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   2726篇
  免费   156篇
  国内免费   74篇
耳鼻咽喉   56篇
儿科学   121篇
妇产科学   52篇
基础医学   327篇
口腔科学   56篇
临床医学   326篇
内科学   558篇
皮肤病学   36篇
神经病学   100篇
特种医学   370篇
外科学   328篇
综合类   95篇
一般理论   1篇
预防医学   96篇
眼科学   51篇
药学   202篇
中国医学   21篇
肿瘤学   160篇
  2023年   19篇
  2022年   42篇
  2021年   65篇
  2020年   37篇
  2019年   55篇
  2018年   54篇
  2017年   41篇
  2016年   50篇
  2015年   65篇
  2014年   104篇
  2013年   115篇
  2012年   136篇
  2011年   139篇
  2010年   125篇
  2009年   102篇
  2008年   106篇
  2007年   128篇
  2006年   106篇
  2005年   107篇
  2004年   76篇
  2003年   62篇
  2002年   88篇
  2001年   79篇
  2000年   66篇
  1999年   61篇
  1998年   75篇
  1997年   81篇
  1996年   82篇
  1995年   68篇
  1994年   50篇
  1993年   57篇
  1992年   25篇
  1991年   58篇
  1990年   44篇
  1989年   56篇
  1988年   35篇
  1987年   46篇
  1986年   32篇
  1985年   41篇
  1984年   29篇
  1983年   27篇
  1982年   26篇
  1981年   23篇
  1980年   24篇
  1979年   7篇
  1978年   6篇
  1977年   12篇
  1976年   7篇
  1975年   6篇
  1966年   3篇
排序方式: 共有2956条查询结果,搜索用时 0 毫秒
101.
The study's objective was to assess the cost‐effectiveness of preoperative transfusion compared with no preoperative transfusion in patients with sickle cell disease undergoing low‐ or medium‐risk surgery. Seventy patients with sickle cell disease (HbSS/Sß0thal genotypes) undergoing elective surgery participated in a multicentre randomised trial, Transfusion Alternatives Preoperatively in Sickle Cell Disease (TAPS). Here, a cost‐effectiveness analysis based on evidence from that trial is presented. A decision‐analytic model is used to incorporate long‐term consequences of transfusions and acute chest syndrome. Costs and health benefits, expressed as quality‐adjusted life years (QALYs), are reported from the ‘within‐trial’ analysis and for the decision‐analytic model. The probability of cost‐effectiveness for each form of management is calculated taking into account the small sample size and other sources of uncertainty. In the range of scenarios considered in the analysis, preoperative transfusion was more effective, with the mean improvement in QALYs ranging from 0.018 to 0.206 per patient, and also less costly in all but one scenario, with the mean cost difference ranging from ?£813 to £26. All scenarios suggested preoperative transfusion had a probability of cost‐effectiveness >0.79 at a cost‐effectiveness threshold of £20 000 per QALY.  相似文献   
102.
Recent federal initiatives have used estimates of population reach as a proxy metric for intervention impact, in part to inform resource allocation and programmatic decisions about competing priorities in the community. However, in spite of its utility, population reach as a singular metric of intervention impact may be insufficient for guiding multifaceted program decisions. A more comprehensive, validated approach to measure or forecast dose may complement reach estimates to inform decision makers about optimal ways to use limited resources.Although federal initiatives in obesity prevention have typically recommended the use of evidence-based community strategies,1 less is known about the level of impact that these strategies can contribute to improving health in the real world. The absence of this type of practice-based information often poses significant challenges to funding agencies and program planners that are tasked with prioritizing and selecting intervention strategies for a city or community. Given that this information is not readily available or regularly reported, recent federal initiatives have begun to request data on intervention impact, using estimates of population reach as a proxy metric for predicting the extent of intervention effectiveness. The Centers for Disease Control and Prevention, for example, recently provided guidance on how to measure and report reach for a range of obesity prevention interventions focused on improving systems and environments in cities and communities across the United States.2 They broadly defined “reach” as the number of unique individuals affected by a program initiative and further refined this concept to include direct reach as the number of unique individuals exposed to the intervention in some way and indirect reach as the number of unique individuals indirectly exposed to the intervention in some way but who are not residents of a targeted community (e.g., visitors).2 To provide more specificity, other agencies and organizations (e.g., the Center for Community Health and Evaluation) have sought to account for the effects of community health interventions by incorporating intervention dose as an additional parameter for consideration in their priority-setting process and program planning.3 In this context, “dose” has been defined as the product of reach (percentage of people exposed to an intervention) and strength (the degree to which people reached by the intervention changed their health behaviors).3 Although dose is a more robust measure of intervention impact, reach is generally easier to estimate and use, given the time constraints and limited availability of relevant data sources to local leaders who must make daily decisions about policy development, program implementation, and operations. It is important to note, however, that the Centers for Disease Control and Prevention and the Center for Community Health and Evaluation differ in their definitions of “reach.” Although the former’s definition distinguishes between direct and indirect number of unique individuals, the latter’s does not, making comparisons of this metric across studies, interventions, places, settings, and times difficult to achieve.Although the aforementioned metrics (reach and dose) can provide meaningful data to inform health and public health decisions,4,5 few strategic planning efforts have incorporated their use in the prioritization process.6 In this article, we describe the effort of the Los Angeles County Department of Public Health (DPH) to systematically incorporate population reach as a proxy metric of intervention impact, using it to guide prioritization of system and environmental change strategies for community implementation (when appropriate). The motivation for writing this article is to inform the efforts of other agencies similarly tasked with addressing the obesity epidemic in their communities but often constrained by limited resources and several competing priorities in their jurisdictions.  相似文献   
103.
