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   482756篇
  免费   9598篇
  国内免费   3976篇
电工技术   9652篇
技术理论   1篇
综合类   6427篇
化学工业   73782篇
金属工艺   27401篇
机械仪表   19308篇
建筑科学   12117篇
矿业工程   6411篇
能源动力   8470篇
轻工业   26097篇
水利工程   8136篇
石油天然气   19084篇
武器工业   506篇
无线电   45111篇
一般工业技术   105446篇
冶金工业   56162篇
原子能技术   14512篇
自动化技术   57707篇
  2021年   5738篇
  2020年   4458篇
  2019年   4974篇
  2018年   22364篇
  2017年   21632篇
  2016年   18909篇
  2015年   6897篇
  2014年   10122篇
  2013年   18252篇
  2012年   16983篇
  2011年   25668篇
  2010年   22023篇
  2009年   20465篇
  2008年   21474篇
  2007年   21882篇
  2006年   12428篇
  2005年   11843篇
  2004年   10787篇
  2003年   10134篇
  2002年   9248篇
  2001年   8503篇
  2000年   8180篇
  1999年   7304篇
  1998年   13547篇
  1997年   10378篇
  1996年   7551篇
  1995年   6105篇
  1994年   5551篇
  1993年   5722篇
  1992年   4744篇
  1991年   4826篇
  1990年   4913篇
  1989年   4685篇
  1988年   4578篇
  1987年   4428篇
  1986年   4363篇
  1985年   4564篇
  1984年   4403篇
  1983年   4276篇
  1982年   4009篇
  1981年   4188篇
  1980年   4140篇
  1979年   4413篇
  1978年   4734篇
  1977年   4797篇
  1976年   5765篇
  1975年   4345篇
  1974年   4382篇
  1973年   4453篇
  1972年   4058篇
排序方式: 共有10000条查询结果,搜索用时 987 毫秒
1.
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   
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.
Xiao  Zhu  Chen  Yanxun  Jiang  Hongbo  Hu  Zhenzhen  Lui  John C. S.  Min  Geyong  Dustdar  Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of...  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.
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel.  相似文献   
9.
Sun  Junli  Wang  Huaibin  Li  Yang  Zhao  Min 《Journal of Porous Materials》2021,28(3):889-894
Journal of Porous Materials - Co3O4 has been widely investigated as a promising candidate anode material for lithium-ion batteries. We report on the porous Co3O4 column synthesized via a simple...  相似文献   
10.
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