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   45916篇
  免费   4929篇
  国内免费   2359篇
电工技术   3095篇
技术理论   3篇
综合类   5501篇
化学工业   2402篇
金属工艺   785篇
机械仪表   2028篇
建筑科学   5737篇
矿业工程   2015篇
能源动力   1184篇
轻工业   6338篇
水利工程   2925篇
石油天然气   4399篇
武器工业   875篇
无线电   2651篇
一般工业技术   3013篇
冶金工业   2680篇
原子能技术   320篇
自动化技术   7253篇
  2024年   312篇
  2023年   823篇
  2022年   1483篇
  2021年   1780篇
  2020年   1862篇
  2019年   1535篇
  2018年   1423篇
  2017年   1594篇
  2016年   1861篇
  2015年   1887篇
  2014年   3064篇
  2013年   2845篇
  2012年   3473篇
  2011年   3665篇
  2010年   2678篇
  2009年   2734篇
  2008年   2509篇
  2007年   2958篇
  2006年   2672篇
  2005年   2357篇
  2004年   1853篇
  2003年   1565篇
  2002年   1146篇
  2001年   977篇
  2000年   721篇
  1999年   613篇
  1998年   436篇
  1997年   412篇
  1996年   341篇
  1995年   281篇
  1994年   216篇
  1993年   173篇
  1992年   109篇
  1991年   103篇
  1990年   79篇
  1989年   96篇
  1988年   52篇
  1987年   46篇
  1986年   45篇
  1985年   41篇
  1984年   46篇
  1983年   47篇
  1982年   37篇
  1981年   20篇
  1980年   16篇
  1979年   17篇
  1966年   14篇
  1963年   17篇
  1961年   13篇
  1958年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
针对移动AdHoc网络路由协议评估中指标的模糊性及其体现信息的不完全问题,提出一种基于可信度的路由协议综合评估方法。该方法根据IETFRFC2501的建议,构造路由协议可信度评估指标模型。结合灰色评估法和层次分析法,将评估路由协议性能的主观因素限制在很小范围内,得到了更客观且准确的协议可信度,使用户可以根据评估结果和实际需要快速选择合适的路由协议。实验结果证明,该方法是有效的。  相似文献   
72.
Histogram equalization is an effective technique to boost image quality and contrast enhancement. However, in some cases the increase in image contrast by traditional histogram equalization exceeds the desired amount Which damages the image properties and wanes its natural look. Histogram division and performing a separate equalization for each sub-histogram is one of the presented solutions. The dividing method and determining the number of sub-histograms are the main problems directly affecting the output image quality. In this study, a method is introduced for automatic determination of the number of sub-histograms and density based histogram division leading to appropriate output with no need for parameter setting. Each main peak is in a separate section. Image contrast is increased with no loss of image specifications through determining the number of sub-histograms based on the number of main peaks. The introduced histogram equalization approach consists of three stages. The first stage, using histogram analysis, produces an automated estimate of number of clusters for image brightness levels. The second, clusters the image brightness levels, and using the provided transfer function, the final stage includes contrast enhancement for each individual cluster separately. The results of the proposed approach demonstrate not only clearer details along with a boost in contrast, but also noticeably more natural appearance in the images.  相似文献   
73.
通过对大学英语网络自主学习运行环境和教学模式的研究,介绍了现有网络学习运行环境包含的各种网络结构、软件架构、学习和考核方法等几个方面,讨论了各种环境因素在实际应用中的优劣与取舍原因,给出了开放教学理念下的网络运行环境研究结果。在研究中能给学生提供充分思考的空间、促进学生在学习中的独立思考和探索精神,进而达到学生素质全面发展的目的。  相似文献   
74.
A new method of estimating per-pixel atmospheric column water vapor (ACWV) and potential differences in the reported band center wavelengths of the HyMap sensor has been developed. The new method uses variations of a second order derivative algorithm (SODA) to assess the impact of atmospheric residual features on calculated surface reflectance spectra after atmospheric compensation. The SODA method provides an alternative to the current band ratio techniques of ACWV estimation and also allows the same form of algorithm to be used for the estimation of possible band shifts. A comparison of in-situ measured surface reflectance at two field sites in Western Australia demonstrates improvement in the resulting spectra when post-flight updates are made to the reported HyMap band center wavelengths and applied during the atmospheric compensation process. The same SODA methodology was varied to estimate the ACWV on a per-pixel basis and found to significantly reduce the appearance of the underlying surface structure on the resulting ACWV images as well as improve the overall accuracy of the estimation. The ACWV estimated from the HyMap imagery at the two field sites was found to agree with in-situ atmospheric ACWV measurements to within 2% and represented a two fold increase in accuracy over a 3 band ratio Continuum Interpolated Band Ratio (CIBR) technique of ACWV estimation.  相似文献   
75.
