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   98473篇
  免费   9282篇
  国内免费   4386篇
耳鼻咽喉   908篇
儿科学   1060篇
妇产科学   819篇
基础医学   10746篇
口腔科学   1870篇
临床医学   12382篇
内科学   13528篇
皮肤病学   881篇
神经病学   4988篇
特种医学   3600篇
外国民族医学   43篇
外科学   9804篇
综合类   17629篇
现状与发展   21篇
一般理论   2篇
预防医学   7439篇
眼科学   2528篇
药学   9950篇
  124篇
中国医学   5576篇
肿瘤学   8243篇
  2025年   117篇
  2024年   1707篇
  2023年   2001篇
  2022年   3980篇
  2021年   5173篇
  2020年   3966篇
  2019年   3188篇
  2018年   3174篇
  2017年   3013篇
  2016年   2796篇
  2015年   4346篇
  2014年   5352篇
  2013年   4786篇
  2012年   7578篇
  2011年   8193篇
  2010年   5645篇
  2009年   4257篇
  2008年   5228篇
  2007年   5153篇
  2006年   4878篇
  2005年   4846篇
  2004年   3211篇
  2003年   2957篇
  2002年   2449篇
  2001年   1933篇
  2000年   1983篇
  1999年   1924篇
  1998年   1253篇
  1997年   1156篇
  1996年   894篇
  1995年   833篇
  1994年   797篇
  1993年   469篇
  1992年   548篇
  1991年   492篇
  1990年   414篇
  1989年   344篇
  1988年   257篇
  1987年   251篇
  1986年   182篇
  1985年   127篇
  1984年   71篇
  1983年   63篇
  1982年   46篇
  1981年   31篇
  1980年   17篇
  1979年   26篇
  1977年   4篇
  1975年   6篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 123 毫秒
1.
OBJECTIVE: To understand the role of nasal mucous epithelial cells to hypoxia in early stage of nasal polyps(NP) formation. METHODS: Epithelial cells of NP and inferior turbinate (IT) were cultured without serum under normal oxygen and hypoxia, and stimulus of inflammatory cytokines. Erythropoietin (EPO) was regarded as hypoxia mark, and expression of vascular endothelial growth factor(VEGF) mRNA and protein derived from epithelial cells were detected respectively by in situ hybridization and ELISA. RESULTS: 1. Under hypoxia, EPO mRNA was expressed intensely in epithelial cells from NP and IT, and there was no significant difference between both of them. This result suggested that EPO might be regarded as a hypoxic mark. 2. The ability of producing VEGF mRNA increased with cytokines stimulation, especially under hypoxia. Protein level of VEGF from epithelial cells of NP and IT increased with cytokines stimulation, especially in hypoxia and was time-dependent. CONCLUSION: Epithelial cells actively produce vast VEGF under hypoxia. The VEGF induced by hypoxia of the mucosa in middle meatus is of importance in the formation of nasal polyps(NP) in early stage, which may be the major cause of NP formation in middle meatus.  相似文献   
2.
3.
A patient with skeletal Class III malocclusion was treated in 2 phases during the early permanent dentition. In phase 1, maxillary protraction was combined with rapid palatal expansion; in phase 2, fixed appliances were placed. The results were good posttreatment, and, 1 year later, a favorable growth tendency could be observed. This report shows that treatment for a patient with skeletal Class III malocclusion can be started in the early permanent dentition, with very good final results.  相似文献   
4.
PURPOSE: Perineural invasion is a frequent occurrence in salivary adenoid cystic carcinoma (ACC) and may prevent complete surgical resection. Studies have indicated that nerve growth factor (NGF) and its high-affinity receptor tyrosine kinase A (TrkA) may play a role in perineural invasion in several malignancies in which perineural invasion is observed. The present study was conducted to investigate the expression of NGF and TrkA in salivary ACC and to examine the effects of NGF on adhesion, migration and invasion capacities of a salivary ACC cell line (SACC-83) in vitro. PATIENTS AND METHODS: Expression of NGF and TrkA was explored using immunohistochemistry in paraffin-embedded tissues of 32 cases of salivary ACC. The effects of NGF on in vitro adhesion, migration, and invasion capacities of the SACC-83 cell line were examined using an MTT assay and a modified Boyden chamber assay respectively. RESULTS: In ACC specimens, 31 (96.9%) and 32 (100%) tumors showed immunoreactivity for NGF and TrkA respectively. Significant correlations were found between NGF/TrkA expression levels and perineural invasion (P < .05). In cell adhesion assay, the percent adherences of SACC-83 cells co-cultured with 25 ng/ml NGF at 1.5 hours and 5, 25 ng/ml NGF at 6 hours were significantly higher than that co-cultured with 0 ng/ml NGF (P < .05). However, high concentration of NGF (500 ng/ml) resulted in a significant inhibition of invasion (P < .05). CONCLUSION: Overexpression of NGF and TrkA in human salivary ACC tissues may constitute a reason for perineural invasion in salivary ACC.  相似文献   
5.
