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   20921篇
  免费   1496篇
  国内免费   676篇
电工技术   981篇
技术理论   3篇
综合类   1257篇
化学工业   3739篇
金属工艺   999篇
机械仪表   1273篇
建筑科学   1601篇
矿业工程   432篇
能源动力   554篇
轻工业   1459篇
水利工程   332篇
石油天然气   1119篇
武器工业   155篇
无线电   2186篇
一般工业技术   3087篇
冶金工业   1172篇
原子能技术   248篇
自动化技术   2496篇
  2024年   74篇
  2023年   285篇
  2022年   450篇
  2021年   590篇
  2020年   492篇
  2019年   446篇
  2018年   471篇
  2017年   592篇
  2016年   536篇
  2015年   707篇
  2014年   847篇
  2013年   1095篇
  2012年   1169篇
  2011年   1246篇
  2010年   1070篇
  2009年   1032篇
  2008年   1105篇
  2007年   1060篇
  2006年   1141篇
  2005年   1108篇
  2004年   702篇
  2003年   656篇
  2002年   608篇
  2001年   530篇
  2000年   677篇
  1999年   733篇
  1998年   632篇
  1997年   562篇
  1996年   493篇
  1995年   459篇
  1994年   335篇
  1993年   250篇
  1992年   208篇
  1991年   171篇
  1990年   134篇
  1989年   117篇
  1988年   90篇
  1987年   44篇
  1986年   48篇
  1985年   43篇
  1984年   18篇
  1983年   5篇
  1982年   14篇
  1981年   13篇
  1980年   11篇
  1979年   6篇
  1978年   3篇
  1977年   3篇
  1976年   4篇
  1970年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
谭飞  王寿林  谷鹏  王毅 《电子测试》2020,(4):75-76,91
工欲善其事,必先利其器。自动化测试工具就是5G时代的利器。本文针对5G时代人工测试面临的挑战,提出5G MANO自动化测试解决方案、原理、方法和流程,并结合ZTEMANO项目中的HATT自动化测试工具和自动化测试实践进行论证。自动化测试,极大的提升测试效率,输出高质量的5G产品,为运营商5G建设贡献力量。  相似文献   
112.
太阳能溴化锂吸收式空调制冷是解决建筑节能降耗和太阳能建筑供能推广应用的重要途径。通过对太阳能热源系统、空调机组制冷系统的性能测试,确定了太阳能吸收式空调的制冷能力和太阳能辐照、冷冻出水温度及水循环流量之间的关系。在太阳能辐照度为700 W/m2、热源供水温度在75℃以上的工况下,溴化锂吸收式空调机组的COP达到0.65左右。太阳能空调内的真空环境和溶液管理措施是影响机组制冷性能的重要因素。  相似文献   
113.
本文首先分析了电信运营商在参与大型盛会通信保障任务期间搭建综合指挥体系的必要性,然后结合奥运会和世博会的差异,介绍了移动运营商在两个盛会中综合指挥体系建设模式的区别,从体系架构、事件处理原则和流程、现场团队部署、体系运转方式四个方面进行了详细的对比阐述和总结。  相似文献   
114.
Gu  M.-Y. Wang  K. Xu  Y.-S. 《Electronics letters》2005,41(12):685-687
The postulate of a linear tensor relation in the measured equation of invariance (MEI) is proposed for three-dimensional (3D) problems. As a result, all three components of the field vector to be solved are coupled in the MEI. Combined with the finite difference method, the present method is applied to the analysis of scattering by 3D conducting objects and results in a significant improvement in the accuracy of numerical results as compared to those obtained with an uncoupled linear relation.  相似文献   
115.
