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   10857篇
  免费   1978篇
  国内免费   1406篇
电工技术   637篇
综合类   1102篇
化学工业   291篇
金属工艺   206篇
机械仪表   823篇
建筑科学   204篇
矿业工程   217篇
能源动力   224篇
轻工业   192篇
水利工程   134篇
石油天然气   417篇
武器工业   227篇
无线电   2556篇
一般工业技术   692篇
冶金工业   276篇
原子能技术   45篇
自动化技术   5998篇
  2024年   49篇
  2023年   149篇
  2022年   354篇
  2021年   345篇
  2020年   372篇
  2019年   354篇
  2018年   337篇
  2017年   448篇
  2016年   529篇
  2015年   603篇
  2014年   815篇
  2013年   730篇
  2012年   929篇
  2011年   909篇
  2010年   848篇
  2009年   826篇
  2008年   838篇
  2007年   855篇
  2006年   712篇
  2005年   621篇
  2004年   466篇
  2003年   444篇
  2002年   313篇
  2001年   248篇
  2000年   203篇
  1999年   168篇
  1998年   145篇
  1997年   126篇
  1996年   75篇
  1995年   70篇
  1994年   67篇
  1993年   42篇
  1992年   36篇
  1991年   25篇
  1990年   30篇
  1989年   21篇
  1988年   16篇
  1987年   4篇
  1986年   10篇
  1985年   12篇
  1984年   16篇
  1983年   17篇
  1982年   10篇
  1981年   8篇
  1980年   3篇
  1979年   8篇
  1978年   6篇
  1977年   4篇
  1976年   7篇
  1956年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
A history of numerical modelling of the Wairakei geothermal field   总被引:1,自引:0,他引:1  
The history of computer modelling of the Wairakei geothermal field is reviewed. It covers the development of lumped-parameter models during the 1970s and then discusses the evolution and first applications of geothermal reservoir simulation techniques. The development of reservoir models of Wairakei at the University of Auckland began in the early 1980s; current models produces good matches against field data. Many future scenarios have been run using the University's models and have been presented at various regulatory hearings. The general conclusion from these scenarios is that Wairakei can continue producing electricity at the current level for at least another 50 years, and if Wairakei is shut down after 100 years of operation it will recover to its pre-exploitation state after a further 300 years.  相似文献   
992.
Two important forces in human behavior are action and inaction. Although action and inaction are commonly associated with the presence and the absence of behavioral activity, they can also be represented as information processing goals. Action (inaction) goals influence decision effort and increase satisfaction with environments that are structured to allow for more (less) processing (Studies 1 and 2). This increased satisfaction can transfer to the decision (Study 3) and can increase the intent to perform a decision-congruent behavior (Studies 4 and 6). Finally, the author shows escalation of action and inaction goals when they are not achieved (Study 5) and rebound of the alternative goal when the focal goal is achieved (Study 6). (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
993.
Abstract

Real-time model-based reservoir management requires efficient computational techniques for optimizing reservoir performance under uncertainty. A variety of algorithms addressing various aspects of this “closed-loop” methodology have been presented by various investigators, but substantial effort is still needed to make the entire process robust and efficient. In our recent work, we introduced an approximate feasible direction optimization algorithm for treating nonlinear path constraints (which are constraints such as maximum liquid production rate, which must be satisfied at every time step) and a new parameterization based on kernel principal component analysis (KPCA) for multipoint geostatistical models. The KPCA representation allows for the use of a gradient-based history-matching procedure that is able to maintain a higher degree of geological realism in the history-matched model. In this article, we combine these procedures with our general adjoint-based optimization technique to provide a full closed-loop capability. This integrated set of algorithms is then applied to a realistic field case. Specifically, we describe the key computational procedures and highlight the linkages required to provide the closed-loop capability. The example case considered is based on a Gulf of Mexico reservoir and involves three injection wells and four production wells operating under bottom hole pressure, total injection rate, and maximum water cut constraints. For this case, it is demonstrated that application of the closed-loop methodology provides a 25% increase in the net present value (NPV) over predictions for a realistic base case. This improvement is almost the same as that achieved using an open-loop approach, which is an idealized formulation in which the geological model is assumed to be known. These results demonstrate that the overall closed-loop procedure will indeed be applicable for practical cases with uncertain geology.  相似文献   
994.
During the past years, several papers have been published that question the use of the CIE colour‐matching functions in the case of metameric samples. Visually matching samples produced on CRT (Cathode Ray Tube) monitors are metameric to most colour stimuli created by illuminating reflecting materials. As CRT monitors are often used in colour design applications, it seemed important to check how well CIE colorimetry will predict such colour matches. To investigate this problem, we set up an experiment in which painted samples were matched with samples produced on a CRT monitor. The colour of incandescent lamp irradiated Munsell samples were visually matched to the mixture of the RGB primaries of a CRT monitor. Both the reflected colour stimuli of the Munsell samples and the emitted stimuli of the monitor were measured spectroradiometrically. Our results imply that there is an observer‐dependent variability among the matches, but we could not find a major difference between the tristimulus data of the hard copy and soft copy presentations that would indicate errors in the CIE colour‐matching functions. The measurement accuracy, quantization errors of the monitor, and the achieved accuracy of the colour matches are treated in this study. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 436–441, 2001  相似文献   
995.
对景象匹配定位导航的工作原理进行了数学化描述,讨论SINS/SMNS组合导航系统的信息融合算法,重点研究了其中两种信息融合算法:外推法和Lyapunov自适应滤波算法.通过仿真实验表明,景象匹配可有效地减小组合导航系统的位置误差.  相似文献   
996.
997.
四环阵天线技术 ,从美国引进以来 ,在 15 0 - 40 0 M频段各类通信系统中 ,已得到了极为广泛的应用 ,但迄今为止 ,尚未见到对这种天线进行讨论的专门文献。作者根据多年来的实践工作与设计经验 ,对四环阵天线进行了基本的分析 ,特别是对有重要实用价值的赋形波瓣异型四环阵的设计进行了充分的讨论。  相似文献   
998.
基于高程选择的SAR景象匹配系统基准图选择准则   总被引:1,自引:1,他引:0  
景象匹配技术是飞行器自主精确制导的关键技术之一,随着武器系统日益精确化,影响匹配制导精度的基准图选择得到了广泛的关注.在合成孔径雷达侧视成像机理的基础上,讨论了高程起伏对SAR图像的影响,引入了图像高程方差的概念.同时,以图像匹配的准确性、稳定性、可靠性为考察量,讨论了各特征参数对匹配性能的影响.文中对真实星载SAR图像进行匹配试验的结果表明,此准则是有效的.  相似文献   
999.
1000.
With the increasing number of available XML documents, numerous approaches for retrieval have been proposed in the literature. They usually use the tree representation of documents and queries to process them, whether in an implicit or explicit way. Although retrieving XML documents can be considered as a tree matching problem between the query tree and the document trees, only a few approaches take advantage of the algorithms and methods proposed by the graph theory. In this paper, we aim at studying the theoretical approaches proposed in the literature for tree matching and at seeing how these approaches have been adapted to XML querying and retrieval, from both an exact and an approximate matching perspective. This study will allow us to highlight theoretical aspects of graph theory that have not been yet explored in XML retrieval.  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