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   369673篇
  免费   5553篇
  国内免费   717篇
电工技术   5094篇
综合类   2459篇
化学工业   58880篇
金属工艺   20509篇
机械仪表   13923篇
建筑科学   7691篇
矿业工程   4414篇
能源动力   5909篇
轻工业   18729篇
水利工程   5661篇
石油天然气   13466篇
武器工业   33篇
无线电   31125篇
一般工业技术   85346篇
冶金工业   43595篇
原子能技术   11593篇
自动化技术   47516篇
  2021年   3892篇
  2020年   3126篇
  2019年   3749篇
  2018年   20738篇
  2017年   19898篇
  2016年   17221篇
  2015年   4962篇
  2014年   7128篇
  2013年   13515篇
  2012年   12839篇
  2011年   20391篇
  2010年   17196篇
  2009年   15170篇
  2008年   16419篇
  2007年   17005篇
  2006年   7700篇
  2005年   7767篇
  2004年   7452篇
  2003年   7273篇
  2002年   6440篇
  2001年   5586篇
  2000年   5613篇
  1999年   4878篇
  1998年   9478篇
  1997年   7392篇
  1996年   5515篇
  1995年   4369篇
  1994年   3993篇
  1993年   4241篇
  1992年   3509篇
  1991年   3603篇
  1990年   3706篇
  1989年   3577篇
  1988年   3472篇
  1987年   3450篇
  1986年   3338篇
  1985年   3517篇
  1984年   3426篇
  1983年   3283篇
  1982年   3177篇
  1981年   3230篇
  1980年   3255篇
  1979年   3369篇
  1978年   3599篇
  1977年   3739篇
  1976年   4463篇
  1975年   3287篇
  1974年   3363篇
  1973年   3414篇
  1972年   3034篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
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.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.  相似文献   
9.
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   
10.
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   
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