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   89786篇
  免费   1158篇
  国内免费   413篇
电工技术   830篇
综合类   2319篇
化学工业   12616篇
金属工艺   4903篇
机械仪表   3152篇
建筑科学   2526篇
矿业工程   573篇
能源动力   1307篇
轻工业   4221篇
水利工程   1371篇
石油天然气   371篇
无线电   9639篇
一般工业技术   17370篇
冶金工业   3635篇
原子能技术   299篇
自动化技术   26225篇
  2022年   78篇
  2021年   102篇
  2020年   93篇
  2019年   100篇
  2018年   14534篇
  2017年   13462篇
  2016年   10057篇
  2015年   733篇
  2014年   402篇
  2013年   586篇
  2012年   3451篇
  2011年   9778篇
  2010年   8541篇
  2009年   5834篇
  2008年   7177篇
  2007年   8094篇
  2006年   404篇
  2005年   1509篇
  2004年   1362篇
  2003年   1391篇
  2002年   742篇
  2001年   209篇
  2000年   265篇
  1999年   164篇
  1998年   162篇
  1997年   120篇
  1996年   159篇
  1995年   92篇
  1994年   98篇
  1993年   86篇
  1992年   76篇
  1991年   70篇
  1990年   57篇
  1989年   75篇
  1988年   48篇
  1987年   51篇
  1986年   45篇
  1985年   60篇
  1984年   61篇
  1983年   54篇
  1982年   45篇
  1981年   48篇
  1979年   39篇
  1968年   45篇
  1966年   45篇
  1965年   44篇
  1958年   38篇
  1957年   36篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
A concept of business intelligent system for financial prediction is considered in this paper. It provides data needed for fast, precise and good business decision support to all levels of management. The aim of the project is the development of a new online analytical processing oriented on case-based reasoning (CBR) where a previous experience for every new problem is taken into account. Methodological aspects have been tested in practice as a part of the management information system development project of “Novi Sad Fair”. A case study of an improved application of CBR in prediction of future payments is discussed in the paper. This paper is originally presented at The International Conference on Hybrid Information Technology 2006, at the special session on “Intelligent Information Systems for Financial Engineering”, November 2006 in Cheju Island, Korea.  相似文献   
82.
The multi-homogeneous Bezout number is a bound for the number of solutions of a system of multi-homogeneous polynomial equations, in a suitable product of projective spaces. Given an arbitrary, not necessarily multi-homogeneous, system, one can ask for the optimal multi-homogenization that would minimize the Bezout number. In this paper it is proved that the problem of computing, or even estimating, the optimal multi-homogeneous Bezout number is actually NP-hard. In terms of approximation theory for combinatorial optimization, the problem of computing the best multi-homogeneous structure does not belong to APX, unless P = NP. Moreover, polynomial-time algorithms for estimating the minimal multi-homogeneous Bezout number up to a fixed factor cannot exist even in a randomized setting, unless BPP ⫆ NP.  相似文献   
83.
In this paper, AssetCollector is presented, which is a system for managing collections of cultural assets. AssetCollector covers the needs of collection curators towards defining, populating and searching a collection in a flexible way, while supporting them in generating reports based on the collection’s assets and reusing them in order to build web sites and CD-ROMs. In order to support the above functionality, the system provides the content structuring subsystem, the content input subsystem, the search subsystem and the report subsystem. The use of the subsystems is straightforward and requires no technical skills from the curators. AssetCollector has been successfully applied for organizing various collections of cultural assets in Greece, such as archaeological sites, museums and published books. In the future, an evaluation procedure is planned in order to further refine the use of the system according to the targeted users’ needs. Furthermore, more import and export facilities will be provided, which will make the system compliant with widely accepted standards.  相似文献   
84.
In this paper, we generalize the Linear VaR method from portfolios with normally distributed risk factors to portfolios with mixture of elliptically distributed ones. We treat both the Expected Shortfall and the Value-at-Risk of such portfolios. Special attention is given to the particular case of a mixture of multivariate t-distributions. This is a part of J. SADEFO-KAMDEM PhD Thesis[12] of the Université de Reims, France . It has been presented at the workshop on modelling and computation in Financial Engineering at Bad Herrenalb, Germany May 6-8, 2003. The author is an associate professor at the Department of mathematics, université d’Evry Val d’Essonne.  相似文献   
85.
86.
Applications of the discrete element method in mechanical engineering   总被引:2,自引:0,他引:2  
Compared to other fields of engineering, in mechanical engineering, the Discrete Element Method (DEM) is not yet a well known method. Nevertheless, there is a variety of simulation problems where the method has obvious advantages due to its meshless nature. For problems where several free bodies can collide and break after having been largely deformed, the DEM is the method of choice. Neighborhood search and collision detection between bodies as well as the separation of large solids into smaller particles are naturally incorporated in the method. The main DEM algorithm consists of a relatively simple loop that basically contains the three substeps contact detection, force computation and integration. However, there exists a large variety of different algorithms to choose the substeps to compose the optimal method for a given problem. In this contribution, we describe the dynamics of particle systems together with appropriate numerical integration schemes and give an overview over different types of particle interactions that can be composed to adapt the method to fit to a given simulation problem. Surface triangulations are used to model complicated, non-convex bodies in contact with particle systems. The capabilities of the method are finally demonstrated by means of application examples. Commemorative Contribution.  相似文献   
87.
88.
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
89.
90.
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