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   4569篇
  免费   113篇
  国内免费   13篇
电工技术   253篇
综合类   4篇
化学工业   1219篇
金属工艺   164篇
机械仪表   82篇
建筑科学   77篇
矿业工程   3篇
能源动力   165篇
轻工业   376篇
水利工程   9篇
石油天然气   4篇
无线电   347篇
一般工业技术   761篇
冶金工业   805篇
原子能技术   117篇
自动化技术   309篇
  2023年   18篇
  2022年   54篇
  2021年   77篇
  2020年   44篇
  2019年   47篇
  2018年   64篇
  2017年   61篇
  2016年   94篇
  2015年   61篇
  2014年   108篇
  2013年   205篇
  2012年   156篇
  2011年   208篇
  2010年   171篇
  2009年   211篇
  2008年   211篇
  2007年   184篇
  2006年   164篇
  2005年   142篇
  2004年   139篇
  2003年   124篇
  2002年   116篇
  2001年   83篇
  2000年   81篇
  1999年   104篇
  1998年   351篇
  1997年   238篇
  1996年   161篇
  1995年   89篇
  1994年   99篇
  1993年   102篇
  1992年   67篇
  1991年   64篇
  1990年   45篇
  1989年   46篇
  1988年   31篇
  1987年   45篇
  1986年   35篇
  1985年   40篇
  1984年   31篇
  1983年   29篇
  1982年   36篇
  1981年   31篇
  1980年   30篇
  1979年   29篇
  1978年   25篇
  1977年   29篇
  1976年   46篇
  1974年   12篇
  1973年   10篇
排序方式: 共有4695条查询结果,搜索用时 15 毫秒
21.
A development of 170GHz/500kW level gyrotron was carried out as R&D work of ITER. The oscillation mode is TE31,8. In a short pulse experiment, the maximum power of 750kW was achieved at 85kV/40A. The efficiency was 22%. In the depressed collector operation, 500kW/36%/50ms was obtained. The maximum efficiency of 40% was obtained at PRF=470kW whereas the power decrease by the electron trapping was observed. Pulse extension was done up to 10s at PRF=170kW with the depressed collector operation. The power was limited by the temperature increase of the output window.  相似文献   
22.
We present a patient with continuous melena, diagnosed as rectal varices bleeding. She had a history of esophageal varices, which was treated by endoscopic ligation therapy. Eight years after the treatment of esophageal varices, the continuous melena began. Colonoscopic examination showed that the melena was caused by rectal varices, which were so severe that they could not be treated by either endoscopic sclerotherapy or surgical devascularization. Taking into considering the overall risk of treating rectal varices, we chose the approach of double balloon-occluded embolotherapy (DBOE) with 5% ethanolamine oleate with iopamodol as a liquid embolic material. DBOE is one of the interventional radiology techniques (Morita et al., Acta Hepatol Jpn 1994;35:109-120), but in this case was a completely new and novel clinical procedure for rectal varices. After the DBOE therapy, the condition of rectal varices was markedly improved. Thus, DBOE might be a new tool for treating inoperable rectal varices.  相似文献   
23.
Ti wire electrodes were immersed in acidic solutions containing H2SO4 and HCl of various concentrations at 353 K to evaluate corrosion rate by measurement of electric resistance change (resistometry). Addition of hydrochloric acid to sulphuric acid solution promoted depassivation of Ti. After depassivation, the immersion potential dropped to the hydrogen evolution potential and a hydride layer was formed on the surface. The hydride layer dissolved continuously in the acidic solution. SEM observation showed that Ti wires dissolved almost uniformly in the early stage and that the dissolution then trace became irregular due to nonuniform growth of the hydride layer. Dissolution rate of a Ti wire was estimated almost accurately by resistometry.  相似文献   
24.
The N-linked oligosaccharide moieties of sycamore (Acer pseudoplatanus L.) laccase are known to be highly heterogeneous. We confirmed that this oligosaccharide heterogeneity was caused not only during the oligosaccharide biosynthesis in Golgi apparatus, but also after the excretion of laccase protein into a culture medium. The culture medium for the sycamore cells (Acer pseudoplatanus L.) contained beta-galactosidase, alpha-L-fucosidase, beta-N-acetylglucosaminidase, alpha-mannosidase and beta-xylosidase activities. We showed that the largest sugar chain in laccase, oligosaccharide F, [formula: see text] was degraded to [formula: see text] by a crude exoglycosidase mixture in the culture medium.  相似文献   
25.
26.
The finite element method (FEM) with the high-order mixed-interpolation-type triangular element is used to solve the problem of practical microstrip lines with arbitrary metallization cross section. Analyses are carried out to produce the frequency characteristics of propagation constant, characteristic impedance, and attenuation constant of shielded microstrip lines with rectangular, trapezoidal, and semi-trapezoidal strip cross sections. A comparison of the numerical results with those of the existing results shows good agreement and thus verifies the versatility of the FEM. Also, the numerical results show the effects of the metallization cross sections on the transmission properties and thus emphasize the importance of considering the practical microstrip configurations in the design of miniaturized MMICs  相似文献   
27.
Highly reliable telecommunication networks require new technologies, such as the reliability specification, design, and evaluation method used at NTT. This paper describes the basic concepts of this method, and the ARDES-NET (Availability Reliability Design and Evaluation System for NETworks) software tool is used to support the reliability design and evaluation. ARDESNET has a user-friendly interface and can be easily put into practice  相似文献   
28.
STUDY OBJECTIVES: To determine the rates of alcohol-related morbidity and mortality in a cohort of intoxicated ED patients 5 years after presentation and to compare them with those of non-intoxicated ED patients. METHODS: The study group comprised 150 consecutive ED patients who presented with intoxication (blood alcohol level higher than 100 mg/dL) in June 1986 and 50 control patients matched for age, sex, ED arrival time, and date. The setting was an urban university hospital ED. Morbidity and mortality over a 5-year follow-up period were measured using hospital ED and admission records from all state Level I trauma centers and computerized statewide databases. RESULTS: The 5-year mortality rate among alcohol-intoxicated patients was 2.4 times that of the comparison group (95% confidence interval, .3 to 18.9). The 5-year death rate among intoxicated patients aged 40 to 69 years was especially high (19%). Thirty-seven percent of the intoxicated patients made at least one alcohol-related ED revisit during the follow-up period, compared with 6% of the comparison group (P < .001). Intoxicated patients were more likely to revisit EDs because of suicidal behavior or domestic violence (P = .001). Admission to an alcohol detoxification unit during the follow-up period occurred in 24% of the intoxicated patients, compared with 10% of the sober controls (P = .03). At least one arrest for drunk driving occurred in 47% of the intoxicated group; the rate was lower, but still substantial, in the comparison group (20%, P < .001). CONCLUSION: A single alcohol-related ED visit is an important predictor of continued problem drinking, alcohol-impaired driving and, possibly, premature death.  相似文献   
29.
30.
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