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   2343篇
  免费   96篇
  国内免费   4篇
电工技术   64篇
综合类   1篇
化学工业   451篇
金属工艺   23篇
机械仪表   67篇
建筑科学   61篇
能源动力   70篇
轻工业   120篇
水利工程   7篇
石油天然气   1篇
无线电   443篇
一般工业技术   481篇
冶金工业   272篇
原子能技术   18篇
自动化技术   364篇
  2023年   10篇
  2022年   29篇
  2021年   46篇
  2020年   30篇
  2019年   25篇
  2018年   38篇
  2017年   45篇
  2016年   55篇
  2015年   47篇
  2014年   65篇
  2013年   167篇
  2012年   111篇
  2011年   128篇
  2010年   113篇
  2009年   140篇
  2008年   127篇
  2007年   131篇
  2006年   77篇
  2005年   74篇
  2004年   75篇
  2003年   59篇
  2002年   58篇
  2001年   45篇
  2000年   42篇
  1999年   54篇
  1998年   103篇
  1997年   93篇
  1996年   54篇
  1995年   43篇
  1994年   39篇
  1993年   38篇
  1992年   28篇
  1991年   29篇
  1990年   38篇
  1989年   25篇
  1988年   34篇
  1987年   22篇
  1986年   16篇
  1985年   20篇
  1984年   9篇
  1983年   12篇
  1982年   3篇
  1981年   9篇
  1980年   3篇
  1979年   6篇
  1977年   4篇
  1976年   6篇
  1975年   6篇
  1973年   2篇
  1971年   2篇
排序方式: 共有2443条查询结果,搜索用时 0 毫秒
101.
With the growth of competition between nations in our knowledge-based world economy, excellence programs are becoming a national agenda item in developing as well as developed Asian countries. The main purpose of this paper is to compare the goals, funding policies and selection criteria of excellence programs in China, Japan, Korea and Taiwan and to analyze the academic achievement of their top ranked universities in three areas: research output, internationalization, and excellence, by using data from the Shanghai Jiao Tong, QS, and HEEACT rankings. The effectiveness of Taiwan??s ??Development Plan for World Class Universities and Research Centers of Excellence?? was assessed as a case study in the paper via a survey targeting on 138 top administrators from 11 Taiwan??s universities and 30 reviewers. The study found that more funding nations had, the more outputs and outcomes they would gain, for example China. The Taiwan case demonstrates that world-class universities and research centers are needed in Asian nations despite the concerns for inequality which they raise.  相似文献   
102.
A new method is studied for preparing nano-ceria by acid leaching MgO from CeO2−MgO mixed powder made by calcining a gel. The MgO in the mixed powder can be leached completely with acetic acid solution at room temperature, but the CeO2 remains unaffected. The surface area (Sg) of the resulting CeO2 increases with Mg/Ce ratio, but approaches constant after the ratio is larger than a given value which is higher for the higher gel calcining temperature. When Mg/Ce is 8 (molar ratio) and the calcining temperature is 1253 K, the Sg of the resulting ceria remains 25.1 m2/g even after annealed at 1253 K for 4 h. In comparison with the conventional methods, CeO2 from the new method shows higher surface area and higher thermal stability.  相似文献   
103.
We investigate in detail the process of CO2-laser writing of long-period fiber gratings (LPFGs) in unannealed and annealed boron-doped fiber samples by using repeated scanning of CO2-laser pulses. We find that the writing dynamics depends strongly on the CO2-laser energy density and the annealing temperature of the fiber. Our results from analyzing the writing dynamics reveal the relative importance of various physical effects arising from glass structure changes due to different writing conditions and thus provide a better understanding of the formation and the properties of CO2-laser written LPFGs.  相似文献   
104.
Eric Yen  王英 《四川建材》2010,36(4):180-183
长期保存(LTP)是一个极具吸引力的新研究领域,其目标是使档案的持续性能保持一段可预见的足够时间。然而这项研究一开始就遭遇了诸多挑战,比如归档时框架、正规方法和工作流模型的缺失,进一步的亏损无法保持档案间的互操作性,以及无信息衰减迹象的信息丢失等。本研究旨在探究各类文件的LTP如何不受时间演变、技术、数字环境变化的影响。基本需求源于存储管理与信息管理的整合,以及数据、元数据、索引等的安全保存。 本文介绍了政府档案管理和知识管理LTP流程有关上述需求的演变发展。资源的有效搜索、数据的有效存储/访问、一致的用户界面、共置备份的恢复图、以及认证和安全管理的动态调整构成随后的任务。接着,论文详细阐述了示范语义数据网格及其注解和服务配套机制,这当中本体起到关键作用。最后,论文总结了习得经验,以及有关LTP语义网格的未来工作。  相似文献   
105.
