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   31219篇
  免费   2723篇
  国内免费   702篇
耳鼻咽喉   237篇
儿科学   1276篇
妇产科学   778篇
基础医学   1820篇
口腔科学   909篇
临床医学   3566篇
内科学   6319篇
皮肤病学   411篇
神经病学   1364篇
特种医学   800篇
外国民族医学   1篇
外科学   2884篇
综合类   4277篇
现状与发展   1篇
预防医学   4527篇
眼科学   329篇
药学   2468篇
  36篇
中国医学   1399篇
肿瘤学   1242篇
  2024年   57篇
  2023年   852篇
  2022年   1334篇
  2021年   2089篇
  2020年   1884篇
  2019年   1744篇
  2018年   1725篇
  2017年   1306篇
  2016年   1193篇
  2015年   1149篇
  2014年   2365篇
  2013年   2248篇
  2012年   1896篇
  2011年   2026篇
  2010年   1615篇
  2009年   1544篇
  2008年   1432篇
  2007年   1464篇
  2006年   1056篇
  2005年   963篇
  2004年   744篇
  2003年   621篇
  2002年   426篇
  2001年   399篇
  2000年   286篇
  1999年   268篇
  1998年   195篇
  1997年   185篇
  1996年   163篇
  1995年   173篇
  1994年   162篇
  1993年   125篇
  1992年   138篇
  1991年   116篇
  1990年   92篇
  1989年   81篇
  1988年   57篇
  1987年   67篇
  1986年   48篇
  1985年   60篇
  1984年   58篇
  1983年   42篇
  1982年   39篇
  1981年   36篇
  1980年   29篇
  1979年   19篇
  1978年   22篇
  1977年   14篇
  1976年   16篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
41.
42.
43.
BackgroundThe relationship between body mass index (BMI) and in-hospital mortality risk among patients with acute myocardial infarction (AMI) remains controversial.Methods and ResultsWe included 35,964 patients diagnosed with AMI in China Acute Myocardial Infarction registry between January 2013 and December 2016. Patients were categorized into 4 groups according to BMI level: BMI <18.5, 18.5–24.9, 25–30, and ≥30 kg/m2 for underweight, normal, overweight, and obese groups, respectively. Clinical data were extracted for each patient, and multivariable logistic regression analysis was used to examine the association between BMI level and in-hospital mortality. Compared with normal-weight patients, obese patients were younger, more often current smokers, and more likely to have hypertension, hyperlipidemia, and diabetes. Multivariable regression analysis results demonstrated that compared with normal group, underweight group had significantly higher in-hospital mortality (odds ratio [OR]: 1.34; 95% confidence interval [CI]: 1.06–1.69; p = 0.016), while overweight group (OR: 0.86; 95% CI: 0.77–0.97; p = 0.011) and obese group (OR: 0.65; 95% CI: 0.46–0.91; p = 0.013) had lower mortality. All subgroups showed a trend toward lower in-hospital mortality risk as BMI increased.ConclusionsOur study provided robust evidence supporting “obesity paradox” in a contemporary large-scale cohort of patients with AMI and demonstrated that increased BMI was independently associated with lower in-hospital mortality.  相似文献   
44.
45.

Objective

To develop a Vaccine Confidence Index (VCI) that is capable of detecting variations in parental confidence towards childhood immunizations centered on trust and concern issues that impact vaccine confidence.

Methods

We used a web-based national poll of 893 parents of children <7?years in 2016 to assess the measures created for the Emory VCI (EVCI). EVCI measures were developed using constructs related to vaccine confidence identified by the U.S. National Vaccine Advisory Committee (i.e., “Information Environment”, “Trust”, “Healthcare Provider”, “Attitudes and Beliefs”, and “Social Norms”). Reliability for EVCI was assessed using Cronbach’s alpha. Using the variables related to each of the constructs, we calculated an overall EVCI score that was then assessed against self-reported childhood vaccine receipt using chi-square and the Cochrane-Armitage trend tests.

Results

Respondents’ EVCI scores could range from 0 to 24, and the full range of values was observed in this sample (Mean?=?17.5 (SD 4.8)). EVCI scores were significantly different (p?≤?0.006 for all comparisons) between parents who indicated their child(ren) received routinely recommended vaccines compared with parents who indicated they had delayed or declined recommended immunizations. There was also a significant, consistent association between higher EVCI scores and greater reported vaccine receipt.

