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   347808篇
  免费   2801篇
  国内免费   962篇
工业技术   351571篇
  2021年   3251篇
  2019年   3163篇
  2018年   11551篇
  2017年   12002篇
  2016年   10247篇
  2015年   3917篇
  2014年   6270篇
  2013年   12655篇
  2012年   10522篇
  2011年   16046篇
  2010年   14045篇
  2009年   13887篇
  2008年   14244篇
  2007年   15339篇
  2006年   7954篇
  2005年   8943篇
  2004年   8153篇
  2003年   7937篇
  2002年   6933篇
  2001年   6280篇
  2000年   6267篇
  1999年   5523篇
  1998年   10460篇
  1997年   8064篇
  1996年   5876篇
  1995年   4938篇
  1994年   4543篇
  1993年   4716篇
  1992年   3945篇
  1991年   4140篇
  1990年   4253篇
  1989年   4085篇
  1988年   3934篇
  1987年   3843篇
  1986年   3754篇
  1985年   3969篇
  1984年   3787篇
  1983年   3662篇
  1982年   3454篇
  1981年   3523篇
  1980年   3524篇
  1979年   3708篇
  1978年   3891篇
  1977年   4007篇
  1976年   4608篇
  1975年   3592篇
  1974年   3646篇
  1973年   3698篇
  1972年   3304篇
  1971年   3042篇
排序方式: 共有10000条查询结果,搜索用时 78 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.
4.
Multimedia Tools and Applications - Mammograms are the images used by radiologists to diagnose breast cancer. Breast cancer is one of the most common cancers in women. The early detection of breast...  相似文献   
5.
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   
6.
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   
7.
Combustion, Explosion, and Shock Waves - Results of a numerical study of mixing, ignition, and combustion of a cold hydrogen jet propagating along the lower wall of a channel parallel to a...  相似文献   
8.
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   
9.
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   
10.
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   
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