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   426348篇
  免费   7953篇
  国内免费   1543篇
电工技术   7278篇
综合类   313篇
化学工业   65575篇
金属工艺   15145篇
机械仪表   12039篇
建筑科学   11362篇
矿业工程   1424篇
能源动力   11656篇
轻工业   45169篇
水利工程   3830篇
石油天然气   4989篇
武器工业   10篇
无线电   50922篇
一般工业技术   78746篇
冶金工业   80672篇
原子能技术   7194篇
自动化技术   39520篇
  2021年   3518篇
  2020年   2673篇
  2019年   3207篇
  2018年   5444篇
  2017年   5459篇
  2016年   5920篇
  2015年   4306篇
  2014年   6878篇
  2013年   20468篇
  2012年   12152篇
  2011年   16318篇
  2010年   12725篇
  2009年   14247篇
  2008年   14888篇
  2007年   14765篇
  2006年   13111篇
  2005年   11980篇
  2004年   11427篇
  2003年   11035篇
  2002年   10413篇
  2001年   10567篇
  2000年   9773篇
  1999年   10442篇
  1998年   26389篇
  1997年   18421篇
  1996年   13910篇
  1995年   10551篇
  1994年   9035篇
  1993年   8894篇
  1992年   6343篇
  1991年   6057篇
  1990年   5785篇
  1989年   5613篇
  1988年   5462篇
  1987年   4608篇
  1986年   4455篇
  1985年   5366篇
  1984年   4846篇
  1983年   4452篇
  1982年   4118篇
  1981年   4254篇
  1980年   3917篇
  1979年   3743篇
  1978年   3549篇
  1977年   4193篇
  1976年   5461篇
  1975年   3044篇
  1974年   2959篇
  1973年   3055篇
  1972年   2421篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
2.
Journal of Materials Science -  相似文献   
3.
Xiao  Zhu  Chen  Yanxun  Jiang  Hongbo  Hu  Zhenzhen  Lui  John C. S.  Min  Geyong  Dustdar  Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of...  相似文献   
4.
5.
6.
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   
7.
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell.  相似文献   
8.
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   
9.
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   
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