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   706篇
  免费   0篇
化学工业   7篇
轻工业   3篇
无线电   3篇
一般工业技术   4篇
冶金工业   688篇
自动化技术   1篇
  2021年   1篇
  2014年   1篇
  2012年   1篇
  2009年   1篇
  2005年   2篇
  2004年   3篇
  2003年   1篇
  2002年   1篇
  2000年   1篇
  1999年   26篇
  1998年   215篇
  1997年   142篇
  1996年   67篇
  1995年   45篇
  1994年   39篇
  1993年   36篇
  1992年   5篇
  1991年   8篇
  1990年   7篇
  1989年   5篇
  1988年   10篇
  1987年   6篇
  1986年   7篇
  1985年   6篇
  1982年   4篇
  1981年   3篇
  1980年   7篇
  1978年   2篇
  1977年   14篇
  1976年   38篇
  1975年   1篇
  1973年   1篇
排序方式: 共有706条查询结果,搜索用时 15 毫秒
101.
102.
Forty human clinical Mycobacterium avium-M. intracellulare complex strains isolated in Greece were characterized to the species level by PCR with three sets of primers specific for one or both species. M. avium predominated in both human immunodeficiency virus-positive and -negative patients, but the frequency of M. intracellulare isolation appeared to be higher in the latter.  相似文献   
103.
104.
OBJECTIVES AND DESIGN: A prospective study of 709 patients undergoing carotid surgery in the U.K. and Ireland was performed to evaluate the performance of vascular surgeons. MATERIALS AND METHODS: Fifty-nine surgeons (range 2-39 cases each) were sampled and all patients undergoing surgery over a 6-month period (1 March 1994-31 August 1994) were included in the study. Indications for surgery were TIA (35.9%), AF (23.3%), CVA (21.4%) and "others" (19.6%). RESULTS: Mean ipsilateral stenosis was 82% (30%-99%). Thirty-one percent of patients had preoperative neurological consults. Shunts were used in 67.6%, tacking sutures in 40.1%, drains in 71.9% and patches in 54.4% of cases. At 30 days there were nine (1.3%) deaths (four cardiac, three neurological). There were 15 ipsilateral postoperative CVAs (2.1%); 19% of patients had one or more complication, usually minor. Statistical analysis showed no independent risk factor for CVA other than seniority of the surgeon. CONCLUSIONS: A combined stroke/death rate of 3% for the series was obtained at 30 days for all cases. This large, validated study suggests that members of the Vascular Society of G.B. and Ireland currently have a very low morbidity/mortality rate for performing carotid surgery. Continued audit is required to ensure that this quality of service does not deteriorate.  相似文献   
105.
Tooth loss diminishes oral function and quality of life, and national health targets aim to reduce population levels of tooth loss. OBJECTIVES: The purpose of this study was to determine tooth loss incidence and predictors of tooth loss among older adults in South Australia. METHODS: Data were obtained from a cohort study of a stratified random sample of community-dwelling dentate people aged 60+ years. Interviews and oral examinations were conducted among 911 individuals at baseline and among 693 of them (76.1%) 2 years later. Incidence rates and relative risks were calculated for population subgroups and multivariate logistic regression was used to construct risk prediction models. A method was developed to calculate 95% confidence intervals (95% CI) for relative risks (RR) from logistic regression models using a Taylor series approximation. RESULTS: Some 19.5% (95% CI = 15.4-23.6%) of people lost one or more teeth during the 2 years. Men, people with a recent extraction, people who brushed their teeth infrequently, smokers and people born outside Australia had significantly (P < 0.05) greater risk of tooth loss. Baseline clinical predictors of tooth loss included more missing teeth, retained roots, decayed root surfaces, periodontal pockets and periodontal recession. In a multivariate model that controlled for baseline clinical predictors, former smokers (RR = 2.55, 95% CI = 1.48-4.40) and current smokers (RR = 2.06, 95% CI = 0.92-4.62) had similarly elevated risks of tooth loss compared with non-smokers. CONCLUSIONS: The findings from this population suggest that a history of smoking contributes to tooth loss through mechanisms in addition to clinical disease processes alone.  相似文献   
106.
BACKGROUND: Endoscopic sclerotherapy (ST), widely used as treatment of bleeding esophageal varices, might cause motility disturbances of the esophagus as well as mucosal damage. We performed this study to evaluate the long-term effects of repeated sclerotherapy on esophageal motility and mucosa. METHODS: Ten patients with liver cirrhosis and bleeding esophageal varices treated with repeated ST were evaluated after the last ST, median 52 months, by esophageal manometry and gastroscopy where forceps biopsies were taken. RESULTS: We found a significant difference in the distal esophageal sphincter intraabdominal length. The distal esophageal sphincter pressure was somewhat lower in the ST group although the difference did not reach statistical significance. There was infiltration of neutrophil leukocytes in biopsies from four patients and normal findings in the rest. CONCLUSIONS: Long-term follow-up evaluation showed statistically longer distal esophageal intraabdominal length in the ST group. No mucosal alterations were found at the histopathological investigation.  相似文献   
107.
