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   20242篇
  免费   1369篇
  国内免费   72篇
耳鼻咽喉   180篇
儿科学   442篇
妇产科学   479篇
基础医学   2967篇
口腔科学   726篇
临床医学   2429篇
内科学   4147篇
皮肤病学   400篇
神经病学   2001篇
特种医学   535篇
外科学   2142篇
综合类   210篇
一般理论   11篇
预防医学   1926篇
眼科学   275篇
药学   1549篇
中国医学   105篇
肿瘤学   1159篇
  2023年   173篇
  2022年   242篇
  2021年   555篇
  2020年   333篇
  2019年   591篇
  2018年   783篇
  2017年   540篇
  2016年   599篇
  2015年   751篇
  2014年   867篇
  2013年   1184篇
  2012年   1722篇
  2011年   1730篇
  2010年   850篇
  2009年   711篇
  2008年   1282篇
  2007年   1258篇
  2006年   1201篇
  2005年   1120篇
  2004年   1071篇
  2003年   958篇
  2002年   881篇
  2001年   168篇
  2000年   147篇
  1999年   151篇
  1998年   114篇
  1997年   102篇
  1996年   112篇
  1995年   64篇
  1994年   55篇
  1993年   54篇
  1992年   80篇
  1991年   68篇
  1990年   80篇
  1989年   78篇
  1988年   64篇
  1987年   62篇
  1986年   68篇
  1985年   60篇
  1984年   76篇
  1983年   49篇
  1982年   66篇
  1981年   57篇
  1980年   51篇
  1979年   36篇
  1977年   29篇
  1975年   27篇
  1974年   31篇
  1973年   25篇
  1972年   27篇
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
911.

Background

There is increasing emphasis on involving intended beneficiaries and other stakeholders in the development of public health interventions to maximise acceptability and remove barriers to adoption, implementation, and maintenance before costly implementation. Yet the processes whereby key actors are engaged in intervention development are rarely reported, and frameworks for carrying out such work remain limited. We outline our approach to involving stakeholders in the optimisation of two school-based relationships and sex education programmes (Project Respect and Positive Choices) and reflect on the challenges of co-producing with teachers, students, and other partners.

Methods

Systematic optimisation of both interventions involved a review of existing literature on effective approaches; consultation with staff and students on intervention content and delivery; drafting of intervention materials; further consultation with schools; and then intervention refinement in preparation for a pilot. Seven focus groups took place in southeast and southwest England involving 75 students aged 13–15 years and 22 school staff. A group of young people trained to advise on public health research were consulted on two occasions and a wide range of sexual health and sex education practitioners and policy makers shared their views at a stakeholder event.

Findings

Consultation provided useful insights to inform intervention adaption in relation to who should deliver the programmes in schools; whether lessons should be taught in single sex classes; the format that guidance and lesson plans should take; the relevance and acceptability to students and teachers; and the need for the flexibility for materials to adapt to different school contexts. Genuine consultation and incorporation of school stakeholder views was challenging where stakeholder availability was limited and intervention development and implementation timelines were tight. Challenges also arose in relation to the weight to give divergent opinions among stakeholders and between stakeholders and researchers.

Interpretation

Carrying out structured stakeholder engagement activities can yield valuable insights that can improve the applicability of interventions to local contexts before they are formally trialled. To genuinely engage stakeholders in intervention development requires sufficient time to both consult and adapt. In such consultations, it is important to attend not just to the voices of those who are the loudest and most powerful.

Funding

National Institute for Health Research (NIHR).  相似文献   
912.

Objectives

There are minimal data regarding clinical outcomes and echocardiographic findings after transcatheter mitral valve-in-valve replacement (TMVR) compared with redo surgical mitral valve replacement (SMVR).

Background

TMVR therapy has emerged as therapy for a degenerated bioprosthetic valve failure.

Methods

The authors retrospectively identified patients with degenerated mitral bioprostheses who underwent redo SMVR or TMVR at 3 U.S. institutions. The authors compared clinical and echocardiographic outcomes of patients who had TMVR with those of patients who underwent redo SMVR.

