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   498972篇
  免费   6639篇
  国内免费   1447篇
电工技术   9201篇
综合类   478篇
化学工业   75292篇
金属工艺   20163篇
机械仪表   15339篇
建筑科学   12022篇
矿业工程   2709篇
能源动力   12070篇
轻工业   43969篇
水利工程   5233篇
石油天然气   9966篇
武器工业   83篇
无线电   59387篇
一般工业技术   97031篇
冶金工业   90969篇
原子能技术   11489篇
自动化技术   41657篇
  2021年   3761篇
  2019年   3644篇
  2018年   6451篇
  2017年   6457篇
  2016年   6886篇
  2015年   4424篇
  2014年   7517篇
  2013年   21473篇
  2012年   12098篇
  2011年   16442篇
  2010年   13258篇
  2009年   15004篇
  2008年   15894篇
  2007年   15726篇
  2006年   14166篇
  2005年   13099篇
  2004年   12382篇
  2003年   12071篇
  2002年   11894篇
  2001年   11752篇
  2000年   11202篇
  1999年   11336篇
  1998年   26657篇
  1997年   19479篇
  1996年   15368篇
  1995年   11829篇
  1994年   10631篇
  1993年   10460篇
  1992年   8227篇
  1991年   7838篇
  1990年   7524篇
  1989年   7406篇
  1988年   7221篇
  1987年   6222篇
  1986年   6131篇
  1985年   7165篇
  1984年   6774篇
  1983年   6118篇
  1982年   5783篇
  1981年   6019篇
  1980年   5716篇
  1979年   5493篇
  1978年   5448篇
  1977年   6317篇
  1976年   8006篇
  1975年   5011篇
  1974年   4857篇
  1973年   4895篇
  1972年   4098篇
  1971年   3849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