全文获取类型
收费全文 | 108866篇 |
免费 | 12137篇 |
国内免费 | 8975篇 |
专业分类
化学 | 46502篇 |
晶体学 | 1449篇 |
力学 | 19929篇 |
综合类 | 1496篇 |
数学 | 27231篇 |
物理学 | 33371篇 |
出版年
2024年 | 166篇 |
2023年 | 1000篇 |
2022年 | 1954篇 |
2021年 | 3087篇 |
2020年 | 2950篇 |
2019年 | 2692篇 |
2018年 | 2513篇 |
2017年 | 3098篇 |
2016年 | 3674篇 |
2015年 | 3269篇 |
2014年 | 4749篇 |
2013年 | 7794篇 |
2012年 | 5764篇 |
2011年 | 6488篇 |
2010年 | 5464篇 |
2009年 | 6450篇 |
2008年 | 6474篇 |
2007年 | 6755篇 |
2006年 | 5840篇 |
2005年 | 4926篇 |
2004年 | 4358篇 |
2003年 | 4165篇 |
2002年 | 6226篇 |
2001年 | 3541篇 |
2000年 | 2969篇 |
1999年 | 2509篇 |
1998年 | 2465篇 |
1997年 | 2010篇 |
1996年 | 1869篇 |
1995年 | 1621篇 |
1994年 | 1547篇 |
1993年 | 1395篇 |
1992年 | 1334篇 |
1991年 | 976篇 |
1990年 | 826篇 |
1989年 | 652篇 |
1988年 | 635篇 |
1987年 | 474篇 |
1986年 | 443篇 |
1985年 | 562篇 |
1984年 | 451篇 |
1983年 | 261篇 |
1982年 | 494篇 |
1981年 | 560篇 |
1980年 | 480篇 |
1979年 | 526篇 |
1978年 | 426篇 |
1977年 | 328篇 |
1976年 | 276篇 |
1973年 | 164篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Rakhim Aitbayev 《Numerical Methods for Partial Differential Equations》2006,22(4):847-866
Efficient multilevel preconditioners are developed and analyzed for the quadrature finite element Galerkin approximation of the biharmonic Dirichlet problem. The quadrature scheme is formulated using the Bogner–Fox–Schmit rectangular element and the product two‐point Gaussian quadrature. The proposed additive and multiplicative preconditioners are uniformly spectrally equivalent to the operator of the quadrature scheme. The preconditioners are implemented by optimal algorithms, and they are used to accelerate convergence of the preconditioned conjugate gradient method. Numerical results are presented demonstrating efficiency of the preconditioners. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
122.
Th. Seyller K.V. Emtsev F. Speck A. Tadich J.D. Riley O. Rader A.M. Shikin 《Surface science》2006,600(18):3906-3911
Photoelectron spectroscopy, low-energy electron diffraction, and scanning probe microscopy were used to investigate the electronic and structural properties of graphite layers grown by solid state graphitization of SiC(0 0 0 1) surfaces. The process leads to well-ordered graphite layers which are rotated against the substrate lattice by 30°. On on-axis 6H-SiC(0 0 0 1) substrates we observe graphitic layers with up to several 100 nm wide terraces. ARUPS spectra of the graphite layers grown on on-axis 6H-SiC(0 0 0 1) surfaces are indicative of a well-developed band structure. For the graphite/n-type 6H-SiC(0 0 0 1) layer system we observe a Schottky barrier height of ?B,n = 0.3 ± 0.1 eV. ARUPS spectra of graphite layers grown on 8° off-axis oriented 4H-SiC(0 0 0 1) show unique replicas which are explained by a carpet-like growth mode combined with a step bunching of the substrate. 相似文献
123.
The molding processes of polymer melts involve geometrically complex dies. Such dies are usually tapered or streamlined to achieve a maximum output rate under conditions of laminar flow. The model of a generalized second-grade fluid of power-law type is used and the results obtained are illustrated by examples of convergent flows in conical and wedge-shaped dies. 相似文献
124.
Huafei Sun 《Geometriae Dedicata》2002,90(1):63-75
We study minimal submanifolds in the locally symmetric and conformally flat Riemannian manifold and generalize Yau's result obtained in J. Amer. Math. 97 (1975), 76–100. 相似文献
125.
This paper is concerned with the implementation and testing of an algorithm for solving constrained least-squares problems. The algorithm is an adaptation to the least-squares case of sequential quadratic programming (SQP) trust-region methods for solving general constrained optimization problems. At each iteration, our local quadratic subproblem includes the use of the Gauss–Newton approximation but also encompasses a structured secant approximation along with tests of when to use this approximation. This method has been tested on a selection of standard problems. The results indicate that, for least-squares problems, the approach taken here is a viable alternative to standard general optimization methods such as the Byrd–Omojokun trust-region method and the Powell damped BFGS line search method. 相似文献
126.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
127.
128.
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
129.
130.
关于AOR迭代法的研究 总被引:5,自引:0,他引:5
陈恒新 《应用数学与计算数学学报》2002,16(1):40-46
本文论证了严格对角占优矩阵之AOR法的误差估计式中的误差估计常数hγ,ω(0≤γ≤ω0)的最小值是h1,1. 相似文献