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   5943篇
  免费   574篇
  国内免费   7篇
耳鼻咽喉   59篇
儿科学   216篇
妇产科学   210篇
基础医学   822篇
口腔科学   64篇
临床医学   590篇
内科学   1219篇
皮肤病学   71篇
神经病学   695篇
特种医学   107篇
外科学   627篇
综合类   67篇
一般理论   10篇
预防医学   820篇
眼科学   145篇
药学   369篇
中国医学   6篇
肿瘤学   427篇
  2024年   17篇
  2023年   161篇
  2022年   207篇
  2021年   511篇
  2020年   278篇
  2019年   339篇
  2018年   312篇
  2017年   219篇
  2016年   229篇
  2015年   247篇
  2014年   293篇
  2013年   340篇
  2012年   484篇
  2011年   401篇
  2010年   207篇
  2009年   159篇
  2008年   271篇
  2007年   309篇
  2006年   245篇
  2005年   218篇
  2004年   183篇
  2003年   148篇
  2002年   129篇
  2001年   43篇
  2000年   35篇
  1999年   40篇
  1998年   31篇
  1997年   20篇
  1996年   21篇
  1995年   19篇
  1994年   14篇
  1993年   9篇
  1992年   22篇
  1991年   31篇
  1990年   25篇
  1989年   20篇
  1988年   27篇
  1987年   38篇
  1986年   18篇
  1985年   23篇
  1984年   18篇
  1983年   14篇
  1982年   14篇
  1981年   9篇
  1980年   9篇
  1977年   12篇
  1976年   10篇
  1975年   9篇
  1974年   8篇
  1968年   8篇
排序方式: 共有6524条查询结果,搜索用时 31 毫秒
51.
Transgender (trans) women experience barriers to access to HIV care, which result in their lower engagement in HIV prevention, treatment and support relative to cisgender people living with HIV. Studies of trans women's barriers to HIV care have predominantly focused on perspectives of trans women, while barriers are most often described at provider, organisation and/or systems levels. Comparing perspectives of trans women and service providers may promote a shared vision for achieving health equity. Thus, this qualitative study utilised focus groups and semi-structured interviews conducted 2018–2019 to understand barriers and facilitators to HIV care from the perspectives of trans women (n = 26) and service providers (n = 10). Barriers endorsed by both groups included: (a) anticipated and enacted stigma and discrimination in the provision of direct care, (b) lack of provider knowledge of HIV care needs for trans women, (c) absence of trans-specific services/organisations and (d) cisnormativity in sexual healthcare. Facilitators included: (a) provision of trans-positive trauma-informed care, (b) autonomy and choice for trans women in selecting sexual health services and (c) models for trans-affirming systems change. Each theme had significant overlap, yet nuanced perspective, between trans women and service providers. Specific recommendations to improve HIV care access for trans women are discussed. These recommendations can be used by administrators and service providers alike to work collaboratively with trans women to reduce barriers and facilitators to HIV care and ultimately to achieve health equity for trans women.  相似文献   
52.
To determine the effect of pharmacologic modulation of alterations of peripheral blood T-cell subsets caused by antigen-induced bronchoconstriction, we administered albuterol immediately after antigen-induced bronchoconstriction in a double-blind to protocol to 12 atopic asthmatic subjects. We also administered cromolyn sodium before antigen to 7 of the same subjects. Peripheral blood T-cell subset composition (CD4, CD8, la) of a highly purified T-cell preparation was determined before, 24, 48, 72, and 168 h after bronchoconstriction. We found that placebo inhalation immediately after antigen-induced bronchoconstriction did not affect subsequent peripheral blood T-cell subset changes (decrease in CD4+ and increase in Ia+ T lymphocytes). In contrast, inhaled albuterol abolished these T-cell subset changes. Although cromolyn sodium significantly decreased the severity of antigen-induced bronchoconstriction, it did not affect T-cell subset composition changes at the dosage used. We conclude that albuterol can ablate T-cell subset changes associated with antigen-induced bronchoconstriction. Cromolyn sodium ameliorates bronchoconstriction, but has no affect on T-cell subset composition changes. This implies that T-cell changes and bronchoconstriction caused by antigen inhalation are mediated through different pathways.  相似文献   
53.
