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   314184篇
  免费   5842篇
  国内免费   353篇
电工技术   4483篇
综合类   235篇
化学工业   54099篇
金属工艺   16354篇
机械仪表   11379篇
建筑科学   6241篇
矿业工程   3901篇
能源动力   5436篇
轻工业   20176篇
水利工程   4698篇
石油天然气   13325篇
武器工业   34篇
无线电   23520篇
一般工业技术   73376篇
冶金工业   46254篇
原子能技术   11410篇
自动化技术   25458篇
  2022年   3031篇
  2021年   4585篇
  2020年   3530篇
  2019年   4128篇
  2018年   7803篇
  2017年   8103篇
  2016年   8557篇
  2015年   4856篇
  2014年   7734篇
  2013年   14844篇
  2012年   11325篇
  2011年   12812篇
  2010年   10388篇
  2009年   10909篇
  2008年   11092篇
  2007年   10408篇
  2006年   8314篇
  2005年   7177篇
  2004年   6962篇
  2003年   6682篇
  2002年   6311篇
  2001年   5796篇
  2000年   5736篇
  1999年   5175篇
  1998年   11805篇
  1997年   8706篇
  1996年   6303篇
  1995年   4748篇
  1994年   4328篇
  1993年   4506篇
  1992年   3515篇
  1991年   3648篇
  1990年   3754篇
  1989年   3649篇
  1988年   3542篇
  1987年   3507篇
  1986年   3397篇
  1985年   3577篇
  1984年   3501篇
  1983年   3324篇
  1982年   3188篇
  1981年   3262篇
  1980年   3291篇
  1979年   3405篇
  1978年   3628篇
  1977年   3740篇
  1976年   4483篇
  1975年   3325篇
  1974年   3384篇
  1973年   3451篇
排序方式: 共有10000条查询结果,搜索用时 31 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.
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   
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