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   15850篇
  免费   1228篇
  国内免费   1168篇
化学   1370篇
晶体学   21篇
力学   694篇
综合类   157篇
数学   6419篇
物理学   2094篇
综合类   7491篇
  2024年   34篇
  2023年   78篇
  2022年   179篇
  2021年   217篇
  2020年   233篇
  2019年   273篇
  2018年   253篇
  2017年   370篇
  2016年   424篇
  2015年   368篇
  2014年   662篇
  2013年   928篇
  2012年   845篇
  2011年   804篇
  2010年   751篇
  2009年   840篇
  2008年   861篇
  2007年   1067篇
  2006年   983篇
  2005年   865篇
  2004年   790篇
  2003年   685篇
  2002年   677篇
  2001年   635篇
  2000年   566篇
  1999年   528篇
  1998年   436篇
  1997年   384篇
  1996年   390篇
  1995年   310篇
  1994年   270篇
  1993年   235篇
  1992年   237篇
  1991年   186篇
  1990年   162篇
  1989年   145篇
  1988年   114篇
  1987年   98篇
  1986年   77篇
  1985年   53篇
  1984年   54篇
  1983年   17篇
  1982年   34篇
  1981年   18篇
  1980年   20篇
  1979年   24篇
  1978年   11篇
  1977年   15篇
  1976年   11篇
  1974年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
基于矩阵解方程的理论,定义出了一个化学元素矩阵,从而找到了一种配平化学方程式的新方法,称之为矩阵解法。  相似文献   
12.
Parallel preconditioners are presented for the solution of general linear systems of equations. The computation of these preconditioners is achieved by orthogonal projections related to the Frobenius inner product. So, minM∈??AM?IF and matrix M0∈?? corresponding to this minimum (?? being any vectorial subspace of ??n(?)) are explicitly computed using accumulative formulae in order to reduce computational cost when subspace ?? is extended to another one containing it. Every step, the computation is carried out taking advantage of the previous one, what considerably reduces the amount of work. These general results are illustrated with the subspace of matrices M such that AM is symmetric. The main application is developed for the subspace of matrices with a given sparsity pattern which may be constructed iteratively by augmenting the set of non‐zero entries in each column. Finally, the effectiveness of the sparse preconditioners is illustrated with some numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
13.
SPECTRUM-PRESERVING ELEMENTARY OPERATORS ON B(X)   总被引:4,自引:0,他引:4  
1.IntroductionLetXbeaninfinitedimensionalcomplexBanachspaceandB(X)theBanachalgebraofallboundedlinearoperatorsonX.ForTEB(X),a(T),asusual,willdenotethespectrumofT.Let4bealinearmapfromB(X)intoitself.4isspectrum-preservingifa(di(T))=a(T)forallTEB(X);4isspectrum-compressingifa(4(T))ga(T)forallTEB(X).Itisclearthatif4isunital(i.e.,ac(I)=I),thenacisspectrum-preserving(spectrum-compressing)ifandonlyif4preservesinvertibilityinbothdirections(preservesinvertibility),i.e.,4(T)isinvertibleifando…  相似文献   
14.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data.  相似文献   
15.
A new compact bandpass filter composed of two coupled linear tapered line resonators (LTLRs) is designed. The two resonators are arranged in different layers. The filter has two transmission zeros on both sides of the passband. It has small size and steep response below its passband. It is also shown that this filter has 0.6 dB low insertion loss at the centre frequency and 10.5% 3dB bandwidth. This work was supported by the Development Foundation of Shanghai Educational Committee (217608) and Shanghai Leading Academic Discipline Project (T0102).  相似文献   
16.
The author gets a blow-up result of C1 solution to the Cauchy problem for a first order quasilinear non-strictly hyperbolic system in one space dimension.  相似文献   
17.
The problem is to determine nonsensitiveness regions for threshold ellipsoids within a regular mixed linear model.  相似文献   
18.
This paper studies the linear EV model when replicate observations are made only on independent variables. We construct the estimates of regression coefficients and prove the consistency and asymptotic normality under some proper conditions. Results obtained reveal the difference between the case where the independent and dependent variables are observed repeatedly and simultaneously and the case studied in this article.  相似文献   
19.
最速下降规则不失为一可用规则   总被引:5,自引:4,他引:1  
本从统计意义上平均迭代次数的观点出发,指出求解线性规划的最速下降规则是可取的,好用的。  相似文献   
20.
线性分式规划最优解集的求法   总被引:5,自引:0,他引:5  
本文使用多面集的表示定理,导出了线性分式规划最优解集的结构,并给出确定全部最优解的计算步骤。  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