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   228062篇
  免费   17000篇
  国内免费   8563篇
电工技术   12468篇
技术理论   15篇
综合类   12497篇
化学工业   39564篇
金属工艺   11687篇
机械仪表   13185篇
建筑科学   18121篇
矿业工程   5477篇
能源动力   6627篇
轻工业   14150篇
水利工程   3528篇
石油天然气   12265篇
武器工业   1448篇
无线电   28121篇
一般工业技术   29435篇
冶金工业   12247篇
原子能技术   2379篇
自动化技术   30411篇
  2024年   945篇
  2023年   3576篇
  2022年   6391篇
  2021年   8803篇
  2020年   6383篇
  2019年   5579篇
  2018年   5998篇
  2017年   6892篇
  2016年   6335篇
  2015年   8077篇
  2014年   10597篇
  2013年   13669篇
  2012年   13607篇
  2011年   15388篇
  2010年   12850篇
  2009年   12753篇
  2008年   12074篇
  2007年   11560篇
  2006年   12077篇
  2005年   10675篇
  2004年   7337篇
  2003年   6470篇
  2002年   5941篇
  2001年   5230篇
  2000年   5349篇
  1999年   6197篇
  1998年   5818篇
  1997年   4762篇
  1996年   4354篇
  1995年   3630篇
  1994年   3029篇
  1993年   2366篇
  1992年   1861篇
  1991年   1386篇
  1990年   1104篇
  1989年   944篇
  1988年   761篇
  1987年   540篇
  1986年   433篇
  1985年   357篇
  1984年   244篇
  1983年   214篇
  1982年   188篇
  1981年   156篇
  1980年   140篇
  1979年   112篇
  1978年   67篇
  1977年   67篇
  1976年   86篇
  1975年   42篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
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   
62.
Field tests of the transmission performance of the ATSC DTV system have been conducted in Taiwan. The test results as well as comparisons against the NTSC system performance are reported and analyzed. From the measured results the reception characteristics of the DTV can be deduced and can provide guidelines for television stations to design the transmission system, schedule equipment deployment, plan service coverage areas, and improve the reception quality of the digital signal  相似文献   
63.
64.
以TD—SCDMA既有进展及面临的挑战与NGBWM的发展走向为基础,重点论述自主创新导向下的TD—SCDMA与NGBWM务实发展战略思考。  相似文献   
65.
In this paper, according to the theory of thin shells, a basic equation in complex form is derived for conical thin shells with linearly varying wall thickness under symmetric loads, and the uniformly valid asymptotic solutions are given.  相似文献   
66.
Cognitive radio (CR) is a dynamic spectrum access technology as a solution to spectrum under-utilization problem in some licensed bands. Operating over an exceedingly wide spectrum, CR systems usually adopt multi-carrier modulation (MCM) to implement flexible channelization. Consequently, efficient channel allocation scheme becomes extremely important to an MCM based CR (MCM-CR) system. In this paper, a maximum likelihood detection model is developed to detect the presence and locations of licensed users (LUs) signals in the frequency domain. Performance of the detection model, including the optimal detection region, detection probability and false alarm probability, is analyzed. A one-order two-state Markovian chain model is proposed to predict channel status information. In particular, a novel subcarrier allocation scheme for MCM-CR systems is proposed, taking into account the confidence of channel estimation, quality of services (QoS) of rental users (RUs) and throughput. To validate the analytical results, simulations have been conducted to show effectiveness of the proposed scheme.  相似文献   
67.
Polyester‐based polyurethane/nano‐silica composites were obtained via in situ polymerization and investigated by Fourier‐transform infrared spectroscopy (FTIR), or FTIR coupled with attenuated total reflectance (FTIR‐ATR), Transmission electron microscopy (TEM), atomic force microscopy (AFM), an Instron testing machine, dynamic mechanical analysis (DMA) and ultraviolet‐visible spectrophotometry (UV‐vis). FTIR analysis showed that in situ polymerization provoked some chemical reactions between polyester molecules and nano‐silica particles. FTIR‐ATR, TEM and AFM analyses showed that both surface and interface contained nano‐silica particles. Instron testing and DMA data showed that introducing nano‐silica particles into polyurethane enhanced the hardness, glass temperature and adhesion strength of polyurethane to the substrate, but also increased the resin viscosity. UV‐vis spectrophotometry showed that nano‐silica obtained by the fumed method did not shield UV radiation in polyurethane films. Copyright © 2003 Society of Chemical Industry  相似文献   
68.
脉冲电镀最佳参数之探索和优化   总被引:3,自引:0,他引:3  
本文利用正交实验法对脉冲电镀各控制参数进行试验,对影响分散能力、镀层可靠性及外观质量的各种因素进行探讨,寻找影响外观质量的显著因子并加以控制,同时进一步优化脉冲电镀的工艺参数。  相似文献   
69.
Self-consistent effects on the starting current of gyrotron oscillators are examined. Field profiles in the open cavity are shown to be sensitive to the interaction dynamics. This can either significantly raise or lower the oscillation threshold, particularly for the low-Q modes. The transition from resonant-mode oscillations at the low magnetic field to backward-wave oscillations at the high magnetic field is demonstrated.  相似文献   
70.
We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.  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