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   8785篇
  免费   588篇
  国内免费   28篇
耳鼻咽喉   67篇
儿科学   354篇
妇产科学   237篇
基础医学   1384篇
口腔科学   126篇
临床医学   1258篇
内科学   1594篇
皮肤病学   158篇
神经病学   953篇
特种医学   202篇
外科学   717篇
综合类   45篇
一般理论   8篇
预防医学   836篇
眼科学   152篇
药学   525篇
中国医学   9篇
肿瘤学   776篇
  2023年   78篇
  2022年   81篇
  2021年   201篇
  2020年   150篇
  2019年   219篇
  2018年   264篇
  2017年   182篇
  2016年   232篇
  2015年   233篇
  2014年   315篇
  2013年   465篇
  2012年   663篇
  2011年   654篇
  2010年   360篇
  2009年   316篇
  2008年   640篇
  2007年   608篇
  2006年   566篇
  2005年   593篇
  2004年   513篇
  2003年   456篇
  2002年   436篇
  2001年   75篇
  2000年   41篇
  1999年   63篇
  1998年   98篇
  1997年   81篇
  1996年   67篇
  1995年   69篇
  1994年   51篇
  1993年   50篇
  1992年   23篇
  1991年   32篇
  1990年   28篇
  1989年   27篇
  1988年   23篇
  1987年   16篇
  1986年   30篇
  1985年   29篇
  1984年   30篇
  1983年   26篇
  1982年   21篇
  1981年   37篇
  1980年   25篇
  1979年   15篇
  1978年   19篇
  1977年   12篇
  1976年   17篇
  1972年   10篇
  1971年   11篇
排序方式: 共有9401条查询结果,搜索用时 15 毫秒
41.
Measurement of global left ventricular function is important in the follow-up of cardiac patients and is a good prognostic indicator in acute cardiac situations. We compared quantitative measurements of global left ventricular function made with radionuclide angiography (RNA) and contrast cardiac ventriculography (CVG) to visual semiquantitative estimates from two-dimensional echocardiographic images (2D-echo). Three hundred and thirty-nine consecutive patients who underwent RNA were assessed with 2D-echo within 3 months. In addition, 92 of these patients also underwent CVG (correlation of ejection fraction between CVG and RNA:r=0.82;P<0.0001). The RNA mean ejection fractions in the four 2D-echo groups (0=normal, 1=slightly, 2=moderate, or 3=severe reduced left ventricular function) differed markedly (P<0.0001); however, there was overlapping among the groups (2D-echo score/RNA ejection fraction: 0=57.3%±12.8%; 1=46.0%±12.9%; 2=29.6%±12.2%; and 3=24.6%±11.5%) and the difference between 2D-echo scores 2 and 3 was not significant. 2D-echo showed a good concordance in RNA classes (0=505; 1=35%–49%; 2=21%–34%; and 3=520% ejection fraction) 0 (133/166; 80%) and 3 (18/30; 60%) but low concordance in classes 1 (27/82; 33%) and 2 (21/61; 34%). For accurate assessment of global left ventricular ejection fraction, visual semiquantitative judgement of a 2D echocardiographic image is limited in comparison to CVG or RNA, especially in patients with a slight or moderate reduction in left ventricular ejection fraction.  相似文献   
42.
43.
44.

Introduction  

It has been well documented that the pineal hormone, melatonin, which plays a major role in the control of reproduction in mammals, also plays a role in the incidence and growth of breast and mammary cancer. The curative effect of melatonin on the growth of dimethylbenz [a]anthracene-induced (DMBA-induced) mammary adenocarcinoma (ADK) has been previously well documented in the female Sprague-Dawley rat. However, the preventive effect of melatonin in limiting the frequency of cancer initiation has not been well documented.  相似文献   
45.
46.
Sampling designs dictated by stereology have proven very useful in recent years to estimate in situ the total number of deposited particles, or of macrophages, in different lung compartments at the light microscopical level. The sampling methods are based on parallel slabs which are subsequently subsampled by disectors. The resulting number estimators are unbiased irrespective of tissue shrinkage or swelling, and they are readily applicable in other contexts (notably in neuroscience). Several variants of the design are available, however, and, although they all yield the same number estimates, their precision, and the mathematical prediction of it, vary among the different estimators and are subjected to theoretical improvement. The present paper constitutes a detailed survey of the latest advances, and it illustrates methods and formulae alike by way of a real example stemming from an earlier study on particle retention and clearance.  相似文献   
47.
