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   3940997篇
  免费   294687篇
  国内免费   6732篇
耳鼻咽喉   56715篇
儿科学   124828篇
妇产科学   105754篇
基础医学   566274篇
口腔科学   112695篇
临床医学   362958篇
内科学   753167篇
皮肤病学   83543篇
神经病学   320468篇
特种医学   151654篇
外国民族医学   1277篇
外科学   591610篇
综合类   89724篇
现状与发展   13篇
一般理论   1616篇
预防医学   318439篇
眼科学   94102篇
药学   294799篇
  90篇
中国医学   7582篇
肿瘤学   205108篇
  2018年   42317篇
  2017年   32092篇
  2016年   35828篇
  2015年   40448篇
  2014年   57871篇
  2013年   87975篇
  2012年   119643篇
  2011年   127212篇
  2010年   75650篇
  2009年   71535篇
  2008年   119715篇
  2007年   127570篇
  2006年   128777篇
  2005年   125190篇
  2004年   120380篇
  2003年   115832篇
  2002年   113429篇
  2001年   175174篇
  2000年   180680篇
  1999年   152920篇
  1998年   45672篇
  1997年   40508篇
  1996年   40086篇
  1995年   38382篇
  1994年   35780篇
  1993年   33587篇
  1992年   121686篇
  1991年   118707篇
  1990年   115366篇
  1989年   111132篇
  1988年   103008篇
  1987年   101159篇
  1986年   95510篇
  1985年   91792篇
  1984年   69337篇
  1983年   59149篇
  1982年   35845篇
  1981年   32100篇
  1979年   65028篇
  1978年   46140篇
  1977年   38712篇
  1976年   36911篇
  1975年   39138篇
  1974年   47717篇
  1973年   45442篇
  1972年   42944篇
  1971年   40183篇
  1970年   37415篇
  1969年   35197篇
  1968年   32329篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Vitamin D can be synthesized in the skin via sunlight exposure as well as ingested through diet. Vitamin D deficiency is currently a major global public health issue, with increasing prevalence in both low and high latitude locations. This cross-sectional analysis aimed to compare the intensity of individual Ultraviolet B radiation levels between women of the same ethnicity living in England and Brazil, respectively; and to investigate the association with circulating 25(OH)D concentrations. We analysed data from 135 Brazilian women (England, n = 56, 51° N; Brazil, n = 79, 16° S) recruited for the D-SOL study (Interaction between Vitamin D Supplementation and Sunlight Exposure in Women Living in Opposite Latitudes). Serum 25(OH)D concentrations were analysed by high performance liquid chromatography tandem mass spectrometry (HPLC-MS), individual UVB radiation via UVB dosimeter badges and dietary intake via 4-day diet diaries. Anthropometric, skin phototype, sociodemographic and lifestyle patterns were also assessed. Mean serum 25(OH)D concentration of England residents was significantly lower than Brazil residents. Daily individual UVB radiation level showed a strong significant positive correlation with serum 25(OH)D concentrations. The required UVB radiation to achieve 75 nmol/L was 2.2 SED and 38.8% of the total variance in 25(OH)D concentrations was explained uniquely by daily individual UVB radiation, after controlling for the influence of age and body mass index. Thus, these results highlight the strong positive association between serum 25(OH)D concentrations and individual UVB radiation and the influence of different individual characteristics and behaviours. Collectively, these factors contribute to meaningful, country-specific, public health strategies and policies for the efficient prevention and treatment of vitamin D inadequacy.  相似文献   
102.
ABSTRACT

