全文获取类型
收费全文 | 5409篇 |
免费 | 635篇 |
国内免费 | 542篇 |
专业分类
化学 | 1516篇 |
晶体学 | 17篇 |
力学 | 428篇 |
综合类 | 133篇 |
数学 | 3270篇 |
物理学 | 1222篇 |
出版年
2024年 | 8篇 |
2023年 | 78篇 |
2022年 | 72篇 |
2021年 | 120篇 |
2020年 | 175篇 |
2019年 | 154篇 |
2018年 | 186篇 |
2017年 | 186篇 |
2016年 | 208篇 |
2015年 | 180篇 |
2014年 | 253篇 |
2013年 | 429篇 |
2012年 | 284篇 |
2011年 | 310篇 |
2010年 | 269篇 |
2009年 | 303篇 |
2008年 | 352篇 |
2007年 | 312篇 |
2006年 | 309篇 |
2005年 | 287篇 |
2004年 | 245篇 |
2003年 | 244篇 |
2002年 | 228篇 |
2001年 | 215篇 |
2000年 | 173篇 |
1999年 | 142篇 |
1998年 | 135篇 |
1997年 | 96篇 |
1996年 | 104篇 |
1995年 | 61篇 |
1994年 | 52篇 |
1993年 | 37篇 |
1992年 | 45篇 |
1991年 | 33篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1974年 | 4篇 |
排序方式: 共有6586条查询结果,搜索用时 45 毫秒
1.
In this work, we present and analyze a mathematical model for tumor growth incorporating ECM erosion, interstitial flow, and the effect of vascular flow and nutrient transport. The model is of phase-field or diffused-interface type in which multiple phases of cell species and other constituents are separated by smooth evolving interfaces. The model involves a mesoscale version of Darcy’s law to capture the flow mechanism in the tissue matrix. Modeling flow and transport processes in the vasculature supplying the healthy and cancerous tissue, one-dimensional (1D) equations are considered. Since the models governing the transport and flow processes are defined together with cell species models on a three-dimensional (3D) domain, we obtain a 3D–1D coupled model. 相似文献
2.
3.
Here we propose and analyze a mathematical model that aims to describe the marble sulphation process occurring in a given material. The model accounts for rugosity as well as for damaging effects. This model is characterized by some technical difficulties that seem hard to overcome from a theoretical viewpoint. Therefore, we introduce some physically reasonable modifications in order to establish the existence of a suitable notion of solution on a given time interval. Numerical simulations are presented and discussed, also in view of further research. 相似文献
4.
5.
6.
José E. Barquera-Lozada 《Journal of computational chemistry》2019,40(30):2602-2610
The induced current density ( J ( r )) provides useful information about the electronic structure of molecules under a magnetic field ( B ). However, the analysis of its topology is cumbersome because of its vectorial nature. We show that its tropicity (direction of rotation) and its strength can be compressed in the triple product B ⋅ ∇ × J ( r ) (tp J ( r )) that is a scalar field. The topology of tp J ( r ) has clear similarities to the Laplacian of the electron density. Additionally, the topology of aromatic and antiaromatic compounds is notoriously different. The vorticity of J ( r ) is helpful to define the circulation of the current density, C, that contrary to other methods, can be easily defined for individual rings in polycyclic molecules. This allows tp J ( r ) to clearly reproduce the Clar's structure of polycyclic aromatic hydrocarbons. © 2019 Wiley Periodicals, Inc. 相似文献
7.
We show that there is no (95, 40, 12, 20) strongly regular graph and, consequently, there is no (96, 45, 24, 18) strongly regular graph, no nontrivial regular two‐graph on 96 vertices, and no partial geometry pg(4, 9, 2). The main idea of the result is based on the star complement technique and requires a moderate amount of computation. 相似文献
8.
Gurusamy Arumugam Jagmohan Tyagi 《Mathematical Methods in the Applied Sciences》2020,43(10):6576-6597
We establish the existence of nonnegative weak solutions to nonlinear reaction–diffusion system with cross-diffusion and nonstandard growth conditions subject to the homogeneous Neumann boundary conditions. We assume that the diffusion operators satisfy certain monotonicity condition and nonstandard growth conditions and prove that the existence of weak solutions using Galerkin's approximation technique. 相似文献
9.
近年来拓扑学在量子力学中得到了广泛的运用.本文将安培环路定理积分式重新表达为一矢量场在轮胎参数面上的第一类陈数积分.数值模拟展示了该积分值为一整数即第一陈数,其代表矢量场的整体性质:当经历连续变换时,矢量场的局部数值发生改变但整体积分值即陈数仍保持不变;若陈数发生改变,则表明矢量场变换的连续性条件发生破坏,矢量场出现奇点.进一步通过高斯映射将该矢量场从参数轮胎面映射到单位球面上,并给出了第一陈数的直观几何意义.理论和数值结果揭示了安培环路定理的拓扑学本质,表明拓扑概念在经典物理学中也会有广泛应用. 相似文献
10.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献