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   1412103篇
  免费   114525篇
  国内免费   3333篇
耳鼻咽喉   18389篇
儿科学   46633篇
妇产科学   41091篇
基础医学   200983篇
口腔科学   37736篇
临床医学   126183篇
内科学   284862篇
皮肤病学   33370篇
神经病学   117010篇
特种医学   53883篇
外国民族医学   464篇
外科学   210984篇
综合类   32770篇
现状与发展   3篇
一般理论   487篇
预防医学   110015篇
眼科学   31818篇
药学   98655篇
  1篇
中国医学   3350篇
肿瘤学   81274篇
  2021年   10882篇
  2019年   11692篇
  2018年   16614篇
  2017年   12697篇
  2016年   14285篇
  2015年   16032篇
  2014年   22620篇
  2013年   33462篇
  2012年   45485篇
  2011年   48032篇
  2010年   28212篇
  2009年   27110篇
  2008年   44425篇
  2007年   46938篇
  2006年   47513篇
  2005年   45963篇
  2004年   43849篇
  2003年   41782篇
  2002年   40266篇
  2001年   73093篇
  2000年   74630篇
  1999年   61621篇
  1998年   17007篇
  1997年   15453篇
  1996年   15605篇
  1995年   14800篇
  1994年   13411篇
  1993年   12592篇
  1992年   45887篇
  1991年   43530篇
  1990年   41536篇
  1989年   39594篇
  1988年   36222篇
  1987年   35395篇
  1986年   32893篇
  1985年   31333篇
  1984年   23855篇
  1983年   20053篇
  1982年   12222篇
  1981年   10790篇
  1979年   20717篇
  1978年   14590篇
  1977年   12097篇
  1976年   11374篇
  1975年   11631篇
  1974年   13998篇
  1973年   13552篇
  1972年   12645篇
  1971年   11501篇
  1970年   10928篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  相似文献   
34.
35.
36.
37.
Behçet disease is a complex, multisystem disease characterized by recurrent oral and genital ulcerations. It rarely occurs in infants or children. Neonatal Behçet disease has been reported in infants whose ulcers resolve at or before 9 weeks of age. Few cases of neonatal Behçet disease persisting into childhood have previously been reported. We report the case of a 1‐month‐old infant who presented with severe recurrent genital ulcerations and at 6 months developed recurrent oral ulcerations. Her orogenital ulcerations continue to recur. Human leukocyte antigen testing revealed HLA‐B51 and B44 positivity. This is a case of pediatric Behçet disease in the neonatal period. Behçet disease should be considered in the differential diagnosis of recurrent genital and oral ulcerations in infants and children.  相似文献   
38.
39.
AimsWe previously showed that the protective effects of endothelial progenitor cells (EPCs)‐released exosomes (EPC‐EXs) on endothelium in diabetes. However, whether EPC‐EXs are protective in diabetic ischemic stroke is unknown. Here, we investigated the effects of EPC‐EXs on diabetic stroke mice and tested whether miR‐126 enriched EPC‐EXs (EPC‐EXsmiR126) have enhanced efficacy.MethodsThe db/db mice subjected to ischemic stroke were intravenously administrated with EPC‐EXs 2 hours after ischemic stroke. The infarct volume, cerebral microvascular density (MVD), cerebral blood flow (CBF), neurological function, angiogenesis and neurogenesis, and levels of cleaved caspase‐3, miR‐126, and VEGFR2 were measured on day 2 and 14.ResultsWe found that (a) injected EPC‐EXs merged with brain endothelial cells, neurons, astrocytes, and microglia in the peri‐infarct area; (b) EPC‐EXsmiR126 were more effective than EPC‐EXs in decreasing infarct size and increasing CBF and MVD, and in promoting angiogenesis and neurogenesis as well as neurological functional recovery; (c) These effects were accompanied with downregulated cleaved caspase‐3 on day 2 and vascular endothelial growth factor receptor 2 (VEGFR2) upregulation till day 14.ConclusionOur results indicate that enrichment of miR126 enhanced the therapeutic efficacy of EPC‐EXs on diabetic ischemic stroke by attenuating acute injury and promoting neurological function recovery.  相似文献   
40.
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