The general objective of our work is to investigate the area and power-delay performances of low-voltage full adder cells in different CMOS logic styles for the predominating tree structured arithmetic circuits. A new hybrid style full adder circuit is also presented. The sum and carry generation circuits of the proposed full adder are designed with hybrid logic styles. To operate at ultra-low supply voltage, the pass logic circuit that cogenerates the intermediate XOR and XNOR outputs has been improved to overcome the switching delay problem. As full adders are frequently employed in a tree structured configuration for high-performance arithmetic circuits, a cascaded simulation structure is introduced to evaluate the full adders in a realistic application environment. A systematic and elegant procedure to scale the transistor for minimal power-delay product is proposed. The circuits being studied are optimized for energy efficiency at 0.18-/spl mu/m CMOS process technology. With the proposed simulation environment, it is shown that some survival cells in stand alone operation at low voltage may fail when cascaded in a larger circuit, either due to the lack of drivability or unsatisfactory speed of operation. The proposed hybrid full adder exhibits not only the full swing logic and balanced outputs but also strong output drivability. The increase in the transistor count of its complementary CMOS output stage is compensated by its area efficient layout. Therefore, it remains one of the best contenders for designing large tree structured arithmetic circuits with reduced energy consumption while keeping the increase in area to a minimum.  相似文献   
116.
Sink scheduling, in the form of scheduling multiple sinks among the available sink sites to relieve the level of traffic burden, is shown to be a promising scheme in wireless sensor networks (WSNs). However, the problem of maximizing the network lifetime via sink scheduling remains quite a challenge since routing issues are tightly coupled. Previous approaches on this topic either suffer from poor performance due to a lack of joint considerations, or are based on relaxed constraints. Therefore, in this paper, we aim to fill in the research blanks. First, we develop a novel notation Placement Pattern (PP) to bound time-varying routes with the placement of sinks. This bounding technique transforms the problem from time domain into pattern domain, and thus, significantly decreases the problem complexity. Then, we formulate this optimization in a pattern-based way and create an efficient Column Generation (CG) based approach to solve it. Simulations not only demonstrate the efficiency of the proposed algorithm but also substantiate the importance of sink mobility for energy-constrained WSNs.  相似文献   
117.
Using thinner wafers can largely reduce the cost of silicon solar cells. One obstacle of using thinner wafers is that few methods can provide good dopant concentration for the back surface field (BSF) and good ohmic contact while generated only in low bowing. In this paper, we have demonstrated the screening–printing B and Al (B/Al) mixture metallization film technique, making use of the screen‐printing technique and the higher solubility of B in silicon to form a B/Al‐BSF. This technique can raise the carrier concentration in the BSF by more than one order of magnitude and reduce the back surface recombination at a low firing temperature (≤800 °C). We have also shown that through the new technique, the metallization paste thickness at the rear could be reduced largely, which however did not degrade the solar cell efficiency. All these efforts are aiming for pushing forward the application of thinner wafers. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
118.
We present a methodology for extracting the 2D power spectral density of a statistically isotropic random rough surface from height measurements by utilizing fast Fourier-Bessel transform. We compute the additional propagation loss due to surface roughness by integrating the extracted spectral density via the formula of absorption enhancement factor. Results for a microstrip demonstrate good correlation between measured and estimated loss up to 20 GHz. It is also possible to choose a random rough surface model for the measured surface and use it to predict the roughness effect on power loss.  相似文献   
119.
A compact Wilkinson power divider using a short circuit anti-coupled line for harmonic suppression is presented in this letter. The structure consists of a pair of anti-coupled line short circuited by a capacitive load realized by a low impedance line. It can offer three finite attenuation poles in the stopband, while arbitrary phase shift can be obtained in the passband. Design procedures have been clearly presented. A 1.8-GHz power divider is designed, fabricated and measured for demonstration. It agreed well with the simulated results. The circuit area of the proposed divider is only 40% of that of the conventional one. Furthermore, the proposed divider has spurious pass-band suppression as high as 20dB.  相似文献   
120.
介绍了传送MPLS(T—MPLS)的发展以及标准化过程,深入分析了T—MPLS对于网络控制平面提出的需求和采用基于分组的传送机制给控制平面带来的挑战。在此基础上,基于现有的ASON/GMPLS控制平面体系,针对T—MPLS面向连接的特性,给出了未来控制平面的发展趋势,以及未来传送网的发展趋势和演进过程。  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