104.
Age-related macular degeneration (AMD) affects the central vision and subsequently may lead to visual loss in people over 60 years of age. There is no permanent cure for AMD, but early detection and successive treatment may improve the visual acuity. AMD is mainly classified into dry and wet type; however, dry AMD is more common in aging population. AMD is characterized by drusen, yellow pigmentation, and neovascularization. These lesions are examined through visual inspection of retinal fundus images by ophthalmologists. It is laborious, time-consuming, and resource-intensive. Hence, in this study, we have proposed an automated AMD detection system using discrete wavelet transform (DWT) and feature ranking strategies. The first four-order statistical moments (mean, variance, skewness, and kurtosis), energy, entropy, and Gini index-based features are extracted from DWT coefficients. We have used five (t test, Kullback–Lieber Divergence (KLD), Chernoff Bound and Bhattacharyya Distance, receiver operating characteristics curve-based, and Wilcoxon) feature ranking strategies to identify optimal feature set. A set of supervised classifiers namely support vector machine (SVM), decision tree, \(k\) -nearest neighbor ( \(k\) -NN), Naive Bayes, and probabilistic neural network were used to evaluate the highest performance measure using minimum number of features in classifying normal and dry AMD classes. The proposed framework obtained an average accuracy of 93.70 %, sensitivity of 91.11 %, and specificity of 96.30 % using KLD ranking and SVM classifier. We have also formulated an AMD Risk Index using selected features to classify the normal and dry AMD classes using one number. The proposed system can be used to assist the clinicians and also for mass AMD screening programs.  相似文献   
105.
106.
107.
108.
INTRODUCTIONChest radiographs (CXRs) are widely used for the screening and management of COVID-19. This article describes the radiographic features of COVID-19 based on an initial national cohort of patients.METHODSThis is a retrospective review of swab-positive patients with COVID-19 who were admitted to four different hospitals in Singapore between 22 January and 9 March 2020. Initial and follow-up CXRs were reviewed by three experienced radiologists to identify the predominant pattern and distribution of lung parenchymal abnormalities.RESULTSIn total, 347 CXRs of 96 patients were reviewed. Initial CXRs were abnormal in 41 (42.7%) out of 96 patients. The mean time from onset of symptoms to CXR abnormality was 5.3 ± 4.7 days. The predominant pattern of lung abnormality was ground-glass opacity on initial CXRs (51.2%) and consolidation on follow-up CXRs (51.0%). Multifocal bilateral abnormalities in mixed central and peripheral distribution were observed in 63.4% and 59.2% of abnormal initial and follow-up CXRs, respectively. The lower zones were involved in 90.2% of initial CXRs and 93.9% of follow-up CXRs.CONCLUSIONIn a cohort of swab-positive patients, including those identified from contact tracing, we found a lower incidence of CXR abnormalities than was previously reported. The most common pattern was ground-glass opacity or consolidation, but mixed central and peripheral involvement was more common than peripheral involvement alone.  相似文献   
109.
Situated models of emotion hypothesize that emotions are optimized for the context at hand, but most neuroimaging approaches ignore context. For the first time, we applied Granger causality (GC) analysis to determine how an emotion is affected by a person’s cultural background and situation. Electroencephalographic recordings were obtained from mainland Chinese (CHN) and US participants as they viewed and rated fearful and neutral images displaying either social or non-social contexts. Independent component analysis and GC analysis were applied to determine the epoch of peak effect for each condition and to identify sources and sinks among brain regions of interest. We found that source–sink couplings differed across culture, situation and culture × situation. Mainland CHN participants alone showed preference for an early-onset source–sink pairing with the supramarginal gyrus as a causal source, suggesting that, relative to US participants, CHN participants more strongly prioritized a scene’s social aspects in their response to fearful scenes. Our findings suggest that the neural representation of fear indeed varies according to both culture and situation and their interaction in ways that are consistent with norms instilled by cultural background.  相似文献   
110.
BackgroundLong-acting injectable (LAI) antipsychotics improve medication adherence in patients with schizophrenia and extend the duration of therapeutic drug levels but with administration of an increased dose. Real-world mortality data in patients prescribed LAIs are lacking. We conducted a population-based cohort study to estimate and compare the incidence rates of all-cause death and completed suicide in patients with schizophrenia/schizoaffective disorder exposed to LAIs and oral antipsychotics.MethodsPatients with a diagnosis of schizophrenia/schizoaffective disorder between January 1, 2015 and November 30, 2019 were enrolled from the Taiwan National Health Insurance Research Database and linked to Death Registry records. Eligible patients were new antipsychotic users. Relative risks of death for each antipsychotic compared with oral paliperidone were evaluated using a Cox proportional hazard model adjusted for age, sex, Charlson Comorbidity Index, index year, bipolar or major depressive or other mood disorders, mental disorders due to drug use, and baseline hospitalization frequency.ResultsThere were 228,791.08 person-years of follow-up (mean 2.48 years). The incidence rates of all-cause death in users of LAI paliperidone administered monthly (PP1M) and every 3 months (PP3M) were 7.40/1,000 person-years (95% confidence interval 5.94–9.11) and 9.93 (5.88–15.79), respectively. The incidences of completed suicide were 2.03/1,000 person-years (1.32–2.99) and 3.10 (1.14–6.88), respectively. No significant associations were observed between PP1M and PP3M compared to oral paliperidone in incidences of all-cause death or for completed suicide.DiscussionNo increased risk of all-cause death or completed suicide was observed in users of antipsychotic LAIs, including PP1M and PP3M.  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