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   443418篇
  免费   43091篇
  国内免费   18021篇
电工技术   24740篇
技术理论   48篇
综合类   28621篇
化学工业   82432篇
金属工艺   23977篇
机械仪表   26670篇
建筑科学   33038篇
矿业工程   13221篇
能源动力   12101篇
轻工业   34154篇
水利工程   8085篇
石油天然气   25705篇
武器工业   3279篇
无线电   50758篇
一般工业技术   54770篇
冶金工业   21857篇
原子能技术   4369篇
自动化技术   56705篇
  2024年   1669篇
  2023年   6321篇
  2022年   11321篇
  2021年   15989篇
  2020年   13050篇
  2019年   12295篇
  2018年   13827篇
  2017年   15436篇
  2016年   14872篇
  2015年   19280篇
  2014年   23416篇
  2013年   28467篇
  2012年   28628篇
  2011年   31107篇
  2010年   27917篇
  2009年   26525篇
  2008年   25539篇
  2007年   24277篇
  2006年   24218篇
  2005年   21248篇
  2004年   14968篇
  2003年   13527篇
  2002年   12801篇
  2001年   11332篇
  2000年   10926篇
  1999年   10940篇
  1998年   8245篇
  1997年   6931篇
  1996年   6476篇
  1995年   5379篇
  1994年   4332篇
  1993年   3010篇
  1992年   2345篇
  1991年   1798篇
  1990年   1422篇
  1989年   1138篇
  1988年   961篇
  1987年   614篇
  1986年   507篇
  1985年   316篇
  1984年   257篇
  1983年   200篇
  1982年   155篇
  1981年   106篇
  1980年   118篇
  1979年   61篇
  1978年   35篇
  1977年   44篇
  1976年   51篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
一种基于EM非监督训II练的自组织分词歧义解决方案   总被引:1,自引:0,他引:1  
摘要本文旨在提供一种基于非监督训练的分词歧义解决方案和一种分词算法。基于EM的思想,每个句子所对应的所有(或一定范围内)的分词结果构成训练集,通过这个训练集和初始的语言模型可以估计出一个新的语言模型。最终的语言模型通过多次迭代而得到。通过一种基于该最终语言模型的统计分词算法,对于每个句子至少带有一个歧义的测试集的正确切分精度达到85.36%(以句子为单位)。  相似文献   
992.
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   
993.
Image reconstruction by using near‐field and far‐field data for an imperfectly conducting cylinder is investigated. A conducting cylinder of unknown shape and conductivity scatters the incident wave in free space and the scattered near and far fields are measured. By using measured fields, the imaging problem is reformulated into an optimization problem and solved by the genetic algorithm. Numerical results show that the convergence speed and final reconstructed results by using near‐field data are better than those obtained by using far‐field data. This work provides both comparative and quantitative information. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 69–73, 2001.  相似文献   
994.
This study presents a novel means of resolving multiple objective goal programming (GP) problems with quasi-convex linear penalty functions. The proposed method initially expresses a quasi-convex function by the maximum operator of two convex functions, then solves it via a linear programming technique. The proposed method does not contain any zero–one variables; nor does it require dividing the multi-objective quasi-convex GP problem into large sub-problems as in conventional methods. Some illustrative examples are provided.  相似文献   
995.
改进遗传算法搜索性能的研究   总被引:1,自引:0,他引:1  
本文针对改进遗传算法的搜索性能,提出了一种新的变异算子-自适应多位变异算子,它根据每一代的每一个体在当代中的优劣程度,自适应地控制其发生变异的位数。适应度差的个体变异的位数多,一方面使差的模式生存机会少,另一方面增加了种群的多样性,同时也扩大了搜索范围。我们用模式定理证明了该算子的有效性,并且我们作的仿真实验也同样表明该算子能大大改进遗传算法的搜索性能。  相似文献   
996.
一种采用80C196KC的伺服控制系统的设计   总被引:1,自引:0,他引:1  
介绍了一块用于三轴稳定跟踪装置中位置伺服控制卡的软、硬件设计。硬件电路实现了数据采集、D/A输出、上下位机通讯和输入输出信号接口等功能。单片机程序采用C96语言编制。软硬结合进行系统联调 ,效果很好  相似文献   
997.
Re-engineering of the design process for concurrent engineering   总被引:20,自引:0,他引:20  
According to the requirements of concurrent engineering, three interdependency relationships (uncoupled relationship, coupled relationship and decoupled relationship) between design activities are presented in this paper. And the coupled relationship plays an important role in concurrent product design process. To represent the precedence relationships among design activities, a directed graph is used to describe the design process. And the interdependency relationship between activities is illustrated by a Design Structure Matrix which is the transpose of the accessibility matrix of the corresponding graph. Using the DSM, an algorithm of recognizing the coupled activities during the design process is presented. Moreover, an algorithm to figure out the order levels of activities during the design process is proposed. And both algorithms are illustrated with a die design example.  相似文献   
998.
Two piezoresistive (n-polysilicon) strain sensors on a thin Si3N4/SiO2 membrane with improved sensitivity were successfully fabricated by using MEMS technology. The primary difference between the two designs was the number of strips of the polysilicon patterns. For each design, a doped n-polysilicon sensing element was patterned over a thin 3 μm Si3N4/SiO2 membrane. A 1000×1000 μm2 window in the silicon wafer was etched to free the thin membrane from the silicon wafer. The intent of this design was to fabricate a flexible MEMS strain sensor similar in function to a commercial metal foil strain gage. A finite element model of this geometry indicates that strains in the membrane will be higher than strains in the surrounding silicon. The values of nominal resistance of the single strip sensor and the multi-strip sensor were 4.6 and 8.6 kΩ, respectively. To evaluate thermal stability and sensing characteristics, the temperature coefficient of resistance [TCR=(ΔR/R0)/ΔT] and the gage factor [GF=(ΔR/R0)/] for each design were evaluated. The sensors were heated on a hot plate to measure the TCR. The sensors were embedded in a vinyl ester epoxy plate to determine the sensor sensitivity. The TCR was 7.5×10−4 and 9.5×10−4/°C for the single strip and the multi-strip pattern sensors. The gage factor was as high as 15 (bending) and 13 (tension) for the single strip sensor, and 4 (bending) and 21 (tension) for the multi-strip sensor. The sensitivity of these MEMS sensors is much higher than the sensitivity of commercial metal foil strain gages and strain gage alloys.  相似文献   
999.
基于双链式存储的可靠通信网合并   总被引:2,自引:0,他引:2  
本文介绍图的双链式存储结构在可靠通讯网合并算法中的应用.  相似文献   
1000.
针对选煤厂生产调度的自身特点,以大屯选煤厂生产调度的实际情况为背景,介绍了基于CSCW的选煤生产调度管理系统,并对此系统的安全性和异构为数据库的访问做了阐述。  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