In this paper, two mutation-based evolving artificial neural networks, which are based on the Fuzzy ARTMAP (FAM) network and evolutionary programming, are proposed. The networks utilize the knowledge base extracted from a set of data to perform search and adaptation. The performances of the two networks are assessed using benchmark problems, with the results analyzed and discussed. The effects of the network parameters are evaluated through a parametric study. The applicability of the networks is also demonstrated using a real fault detection and diagnosis task in a power generation plant. The experimental results consistently indicate the usefulness of the proposed evolutionary FAM-based networks in yielding good classification performances with parsimonious network structures.  相似文献   
106.
Empathy is an essential part of normal social function that people with autism spectrum conditions (ASCs) lack. This study uses the intervention of enhancing empathy via 3D animated scenarios of empathy in a virtual learning environment to help those deficient in empathy. Specifically, this study explores the understanding of empathy, perspective-taking and the performance of understanding of empathy via a collaborative virtual learning environment (CVLE) - empathy system. The study, which used CVLE - 3D empathy systems and three participants diagnosed with ASCs, conducted multiple baseline research for evidence of improved understanding of empathy via system usage. This experimental study lasted 5 months and the experimental results indicate that using the CVLE 3D empathy system had significant and positive effects on participant use of empathy, both within the CVLE 3D empathy system and in terms of maintaining learning in understanding empathy.  相似文献   
107.
A new framework of non-local model for the strain energy density is proposed in this paper. The global strain energy density of the representative volume element is treated as a non-local variable and can be obtained through a special integral of the local strain energy density. The local strain energy density is assumed to be dependent on both the strain and the rotation-gradient. As a result of the non-local model, a new strain gradient theory is derived directly, in which the first and second strain gradients, as well as the triadic and tetradic stress, are introduced in the context of work conjugate. For power law hardening materials, size effects in thin metallic wire torsion and ultra-thin cantilever beam bend are investigated. It is found that the result predicted by the theoretical model is well consistent with the experimental data for the thin wire torsion. On the other hand, the calculation result for the micro-cantilever beam bend clearly shows the size effect.  相似文献   
108.
Corrosion fatigue behavior of the dissimilar metal weldment, Alloy 52-A508, under a simulated BWR coolant condition was studied. Corrosion fatigue crack growth rates of the dissimilar metal weldments were observed to increase with crack extension under the nominal constant ΔK loading mode. It could be accounted for by a decrease in the Cr and Ni contents and the crack closure effect with the weld depth. Finite element analysis on the welding residual stress was performed. The trend of analytical results agreed well with that of the residual stress measurements obtained by a hole-drilling strain gauge method.  相似文献   
109.
In this study, the finite element method is employed to calculate SAW characteristics in (100) AlN/diamond based structures with different electrical interfaces; i.e., IDT/ AlN/diamond, AlN/IDT/diamond, IDT/AlN/thin metal film/ diamond, and thin metal film/AlN/IDT/diamond. The effects of Cu and Al electrodes as well as the thickness of electrode on phase velocity, coupling coefficient, and reflectivity of SAWs are illustrated. Propagation characteristics of SAWs in (002) AlN/diamond-based structures are also presented for comparison. Simulation results show that to retain a large reflectivity for the design of RF filters and duplexers, the Cu IDT/(100) AlN/diamond structure possesses the highest phase velocity and largest coupling coefficient at the smallest AlN film thickness- to-wavelength ratio.  相似文献   
110.
A novel automatic-gain-control (AGC) architecture utilizing wideband current feedback is proposed for the baseband circuit of a wireless endoscope capsule. The baseband circuit consists of a fast-settling wideband AGC loop and an amplitude-shift-keying demodulator. Additional integrators in the reverse signal path provide negative feedback, bandpass-filtering effect, attenuating low-frequency noises, and dc offset from the radio-frequency front end. The baseband circuit fabricated in a 180-nm complementary metal-oxide-semiconductor process achieves a wide-intermediate-frequency (IF) carrier frequency in the range of 0.5-40 MHz, a measured settling time of 2 mus, and an input sensitivity of -57 dBm. The entire baseband demodulator dissipates only 5 mA, with a 1.8-V supply at a data rate of 1.37 Mb/s and an IF carrier frequency of 10 MHz.  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