that became mucous cells and squamous cells. The scale regenerated as a relatively large plate of bone which first appeared between layers of scleroblasts on the floor of the scale pocket and then grew producing circuli and radii. By the fourth day of regeneration, calcium was observed in the cytoplasm of the scleroblasts and at randomly distributed foci in the osseous portion of the scale. The osseous layer was completely calcified by 15 days of regeneration.  相似文献   
988.
The study of the effect of gamma globulin introduced in different doses (0.5 and 0.25 ml/mg) in combination with Fermi rabies vaccine (observations on humans were made) and with cerebral rabies vaccine inactivated by UV irradiation (in animal experiments) demonstrated that the injection of the higher doses of gamma globulin resulted in lower geometrical mean of antibody titers. Therefore, in combined administration of rabies vaccine and gamma globulin for postexposure rabies prevention it is advisable to reduce the dose of gamma globulin by one-half.  相似文献   
989.
Summary Viral leukemogenesis in mice is frequently initiated by proviral activation of a highly conserved cellular gene called Pim-1. Here we report the chromosomal localization of the human homologue by Southern blot analyses of DNAs obtained from human-rodent somatic cell hybrids. The single copy human homologue was assigned to the 6pter-q12 segment.  相似文献   
990.
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