Lacrosse has gained substantial popularity across age groups in the past few decades, but epidemiologic sex differences of lacrosse injuries in emergency settings have not been well described. We characterized and described lacrosse-related injuries presenting to United States Emergency Departments (US EDs) using data from the National Electronic Injury Surveillance System (NEISS). From 1997 to 2015, 7,587 lacrosse-related injuries were treated at US EDs (national estimate of 256,358 injuries). Males accounted for 75.5% of injuries. Average age was 16.0 ± 5.0 (range 5–71) years. Sprains/strains (25.4%), contusions/abrasions (23.9%), and fractures (18.7%) were the most common diagnoses. Females sustained a higher proportion of sprains/strains (36.0%) than males (21.9%) (p< 0.01), while males sustained a higher proportion of fractures (injury proportion ratios [IPR]; 21.3% vs. 10.8%, p< 0.01). Similar proportions of concussions were observed (IPR; 6.1% in males, 6.2% among females). Differences in injury patterns may be secondary to differences in rules and equipment between the two sports.  相似文献   
103.
Objective: Shoulder pain after spinal cord injury (SCI) is attributed to increased mobility demands on the arms and negatively impacts independence and quality of life. Repetitive superior and posterior shoulder joint forces produced during traditional wheelchair (WC) locomotion can result in subacromial impingement if unopposed, as with muscular fatigue or weakness. ROWHEELS® (RW), geared rear wheels that produce forward WC movement with backward rim pulling, could alter these forces.

Design: Cross sectional.

Setting: Research laboratory at a rehabilitation hospital.

Participants: Ten manual WC users with paraplegia.

Outcome measures: Propulsion characteristics and right upper extremity/trunk kinematics and shoulder muscle activity were collected during ergometer propulsion: (1) self-selected free speed reverse propulsion with RW, (2) matched-speed reverse (rSW), and (3) forward propulsion (fSW) with instrumented Smartwheels (SW). Inverse dynamics using right-side SW rim kinetics and kinematics compared shoulder kinetics during rSW and fSW.

Results: Free propulsion velocity, cycle distance and cadence were similar during RW, rSW and fSW. Overall shoulder motion was similar except that peak shoulder extension was significantly reduced in both RW and rSW versus fSW. Anteriorly and inferiorly directed SW rim forces were decreased during rSW versus fSW propulsion, but posteriorly and superiorly directed rim forces were significantly greater. Superior and posterior shoulder joint forces and flexor, adductor, and external rotation moments were significantly less during rSW, without a significant difference in net shoulder forces and moments. Traditional propulsive-phase muscle activity was significantly reduced and recovery-phase muscle activity was increased during reverse propulsion.

Conclusion: These results suggest that reverse propulsion may redirect shoulder demands and prevent subacromial impingement, thereby preventing injury and preserving independent mobility for individuals with paraplegia.  相似文献   
104.
105.
Abstract

Aims

The objective was to evaluate whether sodium intake, assessed with the gold standard 24-h urinary collections, was related to long-term incidence of death, cardiovascular disease (CVD) and diabetes mellitus (DM).  相似文献   
106.
During the ongoing public health crisis, many agencies are reporting COVID-19 health outcome information based on the overall population. This practice can lead to misleading results and underestimation of high risk areas. To gain a better understanding of spatial and temporal distribution of COVID-19 deaths; the long term care facility (LTCF) and household population (HP) deaths must be used. This approach allows us to better discern high risk areas and provides policy makers with reliable information for community engagement and mitigation strategies. By focusing on high-risk LTCFs and residential areas, protective measures can be implemented to minimize COVID-19 spread and subsequent mortality.  These areas should be a high priority target when COVID-19 vaccines become available

