全文获取类型
收费全文 | 8005篇 |
免费 | 778篇 |
国内免费 | 718篇 |
专业分类
化学 | 1352篇 |
晶体学 | 36篇 |
力学 | 917篇 |
综合类 | 142篇 |
数学 | 4900篇 |
物理学 | 2154篇 |
出版年
2024年 | 16篇 |
2023年 | 96篇 |
2022年 | 228篇 |
2021年 | 173篇 |
2020年 | 250篇 |
2019年 | 231篇 |
2018年 | 225篇 |
2017年 | 278篇 |
2016年 | 249篇 |
2015年 | 180篇 |
2014年 | 321篇 |
2013年 | 603篇 |
2012年 | 361篇 |
2011年 | 462篇 |
2010年 | 397篇 |
2009年 | 561篇 |
2008年 | 543篇 |
2007年 | 505篇 |
2006年 | 441篇 |
2005年 | 416篇 |
2004年 | 337篇 |
2003年 | 317篇 |
2002年 | 610篇 |
2001年 | 249篇 |
2000年 | 213篇 |
1999年 | 204篇 |
1998年 | 209篇 |
1997年 | 158篇 |
1996年 | 128篇 |
1995年 | 75篇 |
1994年 | 64篇 |
1993年 | 50篇 |
1992年 | 53篇 |
1991年 | 43篇 |
1990年 | 28篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 23篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1972年 | 3篇 |
1971年 | 12篇 |
1970年 | 9篇 |
排序方式: 共有9501条查询结果,搜索用时 0 毫秒
991.
The effects of finite grid resolution on the statistics of small scales in direct numerical simulations of turbulent mixing of passive scalars are addressed in this paper. Simulations at up to 20483 grid points with grid spacing Δx varied from about 2 to 1/2 Batchelor scales (ηB) show that most conclusions on Schmidt number (Sc) dependence from prior work at less stringent resolution remain qualitatively correct, although simulations at resolution Δx≈ηB are preferred and will give adequate results for many important quantities including the scalar dissipation intermittency exponent and structure functions at moderately high orders. For Sc≥1, since ηB=ηSc−1/2 (where η is the Kolmogorov scale), the requirement Δx≈ηB is more stringent than the corresponding criterion Δx≈η for the velocity field, which is thus well resolved in simulations aimed at high Schmidt number mixing. A simple argument is given to help interpret the effects of Schmidt and Reynolds numbers on trends towards local isotropy and saturation of intermittency at high Schmidt number. The present results also provide evidence for a trend to isotropy at high Reynolds number with fixed Sc=1.0. This is a new observation apparently not detected in less well resolved simulations in the past, and will require further investigation in the future. 相似文献
992.
Jawali C. Umavathi Hafiz Muhammad Ali Sapnali Limbaraj Patil 《Mathematical Methods in the Applied Sciences》2020,43(15):9223-9244
The motivation of the current article is to explore a numerical investigation on steady triply diffusive convection in a vertical channel. Heat is exchanged from the external fluid with the plates. The reference temperature is taken as equal and also as different for the external fluid. Solutions in the absence of viscous dissipation and buoyancy forces are also obtained as special cases. General solutions including the effects of viscous dissipation and buoyancy forces are obtained analytically using the method of perturbation. The analytical solutions can be used only if the Brinkman number is small. Hence to know the flow properties for all values of Brinkman number, we resort to numerical solutions. The effects of thermal Grashof number, solutal Grashof number, and the chemical reaction parameter on the flow field are evaluated numerically. The obtained results are validated against previously published results for special case of the problems. 相似文献
993.
In this paper, we consider the combined quasineutral and low Mach number limit of compressible Euler–Poisson system coupled to a magnetic field. We prove that, as the Debye length and the Mach number tend to zero simultaneously in some way, the solution of compressible Euler–Poisson system coupled to a magnetic field will converge to that of ideal incompressible magnetohydrodynamic equations with a sharp convergence rate. 相似文献
994.
We discuss a version of Nim in which players are allowed to use a move from the traditional form of Nim or to split a pile after adding some predetermined number of coins to the pile. When is odd or negative, the play proceeds as in regular Nim. For even and non-negative, we find three patterns: , and . 相似文献
995.
