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   323920篇
  免费   18736篇
  国内免费   673篇
耳鼻咽喉   4450篇
儿科学   10827篇
妇产科学   10820篇
基础医学   47763篇
口腔科学   8161篇
临床医学   26122篇
内科学   63768篇
皮肤病学   6660篇
神经病学   23393篇
特种医学   12667篇
外国民族医学   43篇
外科学   51818篇
综合类   7819篇
现状与发展   1篇
一般理论   165篇
预防医学   20991篇
眼科学   7469篇
药学   22490篇
中国医学   844篇
肿瘤学   17058篇
  2021年   3234篇
  2019年   3079篇
  2018年   4600篇
  2017年   3375篇
  2016年   3946篇
  2015年   4375篇
  2014年   5781篇
  2013年   8686篇
  2012年   11311篇
  2011年   11589篇
  2010年   7361篇
  2009年   6738篇
  2008年   10525篇
  2007年   11309篇
  2006年   11042篇
  2005年   10631篇
  2004年   10236篇
  2003年   9511篇
  2002年   8973篇
  2001年   13441篇
  2000年   13766篇
  1999年   11580篇
  1998年   3229篇
  1997年   2952篇
  1996年   2789篇
  1995年   2694篇
  1994年   2468篇
  1992年   8400篇
  1991年   8502篇
  1990年   8322篇
  1989年   8120篇
  1988年   7351篇
  1987年   7105篇
  1986年   6761篇
  1985年   6550篇
  1984年   4794篇
  1983年   4150篇
  1982年   2518篇
  1979年   4443篇
  1978年   3240篇
  1977年   2737篇
  1976年   2514篇
  1975年   2841篇
  1974年   3363篇
  1973年   3364篇
  1972年   3121篇
  1971年   2952篇
  1970年   2841篇
  1969年   2583篇
  1968年   2539篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
63.
1. The frequent occurrence of hypothalamo-pituitary dysfunction in patients with eating disorders as well as prior reports that nutritional and endocrine status influence pituitary morphology, led us to hypothesize that pituitary size and shape may be altered in patients with eating disorders. 2. Magnetic resonance imaging (MRI) does not use ionizing radiation and is currently one of the most feasible modalities available to study the pituitary gland in vivo. Using MRI, we have previously reported in a preliminary study that female patients with eating disorders had significantly smaller pituitary glands than controls. In addition MRI excluded any pituitary mass lesions. 3. In this report, we confirm our previous MRI findings and provide further evidence of pituitary abnormalities in an expanded sample of eating disorder patients. Preliminary data on pituitary volume estimates from MRI scans are provided for a subset of patients and controls.  相似文献   
64.
This paper is an attempt to assess the relevance of the inhibitors of fibrinolysis for clot lysis in selected disease states and to discuss the mechanisms leading to acquired abnormal levels of such inhibitors. When compared to 20 control subjects the 30 hypertriglyceridemic patients (14 with type IIb and 16 with type IV) displayed significantly (p less than 0.001) increased plasma plasminogen activator inhibitor (PAI) activity (221 +/- 88% and 290 +/- 104% respectively; mean +/- SD), moderately (p less than 0.01) increased alpha 2 antiplasmin (alpha 2AP) level (112 +/- 11% and 115 +/- 16%) and accordingly an obviously prolonged dilute blood clot lysis time (DBCLT). Neither PAI activity and alpha 2AP level nor DBCLT were significantly different from controls in the 10 patients with hyperlipoproteinemia type IIa. The 18 patients with severe hepatic cirrhosis had low alpha 2AP level (59 +/- 19.7%) and accelerated clot lysis, while mean PAI activity (160 +/- 87%) was slightly (p less than 0.05) increased. In the 17 nephrotic patients alpha 2AP was increased (115 +/- 12%) while PAI activity was similar to controls and DBCLT rather shorter. Two liver secretion enzymes, namely serum cholinesterase and plasma protein C, were found to be decreased in cirrhotic patients, similar to control values in hyperlipoproteinemia type IIa and obviously increased in nephrotic patients as well as in hypertriglyceridemic subjects. The relevance of PAI and alpha 2AP for clot lysis was considered in relation to data in the literature concerning the behaviour of t-PA and factor XIII.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
65.
66.
The caffeine content of all tea or coffee beverages consumed by 17 healthy adults over 24 hours was measured. Plasma caffeine, theophylline, theobromine, and paraxanthine concentrations were determined over the same 24 hours. The average caffeine content per drink was 60.4 +/- 21.8 mg for instant coffee (14-fold range), 80.1 +/- 19.2 mg for brewed coffee (2.8-fold range), and 28.8 +/- 13.7 mg for tea (5.5-fold range). The number of drinks of coffee and tea consumed was a poor index of actual caffeine intake (r2 = 0.42). Caffeine intake correlated poorly with the 24-hour average caffeine concentration (r2 = 0.41), but there was a very good correlation between a single plasma caffeine concentration measured at 5 PM and the 24-hour average concentration (r2 = 0.94). The same was true for paraxanthine (r2 = 0.86). Paraxanthine accounted for 67.3% of the total dimethylxanthines in plasma, while theobromine and theophylline accounted for 24.4% and 8.3%, respectively. Mean caffeine clearance was 1.2 +/- 0.3 ml/min/kg. Plasma caffeine concentration before the first drink in the morning correlated very poorly with caffeine clearance (r2 = 0.07), even when adjusted for caffeine intake (r2 = 0.21).  相似文献   
67.
68.
'Gliosarcomas' have long been considered to be mixed gliomas and sarcomas. The present study failed to define criteria which clearly delineate 'gliosarcomas' from glioblastoma multiforme and suggests that 'gliosarcomas' should be considered as spindle cell glioblastomas. A total of six cases originally diagnosed as 'gliosarcomas' were compared with four cases of glioblastoma multiforme. No clinical or prognostic features were defined which would clearly separate 'gliosarcomas' from glioblastoma multiforme. Macroscopically, biopsies from 'gliosarcomas' ranged from firm, apparently well-circumscribed tumours to poorly circumscribed lesions with a soft consistency resembling glioblastoma multiforme. Histology revealed a continuous spectrum in which 'gliosarcomas' with large reticulin-rich areas of spindle cells merged with typical glioblastomas containing only small islands of spindle cells and reticulin staining. Immunocytochemistry for glial fibrillary acidic protein (GFAP); S100 protein and alpha-smooth muscle actin (ASMA) showed that the majority of cells in reticulin-poor areas of 'gliosarcoma' and glioblastomas expressed S100 protein and GFAP; many expressed ASMA and some expressed both GFAP and ASMA. Spindle cells in reticulin-rich areas of 'gliosarcomas' and glioblastomas most frequently expressed ASMA but many cells also expressed S100 protein and GFAP; some cells expressed both GFAP and ASMA. The results of this study and a review of the literature suggests that there is a clinical, radiological and pathological continuum with glioblastoma and 'gliosarcoma' at different ends of the spectrum. It is suggested, therefore, that most, if not all, 'gliosarcomas' be redesignated as spindle cell glioblastomas and not be considered as a mixture of glioma and sarcoma.  相似文献   
69.
70.
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