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   50390篇
  免费   3970篇
  国内免费   1112篇
耳鼻咽喉   283篇
儿科学   898篇
妇产科学   1375篇
基础医学   5065篇
口腔科学   1106篇
临床医学   5894篇
内科学   8221篇
皮肤病学   376篇
神经病学   1965篇
特种医学   1911篇
外国民族医学   9篇
外科学   3917篇
综合类   7677篇
现状与发展   2篇
预防医学   7363篇
眼科学   375篇
药学   5221篇
  101篇
中国医学   1865篇
肿瘤学   1848篇
  2024年   83篇
  2023年   737篇
  2022年   1255篇
  2021年   2172篇
  2020年   2008篇
  2019年   1745篇
  2018年   1770篇
  2017年   1635篇
  2016年   1722篇
  2015年   1680篇
  2014年   3316篇
  2013年   3485篇
  2012年   3074篇
  2011年   3310篇
  2010年   2506篇
  2009年   2313篇
  2008年   2273篇
  2007年   2401篇
  2006年   1939篇
  2005年   1742篇
  2004年   1515篇
  2003年   1282篇
  2002年   1142篇
  2001年   1006篇
  2000年   865篇
  1999年   794篇
  1998年   655篇
  1997年   664篇
  1996年   642篇
  1995年   538篇
  1994年   537篇
  1993年   419篇
  1992年   428篇
  1991年   401篇
  1990年   331篇
  1989年   319篇
  1988年   283篇
  1987年   240篇
  1986年   223篇
  1985年   288篇
  1984年   245篇
  1983年   153篇
  1982年   206篇
  1981年   172篇
  1980年   159篇
  1979年   141篇
  1978年   105篇
  1977年   102篇
  1976年   93篇
  1975年   96篇
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
21.
22.
23.
Breast elastography has been available for more than 15 years but is not widely incorporated into clinical practice. Many publications report extremely high accuracy for various breast elastographic techniques. However, results in the literature are extremely variable. This variability is most likely due to variations in technique, a relatively steep learning curve, and variability in methods between vendors. This article describes our protocol for performing breast elastography using both strain elastography and shear wave elastography, which produces high sensitivity and specificity. Additionally, we will describe the most commonly known false-positive and false-negative lesions as well as how to detect them.  相似文献   
24.
Purpose:Since the declaration of the lockdown due to COVID-19, the usage of digital devices has gone up across the globe, resulting in a challenge for the visual systems of all ages. The purpose of this study is to assess the impact of the lockdown on digital device usage, and consequently, the ocular surface health implications and circadian rhythm abnormalities related to digital eye strain.Methods:An open online survey was sent through various social media platforms and was open for a period of 2 weeks.Results:A total of 407 usable responses were obtained; the average age of respondents was 27.4 years. Typically, 93.6% of respondents reported an increase in their screen time since the lockdown was declared. The average increase in digital device usage was calculated at about 4.8 ± 2.8 h per day. The total usage per day was found to be 8.65 ± 3.74 hours. Sleep disturbances have been reported by 62.4% of people. Typically, 95.8% of respondents had experienced at least one symptom related to digital device usage, and 56.5% said that the frequency and intensity of these symptoms increased since the lockdown was declared.Conclusion:The study highlighted the drastic increase in use of digital devices after the initiation of the COVID-19 lockdown, and along with it, the slow deterioration of ocular health across all age groups. Awareness about prevention of digital eye strain should be stressed, and going forward, measures to bring these adverse effects to a minimum should be explored.  相似文献   
25.
26.
27.
BackgroundThe relationship of atrial fibrillation (AF) with coronary artery disease (CAD) is well established, yet it is often missed. There is evidence of myocardial ischemia on stress imaging in AF patients in the absence of obstructive CAD. In this prospective cohort, we studied the angiographic profiles of non-valvular AF patients.MethodsThe study was a nonrandomized, prospective, single-center observational study of consecutive patients of persistent non-valvular AF. Patients symptomatic for AF despite optimal medical therapy for 3 months were recruited and all underwent coronary angiograms (CAG). Patients with prior history of CAD were excluded.ResultsA total of 70 patients were followed for a mean duration of 12 ± 1.4 months. The mean age of the study group was 66.07 (±11.49) years. Hypertension was the commonest comorbidity seen in 74% patients. Obstructive CAD was present in 32 (46%) patients, non-obstructive (<50% stenosis) CAD in 17 (24%) patients and normal coronaries in 21 (30%) patients. Overall 49 (70%) patients had evidence of CAD. Amongst patients without obstructive CAD, slow flow was seen in 16 (42%) patients. Lower baseline ejection fraction, lower haemoglobin & albumin levels and higher creatinine levels was associated with increased mortality. In patients without obstructive CAD, hospitalizations for fast ventricular rate were significantly increased in those having slow flow on CAG (p = 0.005).ConclusionsMajority (70%) of our patients had evidence of atherosclerotic CAD on CAG. A large proportion of patients without obstructive CAD had slow flow on CAG.  相似文献   
28.
Background and aimsResting heart rate variability (HRV) and maximal fat oxidation (MFO) during exercise are both considered as a noninvasive biomarkers for early detection of cardiovascular risk factors. Thus, this study aimed to analyze the relationship between resting HRV parameters and MFO during exercise, and the intensity of exercise that elicit MFO (Fatmax) in healthy sedentary adults.Methods and resultsA total of 103 healthy young adults (22.2 ± 2.3 years old, 67% female; from the ACTIBATE cohort) and 67 healthy middle-aged adults (53.1 ± 5.0 years old, 52% female; from the FIT-AGEING cohort) were included in this cross-sectional study. HRV was assessed using a Polar RS800CX heart rate monitor, while MFO and Fatmax were determined during a graded exercise treadmill test using indirect calorimetry. No significant associations were observed for healthy young adults (standardized β coefficients ranged from ?0.063 to 0.094, and all P ≥ 0.347) and for middle-aged adults (standardized β coefficients ranged from ?0.234 to 0.090, and all P ≥ 0.056). Nevertheless, only a weak association was observed between one HRV parameter in time-domain (the percentage of R-R intervals that shows a difference higher than 50 ms [pNN50]) and MFO in the cohort of middle-aged adults (β coefficient = ?0.279, and P = 0.033).ConclusionThe results of this study suggest that resting HRV parameters are not associated with MFO and Fatmax during exercise in two independent cohorts of healthy sedentary young and middle-aged adults, respectively.  相似文献   
29.
Marginal rate-based analyses are widely used for the analysis of recurrent events in clinical trials. In many areas of application, the events are not instantaneous but rather signal the onset of a symptomatic episode representing a recurrent infection, respiratory exacerbation, or bout of acute depression. In rate-based analyses, it is unclear how to best handle the time during which individuals are experiencing symptoms and hence are not at risk. We derive the limiting value of the Nelson-Aalen estimator and estimators of the regression coefficients under a semiparametric rate-based model in terms of an underlying two-state process. We investigate the impact of the distribution of the episode durations, heterogeneity, and dependence on the asymptotic and finite sample properties of standard estimators. We also consider the impact of these features on power in trials designed to test intervention effects on rate functions. An application to a trial of individuals with herpes simplex virus is given for illustration.  相似文献   
30.
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