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   63461篇
  免费   4680篇
  国内免费   333篇
耳鼻咽喉   643篇
儿科学   1606篇
妇产科学   1543篇
基础医学   7845篇
口腔科学   1537篇
临床医学   6384篇
内科学   14402篇
皮肤病学   809篇
神经病学   5013篇
特种医学   1928篇
外国民族医学   2篇
外科学   9860篇
综合类   1016篇
现状与发展   1篇
一般理论   103篇
预防医学   5254篇
眼科学   1850篇
药学   4442篇
中国医学   139篇
肿瘤学   4097篇
  2023年   269篇
  2022年   386篇
  2021年   1155篇
  2020年   729篇
  2019年   1012篇
  2018年   1246篇
  2017年   849篇
  2016年   975篇
  2015年   1138篇
  2014年   1779篇
  2013年   2816篇
  2012年   3782篇
  2011年   4127篇
  2010年   2349篇
  2009年   2196篇
  2008年   4016篇
  2007年   4212篇
  2006年   4041篇
  2005年   4121篇
  2004年   3848篇
  2003年   3460篇
  2002年   3429篇
  2001年   741篇
  2000年   634篇
  1999年   724篇
  1998年   741篇
  1997年   611篇
  1996年   494篇
  1995年   493篇
  1994年   466篇
  1993年   442篇
  1992年   544篇
  1991年   521篇
  1990年   422篇
  1989年   443篇
  1988年   402篇
  1987年   378篇
  1986年   360篇
  1985年   426篇
  1984年   439篇
  1983年   397篇
  1982年   533篇
  1981年   448篇
  1980年   493篇
  1979年   308篇
  1978年   333篇
  1977年   330篇
  1976年   272篇
  1975年   296篇
  1974年   254篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
171.
The ability of serum prostate specific antigen (PSA) and serum acid phosphatase (SAP) to identify skeletal spread was evaluated in untreated patients with prostatic cancer. Twenty patients with scintigraphic evidence of metastatic disease in bone (M1) at diagnosis were compared with 50 untreated patients in whom scans were repeatedly negative during long-term surveillance. Using the present laboratory upper limit of normal (ULN) of 3 iu/l, the sensitivity and specificity of SAP for M1 disease were 80 and 86% respectively. Stepwise discriminant analysis demonstrated that SAP was able to stage patients correctly (bone scan positive or negative) with 81% predictive accuracy at an optimum cut-off limit of 4.6 iu/l. By contrast, whilst PSA (Hybritech) was 100% sensitive for skeletal disease at 10 ng/ml--at the expense of poor (36%) specificity--analysis determined that an optimum cut-off limit of 58 ng/ml led to 79% predictive accuracy for disease in bone. It was concluded that PSA levels > 58 ng/ml are highly indicative of spread to the skeleton, even in the absence of radiological or scintigraphic evidence of metastases.  相似文献   
172.
OBJECTIVE: To identify predisposing factors associated with cardiac rhythm disturbances during the early post-pneumonectomy period (first 7 postoperative days). MATERIALS AND METHODS: During the study period (1995-1999), 259 pneumonectomies were performed for malignant (244 cases) or benign disease (15 cases). Postoperative monitoring of patients included continuous arterial pressure - rhythm monitoring and pulse oximetry. Cardiac rhythm disturbances during the intensive care unit stay were detected on the monitor screen and recorded with a 12-lead electrocardiogram. Cardiac rhythm disturbances associated with electrolytes or fluid balance abnormality, mediastinal deviation or surgical postoperative complications were excluded from the study. Age of patients, preexisting cardiac disease, side of pneumonectomy, intrapericardial procedures, stage of the malignant disease, expected postoperative FEV(1)<1200 ml, intraoperative transfusions of packed red cells, elevated right heart pressures, low postoperative serum magnesium levels and long operative times were considered as predisposing factors for the development of post-pneumonectomy cardiac rhythm disturbances. Statistical analysis has been made using logistic regression analysis, Student t-test and chi-square test. RESULTS: Cardiac rhythm disturbances were detected in 49 patients (18.91%). Atrial fibrillation/flutter (31 cases), supraventricular tachycardia (14 cases), and premature ventricular contractions (four cases) were the observed rhythm disturbances. Right pneumonectomy versus left pneumonectomy (P<0.0001) and intrapericardial pneumonectomy versus standard pneumonectomy (P<0.0001) were identified as strong predisposing factors for the establishment of post-pneumonectomy cardiac rhythm disturbances. Patients who established post-pneumonectomy cardiac rhythm disturbances had significantly higher (P=0.024) right ventricular systolic pressure (42.50+/-15.50 mmHg) when compared with patients who had postoperative sinus rhythm (29.07+/-7.71 mmHg) and had also longer operative times than patients who did not develop rhythm disturbances (P=0.015). Mortality rate in patients who developed post-pneumonectomy rhythm disturbances was 20.40%. CONCLUSIONS: Cardiac rhythm disturbances observed early after pneumonectomy are mainly of supraventricular origin, complicating right and intrapericardial pneumonectomies, patients with elevated right heart pressures and long operative times, and are associated with high mortality rates.  相似文献   
173.
α adrenoreceptor 301–303 deletion polymorphism does not influence basal metabolic rate, insulin resistance or weight gain in Greek women with polycystic ovary syndrome.  相似文献   
174.
175.
