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   40240篇
  免费   3536篇
  国内免费   138篇
耳鼻咽喉   440篇
儿科学   1296篇
妇产科学   791篇
基础医学   5679篇
口腔科学   885篇
临床医学   4452篇
内科学   8807篇
皮肤病学   947篇
神经病学   4144篇
特种医学   1246篇
外国民族医学   1篇
外科学   5703篇
综合类   268篇
一般理论   34篇
预防医学   3555篇
眼科学   518篇
药学   2440篇
中国医学   104篇
肿瘤学   2604篇
  2023年   169篇
  2022年   249篇
  2021年   713篇
  2020年   590篇
  2019年   1007篇
  2018年   1246篇
  2017年   1011篇
  2016年   1014篇
  2015年   1301篇
  2014年   1499篇
  2013年   2118篇
  2012年   2663篇
  2011年   2870篇
  2010年   1712篇
  2009年   1548篇
  2008年   2460篇
  2007年   2490篇
  2006年   2372篇
  2005年   2448篇
  2004年   2316篇
  2003年   2253篇
  2002年   2288篇
  2001年   507篇
  2000年   422篇
  1999年   477篇
  1998年   435篇
  1997年   396篇
  1996年   311篇
  1995年   353篇
  1994年   288篇
  1993年   267篇
  1992年   252篇
  1991年   270篇
  1990年   220篇
  1989年   198篇
  1988年   214篇
  1987年   204篇
  1986年   187篇
  1985年   180篇
  1984年   187篇
  1983年   146篇
  1982年   188篇
  1981年   182篇
  1980年   170篇
  1979年   121篇
  1978年   120篇
  1977年   108篇
  1976年   90篇
  1974年   84篇
  1972年   95篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
(11)C-meta-Hydroxyephedrine (HED) is used in cardiac PET as an index of norepinephrine (NE) reuptake transporter (NET) density and synaptic NE levels. Whereas cardiac uptake is well documented, tracer retention in other tissues with rich noradrenergic innervation is unclear. Dysfunctional sympathetic nervous system (SNS) function in extracardiac metabolic storage tissues (i.e., adipose tissue and skeletal muscle) and endocrine organs contributes to several disorders. The aim of this study was to determine the potential of HED as an index of NE function in brown adipose tissue, lung, pancreas, skeletal muscle, and kidney by identifying NET-specific retention and determining the presence of radiolabeled metabolites. METHODS: Male Sprague-Dawley rats were administered HED and sacrificed at 30 min after tracer injection. Tissues were rapidly excised and counted for radioactivity, and relative tracer retention was quantified. Pretreatment with NET inhibitors established specific HED accumulation. The effect of elevated NE was tested by subcutaneous minipump NE infusion or inhibition of monoamine oxidase. Column-switch high-performance liquid chromatography (HPLC) was used to analyze the presence of radiolabeled metabolites in heart, brown adipose tissue, pancreas, and plasma. RESULTS: NET-specific retention was observed in heart, brown adipose tissue, lung, and pancreas but not in liver, skeletal muscle, or kidney. A dose-dependent response of HED accumulation to treatments elevating NE levels was established in tissues exhibiting specific uptake. At 30 min after tracer administration, HPLC analysis revealed 93%-95% of total radioactivity signal derived from unchanged HED in heart, pancreas, and brown adipose tissue compared with 61% +/- 8% unchanged HED in plasma. CONCLUSION: In addition to the heart, lung, pancreas, and brown adipose tissue exhibit specific and NE-responsive uptake of HED, supporting the potential for novel PET studies of SNS integrity in these tissues.  相似文献   
72.
73.
BACKGROUND: The effective dose for treating glabellar lines with botulinum toxin type A in men has not been studied adequately. OBJECTIVE: To compare the safety, efficacy, and duration of response of four doses of botulinum toxin type A on glabellar rhytids in men. METHODS: Eighty men were randomized to receive a total dose of either 20, 40, 60, or 80 U of botulinum toxin type A (BOTOX, BOTOX Cosmetic, or Vistabel, Allergan, Inc., Irvine, CA, USA) in the glabellar area. Glabellar lines were assessed at rest and maximum frown by a trained observer at baseline, 2 and 4 weeks, and monthly thereafter. Patients provided self-evaluations at the same visits. Adverse events were monitored throughout. RESULTS: The 40, 60, and 80 U doses of botulinum toxin type A were consistently more effective in reducing glabellar lines than the 20 U dose (duration, peak response rate, improvement from baseline). There was a dose-dependent increase in both the response rate at maximum frown and the duration of effect assessed by the trained observer. In addition, the participants reported a dose-dependent reduction in the ability to frown, improvement in their global assessment, and increased feelings of attractiveness, self-confidence, and satisfaction. The incidence of adverse events was not increased with higher doses. CONCLUSION: Male participants with glabellar rhytids benefit from starting doses of at least 40 U of botulinum toxin type A.  相似文献   
74.
