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   22240篇
  免费   1133篇
  国内免费   1027篇
系统科学   1931篇
丛书文集   457篇
教育与普及   359篇
理论与方法论   345篇
现状及发展   947篇
研究方法   53篇
综合类   20307篇
自然研究   1篇
  2024年   70篇
  2023年   129篇
  2022年   227篇
  2021年   306篇
  2020年   226篇
  2019年   131篇
  2018年   876篇
  2017年   917篇
  2016年   669篇
  2015年   537篇
  2014年   640篇
  2013年   705篇
  2012年   1009篇
  2011年   1803篇
  2010年   1667篇
  2009年   1381篇
  2008年   1584篇
  2007年   1761篇
  2006年   902篇
  2005年   837篇
  2004年   753篇
  2003年   753篇
  2002年   904篇
  2001年   826篇
  2000年   616篇
  1999年   674篇
  1998年   449篇
  1997年   470篇
  1996年   412篇
  1995年   365篇
  1994年   337篇
  1993年   287篇
  1992年   233篇
  1991年   227篇
  1990年   192篇
  1989年   176篇
  1988年   169篇
  1987年   92篇
  1986年   48篇
  1985年   18篇
  1984年   4篇
  1983年   3篇
  1980年   2篇
  1977年   2篇
  1976年   1篇
  1974年   1篇
  1973年   1篇
  1972年   3篇
  1967年   1篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The authors concern robust model predictive control for linear continuous systems with polytopic uncertainties and input constraints. At each sampling time, a piecewise constant control sequence is obtained by solving a set of linear matrix inequalities. The sufficient conditions on the existence of the model predictive control are given, and the robust stability of the closed-loop systems is guaranteed. A simulation example illustrates the efficiency of the proposed method.  相似文献   
102.
This paper deals with the development of scientific policy advice by providing a methodology to foster a social learning process. The methodology, called participatory Sustainability Impact Assessment (pSIA), aims to structure complex problem situations, to clarify interests and basic assumptions, to interpret scientific studies, to develop impact assessment, and to explore sensitivity of uncertainty and lack of information. In pSIA workshops the participants are supposed to build conceptual models with different modelling methods, like System Dynamics, Value Chain Analysis, and Morphological Analysis. A case study is presented that describes a workshop series with political as well as academic actors, applying the pSIA approach to an impact assessment of Economic Partnership Agreements between the European Union and the Eastern and Southern Africa Region.
Manuel GottschickEmail: URL: www.agchange.de
  相似文献   
103.
The participation of non-state actors in implementation processes is often understood as a means to increase compliance efficiency. But the implementation of spatial policies frequently focuses on pre-established goals, processes and instruments and thus renders difficult open discourse and shared decision-making. This paper introduces conflict pattern analysis (CPA) as a tool that supports the analysis of the actual actor constellation in order to define efficient approaches that avoid common problems of participatory processes. CPA is a semi-formalised method that helps to identify key-actors, their relations and interaction amongst each other as well as their core beliefs, interests and resources. It aggregates this information to interaction patterns that can be compared, classified and linked to different participatory methods on a theoretically informed basis. Particularly on the local and regional level, this could be the first step for successful (participatory) implementation strategies.  相似文献   
104.
Different from traditional tax audit, supervision with self-audit is a combination of audit by the taxpayer himself and audit by the tax authority. This paper mainly studies a taxpayer's optimal policy of tax evasion under supervision with self-audit and its related properties, in order to deduce some effective suggestions and theoretical bases to restrain tax evasion. Assuming that only a certain proportion of evaded tax can be discovered when the audit is executed, the authors first formulate a static model with self-audit. This model is divided into two stages. At the first stage, taxpayers declare their taxes, then the tax authority chooses audit objects, based on a known probability, and announces the result; if the taxpayer is chosen, he will enter the second stage, during which he has a chance to pay the evaded tax and the corresponding late fees and then is audited by the tax authority. The authors show the existence and uniqueness of the optimal amount of tax evasion at the first stage and the optimal proportion to self-expose at the second stage. The authors also discuss the related properties of the interior solution, and do elasticity analyses on some parameters. Besides, the authors extend the static model into the corresponding two-period model, and study the existence and uniqueness of the solution of the extended model. Finally, under the assumption that tax evasion can only be discovered with a certain probability when the audit is executed, the authors formulate another static model with self-audit and investigate its properties.  相似文献   
105.