During the current public health crisis, many agencies and media outlets are reporting COVID-19 health outcome information based on the overall population of Cook County. As we have demonstrated, overall COVID-19 case counts and mortality can be misleading (details in >Story Map 1). Moreover, they offer little guidance for delivering public health interventions to high risk populations, a critical need during this second and potentially more devastating wave of the pandemic. The University of Illinois Chicago School of Public Health’s Public Health Geographic Information System Program (UIC-SPH-PHGIS) and Purdue research team has been examining spatial and temporal patterns of COVID-19 mortality with a focus on the significant loss of life from COVID-19 among Long-Term Care Facility (LTCF) residents in contrast to mortality in the community among residents of private households (non-LTCF; referred to as household population, HP). The goals of the study are:
  • Improve the accuracy of commonly quoted COVID-19 mortality indicators;
  • Gain a better understanding of spatial and temporal distribution of COVID-19 deaths;
  • Examine the role of race, ethnicity, and socioeconomic status in COVID-19 mortality;
  • Identify population and organizational parameters that can inform strategies for public health interventions.
Prioritizing the allocation of resources based on reliable information is a prerequisite of a successful mitigation strategy and immunization plan. Findings from our research have significant practical implications. The state and federal government face a series of policy decisions both due to the recent surge in positive cases and, when the time comes, the need to rationalize distribution of vaccines to high priority groups beyond healthcare workers and nursing home residents in critical areas. The research team seeks to modify prevailing practices in order to derive reliable information that guides policy decisions. At this stage of the study, we identified high-risk LTCFs and residential areas (HP) of Cook County from readily available, real-time mortality data.  相似文献   
107.
108.
Abstract

Objective: Online videos are commonly used in medical education. The aim of this review was to investigate the role of online instructional videos in teaching procedural skills to postgraduate medical learners.

Methods: This systematic narrative review was conducted according to the PRISMA guidelines. MEDLINE, Cochrane Central Register of Controlled Trials, EMBASE, ERIC and Google Scholar were searched. Full texts that applied to online videos, postgraduate medical learners and procedural skills were included without language restrictions. The methodological quality of the studies was evaluated using a validated tool. A thematic analysis of the studies was carried out using a general inductive approach.

Results: A total of 785 articles were retrieved and the full text was reviewed for 66 articles that met the inclusion and exclusion criteria of the study. Twenty papers that were relevant to the role of online videos in postgraduate medical education of procedural skills were used for this review. They were heterogenous in the outcomes collected and the evidence was of variable quality. There was strong evidence for the use of online videos for procedural skill knowledge acquisition and retention. Online videos were used for various purposes, such as supervision, assessment, postoperative debriefing, providing feedback, and promoting reflection.

Conclusion: Online videos are a valuable educational tool especially for procedural skill knowledge acquisition and retention. Future research needs to be carried out on the appropriate use of platforms in disseminating and using online videos, identifying the factors surrounding the learners, video characteristics, and data protection.  相似文献   
109.
Abstract

Objectives: Overlapping decreases in extrastriatal dopamine D2/D3-receptor availability and glucose metabolism have been reported in subjects with schizophrenia. It remains unknown whether these findings are physiologically related or coincidental.

Methods: To ascertain this, we used two consecutive 18F-fluorodeoxyglucose and 18F-fallypride positron emission tomography scans in 19 healthy and 25 unmedicated schizophrenia subjects. Matrices of correlations between 18F-fluorodeoxyglucose uptake and 18F-fallypride binding in voxels at the same xyz location and AFNI-generated regions of interest were evaluated in both diagnostic groups.

Results: 18F-fluorodeoxyglucose uptake and 18F-fallypride binding potential were predominantly positively correlated across the striatal and extrastriatal grey matter in both healthy and schizophrenia subjects. In comparison to healthy subjects, significantly weaker correlations in subjects with schizophrenia were confirmed in the right cingulate gyrus and thalamus, including the mediodorsal, lateral dorsal, anterior, and midline nuclei. Schizophrenia subjects showed decreased D2/D3-receptor availability in the hypothalamus, mamillary bodies, thalamus and several thalamic nuclei, and increased glucose uptake in three lobules of the cerebellar vermis.

Conclusions: Dopaminergic system may be involved in modulation of grey matter metabolism and neurometabolic coupling in both healthy human brain and psychopathology. Hyperdopaminergic state in untreated schizophrenia may at least partly account for the corresponding decreases in grey matter metabolism.  相似文献   
110.
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