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   331592篇
  免费   2936篇
  国内免费   675篇
电工技术   4812篇
综合类   2406篇
化学工业   51454篇
金属工艺   19856篇
机械仪表   13060篇
建筑科学   6318篇
矿业工程   4317篇
能源动力   5022篇
轻工业   13264篇
水利工程   5328篇
石油天然气   13349篇
武器工业   28篇
无线电   29432篇
一般工业技术   78669篇
冶金工业   34851篇
原子能技术   11383篇
自动化技术   41654篇
  2021年   2790篇
  2019年   2769篇
  2018年   19615篇
  2017年   18794篇
  2016年   15843篇
  2015年   3665篇
  2014年   5591篇
  2013年   10387篇
  2012年   10404篇
  2011年   18169篇
  2010年   15439篇
  2009年   13574篇
  2008年   14837篇
  2007年   15532篇
  2006年   6508篇
  2005年   6767篇
  2004年   6591篇
  2003年   6474篇
  2002年   5684篇
  2001年   5072篇
  2000年   5134篇
  1999年   4328篇
  1998年   7289篇
  1997年   5903篇
  1996年   4496篇
  1995年   3687篇
  1994年   3458篇
  1993年   3659篇
  1992年   3249篇
  1991年   3407篇
  1990年   3508篇
  1989年   3382篇
  1988年   3289篇
  1987年   3277篇
  1986年   3172篇
  1985年   3325篇
  1984年   3267篇
  1983年   3159篇
  1982年   3004篇
  1981年   3063篇
  1980年   3084篇
  1979年   3272篇
  1978年   3499篇
  1977年   3470篇
  1976年   3922篇
  1975年   3213篇
  1974年   3296篇
  1973年   3347篇
  1972年   2991篇
  1971年   2757篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
1.
Journal of Communications Technology and Electronics - A quantitative comparison of the spectral characteristics of the human visual system and matrix photodetectors is carried out. Criteria for a...  相似文献   
2.
Wireless Personal Communications - Chronic kidney disease (CKD) is a gradual loss of kidney function over the period of time and it is irrevocable once functionality reaches the critical state....  相似文献   
3.
Objective

Neonatal brain and cardiac imaging would benefit from the increased signal-to-noise ratio levels at 7 T compared to lower field. Optimal performance might be achieved using purpose designed RF coil arrays. In this study, we introduce an 8-channel dipole array and investigate, using simulations, its RF performances for neonatal applications at 7 T.

Methods

The 8-channel dipole array was designed and evaluated for neonatal brain/cardiac configurations in terms of SAR efficiency (ratio between transmit-field and maximum specific-absorption-rate level) using adjusted dielectric properties for neonate. A birdcage coil operating in circularly polarized mode was simulated for comparison. Validation of the simulation model was performed on phantom for the coil array.

Results

The 8-channel dipole array demonstrated up to 46% higher SAR efficiency levels compared to the birdcage coil in neonatal configurations, as the specific-absorption-rate levels were alleviated. An averaged normalized root-mean-square-error of 6.7% was found between measured and simulated transmit field maps on phantom.

Conclusion

The 8-channel dipole array design integrated for neonatal brain and cardiac MR was successfully demonstrated, in simulation with coverage of the baby and increased SAR efficiency levels compared to the birdcage. We conclude that the 8Tx-dipole array promises safe operating procedures for MR imaging of neonatal brain and heart at 7 T.

  相似文献   
4.
Refractories and Industrial Ceramics - The paper introduces a promising technology for utilizing a traditional scheme for implementing a flow-through micro-arc oxidation method to restore localized...  相似文献   
5.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread...  相似文献   
6.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
7.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  相似文献   
8.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  相似文献   
9.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
10.
Glass and Ceramics - Ceramic bricks based on low-melting clay and ferro-dust from self-disintegrating, low-carbon, ferrochrome slags, graded from M100 to M175, respectively, were obtained in the...  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