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   434231篇
  免费   4263篇
  国内免费   827篇
电工技术   7350篇
综合类   299篇
化学工业   66045篇
金属工艺   25524篇
机械仪表   16383篇
建筑科学   8232篇
矿业工程   5073篇
能源动力   8362篇
轻工业   22012篇
水利工程   6554篇
石油天然气   16494篇
武器工业   41篇
无线电   40794篇
一般工业技术   103099篇
冶金工业   62147篇
原子能技术   14382篇
自动化技术   36530篇
  2021年   4039篇
  2019年   3935篇
  2018年   12297篇
  2017年   12636篇
  2016年   11248篇
  2015年   4783篇
  2014年   7721篇
  2013年   16539篇
  2012年   12592篇
  2011年   18721篇
  2010年   15991篇
  2009年   16221篇
  2008年   16760篇
  2007年   17597篇
  2006年   10389篇
  2005年   11120篇
  2004年   10079篇
  2003年   9801篇
  2002年   8846篇
  2001年   8301篇
  2000年   8131篇
  1999年   7546篇
  1998年   16287篇
  1997年   12028篇
  1996年   9147篇
  1995年   7092篇
  1994年   6425篇
  1993年   6710篇
  1992年   5395篇
  1991年   5473篇
  1990年   5384篇
  1989年   5201篇
  1988年   5117篇
  1987年   4796篇
  1986年   4755篇
  1985年   5192篇
  1984年   4964篇
  1983年   4763篇
  1982年   4430篇
  1981年   4459篇
  1980年   4518篇
  1979年   4707篇
  1978年   4828篇
  1977年   5029篇
  1976年   5769篇
  1975年   4448篇
  1974年   4461篇
  1973年   4555篇
  1972年   4053篇
  1971年   3701篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
1.
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.
5.
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   
6.
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   
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.
Piperine is an alkaloid that has extensive pharmacological activity and impacts other active substances bioavailability due to inhibition of CYP450 enzymes, stimulation of amino acid transporters and P-glycoprotein inhibition. Low solubility and the associated low bioavailability of piperine limit its potential. The combination of piperine with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) causes a significant increase in its solubility and, consequently, an increase in permeability through gastrointestinal tract membranes and the blood–brain barrier. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) were used to characterize interactions between piperine and HP-β-CD. The observed physicochemical changes should be combined with the process of piperine and CD system formation. Importantly, with an increase in solubility and permeability of piperine as a result of interaction with CD, it was proven to maintain its biological activity concerning the antioxidant potential (2,2-diphenyl-1-picryl-hydrazyl-hydrate assay), inhibition of enzymes essential for the inflammatory process and for neurodegenerative changes (hyaluronidase, acetylcholinesterase, butyrylcholinesterase).  相似文献   
10.
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   
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