PURPOSE: To determine and compare the diagnostic performance of fetal middle cerebral (MCA), renal (RA), and umbilical (UA) arterial Doppler ultrasonography (US) for prediction of adverse perinatal outcome in suspected intrauterine growth restriction (IUGR). MATERIALS AND METHODS: Two hundred ninety-three small-for-gestational age fetuses (24-39 weeks at recruitment and US-estimated weight or abdominal circumference below 10th percentile) were prospectively examined with Doppler US of the UA, MCA, and RA. Clinicians were blinded to MCA and RA Doppler measurements. RESULTS: Seventy-six fetuses (25.9%) had at least one major or minor adverse perinatal outcome. Major outcomes included stillbirth, neonatal death, neurologic complication, and necrotizing enterocolitis. The MCA pulsatility index (PI), compared with the UA PI and RA PI, was more sensitive (72.4% vs 44.7% and 8.3%) but less specific (58.1% vs 86.6% and 92.6%) in predicting adverse outcome. The UA PI had the highest positive likelihood ratio (ratio, 3.3); the MCA PI had the lowest negative likelihood ratio (ratio, 0.48). When gestational age at the first Doppler US examination was less than 32 weeks, the MCA PI had a sensitivity of 95.5% and negative predictive value of 97.7% for major adverse outcome (negative likelihood ratio, 0.10). CONCLUSION: In suspected IUGR, while an abnormal UA PI is a better predictor of adverse perinatal outcome than an abnormal MCA or RA PI, a normal MCA PI may help to identify fetuses without major adverse perinatal outcome, especially before 32 weeks gestational age.  相似文献   
54.
Changes in allograft bone irradiated at different temperatures   总被引:6,自引:0,他引:6  
Secondary sterilisation of allograft bone by gamma irradiation is common, but the conditions under which it is performed vary between tissue banks. Some do so at room temperature, others while the bone is frozen. Bone is made brittle by irradiation because of the destruction of collagen alpha chains, probably mediated by free radicals generated from water molecules. Freezing reduces the mobility of water molecules and may therefore decrease the production of free radicals. We found that bone irradiated at -78 degrees C was less brittle and had less collagen damage than when irradiated at room temperature. These findings may have implications for bone-banking.  相似文献   
55.
We have designed a novel vaccine strategy which enables display of short peptides expressed from chimeras of the gene encoding the coat protein of the RNA bacteriophage MS2 and inserted foreign DNA. MS2 coat protein has a beta-hairpin loop at the N-terminus which forms the most radially distinct feature of the mature capsid. The coat protein gene was modified to enable insertion of DNA at the central part of the beta-hairpin loop. Upon expression of the recombinant gene in E. coli, the MS2 coat protein subunits self-assemble into capsids, each comprising 180 copies of the monomer. This system was used to produce chimeras containing a putatively protective epitope, T1, from the immunodominant liver stage antigen-1 (LSA-1) of the malaria parasite Plasmodium falciparum. The immunogenicity of the native MS2 capsid and the recombinant construct was investigated in BALB/c (H-2(d)) mice. The native protein appeared to elicit both humoral and cellular immune responses, observed as a predominance of type 2 cytokines but with a mixed profile of immunoglobulin isotypes. In contrast, the LSA-1 chimera stimulated a type 1-polarised response, with significant upregulation of interferon-gamma, a finding which corroborates naturally acquired resistance to liver stage malaria. These results validate RNA phage capsid display of immunogenic determinants as a basis for the development of novel peptide vaccines and indicate that further evaluation of MS2 coat protein as a vector for malaria epitopes is merited.  相似文献   
56.
