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   2349篇
  免费   138篇
  国内免费   27篇
耳鼻咽喉   21篇
儿科学   112篇
妇产科学   46篇
基础医学   239篇
口腔科学   196篇
临床医学   178篇
内科学   506篇
皮肤病学   44篇
神经病学   135篇
特种医学   174篇
外科学   221篇
综合类   50篇
预防医学   286篇
眼科学   30篇
药学   146篇
中国医学   13篇
肿瘤学   117篇
  2023年   35篇
  2022年   63篇
  2021年   96篇
  2020年   58篇
  2019年   65篇
  2018年   74篇
  2017年   57篇
  2016年   55篇
  2015年   64篇
  2014年   90篇
  2013年   102篇
  2012年   173篇
  2011年   150篇
  2010年   90篇
  2009年   70篇
  2008年   125篇
  2007年   94篇
  2006年   109篇
  2005年   94篇
  2004年   69篇
  2003年   55篇
  2002年   65篇
  2001年   36篇
  2000年   43篇
  1999年   48篇
  1998年   39篇
  1997年   47篇
  1996年   49篇
  1995年   25篇
  1994年   32篇
  1993年   28篇
  1992年   23篇
  1991年   19篇
  1990年   25篇
  1989年   36篇
  1988年   33篇
  1987年   19篇
  1986年   29篇
  1985年   9篇
  1984年   13篇
  1983年   10篇
  1982年   12篇
  1981年   5篇
  1980年   11篇
  1979年   5篇
  1978年   12篇
  1977年   7篇
  1976年   16篇
  1975年   7篇
  1965年   3篇
排序方式: 共有2514条查询结果,搜索用时 15 毫秒
71.
Background The immunohistochemical expression of vascular endothelial growth factor is a prognostic marker in several cancer types. In salivary gland tumors, the association between vascular endothelial growth factor and prognosis remains unclear. The purpose of this study was to perform a systematic review and meta-analysis to assess whether the immunohistochemical expression of vascular endothelial growth factor in patients with salivary gland neoplasms presents prognostic value. Material and Methods Immunohistochemical studies assessing the predictive value of vascular endothelial growth factor in salivary gland neoplasms were systematically reviewed using PubMed, Scopus, Embase, Cochrane Library, and Web of Science databases. It was assessed any survival rates. The fixed-effect model with an adjusted hazard ratio (HR) and 95% confidence intervals (95% CI) as effect measures were performed in the meta-analysis. The Quality in Prognosis Studies (QUIPS) tool was used to assess the quality of the included studies, and the evidence quality was assessed by the Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) system. Results The immunohistochemical overexpression of vascular endothelial growth factor in patients with salivary gland neoplasms was associated with shortened survival (HR=5.37, 95% CI: 2.67-10.83, P = 0.00001). In addition, the presence of vascular endothelial growth factor was tightly associated with tumor size, lymph node metastasis, clinical stage, perineural invasion, vascular invasion, poor local control of the disease, and recurrence. Conclusions The immunohistochemical overexpression of vascular endothelial growth factor in patients with salivary gland neoplasms has prognostic value and was associated with decreased survival time. However, more primary well-designed studies are necessary to increase the level of evidence. Key words:Salivary gland neoplasms, salivary glands, head and neck neoplasms, vascular endothelial growth factors, prognosis.  相似文献   
72.

Introduction

The acute surgical model has been trialled in several institutions with mixed results. The aim of this study was to determine whether the acute surgical model provides better outcomes for patients with acute biliary presentation, compared with the traditional emergency surgery model of care.

Methods

A retrospective review was carried out of patients who were admitted for management of acute biliary presentation, before and after the establishment of an acute surgical unit (ASU). Outcomes measured were time to operation, operating time, after-hours operation (6pm – 8am), length of stay and surgical complications.

Results

A total of 342 patients presented with acute biliary symptoms and were managed operatively. The median time to operation was significantly reduced in the ASU group (32.4 vs 25.4 hours, p=0.047), as were the proportion of operations performed after hours (19.5% vs 2.5%, p<0.001) and the median length of stay (4 vs 3 days, p<0.001). The median operating time, rate of conversion to open cholecystectomy and wound infection rates remained similar.

