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   3406258篇
  免费   232052篇
  国内免费   8754篇
耳鼻咽喉   46030篇
儿科学   110597篇
妇产科学   92012篇
基础医学   475497篇
口腔科学   94743篇
临床医学   310738篇
内科学   665986篇
皮肤病学   77573篇
神经病学   279124篇
特种医学   131603篇
外国民族医学   953篇
外科学   506321篇
综合类   73006篇
现状与发展   5篇
一般理论   1301篇
预防医学   266833篇
眼科学   75493篇
药学   248577篇
  83篇
中国医学   6663篇
肿瘤学   183926篇
  2019年   27600篇
  2018年   37554篇
  2017年   28749篇
  2016年   33048篇
  2015年   37132篇
  2014年   51466篇
  2013年   77543篇
  2012年   102673篇
  2011年   108823篇
  2010年   65492篇
  2009年   62711篇
  2008年   101310篇
  2007年   107777篇
  2006年   109514篇
  2005年   105189篇
  2004年   101413篇
  2003年   97697篇
  2002年   94102篇
  2001年   162178篇
  2000年   166602篇
  1999年   140185篇
  1998年   40472篇
  1997年   36010篇
  1996年   36460篇
  1995年   35438篇
  1994年   32684篇
  1993年   30571篇
  1992年   110454篇
  1991年   106659篇
  1990年   103308篇
  1989年   99454篇
  1988年   91366篇
  1987年   89785篇
  1986年   84467篇
  1985年   80718篇
  1984年   60452篇
  1983年   51180篇
  1982年   30435篇
  1981年   27255篇
  1979年   53953篇
  1978年   38323篇
  1977年   32361篇
  1976年   30035篇
  1975年   32067篇
  1974年   38045篇
  1973年   36299篇
  1972年   33897篇
  1971年   31461篇
  1970年   28934篇
  1969年   27521篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
BACKGROUND AND PURPOSE:The coronavirus disease 2019 (COVID-19) pandemic has led to decreases in neuroimaging volume. Our aim was to quantify the change in acute or subacute ischemic strokes detected on CT or MR imaging during the pandemic using natural language processing of radiology reports.MATERIALS AND METHODS:We retrospectively analyzed 32,555 radiology reports from brain CTs and MRIs from a comprehensive stroke center, performed from March 1 to April 30 each year from 2017 to 2020, involving 20,414 unique patients. To detect acute or subacute ischemic stroke in free-text reports, we trained a random forest natural language processing classifier using 1987 randomly sampled radiology reports with manual annotation. Natural language processing classifier generalizability was evaluated using 1974 imaging reports from an external dataset.RESULTS:The natural language processing classifier achieved a 5-fold cross-validation classification accuracy of 0.97 and an F1 score of 0.74, with a slight underestimation (−5%) of actual numbers of acute or subacute ischemic strokes in cross-validation. Importantly, cross-validation performance stratified by year was similar. Applying the classifier to the complete study cohort, we found an estimated 24% decrease in patients with acute or subacute ischemic strokes reported on CT or MR imaging from March to April 2020 compared with the average from those months in 2017–2019. Among patients with stroke-related order indications, the estimated proportion who underwent neuroimaging with acute or subacute ischemic stroke detection significantly increased from 16% during 2017–2019 to 21% in 2020 (P = .01). The natural language processing classifier performed worse on external data.CONCLUSIONS:Acute or subacute ischemic stroke cases detected by neuroimaging decreased during the COVID-19 pandemic, though a higher proportion of studies ordered for stroke were positive for acute or subacute ischemic strokes. Natural language processing approaches can help automatically track acute or subacute ischemic stroke numbers for epidemiologic studies, though local classifier training is important due to radiologist reporting style differences.

There is much concern regarding the impact of the coronavirus disease 2019 (COVID-19) pandemic on the quality of stroke care, including issues with hospital capacity, clinical resource re-allocation, and the safety of patients and clinicians.1,2 Previous reports have shown that there have been substantial decreases in stroke neuroimaging volume during the pandemic.3,4 In addition, acute ischemic infarcts have been found on neuroimaging studies in many hospitalized patients with COVID-19, though the causal relationship is unclear.5,6 Studies like these and other epidemiologic analyses usually rely on the creation of manually curated databases, in which identification of cases can be time-consuming and difficult to update in real-time. One way to facilitate such research is to use natural language processing (NLP), which has shown utility for automated analysis of radiology report data.7 NLP algorithms have been developed previously for the classification of neuroradiology reports for the presence of ischemic stroke findings and acute ischemic stroke subtypes.8,9 Thus, NLP has the potential to facilitate COVID-19 research.In this study, we developed an NLP machine learning model that classifies radiology reports for the presence or absence of acute or subacute ischemic stroke (ASIS), as opposed to chronic stroke. We used this model to quantify the change in ASIS detected on all CT or MR imaging studies performed at a large comprehensive stroke center during the COVID-19 pandemic in the United States. We also evaluated NLP model generalizability and different training strategies using a sample of radiology reports from a second stroke center.  相似文献   
62.

