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   2603篇
  免费   188篇
  国内免费   20篇
耳鼻咽喉   5篇
儿科学   129篇
妇产科学   69篇
基础医学   296篇
口腔科学   45篇
临床医学   203篇
内科学   571篇
皮肤病学   39篇
神经病学   183篇
特种医学   150篇
外国民族医学   1篇
外科学   526篇
综合类   55篇
预防医学   244篇
眼科学   34篇
药学   77篇
中国医学   1篇
肿瘤学   183篇
  2023年   21篇
  2022年   44篇
  2021年   75篇
  2020年   49篇
  2019年   69篇
  2018年   79篇
  2017年   60篇
  2016年   62篇
  2015年   51篇
  2014年   71篇
  2013年   106篇
  2012年   153篇
  2011年   185篇
  2010年   97篇
  2009年   92篇
  2008年   150篇
  2007年   131篇
  2006年   118篇
  2005年   111篇
  2004年   98篇
  2003年   117篇
  2002年   87篇
  2001年   78篇
  2000年   71篇
  1999年   62篇
  1998年   24篇
  1997年   23篇
  1996年   25篇
  1995年   16篇
  1994年   20篇
  1993年   12篇
  1992年   47篇
  1991年   54篇
  1990年   32篇
  1989年   33篇
  1988年   37篇
  1987年   31篇
  1986年   29篇
  1985年   16篇
  1984年   13篇
  1983年   15篇
  1982年   16篇
  1981年   12篇
  1980年   15篇
  1979年   21篇
  1977年   10篇
  1972年   9篇
  1970年   6篇
  1969年   6篇
  1967年   11篇
排序方式: 共有2811条查询结果,搜索用时 15 毫秒
71.
STUDY OBJECTIVE: To test the hypothesis that residency-trained emergency physicians who left the practice of emergency medicine do not differ significantly from those who continue to practice. DESIGN: A retrospective cohort study using a mailed questionnaire. TYPE OF PARTICIPANTS: Eight hundred fifty-eight emergency medicine residency graduates from 1978 through 1982. METHODS: A mailed questionnaire was used to obtain data from the study population. Individuals who did not respond to the first mailing were sent a second survey six weeks later. A sample of 10% of nonrespondents was contacted by telephone and compared with respondents on five variables. Respondents were divided into physicians who continued to practice emergency medicine and those who had elected to leave the specialty. The variables used to compare the two groups included personal and professional demographics, career satisfaction, and satisfaction with training. chi 2, Fisher's exact t-test, and logistic regression were used to analyze the data with an a priori level of significance set at .05. MEASUREMENTS AND MAIN RESULTS: There were 539 complete responses for a response rate of 62.8%. No statistical differences between responders and nonresponders were identified. The ten-year survival rate of respondents was 84.9%. Those who left emergency medicine were less likely to be board certified in emergency medicine (P less than .001), were more likely to be board certified in another field (P = .001), were less likely to work with residents during their emergency medicine practice (P = .009), and were more likely to report an annual gross income of less than $100,000 per year (P less than .001). Emergency physicians who have left the field were less likely to report being satisfied or very satisfied with their initial choice of emergency medicine as a specialty (P = .001). There was no difference in satisfaction with the quality of emergency medicine residency training (P = .183). CONCLUSION: Career longevity of residency-trained emergency physicians has been greater than early predictions. Interactions with residents, higher income, satisfaction with training decision, and board certification in emergency medicine are variables associated with a higher retention rate.  相似文献   
72.
73.
74.
The hemodynamic consequences of atrioventricular (AV) synchrony during ventricular tachycardia were evaluated during cardiac electrophysiologic testing. The relationship between stroke volume and the AV interval was investigated on a beat-by-beat basis in six patients during induced monomorphic ventricular tachycardia. Stroke volume was calculated either (1) in the right ventricle using impedance catheter method (four patients) or (2) in the left ventricle using Doppler measurement of aortic blood velocity (two patients). The impedance catheter method underestimated stroke volume by a factor of 4.2 +/- 2.4 compared with the thermodilution cardiac output method. However, there was a highly linear relationship between both methods for computing stroke volume (r greater than 0.9). Five patients had complete AV dissociation during ventricular tachycardia, and different AV intervals spanned the entire tachycardia cycle lengths. Largest stroke volumes were associated with optimal AV intervals within 120 and 230 msec, resulting in a 97 +/- 59% increase in stroke volume over ventricular tachycardia cycles not associated with atrial activity. Customized atrial pacing during ventricular tachycardia may provide a valuable means for artificially establishing the hemodynamically optimal AV interval and eliminating the ventricular tachycardia cycles not preceded by atrial activity.  相似文献   
75.
Like many primary tumors, human adenovirus type 12 (Ad12)-transformed mouse cells express greatly reduced levels of the major histocompatibility complex (MHC) class I antigens and are highly tumorigenic in immunocompetent hosts. Expression of a transfected class I gene by these cells can abrogate their tumorigenicity. Both the K and the L class I genes can suppress the malignant phenotype. Previous studies showed that interferon can induce class I gene expression in certain Ad12-transformed cells and can suppress their tumorigenic phenotype. We now demonstrate that preimmunization of mice with a nontumorigenic dose of interferon-treated Ad12-transformed tumor cells can afford protection against a subsequent challenge by a tumorigenic dose of untreated Ad12-transformed tumor cells. Similar immunity can also be induced by using cells transfected with the K gene, and the observed protection appears specific to Ad12-transformed cells. Significant protection can be achieved even if immunization is provided subsequent to the tumor challenge. Since increasing numbers of human tumors have been found to have reduced levels of MHC class I antigens, the prospect of therapy by immunization with the parental tumor cells that have been manipulated to induce class I gene expression offers an attractive experimental model.  相似文献   
76.
Transduction of a bacterial gene into mammalian cells.   总被引:5,自引:0,他引:5       下载免费PDF全文
The transduction of an Escherichia coli gene into mammalian cells is described. A supressor tRNA gene was linked to a simian virus 40 (SV40) vector in vitro and the recombinant was used to transfect rat embryo cells and monkey kidney cells. The hybrid SV40 genome, SV40-su+ III, retained genetic information required for autonomous replication and cellular transformation and had a 1300-base-pair DNA segment in the late gene region (between the restriction endonuclease sits Hpa II at 0.735 and EcoRI at 0/1.0 on the SV40 genetic map) replaced by an 870-base-pair bacterial DNA segment containing the suppressor tRNA gene, su+ III (tRNATyrsu+III). The structure and fate of the SV40-su+III chimera were determined by DNA reassociation kinetic analysis and restriction enzyme cleavage of the total cellular DNA from transformed rat embryo cells and persistently infected monkey cells. Hybridization with radiolabeled probes specific for vector (SV40) or su+III DNA sequences revealed primarily nonintegrated or free hybrid genomes. In cloned lines of both cell types, the bacterial DNA segment was recovered intact, as judged by the length of the segment excised by restriction endonucleases and its ability to hybridize to the radiolabeled bacterial DNA probe and not to the SV40 probe.  相似文献   
77.
Elhajj I  Uthman I  Chahel A  Khoury F  Arayssi T  Taher A 《Lupus》2004,13(10):812-814
Familial clustering of elevated antiphospholipid antibody levels has been described, but the reports are heterogeneous with regard to the characterization of the antiphospholipid syndrome (APS), coexisting autoimmune diseases and clinical implications. We report a familial occurrence of APS in two patients, in the presence of SLE in the mother and absence of autoimmune diseases in the daughter along with acquired circulating inhibitors in both cases: platelet inhibitor and factor IX inhibitor, respectively.  相似文献   
78.
To identify predictors of clinical coronary artery disease, 110 insulin-requiring diabetic patients with no symptoms suggestive of cardiac disease and with a normal resting ECG underwent metabolic and noninvasive cardiovascular screening including a history and physical examination, exercise ECG, M-mode echocardiography, and chemical laboratory testing. During a median follow-up interval of 100 months, 14 of these patients had clinical evidence of coronary artery disease consisting of acute myocardial infarction, sudden cardiac death, or anginal chest pain with angiographic documentation of occlusive coronary artery disease. Baseline variables that were univariately predictive of subsequent clinical coronary disease included age, peak treadmill heart rate, and retinal neovascularization. According to multivariate analysis the peak treadmill heart rate was the single most important predictor of subsequent development of clinical coronary disease. A treadmill ECG result that was either abnormal or inconclusive because of failure to achieve 90% of predicted maximal heart rate identified each patient in whom clinical coronary artery disease developed within 50 months after entry testing. Thus the entry treadmill ECG provided prognostic information not available from the history and physical examination results, but little further prognostic information was provided after the first 50 months of follow-up, suggesting the need for serial testing.  相似文献   
79.
80.

