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   64864篇
  免费   3529篇
  国内免费   150篇
电工技术   717篇
综合类   254篇
化学工业   12720篇
金属工艺   1299篇
机械仪表   1401篇
建筑科学   2066篇
矿业工程   167篇
能源动力   1669篇
轻工业   9424篇
水利工程   589篇
石油天然气   273篇
武器工业   11篇
无线电   3858篇
一般工业技术   10385篇
冶金工业   13980篇
原子能技术   384篇
自动化技术   9346篇
  2023年   501篇
  2022年   1006篇
  2021年   1763篇
  2020年   1308篇
  2019年   1491篇
  2018年   2136篇
  2017年   2156篇
  2016年   2230篇
  2015年   1704篇
  2014年   2244篇
  2013年   4304篇
  2012年   3444篇
  2011年   3684篇
  2010年   2858篇
  2009年   2740篇
  2008年   2543篇
  2007年   2351篇
  2006年   1736篇
  2005年   1614篇
  2004年   1618篇
  2003年   1442篇
  2002年   1407篇
  2001年   1142篇
  2000年   960篇
  1999年   1000篇
  1998年   4309篇
  1997年   2898篇
  1996年   1945篇
  1995年   1202篇
  1994年   951篇
  1993年   1074篇
  1992年   423篇
  1991年   494篇
  1990年   380篇
  1989年   355篇
  1988年   365篇
  1987年   302篇
  1986年   279篇
  1985年   321篇
  1984年   260篇
  1983年   203篇
  1982年   262篇
  1981年   269篇
  1980年   277篇
  1979年   181篇
  1978年   157篇
  1977年   429篇
  1976年   843篇
  1975年   134篇
  1973年   130篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
This paper presents a novel framework for manufacturing and cost-related knowledge formalization. This artefact allows industries to capitalize the knowled  相似文献   
82.
83.
A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94%?Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1?MHz, low dielectric losses, (~10?3 at 1?MHz, and a large dielectric strength, ~60?kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications.  相似文献   
84.
In the perspective of fuelling the future generations of gas turbines by hydrogen rich syngas, the evaluation of the effect of a higher water vapour content into the flue gases on the TBC used, or potentially usable, is a need. For this purpose YPSZ APS TBC with two different microstructures have been exposed for 500?h at different temperatures in the range 1000?°C–1250?°C either in air and air +20% vol. H2O. The comparison between the different testing conditions has been performed in terms of sintering kinetics and phase stability, as evaluated by thermal diffusivity measurements and Synchrotron X-Rays diffraction, respectively. Furthermore the characterisation of thermal properties of two innovative TBCs (GZO-YPSZ and YAG) potentially able to withstand the CMAS attack and erosive environments, respectively, has been carried out.No clear evidence of a different behaviour of TBC has been observed, at least in the considered aging time and temperature range.  相似文献   
85.
Extracellular vesicles (EVs) are a heterogeneous group of cell-derived submicron vesicles released under physiological or pathological conditions. EVs mediate the cellular crosstalk, thus contributing to defining the tumor microenvironment, including in epithelial ovarian cancer (EOC). The available literature investigating the role of EVs in EOC has been reviewed following PRISMA guidelines, focusing on the role of EVs in early disease diagnosis, metastatic spread, and the development of chemoresistance in EOC. Data were identified from searches of Medline, Current Contents, PubMed, and from references in relevant articles from 2010 to 1 April 2020. The research yielded 194 results. Of these, a total of 36 papers, 9 reviews, and 27 original types of research were retained and analyzed. The literature findings demonstrate that a panel of EV-derived circulating miRNAs may be useful for early diagnosis of EOC. Furthermore, it appears clear that EVs are involved in mediating two crucial processes for metastatic and chemoresistance development: the epithelial–mesenchymal transition, and tumor escape from the immune system response. Further studies, more focused on in vivo evidence, are urgently needed to clarify the role of EV assessment in the clinical management of EOC patients.  相似文献   
86.
87.
The Journal of Supercomputing - Deadlock-free dynamic network reconfiguration process is usually studied from the routing algorithm restrictions and resource reservation perspective. The dynamic...  相似文献   
88.
89.
Abstract

In this work, a new g-C3N4-based Z-scheme with γ-Fe2O3 and β-Ag2Se both n-type semiconductors, and graphite to favor electron exchange is presented. The composite material was studied by XRD, FTIR, UV-Vis, TEM, XPS, TGA, DSC and TOF-SIMS, and the ability of this photocatalytic system to act as a photo-reductant was assessed using crystal violet (CV+) dye. Solar light driven photo-reduction of CV+ in the presence of tri-sodium citrate evidenced a synergistic enhancement of the activity of the composite toward reduction, with ~20 times higher conversion rates per unit of surface area than those of g-C3N4. Photo-oxidation experiments under Xe lamp irradiation in the presence of H2O2 also showed that the AgFeCN composite featured a higher activity (~8×) than g-C3N4. This Z-scheme may deserve further study as a photo-reductant to obtain hydrogen or hydrogenated compounds. Moreover, the use of CV+ may represent a facile procedure that can aid in the selection of new photocatalysts to be used in hydrogen production.  相似文献   
90.
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