Conclusions

Implementation of an ASU can lead to objective differences in outcomes for patients who present with acute cholecystitis. In our study, the ASU significantly reduced time to operation, the number of operations performed after hours and length of stay.  相似文献   
73.
74.
Influence of hydroxyurea on fetal hemoglobin production in vitro   总被引:1,自引:0,他引:1  
Miller  BA; Platt  O; Hope  S; Dover  G; Nathan  DG 《Blood》1987,70(6):1824-1829
Cytotoxic drugs increase circulating fetal hemoglobin levels. We examined the mechanism by measuring the fetal hemoglobin produced per BFU-E-derived erythroblast following hydroxyurea treatment in vivo and in vitro. Treatment of four sickle cell patients increased the percentage of circulating F reticulocytes. The frequencies of bone marrow or peripheral blood BFU-E or CFU-E-derived colonies and their fetal hemoglobin content were unaffected. In all cases, the number of erythroid cells/progenitor-derived colony increased. To explore further the effect of hydroxyurea on fetal hemoglobin production, we added 50 mumol/L hydroxyurea to cultures of peripheral blood BFU-E-derived erythroblasts on 1 of 9 days (day 5 through 13) to nine samples. These BFU-E were derived from the peripheral blood of normal donors, sickle trait donors, and sickle cell anemia patients and from the bone marrows of monkeys. This concentration of hydroxyurea was selected so that the frequency of BFU-E and their size was moderately decreased. Addition of hydroxyurea to these progenitor-derived erythroid cells had no effect on fetal hemoglobin content per cell. Neither did transient exposure of progenitors to hydroxyurea prior to culture in nontoxic concentrations (0 to 500 mumol/L) result in a significant increase in fetal hemoglobin content in progenitor-derived erythroblasts. These data suggest that hydroxyurea does not directly alter the HbF program expressed by progenitor-derived erythroid cells. Instead, it enhances hemoglobin F content secondarily, possibly by inducing alterations in erythropoiesis.  相似文献   
75.
OBJECTIVE: To ascertain the prevalence of rheumatoid arthritis (RA) in Tucumán, Argentina. METHODS: The study was conducted between January 1, 1998, and December 31, 1999, in Tucumán province in northwest Argentina. Outpatient and hospitalization medical records for all patients with RA aged > or = 16 years were reviewed. Diagnosis was by 1987 American College of Rheumatology (ACR) criteria for RA and the population data were based on the 1991 national census. Prevalence rates, with 95% CI, were calculated using the number of San Miguel de Tucumán residents who fulfilled the 1987 ACR criteria for RA as numerator, and the city population aged > or = 16 as denominator. Crude and age-specific prevalence rates were calculated as number of cases/1,000 inhabitants. RESULTS: We identified 695 cases of RA. Sex-specific and overall prevalence rates (per 1,000) were 1.97 (95% CI 1.8-2) for all, 0.6 (95% CI 0.49-0.73) for men, 3.2 (95% CI 2.9-3.5) for women. CONCLUSION: Prevalence of RA is low in residents of Tucumán, Argentina, and comparable with rates observed in epidemiological surveys from Southern European countries.  相似文献   
76.
77.
78.
New ceramic formulations based on scheelite tailing were developed, and their potential in the ceramic industry was evaluated. Green bodies with different contents of scheelite tailing (0–8 wt%) were sintered (1150 °C, 1200 °C, and 1250 °C) and characterized in terms of the main mineralogical phases, microstructure, and physico-mechanical properties. The mullite was the main phase identified in all sintered temperatures. This result was also ratified with the aid of scanning electron microscope (SEM) images, in which small needles of the mullite were detected. The presence of mullite is required because it contributes to increasing the mechanical resistance of the material. The physico-mechanical properties measured (water absorption, linear shrinkage, apparent porosity, and flexural strength) were compared to the ISO 13006, and the samples sintered at 1150 °C presented potential to be used as semi-stoneware, while those sintered at 1200 °C and 1250 °C can be employed stoneware and porcelain tiles, respectively.  相似文献   
79.
BACKGROUNDThere has been an increase in cases of inflammatory bowel disease (IBD) in recent years. There is also greater access and availability of immunosuppressive and biological agents, which increase the risk of opportunistic infection despite improving the quality of life and promoting mucosal healing. Tuberculosis (TB) remains a public health problem, and it has a high incidence in several countries. Therefore, knowledge of the risk of developing TB in patients with IBD is important.AIMTo evaluate the risk of active TB in patients with IBD under treatment from an endemic area in Latin America.METHODSA standard questionnaire included demographic variables, clinical aspects of IBD disease, history of active TB during treatment, active TB characteristics and evolution, initial screening and results and time from the start of anti-tumor necrosis factor alpha (TNFα) to TB development.RESULTSAzathioprine, anti-TNFα and the combination of these two drugs were associated with a higher risk of active TB incidence. The TNFα blockers increased the relative risk of developing active TB compared to other treatments. All four multivariable models showed that the use of TNFα blockers alone or in combination with azathioprine was an important risk factor for the incidence of active TB. After adjustment for sex, age, type of IBD and latent TB, anti-TNFα with azathioprine increased the relative risk to 17.8 times more than conventional treatment. Late TB, which was diagnosed 3 mo after the start of anti-TNFα, was the most frequent.CONCLUSIONTreatment with anti-TNFα increased the risk of active TB in IBD patients from an endemic area in Latin America. This risk was increased when anti-TNFα was combined with azathioprine. The time from the beginning of the treatment to the active TB diagnosis suggests a new TB infection.  相似文献   
80.
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