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   213224篇
  免费   20458篇
  国内免费   5422篇
耳鼻咽喉   1455篇
儿科学   4366篇
妇产科学   2757篇
基础医学   28577篇
口腔科学   4103篇
临床医学   23633篇
内科学   31166篇
皮肤病学   2819篇
神经病学   23235篇
特种医学   26010篇
外国民族医学   46篇
外科学   18623篇
综合类   20003篇
现状与发展   18篇
预防医学   8096篇
眼科学   2591篇
药学   21752篇
  96篇
中国医学   5037篇
肿瘤学   14721篇
  2023年   3274篇
  2022年   6850篇
  2021年   9338篇
  2020年   8082篇
  2019年   9134篇
  2018年   8795篇
  2017年   8486篇
  2016年   8072篇
  2015年   8482篇
  2014年   13318篇
  2013年   12931篇
  2012年   11491篇
  2011年   13046篇
  2010年   10611篇
  2009年   10830篇
  2008年   10586篇
  2007年   9438篇
  2006年   8293篇
  2005年   7387篇
  2004年   6285篇
  2003年   5356篇
  2002年   4058篇
  2001年   3674篇
  2000年   3124篇
  1999年   2740篇
  1998年   2590篇
  1997年   2455篇
  1996年   2158篇
  1995年   1925篇
  1994年   1688篇
  1993年   1510篇
  1992年   1188篇
  1991年   1034篇
  1990年   854篇
  1989年   708篇
  1988年   665篇
  1987年   637篇
  1986年   684篇
  1985年   1770篇
  1984年   2484篇
  1983年   1657篇
  1982年   1757篇
  1981年   1647篇
  1980年   1412篇
  1979年   1222篇
  1978年   1011篇
  1977年   855篇
  1976年   971篇
  1975年   663篇
  1973年   618篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
IntroductionSunlight exposure is the main source of vitamin D. Our aim was to describe both sun exposure and sun protection behaviour in a series of patients with inflammatory bowel disease (IBD), and to study their potential association with vitamin D concentration.Patients and methodsA cross sectional, observational study. The clinical-demographic variables were obtained via clinical interviews and medical history review. The sunlight exposure assessment was carried out using the Sun Exposure Questionnaire and the concentration of 25-hydroxy vitamin D (25OHD) was measured by an electro-chemiluminescence immunoassay. Questionnaires were conducted on quality of life, physical activity, weekly vitamin D intake and sun protection behaviour.Results149 patients were included. In 69% of patients, deficient or insufficient 25OHD values were recorded. 67% showed low sun exposure. A modest significant correlation was observed between the total score of the solar exposure questionnaire and the 25OHD concentration in the complete series (r = 0.226, P = .006) and in the summer (r = 0.274, P = .01). The sun protection behaviour questionnaire score did not influence the 25OHD concentration. In the multivariate analysis, only the presence of clinical activity was associated with low sun exposure (OR = 3.23).DiscussionSun exposure according to the questionnaire used was low, was associated with the presence of clinical activity and was weakly correlated with serum 25OHD concentration. More studies are needed to explore the use of individual questionnaires for sun exposure and its relationship with vitamin D in patients with IBD.  相似文献   
93.
94.
95.
96.
97.
A pulmonary artery (PA) sling is a very rare congenital cardiovascular anomaly, and only a few studies have reported PA slings in fetuses. The relationship of the PA, aorta, ductus arteriosus, and trachea can be evaluated in the 3‐vessel and 3‐vessel and trachea views during fetal echocardiography. A PA sling can be detected by abnormal positioning of the left PA in relation to the trachea when sweeping from the 3‐vessel view cranially to the 3‐vessel and trachea view. Here we report 3 cases of fetal PA slings and their follow‐ups. Two cases were confirmed by postnatal echocardiography, and the other case was confirmed by a cardiovascular cast after pregnancy termination. We emphasize that the 3‐vessel and 3‐vessel and trachea views are of crucial importance in the prenatal diagnosis of a PA sling.  相似文献   
98.
《Journal of thoracic oncology》2021,16(10):1694-1704
IntroductionIn patients with NSCLC, the prognostic significance of the tumor microenvironment (TME) immune composition has been revealed using single- or dual-marker staining on sequential tissue sections. Although these studies reveal that relative abundance and localization of immune cells are important parameters, deeper analyses of the NSCLC TME are necessary to refine the potential application of these findings to clinical care. Currently, the complex spatial relationships between cells of the NSCLC TME and potential drivers contributing to its immunologic composition remain unknown.MethodsWe used multispectral quantitative imaging on the lung adenocarcinoma TME in 153 patients with resected tumors. On a single slide per patient, we evaluated the TME with markers for CD3, CD8, CD14, CD19, major histocompatibility complex II (MHCII), cytokeratin, and 4′,6-diamidino-2-phenylindole (DAPI). Image analysis, including tissue segmentation, phenotyping, and spatial localization, was performed.ResultsSpecimens wherein greater than or equal to 5% of lung cancer cells expressed MHCII (MHCIIhi TME) had increased levels of CD4+ and CD8+ T cells and CD14+ cell infiltration. In the MHCIIhi TME, the immune infiltrate was closer to cancer cells and expressed an activated phenotype. Morphologic image analysis revealed cancer cells in the MHCIIhi TME more frequently interfaced with CD4+ and CD8+ T cells. Patients with an MHCIIhi TME experienced improved overall survival (p = 0.046).ConclusionsLung cancer cell-specific expression of MHCII associates with levels of immune cell infiltration, spatial localization, and activation status within the TME. This suggests that cancer cell-specific expression of MHCII may represent a biomarker for the immune system’s recognition and activation against the tumor.  相似文献   
99.
Objectives: To examine the factors associated with increase in lumbar spine bone mineral density (LS-BMD) by bisphosphonates (BPs) with active vitamin D analog (aVD).

Methods: Two independent postmenopausal osteoporotic patients treated by BPs with aVD for 24 months (Study 1: n?=?93, Study 2: n?=?99) were retrospectively analyzed.

Results: In Study 1, LS-BMD of the patients significantly increased for 24 m (5.4%, p?r2: 0.088, p?=?.02). While average sCa of the patients was 9.2?mg/dL before treatment, it increased time-dependently to 9.6?mg/dL for 24 m by treatment. As each patient had their LS-BMD five times during the study, there were four instances of %LS-BMD in each patient, resulting in 372 instances of %LS-BMD in Study 1. The smallest Akaike’s information criterion value for the most appropriate cut-off levels of sCa for %LS-BMD by treatment every 6 m was 9.3?mg/dL. The %LS-BMD by treatment for 6 m during 24 m period in patients with sCa ≥9.3?mg/dL (1.5%) was significantly higher than that in patients with sCa <9.3?mg/dL (0.8%, p?=?.038). The results of Study 2 were similar to those of Study 1, confirming the phenomena observed.

Conclusion: sCa was associated with an increased LS-BMD by BPs with aVD.  相似文献   
100.
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