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   331232篇
  免费   4692篇
  国内免费   1404篇
电工技术   6550篇
技术理论   1篇
综合类   1795篇
化学工业   52119篇
金属工艺   22000篇
机械仪表   14583篇
建筑科学   7486篇
矿业工程   5022篇
能源动力   5338篇
轻工业   13197篇
水利工程   5423篇
石油天然气   15099篇
武器工业   246篇
无线电   28219篇
一般工业技术   80475篇
冶金工业   37536篇
原子能技术   12054篇
自动化技术   30185篇
  2021年   4189篇
  2020年   3319篇
  2019年   3686篇
  2018年   12109篇
  2017年   12741篇
  2016年   10818篇
  2015年   4833篇
  2014年   7170篇
  2013年   12397篇
  2012年   11296篇
  2011年   16500篇
  2010年   14540篇
  2009年   14060篇
  2008年   14297篇
  2007年   15245篇
  2006年   7908篇
  2005年   9030篇
  2004年   7717篇
  2003年   7332篇
  2002年   6315篇
  2001年   5536篇
  2000年   5732篇
  1999年   5002篇
  1998年   7900篇
  1997年   6412篇
  1996年   4974篇
  1995年   4093篇
  1994年   3807篇
  1993年   3927篇
  1992年   3446篇
  1991年   3562篇
  1990年   3617篇
  1989年   3475篇
  1988年   3380篇
  1987年   3328篇
  1986年   3208篇
  1985年   3362篇
  1984年   3293篇
  1983年   3172篇
  1982年   3010篇
  1981年   3064篇
  1980年   3099篇
  1979年   3277篇
  1978年   3511篇
  1977年   3483篇
  1976年   3945篇
  1975年   3218篇
  1974年   3300篇
  1973年   3348篇
  1972年   2995篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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   
2.
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   
3.
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   
4.
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   
5.
Multimedia Tools and Applications - In geometry-based point cloud compression, the geometry information is typically compressed using octree coding. In octree coding, the size of the blocks in the...  相似文献   
6.
This work evaluated the synergistic effects of combined high-intensity ultrasound (HIU) with β-cyclodextrin (β-CD) treatments on inhibiting browning of apple juice and explored the mechanism through simulation system. The combined treatment of 300 W HIU with 0.006 g mL−1 β-CD had a synergistic impact on maintaining juice colour, resulting in a 39.06% reduction in browning degree, only a 36.64% decrease in total phenolic content, and a 17.82% reduction in PPO activity. The inhibition of enzymatic browning in simulated system revealed that HIU suppressed the enzyme (Polyphenol oxidase, PPO) and β-CD inhibited enzyme (PPO) and embedded substrate (polyphenol). The results of spectroscopic analysis showed that the particle-size distribution of PPO narrowed, the content of α-helix in the secondary structure increased, the fluorescence intensity increased, and the maximum wavelength was red-shifted after HIU and β-CD treatment. Changes in structure could further result in PPO activity loss. Hence, the combined treatment could synthetically alleviate the browning of apple juice.  相似文献   
7.
8.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread...  相似文献   
9.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
10.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  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