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   1891076篇
  免费   179067篇
  国内免费   1834篇
  2021年   19012篇
  2018年   21151篇
  2017年   19897篇
  2016年   30820篇
  2015年   44427篇
  2014年   52744篇
  2013年   79039篇
  2012年   55444篇
  2011年   48766篇
  2010年   51014篇
  2009年   50334篇
  2008年   43740篇
  2007年   43743篇
  2006年   44764篇
  2005年   45908篇
  2004年   44533篇
  2003年   41754篇
  2002年   39744篇
  2001年   62452篇
  2000年   60773篇
  1999年   53291篇
  1998年   29035篇
  1997年   28757篇
  1996年   27661篇
  1995年   25918篇
  1994年   25464篇
  1993年   24822篇
  1992年   44862篇
  1991年   43295篇
  1990年   41947篇
  1989年   41975篇
  1988年   38690篇
  1987年   37039篇
  1986年   34870篇
  1985年   36461篇
  1984年   32815篇
  1983年   28710篇
  1982年   25661篇
  1981年   24290篇
  1980年   22784篇
  1979年   29430篇
  1978年   25459篇
  1977年   23764篇
  1976年   22821篇
  1975年   23724篇
  1974年   25378篇
  1973年   25524篇
  1972年   22421篇
  1971年   20423篇
  1970年   17939篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
The use of modernized photometric accessories to a model microscope manufactured by the Leningrad Optico-Mechanical Amalgamation (USSR), as well as the practical application of innovations facilitating and standardizing research work, has made it possible to obtain objective data indicating the presence of significant, direct, linear correlation between infectious activity and the intensity of fluorescence emitted by fluorescent antibodies bound with the antigen of 11 studied variants of Japanese encephalitis virus in continuous cell lines. The study of the dynamics of fluorescence intensity permitted the objective evaluation of the previously revealed regularity in the increase of the intensity of the induced fluorescence of Japanese encephalitis antigen in continuous cell cultures.  相似文献   
992.
993.
A high-performance liquid chromatographic procedure is reported for reproducibly and sensitively quantitating caffeine and its N-demethylated metabolite paraxanthine in micro-samples. A 5-μm reversed-phase radial compression column and 214-nm fixed wavelength ultraviolet detector were used to attain a sensitivity sufficient to quantitate these compounds at concentratios as low as 80 ng/ml using only 25 μl of sample. The assay is applicable to microliter samples of whole blood, serum, plasma, saliva, amniotic, cerebro-spinal and gastric fluids such as might be obtained in studies involving small animals or neonates. The utility of the assay is illustrated with caffeine and paraxanthine levels measured in several maternal and fetal fluids following constant-rate intravenous infusion of caffeine into a rabbit throughout pregnancy.  相似文献   
994.
995.
We have introduced into the wide host range conjugative plasmid RP4, a mini-Mu derivative which was known to be able to transpose spontaneously in E. coli K-12, and to induce in such a host several kinds of chromosomal rearrangements including replicon fusions. Unlike RP4, RP4::mini-Mu can mediate the transfer of the host chromosome to a recipient bacterium and generate R primes at high frequencies (10?4 for the transfer of a given marker, 10?5 for the formation of R primes carrying a given marker). Two such RP4::mini-Mu plasmids were introduced into one Salmonella typhimurium strain, one Klebsiella pneumoniae strain, and one Proteus mirabilis strain. Each of these three strains were mated with an E. coli K-12 recipient and transconjugants carrying R primes were recovered in all three cases at frequencies ranging from 5 × 10?6 to 10?7.  相似文献   
996.
997.
A double antibody radioimmunoassay technique is described for the measurement of anti-zona antibodies in the peripheral plasma of marmosets actively immunized against intact cow zonae pellucidae. The method has been shown to be a reliable, repeatable indicator of antibody titer, enabling direct comparison of the response obtained between marmosets. This is the first report of a procedure describing the active immunization of a primate against zona antigens, and the first time a radioimmunoassay technique has been used to monitor profiles of anti-cow zona antibody production following active immunization. The method should prove to be a useful tool in the evaluation of zona antigens as agents for immunocontraception.  相似文献   
998.
999.
Physicians with an interest in pain have long suggested that the poor complain more and have a higher prevalence of neuroticism than do higher social groups. This assumption was tested by analysing the pain patterns in 500 consecutive patients attending a pain relief clinic. Results implied that scores for presenting pain, anxiety, and depression were similar to all social groups. After treatment scores for residual pain were significantly lower in all social classes, with greatest reduction in classes III, IV, and V. Almost identical results were obtained in a subgroup of patients with cancer but not in a subgroup with sciatica. That patients from the lower social classes have a higher perception of pain and are more neurotic than other group is a myth, probably resulting from poor communication between clinicians and patients of dissimilar socioeconomic class.  相似文献   
1000.
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