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   3211959篇
  免费   257454篇
  国内免费   9332篇
耳鼻咽喉   45270篇
儿科学   100948篇
妇产科学   86463篇
基础医学   446606篇
口腔科学   92038篇
临床医学   293695篇
内科学   634942篇
皮肤病学   69727篇
神经病学   269678篇
特种医学   129203篇
外国民族医学   1111篇
外科学   489790篇
综合类   76924篇
现状与发展   3篇
一般理论   1300篇
预防医学   262443篇
眼科学   73655篇
药学   233699篇
  9篇
中国医学   5771篇
肿瘤学   165470篇
  2018年   32878篇
  2016年   29209篇
  2015年   32896篇
  2014年   46858篇
  2013年   71103篇
  2012年   92298篇
  2011年   98315篇
  2010年   59301篇
  2009年   57154篇
  2008年   92782篇
  2007年   98838篇
  2006年   99972篇
  2005年   97357篇
  2004年   93454篇
  2003年   90551篇
  2002年   88159篇
  2001年   147422篇
  2000年   152426篇
  1999年   128339篇
  1998年   38650篇
  1997年   34861篇
  1996年   35180篇
  1995年   34648篇
  1994年   32473篇
  1993年   30398篇
  1992年   104910篇
  1991年   101683篇
  1990年   98107篇
  1989年   93998篇
  1988年   87465篇
  1987年   86269篇
  1986年   81640篇
  1985年   78457篇
  1984年   59798篇
  1983年   50962篇
  1982年   31515篇
  1981年   28347篇
  1980年   26670篇
  1979年   55703篇
  1978年   39835篇
  1977年   33554篇
  1976年   31357篇
  1975年   32913篇
  1974年   40106篇
  1973年   38201篇
  1972年   35729篇
  1971年   33106篇
  1970年   30930篇
  1969年   28800篇
  1968年   26490篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Adolescent stress is an emerging area of importance in considerations of the health of young people. Exposure to stress predicts a range of both physical and mental health problems in adolescents and relates, as well, to the initiation of important health risk behaviours. Yet the measurement of stress in adolescents has been as fraught with methodological difficulty as it has been for adults. This paper examines the Adolescent Stress Questionnaire (ASQ) which was developed specifically to address the domain of stressors specific to adolescent experience and looks at three cohorts of responses to this questionnaire over time (1995, 1998 and 2001). It assesses the stability of the original 7‐factor structure of the ASQ over time, and while confirmatory factor analysis indicates that stability to be acceptable, it also suggests that either adolescent stressors themselves, or the language by which they are reported, vary sufficiently over time to warrant the refinement of the instrument. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
992.
993.
994.
995.
OBJECTIVE: To determine the aetiological agents and outcome of severe community-acquired pneumonia (SCAP) in children admitted to the paediatric intensive care unit (PICU) at Kalafong Hospital, Pretoria. PATIENTS AND METHODS: An audit was done after a protocol was implemented to identify the aetiological agents in children with life-threatening SCAP admitted to the PICU from the emergency room. The following investigations were done as per protocol: blood culture, culture of the tracheal aspirate, immunofluorescence and culture of the nasopharyngeal aspirate, microscopy and culture of the gastric juice for Mycobacterium tuberculosis, and determination of HIV status. The following data, documented prospectively, were obtained from patient records: date of admission, age, gender, weight, duration of ventilation, duration of stay in the PICU, survival or death, and severity of illness as determined by means of the score for acute neonatal physiology (SNAP) or paediatric risk of mortality (PRISM) score depending on the child's age. RESULTS: Twenty-three children were admitted over a 1-year period (1 November 1994-30 October 1995). Their median age was 10 weeks (range 2 weeks-5 years) and the sex distribution was equal. Two children were HIV-infected. Twenty children received mechanical ventilation for a median period of 6.5 days (range 2-16 days). Aetiological agents were identified in 15/23 children (65%). Respiratory syncytial virus (RSV) was the most common pathogen, identified in 7/23 children, Klebsiella pneumoniae was the most common bacterial pathogen, identified in 5 children (2 blood cultures and 3 tracheal aspirates). Tuberculosis was not diagnosed. The mean PRISM score was similar in survivors and children who died. The case fatality rate was 30%. The 7 children who died had a median arterial oxygen tension/fraction of inspired oxygen (PaO2/FiO2) ratio of 94 (range 32-111) and the 16 survivors had a median ratio of 146 (range 51-252) (P = 0.01) on admission. Both HIV-infected children died and postmortem examination showed a pneumonia due to Pneumocystis carinii and cytomegalovirus. CONCLUSIONS: SCAP occurs in very young children. One or more pathogens were isolated in 65% of cases. Viral pathogens predominated, with RSV being the most common. The yield of positive blood cultures was low at 17%. Streptococcus pneumoniae and Haemophilus influenzae were not found. The case fatality rate was 30% and death was more likely with a low PaO2/FiO2 ratio on admission.  相似文献   
996.
