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   1200篇
  免费   5篇
  国内免费   2篇
电工技术   1篇
综合类   3篇
化学工业   32篇
金属工艺   3篇
机械仪表   5篇
建筑科学   12篇
轻工业   21篇
水利工程   9篇
石油天然气   4篇
无线电   22篇
一般工业技术   31篇
冶金工业   1053篇
原子能技术   3篇
自动化技术   8篇
  2021年   2篇
  2017年   2篇
  2015年   1篇
  2014年   3篇
  2013年   9篇
  2012年   1篇
  2011年   7篇
  2010年   7篇
  2009年   5篇
  2008年   9篇
  2007年   8篇
  2006年   8篇
  2005年   8篇
  2004年   6篇
  2003年   10篇
  2002年   4篇
  2001年   2篇
  2000年   6篇
  1999年   35篇
  1998年   370篇
  1997年   195篇
  1996年   119篇
  1995年   58篇
  1994年   36篇
  1993年   77篇
  1992年   6篇
  1991年   13篇
  1990年   5篇
  1989年   10篇
  1988年   8篇
  1987年   7篇
  1986年   9篇
  1985年   11篇
  1984年   4篇
  1983年   3篇
  1982年   9篇
  1981年   7篇
  1980年   11篇
  1979年   5篇
  1978年   4篇
  1977年   16篇
  1976年   73篇
  1975年   3篇
  1974年   1篇
  1971年   3篇
  1970年   3篇
  1969年   1篇
  1966年   2篇
  1963年   2篇
  1956年   1篇
排序方式: 共有1207条查询结果,搜索用时 15 毫秒
91.
A 77-year-old man was admitted because of massive pericardial effusion and cardiac tumor. Cytological examination of the effusion and histological examination of a subcutaneous tumor in the chest wall revealed diffuse large B cell lymphoma. The immunophenotype of tumor cells was CD5+ CD20+ CD22+ CD38+ HLA-DR+ CD19-. Chromosome analysis revealed complex abnormal karyotypes containing t(8;14) (q24;q32). C-myc gene rearrangement was shown by Southern blotting. Chemotherapy with pirarubicin, cyclophosphamide, vincristin, and prednisolone (THP-COP) was not effective for his lymphoma. He suffered from cardiac tamponade and died at 5 months after diagnosis. Autopsy revealed a large cardiac tumor, extensive epicardial infiltration, tiny tumors in the lung and pancreas, but no lymphadenopathy, the combination of which suggested a primary cardiac lymphoma. Immunohistochemistry for p53 protein showed nuclear staining of more than 50% of the lymphoma cells. In situ hybridization for EBER-1 was negative. Rearrangement of c-myc gene and overexpression of p53 protein are usually observed in Burkitt's lymphoma and some cases of high grade lymphomas including AIDS-associated non-Hodgkin lymphomas. In this case the association of these molecular findings and resistance to chemotherapy is suggested.  相似文献   
92.
93.
Pregnancy outcomes in women with a false-positive midtrimester multiple marker screening test (MMST) were reviewed. A genetic database was used to identify all women > or = age 30 who had a MMST at 15-20 weeks of gestation, a targeted ultrasound, and amniocentesis, and complete pregnancy outcome data. All patients with an abnormal fetal ultrasound (US) or karyotype were excluded. The incidence of adverse outcomes (defined as fetal death, preterm delivery, or a birth weight less than the 10th percentile for gestational age), in those women with a positive MMST (risk of Down's syndrome > or = 1:190) was compared to the incidence of adverse outcomes in control women with negative MMST. Chi-square analysis and Fisher's exact tests were used for comparisons as appropriate. Complete data was available from 1135 women. Seventy-seven percent were over age 35. Two hundred and forty-six women (22%) had a positive multiple marker test. No significant differences in outcomes were discovered after comparisons to controls: fetal death 1 of 246 (0.4%) versus 12 of 889 (1.3%), p = 0.32; preterm delivery 32 of 246 (13.0%) versus 147 of 889 (16.5%), p = 0.17; birth weight less than the 10th percentile, 9 of 246 (3.7%) versus 30 of 889 (3.4%), p = 0.83. Our data suggest that women > or = age 30 with a false-positive MMST and a normal midtrimester obstetrical sonogram are not at an increased risk for adverse pregnancy outcomes in later gestation.  相似文献   
94.
