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   2010170篇
  免费   155709篇
  国内免费   3050篇
耳鼻咽喉   27408篇
儿科学   66566篇
妇产科学   56777篇
基础医学   295716篇
口腔科学   59250篇
临床医学   177188篇
内科学   385712篇
皮肤病学   43696篇
神经病学   157699篇
特种医学   79116篇
外国民族医学   529篇
外科学   305007篇
综合类   46273篇
现状与发展   3篇
一般理论   651篇
预防医学   155566篇
眼科学   46451篇
药学   153391篇
  3篇
中国医学   3781篇
肿瘤学   108146篇
  2018年   18524篇
  2015年   18491篇
  2014年   25451篇
  2013年   38973篇
  2012年   52646篇
  2011年   56244篇
  2010年   33057篇
  2009年   31497篇
  2008年   53891篇
  2007年   57017篇
  2006年   57998篇
  2005年   56044篇
  2004年   55302篇
  2003年   52788篇
  2002年   51883篇
  2001年   93315篇
  2000年   96720篇
  1999年   81636篇
  1998年   21976篇
  1997年   19899篇
  1996年   20085篇
  1995年   19470篇
  1994年   18306篇
  1993年   17337篇
  1992年   67028篇
  1991年   66296篇
  1990年   65242篇
  1989年   63054篇
  1988年   58561篇
  1987年   57751篇
  1986年   54842篇
  1985年   53058篇
  1984年   39535篇
  1983年   33978篇
  1982年   19651篇
  1981年   17763篇
  1980年   16672篇
  1979年   37965篇
  1978年   26592篇
  1977年   22445篇
  1976年   21295篇
  1975年   22918篇
  1974年   27854篇
  1973年   26630篇
  1972年   24771篇
  1971年   23424篇
  1970年   21568篇
  1969年   20342篇
  1968年   18734篇
  1967年   16971篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Abstract: Data from the National Education Longitudinal Study were combined with census data at the zip code level to examine the impact of neighborhood racial and ethnic diversity and consolidated inequality, in addition to individual, family, and school factors, on the likelihood of dropping out of high school. Results indicate that while the effects for diversity and consolidated inequality did not support the stated hypotheses, main effects for family risk and prior academic achievement were significant and in the stated direction. Also, when controlling for individual, family, school, and neighborhood characteristics, African Americans were less likely than White students to drop out of school. Implications for contextual effects research and educational outcomes are discussed.  相似文献   
102.
103.
104.
105.
Introduction Recent reviews found problem gamblers are heterogeneous and recommended subtyping gamblers in treatment studies. Objective Review factors (stage of change, preferred gambling activity, co-occurring disorder, and temporal instability of symptoms) for subtyping by evaluating the evidence for their effects on gambling treatment. Methods Literature review, evidence grading. Results Evidence is limited that any of the reviewed factors affects gambling treatment. Substantial evidence from prospective studies and other evidence from cross-sectional studies and the strong placebo response among pathological gamblers support the temporal instability of gambling symptoms. Conclusions Multiple studies are needed to develop the evidence base needed to subtype gamblers in treatment. Changes in the diagnostic criteria of pathological gambling may be necessary, especially to specify the persistence of gambling-related symptoms.  相似文献   
106.
OBJECTIVE: To evaluate the prenatal distribution, associated conditions and outcome of the different types of right aortic arch (RAA) detected in fetal life. METHODS: This was a retrospective review of all cases of RAA detected prenatally between 1998 and 2005 in two tertiary referral centers. RESULTS: In the study period 71 cases of RAA were detected; 26 (37%) had RAA with aberrant left subclavian artery, 23 (32%) had RAA with mirror-image branching, 20 (28%) had RAA of unknown type and two (3%) had double aortic arch. While 20/26 cases with RAA and aberrant left subclavian artery were isolated findings, all 23 cases with RAA and mirror-image branching were associated with cardiac defects, namely tetralogy of Fallot (43%) or pulmonary atresia with ventricular septal defect (22%). Of the 20 cases with RAA, 19 of unknown type were associated with heterotaxy syndromes and had additional cardiac malformations and ambiguities of the situs. The two cases with DAA were isolated findings. Seven cases in our series (10%) had a microdeletion 22q11 and these were significantly associated with extracardiac malformations. The outcome in our series depended solely on the associated cardiac and extracardiac malformations, with the exception of one infant with isolated DAA, in whom a surgical correction was warranted. CONCLUSIONS: RAA detected in fetal life is associated frequently with other cardiac/non-cardiac malformations, heterotaxy syndromes and microdeletions 22q11. The associated conditions vary depending on the branching type of the brachiocephalic vessels and the presence of extracardiac malformations.  相似文献   
107.
108.
BACKGROUND CONTEXT: Substantial variation exists regarding the use of sedation before interventional spine techniques. Patient preference should play an important role in decision making regarding the need for sedation. However, little is known about patients' anxiety levels before spinal injections and their perceptions about the necessity of sedation. PURPOSE: To determine patient perception for need for sedation before epidural steroid injections and zygapophyseal joint injections. STUDY DESIGN/SETTING: Survey of consecutive spinal injection patients in an outpatient spine center. PATIENT SAMPLE: 500 consecutive lumbar, thoracic, and cervical patients receiving spinal injections. OUTCOME MEASURES: A 12-item questionnaire assessing patients' perceived anxiety before to a spinal injection. METHODS: Subjects were given the questionnaire after their spinal injection. Percentages requesting sedation for a first and potential second procedure were assessed. Additionally, anxiety level and pain rating, location of injection, age, sex, and other medication use were analyzed to determine the effect on the request for sedation. RESULTS: 17% of patients questioned requested sedation before an injection, and 28% would request sedation if they were to have a second injection. CONCLUSIONS: Routine sedation before diagnostic and therapeutic injections is not necessary as the majority of patients would not request sedation before the procedure when given the option. However, in some patients sedation is indicated, and all patients would benefit from educational material on sedation before the injection.  相似文献   
109.
110.
The purpose of this work was to investigate the use of an intravascular contrast agent to determine perfusion kinetics in skeletal muscle. A two-compartment kinetic model was used to represent the flux of contrast agent between the intravascular space and extravascular extracellular space (EES). The relationship between the image signal-to-noise ratio (SNR) and errors in estimating permeability surface area product (Ktrans), interstitial volume (ve), and plasma volume (vp) for linear and nonlinear curve-fitting methods was estimated from Monte Carlo simulations. Similar results were obtained for both methods. For an image SNR of 60, the estimated errors in these parameters were 10%, 22%, and 17%, respectively. In vivo experiments were conducted in rabbits to examine physiological differences between these parameters in the soleus (SOL) and tibialis anterior (TA) muscles in the hind limb. Values for Ktrans were significantly higher in the SOL (3.2+/-0.9 vs. 2.0+/-0.5x10(-3) min-1), as were values for vp (3.4+/-0.8 vs. 2.1+/-0.7%). Differences in ve for the two muscles (8.7+/-2.2 vs. 8.5+/-1.6%) were not found to be significant. These results demonstrate that relevant physiological metrics can be calculated in skeletal muscle using MRI with an intravascular contrast agent.  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