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   1024970篇
  免费   65584篇
  国内免费   2603篇
耳鼻咽喉   14053篇
儿科学   31864篇
妇产科学   28998篇
基础医学   141883篇
口腔科学   27195篇
临床医学   86912篇
内科学   208551篇
皮肤病学   20337篇
神经病学   81730篇
特种医学   40349篇
外国民族医学   348篇
外科学   160186篇
综合类   20973篇
现状与发展   1篇
一般理论   336篇
预防医学   75228篇
眼科学   23252篇
药学   71641篇
  20篇
中国医学   1952篇
肿瘤学   57348篇
  2019年   8472篇
  2018年   11237篇
  2017年   8852篇
  2016年   9522篇
  2015年   10746篇
  2014年   15420篇
  2013年   24079篇
  2012年   32543篇
  2011年   34369篇
  2010年   20553篇
  2009年   19426篇
  2008年   32819篇
  2007年   35153篇
  2006年   34980篇
  2005年   34516篇
  2004年   33180篇
  2003年   32028篇
  2002年   31528篇
  2001年   42987篇
  2000年   44001篇
  1999年   37765篇
  1998年   11411篇
  1997年   10442篇
  1996年   10207篇
  1995年   9551篇
  1994年   9069篇
  1993年   8471篇
  1992年   29458篇
  1991年   28193篇
  1990年   27492篇
  1989年   26397篇
  1988年   24510篇
  1987年   24146篇
  1986年   23205篇
  1985年   22147篇
  1984年   16884篇
  1983年   14513篇
  1982年   9202篇
  1981年   8091篇
  1979年   15447篇
  1978年   10961篇
  1977年   9380篇
  1976年   8804篇
  1975年   9611篇
  1974年   11313篇
  1973年   10736篇
  1972年   10125篇
  1971年   9284篇
  1970年   8929篇
  1969年   8302篇
排序方式: 共有10000条查询结果,搜索用时 906 毫秒
91.

Background

Identification of the risk of falls is important among older inpatients. This study aims to examine performance criteria (i.e.; sensitivity, specificity, positive predictive value, negative predictive value and accuracy) for fall prediction resulting from a nurse assessment and an artificial neural networks (ANNs) analysis in older inpatients hospitalized in acute care medical wards.

Methods

A total of 848 older inpatients (mean age, 83.0±7.2 years; 41.8% female) admitted to acute care medical wards in Angers University hospital (France) were included in this study using an observational prospective cohort design. Within 24 hours after admission of older inpatients, nurses performed a bedside clinical assessment. Participants were separated into non-fallers and fallers (i.e.; ≥1 fall during hospitalization stay). The analysis was conducted using three feed forward ANNs (multilayer perceptron [MLP], averaged neural network, and neuroevolution of augmenting topologies [NEAT]).

Results

Seventy-three (8.6%) participants fell at least once during their hospital stay. ANNs showed a high specificity, regardless of which ANN was used, and the highest value reported was with MLP (99.8%). In contrast, sensitivity was lower, with values ranging between 98.4 to 14.8%. MLP had the highest accuracy (99.7).

