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   490687篇
  免费   6278篇
  国内免费   2004篇
电工技术   8879篇
综合类   689篇
化学工业   69841篇
金属工艺   18826篇
机械仪表   14571篇
建筑科学   11639篇
矿业工程   2288篇
能源动力   13056篇
轻工业   40215篇
水利工程   4858篇
石油天然气   8382篇
武器工业   56篇
无线电   61982篇
一般工业技术   97911篇
冶金工业   94272篇
原子能技术   11407篇
自动化技术   40097篇
  2021年   3952篇
  2020年   2968篇
  2019年   3693篇
  2018年   6288篇
  2017年   6380篇
  2016年   6721篇
  2015年   4352篇
  2014年   7622篇
  2013年   21563篇
  2012年   12168篇
  2011年   16843篇
  2010年   13245篇
  2009年   15264篇
  2008年   15969篇
  2007年   15969篇
  2006年   13931篇
  2005年   12709篇
  2004年   12478篇
  2003年   12393篇
  2002年   11815篇
  2001年   12303篇
  2000年   11399篇
  1999年   12190篇
  1998年   31044篇
  1997年   21648篇
  1996年   16579篇
  1995年   12546篇
  1994年   11103篇
  1993年   11148篇
  1992年   7904篇
  1991年   7579篇
  1990年   7353篇
  1989年   7166篇
  1988年   6781篇
  1987年   5943篇
  1986年   5858篇
  1985年   6454篇
  1984年   5949篇
  1983年   5605篇
  1982年   5274篇
  1981年   5170篇
  1980年   5108篇
  1979年   4771篇
  1978年   4645篇
  1977年   5336篇
  1976年   7221篇
  1975年   3876篇
  1974年   3806篇
  1973年   3768篇
  1972年   3263篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
31.
This work presents the dielectric properties of YNbO4 (YNO)–TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of ?8.96 ppm.°C?1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below ?10 dB at the resonant frequency, with a realised gain of 4.94 – 5.76 dBi, a bandwidth of 665–1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO–TiO2 composites are interesting candidates for microwave operating devices.  相似文献   
32.
Wireless Personal Communications - In recent years, the emergence of Internet of things and cyber-physical system provide a proactive and efficacious solution to enable remote monitoring, machine...  相似文献   
33.
Multimedia Tools and Applications - In this paper, a hashing based watermarking technique for the protection and authentication of document image is proposed. Message Digest 5 (MD5) hashing is...  相似文献   
34.
Journal of Materials Science: Materials in Electronics - Nano Mn0.95M0.05S (M ≡ Cu, Mg) samples were produced using molten salt solid state reaction method. Rietveld analysis of X-ray...  相似文献   
35.
Journal of Engineering Physics and Thermophysics - A numerical investigation has been made into the interaction of slender (5–20 calibers) steel cylinder strikers with orthotropic compost...  相似文献   
36.
Journal of Engineering Physics and Thermophysics - Results of investigation into the influence of a corrosion process on thermotechnical characteristics of heat pipes of low-temperature range are...  相似文献   
37.
Deshmukh  P.  Sar  S. K.  Smječanin  N.  Nuhanović  M.  Lalwani  R. 《Radiochemistry》2022,64(4):532-542
Radiochemistry - Magnetically modified waste bark of the Aegle marmelos tree was prepared by using green synthesis method and was used in a batch system for U(VI) removal from aqueous solution. The...  相似文献   
38.
This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al2O3)-doped V2O5 ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V2O5 phase formation with increasing strain on the doping of Al2O3 in place of V2O5 in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO5] polyhedra converts into [VO4] polyhedra on the doping of Al2O3 into V2O5. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability.  相似文献   
39.
Extracellular vesicles (EVs) are membranous structures, which are secreted by almost every cell type analyzed so far. In addition to their importance for cell-cell communication under physiological conditions, EVs are also released during pathogenesis and mechanistically contribute to this process. Here we summarize their functional relevance in asthma, one of the most common chronic non-communicable diseases. Asthma is a complex persistent inflammatory disorder of the airways characterized by reversible airflow obstruction and, from a long-term perspective, airway remodeling. Overall, mechanistic studies summarized here indicate the importance of different subtypes of EVs and their variable cargoes in the functioning of the pathways underlying asthma, and show some interesting potential for the development of future therapeutic interventions. Association studies in turn demonstrate a good diagnostic potential of EVs in asthma.  相似文献   
40.
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via...  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