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   1700633篇
  免费   156543篇
  国内免费   1629篇
  2021年   18377篇
  2019年   16298篇
  2018年   20085篇
  2017年   18883篇
  2016年   29701篇
  2015年   43099篇
  2014年   51253篇
  2013年   77342篇
  2012年   49247篇
  2011年   41480篇
  2010年   48660篇
  2009年   48473篇
  2008年   37700篇
  2007年   37207篇
  2006年   39169篇
  2005年   40589篇
  2004年   39239篇
  2003年   36537篇
  2002年   34513篇
  2001年   53342篇
  2000年   51002篇
  1999年   46124篇
  1998年   27766篇
  1997年   27487篇
  1996年   26624篇
  1995年   24825篇
  1994年   24423篇
  1993年   23734篇
  1992年   38832篇
  1991年   37422篇
  1990年   36131篇
  1989年   36323篇
  1988年   33340篇
  1987年   32027篇
  1986年   30016篇
  1985年   31599篇
  1984年   29167篇
  1983年   25696篇
  1982年   23673篇
  1981年   22550篇
  1980年   21174篇
  1979年   25362篇
  1978年   22444篇
  1977年   21036篇
  1976年   20286篇
  1975年   20659篇
  1974年   21764篇
  1973年   21967篇
  1972年   19030篇
  1971年   17292篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
902.
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   
903.
904.
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   
905.
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   
906.
907.
Data are presented to show how the number and growth of juvenile salmon in streams in the Scottish Highlands are influenced by various physical (temperature, water chemistry, depth and velocity, type of substratum) and biotic (food resources, competition, recruitment) factors.  相似文献   
908.
Cultured astrocytes from a syncytium after maturation   总被引:2,自引:0,他引:2  
The formation of functional gap junctions between astrocytes was investigated during differentiation of these cells in culture. Precursor cells of GFA (glial fibrillary acidic) protein-positive astrocytes were cultured in a chemically defined medium as a homogeneous population. These cells were rarely coupled to one neighbour, as revealed by electrical and dye coupling and never formed a large syncytium, as investigated by injection and spread of Lucifer Yellow. Differentiation with respect to GFA protein accumulation can be induced in these cells by culturing in horse serum-containing medium. The formation of functional junctions developed within 2 weeks in about 20% of the cells. Coupled cells formed a large syncytium. When the astrocytes were co-cultured with primary cerebellar cells (consisting predominantly of small neurons) after the switch to serum-containing medium the percentage of coupled astrocytes increased to about 65%. Again the coupled cells formed a large syncytium. Since no physical contact was possible between the astrocyte cultures and the primary cerebellar cells the stimulation of coupling had to be signalized by soluble factor(s).  相似文献   
909.
910.
Experiments on the laboratory cultures of lice infected by Weigl's method revealed that the spontaneous, erythromycin-resistant mutant of R. prowazekii strain E, adapted to the vector's organism, retained its resistance to erythromycin during 50 successive passages without the maintenance concentrations of this antibiotic. The above strain remained sensitive to tetracycline and levomycetin. Its level of sensitivity to the latter antibiotics was similar to that of R. prowazekii strains cultivated in the vector's organism for a long time.  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