Conclusions

Performance criteria for fall prediction resulting from a bedside nursing assessment and an ANNs analysis was associated with a high specificity but a low sensitivity, suggesting that this combined approach should be used more as a diagnostic test than a screening test when considering older inpatients in acute care medical ward.
  相似文献   
92.
We conducted an evaluation of a patient-centered medical home demonstration sponsored by the Centers for Medicare & Medicaid Services. We implemented a quasi-experimental pre-post with a comparison group design. Traditional propensity score weighting failed to achieve balance (exchangeability) between the two groups on several critical characteristics. In response, we incorporated a relatively new alternative known as entropy balancing. Our objective is to share lessons learned from using entropy balancing in a quasi-experimental study design. We document the advantages and challenges with using entropy balancing. We also describe a set of best practices, and we present a series of illustrative analyses that empirically demonstrate the performance of entropy balancing relative to traditional propensity score weighting. We compare alternative approaches based on: (i) covariate balance (e.g., standardized differences); (ii) overlap in conditional treatment probabilities; and (iii) the distribution of weights. Our comparison of overlap is based on a novel approach we developed that uses entropy balancing weights to calculate a pseudo-propensity score. In many situations, entropy balancing provides remarkably superior covariate balance compared to traditional propensity score weighting methods. Entropy balancing is also preferred because it does not require extensive iterative manual searching for an optimal propensity score specification. However, we demonstrate that there are some situations where entropy balancing “fails”. Specifically, there are instances where entropy balancing achieves adequate covariate balance only by using a distribution of weights that dramatically up-weights a small set of observations, giving them a disproportionately large and undesirable influence.  相似文献   
93.
Inhalation of ash can be of great concern for affected communities, during and after volcanic eruptions. Governmental and humanitarian agencies recommend and distribute a variety of respiratory protection (RP), most commonly surgical masks. However, there is currently no evidence on how effective such masks are in protecting wearers from volcanic ash. In Part I of this study (Mueller et al., 2018), we assessed the filtration efficiency (FE) of 17 materials from different forms of RP against volcanic ash and a surrogate, low-toxicity dust, Aloxite. Based on those results, we now present the findings from a volunteer simulation study to test the effect of facial fit through assessment of Total Inward Leakage (TIL).Four different disposable RP types that demonstrated very high median FE (≥96% for Aloxite; ≥89% for volcanic ash) were tested without provision of training on fit. These were an industry-certified mask (N95-equiv.); a surgical mask from Japan designed to filter PM2.5; a flat-fold basic mask from Indonesia; and a standard surgical mask from Mexico, which was also tested with an added medical bandage on top, as an additional intervention to improve fit.Ten volunteers (6 female, 4 male) were recruited. Each RP type was worn by volunteers under two different conditions simulating cleaning-up activities during/after volcanic ashfall. Each activity lasted 10?min and two repeats were completed for each RP type per activity. Dust (as PM2.5) concentration inside and outside the mask was measured with two TSI SidePak aerosol monitors (Models AM510 and AM520, TSI, Minnesota, USA) to calculate TIL. A questionnaire was administered after each test to collect perceptions of fit, comfort, protection and breathability.The best-performing RP type, across both activities, was the industry-certified N95-equiv. mask with 9% mean TIL. The standard surgical mask and the basic flat-fold mask both performed worst (35% TIL). With the additional bandage intervention, the surgical mask mean TIL improved to 24%. The PM2.5 surgical mask performed similarly, with 22% TIL. The N95-equiv. mask was perceived to provide the best protection, but was also perceived as being uncomfortable and more difficult to breathe through.This study provides a first objective evidence base for the effectiveness of a selection of RP types typically worn around the world during volcanic crises. The findings will help agencies to make informed decisions on the procurement and distribution of RP in future eruptions.  相似文献   
94.
95.
96.
Dominicans are the largest migrant community in Puerto Rico, yet understudied. We compared risk factors and health conditions of Dominicans versus Puerto Ricans (PRs). Cross-sectional survey of Dominicans (n?=?55) and PRs (n?=?310) aged 30–75 years, assessed with validated questionnaires and standardized anthropometric measurements. Significantly, more Dominicans than PRs had attained <8th grade education (37.7 vs. 8.0%), reported household income ≤$10,000 (76.1 vs. 56.9%), lacked health insurance (19.6 vs. 5.5%), and reported food insecurity (24.5 vs. 12.1%). They spent fewer hours/day watching television (2.9 vs. 3.8), and were less likely to smoke (7.6 vs. 19.6%). Medically-diagnosed depression was lower among Dominicans than PRs (9.6 vs. 23.0%); questionnaire-based high depressive symptomatology was similar (47.9 vs. 52.8%). Dominicans living in Puerto Rico had more socioeconomic risk factors but healthier lifestyle behaviors and lower prevalence of medically-diagnosed depression than PRs. Tailored approaches are needed to ameliorate disparities in each ethnic group.  相似文献   
97.
98.
99.
100.
Clinical studies of incidences of the number of canals in human teeth should correlate with the percentages obtained in laboratory samples. In this study the incidence of two canals in the mandibular incisors was compared with figures obtained from in vitro extracted teeth, as well as from one clinical study. A very low percentage was obtained from the examination of clinical records, and this could be due to racial differences in the samples examined.  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