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   13913篇
  免费   1210篇
  国内免费   596篇
电工技术   765篇
技术理论   1篇
综合类   938篇
化学工业   2578篇
金属工艺   738篇
机械仪表   892篇
建筑科学   974篇
矿业工程   394篇
能源动力   406篇
轻工业   967篇
水利工程   255篇
石油天然气   709篇
武器工业   92篇
无线电   1546篇
一般工业技术   1886篇
冶金工业   633篇
原子能技术   182篇
自动化技术   1763篇
  2024年   57篇
  2023年   247篇
  2022年   349篇
  2021年   564篇
  2020年   469篇
  2019年   366篇
  2018年   434篇
  2017年   477篇
  2016年   388篇
  2015年   546篇
  2014年   673篇
  2013年   853篇
  2012年   827篇
  2011年   813篇
  2010年   799篇
  2009年   726篇
  2008年   674篇
  2007年   720篇
  2006年   727篇
  2005年   589篇
  2004年   417篇
  2003年   468篇
  2002年   546篇
  2001年   440篇
  2000年   356篇
  1999年   375篇
  1998年   323篇
  1997年   288篇
  1996年   245篇
  1995年   195篇
  1994年   164篇
  1993年   117篇
  1992年   102篇
  1991年   83篇
  1990年   62篇
  1989年   48篇
  1988年   41篇
  1987年   24篇
  1986年   31篇
  1985年   10篇
  1984年   16篇
  1983年   8篇
  1982年   8篇
  1981年   11篇
  1980年   14篇
  1979年   6篇
  1978年   3篇
  1977年   3篇
  1976年   8篇
  1959年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Exploration of Reactivity of Eu(TTA)2(phen)(MA)   总被引:1,自引:0,他引:1  
The reactivity of Eu(TTA)2(phen)(MA) (HTTA=2-thenoyltrifluoroacetone, MA=maleic anhydride) was studied. A series of products were prepared by direct polymerization, suspension polymerization, and alternate suspension and solution copolymerization with the styrene. And then we reactivity of these products were studied. The complexes were investigated and characterized by X-ray Diffraction (XRD), gel permeation chromatography (GPC) and fluorescence spectrophotometer. Although high polymerization degree is not found in the exploration of reactivity, it is found that the fluorescent intensity of complexes prepared by suspension polymerization increases significantly compared with the original particles, which is five times higher than that of the pure rare earth complex.  相似文献   
982.
The doping effect of rare earth elements (Tb and Sm) on the electronic structure of (110) martensitic twin boundary in Ni2MnGa alloys was investigated by using ab initio method within the DFT and the supercell implementation. The calculated results show that the atomic relaxation lowers the boundary energy and the segregation energy. Sm seems easier to segregate to the boundary and has a greater doping effect compared with Tb due to its lower segregation energy and bigger bonder order with neighboring atoms. Tb makes a greater contribution to the magnetic properties of the twin boundary than Sm.  相似文献   
983.
本文提出了带隙结构的运算放大器,把带隙基准和运算放大器有机的结合到一起,有效的节省了芯片面积,并有很好的精度和动态响应特性。本文阐述了该结构的工作原理,对整体结构进行分析,重点阐述了带隙结构的特点。采用0.8μm BiCMOS工艺,通过HSPICE进行仿真验证,得到其开环增益为63.4dB,电源抑制比为106.4dB。  相似文献   
984.
针对政府信息化建设中的特殊应用,借鉴MAS思想提出了全局流程的概念,并把全局流程与局部流程区分开来.在此基础上建立了全局流程集成平台,详细讨论了平台的设计思想、结构和关键的组成部分.实践表明,平台的流程描述能力强、层次结构清晰,具有通用性,能体现Agent的自治性、自主性、协作性和适应性,有效地支持了电子政务中典型应用的开发,适合作为开发以业务流程为中心的应用系统的支撑平台.  相似文献   
985.