OBJECTIVE: Traditional assessments of the microbial flora associated with acute bacterial rhinosinusitis have relied on maxillary sinus punctures (taps) and culture. These taps are now considered the gold standard for obtaining cultures and are used as the method of identifying bacterial pathogens in antimicrobial trials. Maxillary sinus taps are limited by discomfort to the patients and technical concerns. Because of these factors, the standard of performing taps has limited antibiotic trials and microbial surveillance. Alternatives to maxillary sinus taps have been explored. STUDY DESIGN: We conducted a retrospective, systematic review of the literature from 1950 to 2000 of articles comparing culture techniques in the nose and paranasal sinuses for acute bacterial rhinosinusitis. RESULTS: Nasal cultures have poor correlation to maxillary sinus cultures, whereas there is 60% to 85% concordance between endoscopically guided middle meatal cultures and maxillary sinus cultures. These studies, however, are all limited by small sample sizes and therefore are inadequate to make any concrete recommendations regarding the relative role of endoscopically guided middle meatal cultures as a formal method of pathogen identification in acute bacterial rhinosinusitis. CONCLUSION: A formal prospective study with sufficient sample size to assess the concordance between the microbial flora of the maxillary sinus punctures and middle meatal cultures in acute rhinosinusitis is recommended.  相似文献   
997.
OBJECTIVES: Diagnostic accuracy of the ThinPrep process (Cytyc, Boxborough, MA) was compared with that of conventional (smear) cytopreparation for fine-needle aspiration (FNA) of head and neck masses. METHODS: In a prospective, randomized, single-blinded study, 209 patients served as their own controls and underwent 236 FNAs using ThinPrep and conventional (smear) cytopreparatory techniques. RESULTS: ThinPrep produced less air-drying artifact and less mechanical distortion than the conventional method. The conventional technique was diagnostic in 63% of samples; the ThinPrep technique was diagnostic in 55% of samples. When all results were combined, pathologists subjectively preferred the conventional technique but accepted use of ThinPrep as the only cytopreparatory technique for most head and neck masses. CONCLUSIONS: For adequately experienced cytopathologists, ThinPrep is acceptable for FNA of salivary masses, neck cysts, metastatic lymph nodes, and thyroid lesions. Conventional smear technique should be used for FNA of nonmetastatic lymphoid lesions. Use of ThinPrep can complement use of the conventional (smear) cytopreparatory technique when aspirate is nondiagnostic or bloody, when the patient has a blood-borne infectious disease, when the clinician is inexperienced, or when aspirate has entered the syringe.  相似文献   
998.
999.
Working memory dysfunction is considered to be fundamental to the cognitive and clinical features evident in schizophrenia. Functional neuroimaging studies have begun to elucidate the neurobiological basis of such deficits, however, interpretation of these studies may be confounded by performance impairment, when the cognitive load exceeds the limited response capacity of patients with schizophrenia. In this study, patients were pre-selected on the basis of intact performance on a relatively low-load verbal working memory task, in order to mitigate against performance confounds. Subjects included 20 right-handed male subjects with chronic schizophrenia, and 20 right-handed, age-matched, male healthy controls, without personal or familial psychiatric history. All subjects underwent fMRI scanning whilst performing a verbal n-back task. There were no significant between-group differences in target identification; the patient group showed a significantly increased mean response latency. Both groups demonstrated robust fronto-parietal activation. In the control subjects, the power of functional response was positively correlated with reaction time in bilateral posterior parietal cortex, however, this coupling of behavioural performance and cerebral response was not evident in the patients. This deficit, apparent within the performance capacity of the patients, may represent a fundamental abnormality in schizophrenia, and may compromise performance at higher cognitive loads.  相似文献   
1000.
BACKGROUND: Gastric cancer (GC) is the leading cause of cancer deaths in China. Our study prospectively evaluated the impact of repeated endoscopic screens on GC mortality in a high-risk population in China. METHODS: Between 1989 and 1999, a population-based gastroscopic screening was conducted in 4,394 residents of Linqu County, China, a region with the highest rates of GC worldwide. Residents ages 35 to 64 years received initial gastroscopies with biopsies in 1989. Repeated endoscopies were performed in 1994 and 1999. Cancer occurrences and deaths were actively monitored throughout the entire period until July 2000. Mortality from GC was compared with expected values based on mortality rates obtained for Linqu in the 1990-1992 Chinese Cancer Mortality Survey. RESULTS: Between March 1989 and July 2000, 39,303 person-years were accumulated; 85 new GCs occurred, 29 (34.5%) were in early stage. Fifty-eight cases (68%) were identified at one of the screens. The number of observed deaths from GC (37) was close to the expected (36.8). The standardized mortality ratio was 1.01 (95% CI 0.72-1.37) for the entire cohort, 1.13 (95% CI 0.77-1.57) for males, and 0.65 (95% CI 0.26-1.32) for females. CONCLUSIONS: Despite high population coverage with repeated screens, no reduction in GC mortality was observed in this high-risk population in China.  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