Introduction and aim

Operative fixation of distal radius fractures using fixed-angle devices has become increasingly common. Although good to excellent results have been reported in acute fractures, little is currently known regarding the fixation of healing displaced distal radius fractures that were presented late. The aim of this study was to evaluate the results of internal fixation of distal radius fractures presented late (>21 days) as compared with an acute-care control group.

Methods

Forty patients operated on for displaced distal radius fractures, presenting more than 21 days after injury (delayed treatment (DT) group), were compared with 75 age-matched controls with acute fracture repair (≤21 days). The same surgical approach was used in both groups, together with dorsal soft-tissue and brachioradialis release. No osteotomy was required. Direct and indirect reduction aids were used. A fixed-angle device (DVR; Biomet Inc., Warsaw, IN, USA) was used in both groups. Mean follow-up was 3.4 years. Quick DASH (Disabilities of the Arm, Shoulder and Hand) and Short Form 12 scores were used to evaluate outcome, as well as radiographic analysis for Arbeitsgemeinschaft für Osteosynthesefragen(AO)/Orthopaedic Trauma Association(OTA) classification, volar tilt, radial inclination and radial length.

Results

Average age was 53 years in both groups and male to female (M/F) ratio was similar in the study groups. Mean time to surgery was 30 days in the DT group and 8 days in the control group. There were significantly more type C (91.5% vs. 67.5%) fractures in the control group. The average quick DASH score was 27.1 in the DT group as compared with 6.3 in the control group (p < 0.03); however, when controlling for two outlier cases with complications (hardware irritation and a sensory neuropathy) there was no significant difference. Volar tilt, radial inclination and length were similar in both groups and were within normal anatomical values.

Conclusions

Delayed primary operative fixation of displaced unstable distal radial fractures is a viable option for cases that were presented late, with predictable, favourable results. Neither extensile approaches nor formal osteotomies are required.  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