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   260424篇
  免费   21557篇
  国内免费   11484篇
电工技术   15878篇
技术理论   17篇
综合类   16966篇
化学工业   43238篇
金属工艺   14766篇
机械仪表   16269篇
建筑科学   21010篇
矿业工程   7815篇
能源动力   7430篇
轻工业   17273篇
水利工程   4734篇
石油天然气   15436篇
武器工业   2041篇
无线电   29882篇
一般工业技术   30728篇
冶金工业   12897篇
原子能技术   2885篇
自动化技术   34200篇
  2024年   1191篇
  2023年   4614篇
  2022年   8359篇
  2021年   11265篇
  2020年   8615篇
  2019年   6880篇
  2018年   7868篇
  2017年   8873篇
  2016年   7810篇
  2015年   10449篇
  2014年   13080篇
  2013年   15831篇
  2012年   17180篇
  2011年   18245篇
  2010年   15574篇
  2009年   14900篇
  2008年   14304篇
  2007年   13376篇
  2006年   13838篇
  2005年   12007篇
  2004年   8007篇
  2003年   6820篇
  2002年   6152篇
  2001年   5506篇
  2000年   5713篇
  1999年   6680篇
  1998年   5483篇
  1997年   4585篇
  1996年   4450篇
  1995年   3620篇
  1994年   2942篇
  1993年   2109篇
  1992年   1712篇
  1991年   1320篇
  1990年   950篇
  1989年   785篇
  1988年   627篇
  1987年   431篇
  1986年   326篇
  1985年   216篇
  1984年   172篇
  1983年   122篇
  1982年   123篇
  1981年   102篇
  1980年   84篇
  1979年   33篇
  1978年   27篇
  1977年   24篇
  1976年   26篇
  1975年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
There is no good method to measure the shape and the strain distributions of a structure changing with time. We have previously proposed the Fourier transform grid method (FTGM) to measure the three-dimensional shape and surface strain distributions of stationary objects by analysing the two-dimensional grating images recorded with two cameras. In the stereoscopic method, it is very important to determine the accurate geometric parameters of the camera system. In this paper, the positions and the directions of cameras are accurately determined using the FTGM applied to images of a reference object on which a two-dimensional grating is drawn. Applications for analysing shape and strain distributions of vibrating rubber plates and a moving human skin are shown.  相似文献   
42.
WCDMA与GSM在空中接口上存在较大差异,WCDMA基于码分多址技术,GSM基于时分多址技术。GSM主要处理语音和低速数据,而WCDMA引入了多种速率的数据业务,根据业务的QoS进行资源控制和分配,因此在无线网络规划方法上,WCDMA与GSM存在较大差异。文章从容量规划、覆盖规划、蜂窝布局、规划流程、网络评估等方面对WCDMA与GSM的无线网络规划进行了比较和分析。  相似文献   
43.
In this paper, we address agent coordination from a dynamic systems perspective and propose a dynamic coordination model, which is inspired by biological metabolic systems. A new coordination mechanism through dynamic local adjustment (CDLA) is presented, and coordination is achieved when every agent utilizes explicitly the global system dynamics and performs iteratively a dynamic local adjustment procedure. The CDLA mechanism is investigated in an example multiagent shop floor system. The results show that the example manufacturing process is well-coordinated and the coordination approach is practically applicable and effective  相似文献   
44.
In this study, distribution and history of residual stresses in plaque-like geometries are simulated based on linear thermoviscoelastic model, which helps to understand the mechanics and evolution of the residual stresses in the injection molding process. The numerical calculation of direction, combined with the specified boundary conditions. Results show that the stress variation across the thickness exhibits a high surface tensile value changing to a compressive peak value close to the surface, with the core region experiencing a parabolic tensile peak. Residual stress distribution throughout the thickness is almost same along the flowpath and the final residual stresses value near the gate is lower than the value near the end of flowpath.  相似文献   
45.
Focused ion beam (FIB) and nano-probing were applied for failure analysis of three-dimensional stacked circuits with copper through-silicon-vias between the stacked chips. The failure analysis was done after high temperature storage and thermal cycling tests. Passive voltage contrast in FIB allowed to pinpoint the open sites. FIB cross-sections showed the presence of opens at the bottom of the copper vias. The failure cause was suspected to be an interlayer particle, which was confirmed by optical profilometry. Nano-probing was used on another sample to pinpoint the failure location through the measurement of the local resistance within the daisy chains. The failure was traced out to be related with surface contamination.  相似文献   
46.
La doping effects on intergrowth Bi2WO6–Bi3TiNbO9 ferroelectric ceramics were studied by X-ray diffraction, electron probe microanalysis and dielectric spectroscopy. It was found that the La3+ distribution, ferroelectric phase transition and dielectric relaxation behavior are apparently affected by La doping. With increasing La3+ content, the site of dopant ion varies, the grain growth of Bi5TiNbWO15 is restrained, the Curie temperature is reduced and broadened. Furthermore, two dielectric relaxation loss peaks were observed both in temperature and frequency spectra. The calculated relaxation parameters revealed the oxygen vacancy related to the relaxation process.  相似文献   
47.
Although packet delay and loss are two important parameters of the Internet performance, to the best of our knowledge, the evolution of large‐scale IPv6 delay and loss performance has previously not been studied. In this paper, we analyze more than 600 end‐to‐end IPv6 paths between about 26 testboxes of RIPE Network Coordination Centre over two years, and compare the delay and loss performance over time with their IPv4 counterparts. We present and discuss the measurement methodologies and show that IPv6 paths have a higher delay and loss than their IPv4 counterparts. The main reason for the worse performance stems from IPv6‐in‐IPv4 tunnels rather than from native IPv6 paths and such tunnels are still widely used today. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
48.
宣钢l260m^3高炉大修改造时将炉容扩大到l350m^3,对高炉本体系统设备及冷却系统、自动控制及检测系统进行了全面的改造更新,在炉腹、炉腰及炉身下部高热负荷区域采用铜冷却壁,取消炉身中上部铸铁冷却壁凸台,并采用薄内衬等先进、适用、可靠、成熟的技术。  相似文献   
49.
利用电机学理论分析了影响电机起动转矩、起动电流、最大转矩和最小转矩的因素。  相似文献   
50.
Resistance microwelding of fine crossed nickel wires is of increasing industrial importance for electrical connections in downsized electronic and medical devices, but the understanding of the process is very limited. A study has, therefore, been performed to clarify the basic joining mechanisms, in which the effects of main process parameters (welding current and force and weld time) were investigated by detailed mechanical testing and metallurgical examinations. A bonding mechanism with main process stages (wire cold collapse, surface melting, molten-phase squeeze-out and, solid-state bonding) was proposed. A new technique has also been developed to optimize the process by initiating the welding current well before the electrode force has reached its full nominal value.  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