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   1562757篇
  免费   30633篇
  国内免费   8408篇
电工技术   36402篇
技术理论   1篇
综合类   8384篇
化学工业   271730篇
金属工艺   66141篇
机械仪表   44870篇
建筑科学   49207篇
矿业工程   12326篇
能源动力   51043篇
轻工业   118352篇
水利工程   16342篇
石油天然气   38818篇
武器工业   404篇
无线电   200028篇
一般工业技术   291221篇
冶金工业   188292篇
原子能技术   34250篇
自动化技术   173987篇
  2021年   16872篇
  2020年   12999篇
  2019年   15557篇
  2018年   16133篇
  2017年   15403篇
  2016年   22082篇
  2015年   18659篇
  2014年   30396篇
  2013年   89656篇
  2012年   38091篇
  2011年   50459篇
  2010年   44025篇
  2009年   52178篇
  2008年   47016篇
  2007年   44011篇
  2006年   47108篇
  2005年   41251篇
  2004年   43044篇
  2003年   42887篇
  2002年   41871篇
  2001年   39137篇
  2000年   37208篇
  1999年   36903篇
  1998年   53839篇
  1997年   44454篇
  1996年   38811篇
  1995年   32897篇
  1994年   30557篇
  1993年   30285篇
  1992年   26693篇
  1991年   23939篇
  1990年   24060篇
  1989年   23103篇
  1988年   21712篇
  1987年   19833篇
  1986年   19235篇
  1985年   22584篇
  1984年   22572篇
  1983年   20558篇
  1982年   19481篇
  1981年   19239篇
  1980年   17922篇
  1979年   18442篇
  1978年   17698篇
  1977年   17855篇
  1976年   19578篇
  1975年   15934篇
  1974年   15449篇
  1973年   15540篇
  1972年   13062篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread...  相似文献   
42.
Telecommunication Systems - Energy saving in User Equipment (UE) is one of the important issues for limited sources of power in the device. It is critical for the UE to maximize its energy...  相似文献   
43.
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   
44.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  相似文献   
45.
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   
46.
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   
47.
Mobile Networks and Applications - Project MindCatcher is an art/research project which has the intention to explore the potential of interactive artistic environments for measuring and a better...  相似文献   
48.
杨婉雨  尹铫  李超  白国锋 《声学技术》2022,41(2):186-192
针对提高水声材料设计中动态参数输入精度的问题,提出了一种复杨氏模量及泊松比准确测试方法。对于复杨氏模量测试,通过将Williams-Landel-Ferry(WLF)方程引入到Havriliak-Negami(H-N)模型中,采用信赖域反射算法对未知参数进行拟合得到材料参数宽频域主曲线。对于泊松比测试,根据同一材料不同形状因子表观杨氏模量之比与泊松比存在唯一量化关系的特性,仅通过两种不同形状因子试样的准静态有限元模拟,获得表观杨氏模量比值与泊松比量化曲线。因此,根据橡胶样品表观杨氏模量测试结果,可以直接利用局部加权回归获得其泊松比。最后,将前述材料制成直径为55 mm、厚度为50 mm的声管样品,放置在水声管中进行吸声系数测试。同时,把橡胶的复杨氏模量和泊松比的测量结果输入到水-橡胶-水分层介质模型中进行吸声系数计算。结果表明两者吻合,验证了上述测试方法的正确性和有效性。  相似文献   
49.
Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface.  相似文献   
50.
In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content.  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