95.
Since the Latin American cholera epidemic began in 1991, 447 isolates of Vibrio cholerae O1 from the Western Hemisphere have been assayed by multilocus enzyme electrophoresis (MEE) to determine allelic variation among 16 enzyme-encoding genes. Two electrophoretic types (ETs) were identified among toxigenic isolates from Latin America: 323 were ET 4, the ET associated with the Latin American epidemic, and 29 were ET 3. Twenty-three of these ET 3 isolates had a distinctive antimicrobial resistance pattern also seen in isolates imported into the United States from Latin America and Southeast Asia. These resistant isolates had an identical ribotype and nearly identical pulsed-field gel electrophoresis (PFGE) patterns. Most nontoxigenic isolates analyzed were not precursors or descendants of toxigenic epidemic strains. MEE provided a population genetic frame-work for the interpretation of PFGE and ribotype data from the isolates in this study. All three methods identified 2 distinct strains of toxigenic V. cholerae O1 currently epidemic in Latin America.  相似文献   
96.
A case-control study of traffic risk factors and child pedestrian injury   总被引:1,自引:0,他引:1  
BACKGROUND: Pedestrian injuries in children constitute an important cause of mortality and morbidity. Specific hazards which contribute to these injuries need to be identified to enable the development of preventive strategies. METHODS: A population-based case-control study was conducted in which 40 aspects of traffic and road environment that contribute to the likelihood of childhood pedestrian injury were examined. The factors of interest were measured at 100 places of injury and 200 control sites between December 1991 and December 1993. RESULTS: The volume of traffic (odds ratio [OR] = 2.16 for an increase of 100 vehicles per hour) in combination with the proportion of vehicles exceeding the speed limit (OR = 1.04) for each 1% increase in average speed, and the presence of footpaths (OR = 11.0) were associated with significant increase in the risk of injury. A graded inverse relationship was present between socioeconomic status and the odds of pedestrian injury. CONCLUSIONS: These findings have obvious implications for public health as features of the physical environment are potentially modifiable.  相似文献   
97.
98.
99.
BACKGROUND: There is no satisfactory medical therapy for patients with primary sclerosing cholangitis. Ursodiol (ursodeoxycholic acid) benefits patients with primary biliary cirrhosis, another cholestatic liver disease. METHODS: From May 1989 to July 1995, we enrolled 105 patients with well-documented primary sclerosing cholangitis in a randomized, double-blind study comparing ursodiol (13 to 15 mg per kilogram of body weight per day in divided doses) with placebo. The primary outcome was the time to treatment failure, defined as death; liver transplantation; histologic progression by two stages (of four) or progression to cirrhosis; the development of varices, ascites, or encephalopathy; sustained quadrupling of the serum bilirubin concentration; marked worsening of fatigue or pruritus; inability to tolerate the drug; or voluntary withdrawal from the study. RESULTS: We analyzed data on the 51 patients in each group with at least 3 months of follow-up; the median follow-up was 2.2 years. There was no significant difference between the groups in time to treatment failure (relative risk of treatment failure in the ursodiol group, 1.01; 95 percent confidence interval, 0.6 to 1.7). During the first two years of follow-up, treatment was unsuccessful in 17 of 32 patients (53 percent) in the placebo group and 16 of 31 (52 percent) in the ursodiol group. There were also no differences in time to treatment failure for patients with early-stage disease or in time to liver transplantation. Ursodiol, but not placebo, was associated with improvement in serum alkaline phosphatase, aspartate aminotransferase, bilirubin, and albumin levels at one and two years. CONCLUSIONS: In a group of patients with well-defined primary sclerosing cholangitis, ursodiol provided no clinical benefit.  相似文献   
100.
To evaluate the usefulness of transendoscopic sonography we studied two new sono probes 6 F in diameter in 17 fresh specimens. We saw precise imaging of well-known anatomical structures and also gained an additional dimension in endoscopy, as the sono adds to the endo-view a transverse scan like a mini-CT at the tip of the probe. We also experienced the navigation characteristic of this imaging technique, both in real time and on line. Some 3-D reconstructions of the ventricular system were examined. The equipment has been used in clinical practice and must now be adapted for neurosurgery.  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