全文获取类型
收费全文 | 3583篇 |
免费 | 487篇 |
国内免费 | 254篇 |
专业分类
化学 | 365篇 |
晶体学 | 36篇 |
力学 | 763篇 |
综合类 | 51篇 |
数学 | 1863篇 |
物理学 | 1246篇 |
出版年
2024年 | 8篇 |
2023年 | 36篇 |
2022年 | 53篇 |
2021年 | 87篇 |
2020年 | 77篇 |
2019年 | 116篇 |
2018年 | 106篇 |
2017年 | 106篇 |
2016年 | 101篇 |
2015年 | 108篇 |
2014年 | 179篇 |
2013年 | 356篇 |
2012年 | 158篇 |
2011年 | 206篇 |
2010年 | 174篇 |
2009年 | 227篇 |
2008年 | 227篇 |
2007年 | 231篇 |
2006年 | 204篇 |
2005年 | 198篇 |
2004年 | 166篇 |
2003年 | 180篇 |
2002年 | 166篇 |
2001年 | 138篇 |
2000年 | 107篇 |
1999年 | 96篇 |
1998年 | 85篇 |
1997年 | 80篇 |
1996年 | 73篇 |
1995年 | 49篇 |
1994年 | 38篇 |
1993年 | 25篇 |
1992年 | 41篇 |
1991年 | 26篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有4324条查询结果,搜索用时 15 毫秒
831.
832.
This article presents a multilevel parallel preconditioning technique for solving general large sparse linear systems of equations. Subdomain coloring is invoked to reorder the coefficient matrix by multicoloring the adjacency graph of the subdomains, resulting in a two‐level block diagonal structure. A full binary tree structure is then built to facilitate the construction of the preconditioner. A key property that is exploited is the observation that the difference between the inverse of the original matrix and that of its block diagonal approximation is often well approximated by a low‐rank matrix. This property and the block diagonal structure of the reordered matrix lead to a multicolor low‐rank (MCLR) preconditioner. The construction procedure of the MCLR preconditioner follows a bottom‐up traversal of the tree . All irregular matrix computations, such as ILU factorizations and related triangular solves, are restricted to leaf nodes where these operations can be performed independently. Computations in nonleaf nodes only involve easy‐to‐optimize dense matrix operations. In order to further reduce the number of iteration of the Preconditioned Krylov subspace procedure, we combine MCLR with a few classical block‐relaxation techniques. Numerical experiments on various test problems are proposed to illustrate the robustness and efficiency of the proposed approach for solving large sparse symmetric and nonsymmetric linear systems. 相似文献
833.
834.
L. M. Kozhevnikova 《复变函数与椭圆型方程》2020,65(3):333-367
ABSTRACTThe Dirichlet problem in arbitrary domains for a wide class of anisotropic elliptic equations of the second order with variable exponent nonlinearities and the right-hand side as a measure is considered. The existence of an entropy solution in anisotropic Sobolev spaces with variable exponents is established. It is proved that the obtained entropy solution is a renormalized solution of the considered problem. 相似文献
835.
ABSTRACT Azo dyes are a group of chemical moieties joined by azo (-N=N-) group with potential usefulness in different industrial applications. But these dyes are not devoid of hazardous consequence because of poor affinity for the fibre and discharge into the water stream. The chemical aspects of 72 azo dyes towards cellulose fibre in terms of their affinity by QSPR have been explored in the present work. We have employed two approaches, namely balance of correlation without IIC (TF1) and balance of correlation with IIC (TF2), to generate 16 QSAR models from 8 splits. The determination coefficient of calibration and validation set was found higher when the QSPR models were developed using the index of ideality correlation (IIC) parameter (TF2). The model developed with TF2 for split 3 was considered as a prominent model because the determination coefficient of the validation set was maximum (r 2 = 0.9468). The applicability domain (AD) was also analysed based on ‘statistical defect’, d(A) for a SMILES attribute. The mechanistic interpretation was done by identifying the SMILES attributes responsible for the promoter of endpoint increase and promoter of endpoint decrease. These SMILES attributes were applied to design 15 new dyes with higher affinity for cellulose fibre. 相似文献
836.
837.
838.
839.
主要解决了如下问题 :对于从河流 L取水并输送到 L同岸的两个用水点 A,B的输水工程(图 1) ,当修建各段输水管道的耗资系数分别为 k1,k2 ,k3 时 ,如何确定抽水点 P及分水点 O才能使加权和值w =k1OA+ k2 OB+ k3OP为最小 . 相似文献
840.
Yu. Vassilevski 《Numerical Linear Algebra with Applications》2004,11(4):327-341
A new two‐level black‐box preconditioner based on the hybrid domain decomposition technique is proposed and studied. The preconditioner is a combination of an additive Schwarz preconditioner and a special smoother. The smoother removes dependence of the condition number on the number of subdomains and variations of the diffusion coefficient and leaves minor sensitivity to the problem size. The algorithm is parallel and pure algebraic which makes it a convenient framework for the construction parallel black‐box preconditioners on unstructured meshes. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献