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   1770191篇
  免费   167610篇
  国内免费   1494篇
  2021年   18428篇
  2019年   16284篇
  2018年   20208篇
  2017年   19046篇
  2016年   29835篇
  2015年   43329篇
  2014年   51453篇
  2013年   77593篇
  2012年   51550篇
  2011年   44122篇
  2010年   49243篇
  2009年   48913篇
  2008年   40250篇
  2007年   39786篇
  2006年   41563篇
  2005年   42720篇
  2004年   41599篇
  2003年   38793篇
  2002年   36631篇
  2001年   56572篇
  2000年   54396篇
  1999年   48838篇
  1998年   28337篇
  1997年   28102篇
  1996年   27161篇
  1995年   25353篇
  1994年   24958篇
  1993年   24372篇
  1992年   41576篇
  1991年   40006篇
  1990年   38651篇
  1989年   38888篇
  1988年   35730篇
  1987年   34297篇
  1986年   32232篇
  1985年   33674篇
  1984年   30784篇
  1983年   27148篇
  1982年   24601篇
  1981年   23286篇
  1980年   21982篇
  1979年   27349篇
  1978年   23879篇
  1977年   22214篇
  1976年   21284篇
  1975年   21907篇
  1974年   22942篇
  1973年   23100篇
  1972年   20124篇
  1971年   18318篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
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   
953.
954.
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   
955.
956.
A microcomputer mainframe linked system is described which allows video camera data capture and storage of one-dimensional whole-cell protein electrophoresis gel images, processing of normalized traces to produce a similarity matrix, and analysis of the matrix using the commercial cluster analysis program CLUSTAN. A new similarity coefficient is introduced which takes into account both band position and intensity. Forty-five strains of Haemophilus influenzae, including the eight biotypes and six serotypes, were analyzed using this system. Results demonstrated groupings which are consistent with known genetic relationships.  相似文献   
957.
1. Nile crocodiles, reared in fresh water and exposed acutely to seawater, suffer marked dehydration and hypernatraemia. Cloacal urine osmolarity and potassium concentration increased markedly but urine sodium remains low. 2. Hypernatraemia is increased when secretion from the lingual salt glands is prevented. 3. C. niloticus appears not to drink seawater. 4. Similarities in osmoregulatory response between estuarine and Nile crocodiles suggest that the lingual salt glands of C. niloticus are functional in salt water, playing an important role in sodium balance. 5. Significant differences in the function of the renal/cloacal complex of Alligator and Crocodylus emphasize further the differences between these two groups of crocodilian and provide support for the postulated marine ancestry of many or all of the Crocodylidae.  相似文献   
958.
An apparently novel human plasma and urinary protein of low molecular weight was isolated from several highly purified preparations of protein HC by gel chromatography and high voltage electrophoresis with a yield of about 8 mg/g. The protein has a molecular weight of about 20,000, neutral electrophoretic mobility at pH 6.5 and a high content of half-cystine. It is associated with a yellow-brown chromophore like protein HC and could be demonstrated in all investigated preparations of isolated human, rabbit and guinea-pig protein HC and alpha 1-microglobulin.  相似文献   
959.
The photoacoustic spectroscopic studies of purple pigmented leaves revealed the occurrence of anthocyanins and betalains in some local weed species growing on soils with low moisture levels. The pigmentation intensities were higher in C4 plants than in C3 plants. An inverse correlation was observed between pigmentation intensities and soil moisture levels. This work is a part of the UNEP Research Project granted to Prof. D. O. Hall, UNEP Coordinator, Department of Plant Sciences, King’s College; London.  相似文献   
960.
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