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   266687篇
  免费   3190篇
  国内免费   282篇
电工技术   4389篇
综合类   146篇
化学工业   44323篇
金属工艺   15686篇
机械仪表   10515篇
建筑科学   5074篇
矿业工程   3877篇
能源动力   4189篇
轻工业   12302篇
水利工程   4221篇
石油天然气   13028篇
武器工业   28篇
无线电   21318篇
一般工业技术   67680篇
冶金工业   32662篇
原子能技术   11281篇
自动化技术   19440篇
  2021年   3181篇
  2019年   3074篇
  2018年   6076篇
  2017年   6378篇
  2016年   6796篇
  2015年   3679篇
  2014年   6095篇
  2013年   11584篇
  2012年   8207篇
  2011年   10031篇
  2010年   8235篇
  2009年   8955篇
  2008年   9138篇
  2007年   8790篇
  2006年   7013篇
  2005年   6082篇
  2004年   5906篇
  2003年   5733篇
  2002年   5589篇
  2001年   5297篇
  2000年   5253篇
  1999年   4494篇
  1998年   7357篇
  1997年   6039篇
  1996年   4603篇
  1995年   3827篇
  1994年   3573篇
  1993年   3751篇
  1992年   3339篇
  1991年   3463篇
  1990年   3577篇
  1989年   3445篇
  1988年   3346篇
  1987年   3340篇
  1986年   3218篇
  1985年   3470篇
  1984年   3427篇
  1983年   3259篇
  1982年   3102篇
  1981年   3179篇
  1980年   3170篇
  1979年   3349篇
  1978年   3580篇
  1977年   3532篇
  1976年   3989篇
  1975年   3297篇
  1974年   3365篇
  1973年   3409篇
  1972年   3024篇
  1971年   2787篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
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.
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized...  相似文献   
7.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
8.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  相似文献   
9.
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   
10.
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   
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