The mechanism of action of psoralen plus UVA (PUVA) and photopheresis is not entirely understood. These therapies are assumed to be immunomodulating partly by gradually decreasing leukocyte viability. We investigated whether this delayed form of cell death was due to apoptosis. Untreated and treated (PUVA exposed) leukocytes obtained from six patients with systemic sclerosis and (untreated) leukocytes from healthy control individuals were studied. Qualitative gel electrophoresis and quantitative in situ nick translation analysis of DNA fragmentation was performed. Apoptosis of the treated cells did occur (gel electrophoresis) after 24 h. At t = 0 h, immediately after exposure to PUVA, there was no evidence of DNA fragmentation in the treated cells. The percentage of treated cells undergoing apoptosis was 20-55% at t = 24 h (in situ nick translation). The untreated leukocytes of the patients and the healthy individuals showed no distinctive rise in apoptotic cells. Apoptosis of the leukocytes after PUVA or photopheresis treatment might be a mechanism of action and might explain the therapeutic response.  相似文献   
108.
BACKGROUND/AIMS: Liver failure in infancy can result from several disorders of the mitochondrial respiratory chain. In some patients, levels of mitochondrial DNA are markedly reduced, a phenomenon referred to as mitochondrial DNA depletion. To facilitate diagnosis of this condition, we have reviewed the clinical and pathological features in five patients with mitochondrial DNA depletion. METHODS: Cases were identified by preparing Southern blots of DNA from muscle and liver, hybridising with appropriate probes and quantifying mitochondrial DNA relative to nuclear DNA. RESULTS: All our patients with mitochondrial DNA depletion died of liver failure. Other problems included hypotonia, hypoglycaemia, neurological abnormalities (including Leigh syndrome) and cataracts. Liver histology showed geographic areas of fatty change, bile duct proliferation, collapse of liver architecture and fibrosis; some cells showed decreased cytochrome oxidase activity. Muscle from three patients showed mitochondrial proliferation, with loss of cytochrome oxidase activity in some fibres but not in others; in these cases, muscle mitochondrial DNA levels were less than 5% of the median control value. The remaining two patients (from a single pedigree) had normal muscle histology and histochemistry associated with less severe depletion of mitochondrial DNA in muscle. CONCLUSIONS: Liver failure is common in patients with mitochondrial DNA depletion. Associated clinical features often include neuromuscular disease. Liver and muscle histology can be helpful in making the diagnosis. Mitochondrial DNA levels should be measured whenever liver failure is thought to have resulted from respiratory chain disease.  相似文献   
109.
BACKGROUND: High-frequency ultrasound biomicroscopy has allowed eye care specialists to evaluate posterior extension of anterior segment tumors. This article evaluates the role of ultrasound biomicroscopy for the diagnosis and management of anterior segment tumors. METHODS: Fourteen patients with anterior segment tumors were selected for evaluation. Each patient underwent a complete clinical examination followed by slit-lamp photography and ultrasound biomicroscopy. RESULTS: Unlike standard ultrasonography of anterior segment tumors, high-frequency ultrasound biomicroscopy allowed quantitative measurements of tumor size, extension within and posterior to the iris, as well as differentiation of solid and cystic lesions. These characteristics were used to differentially diagnose anterior segment tumors and document the response of iridociliary body melanomas to radiotherapy. CONCLUSIONS: This study demonstrates how ultrasound biomicroscopy has become an effective and necessary procedure, used for both the diagnosis and management of anterior segment tumors.  相似文献   
110.
BACKGROUND AND PURPOSE: An animal model of incomplete forebrain ischemia resembling human hemodynamic insufficiency was established. The model allows examination of acute and chronic changes of local cerebral blood flow (lCBF) and reserve capacity in correlation with behavioral parameters. METHODS: Anesthetized male Wistar-Kyoto rats underwent bilateral carotid occlusion (BCO). Laser-Doppler scanning of lCBF at baseline conditions and after acetazolamide was done 30 minutes after BCO, motor and memory function tests were administered after 1 and 2 days, and both investigations were repeated after 1, 2, 4, and 6 weeks. A sham-operated and a control group without any vessel manipulation served as controls. RESULTS: lCBF dropped within 60 minutes after surgery by 62% (P<0.001) in 10 animals surviving BCO (BCOsurvival) and by 69% in 5 rats that died within 9 days (BCOlethal). Acetazolamide increased lCBF to 142.33% in controls, to 136.66% in sham-operated rats (both significant), and to 104.80% in BCOsurvival (not significant), and it decreased flow by 23.1% in BCOlethal rats (P<0.001). Baseline lCBF normalized within 4 weeks. Total motor function scores were significantly reduced from 9 points preoperatively to 5.80+/-0.65 in BCOlethal and 6.68+/-0.54 points in BCOsurvival rats 1 day after occlusion. Memory retention function remained impaired after BCO, as did the acetazolamide response, which correlated with motor score and was inversely related to maze exploration time. CONCLUSIONS: This model allows long-term follow-up of cerebral function, lCBF, and reserve capacity in a pathophysiological setting similar to hemodynamic insufficiency in humans.  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