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   507583篇
  免费   50434篇
  国内免费   242篇
  2018年   4901篇
  2017年   4556篇
  2016年   6451篇
  2015年   8246篇
  2014年   9910篇
  2013年   13782篇
  2012年   15885篇
  2011年   16171篇
  2010年   11074篇
  2009年   9938篇
  2008年   14357篇
  2007年   14856篇
  2006年   13785篇
  2005年   13134篇
  2004年   12981篇
  2003年   12459篇
  2002年   12473篇
  2001年   25073篇
  2000年   25485篇
  1999年   19398篇
  1998年   6065篇
  1997年   6319篇
  1996年   5882篇
  1995年   5471篇
  1994年   5350篇
  1993年   5252篇
  1992年   15867篇
  1991年   15604篇
  1990年   14975篇
  1989年   14602篇
  1988年   13525篇
  1987年   12695篇
  1986年   11601篇
  1985年   11657篇
  1984年   9357篇
  1983年   8102篇
  1982年   5771篇
  1981年   5134篇
  1980年   4884篇
  1979年   8895篇
  1978年   6785篇
  1977年   6133篇
  1976年   5612篇
  1975年   6588篇
  1974年   7048篇
  1973年   6917篇
  1972年   6439篇
  1971年   5679篇
  1970年   5077篇
  1969年   4804篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The first appearance, the 12-year follow-up, and the autopsy of a patient with a strange soft-tissue tumor in the lower leg region are described. Although it was originally taken for a malignant synovial tumor, its peculiar distribution pattern, together with its histologic picture, confirmed the final diagnosis as an epithelioid sarcoma.  相似文献   
992.
In Mytilus and Leucophaea the high-affinity binding site density is significantly lower in old animals than in young animals, whereas the low-affinity site density remains unchanged. In Mytilus the estimated met-enkephalin and met-enkephalin-Arg6-Phe7 levels are significantly higher in old than in young animals. In Leucophaea only the met-enkephalin level can be determined, and it is also higher in old animals. The decrease in the high-affinity binding site density and the corresponding increase in endogenous enkephalin levels suggest the existence of an opioid compensatory mechanism associated with the aging process. In Mytilus there is a demonstrated decrease with age in intraganglionic dopamine levels in response to applied opiates. In addition, the inhibition of dopamine-stimulated adenylate cyclase activity by opiates also decreases in older animals. In Leucophaea the sex difference in opioid binding densities diminishes with age.  相似文献   
993.
The amide content of total proteins and protein fractions (alpha-, beta-, gamma-cristallins and albuminoid) from cortex and nuclear lens zones of cattle has been investigated. The amide content in proteins of cortex and nuclear lens of young animals (1,5-2 years old) is the same. The decrease of the amide content in the proteins of nuclear lenz zone of old animals (6-12 years old) is due to fraction of readily hydrolysed amides. The data obtained prove the posttranslational desamidation of lens proteins at ageing. beta-Cristallines--the proteins with the highest amides content is exposed to posttranslational desamidation most of all.  相似文献   
994.
995.
996.
997.
Ammonium chloride and chloroquine protected a variety of cell lines against diphtheria toxin and the toxic lectin modeccin. Experiments where the ability of antibody to neutralize the toxin was measured indicate that in the presence of ammonium chloride and chloroquine, modeccin remains at the cell surface and that the two compounds inhibit the uptake of modeccin into the cytoplasm. A cell line tolerating increased concentrations of modeccin was not protected against modeccin by ammonium chloride or chloroquine, whereas the compounds did protect these cells against diphtheria toxin.  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.
C. P. W. Warren  K. S. Tse 《CMAJ》1974,110(4):425-427,429
Using a solid-phase radioimmunoassay, serum IgE level was determined in 46 normal subjects, 53 patients with bronchial asthma, 44 patients with chronic bronchitis and / or emphysema, and 19 patients with restrictive lung disease. Sputum IgE was measured simultaneously in 51 of the subjects. The range of serum IgE concentration in the normal subjects was wide. It varied between 15 and 750 ng/ml with a mean of 135 ng. Asthmatic patients had significantly higher levels of serum IgE with a mean of 579 ng/ml, but only 30% fell outside the normal 95% confidence limits. Patients with chronic bronchitis, emphysema and restrictive lung diseases had normal IgE levels. There was a significant correlation between serum and sputum IgE levels.  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