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   3266篇
  免费   224篇
  国内免费   14篇
耳鼻咽喉   30篇
儿科学   59篇
妇产科学   42篇
基础医学   465篇
口腔科学   37篇
临床医学   406篇
内科学   619篇
皮肤病学   23篇
神经病学   389篇
特种医学   175篇
外科学   426篇
综合类   26篇
一般理论   8篇
预防医学   368篇
眼科学   37篇
药学   230篇
中国医学   8篇
肿瘤学   156篇
  2024年   4篇
  2023年   30篇
  2022年   59篇
  2021年   102篇
  2020年   65篇
  2019年   103篇
  2018年   118篇
  2017年   73篇
  2016年   92篇
  2015年   124篇
  2014年   134篇
  2013年   179篇
  2012年   279篇
  2011年   281篇
  2010年   163篇
  2009年   120篇
  2008年   240篇
  2007年   205篇
  2006年   168篇
  2005年   194篇
  2004年   162篇
  2003年   141篇
  2002年   156篇
  2001年   35篇
  2000年   28篇
  1999年   28篇
  1998年   25篇
  1997年   18篇
  1996年   11篇
  1995年   12篇
  1994年   9篇
  1993年   7篇
  1992年   10篇
  1991年   13篇
  1990年   12篇
  1989年   8篇
  1988年   6篇
  1987年   9篇
  1986年   7篇
  1985年   10篇
  1984年   7篇
  1983年   3篇
  1980年   7篇
  1978年   5篇
  1977年   3篇
  1975年   4篇
  1974年   4篇
  1973年   8篇
  1971年   3篇
  1959年   2篇
排序方式: 共有3504条查询结果,搜索用时 12 毫秒
61.
Treatment of hot flashes with transdermal estradiol administration   总被引:2,自引:0,他引:2  
A randomized prospective double blind study was performed to assess the ability of a transdermal therapeutic system (TTS) delivering estradiol (E2) to suppress hot flashes (HFs) in symptomatic postmenopausal women. Patients were given placebo or E2 in four doses for a 20-day period, and serum gonadotropin and estrogen levels and the occurrences of HFs were measured. Administration of placebo had no measurable effect on either estrogen or gonadotropin levels or the occurrence of HFs. A dose-response relationship was found between the rate of E2 administered and the circulating level of E2, with 25, 50, 100, and 200 micrograms/24 h dosages raising the mean E2 concentrations from mean baseline levels of 5-8 pg/ml to 18, 38, 73, and 100 pg/ml, respectively. Estrone levels also increased with TTS application, but to a lesser extent than did E2 levels. Dose-response reductions of FSH and LH with increasing amounts of E2 administration occurred, but gonadotropin levels were not lowered in any of the patients into the ranges found in premenopausal women. TTS application significantly suppressed the occurrence of HFs at the 50 micrograms/24 h dosage and higher. A significant negative correlation (r = 0.6045; P less than 0.001) between E2 levels and the rates of occurrence of HFs was found during hormone administration. Based on this regression, 50% and 100% reductions of HFs should occur at 61 and 122 pg/ml E2. These data indicate that the transdermal delivery of E2 with these systems significantly reduced the occurrence of HFs and allowed definition of the therapeutic range of hormone replacement in terms of lost ovarian function, as reflected by circulating E2 levels.  相似文献   
62.
GeroScience - A variety of diets have been studied for possible anti-aging effects. In particular, studies of intermittent fasting and time-restricted feeding in laboratory rodents have found...  相似文献   
63.
64.
We developed a simple and fully automated method for detecting artifacts in the R-R interval (RRI) time series of the ECG that is tailored to the intensive care unit (ICU) setting. From ECG recordings of 50 adult ICU-subjects we selected 60 epochs with valid R-peak detections and 60 epochs containing artifacts leading to missed or false positive R-peak detections. Next, we calculated the absolute value of the difference between two adjacent RRIs (adRRI), and obtained the empirical probability distributions of adRRI values for valid R-peaks and artifacts. From these, we calculated an optimal threshold for separating adRRI values arising from artifact versus non-artefactual data. We compared the performance of our method with the methods of Berntson and Clifford on the same data. We identified 257,458 R-peak detections, of which 235,644 (91.5%) were true detections and 21,814 (8.5%) arose from artifacts. Our method showed superior performance for detecting artifacts with sensitivity 100%, specificity 99%, precision 99%, positive likelihood ratio of 100 and negative likelihood ratio <0.001 compared to Berntson’s and Clifford’s method with a sensitivity, specificity, precision and positive and negative likelihood ratio of 99%, 78%, 82%, 4.5, 0.013 for Berntson’s method and 55%, 98%, 96%, 27.5, 0.460 for Clifford’s method, respectively. A novel algorithm using a patient-independent threshold derived from the distribution of adRRI values in ICU ECG data identifies artifacts accurately, and outperforms two other methods in common use. Furthermore, the threshold was calculated based on real data from critically ill patients and the algorithm is easy to implement.  相似文献   
65.
66.