Waveform diversity based sonar system for target localization   总被引:1,自引:1,他引:1       下载免费PDF全文
A new monostatic army system taking advantage of diverse waveforms to improve the performance of underwater target localization is proposed.Unlike the coherent signals between different elements in common active array,the transmitted signals from different elements here are spatially orthogonal waveforms which allow for array processing in the transit mode and result in an extension of array aperture.The mathematical derivation of Capon estimator for this sonar system is described in detail.And the performance of this orthogonal-waveform based sonar is analyzed and compared with that of its phased-array counterpart by water tank experiments.Experimental results show that this sonar system could achieve 12 dB-15 dB additional array gain over its phased-array counterpart,which means a doubling of maximum detection range.Moreover,the angular resolution is significantly improved at lower SNR.  相似文献   
106.
Process capability analysis and estimation scheme for autocorrelated data   总被引:1,自引:0,他引:1  
<正>Autocorrelation is prevalent in continuous production processes,such as the processes in the chemical and pharmaceutical industries.With the development of measurement technology and data acquisition technology,sampling frequency is getting higher and the existence of autocorrelation cannot be ignored.This paper analyzes five estimation schemes of process capability for autocorrelated data.Comparisons among these schemes are discussed for small sample and large sample.In conclusion,this paper gives a procedure of process capability analysis for autocorrelated data.  相似文献   
107.
Patent documents are unique external sources of information that reveal the core technology underlying new inventions.Patents also serve as a strategic data source that can be mined to discover state-of-the-art technical development and subsequently help guide R&D investments.This research incorporates an ontology schema to extract and represent patent concepts.A clustering algorithm with non-exhaustive overlaps is proposed to overcome deficiencies with exhaustive clustering methods used in patent mining and technology discovery.The non-exhaustive clustering approach allows for the clustering of patent documents with overlapping technical findings and claims,a feature that enables the grouping of patents that define related key innovations.Legal advisors can use this approach to study potential cases of patent infringement or devise strategies to avoid litigation.The case study demonstrates the use of non-exhaustive overlaps algorithm by clustering US and Japan radio frequency identification (RFID) patents and by analyzing the legal implications of automated discovery of patent infringement.  相似文献   
108.
The relationship between tacit knowledge and informal networks has not been fully explored.Tacit knowledge cannot be well managed directly,because it is deeply embedded in individual actions and experiences.This study proposes an approach to managing informal networks as a new middle way to facilitate the sharing and transferring of tacit knowledge,owing to the fact that tacit knowledge is mostly shared and transferred through informal networks.To support the idea of the approach,an empirical case study of applying the approach to management of a large scientific project is also included.Our findings suggest that informal networks play essential roles for management of tacit knowledge,and thus good management of informal networks can lead to efficient sharing and transferring of tacit knowledge.  相似文献   
109.
模糊检索系统研究   总被引:1,自引:0,他引:1  
模糊性是人类思维和客观事物普遍具有的属性之一。为了克服现行计算机信息系统的局限性 ,模糊检索应运而生。运用模糊技术开发的计算机信息系统既允许用户用自然语言进行信息查询 ,又能给出输出信号项与用户查询的关联度 ,协助用户完成信息处理任务 ,因而具有一定的人脑进行模糊信息处理的能力。简要讨论了模糊检索系统的结构 ,模糊知识库及其管理 ,模糊数据库的组织等。  相似文献   
110.
近程雷达目标多分量信号处理研究   总被引:1,自引:0,他引:1  
以目标多点散射模型为背景 ,提出了FM近程雷达回波混频后多分量信号模型。证明单频信号瞬时频率定义不适合多分量信号。首次提出利用TLS -拓广ESPRIT结合数理统计方法求解多分量信号平均频率。计算机模拟表明 ,该方法用于测距时 ,测试精度高。  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