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   2047196篇
  免费   149702篇
  国内免费   3139篇
耳鼻咽喉   29563篇
儿科学   64076篇
妇产科学   54269篇
基础医学   290100篇
口腔科学   58026篇
临床医学   178087篇
内科学   405800篇
皮肤病学   43833篇
神经病学   159658篇
特种医学   81237篇
外国民族医学   725篇
外科学   322813篇
综合类   42080篇
现状与发展   2篇
一般理论   576篇
预防医学   146959篇
眼科学   46031篇
药学   155111篇
  5篇
中国医学   4206篇
肿瘤学   116880篇
  2018年   20157篇
  2017年   15469篇
  2016年   17098篇
  2015年   19328篇
  2014年   26742篇
  2013年   40272篇
  2012年   55121篇
  2011年   58082篇
  2010年   34721篇
  2009年   33188篇
  2008年   56223篇
  2007年   59839篇
  2006年   60688篇
  2005年   58809篇
  2004年   57346篇
  2003年   55447篇
  2002年   54453篇
  2001年   107529篇
  2000年   111599篇
  1999年   94223篇
  1998年   23891篇
  1997年   21353篇
  1996年   21793篇
  1995年   20506篇
  1994年   19223篇
  1993年   17766篇
  1992年   73332篇
  1991年   71158篇
  1990年   69065篇
  1989年   66545篇
  1988年   61024篇
  1987年   59768篇
  1986年   55736篇
  1985年   53490篇
  1984年   39172篇
  1983年   33044篇
  1982年   18258篇
  1981年   16326篇
  1979年   34909篇
  1978年   23835篇
  1977年   20415篇
  1976年   18409篇
  1975年   20111篇
  1974年   23813篇
  1973年   22726篇
  1972年   21210篇
  1971年   19678篇
  1970年   18638篇
  1969年   17158篇
  1968年   15559篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Experiments were performed to determine the effect of pin channel preparation with standard and reduction speed handpieces, and pin seating by hand and with motor drive. The greatest retention was achieved by preparation with a standard handpiece at 6000 rpm, and manual pin placement with a hand driver. The most consistent retention values were achieved using the reduction handpiece. All preparation and placement combinations examined produced a clinically acceptable result.  相似文献   
992.
In human plasma, heparin cofactor II (HCII) is a thrombin inhibitor which displays similarities with antithrombin III (ATIII). As previously reported for hereditary ATIII deficiency, cases of recurrent thrombosis were reported in patients with hereditary HCII deficiency. Here, plasma HCII activity was studied in 372 patients with a history of thrombosis, classified according to their anticoagulant therapy. The mean plasma HCII level was significantly higher in patients with acute deep vein thrombosis (DVT) under heparin therapy than in patients with a history of thrombosis, who were studied more than 3 months after the acute event, and were either on, or had been on, oral anticoagulant therapy. HCII and fibrinogen were significantly correlated in all three groups of patients. These results were strengthened by those of a follow-up study in 23 patients with acute DVT. Changes in plasma HCII activity paralleled those of fibrinogen. This suggests that HCII might behave like an acute phase reactant in patients with thrombosis and that the measurement of its plasma level as a risk factor for thrombosis should be performed some time after the acute episode. In conclusion, the prevalence of HCII deficiency in patients with a history of thrombosis might have been underestimated in series which included patients with acute thrombosis.  相似文献   
993.
994.
