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   283248篇
  免费   5192篇
  国内免费   837篇
电工技术   5542篇
综合类   397篇
化学工业   42804篇
金属工艺   10949篇
机械仪表   9008篇
建筑科学   7455篇
矿业工程   1277篇
能源动力   6927篇
轻工业   25757篇
水利工程   2715篇
石油天然气   3951篇
武器工业   69篇
无线电   36305篇
一般工业技术   55974篇
冶金工业   47334篇
原子能技术   5596篇
自动化技术   27217篇
  2021年   2695篇
  2020年   2024篇
  2019年   2516篇
  2018年   4246篇
  2017年   4373篇
  2016年   4696篇
  2015年   3127篇
  2014年   5069篇
  2013年   13206篇
  2012年   7833篇
  2011年   10498篇
  2010年   8289篇
  2009年   9042篇
  2008年   9976篇
  2007年   9828篇
  2006年   8740篇
  2005年   7878篇
  2004年   7497篇
  2003年   7285篇
  2002年   6922篇
  2001年   6868篇
  2000年   6535篇
  1999年   6562篇
  1998年   14515篇
  1997年   10530篇
  1996年   8335篇
  1995年   6613篇
  1994年   5889篇
  1993年   5725篇
  1992年   4692篇
  1991年   4317篇
  1990年   4158篇
  1989年   3865篇
  1988年   3715篇
  1987年   3264篇
  1986年   3136篇
  1985年   3760篇
  1984年   3559篇
  1983年   3138篇
  1982年   2965篇
  1981年   3079篇
  1980年   2866篇
  1979年   2724篇
  1978年   2585篇
  1977年   3023篇
  1976年   3639篇
  1975年   2398篇
  1974年   2375篇
  1973年   2381篇
  1972年   1880篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
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.
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized...  相似文献   
5.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
6.
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   
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