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   609253篇
  免费   7225篇
  国内免费   1657篇
电工技术   11338篇
综合类   500篇
化学工业   96239篇
金属工艺   24971篇
机械仪表   19730篇
建筑科学   13648篇
矿业工程   4550篇
能源动力   15629篇
轻工业   49952篇
水利工程   7418篇
石油天然气   15903篇
武器工业   77篇
无线电   64504篇
一般工业技术   125057篇
冶金工业   103472篇
原子能技术   16040篇
自动化技术   49107篇
  2021年   5886篇
  2020年   4308篇
  2019年   5580篇
  2018年   9784篇
  2017年   10030篇
  2016年   10501篇
  2015年   6490篇
  2014年   10959篇
  2013年   28083篇
  2012年   16903篇
  2011年   22549篇
  2010年   18190篇
  2009年   20244篇
  2008年   20452篇
  2007年   20158篇
  2006年   17504篇
  2005年   15797篇
  2004年   15104篇
  2003年   14737篇
  2002年   14280篇
  2001年   13875篇
  2000年   13312篇
  1999年   12999篇
  1998年   30194篇
  1997年   21832篇
  1996年   16944篇
  1995年   13050篇
  1994年   11782篇
  1993年   11527篇
  1992年   8964篇
  1991年   8771篇
  1990年   8659篇
  1989年   8401篇
  1988年   8057篇
  1987年   7306篇
  1986年   7076篇
  1985年   7956篇
  1984年   7192篇
  1983年   6892篇
  1982年   6223篇
  1981年   6320篇
  1980年   6055篇
  1979年   6127篇
  1978年   6027篇
  1977年   6672篇
  1976年   8319篇
  1975年   5466篇
  1974年   5259篇
  1973年   5292篇
  1972年   4585篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Sanad  M. H.  Marzook  F.  Saleh  G. M.  Farag  A. B.  Talaat  H. M. 《Radiochemistry》2019,61(4):478-482
Radiochemistry - Azathioprine, an antitumor agent, was labeled with 99mTc using stannous chloride dihydrate as a reducing agent. Factors such as the amounts of the reducing agent and substrate, pH,...  相似文献   
142.
143.
Electrospark treatment of OT4-1 titanium alloy was performed sequentially with a STIM-20N hard-alloy electrode (TiC–20% Ni) and carbon-containing material (graphite and carbon-based composite materials). Kinetics of the mass transfer of the hard-alloy electrode was studied. The cathode mass loss during the first minute of the treatment was established. The kinetics results were processed using the methods of mathematical statistics. The erosion resistance of the applied carbon-containing materials was determined. Phase composition and relief of the coatings formed were analyzed. It was found that the application of the carbon-containing material increases the content of refractory phases in the coatings. Increase in the time of the treatment using the carbon-containing materials decreases the roughness of the coatings.  相似文献   
144.
Estimation of earth-fill dam height and dimension of spillway are strongly depend on accurate evaluation of dam overtopping reliability. Ideally, whole random and effective variables on overtopping should be considered for dam overtopping reliability assessment. However, taking into account all affecting random variables as well as overtopping reliability assessment using algorithms such as Monte Carlo (MC) could be excessively time consuming and impossible in some cases. In this study, new approach has been introduced as conditional reliability method and it has been tried to reduce the simulations time significantly by using combination of rainfall threshold theory, SUFI (Sequential Uncertainty Fitting) and MC methods. According two defined indexes, the obtain results shown, the relative error of new approach in computation of Jamishan dam overtopping reliability is less than 0.23%. Also, time saving in new method against to regular MC method is more than 87%. So, the new introduced method has more efficiency with acceptable accuracy for assessment of dam overtopping reliability. In addition, among hydrological and hydraulic uncertainties, hydrological uncertainties have more effect on overtopping reliability.  相似文献   
145.
146.
147.
148.
149.
Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives: (1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards.  相似文献   
150.
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