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   565861篇
  免费   7133篇
  国内免费   1573篇
电工技术   10741篇
综合类   649篇
化学工业   84021篇
金属工艺   25916篇
机械仪表   20086篇
建筑科学   13336篇
矿业工程   3470篇
能源动力   12730篇
轻工业   45468篇
水利工程   6275篇
石油天然气   11325篇
武器工业   94篇
无线电   65525篇
一般工业技术   114220篇
冶金工业   95723篇
原子能技术   12395篇
自动化技术   52593篇
  2021年   4181篇
  2019年   4009篇
  2018年   13258篇
  2017年   13677篇
  2016年   11321篇
  2015年   5354篇
  2014年   8372篇
  2013年   22527篇
  2012年   14877篇
  2011年   23344篇
  2010年   19907篇
  2009年   20782篇
  2008年   21516篇
  2007年   22786篇
  2006年   14791篇
  2005年   15958篇
  2004年   14020篇
  2003年   13418篇
  2002年   12523篇
  2001年   11884篇
  2000年   11591篇
  1999年   11536篇
  1998年   26827篇
  1997年   19682篇
  1996年   15406篇
  1995年   11838篇
  1994年   10668篇
  1993年   10488篇
  1992年   8252篇
  1991年   7852篇
  1990年   7534篇
  1989年   7409篇
  1988年   7229篇
  1987年   6222篇
  1986年   6141篇
  1985年   7181篇
  1984年   6785篇
  1983年   6128篇
  1982年   5792篇
  1981年   6020篇
  1980年   5726篇
  1979年   5507篇
  1978年   5462篇
  1977年   6317篇
  1976年   8012篇
  1975年   5011篇
  1974年   4863篇
  1973年   4901篇
  1972年   4101篇
  1971年   3852篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the...  相似文献   
2.
Virtual Reality - It is generally accepted that natural environments reduce stress and improve mood. Since access to natural environments is sometimes limited, virtual natural environments,...  相似文献   
3.
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   
4.
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical...  相似文献   
5.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.  相似文献   
6.
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   
7.
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   
8.
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   
9.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  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