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   311913篇
  免费   4339篇
  国内免费   1072篇
电工技术   4875篇
综合类   156篇
化学工业   50691篇
金属工艺   18373篇
机械仪表   11929篇
建筑科学   5758篇
矿业工程   3922篇
能源动力   5698篇
轻工业   16552篇
水利工程   4644篇
石油天然气   13940篇
武器工业   33篇
无线电   24704篇
一般工业技术   76534篇
冶金工业   44782篇
原子能技术   11743篇
自动化技术   22990篇
  2021年   3697篇
  2020年   3011篇
  2019年   3709篇
  2018年   7142篇
  2017年   7423篇
  2016年   7837篇
  2015年   4450篇
  2014年   7094篇
  2013年   14505篇
  2012年   10213篇
  2011年   12107篇
  2010年   9893篇
  2009年   10780篇
  2008年   10709篇
  2007年   10474篇
  2006年   8302篇
  2005年   7232篇
  2004年   7100篇
  2003年   6762篇
  2002年   6543篇
  2001年   6284篇
  2000年   6094篇
  1999年   5503篇
  1998年   11051篇
  1997年   8616篇
  1996年   6585篇
  1995年   5048篇
  1994年   4519篇
  1993年   4748篇
  1992年   3888篇
  1991年   4011篇
  1990年   4024篇
  1989年   3880篇
  1988年   3686篇
  1987年   3662篇
  1986年   3512篇
  1985年   3702篇
  1984年   3569篇
  1983年   3428篇
  1982年   3291篇
  1981年   3356篇
  1980年   3441篇
  1979年   3523篇
  1978年   3736篇
  1977年   3956篇
  1976年   4844篇
  1975年   3436篇
  1974年   3489篇
  1973年   3557篇
  1972年   3165篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
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   
3.
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   
4.
5.
6.
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   
7.
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   
8.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
9.
Water Resources Management - The water evaluation and planning (WEAP) approach and the invasive weed optimization algorithm (IWOA) are herein employed to determine the optimal operating policies in...  相似文献   
10.
Photoresponsive biomaterials are experiencing a transition from in vitro models to in vivo demonstrations that point toward clinical translation. Dynamic hydrogels for cell encapsulation, light-responsive carriers for controlled drug delivery, and nanomaterials containing photosensitizers for photodynamic therapy are relevant examples. Nonetheless, the step to the clinic largely depends on their combination with technologies to bring light into the body. This review highlights the challenge of photoactivation in vivo, and presents strategies for light management that can be adopted for this purpose. The authors’ focus is on technologies that are materials-driven, particularly upconversion nanoparticles that assist in “direct path” light delivery through tissue, and optical waveguides that “clear the path” between external light source and in vivo target. The authors’ intention is to assist the photoresponsive biomaterials community transition toward medical technologies by presenting light delivery concepts that can be integrated with the photoresponsive targets. The authors also aim to stimulate further innovation in materials-based light delivery platforms by highlighting needs and opportunities for in vivo photoactivation of biomaterials.  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