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   570241篇
  免费   57609篇
  国内免费   814篇
  2018年   5812篇
  2017年   5818篇
  2016年   9197篇
  2015年   15198篇
  2014年   16371篇
  2013年   20170篇
  2012年   22691篇
  2011年   20720篇
  2010年   14365篇
  2009年   13242篇
  2008年   17036篇
  2007年   17646篇
  2006年   16733篇
  2005年   22434篇
  2004年   21449篇
  2003年   18670篇
  2002年   15080篇
  2001年   20291篇
  2000年   19473篇
  1999年   16785篇
  1998年   6622篇
  1997年   6290篇
  1996年   5918篇
  1995年   5754篇
  1994年   5436篇
  1993年   5435篇
  1992年   14409篇
  1991年   14352篇
  1990年   14159篇
  1989年   13567篇
  1988年   12737篇
  1987年   12011篇
  1986年   11363篇
  1985年   11209篇
  1984年   9265篇
  1983年   7941篇
  1982年   6067篇
  1981年   5578篇
  1980年   5194篇
  1979年   8571篇
  1978年   6954篇
  1977年   6164篇
  1976年   5794篇
  1975年   6722篇
  1974年   7423篇
  1973年   7215篇
  1972年   6412篇
  1971年   6001篇
  1970年   5144篇
  1969年   5051篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A survey was done of Canadians who had been interned by the Japanese during World War II to assess the prevalence of latent infection with Strongyloides stercoralis in this group. Packages containing three mail-in kits and a questionnaire were sent to 992 men, 694 (70%) of whom responded. Larvae were found in the stool specimens of four of the respondents. Examination of stool specimens after formalin-ether concentration was the most successful method of detecting Strongyloides larvae. The Baermann concentration technique yielded negative results in all four men. Three of the four cases of strongyloidiasis were detected after sampling of three fecal specimens. In the fourth case additional specimens were requested on the basis of data derived from the questionnaire. The most frequently cited clinical manifestations were abdominal pain, weight loss, diarrhea and rashes.  相似文献   
993.
994.
The influence of brain acid extract products, isolated by high-performance liquid chromatography on H3-diazepam binding was investigated in synaptosomal membranes of C57BL/6 and BALB/c mice. Fractions with stimulatory and inhibitory activity were isolated. Quantitative and qualitative differences in the effects and structure of ACTH-immunoreactive peptide fractions under study were established.  相似文献   
995.
Summary Subcultures of smooth muscle cells derived from rat thoracic aorta were grown on plane plastic substrata and on plastic substrata having ridges molded in them by a heated, ruled template. The cells were found to have a very high degree of contact guidance when distributed sparsely on the ridged substrata. When the cell density increased multilayered, elongated colonies formed. On plane substrata these were irregular, curved, and disposed in all directions. On the ridged substrata, however, the colonies were straight, evenly spaced, and positioned at right angles to the ridges. Supported by Grant MT1011 from the Medical Research Council of Canada.  相似文献   
996.
The introduction of either PGF (10?7 M) or TPA (10?7 M) stimulated, ouabain-sensitive 86Rb+ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF at these concentrations stimulated the incorporation of 3H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na+/K+ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in 3H-TdR incorporation and ouabain-sensitive 86Rb+ influxes with 10?7 M TPA, whereas PGF stimulated a significant increase in 3H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive 86Rb+ influx in both. Therefore, although there appears to be a close correlation between Na+/K+ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF cannot be confirmed.  相似文献   
997.
Astrocytes have long been considered as just providing trophic support for neurons in the central nervous system, but recently several studies have highlighted their importance in many functions such as neurotransmission, metabolite and electrolyte homeostasis, cell signaling, inflammation, and synapse modulation. Astrocytes are, in fact, part of a bidirectional crosstalk with neurons. Moreover, increasing evidence is stressing the emerging role of astrocyte dysfunction in the pathophysiology of neurological disorders, including neurodegenerative disease, stroke, epilepsy, migraine, and neuroinflammatory diseases.  相似文献   
998.
Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 1018 W/cm2 in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors.  相似文献   
999.
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