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   444037篇
  免费   5745篇
  国内免费   1797篇
电工技术   7705篇
综合类   664篇
化学工业   64333篇
金属工艺   17786篇
机械仪表   13302篇
建筑科学   10667篇
矿业工程   2685篇
能源动力   11307篇
轻工业   36731篇
水利工程   4968篇
石油天然气   9055篇
武器工业   49篇
无线电   52051篇
一般工业技术   88990篇
冶金工业   83083篇
原子能技术   11276篇
自动化技术   36927篇
  2021年   3486篇
  2019年   3356篇
  2018年   5704篇
  2017年   5818篇
  2016年   6191篇
  2015年   4009篇
  2014年   6899篇
  2013年   19620篇
  2012年   11214篇
  2011年   15519篇
  2010年   12230篇
  2009年   14057篇
  2008年   14450篇
  2007年   14543篇
  2006年   12460篇
  2005年   11549篇
  2004年   11306篇
  2003年   10976篇
  2002年   10476篇
  2001年   10645篇
  2000年   10252篇
  1999年   10618篇
  1998年   25738篇
  1997年   18320篇
  1996年   14256篇
  1995年   10702篇
  1994年   9618篇
  1993年   9501篇
  1992年   7077篇
  1991年   6778篇
  1990年   6483篇
  1989年   6565篇
  1988年   6105篇
  1987年   5435篇
  1986年   5343篇
  1985年   6058篇
  1984年   5580篇
  1983年   5195篇
  1982年   4764篇
  1981年   4852篇
  1980年   4765篇
  1979年   4634篇
  1978年   4667篇
  1977年   5207篇
  1976年   6898篇
  1975年   3964篇
  1974年   3850篇
  1973年   3859篇
  1972年   3214篇
  1971年   2915篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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.
Food Science and Biotechnology - A rich source of nutrients, figs have a number of clinically validated benefits. This study aimed to evaluate the in vitro simulated gastrointestinal digestion, and...  相似文献   
4.
5.
Multimedia Tools and Applications - In this work, a new fuzzy logic-based algorithm is proposed for the enhancement of low light color images. A generalization of a fuzzy set known as an...  相似文献   
6.

We discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.

  相似文献   
7.
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   
8.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.  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 - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  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