Cones and foci: A mechanical framework for protocol verification   总被引:1,自引:0,他引:1  
We define a cones and foci proof method, which rephrases the question whether two system specifications are branching bisimilar in terms of proof obligations on relations between data objects. Compared to the original cones and foci method from Groote and Springintveld, our method is more generally applicable, because it does not require a preprocessing step to eliminate τ-loops. We prove soundness of our approach and present a set of rules to prove the reachability of focus points. Our method has been formalized and proved correct using PVS. Thus we have established a framework for mechanical protocol verification. We apply this framework to the Concurrent Alternating Bit Protocol.
  相似文献   
986.
In this paper, we have developed a new micromirror with a compact footprint which can be rapidly tilted to large angles. The micromirror is supported by a liquid-metal drop (LMD) with low vapor pressure and is rotated by an electrostatic torque. A torsional spring model is proposed to predict the equivalent torsional constant of the LMD and the resonant frequency of the mirror. Micromirrors (1 mmtimes1 mmtimes25 mum) and actuating electrodes are microfabricated with a centralized wetting area surrounded by a nonwetting parylene area to confine the LMD. Our measurements of the mirror show the average snap-down voltage of ~ 79 V and the resonant frequency of 165 Hz. A single mirror is actuated to steer a laser beam with a maximum deflected angle of 23.6deg. A 1times3 mirror array is demonstrated for light switching, and has greater than 1 : 64 idle/deflection contrast. We also test the stability of the mirror to mechanical shake up to 56 g (g = 9.807 m/s2). The prototype mirror has 3.6 million cycles of operation  相似文献   
987.
The solution of Markov Decision Processes (MDPs) often relies on special properties of the processes. For two-level MDPs, the difference in the rates of state changes of the upper and lower levels has led to limiting or approximate solutions of such problems. In this paper, we solve a two-level MDP without making any assumption on the rates of state changes of the two levels. We first show that such a two-level MDP is a non-standard one where the optimal actions of different states can be related to each other. Then we give assumptions (conditions) under which such a specially constrained MDP can be solved by policy iteration. We further show that the computational effort can be reduced by decomposing the MDP. A two-level MDP with M upper-level states can be decomposed into one MDP for the upper level and M to M(M-1) MDPs for the lower level, depending on the structure of the two-level MDP. The upper-level MDP is solved by time aggregation, a technique introduced in a recent paper [Cao, X.-R., Ren, Z. Y., Bhatnagar, S., Fu, M., & Marcus, S. (2002). A time aggregation approach to Markov decision processes. Automatica, 38(6), 929-943.], and the lower-level MDPs are solved by embedded Markov chains.  相似文献   
988.
We present an algorithm that modifies the original formulation proposed in Wan and Kothare [Efficient robust constrained model predictive control with a time-varying terminal constraint set, Systems Control Lett. 48 (2003) 375–383]. The modified algorithm can be proved to be robustly stabilizing and preserves all the advantages of the original algorithm, thereby overcoming the limitation pointed out recently by Pluymers et al. [Min–max feedback MPC using a time-varying terminal constraint set and comments on “Efficient robust constrained model predictive control with a time-varying terminal constraint set”, Systems Control Lett. 54 (2005) 1143–1148].  相似文献   
989.
沸石、骨炭、活性氧化铝除氟效果研究   总被引:17,自引:0,他引:17  
对沸石、骨炭和活性氧化铝三种除氟剂的除氟性能,处理后的水质通过静态和动态实验进行了比较,结果表明沸石价格低廉,具有越用越好的趋势,处理后的水质和水量能满足家庭饮用水的需要,适用于高氟区家庭使用,骨炭和活性氧化铝除氟效果较好,技术成熟,适用于处理厂集中处理使用。  相似文献   
990.
利用扫描电子显微镜(SEM)、电子探针(EPXM)和电子能谱(EDXA)对骨料颗粒和水泥浆体界面过渡区(ITZ)进行了研究,研究的重点是老混凝土中骨料-水泥界面过渡区的微观结构特征和成份分布,结果表明,老混凝土由于在成熟度高,其ITZ中水化物十分丰富,密实度高。ITZ内部和外部的水化产物组成存在一定的差别,表现在Ca,K和Fe等元素富集于ITZ,而Si元素在此区域的含量相对较低,对于特定的元素或物质在ITZ中的富集现象的研究,有助于提高对混凝土材料稳定性的认识。  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