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   925篇
  免费   0篇
化学工业   5篇
机械仪表   1篇
无线电   1篇
冶金工业   865篇
自动化技术   53篇
  2020年   1篇
  2015年   1篇
  2014年   23篇
  2012年   6篇
  2011年   11篇
  2010年   11篇
  2006年   1篇
  2005年   2篇
  2003年   1篇
  2000年   1篇
  1999年   30篇
  1998年   266篇
  1997年   142篇
  1996年   78篇
  1995年   51篇
  1994年   38篇
  1993年   44篇
  1992年   5篇
  1991年   15篇
  1990年   9篇
  1989年   8篇
  1988年   6篇
  1987年   5篇
  1986年   9篇
  1985年   6篇
  1983年   3篇
  1982年   4篇
  1981年   8篇
  1980年   11篇
  1979年   3篇
  1978年   1篇
  1977年   33篇
  1976年   88篇
  1975年   1篇
  1955年   2篇
  1954年   1篇
排序方式: 共有925条查询结果,搜索用时 15 毫秒
101.
102.
BACKGROUND: The early detection of effects caused by radiotherapy on bone mineralisation has influence on clinical treatment. Usually the follow-up is done by conventional X-rays, presenting a loss of calcification of at least 30%. Quantitative CT-measurements are much more sensitive. PATIENTS AND METHODS: In a prospective study we evaluated the CT-scans of 14 patients with multiple vertebral metastases of mamma carcinoma. Our patients underwent SEQCT (one 10 mm slice in each affected vertebral body, 80 kV, 250 mAs) before and immediately after radiation therapy (total dose 30 Gy to 36 Gy) followed by further examinations 6 weeks and 3 months later. RESULTS: While there is no significant change in increased BMD (bone mineral density) of osteosclerotic and decreased BMD of osteolytic metastases just after therapy, the following examinations present an increase of BMD in osteolytic metastases 6 weeks after therapy more distinct 3 months after. Osteosclerotic metastases show a decline in bone density. In mixed metastases is no significant change while normal bone lying in the irradiation field demineralizes. Additive chemotherapy is very important especially for mineralisation of lytic metastases. Referring to mixed metastasis in one vertebral body we suggest a separate evaluation of the left and right side. CONCLUSION: Mineralizing effects of radiation therapy depend on the characteristics of the metastases. Supported by QCT histopathological change can be documented and exactly demonstrated to the clinician.  相似文献   
103.
104.
OBJECTIVE: To update the 1984 recommendations of the Canadian Task Force on the Periodic Health Examination on the routine screening of asymptomatic patients for infection with Chlamydia trachomatis. OPTIONS: Screening, with the use of culture or nonculture tests, of the general population, of certain high-risk groups or of all pregnant women; or no routine screening. OUTCOMES: Rates of asymptomatic and symptomatic chlamydial infection, perinatal complications, longterm complications of infection (i.e., pelvic inflammatory disease, infertility and ectopic pregnancy), coinfection with other sexually transmitted diseases, disease spread, hospital care, complications of therapy and costs of infection and of screening. EVIDENCE: Search of MEDLINE for articles published between Jan. 1, 1983, and Dec. 31, 1995, with the use of the major MeSH heading "chlamydial infections," references from recent review articles and recommendation by other organizations. VALUES: The evidence-based methods of the Canadian Task Force on the Periodic Health Examination were used. Advice from reviewers and experts and recommendations of other organizations were taken into consideration. Prevention of symptomatic disease and decreased overall costs were given high values. BENEFITS, HARMS AND COSTS: The greatest potential benefits of screening asymptomatic patients for chlamydial infections are the prevention of complications, especially infertility and perinatal complications, and the prevention of disease spread. There is no evidence that screening of the general population for chlamydial infections leads to a reduction in complications, and screening may increase costs. However, there is evidence that annual screening of selected high-risk groups and of pregnant women during the first trimester is beneficial in preventing symptoms and reducing the overall cost resulting from infection. RECOMMENDATIONS: There is fair evidence to support screening and treatment of pregnant women during the first trimester (grade B recommendation) as well as annual screening and treatment of high-risk groups (sexually active women less than 25 years of age, men or women with new or multiple sexual partners during the preceding year, women who use nonbarrier contraceptive methods and women who have symptoms of chlamydial infection: cervical friability, mucopurulent cervical discharge or intermenstrual bleeding; grade B recommendation). There is fair evidence to exclude routine screening of the general population (grade D recommendation). VALIDATION: These recommendations are similar to those of the US Preventive Services Task Force and the US Centers for Disease Control and Prevention, Atlanta. SPONSOR: These guidelines were developed and endorsed by the Canadian Task Force on the Periodic Health Examination, which is funded by Health Canada and the National Health Canada and the National Health Research and Development Program. The principal author (H.D.D.) was supported in part by the Ontario Ministry of Health and the Canadian Infectious Diseases Society Lilly Fellowship.  相似文献   
105.
With random amplified polymorphic DNA (RAPD) markers, we have tagged a genomic region in Populus sp. involved in qualitative resistance to Melampsora larici-populina. Our approach was based on three steps: use of RAPD markers that can be quickly and efficiently researched: application of "bulked segregant analysis" technique on individuals of one interspecific family P. trichocarpa x P. deltoides to search for RAPD markers linked to resistance; and validation of these markers in two other families linked with the first one in a 2 x 2 factorial mating design. Of five detected markers, only one marker M03/04_480 was polymorphic in the three segregating families, involving 89 individuals and four different parents. We have estimated the recombination value of 1 cM with 1 cM sampling error.  相似文献   
106.
AIM: To compare a thromboxane antagonist (GR3219) with aspirin in patients with prolonged chest pain and ST segment depression to see if the frequency of attacks of chest pain was reduced. METHODS: The trial was part of a study comparing GR3219 with aspirin, and streptokinase with placebo and comprised the GR3219/aspirin leg. Thirty one patients were randomly assigned to GR3219 80 mg twice daily and 28 to aspirin 300 mg daily. The patients were under the age of 76 and admitted to a coronary care unit within 6 hours of continuous chest pain. The ECG showed at least 1 mm of flat or down-going ST segment. The patients kept diaries of their pain over the subsequent 31 days. RESULTS: Seventy percent of patients developed further chest pain. There was no difference between the pattern of recurrent chest pain according to which drug was used. CONCLUSIONS: The hypothesis that specific thromboxane A blockade with GR3219 would be more efficacious than aspirin was not supported by these results.  相似文献   
107.
108.
109.
110.
The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different modalities in a short amount of time and with minimal operator intervention. METHODS: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting based on 50% of the maximum soft-tissue value in the study. These surfaces were converted into three-dimensional volumes and used to register the CT and PET studies in three dimensions using a sum of least squares fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accuracy of the fit was evaluated through a phantom study and preliminary clinical evaluation. RESULTS: A phantom study was performed to determine the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Preliminary clinical evaluation was also performed with encouraging results. CONCLUSION: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action.  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