48.
IntroductionIsoniazid preventive therapy (IPT) can reduce the risk of tuberculosis (TB) in children living with HIV (CLHIV), but data on the outcomes of the IPT cascade in CLHIV are limited.MethodsWe evaluated the IPT cascade among CLHIV aged <15 years and newly enrolled in HIV care in eight HIV clinics in western Kenya. Medical record data were abstracted from September 2015 through July 2019. We assessed the proportion of CLHIV completing TB symptom screening, IPT eligibility assessment, IPT initiation and completion. TB incidence rate was calculated stratified by IPT initiation and completion status. Risk factors for IPT non‐initiation and non‐completion were assessed using Poisson regression with generalized linear models.ResultsOverall, 856 CLHIV were newly enrolled in HIV care, of whom 98% ([95% CI 97–99]; n = 841) underwent screening for TB symptoms and IPT eligibility. Of these, 13 (2%; 95% CI 1–3) were ineligible due to active TB and 828 (98%; 95% CI 97–99) were eligible. Five hundred and fifty‐nine (68%; 95% CI 64–71) of eligible CLHIV initiated IPT; median time to IPT initiation was 3.6 months (interquartile range [IQR] 0.5–10.2). Overall, 434 (78%; 95% CI 74–81) IPT initiators completed. Attending high‐volume HIV clinics (aRR = 2.82; 95% CI 1.20–6.62) was independently associated with IPT non‐initiation. IPT non‐initiation had a trend of being higher among those enrolled in the period 2017–2019 versus 2015–2016 (aRR = 1.91; 0.98–3.73) and those who were HIV virally non‐suppressed (aRR = 1.90; 95% CI 0.98–3.71). Being enrolled in 2017–2019 versus 2015–2016 (aRR = 1.40; 1.01–1.96) was independently associated with IPT non‐completion. By 24 months after IPT screening, TB incidence was four‐fold higher among eligible CLHIV who never initiated (8.1 per 1000 person years [PY]) compared to CLHIV who completed IPT (2.1 per 1000 PY; rate ratio [RR] = 3.85; 95% CI 1.08–17.15), with a similar trend among CLHIV who initiated but did not complete IPT (8.2/1000 PY; RR = 4.39; 95% CI 0.82–23.56).ConclusionsDespite high screening for eligibility, timely IPT initiation and completion were suboptimal among eligible CLHIV in this programmatic cohort. Targeted programmatic interventions are needed to address these drop‐offs from the IPT cascade by ensuring timely IPT initiation after ruling out active TB and enhancing completion of the 6‐month course to reduce TB in CLHIV.  相似文献   
49.
50.
Noncomparative contraceptive efficacy of cellulose sulfate gel   总被引:1,自引:0,他引:1  
OBJECTIVE: To estimate the 6-month cumulative probability of pregnancy, short-term adverse effects, and acceptability of cellulose sulfate vaginal contraceptive gel. METHODS: Two hundred fertile heterosexual couples were enrolled in this single-center, phase II, 6-month noncomparative study conducted at the California Family Health Council in Los Angeles, California. Couples did not desire pregnancy, were at low risk for sexually transmitted diseases, and agreed to use 3.5 mL of cellulose sulfate gel intravaginally before each coital act as their primary means of contraception. Scheduled follow-up visits took place after one menstrual cycle and at study completion, which occurred after 6 months and six menstrual cycles had elapsed. In addition, participants were instructed to call the site at the onset of each menses to review their diary cards. RESULTS: The cumulative probabilities of pregnancy during 6 months and six cycles of typical use were 13.4% (95% confidence interval [CI] 7.5-19.4%) and 13.9% (95% CI 7.7-20.2%), respectively, and during 6 cycles of correct and consistent ("perfect") use: 3.9% (95% CI 0.0-9.2%). Slightly over one fourth of the women and one man reported experiencing gel-related adverse events, two thirds of which were mild and only possibly related to the gel. Three quarters of women and men reported that they would buy cellulose sulfate gel for contraception. CONCLUSION: Cellulose sulfate vaginal gel yields pregnancy rates comparable to nonoxynol-9 and few adverse events among couples at low risk for sexually transmitted diseases.  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