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   921634篇
  免费   63786篇
  国内免费   2486篇
耳鼻咽喉   12754篇
儿科学   29351篇
妇产科学   26810篇
基础医学   128794篇
口腔科学   25359篇
临床医学   76626篇
内科学   187936篇
皮肤病学   19459篇
神经病学   72394篇
特种医学   37163篇
外国民族医学   345篇
外科学   146107篇
综合类   19667篇
现状与发展   1篇
一般理论   268篇
预防医学   66100篇
眼科学   20756篇
药学   65618篇
中国医学   1930篇
肿瘤学   50468篇
  2019年   7250篇
  2018年   10210篇
  2017年   7852篇
  2016年   8396篇
  2015年   9504篇
  2014年   13359篇
  2013年   20416篇
  2012年   27319篇
  2011年   28982篇
  2010年   17460篇
  2009年   16513篇
  2008年   27178篇
  2007年   28890篇
  2006年   28924篇
  2005年   28320篇
  2004年   27107篇
  2003年   26163篇
  2002年   25666篇
  2001年   41617篇
  2000年   42791篇
  1999年   36505篇
  1998年   10107篇
  1997年   9254篇
  1996年   9173篇
  1995年   8531篇
  1994年   8145篇
  1993年   7635篇
  1992年   28307篇
  1991年   27081篇
  1990年   26497篇
  1989年   25430篇
  1988年   23640篇
  1987年   23251篇
  1986年   22338篇
  1985年   21226篇
  1984年   15865篇
  1983年   13560篇
  1982年   8119篇
  1979年   14660篇
  1978年   10246篇
  1977年   8676篇
  1976年   8180篇
  1975年   9001篇
  1974年   10732篇
  1973年   10207篇
  1972年   9680篇
  1971年   8937篇
  1970年   8596篇
  1969年   8040篇
  1968年   7694篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Piecewise constant incidence models were developed to estimate the force of infection in women from age-and time-specific antenatal or neonatal seroprevalence data. Differential inclusion of infected women in sero-surveys compared to uninfected women was taken into account, with respect to both changes in inclusion rate following infection, and changes in relative inclusion rate over calendar time. These models were applied to anonymous HIV seroprevalence data collected from neonates born to black and Hispanic women in New York City 1988-1992, with incidence and fertility parameters estimated by maximum likelihood. Estimates of inclusion rate parameters accorded well with what is known about the natural history of HIV. The data could not distinguish between additive and multiplicative combination of the effects of age and time on incidence. Incidence was strongly dependent on age with the highest incidence in women aged 20-34 years. There was strong evidence that incidence had been falling in Hispanic women since 1982-1984. The results illustrate the extent to which trends in incidence over time may be confounded by changes in the relative inclusion rate of infected and uninfected women.  相似文献   
72.
Adverse ocular effects associated with niacin therapy.   总被引:2,自引:0,他引:2       下载免费PDF全文
In a retrospective survey of patients taking medication for hyperlipidaemia, those taking niacin (nicotinic acid) were more likely (p < 0.05) to report sicca syndromes, blurred vision, eyelid oedema, and macular oedema compared with those who never took niacin. Additionally, 7% of those taking niacin discontinued the drug owing to adverse ocular side effects, while none of the other lipid lowering agents were found to cause these side effects (p = 0.016). Data from spontaneous reporting systems support a possible association of decreased vision, cystoid macular oedema, sicca-like symptoms, discoloration of the eyelids with or without periorbital or eyelid oedema, proptosis, loss of eyebrow or eyelashes, and superficial punctate keratitis with the use of niacin in high doses. Decreased vision may be marked, and if the drug is not discontinued, may progress to cystoid macular oedema. All ocular side effects listed above are reversible if the association with niacin is recognised and the drug is discontinued; both the incidence and severity of the ocular side effects seem to be dose dependent.  相似文献   
73.
74.
Of 431 patients with gastric cancer observed in our institution, 23 (5.3%) had early gastric cancer (EGC). Macroscopic presentation, histology, depth of invasion, and lymph node involvement were evaluated in all the cases. All patients underwent surgery and an intensive follow-up was performed. Five of the 23 patients progressed, and the risk factors were examined. Histology seemed to be the main prognostic factor in our study, since intestinal type of EGC was associated to a significantly better prognosis. Total gastrectomy is indicated in the proximal localization of EGC, and should perhaps be performed also in cases presenting undifferentiated histology.  相似文献   
75.
Premalignant lesions of the penis include cutaneous horn, balanitis xerotica obliterans, and leukoplakia. The true incidence of progression of each of these to squamous-cell carcinoma is unknown. Bowenoid papulosis, erythroplasia of Queyrat, and Bowen's disease are histologically identical to in situ carcinoma. Although the first is consistently benign, the latter two regularly evolve into invasive cancer. Malignant scrotal lesions include squamous-cell carcinoma, liposarcoma, leiomyosarcoma, basal-cell carcinoma, extramammary Paget's disease, erythroplasia of Queyrat, malignant melanoma, and metastases. Hemangioma can be confused with carcinoma.  相似文献   
76.
77.
78.
Fetal B lymphocytes in mice and humans use a limited number of the available VH gene segments. Mouse fetal B cells primarily utilize 3' VH elements, suggesting that the localization of these elements determines their rearrangement frequency. The previously reported non-random usage of human VH genes has been more difficult to explain. In this study the authors analysed the expression of the most proximal 3' human VH element (VH6) using a monoclonal antibody (JE-6). VH6 expression was assessed in various B cell differentiation stages from fetal liver, bone marrow and spleen at 12–20 weeks of gestation. The authors demonstrate that the level of VH6 expression does not exceed a stochastic usage frequency. This suggests that the localization of VH6 does not significantly promote its expression during human fetal life, and that other factors must affect the usage of VH genes during human fetal development.  相似文献   
79.
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