《Mathematical Methods in the Applied Sciences》2018,41(14):5388-5403
A reaction‐diffusion system with free boundary is proposed to describe the transmission of the dengue disease from mosquitoes to humans. In addition to the classical basic reproduction number R0, the spatial‐temporal basic reproduction number is introduced to determine the persistence and eradication of the disease. Some sufficient conditions for the disease vanishing or spreading are obtained. The disease will go extinct under one of the conditions: the classical basic reproduction number R0 < 1 and the spatial‐temporal basic reproduction number with small expanding capability. The spread of the disease in the whole area is possible if for some t≥0. Numerical simulations are also given to illustrate the theoretical results. 相似文献
996.
本文考虑求解Helmholtz方程的有限元方法的超逼近性质以及基于PPR后处理方法的超收敛性质.我们首先给出了矩形网格上的p-次元在收敛条件k(kh)2p+1≤C0下的有限元解和基于Lobatto点的有限元插值之间的超逼近以及重构的有限元梯度和精确解之间的超收敛分析.然后我们给出了四边形网格上的线性有限元方法的分析.这些估计都给出了与波数k和网格尺寸h的依赖关系.同时我们回顾了三角形网格上的线性有限元的超收敛结果.最后我们给出了数值实验并且结合Richardson外推进一步减少了误差. 相似文献
997.
The rainbow number for the graph in is defined to be the minimum integer such that any -edge-coloring of contains a rainbow . As one of the most important structures in graphs, the rainbow number of matchings has drawn much attention and has been extensively studied. Jendrol et al. initiated the rainbow number of matchings in planar graphs and they obtained bounds for the rainbow number of the matching in the plane triangulations, where the gap between the lower and upper bounds is . In this paper, we show that the rainbow number of the matching in maximal outerplanar graphs of order is . Using this technique, we show that the rainbow number of the matching in some subfamilies of plane triangulations of order is . The gaps between our lower and upper bounds are only . 相似文献
998.
Benjamin Braun Hugo Corrales Scott Corry Luis David García Puente Darren Glass Nathan Kaplan Jeremy L. Martin Gregg Musiker Carlos E. Valencia 《Discrete Mathematics》2018,341(10):2949-2963
Let be a finite, connected graph. An arithmetical structure on is a pair of positive integer vectors such that , where is the adjacency matrix of . We investigate the combinatorics of arithmetical structures on path and cycle graphs, as well as the associated critical groups (the torsion part of the cokernels of the matrices ). For paths, we prove that arithmetical structures are enumerated by the Catalan numbers, and we obtain refined enumeration results related to ballot sequences. For cycles, we prove that arithmetical structures are enumerated by the binomial coefficients , and we obtain refined enumeration results related to multisets. In addition, we determine the critical groups for all arithmetical structures on paths and cycles. 相似文献
999.
Michael Tait 《Discrete Mathematics》2018,341(1):104-108
Let denote that any -coloring of contains a monochromatic . The degree Ramsey number of a graph , denoted by , is . We consider degree Ramsey numbers where is a fixed even cycle. Kinnersley, Milans, and West showed that , and Kang and Perarnau showed that . Our main result is that and . Additionally, we substantially improve the lower bound for for general . 相似文献
1000.
The boxicity of a graph is the smallest integer such that is the intersection of interval graphs, or equivalently, that is the intersection graph of axis-aligned boxes in . These intersection representations can be interpreted as covering representations of the complement of with co-interval graphs, that is, complements of interval graphs. We follow the recent framework of global, local and folded covering numbers (Knauer and Ueckerdt, 2016) to define two new parameters: the local boxicity and the union boxicity of . The union boxicity of is the smallest such that can be covered with
vertex–disjoint unions of co-interval graphs, while the local boxicity of is the smallest such that can be covered with co-interval graphs, at most at every vertex.We show that for every graph we have and that each of these inequalities can be arbitrarily far apart. Moreover, we show that local and union boxicity are also characterized by intersection representations of appropriate axis-aligned boxes in . We demonstrate with a few striking examples, that in a sense, the local boxicity is a better indication for the complexity of a graph, than the classical boxicity. 相似文献