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   138705篇
  免费   10771篇
  国内免费   5502篇
电工技术   7570篇
技术理论   11篇
综合类   8508篇
化学工业   22989篇
金属工艺   7281篇
机械仪表   8458篇
建筑科学   10799篇
矿业工程   3992篇
能源动力   3943篇
轻工业   8723篇
水利工程   2279篇
石油天然气   7657篇
武器工业   943篇
无线电   17073篇
一般工业技术   17437篇
冶金工业   7052篇
原子能技术   1590篇
自动化技术   18673篇
  2024年   582篇
  2023年   2332篇
  2022年   3969篇
  2021年   5543篇
  2020年   4247篇
  2019年   3559篇
  2018年   3991篇
  2017年   4441篇
  2016年   3929篇
  2015年   5281篇
  2014年   6521篇
  2013年   8121篇
  2012年   8517篇
  2011年   9090篇
  2010年   7886篇
  2009年   7729篇
  2008年   7673篇
  2007年   7134篇
  2006年   7329篇
  2005年   6500篇
  2004年   4468篇
  2003年   3770篇
  2002年   3390篇
  2001年   3182篇
  2000年   3287篇
  1999年   3827篇
  1998年   3269篇
  1997年   2831篇
  1996年   2552篇
  1995年   2134篇
  1994年   1714篇
  1993年   1324篇
  1992年   1051篇
  1991年   809篇
  1990年   657篇
  1989年   545篇
  1988年   421篇
  1987年   323篇
  1986年   232篇
  1985年   183篇
  1984年   116篇
  1983年   87篇
  1982年   94篇
  1981年   67篇
  1980年   53篇
  1979年   33篇
  1978年   26篇
  1977年   26篇
  1976年   42篇
  1973年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The tool portfolio of a plant refers to the makeup, in quantity and type, of processing machines in the plant. It is determined by taking into consideration the future trends of process and machine technologies and the forecasts of product evolution and product demands. Portfolio planning is also a multicriteria decision-making task involving tradeoffs among, investment cost, throughput, cycle time, and risk. Tool portfolio planning is a complex task that has strong bearing on manufacturing efficiency. In the first part of this paper, a multicriteria economic decision model is presented for optimal configuration. of the portfolio and to determine the optimal factory loading. The second and third parts of the paper contain applications of the model. If plants are closely located or have a twin-plant design, portfolio planning at multiple plants can be integrated to enhance the overall effectiveness of portfolios. In the second part, a novel methodology for arbitrating capacity backup between plants is described. Because the economic model is constructed upon a valuation of both cycle time and throughput, it is a suitable method for the evaluation of cycle time reduction projects. The application procedure is outlined in the third part.  相似文献   
32.
STUDYONRESIDUESOF~(14)C-FENITROTHIONINMODELRICE-FISHECOSYSTEMANDFIELDRICE-FISHECOSYSTEMZhangZhongliang(张仲良);WangHuaxin(王化新);G?..  相似文献   
33.
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device  相似文献   
34.
TimWu 《电信科学》2002,18(5):77-78
随着数据业务的发展,目前在城域网领域出现了3种很有希望的新技术:MPLS(多协议标记交换)、10 Gbit/s以太网和弹性分组环(RPR).这三种技术都各自有着自己的特点和优点,然而仅仅采用某一项技术并不能解决网络中的全部问题,将这三种技术综合应用就成为一种必要,本文将简要分析这几种技术,及其它们综合起来协同工作的必要性和现实意义.  相似文献   
35.
Based on the concepts of cascade multilevel converters and one-cycle technique, comparisons are conducted to characterize the distortion of the pulsewidth modulation (PWM) and one-cycle control methods that were applied to converters. Simulation results for the different control schemes are obtained in PSIM software initially to see the effect of one-cycle control different from that of PWM control. Through the comparisons, the advantages and disadvantages are identified for each method. The one-cycle scheme is better than PWM control in reducing undesirable harmonics and tracing dynamic waveforms. Simulation and experimental results are also provided to verify the conclusions.  相似文献   
36.
The viability of distributed control restoration using digital cross-connect systems (DCS) depends on its capability for restoring services within specified time requirements, and its economics for providing restoration compared to other alternatives. The authors report a Bellcore study for the impact of the DCS architecture on distributed restoration. This study concludes that currently proposed distributed control DCS self-healing schemes may not meet the 2 second restoration objective for large metropolitan local exchange carrier's networks, regardless of the distributed algorithm used, if the present DCS system architecture which uses serial message processing and serial path cross-connection remains unchanged. They also discuss several DCS architecture enhancement options, including a parallel processing/cross-connect DCS architecture, which may improve the service restoration time  相似文献   
37.
Design issues of photonic integrated devices for WDM applications based on Rowland circle gratings have been studied. Effects of grating period, diffraction order, grating aperture (size), and Rowland circle size on device performance are discussed. The point spread function of a typical Rowland circle grating is evaluated numerically which yields an optical image (spot) size of several microns in diameter. Our study shows that there is a tradeoff between channel dispersion and feedback efficiency in choosing the grating period when a Rowland circle grating is used as the wavelength-selective element for a parallel-waveguide-type wavelength division multiplexing device  相似文献   
38.
In recent years industries have increasingly used customer relationship labor in management as a tool to improve their position in the marketplace. This research involves using a data warehouse, decision-tree-based data mining, and neural network pattern classification analysis to isolate the causes of non-conformity in IC packaging. The correctness of the classification analysis produced using the two methods is compared. Our objective is to establish an information analysis system, that is able to quickly identify the causes of problems thereby reducing the time taken to solve quality-related problems. It is shown that predictions made about the target group using decision tree analysis are more accurate than those made by neural network classification, indicating that decision tree analysis is an effective means of classification analysis of a company's quality problems.  相似文献   
39.
Aggregates of carbon black (CB) in a polymer matrix have a tendency to form a CB network. The dynamic mechanical properties of binary systems of chlorinated polyethylene (CPE) and CB or 3,9‐bis{1,1‐dimethyl‐2[β‐(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionyloxy]ethyl}‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) and their ternary systems were investigated. It was found that the dynamic mechanical properties of those systems depend on the colloidal properties, surface oxides, and surface modification of CB. For binary systems of CPE and CB, oxidized CB gives a high modulus at low strain amplitude and a large Payne effect compared with untreated CB. In contrast, the reverse effect was observed for their ternary systems. Consequently, a good micro‐dispersion is obtainable by surface modification due to physical adsorption of AO‐80 on oxidized CB particles via hydrogen bonds. © 2003 Society of Chemical Industry  相似文献   
40.
在3G牌照正式发放之前,我们仍然需要为新一轮大规模网络建设继续做准备。3G网络和现有2G网络如何互连互通,数据用户如何在3G网络和2G网络之间进行无缝连接,如何使系统网络方便地演进到IMS构架,这些问题都需要大家思考。一个经济有效且易于演进的网络结构,将对运营商顺利开展新一代移动业务,快速抢占发展的制高点,起到相当关键的作用。  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