Results

Sixty-two patients underwent TMVR and 59 patients underwent SMVR during the study period. Mean age and the Society of Thoracic Surgeons Predicted Risk of Mortality (STS PROM) scores were significantly higher in patients with TMVR than in those with SMVR (age 74.9 ± 9.4 years vs. 63.7 ± 14.9 years; p < 0.001; STS PROM 12.7 ± 8.0% vs. 8.7 ± 10.1%; p < 0.0001). Total procedure time, intensive care unit hours, and post-procedure length of stay were all significantly shorter in the TMVR group. There was no difference in mortality at 1 year between the 2 groups (TMVR 11.3% vs. SMVR 11.9%; p = 0.92). Mean mitral valve pressure gradient and the grade of mitral regurgitation (MR) were similar between the TMVR group and the SMVR group (mitral valve pressure gradient 7.1 ± 2.5 mm Hg vs. 6.5 ± 2.5 mm Hg; p = 0.42; MR [≥moderate] 3.8% vs. 5.6%; p = 1.00) at 30 days. At 1 year, the mitral valve pressure gradient was higher in the TMVR group (TMVR 7.2 ± 2.7 vs. SMVR 5.5 ± 1.8; p = 0.01), although there was no difference in the grade of MR.

Conclusions

Despite the higher STS PROM in TMVR patients, there was no difference in 1-year mortality between the TMVR and SMVR groups. Echocardiographic findings after TMVR were similar to SMVR at 30 days. There was a statistically significant difference in mitral gradient at 1 year, though this is likely not clinically important. TMVR may be an alternative to SMVR in patients with previous mitral bioprosthetic valves.  相似文献   
913.
Randomized controlled trials (RCTs) are essential to develop advances in heart failure (HF). The need for increasing numbers of patients (without substantial cost increase) and generalization of results led to the disappearance of international boundaries in large RCTs. The significant geographic differences in patients' characteristics, outcomes, and, most importantly, treatment effect observed in HF trials have recently been highlighted. Whether the observed regional discrepancies in HF trials are due to trial‐specific issues, patient heterogeneity, structural differences in countries, or a complex interaction between factors are the questions we propose to debate in this review. To do so, we will analyse and review data from HF trials conducted in different world regions, from heart failure with preserved ejection fraction (HF‐PEF), heart failure with reduced ejection fraction (HF‐REF), and acute heart failure (AHF). Finally, we will suggest objective and actionable measures in order to mitigate regional discrepancies in future trials, particularly in HF‐PEF where prognostic modifying treatments are urgently needed and in which trials are more prone to selection bias, due to a larger patient heterogeneity.  相似文献   
914.
Human adenoviruses (AdVs) typically cause mild illnesses in otherwise healthy hosts. We investigated a pediatric outbreak of acute respiratory infection with fatal outcomes that occurred in Lisbon, Portugal, in 2004. Biological specimens were collected from 83 children attending two nurseries, a kinesiotherapy clinic, and the household of a nanny. Adenovirus infection was confirmed in 48 children by PCR and virus isolation. Most (96%) isolates were classified as being of subspecies B1. Phylogenetic analysis of fiber and hexon gene sequences revealed that most infants were infected with AdV serotype 3 (AdV3) strains. Infants attending one nursery harbored a new recombinant strain containing an AdV serotype 7 hexon and serotype 3 fiber (AdV7/3). Both the AdV3 and the AdV7/3 strains caused fatal infections. Two different serotype 3 strains were circulating in Lisbon in 2004, and the new AdV7/3 recombinant type originated from only one of those strains. These results demonstrate that recombination leads to the emergence of new adenovirus strains with epidemic and lethal potential.Human adenoviruses (HAdVs) have been associated with a wide spectrum of clinical diseases with respiratory and gastrointestinal symptoms (23, 32). Severe illness can occur in newborns, elderly individuals, and patients with underlying medical conditions. In otherwise healthy adults, infections caused by human adenoviruses do not represent a life-threatening clinical condition. Adenoviruses are characterized by a linear double-stranded DNA genome of 2 to 45 kbp that encodes 30 to 40 proteins (6). HAdV comprises 51 serotypes (HAdV-1 to HAdV-51), on the basis of type-specific antiserum-mediated neutralization of infectivity (10). The serotypes can be divided into seven species, named HAdV-A to HAdV-G, on the basis of hemagglutination inhibition and biochemical criteria (13). HAdV-B is further classified into subspecies B1 and B2, which use different cellular receptors for viral entry (29). These variants can be segregated by different geographic areas, time periods, and clinical conditions.Serotype identification is critical for epidemiological surveillance, the detection of new strains, assessment of treatment efficacy, and understanding the pathogenesis of HAdV. For example, acute respiratory disease is primarily caused by HAdV-B1 serotypes 3, 7, 16, and 21; HAdV-B2 serotypes 11 and 14; and HAdV-E serotype 4 (8, 23, 25, 28, 35, 38, 41). Respiratory infections caused by HAdV-B1 serotypes 3 and 7 (16) and HAdV-B2 serotype 14 (17) are potentially fatal. Neutralization tests are the classical reference method