Background

In November 2017, the World Health Organization received initial reports of suspected diphtheria cases in camps established for displaced Rohingyas in Cox’s Bazar district, Bangladesh. By January 11, 2018, over 4,000 suspected cases of diphtheria and 30 deaths were reported. The Bangladesh government and partners implemented a diphtheria vaccination campaign in December 2017. Outbreak response staff reported anecdotal evidence of vaccine hesitancy. Our assessment aimed to understand vaccination barriers and opportunities to enhance vaccine demand among displaced Rohingyas in Bangladesh.

Methods

In January 2018, we conducted a qualitative assessment consisting of nine focus group discussions and 15 key informant interviews with displaced Rohingyas in three camps. Participants included mothers and fathers with under five-year-old children, community volunteers, majhis (camp leaders), Islamic religious leaders, traditional and spiritual healers, and teachers. We recruited participants using purposive sampling, and analyzed the data thematically.

Results

Across focus groups and in-depth interviews, trusted information sources cited by participants included religious leaders, elders, village doctors, pharmacists, majhis, and mothers trained by non-governmental organizations to educate caregivers. Treatment of diphtheria and measles was usually sought from multiple sources including traditional and spiritual healers, village doctors, pharmacies, and health clinics. Major barriers to vaccination included: various beliefs about vaccination causing people to become Christian; concerns about multiple vaccines being received on the same day; worries about vaccination side effects; and, lack of sensitivity to cultural gender norms at the vaccination sites.

Conclusion

Although vaccination was understood as an important intervention to prevent childhood diseases, participants reported numerous barriers to vaccination. Strengthening vaccine demand and acceptance among displaced Rohingyas can be enhanced by improving vaccination delivery practices and engaging trusted leaders to address religious and cultural barriers using community-based channels.  相似文献   
63.
Abstract

Introduction: Student-staff partnerships as a concept to improve medical education have received a growing amount of attention. Such partnerships are collaborations in which students and teachers seek to improve education by each adding their unique contribution to decision-making and implementation processes. Although previous research has demonstrated that students are favourable to this concept, teachers remain hesitant. The present study investigated teachers’ conceptions of student-staff partnerships and of the prerequisites that are necessary to render such partnerships successful and enhance educational quality.

Method: We conducted semi-structured interviews with 14 course coordinators who lead course design teams and also teach in 4 bachelor health programmes, using Bovill and Bulley’s levels of student participation as sensitising concepts during data analysis.

Results: The results pointed to three different conceptions of student-staff partnerships existing among teachers: Teachers teach and students study; teachers teach and value students’ feedback; and teachers and students co-create. The prerequisites for effective co-creation teachers identified were: Teachers must be open to involve students and create dialogues; students must be motivated and have good communication skills; the organisation must be supportive; and teachers should have the final say.

Conclusion: We conclude that teachers’ conceptions are consistent with Bovill and Bulley’s levels of student participation. Under certain conditions, teachers are willing to co-create and reach the highest levels of student participation.  相似文献   
64.

Background

Spontaneous decolonization of antibiotic-resistant bacteria (ARB) takes time: approximately 25% after 30 days for carbapenem-producing Enterobacteriaceae or extended-spectrum beta-lactamase-producing Enterobacteriaceae. Faecal microbiota transplantation (FMT) has been proposed as a new strategy to promote decolonization in order to reduce the risk of superinfection due to these ARB. This paper discusses the literature on the use of FMT for this indication, and the improvement levers available to promote its efficacy.

Methods

Literature available to date concerning the use of FMT to eradicate ARB was reviewed, and the different factors that may have influenced the efficacy of decolonization were evaluated.

Results

Four axes that could have played major roles in the efficacy of FMT were identified: bowel preparation before FMT; donor; dose; and thermal conditioning of faeces. The positive or negative impact of each on the outcome of FMT is discussed.

