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   34337篇
  免费   2282篇
  国内免费   155篇
耳鼻咽喉   257篇
儿科学   1091篇
妇产科学   836篇
基础医学   4431篇
口腔科学   682篇
临床医学   3561篇
内科学   6882篇
皮肤病学   546篇
神经病学   3489篇
特种医学   976篇
外国民族医学   3篇
外科学   4790篇
综合类   328篇
一般理论   32篇
预防医学   2804篇
眼科学   772篇
药学   2489篇
中国医学   39篇
肿瘤学   2766篇
  2023年   245篇
  2022年   442篇
  2021年   832篇
  2020年   519篇
  2019年   782篇
  2018年   891篇
  2017年   676篇
  2016年   713篇
  2015年   875篇
  2014年   1199篇
  2013年   1661篇
  2012年   2577篇
  2011年   2569篇
  2010年   1484篇
  2009年   1250篇
  2008年   2322篇
  2007年   2521篇
  2006年   2250篇
  2005年   2179篇
  2004年   2199篇
  2003年   1961篇
  2002年   1803篇
  2001年   263篇
  2000年   209篇
  1999年   296篇
  1998年   377篇
  1997年   328篇
  1996年   267篇
  1995年   214篇
  1994年   196篇
  1993年   203篇
  1992年   189篇
  1991年   162篇
  1990年   132篇
  1989年   119篇
  1988年   107篇
  1987年   117篇
  1986年   106篇
  1985年   97篇
  1984年   110篇
  1983年   113篇
  1982年   112篇
  1981年   109篇
  1980年   97篇
  1979年   79篇
  1978年   77篇
  1977年   66篇
  1976年   71篇
  1975年   67篇
  1972年   61篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
BackgroundLittle is known about the extent of ordering low-value services by.PurposeTo compare the rates of low-value back images ordered by primary care physicians (PCMDs) and primary care nurse practitioners (PCNPs).MethodWe used 2012 and 2013 Medicare Part B claims for all beneficiaries in 18 hospital referral ?regions (HRRs) and a measure of low-value back imaging from Choosing Wisely. Models included random clinician effect and fixed effects for beneficiary age, disability, Elixhauser comorbidities, clinician sex, the emergency department setting, back pain visit volume, organization, and region (HRR).FindingsPCNPs (N = 231) and PCMDs (N = 4,779) order low-value back images at similar rates (NP: all images: 26.5%; MRI/CT: 8.4%; MD: all images: 24.5%; MRI/CT: 7.7%), with no detectable significant difference when controlling for covariates.DiscussionPCNPs and PCMDs order low-value back images at an effectively similar rate.  相似文献   
4.
5.
6.
7.
8.
9.

Background

In the emergency department, rib fractures are a common finding in patients who sustain chest trauma. Rib fractures may be a sign of significant, underlying pathology, especially in the elderly patients where rib fractures are associated with significant morbidity and mortality. To date, no studies have evaluated the ability of ultrasound to detect rib fractures using cadaver models and subsequently use this model as a teaching tool.

Objectives

The purpose of this study was to determine if it is possible to generate rib fractures on cadaver models which could be accurately identified using ultrasound.

Methods

This was a cross-sectional study performed during one session at a cadaver lab. A single hemithorax from four adult cadavers were used as models. Single rib fractures on each of rib five through eight were created. Four subjects, blinded to the normal versus fractured ribs, were asked to identify the presence of a fracture on each rib.

Results

A total of 8 of 16 potential ribs had fractured induced by study staff. Mean accuracy was 55% for all subjects. The overall sensitivity and specificity for detecting rib fractures was 50% (CI: 31.89–68.11) and 59.38% (CI: 35.69–73.55) respectively. The overall PPV and NPV was 55.17% and 54.29% respectively.

Conclusions

In this pilot study, subjects were not able to detect induced rib fractures using ultrasound on cadaver models. The use of this model as a teaching tool in the detection of rib fractures requires further investigation.  相似文献   
10.
Parabens are antimicrobial additives found in a wide array of consumer products. However, the halogenated compounds formed from parabens during wastewater disinfection are a potential environmental concern. In order to identify these transformation products and investigate their mechanism of formation, a synthetic route to ethyl parabens labeled with the stable isotope carbon-13 at specific positions within the benzene ring was developed. This efficient two-step procedure starts from commercially available 13C-labeled phenols and involves (1) initial acylation of the phenol via a Houben–Hoesch reaction with trichloroacetonitrile followed by (2) a modified haloform reaction of the resulting trichloromethyl ketone to afford the corresponding 13C-labeled ethyl parabens in 65%–80% overall yield. The scope of the modified haloform reaction was also investigated, allowing for the synthesis of other parabens derived from primary or secondary alcohols, including 13C- and deuterium-labeled esters. In addition, 4-hydroxybenzoic acid can be formed directly from the common trichloromethyl ketone intermediate upon treatment with lithium hydroxide. This protocol complements existing methods for preparing 13C-labeled paraben derivatives and offers the specific advantages of exhibiting complete regioselectivity in the Houben–Hoesch reaction (to form the para-disubstituted product) and avoiding the need for protecting groups in the modified haloform reaction that forms the paraben esters.  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