Conclusions

We developed EVCI to reliably measure parental vaccine confidence, with individuals’ scores linked to parental vaccine-related attitudes, intentions, and behaviors. As such, EVCI may be a useful tool for future monitoring of both population and individual confidence in childhood immunization.  相似文献   
46.
Safety standards for clinical diagnostic ultrasonic devices were developed for use in relatively low-frequency systems (1–10 MHz), under the assumption that non-linear effects would be negligible. This article reviews ways in which neglecting non-linear wave propagation affects the measurements and calculations required to comply with safety standards and U.S. Food and Drug Administration guidance that recognizes these standards. An attempt is made to evaluate whether ignoring non-linear effects could result in significant error in the exposure quantities defined in these standards at either low or high frequencies, based on published literature. This article maintains that although non-linear effects have been considered in some parts of safety standards related to hydrophone requirements, the coverage is inadequate, especially for modern equipment with high working frequencies. A new approach is required to assess the magnitude of thermal heating for recently developed high-frequency systems to incorporate non-linear effects. In contrast, the current approach for evaluating the risk of cavitation can be used after appropriate modifications.  相似文献   
47.
Pre-operative optimisation is a heterogenous group of interventions aimed at improving peri-operative outcomes. To understand the evidence for pre-operative optimisation in the developing world, we systematically reviewed Cochrane reviews on the topic according to the Human Developmental Index (HDI) of the country where patient recruitment occurred. We used summary statistics and cartograms to describe the HDI, year of publication, timing of pre-operative intervention and risk of bias associated with each included trial. We assessed the impact of multinational trials on the risk of bias introduced by countries of differing HDI. Four-hundred and nine trials representing 51 countries and 89,389 randomly allocated participants were summarised in this review. Four-hundred and nineteen out of 451 (93%) trial populations (i.e. a group of study participants from one country) were from high and very high HDI countries. The median (IQR [range]) HDI of countries were 0.862 (0.806–0.892 [0.445–0.949]). Three of the 409 included trials were multinational, representing 32 countries and 37,736 out of 89,389 (42.2%) included participants. Africa was the least represented continent, with only 4 included trials and 566 participants, of which 62.3% were from one multinational trial. The overall risk of bias was high or unclear in 381 out of 409 (93%) trials. Inclusion of multinational trials decreased the proportion of trial populations introducing high or unclear risk of bias by 9.4% (95%CI 5.1–13.7; p < 0.0001). Half of the world's population live in low- and middle-HDI countries. This population is poorly represented in systematically reviewed evidence on pre-operative optimisation. Multinational trials increase the knowledge contribution from low- and middle-HDI countries and decrease risk of bias in systematic reviews.  相似文献   
48.
49.
50.
BackgroundPreclinical studies have demonstrated that high mechanical index (MI) impulses from a diagnostic ultrasound transducer during an intravenous microbubble infusion (sonothrombolysis) can restore epicardial and microvascular flow in acute ST-segment elevation myocardial infarction (STEMI).ObjectivesThis study tested the clinical effectiveness of sonothrombolysis in patients with STEMI.MethodsPatients with their first STEMI were prospectively randomized to either diagnostic ultrasound–guided high MI impulses during an intravenous Definity (Lantheus Medical Imaging, North Billerica, Massachusetts) infusion before, and following, emergent percutaneous coronary intervention (PCI), or to a control group that received PCI only (n = 50 in each group). A reference first STEMI group (n = 203) who arrived outside the randomization window was also analyzed. Angiographic recanalization before PCI, ST-segment resolution, infarct size by magnetic resonance imaging, and systolic function (LVEF) at 6 months were compared.ResultsST-segment resolution occurred in 16 (32%) high MI PCI versus 2 (4%) PCI-only patients before PCI, and angiographic recanalization was 48% in high MI/PCI versus 20% in PCI only and 21% in the reference group (p < 0.001). Infarct size was reduced (29 ± 22 g high MI/PCI vs. 40 ± 20 g PCI only; p = 0.026). LVEF was not different between groups before treatment (44 ± 11% vs. 43 ± 10%), but increased immediately after PCI in the high MI/PCI group (p = 0.03), and remained higher at 6 months (p = 0.015). Need for implantable defibrillator (LVEF ≤30%) was reduced in the high MI/PCI group (5% vs. 18% PCI only; p = 0.045).ConclusionsSonothrombolysis added to PCI improves recanalization rates and reduces infarct size, resulting in sustained improvements in systolic function after STEMI. (Therapeutic Use of Ultrasound in Acute Coronary Artery Disease; NCT02410330).  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