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   248624篇
  免费   1922篇
  国内免费   260篇
电工技术   4036篇
综合类   90篇
化学工业   39749篇
金属工艺   15177篇
机械仪表   10069篇
建筑科学   4164篇
矿业工程   3789篇
能源动力   3892篇
轻工业   9604篇
水利工程   4103篇
石油天然气   13055篇
武器工业   28篇
无线电   20222篇
一般工业技术   62949篇
冶金工业   32254篇
原子能技术   11161篇
自动化技术   16464篇
  2021年   2749篇
  2019年   2738篇
  2018年   5451篇
  2017年   5726篇
  2016年   6061篇
  2015年   3063篇
  2014年   5344篇
  2013年   10110篇
  2012年   7326篇
  2011年   8948篇
  2010年   7319篇
  2009年   8122篇
  2008年   8197篇
  2007年   7881篇
  2006年   6374篇
  2005年   5581篇
  2004年   5495篇
  2003年   5320篇
  2002年   5150篇
  2001年   4966篇
  2000年   4946篇
  1999年   4257篇
  1998年   7195篇
  1997年   5849篇
  1996年   4441篇
  1995年   3671篇
  1994年   3439篇
  1993年   3635篇
  1992年   3223篇
  1991年   3347篇
  1990年   3469篇
  1989年   3346篇
  1988年   3250篇
  1987年   3247篇
  1986年   3141篇
  1985年   3310篇
  1984年   3244篇
  1983年   3133篇
  1982年   2979篇
  1981年   3030篇
  1980年   3063篇
  1979年   3255篇
  1978年   3486篇
  1977年   3457篇
  1976年   3915篇
  1975年   3224篇
  1974年   3297篇
  1973年   3338篇
  1972年   2996篇
  1971年   2751篇
排序方式: 共有10000条查询结果,搜索用时 33 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