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   483866篇
  免费   7587篇
  国内免费   1337篇
电工技术   8141篇
综合类   317篇
化学工业   76204篇
金属工艺   20463篇
机械仪表   14785篇
建筑科学   11270篇
矿业工程   3582篇
能源动力   11220篇
轻工业   40582篇
水利工程   5776篇
石油天然气   12711篇
武器工业   40篇
无线电   50789篇
一般工业技术   98390篇
冶金工业   87774篇
原子能技术   12239篇
自动化技术   38507篇
  2021年   4548篇
  2019年   4189篇
  2018年   7847篇
  2017年   7860篇
  2016年   8409篇
  2015年   5247篇
  2014年   8463篇
  2013年   21522篇
  2012年   13411篇
  2011年   16963篇
  2010年   13689篇
  2009年   15138篇
  2008年   15725篇
  2007年   15315篇
  2006年   13221篇
  2005年   12134篇
  2004年   11244篇
  2003年   10809篇
  2002年   10642篇
  2001年   10398篇
  2000年   9890篇
  1999年   10103篇
  1998年   25915篇
  1997年   18580篇
  1996年   14145篇
  1995年   10564篇
  1994年   9355篇
  1993年   9434篇
  1992年   7012篇
  1991年   6967篇
  1990年   6685篇
  1989年   6662篇
  1988年   6571篇
  1987年   5631篇
  1986年   5718篇
  1985年   6512篇
  1984年   6163篇
  1983年   5711篇
  1982年   5328篇
  1981年   5424篇
  1980年   5310篇
  1979年   5224篇
  1978年   5329篇
  1977年   5973篇
  1976年   7589篇
  1975年   4829篇
  1974年   4576篇
  1973年   4702篇
  1972年   4084篇
  1971年   3737篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the...  相似文献   
2.
3.
4.
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   
5.
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   
6.
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical...  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.
Multimedia Tools and Applications - The three-dimensional models of brain tumors serve as diagnostic assistance for physicians, surgeons, and radiologists. The proposed system establishes an...  相似文献   
9.
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   
10.
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   
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