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   8713篇
  免费   494篇
  国内免费   18篇
耳鼻咽喉   23篇
儿科学   185篇
妇产科学   240篇
基础医学   1091篇
口腔科学   128篇
临床医学   1463篇
内科学   1381篇
皮肤病学   94篇
神经病学   726篇
特种医学   191篇
外科学   888篇
综合类   134篇
一般理论   9篇
预防医学   1323篇
眼科学   170篇
药学   597篇
中国医学   11篇
肿瘤学   571篇
  2023年   33篇
  2022年   57篇
  2021年   140篇
  2020年   106篇
  2019年   145篇
  2018年   195篇
  2017年   137篇
  2016年   149篇
  2015年   174篇
  2014年   231篇
  2013年   450篇
  2012年   576篇
  2011年   621篇
  2010年   361篇
  2009年   327篇
  2008年   586篇
  2007年   637篇
  2006年   606篇
  2005年   631篇
  2004年   612篇
  2003年   545篇
  2002年   526篇
  2001年   93篇
  2000年   88篇
  1999年   121篇
  1998年   94篇
  1997年   102篇
  1996年   75篇
  1995年   64篇
  1994年   70篇
  1993年   58篇
  1992年   47篇
  1991年   44篇
  1990年   47篇
  1989年   51篇
  1988年   40篇
  1987年   39篇
  1986年   24篇
  1985年   30篇
  1984年   34篇
  1983年   41篇
  1982年   35篇
  1981年   24篇
  1980年   20篇
  1979年   24篇
  1978年   19篇
  1977年   10篇
  1974年   13篇
  1973年   11篇
  1971年   13篇
排序方式: 共有9225条查询结果,搜索用时 171 毫秒
31.
Although cognitive impairment is commonly associated with Parkinson's disease, the relative importance of cortical and subcortical pathologic changes to the development of dementia is controversial. Characteristic abnormalities in cortical glucose metabolism have been reported previously in Alzheimer's disease, a disease in which cortical changes predominate. We measured cerebral glucose metabolism with positron emission tomography in 20 control subjects and in 14 patients with PD with mental status ranging from normal to severely demented to determine whether changes in cortical glucose metabolism occur in early PD and whether the degree and pattern of metabolic change relate to the severity of dementia. The patients were divided into demented and nondemented groups according to the results of neuropsychological assessment. Age-adjusted covariance analyses were performed, since the age distribution varied between groups. The nondemented patients with PD showed widespread cortical glucose hypometabolism without any selective temporoparietal defects. The pattern of glucose hypometabolism seen in the demented patients with PD resembled that described in patients with Alzheimer's disease; ie, there was a global decrease in glucose metabolism, with more severe abnormalities observed in the temporoparietal regions.  相似文献   
32.
33.
INTRODUCTION: Clinical decisions are based on x-ray measures of radiographs. However, the reliability of assessing the angular measurement of fractured femurs in children is unknown. The purpose of this study was to determine the intra- and interrater reliability of an x-ray assessment of femoral shaft fracture angulation in children. METHODS: On 2 occasions, 3 raters evaluated 30 radiographs of children aged 4 to 10 years, 3 to 24 months after a femoral fracture. The radiographs were evaluated by an orthopedic surgeon, an orthopedic fellow and a research assistant, using a standardized methodology. Reliability was assessed with the intraclass correlation coefficient (ICC), an index of concordance that ranges from 01, where > 0.75 indicates excellent concordance. RESULTS: The ICC for the intrarater ranged from 0.75 to 0.97. The interrater reliability ICC for anterior or posterior angulation was 0.91 (95% confidence interval [CI] 0.840.95) and for varus or valgus angulation was 0.90 (95% CI 0.790.95). A change in measurement of more than 5 degrees exceeds the variation in measurement and, therefore, can be attributed to a true shift in fracture position. CONCLUSIONS: With specific standardized protocols, radiographic assessment of femoral fractures is reliable, irrespective of the examiner's level of experience.  相似文献   
34.
This study uses data from a population-based survey to examine the fertility schedules of 704 women in a rural district of Malawi. The main objective is to assess self-reported fecundity status as a measure of fertility impairment. Life tables are used to examine the timing and tempo of births for women reporting difficulty getting pregnant as compared to women with no reported fecundity difficulties. Results of the analysis indicate that women with self-reported fecundity difficulties are older at each birth and have longer median birth intervals than do women with no reported difficulties. Cox proportional hazards models show that the report of a difficulty getting pregnant is significantly associated with at least a 30% lower likelihood of a first, second, or third birth. The relationships are not modified when accounting for demographic characteristics, previous sexual behaviors, or STI status.  相似文献   
35.
An anthropomorphic airway tree phantom was imaged with both hyperpolarized (HP) 3He MRI using a dynamic projection scan and computed tomography (CT). Airway diameter measurements from the HP 3He MR images obtained using a newly developed model-based algorithm were compared against their corresponding CT values quantified with a well-established method. Of the 45 airway segments that could be evaluated with CT, only 14 airway segments (31%) could be evaluated using HP 3He MRI. No airway segments smaller than approximately 4 mm in diameter and distal to the fourth generation were adequate for analysis in MRI. For the 14 airway segments measured, only two airway segments yielded a non-equivalent comparison between the two imaging modalities, while eight more had inconclusive comparison results, leaving only four airway segments (29%) that satisfied the designed equivalence criteria. Some of the potential problems in airway diameter quantification described in the formulation of the model-based algorithm were observed in this study. These results suggest that dynamic projection HP 3He MRI may have limited utility for measuring airway segment diameters, particularly those of the central airways.  相似文献   
36.
37.
38.
39.
40.
Schools of public health have been cautioned about producing graduates and research that were disconnected from public interest. Although institutions may implement a variety of strategies to rectify the situation, institutional structural and cultural barriers impede progress. Public health practice coordinators in accredited schools of public health were surveyed to describe the presence of structural and cultural barriers to academic public health practice using the Stevens model. Administrative leadership and faculty reward systems are described as critical to advance academic public health practice.  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