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   249692篇
  免费   1945篇
  国内免费   263篇
电工技术   4046篇
综合类   94篇
化学工业   40178篇
金属工艺   15161篇
机械仪表   10074篇
建筑科学   4217篇
矿业工程   3758篇
能源动力   3897篇
轻工业   9818篇
水利工程   4097篇
石油天然气   13039篇
武器工业   28篇
无线电   20269篇
一般工业技术   62914篇
冶金工业   32614篇
原子能技术   11147篇
自动化技术   16549篇
  2021年   2755篇
  2019年   2740篇
  2018年   5442篇
  2017年   5722篇
  2016年   6057篇
  2015年   3066篇
  2014年   5345篇
  2013年   10144篇
  2012年   7319篇
  2011年   8951篇
  2010年   7331篇
  2009年   8134篇
  2008年   8215篇
  2007年   7887篇
  2006年   6409篇
  2005年   5585篇
  2004年   5511篇
  2003年   5335篇
  2002年   5166篇
  2001年   4974篇
  2000年   4955篇
  1999年   4288篇
  1998年   7274篇
  1997年   5896篇
  1996年   4472篇
  1995年   3691篇
  1994年   3457篇
  1993年   3659篇
  1992年   3242篇
  1991年   3387篇
  1990年   3505篇
  1989年   3393篇
  1988年   3283篇
  1987年   3273篇
  1986年   3173篇
  1985年   3333篇
  1984年   3260篇
  1983年   3162篇
  1982年   3004篇
  1981年   3055篇
  1980年   3077篇
  1979年   3264篇
  1978年   3502篇
  1977年   3478篇
  1976年   3933篇
  1975年   3222篇
  1974年   3299篇
  1973年   3350篇
  1972年   2996篇
  1971年   2759篇
排序方式: 共有10000条查询结果,搜索用时 15 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