used for the typing of adenovirus and require virus isolation from infected organs or tissues (20). The main type-specific neutralizing epitope, the ɛ determinant, consists of loop 1 (L1) and loop 2 (L2) on the hexon protein, the major capsid protein and the most abundant structural protein (26). Cases of the failure of neutralization with the available antisera require extensive cross-neutralization studies to define a new HAdV type. To circumvent the practical problems associated with traditional serum neutralization studies, molecular methods for the typing of adenovirus have been established. Examples are restriction fragment length polymorphism (RFLP) analysis of adenoviral DNA (16), PCR-based assays (1, 36), and microarray-based methods (36). However, these methods cannot discriminate between all serotypes and do not allow detailed studies of molecular epidemiology and viral evolution to be performed.More recently, analysis of the nucleotide and amino acid sequences from different genes has shown that adenovirus species form three distinct phylogenetic clusters: HAdV-C belongs to cluster 1; HAdV-A and HAdV-F belong to cluster 2; and HAdV-B, HAdV-D, and HAdV-E belong to cluster 3 (6, 22). In addition, phylogenetic analysis of selected gene fragments has increasingly been used to classify human adenoviruses at the serotype and species levels (7, 19, 40), to detect cases of coinfection with multiple adenoviral species (36, 38), and to identify new recombinant strains formed between similar species (18, 37, 41) or different species (19). Finally, phylogenetic analysis has become an important tool in the epidemiological investigation of many disease outbreaks caused by adenovirus (11, 17, 27, 40, 41). In the present study, we have used epidemiological, virological, and molecular phylogenetic methods to investigate the causes and origin of a recent outbreak of acute respiratory infection in Lisbon, Portugal, that resulted in the deaths of two children.  相似文献   
915.
Non-traumatic osteonecrosis of the femoral head (ONFH) usually affects adults younger than 50 years and frequently leads to femoral head collapse and subsequent arthritis of the hip. It is becoming more prevalent along with increasing use of corticosteroids for the adjuvant therapy of leukemia and other myelogenous diseases as well as management of organ transplantation. This review updated knowledge on the pathogenesis, classification criteria, staging system, and treatment of ONFH.  相似文献   
916.
917.
918.
Primary familial brain calcification (PFBC) is a heterogeneous neuropsychiatric disorder, with affected individuals presenting a wide variety of motor and cognitive impairments, such as migraine, parkinsonism, psychosis, dementia, and mood swings. Calcifications are usually symmetrical, bilateral, and found predominantly in the basal ganglia, thalamus, and cerebellum. So far, variants in three genes have been linked to PFBC: SLC20A2, PDGFRB, and PDGFB. Variants in SLC20A2 are responsible for most cases identified so far and, therefore, the present review is a comprehensive worldwide summary of all reported variants to date. SLC20A2 encodes an inorganic phosphate transporter, PiT‐2, widely expressed in various tissues, including brain, and is part of a major family of solute carrier membrane transporters. Fifty variants reported in 55 unrelated patients so far have been identified in families of diverse ethnicities and only few are recurrent. Various types of variants were detected (missense, nonsense, frameshift) including full or partial SLC20A2 deletions. The recently reported SLC20A2 knockout mouse will enhance our understanding of disease mechanism and allow for screening of therapeutic compounds. In the present review, we also discuss the implications of these recent exciting findings and consider the possibility of treatments based on manipulation of inorganic phosphate homeostasis.  相似文献   
919.
920.
Due to the limited self‐repair capacity of cartilage, regenerative medicine therapies for the treatment of cartilage defects must use a significant amount of cells, preferably applied using a hydrogel system that can promise their delivery and functionality at the specific site. This paper discusses the potential use of κ‐carrageenan hydrogels for the delivery of stem cells obtained from adipose tissue in the treatment of cartilage tissue defects. The developed hydrogels were produced by an ionotropic gelation method and human adipose stem cells (hASCs) were encapsulated in 1.5% w/v κ‐carrageenan solution at a cell density of 5 × 106 cells/ml. The results from the analysis of the cell‐encapsulating hydrogels, cultured for up to 21 days, indicated that κ‐carrageenan hydrogels support the viability, proliferation and chondrogenic differentiation of hASCs. Additionally, the mechanical analysis demonstrated an increase in stiffness and viscoelastic properties of κ‐carrageenan gels with their encapsulated cells with increasing time in culture with chondrogenic medium. These results allowed the conclusion that κ‐carrageenan exhibits properties that enable the in vitro functionality of encapsulated hASCs and thus may provide the basis for new successful approaches for the treatment of cartilage defects. Copyright © 2013 John Wiley & Sons, Ltd.  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