Conclusion

Although FMT is very efficient for the eradication of Clostridium difficile, the same ‘recipe’ cannot be used for the eradication of ARB. Working together with expert centres may help to improve the efficacy of FMT for this indication, and enable the reduction of in-hospital isolation precautions.  相似文献   
65.

Objectives

Triazole resistance in Aspergillus spp. is emerging and complicates prophylaxis and treatment of invasive aspergillosis (IA) worldwide. New polymerase chain reaction (PCR) tests on broncho-alveolar lavage (BAL) fluid allow for detection of triazole resistance at a genetic level, which has opened up new possibilities for targeted therapy. In the absence of clinical trials, a modelling study delivers estimates of the added value of resistance detection with PCR, and which empiric therapy would be optimal when local resistance rates are known.

Design

A decision-analytic modelling study was performed based on epidemiological data of IA, extended with estimated dynamics of resistance rates and treatment effectiveness. Six clinical strategies were compared that differ in use of PCR diagnostics (used vs not used) and in empiric therapeutic choice in case of unknown triazole susceptibility: voriconazole, liposomal amphotericin B (LAmB) or both. Outcome measures were proportion of correct treatment, survival and serious adverse events.

Results

Implementing aspergillus PCR tests was projected to result in residual treatment-susceptibility mismatches of <5% for a triazole resistance rate up to 20% (using voriconazole). Empiric LAmB outperformed voriconazole at resistance rates >5–20%, depending on PCR use and estimated survival benefits of voriconazole over LAmB. Combination therapy of voriconazole and LAmB performed best at all resistance rates, but the advantage over the other strategies should be weighed against the expected increased number of drug-related serious adverse events. The advantage of combination therapy over LAmB monotherapy became smaller at higher triazole resistance rates.

Conclusions

Introduction of current aspergillus PCR tests on BAL fluid is an effective way to increase the proportion of patients that receive targeted therapy for IA. The results indicate that close monitoring of background resistance rates and adverse drug events are important to attain the potential benefits of LAmB. The choice of strategy ultimately depends on the probability of triazole resistance, the availability of PCR and individual patient characteristics.  相似文献   
66.
ObjectiveTo evaluate the outcomes after septal myectomy in patients with obstructive hypertrophic cardiomyopathy according to atrial fibrillation and surgical ablation of atrial fibrillation.MethodsWe reviewed patients with obstructive hypertrophic cardiomyopathy who underwent septal myectomy at the Mayo Clinic from 2001 to 2016. History of atrial fibrillation was obtained from patient histories and electrocardiograms. All-cause mortality was the primary end point.ResultsA total of 2023 patients underwent septal myectomy, of whom 394 (19.5%) had at least 1 episode of atrial fibrillation preoperatively. Among patients with atrial fibrillation, 76 (19.3%) had only 1 known episode, 278 (70.6%) had recurrent paroxysmal atrial fibrillation, and 40 (10.2%) had persistent atrial fibrillation. Surgical ablation was performed in 190 patients at the time of septal myectomy, including 148 with pulmonary vein isolation and 42 with the classic maze procedure. Among all patients, operative mortality was 0.4%, and there were no early deaths in patients undergoing surgical ablation. Over a median follow-up of 5.6 years, patients with preoperative atrial fibrillation had increased mortality (hazard ratio, 1.36; 95% confidence interval, 0.97-1.91; P = .070) after multivariable adjustment for comorbidities. When considering the impact of atrial fibrillation with or without surgical treatment, the adjusted hazard ratio for mortality in patients undergoing ablation compared with no ablation was 0.93 (95% confidence interval, 0.52-1.69; P = .824).ConclusionsAtrial fibrillation is present preoperatively in one-fifth of patients with obstructive hypertrophic cardiomyopathy undergoing myectomy and showed a trend toward higher all-cause mortality. Survival of patients undergoing septal myectomy with preoperative atrial fibrillation was similar between those who did and did not receive concomitant surgical ablation.  相似文献   
67.
Graphical abstract summarizing the overall results of our study comparing reintervention for a main or central branch pulmonary artery reconstruction site and various patch materials. Autologous pericardium was associate with the lowest reintervention and was free. Multivariable analysis demonstrated lack of superiority of homograft branch patch, which clearly has a much higher cost.
  相似文献   
68.
69.
70.
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