D Burnett  R A Stockley 《Thorax》1981,36(7):512-516
Serum alpha 2 macroglobulin concentrations were measured in patients with chronic obstructive airways disease and an age-matched group of control subjects. The mean serum level of alpha 2 macroglobulin was significantly lower in bronchitic subjects with acute chest infections than the mean value of the controls. No significant differences were observed between serum alpha 2 macroglobulin values in controls, subjects with "emphysema", and bronchitic patients who did not have chest infections. Sputum alpha 2 macroglobulin concentrations were compared in sputum samples from bronchitic patients with and without acute chest infections. The protein was detected (greater than 0.2 mg/l) in 94% of sputum samples from infected subjects but only 60% of non-infected sputum samples. Concentrations of alpha 2 macroglobulin in infected samples were significantly higher than the non-infected samples. Sputum/serum concentration ratios of alpha 2 macroglobulin were also significantly higher in infected samples but this difference was eliminated by "correcting" the values with the albumin sputum/serum ratios of the same samples. The results suggest that alpha 2 macroglobulin concentrations are higher in bronchial secretions during chest infection because of increased transudation from the blood rather than the presence of significant local secretion.  相似文献   
57.
Biological response modifiers in the management of rheumatoid arthritis.   总被引:2,自引:0,他引:2  
The management of rheumatoid arthritis (RA) with biological response modifiers (BRMs) is reviewed. RA, an autoimmune disorder affecting 1-2% of the world's population, is characterized by inflammation of synovial tissues, joint swelling, stiffness, and pain that may progress to joint erosion. There is strong evidence that inflammatory mediators, such as tissue necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1), play a critical role in the pathogenesis of this disorder. IL-1-receptor antagonist (IL-1Ra) is produced in healthy subjects and helps to protect against the adverse effects associated with IL-1 overexpression. Administration of IL-1Ra or similar agents may reduce the effects of IL-1 and ameliorate inflammatory conditions. Traditional treatment of RA has been based on symptomatic management with non-steroidal antiinflammatory drugs, disease-modifying antirheumatic drugs, and corticosteroids, each of which has substantial drawbacks in terms of effectiveness or adverse effects. Newer therapeutic strategies for blocking the biological effects of inflammatory cytokines include antibodies directed against TNF (e.g., infliximab), soluble receptors (e.g., etanercept) and receptor antagonists to IL-1 (anakinra) [corrected]. Clinical trials indicate that these BRMs may be more effective than traditional agents because they are able to alter joint remodeling in addition to attenuating symptoms. Anti-TNF therapies may be associated with increased risk for infections, sepsis, tuberculosis reactivation, demyelination disorders, and blood dyscrasias; anakinra appears to be safer. Combination therapy with BRMs may be more appropriate for RA than monotherapy. The role of BRMs in the treatment of RA will evolve as investigators learn more about the drugs and the disorder.  相似文献   
58.
59.
60.
This article estimates the population prevalence of current injection drug users (IDUs) in 96 large US metropolitan areas to facilitate structural analyses of its predictors and sequelae and assesses the extent to which drug abuse treatment and human immunodeficiency virus (HIV) counseling and testing are made available to drug injectors in each metropolitan area. We estimated the total number of current IDUs in the United States and then allocated the large metropolitan area total among large metropolitan areas using four different multiplier methods. Mean values were used as best estimates, and their validity and limitations were assessed. Prevalence of drug injectors per 10,000 population varied from 19 to 173 (median 60; interquartile range 42–87). Proportions of drug injectors in treatment varied from 1.0% to 39.3% (median 8.6%); and the ratio of HIV counseling and testing events to the estimated number of IDUs varied from 0.013 to 0.285 (median 0.082). Despite limitations in the accuracy of these estimates, they can be used for structural analyses of the correlates and predictors of the population density of drug injectors in metropolitan areas and for assessing the extent of service delivery to drug injectors. Although service provision levels varied considerably, few if any metropolitan areas seemed to be providing adequate levels of services.  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