首页 | 官方网站   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   247346篇
  免费   1916篇
  国内免费   260篇
工业技术   249522篇
  2021年   2711篇
  2019年   2732篇
  2018年   5430篇
  2017年   5713篇
  2016年   6047篇
  2015年   3054篇
  2014年   5324篇
  2013年   10084篇
  2012年   7305篇
  2011年   8932篇
  2010年   7298篇
  2009年   8112篇
  2008年   8178篇
  2007年   7862篇
  2006年   6359篇
  2005年   5563篇
  2004年   5484篇
  2003年   5301篇
  2002年   5133篇
  2001年   4949篇
  2000年   4939篇
  1999年   4254篇
  1998年   7035篇
  1997年   5692篇
  1996年   4270篇
  1995年   3634篇
  1994年   3404篇
  1993年   3604篇
  1992年   3198篇
  1991年   3339篇
  1990年   3464篇
  1989年   3339篇
  1988年   3244篇
  1987年   3241篇
  1986年   3136篇
  1985年   3301篇
  1984年   3237篇
  1983年   3124篇
  1982年   2973篇
  1981年   3022篇
  1980年   3058篇
  1979年   3244篇
  1978年   3478篇
  1977年   3448篇
  1976年   3902篇
  1975年   3209篇
  1974年   3288篇
  1973年   3330篇
  1972年   2986篇
  1971年   2747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-23

京公网安备 11010802026262号