OBJECTIVE: To determine the natural history of colonization with vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and resistant gram-negative bacilli among long-term-care facility (LTCF) residents. DESIGN: Observational cohort study. SETTING: A 355-bed LTCF with a ventilator unit and a subacute unit. PARTICIPANTS: Residents with colonization or infection with VRE, MRSA, or resistant gram-negative bacilli housed at the LTCF between December 1, 1999, and February 29, 2000. METHODS: Cultures of clinical and surveillance sites were performed at regular intervals. Charts were reviewed for clinical characteristics associated with clearance of colonization. Kaplan-Meier curves were constructed to analyze the number of days to clearance of colonization. RESULTS: Forty-nine residents had 65 episodes of colonization (27 VRE, 30 MRSA, and 8 resistant gram-negative bacilli). Eighteen (28%) of the episodes cleared. The clearance rate was 2.7 episodes per 1,000 person-days. Clearance occurred significantly more often with resistant gram-negative bacilli colonization compared with VRE or MRSA colonization (6 [75%] vs 12 [21%]; P = .007; relative risk, 4.17; 95% confidence interval, 1.26 to 11.8). There was a trend toward longer use of antimicrobial agents among residents with persistent colonization. Infections occurred most frequently with MRSA. The urinary tract was the most common site of infection. CONCLUSION: Among LTCF residents, colonization with resistant gram-negative bacilli is four times more likely to clear than colonization with VRE or MRSA. Performance of surveillance cultures at regular intervals may reduce the need for contact precautions for LTCF residents with resistant gram-negative bacilli colonization.  相似文献   
176.
The present study sought to investigate the moderating function that social problem-solving effectiveness serves in relation to negative stressful life events and depressive symptomatology. It was also hypothesized that knowledge of problem solving would improve upon the prediction of level of depressive symptoms beyond the assessment of stressful events. Results involving 462 undergraduate students provide support for both predictions. Specifically, findings from a multiple regression analysis indicated that (1) differences in reported depressive mood between subjects under high and low stress levels were minimal for individuals characterized as effective problem-solvers, relative to those persons with problem-solving scores reflective of ineffective problem solving; and (2) assessment of problem-solving scores and their interaction with stress level provided for an additional three times the amount of explained variance in predicting depression scores beyond life stress scores. Additionally, a cross-validation of the regression analysis was conducted and found to result in a minimal amount of shrinkage that could be due to samplespecific characteristics.We would like to extend our appreciation to two anonymous reviewers for their helpful comments on an earlier draft of this article. The study was supported in part by a grant funded by Fairleigh Dickinson University to the first author.  相似文献   
177.
The purpose of this study is to identify correlates of dental student stress. Associations between characteristics of dental students and their stress levels are examined, along with the association of stress with drug use and health problems. A total of 300 out of 315 dental students completed a questionnaire that measured the frequency and stressfulness of 31 stressors; drug use; health problems; and student characteristics including Type A behavior, career commitment, demographics, and lifestyle variables. Characteristics that were associated with a higher stress level were a higher level of Type A behavior and lower level of career commitment. Greater stress was also associated with a greater frequency of health problems. The results suggest an interactional stress model in which the personalities and attitudes of students are important mediators of the stress response.  相似文献   
178.
Objectives
To explore medical students' use of computer tutorials embedded in a busy clinical setting; to demonstrate that such tutorials can increase knowledge gain over and above that attributable to the clinical rotation itself.
Methods
Six tutorials were installed on a computer placed in a central area in an emergency department. Each tutorial was made up of between 33 and 85 screens of information that include text, graphics, animations, and questions. They were designed to be brief (10 minutes), focused, interactive, and immediately relevant. The authors evaluated the intervention using quantitative research methods, including usage tracking, surveys of faculty and students, and a randomized pretest-posttest study.
Results
Over 46 weeks, 95 medical students used the tutorials 544 times, for an overall average of 1.7 times a day. The median time spent on completed tutorials was 11 minutes (average [SD], 14 [±12] minutes). Seventy-four students completed the randomized study. They completed 65% of the assigned tutorials, resulting in improved examination scores compared with the control (effect size, 0.39; 95% confidence interval = 0.15 to 0.62). Students were positively disposed to the tutorials, ranking them as "valuable." Fifty-four percent preferred the tutorials to small group teaching sessions with a preceptor. The faculty was also positive about the tutorials, although they did not appear to integrate the tutorials directly into their teaching.
Conclusions
Medical students on rotation in a busy clinical setting can and will use appropriately presented computer tutorials. The tutorials are effective in raising examination scores.  相似文献   
179.
180.
Patients with anorexia nervosa have neuroendocrine and behavioral alterations that starvation and weight loss are thought to cause, or contribute to, since they are reversed by weight restoration. We have found that anorexics have starvation-related disturbances of neuropeptide Y (NPY), corticotropin-releasing hormone (CRH), and beta-endorphin, as determined by their measurements in cerebrospinal fluid. The relationship between these neuropeptides and several symptoms in anorexia, together with findings in experimental animals, raise a possibility that changes in the activity of these neuropeptides contribute to neuroendocrine and behavioral alterations in anorexia. Specifically, a disturbance of central nervous system CRH activity is likely to be responsible for hypercortisolemia, while a disturbance of central nervous system NPY may contribute to amenorrhea. In addition, disturbances of these neuropeptides could contribute to other symptoms such as increased physical activity, hypotension, reduced sexual interest, depression, and pathological feeding behavior.  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