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   81260篇
  免费   7548篇
  国内免费   4872篇
电工技术   6112篇
技术理论   2篇
综合类   6425篇
化学工业   12598篇
金属工艺   4699篇
机械仪表   5311篇
建筑科学   6337篇
矿业工程   2388篇
能源动力   2361篇
轻工业   5048篇
水利工程   1608篇
石油天然气   4523篇
武器工业   998篇
无线电   9958篇
一般工业技术   8979篇
冶金工业   3197篇
原子能技术   1121篇
自动化技术   12015篇
  2024年   369篇
  2023年   1199篇
  2022年   2211篇
  2021年   3255篇
  2020年   2488篇
  2019年   2029篇
  2018年   2292篇
  2017年   2612篇
  2016年   2279篇
  2015年   3325篇
  2014年   4135篇
  2013年   5104篇
  2012年   5500篇
  2011年   5987篇
  2010年   5537篇
  2009年   5277篇
  2008年   5104篇
  2007年   4821篇
  2006年   4780篇
  2005年   4049篇
  2004年   2987篇
  2003年   2636篇
  2002年   2627篇
  2001年   2322篇
  2000年   1990篇
  1999年   1771篇
  1998年   1245篇
  1997年   1069篇
  1996年   1017篇
  1995年   819篇
  1994年   658篇
  1993年   524篇
  1992年   412篇
  1991年   280篇
  1990年   235篇
  1989年   186篇
  1988年   160篇
  1987年   90篇
  1986年   77篇
  1985年   45篇
  1984年   24篇
  1983年   27篇
  1982年   45篇
  1981年   24篇
  1980年   17篇
  1979年   6篇
  1977年   7篇
  1976年   5篇
  1959年   5篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The effect of pressure on combustion and heat transfer is analyzed. The research is based on the basic combustion and heat transfer theorem. A correction for the heat calculation method for pressurized furnace is made on the basis of the normal pressure case. The correction takes the effect of pressurizing into account. The results show that the correction is reasonable and the method is applicable to combustion and heat transfer of the marine supercharged boiler.  相似文献   
32.
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications.  相似文献   
33.
基于MoCA标准的家庭网络研究   总被引:1,自引:0,他引:1  
本文描述了一种基于MOCA标准的家庭网络,并对该网络及设备进行了基本性能的测试.本文首先介绍了家庭网络的发展现状,对目前的各种家庭网络标准进行了比较.在此基础上详细描述了基于MOCA标准的家庭网络,并对该网络的设计,实现、网络性能进行了详述.然后对该网络进行了测试并得出了相关的测试结论.最后指出该网络的不足及改进之处.  相似文献   
34.
35.
偏高岭土的研究现状及展望   总被引:9,自引:0,他引:9  
简要介绍了偏高岭土的反应机理和在国内外的研究现状。同时对偏高岭土的研究进行了展望 ,提出因麦特林水泥原料丰富 ,污染小 ,加工简单 ,性能优越 ,其应用前景广阔 ,应对其加强研究。  相似文献   
36.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm.  相似文献   
37.
Experimental Research on Erbium-doped Superfluorescent Fiber Source   总被引:1,自引:0,他引:1  
The effects of the variations in fiber length, fiber mirror reflectance on efficiency and output power are experimentally investigated for erbium-doped double pass backward superfluorescent fiber sources (SFSs). The influence of fiber length on mean wavelength stability (MWS) has also been demonstrated. By incorporating a short section of un-pumped erbium-doped fiber (EDF) at the output port, the pump power dependent on MWS becomes independent of pumped EDF length. This is a novel phenomenon that hasn‘t been reported up to now,and should be helpful to SFS fabrication and theory analysis. By using a fiber Michelson interferometer as spectrum slicing component,a multi-wavelength fiber source (MWFS) with ~20 channels (from 1542nm to 1559nm) is got. The MWFS has a channel spacing of ~0. 8 nm which satisfies ITUstandard. The intensity fluctuation among channels is less than 0.5dB,and the extinction ratio of all channels is above 14dB. This kind of MWFS should be useful to wavelength division multiplexing systems.  相似文献   
38.
The present study is a continuation of our previous work with the aim to reduce problems caused by standard higher order elements in contact problems. The difficulties can be attributed to the inherent property of the Galerkin method which gives uneven distributions of nodal forces resulting in oscillating contact pressures. The proposed remedy is use of piece‐wise linear weight functions. The methods to establish stiffness and/or mass matrix for 8‐node quadrilateral element in 2D are presented, i.e. the condensing and direct procedures. The energy and nodal displacement error norms are also checked to establish the convergence ratio. Interpretation of calculated contact pressures is discussed. Two new 2D 8‐node quadrilateral elements, QUAD8C and QUAD8D, are derived and tested in many examples, which show their good performance in contact problems. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
39.
40.
根据滑坡发生的初始条件、滑坡成因及方式表象,对常见的蠕变倾覆滑坡、卸荷滑坡、震动液化平推滑坡、潜蚀塌陷滑坡、溶蚀下陷滑坡、孔隙水压浮动滑坡和人工切蚀或冲(浪)蚀—加载滑坡等机理进行了分析.  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