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   1426篇
  免费   1篇
  国内免费   1篇
综合类   2篇
化学工业   7篇
轻工业   3篇
无线电   2篇
一般工业技术   3篇
冶金工业   1407篇
自动化技术   4篇
  2021年   1篇
  2018年   1篇
  2011年   2篇
  2010年   5篇
  2008年   1篇
  2007年   1篇
  2005年   1篇
  2004年   1篇
  2003年   2篇
  2000年   1篇
  1999年   36篇
  1998年   451篇
  1997年   257篇
  1996年   145篇
  1995年   81篇
  1994年   79篇
  1993年   81篇
  1992年   13篇
  1991年   21篇
  1990年   20篇
  1989年   18篇
  1988年   19篇
  1987年   10篇
  1986年   17篇
  1985年   12篇
  1983年   1篇
  1982年   5篇
  1981年   7篇
  1980年   11篇
  1978年   1篇
  1977年   30篇
  1976年   93篇
  1975年   3篇
  1955年   1篇
排序方式: 共有1428条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
This study assessed the presence of cytomegalovirus (CMV) in bronchoalveolar lavage (BAL) in three subpopulations of HIV-infected patients and correlated its presence with clinical status during 3 mo of follow-up. Nineteen asymptomatic volunteers, six patients with CMV retinitis, and 46 patients with acute pulmonary symptoms underwent BAL and were assessed for CMV by cytopathology, conventional shell vial cultures, and antigen detection. Transbronchial biopsies were also obtained when possible and evaluated for histopathologic changes of CMV. All patients were followed for approximately 3 mo. Cytomegalovirus was detected in BAL in nine of 19 (47%) asymptomatic volunteers, in all six patients with CMV retinitis, and in 33 of 46 (72%) patients with pulmonary symptoms. Only one symptomatic patient with a positive CMV BAL culture developed clinically significant CMV pulmonary disease; this patient developed disseminated CMV and died. The only other death occurred in a patient with CMV retinitis who developed staphylococcal bacteremia. None of the asymptomatic volunteers or patients with CMV retinitis developed evidence of CMV pneumonia or any other organ disease with CMV. Cytomegalovirus is frequently detected in BAL from HIV-infected patients regardless of their pulmonary symptoms and its presence does not clinically predict significant pulmonary morbidity or mortality in 3 mo of follow-up.  相似文献   
105.
106.
107.
BACKGROUND AND OBJECTIVE: To evaluate the adjunctive use of mitomycin-C (MMC) during trabeculotomy and trabeculectomy for eyes with high-risk congenital glaucoma. PATIENTS AND METHODS: A prospective, randomized, double-blind study was performed to compare the effect of a single, 4-minute intraoperative exposure to 0.2 mg/ml (group 1) or 0.4 mg/ml (group 2) of MMC on trabeculotomy with trabeculectomy in 16 high-risk cases (30 eyes) of congenital glaucoma. RESULTS: The preoperative and final postoperative intraocular pressures (IOPs) of the two groups did not differ significantly. At the final follow-up, IOP control (< 21 mm Hg) without medications was achieved in 60% of the eyes in group 1 and in 86.67% of the eyes in group 2 (P = 21). With medication, IOP control was achieved in 86.7% of the eyes of each group. In both groups, the rate of surgical failure was 13.3%. Avascular, thin, sharply demarcated blebs were noted in 33.3% of the eyes from group 1 and in 66.67% of those from group 2 (P = .14). Intraoperative and postoperative hyphema and postoperative hypotony were the complications encountered in both groups, whereas serous choroidal detachment and wound leakage were seen only in group 2. CONCLUSIONS: Intraoperative MMC applied at a concentration of 0.2 mg/ml controlled postoperative IOP as effectively as a 0.4-mg/ml concentration in high-risk cases of congenital glaucoma, but with a lower incidence of complications and thin-walled blebs.  相似文献   
108.
OBJECTIVE: To determine whether neurological and psychiatric symptoms predict survival time among patients with Alzheimer disease (AD) after adjusting for the influence of sociodemographic variables, health conditions, and dementia severity separately for men and women. DESIGN: The sample consisted of 936 men and women diagnosed as having probable or possible AD at 1 of 7 Alzheimer's Disease Diagnostic and Treatment Centers throughout California from 1986 through 1990. Data on dementia severity, comorbid conditions, and demographic characteristics were collected at the time of AD diagnosis. Data on vital status and dates of death were obtained by linking the patient file to several administrative databases maintained by the California State and federal governments. The mean length of follow-up was 31 months. Data were analyzed with Kaplan-Meier survival curves and Cox proportional hazards models. RESULTS: Men had shorter survival times than did women (log-rank test, 30.93, P < .001). Among men, but not women, survival times were negatively associated with selected neurological and psychiatric symptoms. Among women, but not men, a history of cardiovascular conditions was associated with poorer survival. CONCLUSIONS: Patterns of survival and predictors of survival time among patients with AD differ by sex. Future studies of survival and progression of AD need to examine men and women separately.  相似文献   
109.
BACKGROUND: The purpose of this study was to analyse which lifestyle parameters (daily physical activity, dietary intake, smoking habits and alcohol consumption) discriminate between participants at high-risk and those at low-risk for coronary heart disease (CHD) [systolic and diastolic blood pressure (SBP/DBP), total serum cholesterol (TC), high-density lipoprotein cholesterol (HDL), the TC: HDL ratio, body fatness (sum of skinfolds [SSF]) and cardiopulmonary fitness (VO2-max)]. METHODS: The data were derived from the Amsterdam Growth and Health Study (AGHS); an observational longitudinal study in which six repeated measurements were carried out over a period of 15 years on 181 participants aged 13 years at entry to the study. To assess possible discriminating factors, generalized estimating equations were used. This method makes use of risk group changing behaviour over time by using all available longitudinal data. RESULTS: For DBP no significant relationships were found; high risk for SBP was inversely related to smoking habits (OR=0.52; P<0.01). No significant relationships were found for TC; high risk for HDL was positively related to the intake of carbohydrates (OR=1.2; P=0.02) and to smoking habits (OR=1.6; P=0.04); high risk for the TC:HDL ratio was positively related to the intake of carbohydrates (OR=1.3; P=0.01). High risk for SSF was positively related to the intake of protein (OR=1.5; P<0.01) and smoking habits (OR=1.8; P=0.01) and inversely related to daily physical activity (OR=0.81; P=0.01). High risk for VO2-max was inversely related to daily physical activity (OR=0.67; P<0.01). CONCLUSIONS: In the relative young and healthy population of the AGHS during adolescence and young adulthood, physical inactivity was the most important lifestyle parameter related to high risk for CHD.  相似文献   
110.
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