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   377155篇
  免费   4906篇
  国内免费   444篇
电工技术   5810篇
综合类   208篇
化学工业   61214篇
金属工艺   20280篇
机械仪表   13547篇
建筑科学   7151篇
矿业工程   4558篇
能源动力   6683篇
轻工业   22009篇
水利工程   5931篇
石油天然气   16642篇
武器工业   36篇
无线电   31245篇
一般工业技术   87996篇
冶金工业   57329篇
原子能技术   13712篇
自动化技术   28154篇
  2021年   4252篇
  2019年   4154篇
  2018年   7915篇
  2017年   8121篇
  2016年   8619篇
  2015年   4795篇
  2014年   7886篇
  2013年   16487篇
  2012年   11415篇
  2011年   13684篇
  2010年   11213篇
  2009年   12150篇
  2008年   12234篇
  2007年   11864篇
  2006年   9723篇
  2005年   8647篇
  2004年   8379篇
  2003年   8107篇
  2002年   7853篇
  2001年   7600篇
  2000年   7386篇
  1999年   6891篇
  1998年   14784篇
  1997年   11156篇
  1996年   8233篇
  1995年   6389篇
  1994年   5766篇
  1993年   5994篇
  1992年   4789篇
  1991年   4902篇
  1990年   4977篇
  1989年   4791篇
  1988年   4693篇
  1987年   4540篇
  1986年   4457篇
  1985年   4666篇
  1984年   4493篇
  1983年   4376篇
  1982年   4124篇
  1981年   4314篇
  1980年   4259篇
  1979年   4476篇
  1978年   4792篇
  1977年   4988篇
  1976年   6207篇
  1975年   4373篇
  1974年   4421篇
  1973年   4517篇
  1972年   4070篇
  1971年   3719篇
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
1.
2.
Grachev  A. I. 《Semiconductors》2022,56(2):67-70
Semiconductors - In this work, we discuss for the first time the principle of rotation in the constant electric field of a conducting particle with participation of the Lorentz force, which ensures...  相似文献   
3.
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   
4.
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   
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