Objective

To identify predictors for back pain, leg pain, and activity limitation in patients with early persistent low back disorders (LBDs).

Design

Prospective inception cohort study.

Setting

Primary care private physiotherapy clinics in Melbourne, Australia.

Participants

Individuals (N=300) aged 18-65 years with low back and/or referred leg pain of ≥6 weeks and ≤6 months duration.

Interventions

Not applicable.

Main Outcome Measures

Numeric rating scales for back pain and leg pain as well as the Oswestry Disability Scale.

Results

Prognostic factors included sociodemographics, treatment related factors, subjective/physical examination, subgrouping factors, and standardized questionnaires. Univariate analysis followed by generalized estimating equations were used to develop a multivariate prognostic model for back pain, leg pain, and activity limitation. Fifty-eight prognostic factors progressed to the multivariate stage where 15 showed significant (P<.05) associations with at least 1 of the 3 outcomes. There were 5 indicators of positive outcome (2 types of LBD subgroups, paresthesia below waist, walking as an easing factor, and low transversus abdominis tone) and 10 indicators of negative outcome (both parents born overseas, deep leg symptoms, longer sick leave duration, high multifidus tone, clinically determined inflammation, higher back and leg pain severity, lower lifting capacity, lower work capacity, and higher pain drawing percentage coverage). The preliminary model identifying predictors of LBDs explained up to 37% of the variance in outcome.

Conclusions

This study evaluated a comprehensive range of prognostic factors reflective of both the biomedical and psychosocial domains of LBDs. The preliminary multivariate model requires further validation before being considered for clinical use.  相似文献   
67.
68.
We investigate whether and how a change in performance‐related payment motivated General Practitioners (GPs) in Scotland. We evaluate the effect of increases in the performance thresholds required for maximum payment under the Quality and Outcomes Framework in April 2006. A difference‐in‐differences estimator with fixed effects was employed to examine the number of patients treated under clinical indicators whose payment schedules were revised and to compare these with the figures for those indicators whose schedules remained unchanged. The results suggest that the increase in the maximum performance thresholds increased GPs' performance by 1.77% on average. Low‐performing GPs improved significantly more (13.22%) than their high‐performing counterparts (0.24%). Changes to maximum performance thresholds are differentially effective in incentivising GPs and could be used further to raise GPs' performance across all indicators. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
69.
Two potent glucocorticoid receptor agonists were prepared labeled with carbon‐14 and with stable isotopes to perform drug metabolism, pharmacokinetics, and bioanalytical studies. Carbon‐14 labeled (1) was obtained from an enantiopure alkyne (5) via a Sonogashira coupling to a previously reported 5‐amino‐4‐iodo‐[2‐14C]pyrimidine [14C]‐(6), followed by a base‐mediated cyclization (1) in 72% overall radiochemical yield. Carbon‐14 labeled (2) was prepared in five steps employing a key benzoic acid intermediate [14C]‐(13), which was synthesized in one pot from enolization of trifluoromethylketone (12), followed by bromine–magnesium exchange and then electrophile trapping reaction with [14C]‐carbon dioxide. A chiral auxiliary (S)‐1‐(4‐methoxyphenyl)ethylamine was then coupled to this acid to give [14C]‐(15). Propargylation and separation of diastereoisomers by crystallizations gave the desired diastereomer [14C]‐(17) in 34% yield. Sonogashira coupling to iodopyridine (10) followed by cyclization to the azaindole [14C]‐(18) and finally removal of the chiral auxiliary gave [14C]‐(2) in 7% overall yield. For stable isotope syntheses, [13C6]‐(1) was obtained in three steps using [13C4]‐(6) and trimethylsilylacetylene‐[13C2] in 26% yield, while [2H5]‐(2) was obtained by first preparing the iodopyridine [2H5]‐(10) in five steps. Then, Sonogashira coupling to chiral alkyne (24) and cyclization gave [2H5]‐(2) in 42% overall yield.  相似文献   
70.
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