This study investigated the association of blood pressure with blood oxidative stress-related parameters in normotensive and hypertensive subjects. A cross-sectional design was applied to 31 hypertensive patients and 35 healthy normotensive subjects. All subjects were men between the ages of 35 and 60 years. Exclusion criteria were obesity, dyslipidemia, diabetes mellitus, smoking and current use of any medication. All patients underwent 24-h ambulatory blood pressure monitoring and sampling of blood and urine. Antioxidant enzymes activity, reduced/oxidized glutathione ratio (GSH/GSSG), and lipid peroxidation (malondialdehyde) were determined in erythrocytes. Parameters measured in the plasma of test subjects were plasma antioxidant status, lipid peroxidation (8-isoprostane), plasma vitamin C and E, and the blood pressure modulators renin, aldosterone, endothelin-1 and homocysteine. Daytime systolic and diastolic blood pressures of hypertensives were negatively correlated with plasma antioxidant capacity (r=-0.46, p<0.009 and r=-0.48, p<0.007), plasma vitamin C levels (r=-0.53, p<0.003 and r=-0.44, p<0.02), erythrocyte activity of antioxidant enzymes, and erythrocyte GSH/GSSG ratio, with hypertensives showing higher levels of oxidative stress. Blood pressures showed a positive correlation with both plasma and urine 8-isoprostane. Neither plasma vitamin E nor the assessed blood pressure modulator levels showed significant differences between the groups or correlation with blood pressures. These findings demonstrate a strong association between blood pressure and some oxidative stress-related parameters and suggest a possible role of oxidative stress in the pathophysiology of essential hypertension.  相似文献   
75.
76.
77.
We sought whether microdamage could rise in postmenopausal osteoporotic women on long-term bisphosphonates, as suggested by recent animal studies. We found few microcracks in iliac bone biopsies, despite a marked reduction in bone turnover. INTRODUCTION: Animal studies suggest that bisphosphonates (BPs) could increase microdamage frequency in a dose-dependent manner, caused by excessively suppressed bone turnover. However, there is limited data in humans receiving BP therapeutic doses for >3 yr. MATERIALS AND METHODS: We measured microcrack frequency and histomorphometry parameters on transiliac bone biopsies in 50 postmenopausal osteoporotic women (mean age = 68 yr) who had received BP therapy (3 on intravenous pamidronate, 37 on oral alendronate, and 10 on oral risedronate) for at least 3 yr (mean treatment duration = 6.5 yr). We compared these results with transiliac bone biopsies obtained from 12 cadavers. We used bulk staining with green calcein as a fluorochrome. The microcracks were quantified in three 100-microm-thick sections using optic microscopy and were confirmed by laser confocal microscopy. Microcrack frequency (number of microcracks/mm2 of bone tissue) was compared between treated women and controls using nonparametric tests. We also explored predictors of microcrack frequency, including age, duration of BP therapy, and activation frequency. RESULTS: Among treated women, cancellous bone microcrack frequency was low (mean, 0.13 microcracks/mm2) and did not differ significantly from that observed in controls (0.05 microcracks/mm2; p = 0.59). Of note, 54% of the treated women and 58% of the controls had no observable microcracks. There was no association between microcrack frequency and the duration of BP therapy (for microcracks/mm2 and duration, Spearman r = 0.04, p = 0.80) and between patients' ages and the number of microcracks (Spearman r = -0.09, p = 0.61). Although bone remodeling parameters were suppressed in treated women, we found no relationship between microcrack density and activation frequency (Spearman r = -0.003, p = 0.99). Also, microcrack frequency was not increased in women with prevalent vertebral fracture compared with those without fractures. CONCLUSIONS: Among postmenopausal osteoporotic women on long-term BPs, microcrack frequency in the iliac bone is low, despite a marked reduction of bone turnover.  相似文献   
78.
The aim of this study was to evaluate the effectiveness of incremental and maximum bite advancement during treatment of Class II Division 1 malocclusion with the Twin-block appliance in the permanent dentition. It was performed at 3 district general hospitals in the United Kingdom with 4 operators. Two hundred three patients, 10-14 years old, were randomized. Control patients had the initial bite taken edge-to-edge for appliance construction with a standard Twin-block. Experimental patients had 2 mm initial bite advancement and subsequent 2 mm advancements at 6 weekly intervals with a Twin-block appliance incorporating advancement screws. Data were collected at the start and the finish of Twin-block treatment. The use of incremental advancement of the Twin-block did not confer any advantages in terms of process and outcome of the treatment. However, patient compliance was influenced by operator and patient age. The duration of treatment was influenced by operator and initial overjet. Incremental bite advancement produced no advantages over maximum advancement.  相似文献   
79.
Aim: The purpose of this project was to operationalize and apply a previously identified set of performance measures designed to evaluate services for those experiencing a first episode of a schizophrenia spectrum disorder. Methods: Operational definitions were developed for previously identified measures through an iterative process of discussions between clinical experts and health‐care evaluators. Data were collected from existing sources including corporate databases, clinical databases and chart review. Results: Definitions were developed for 44 measures covering seven of eight domains recommended for service level evaluation by the Canadian Institute for Health Information domains. Forty measures could be calculated. Conclusions: The measures represent a comprehensive set of performance measures suitable for the evaluation of services for people with a first‐episode psychosis. The measures could be used by other services in order to establish standards and norms for routine clinical practice.  相似文献   
80.
This article discusses the cardiovascular protection afforded by low to moderate consumption of ethanol and the role of ethanol-induced preconditioning. Ethanol, a compound that is found in many popular beverages, has a whole range of cardiovascular protective effects when consumed in low to moderate doses. Although they have yet to be totally clarified, recent data suggest that a combination of several actions at the biochemical and molecular levels play a role in this protection. These include favorable changes in lipid metabolism, antioxidant effects, changes in hemostasis and platelet aggregation, arterial vasodilation mediated by NO release, induction of the expression of cardioprotective proteins, insulin sensitization and lower levels of inflammatory markers. Special emphasis will be given to ethanol-induced preconditioning. Some of the compounds present in red and white wine, such as resveratrol and quercetin, are also partly responsible for some of the cardioprotective effects of alcoholic drinks. These are due to antioxidant effects and changes in platelet aggregation, endothelial function and inflammatory response. The last part of the paper will focus on the clinical applications and possibilities raised by these new findings.  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