Suitability evaluation of urban construction land based on geo-environmental factors is the process of determining the fitness of a given tract of land for construction. This process involves a consideration of the geomorphology, geology, engineering geology, geological hazards, and other geological factors and is the basis of urban construction land planning and management. With the support of Geographic Information Systems (GIS), grid analysis, and geo-spatial analysis techniques, four factor groups comprising nine separate subfactors of geo-environmental attributes were selected to be used in the evaluation of the suitability level for construction land in Hangzhou. This was based on K-means clustering and back-propagation (BP) neural network methods due to their advantages in fast computing, unique adaptive capacity, and self-organization. Simultaneously, the evaluation results based on K-means clustering and BP neural network were compared and analyzed, and the accuracy evaluation was set. The results showed that the geo-environmental suitability evaluation results of construction land based on K-means clustering and BP neural network were similar in terms of the distribution and scale of construction land suitability level. At the same time, the results of the two evaluation methods were consistent with the variability in suitability level, engineering geology, and hydrogeology of Hangzhou. The results also showed that the real advantage of the methods proposed in this paper lies in their capacity to streamline the mapping process and to ensure that the results are consistent throughout. The suitability level of the urban construction land based on the geo-environment in Hangzhou was divided into four construction sites: land for building super high-rise and high-rise buildings, land for building multistorey buildings, land for low-rise buildings, and nonbuilding land. The results of the suitability evaluation for each category will provide a scientific basis for decision-making in urban development in Hangzhou.  相似文献   
76.
Every organisation exists or is created for the achievement of one or more goals. To ensure continued success, the organisation should monitor its performance with respect to the formulated goals. In practice the performance of an organisation is often evaluated by estimating its performance indicators. In most existing approaches for organisation modelling the relation between performance indicators and goals remains implicit. This paper proposes a formal framework for modelling goals based on performance indicators and defines mechanisms for establishing goal satisfaction, which enable evaluation of organisational performance. Methodological and analysis issues related to goals are also discussed in the paper. The described framework is a part of a general framework for organisation modelling and analysis.  相似文献   
77.
This paper describes the evaluation of a WSD method withinSENSEVAL. This method is based on Semantic Classification Trees (SCTs)and short context dependencies between nouns and verbs. The trainingprocedure creates a binary tree for each word to be disambiguated. SCTsare easy to implement and yield some promising results. The integrationof linguistic knowledge could lead to substantial improvement.  相似文献   
78.
An Internet-based negotiation server for e-commerce   总被引:6,自引:0,他引:6  
This paper describes the design and implementation of a replicable, Internet-based negotiation server for conducting bargaining-type negotiations between enterprises involved in e-commerce and e-business. Enterprises can be buyers and sellers of products/services or participants of a complex supply chain engaged in purchasing, planning, and scheduling. Multiple copies of our server can be installed to complement the services of Web servers. Each enterprise can install or select a trusted negotiation server to represent his/her interests. Web-based GUI tools are used during the build-time registration process to specify the requirements, constraints, and rules that represent negotiation policies and strategies, preference scoring of different data conditions, and aggregation methods for deriving a global cost-benefit score for the item(s) under negotiation. The registration information is used by the negotiation servers to automatically conduct bargaining type negotiations on behalf of their clients. In this paper, we present the architecture of our implementation as well as a framework for automated negotiations, and describe a number of communication primitives which are used in the underlying negotiation protocol. A constraint satisfaction processor (CSP) is used to evaluate a negotiation proposal or counterproposal against the registered requirements and constraints of a client company. In case of a constraint violation, an event is posted to trigger the execution of negotiation strategic rules, which either automatically relax the violated constraint, ask for human intervention, invoke an application, or perform other remedial operations. An Event-Trigger-Rule (ETR) server is used to manage events, triggers, and rules. Negotiation strategic rules can be added or modified at run-time. A cost-benefit analysis component is used to perform quantitative analysis of alternatives. The use of negotiation servers to conduct automated negotiation has been demonstrated in the context of an integrated supply chain scenario. Received: 30 October 2000 / Accepted: 12 January 2001 Published online: 2 August 2001  相似文献   
79.
大型复杂仿真系统相似性模糊综合评判   总被引:3,自引:0,他引:3  
利用模糊数学对仿真模型进行相似性检验,提出了定量与定性相结合、主观与客观相结合的仿真模型与实现模型相似性模糊综合评判法,并给出了各种实用算法和适用场合,对处理“黑盒”和“灰盒”的仿真模型检验具有参考价值。  相似文献   
80.
系统采用Oracle数据库作为开发平台,VB.net为开发工具研制而成。系统借鉴银行和电力企业信用等级评价的规则,结合水司水费收缴的历史纪录及各客户的实际情况,运用自动采集程序,从原有的营销系统和财务系统自动录入数据,再通过优化的模糊概率、神经网络程序,对用户进行交纳水费信用等级评定,建立客户交纳水费风险预警机制。  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