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   152511篇
  免费   5355篇
  国内免费   6437篇
  2024年   145篇
  2023年   738篇
  2022年   1714篇
  2021年   2946篇
  2020年   2056篇
  2019年   2616篇
  2018年   14015篇
  2017年   12398篇
  2016年   9924篇
  2015年   4033篇
  2014年   4570篇
  2013年   4900篇
  2012年   9446篇
  2011年   17418篇
  2010年   15207篇
  2009年   11128篇
  2008年   13175篇
  2007年   14336篇
  2006年   3056篇
  2005年   2795篇
  2004年   3055篇
  2003年   2979篇
  2002年   2403篇
  2001年   1457篇
  2000年   1175篇
  1999年   794篇
  1998年   525篇
  1997年   424篇
  1996年   395篇
  1995年   374篇
  1994年   367篇
  1993年   293篇
  1992年   352篇
  1991年   321篇
  1990年   235篇
  1989年   215篇
  1988年   154篇
  1987年   212篇
  1986年   155篇
  1985年   138篇
  1984年   116篇
  1983年   121篇
  1982年   90篇
  1981年   85篇
  1979年   67篇
  1978年   67篇
  1976年   54篇
  1973年   66篇
  1972年   302篇
  1971年   308篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
122.
123.

Backgound  

It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT).  相似文献   
124.
125.
126.
127.
The iron metabolism was studied in serum blood samples collected from 26 professional sportsmen undergoing intensive physical exercises using EPR combined with hematological and biochemical laboratory tests. Only 23% of EPR spectra (n = 6) were practically normal while in the rest spectra additional abnormal absorption lines were detected. Presumably, the significant portion of new signals may be caused by different cytochromes. Moreover, the anisotropic signals with g 1 ? 2.02; g 2 ? 1.94 and g 3 ? 1.86 registered in some spectra pointed to the sulfur-iron centers. There was nearly linear correlation between the concentration of Fe3+ in transferrin (Fe3+-Tf) obtained from the EPR spectra and the serum iron concentration measured by absorption photometry both for sportsmen and controls (healthy individuals and patients with different diseases). At equal serum iron concentrations the Fe3+-Tf level was higher in sportsmen than that in controls. The Pearson correlation coefficient (r) for Fe3+-Tf and serum iron values was equal to 0.89 in sportsmen versus r = 0.97 in controls. Additional new lines in serum EPR spectra of professional sportsmen prove the suitability of EPR assay for scheduled medical exams since routine biochemical and hematological tests are insufficient to discover all abnormalities in iron metabolism under intensive physical exercises.  相似文献   
128.
129.
ADHD is a neurodevelopmental syndrome that often persists into adulthood. It is possible that different criteria are necessary for older adults than younger adults: the manifestations of ADHD could change with age; other conditions with onset in later life share presenting symptoms with ADHD; different contextual challenges and patterns of compensatory support may exist. For these reasons, we reviewed evidence for the validity of DSM ADHD criteria in adulthood for individuals over the age of 50. Specifically, we evaluated evidence that the DSM criteria for ADHD identify a valid syndrome in older adults based on clinical presentation, laboratory or testing findings, absence of alternate diagnosis to explain symptoms, course of the syndrome, or familial presence of the condition. We found evidence that various ADHD criteria identify subjects with clinical presentations similar to that seen in younger adults, but only 92 well-described cases have been reported in the literature. ADHD traits also may be less common in the general population of older adults than in younger adults, suggesting that the threshold for an atypical burden of ADHD traits may be lower in older populations. Future research can establish a richer basis for validity of diagnostic criteria for ADHD in older adults.  相似文献   
130.
The need for selection of the optimal material for the manufacturing of cardio-patches can be resolved by the use of cryostored autologous pericardial tissue. This short communication is a concise fragment of a large-scale research and demonstrates only the efficiency of cell culturing before and after pericardial preservation in the low temperature conditions.  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