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   250620篇
  免费   1936篇
  国内免费   264篇
电工技术   4051篇
综合类   91篇
化学工业   40520篇
金属工艺   15202篇
机械仪表   10097篇
建筑科学   4234篇
矿业工程   3765篇
能源动力   3889篇
轻工业   9799篇
水利工程   4092篇
石油天然气   13014篇
武器工业   28篇
无线电   20352篇
一般工业技术   63073篇
冶金工业   32879篇
原子能技术   11165篇
自动化技术   16569篇
  2021年   2762篇
  2019年   2736篇
  2018年   5440篇
  2017年   5722篇
  2016年   6069篇
  2015年   3065篇
  2014年   5344篇
  2013年   10143篇
  2012年   7345篇
  2011年   8977篇
  2010年   7323篇
  2009年   8137篇
  2008年   8211篇
  2007年   7909篇
  2006年   6395篇
  2005年   5602篇
  2004年   5521篇
  2003年   5332篇
  2002年   5170篇
  2001年   4970篇
  2000年   4979篇
  1999年   4305篇
  1998年   7381篇
  1997年   5937篇
  1996年   4514篇
  1995年   3701篇
  1994年   3474篇
  1993年   3679篇
  1992年   3252篇
  1991年   3382篇
  1990年   3497篇
  1989年   3393篇
  1988年   3283篇
  1987年   3287篇
  1986年   3180篇
  1985年   3349篇
  1984年   3297篇
  1983年   3181篇
  1982年   3024篇
  1981年   3081篇
  1980年   3102篇
  1979年   3273篇
  1978年   3507篇
  1977年   3485篇
  1976年   3968篇
  1975年   3223篇
  1974年   3311篇
  1973年   3354篇
  1972年   2999篇
  1971年   2764篇
排序方式: 共有10000条查询结果,搜索用时 140 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