1. alpha 2-Adrenoceptors on platelet membranes and beta 2-adrenoceptors on lymphocytes were studied in 24 patients with primary Raynaud's phenomenon and in 24 age- and sex-matched control subjects. In two subgroups, a standardized mental arithmetic test and a finger-cooling test were performed. 2. Baseline blood pressure, heart rate and forearm blood flow did not differ between the two groups. 3. Baseline skin microcirculation (laser Doppler flux) was decreased in primary Raynaud's phenomenon (19 +/- 15 arbitrary units) compared with control subjects (33 +/- 14 arbitrary units) (P less than 0.01). 4. Baseline plasma noradrenaline concentration (2.00 +/- 1.44 versus 1.16 +/- 0.36 nmol/l) and alpha 2-adrenoceptor density (301 +/- 119 versus 210 +/- 82 fmol/mg) were increased in patients with primary Raynaud's phenomenon in comparison with the control subjects. The alpha 2-adrenoceptor density/beta 2-adrenoceptor density ratio in patients with primary Raynaud's phenomenon was, with a value of 0.37 +/- 0.04, higher than in the control subjects, where a value of 0.25 +/- 0.02 was measured (P less than 0.001). Plasma adrenaline concentration, beta 2-adrenoceptor density and the antagonist affinity to both receptor subtypes did not differ between both groups under baseline conditions. 5. Whereas during the finger-cooling test no differences were seen in the responses of the parameters measured, the mental arithmetic test induced an increase in laser Doppler flux in patients with primary Raynaud's phenomenon and a decrease in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
995.
Liver histopathology in clinical Reye syndrome   总被引:1,自引:0,他引:1  
Analysis of the liver histopathology in 19 children with clinical Reye syndrome (RS) revealed that nine had diffuse panlobular steatosis, one giant cell hepatitis, one a mild choledochal cyst with inflammation, two multifocal spotty necrosis and one multiple centrilobular necrosis, the other five being normal. Four of the nine patients with diffuse panlobular steatosis showed microvesicular fatty droplets with central nuclei, which was consistent with findings characteristic for typical RS. Two cases showed a periportal area dominant macrovesicular fatty change, which was highly suggestive for metabolic disorder. In the other three cases, the findings were so variable in terms of the size of lipid droplets and the location of nuclei in hepatocytes that it was not possible to provide any clue for defining a diagnosis. These results confirmed the legitimacy of the diagnostic criteria of RS which included a liver biopsy as one of the mandatory conditions. They also indicated that RS-mimicking clinical pictures can be presented by miscellaneous conditions in which liver histology does not necessarily helpful in establishing definite diagnosis.  相似文献   
996.
ABSTRACT. A girl with phenylketonuria and mild mental retardation developed a behaviour disorder and anorexia nervosa at the age of 14. The anorexic symptoms disappeared at the age of 20, but the behaviour disorder worsened, leading to compulsory detention in a psychiatric hospital. Serum phenylalanine levels may have influenced the course of the disorder.  相似文献   
997.
998.
999.
In preventive medicine and occupational health, decision-makers face uncertainty, divergent opinions, and varying needs. In the Swiss aluminum industry, screening for industrial fluorosis illustrates how decision analysis and cost-effectiveness analysis can provide rational and explicit models of decision-making in such contexts. Data on fluoride-exposed potroom workers are used to compare the cost-effectiveness of two strategies: mass screening of fluorosis versus individual detection of the disease on the basis of the worker's symptoms. A decision-analysis and a sensitivity analysis are performed to assess the impact of the screening program for different levels of expected prevalence of the disease. The optimal decision, in economic terms, is the one that minimizes the pension and screening-related costs and maximizes the number of years of full working capacity. Swiss data suggest that a diagnosis of clinical fluorosis is unlikely before 10 years of exposure to fluoride. Between 10 and 30 years of exposure to fluoride, mass screening may be more cost-effective than individual detection of the disease, even when the expected prevalence of the disease in a given industrial setting is less than 10%.  相似文献   
1000.
In clinical diagnosis, a patient's symptoms are observed and the probabilities of various diseases are assessed. A widely used method of formalizing this approach is independent Bayes in which symptoms are assumed to be independent conditional on the disease category. Correspondence analysis provides a method for examining the dependence between symptoms and assists in the selection of a reduced set of symptoms for the application of the independent Bayes method. This approach is illustrated on two data sets concerned with patients attending Accident and Emergency departments with chest pain and acute abdominal pain, respectively.  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