Laryngeal tuberculosis: a review of 26 cases.   总被引:2,自引:0,他引:2  
OBJECTIVES: To review the clinical characteristics of laryngeal tuberculosis. STUDY DESIGN: Retrospective case series. SUBJECTS AND METHODS: Medical records of 26 histopathology-confirmed cases in a tertiary medical center from 1992 to 2006. RESULTS: The female patients were significantly younger than male patients. Hoarseness is the most common symptom (84.6%) because true vocal fold is most commonly involved (80.8%). Infection usually involves unilateral (66.7%) and right-side larynx but multiple subsites of the larynx (57.7%). The appearance of the affected larynx may have mixed features and change before diagnosis. Laryngeal tuberculosis is usually misdiagnosed as laryngeal cancer, especially in patients with malignant signs such as enlarged cervical lymph nodes and vocal fold immobility. Chest film is better than sputum examinations for screening. CONCLUSION: We should be especially alert about TB infection when facing young female patients with unusual laryngeal lesions. Extensive laser excision before diagnosis should be avoided because after antituberculous treatment, prognosis is usually good and vocal fold immobility could be reversible.  相似文献   
6.
Population toxicokinetics of tetrachloroethylene   总被引:1,自引:0,他引:1  
 In assessing the distribution and metabolism of toxic compounds in the body, measurements are not always feasible for ethical or technical reasons. Computer modeling offers a reasonable alternative, but the variability and complexity of biological systems pose unique challenges in model building and adjustment. Recent tools from population pharmacokinetics, Bayesian statistical inference, and physiological modeling can be brought together to solve these problems. As an example, we modeled the distribution and metabolism of tetrachloroethylene (PERC) in humans. We derive statistical distributions for the parameters of a physiological model of PERC, on the basis of data from Monster et al. (1979). The model adequately fits both prior physiological information and experimental data. An estimate of the relationship between PERC exposure and fraction metabolized is obtained. Our median population estimate for the fraction of inhaled tetrachloroethylene that is metabolized, at exposure levels exceeding current occupational standards, is 1.5% [95% confidence interval (0.52%, 4.1%)]. At levels approaching ambient inhalation exposure (0.001 ppm), the median estimate of the fraction metabolized is much higher, at 36% [95% confidence interval (15%, 58%)]. This disproportionality should be taken into account when deriving safe exposure limits for tetrachloroethylene and deserves to be verified by further experiments. Received: 20 April 1995/Accepted: 24 August 1995  相似文献   
7.
8.
Inactivated whole avian influenza virus (AIV) vaccine provides protection against homologous haemagglutinin (HA) subtype virus, but poor protection against a heterologous HA virus. Moreover, it induces chickens to produce antibodies to cross-reactive antigens, especially nucleoprotein, which is limits AIV serological surveillance. In this study, a recombinant fowlpox virus co-expressing HA (H5 subtype) and NA (N1 subtype) genes of AIV was evaluated for its ability to protect chickens against intramuscular challenge with a lethal dose of highly pathogenic (HP) AIV. Susceptible chickens were also vaccinated by wing-web puncture with the parent fowlpox vaccine virus. Following challenge 4 weeks later with HPAIV, all chickens vaccinated with recombinant virus were protected, while the chickens vaccinated with either the unaltered parent fowlpox vaccine virus or unvaccinated controls experienced 100% mortality following challenge. This protection was accompanied by the high levels of specific antibody to the respective components of the recombinant vaccine. The above results showed that rFPV-HA-NA could be a potential vaccine to replace current inactivated vaccines for preventing AI.  相似文献   
9.
益气活血汤对老年肺心病心衰患者血液流变学的影响   总被引:3,自引:0,他引:3  
目的探讨益气活血汤对老年肺心病心衰患者血液流变性的影响。方法将48例肺心病心衰患者随机分为两组,均采用常规西医治疗,治疗组加用益气活血汤;观察两组治疗前后血液流变学指标变化情况。结果治疗组治疗前后比较,各项血液流变学指标改变差异有显著性,对照组治疗前后比较无统计学意义;治疗组各项指标与对照组比较差异有显著性。结论益气活血汤对肺心病心衰有改善血液流变性的作用。  相似文献   
10.
An open, randomized, cross-over study was performed to compare the efficacy and acceptability of two breath-actuated inhalers, the Turbohaler (T) and Diskhaler (D), for delivery of beta-agonists. Thirty six adults with chronic asthma requiring beta-agonists four times daily were treated with terbutaline 500 micrograms via T and salbutamol 400 micrograms via D four times daily, each period lasting four weeks. Additional bronchodilator via pressurized aerosol was permitted as required. Peak expiratory flow (PEF) was recorded in the morning (before and after beta-agonist) and in the evening. The mean morning PEF was higher during the first two weeks using T (295 l.min-1) than whilst using D (281 l.min-1, p < 0.01), but this difference did not persist during the second two weeks and there were no differences in post-bronchodilator PEF or rescue beta-agonist use. After four weeks, > 90% of patients used both inhaler devices efficiently and they were equally acceptable in terms of ease of use and convenience to carry. The Diskhaler and Turbohaler achieve similar clinical efficacy for delivery of beta-agonists.  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