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   14788篇
  免费   1434篇
  国内免费   1635篇
化学   1407篇
晶体学   20篇
力学   942篇
综合类   425篇
数学   11475篇
物理学   3588篇
  2024年   27篇
  2023年   163篇
  2022年   215篇
  2021年   309篇
  2020年   290篇
  2019年   376篇
  2018年   338篇
  2017年   436篇
  2016年   493篇
  2015年   394篇
  2014年   721篇
  2013年   969篇
  2012年   663篇
  2011年   866篇
  2010年   761篇
  2009年   1034篇
  2008年   1123篇
  2007年   1155篇
  2006年   996篇
  2005年   861篇
  2004年   652篇
  2003年   709篇
  2002年   632篇
  2001年   520篇
  2000年   575篇
  1999年   467篇
  1998年   450篇
  1997年   360篇
  1996年   272篇
  1995年   144篇
  1994年   162篇
  1993年   92篇
  1992年   78篇
  1991年   71篇
  1990年   51篇
  1989年   46篇
  1988年   40篇
  1987年   26篇
  1986年   28篇
  1985年   51篇
  1984年   43篇
  1983年   16篇
  1982年   35篇
  1981年   21篇
  1980年   28篇
  1979年   21篇
  1978年   14篇
  1977年   16篇
  1976年   14篇
  1975年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The feature selection consists of obtaining a subset of these features to optimally realize the task without the irrelevant ones. Since it can provide faster and cost-effective learning machines and also improve the prediction performance of the predictors, it is a crucial step in machine learning. The feature selection methods using support machines have obtained satisfactory results, but the noises and outliers often reduce the performance. In this paper, we propose a feature selection approach using fuzzy support vector machines and compare it with the previous work, the results of experiments on the UCI data sets show that feature selection using fuzzy SVM obtains better results than using SVM.  相似文献   
82.
Recently adaptive wavelet methods have been developed which can be shown to exhibit an asymptotically optimal accuracy/work balance for a wide class of variational problems including classical elliptic boundary value problems, boundary integral equations as well as certain classes of noncoercive problems such as saddle point problems. A core ingredient of these schemes is the approximate application of the involved operators in standard wavelet representation. Optimal computational complexity could be shown under the assumption that the entries in properly compressed standard representations are known or computable in average at unit cost. In this paper we propose concrete computational strategies and show under which circumstances this assumption is justified in the context of elliptic boundary value problems. Dedicated to Charles A. Micchelli on the occasion of his 60th birthday Mathematics subject classifications (2000) 41A25, 41A46, 65F99, 65N12, 65N55. This work has been supported in part by the Deutsche Forschungsgemeinschaft SFB 401, the first and third author are supported in part by the European Community's Human Potential Programme under contract HPRN-CT-202-00286 (BREAKING COMPLEXITY). The second author acknowledges the financial support provided through the European Union's Human Potential Programme, under contract HPRN-CT-2002-00285 (HASSIP) and through DFG grant DA 360/4–1.  相似文献   
83.
A method for solving a linear system is defined. It is a Lanczos-type method, but it uses formal vector orthogonality instead of scalar orthogonality. Moreover, the dimension of vector orthogonality may vary which gives a large freedom in leading the algorithm, and controlling the numerical problems. The ideas of truncated and restarted methods are revisited. The obtained residuals are exactly orthogonal to a space of increasing dimension. Some experiments are done, the problem of finding automaticaly good directions of projection remains partly open.  相似文献   
84.
The paper continues investigations of stationarity and regularity properties of collections of sets in normed spaces. It contains a summary of different characterizations (both primal and dual) of regularity and a list of sufficient conditions for a collection of sets to be regular.  相似文献   
85.
研究了基于支持向量机的后验概率的应用,提出了对样本集进行分解,以产生局部后验概率,根据模式的稳健性对局部后验概率进行凸组合融合的方法.  相似文献   
86.
We will be mainly concerned with some important fiber spaces over Teichmuller spaces, including the Bers fiber space and Teichmuller curve, establishing an isomorphism theorem between "punctured" Teichmuller curves and determining the biholomorphic isomorphisms of these fiber spaces.  相似文献   
87.
In this paper there is stated a result on sets in ordered linear spaces which can be used to show that some properties of the sets are inherited by their convex hulls under suitable conditions. As applications one gives a characterization of weakly efficient points and a duality result for nonconvex vector optimization problems.  相似文献   
88.
Nonlinear Time Series Analysis Since 1990:Some Personal Reflections   总被引:5,自引:0,他引:5  
Abstract I reflect upon the development of nonlinear time series analysis since 1990 by focusing on five majorareas of development. These areas include the interface between nonlinear time series analysis and chaos,thenonparametric/semiparametric approach,nonlinear state space modelling,financial time series and nonlinearmodelling of panels of time series.  相似文献   
89.
一类多线性积分算子的端点有界性   总被引:3,自引:0,他引:3  
刘岚喆  陆善镇 《数学学报》2006,49(5):961-972
本文对一类相关于非卷积型算子的多线性算子,证明了其在端点情形上的有界性,该算子包括Littlewood-Paley算子和Marcinkiewicz算子.  相似文献   
90.
该文基于热声环境,采用厘米级扁管和deltaE数值计算对微型热声换热器进行了优化设计。  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