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   868538篇
  免费   60196篇
  国内免费   1666篇
耳鼻咽喉   10815篇
儿科学   27321篇
妇产科学   20688篇
基础医学   134313篇
口腔科学   23715篇
临床医学   77961篇
内科学   168918篇
皮肤病学   18628篇
神经病学   65310篇
特种医学   32270篇
外国民族医学   85篇
外科学   126426篇
综合类   15850篇
现状与发展   3篇
一般理论   326篇
预防医学   68063篇
眼科学   19018篇
药学   63630篇
  3篇
中国医学   2623篇
肿瘤学   54434篇
  2021年   8508篇
  2019年   8479篇
  2018年   11640篇
  2017年   9096篇
  2016年   10032篇
  2015年   11256篇
  2014年   15499篇
  2013年   21958篇
  2012年   31102篇
  2011年   32164篇
  2010年   18451篇
  2009年   17557篇
  2008年   29421篇
  2007年   31256篇
  2006年   31277篇
  2005年   29531篇
  2004年   27872篇
  2003年   26340篇
  2002年   25139篇
  2001年   40482篇
  2000年   40929篇
  1999年   34114篇
  1998年   9758篇
  1997年   8247篇
  1996年   8540篇
  1995年   7928篇
  1994年   7275篇
  1993年   6692篇
  1992年   25543篇
  1991年   25235篇
  1990年   24492篇
  1989年   24102篇
  1988年   21889篇
  1987年   21043篇
  1986年   20032篇
  1985年   18848篇
  1984年   13825篇
  1983年   11719篇
  1982年   6522篇
  1979年   12368篇
  1978年   8666篇
  1977年   7292篇
  1976年   6944篇
  1975年   7627篇
  1974年   8923篇
  1973年   8556篇
  1972年   8016篇
  1971年   7479篇
  1970年   7147篇
  1969年   6565篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
In order to investigate the possibility that the theory of two-stage carcinogenesis can be applied to neurogenic carcinogenesis, we analyzed the promoting effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the in vitro malignant transformation of fetal rat brain cells exposed in utero to ethylnitrosourea (ENU). Rat brain cells were transferred to a cultured system at 72 h after a single pulse of ENU (50 mg/kg body weight) to pregnant SD-JCL rats on the 18th day of gestation. The positive findings of glial fibrillary acidic protein and S-100 protein in primary cultured cells by the analysis of immunohistochemistry revealed the neuroglial origin of transformed cells. These cells were divided into 12 groups and were treated twice per week with or without TPA at concentrations from 0.1 to 50.0 ng/ml. From the results of cellular morphology, Concanavalin A agglutinability, colony forming capacity in semisolid soft agar, and tumorigenicity in vivo, malignant transformation of fetal rat brain cells appeared earlier in the ENU group treated with TPA than in the untreated ENU group. On the basis of these observations, it is suggested that TPA might be effective as a tumor promoter on ENU-induced neurogenic carcinogenesis.  相似文献   
994.
Background Dendritic cells (DC) mediate inflammation in rodent models of allergic airway disease, but the role played by human respiratory‐tract DC (hRTDC) in atopic asthma remains poorly defined. Recent data suggest that CD1 antigen presentation by hRTDC may contribute to asthma pathogenesis. Objective To investigate the influence of hRTDC on the balance between atopy and allergic asthma in human subjects and to determine whether CD1 expression by hRTDC is modulated during asthmatic inflammation. Methods Sputum cells were induced from steroid‐naïve, allergen‐challenged and allergen‐naïve subjects (atopic asthmatics, atopic non‐asthmatics and non‐atopic controls). hRTDC were identified using monoclonal antibody labelling and analysis by flow cytometry. Results hRTDC stained HLA‐DR+ (negative for markers of other cell lineages) were predominantly myeloid and comprised ∼0.5% of viable sputum cells. Sputum cells were potent stimulators of allogeneic CD4+ naïve T cells and enrichment/depletion experiments correlated stimulatory potency with DC numbers. Sputum contained cells that exhibited typical dendritic morphology when analysed by electron microscopy. Myeloid hRTDC were endocytically active, but uptake of FITC‐dextran was enhanced in cells from asthmatics (P<0.001). Despite their increased endocytic capacity, asthmatic myeloid hRTDC appeared mature and expressed increased levels of maturation markers (P<0.05–P<0.001), CD1c, CD1d and langerin (P<0.05). CD1c expression by asthmatic myeloid hRTDC was enhanced upon in vivo allergen challenge (three to ninefold within 24 h; P<0.05). CD11cCD123high hRTDC were only detected in asthmatic sputum and were increased in number following allergen challenge. Conclusion Despite limited cell numbers, it proved possible to analyse human RTDC in induced sputum, providing evidence that increased antigen uptake and enhanced CD1 presentation by activated hRTDC may contribute to allergic airway disease. CD1 presentation by hRTDC in atopic asthma may therefore constitute a novel target for future intervention strategies.  相似文献   
995.
Lymphocytic adenohypophysitis of pregnancy with complete recovery   总被引:1,自引:0,他引:1  
A case of lymphocytic adenohypophysitis in a postpartum woman who became symptomatic during her 8th month of pregnancy is presented. The clinical presentation, endocrine findings, pathological findings, and operative management are discussed. Transient hypopituitarism is documented. Unlike most previously published cases, this woman had complete recovery of anterior pituitary function.  相似文献   
996.
997.
In situ cDNA:mRNA hybridization is a technique that has been developed for the visualization of cDNA:mRNA hybrids in individual cells. To use this technique to answer questions of regulation in heterogeneous populations of cells in the brain, it must be combined with other procedures allowing for the identification of functional subgroups of neurons. We report here a procedure by which in situ cDNA:mRNA hybridization may be combined with retrograde axonal tracing using the fluorescent tracer fast blue. Using this technique, it now becomes possible to measure mRNA regulation in functional subsets of cells defined by their axonal projections.  相似文献   
998.
999.
The degree of concordance of growth rates of primary tumors with corresponding recurrences was investigated by using data from 184 patients with breast cancer with measurable recurrences. For conduction of this examination, the detection processes of both the primary tumor and the recurrence were explored. The probability of detection of a recurrence per unit time was found to be nearly proportional to the tumor's diameter. Approximately 60,000 cells initiated the recurrence, and the distribution of doubling times of the recurrences was exponential, with a mean of 2.1 months. The probability of detection of the primary tumor per unit time was approximately proportional to its volume. The distribution of doubling times of primary tumors was nearly exponential; from other evidence, we inferred that the mean doubling time was also close to 2.1 months. Several techniques to measure growth rate agreement between the primary and recurrent tumors within individuals were developed, and all of them yielded the result that the growth rates are nearly unrelated.  相似文献   
1000.
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