全文获取类型
收费全文 | 1397篇 |
免费 | 81篇 |
国内免费 | 32篇 |
专业分类
化学 | 55篇 |
晶体学 | 1篇 |
力学 | 308篇 |
综合类 | 2篇 |
数学 | 350篇 |
物理学 | 457篇 |
无线电 | 337篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 17篇 |
2021年 | 10篇 |
2020年 | 40篇 |
2019年 | 21篇 |
2018年 | 35篇 |
2017年 | 44篇 |
2016年 | 44篇 |
2015年 | 59篇 |
2014年 | 94篇 |
2013年 | 117篇 |
2012年 | 60篇 |
2011年 | 100篇 |
2010年 | 86篇 |
2009年 | 85篇 |
2008年 | 77篇 |
2007年 | 68篇 |
2006年 | 47篇 |
2005年 | 44篇 |
2004年 | 52篇 |
2003年 | 47篇 |
2002年 | 41篇 |
2001年 | 32篇 |
2000年 | 22篇 |
1999年 | 39篇 |
1998年 | 19篇 |
1997年 | 32篇 |
1996年 | 26篇 |
1995年 | 9篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1510条查询结果,搜索用时 15 毫秒
181.
M. Daoulatli 《Journal of Differential Equations》2018,264(7):4260-4302
In this paper we study the behaviors of the energy of solutions of the wave equations with localized nonlinear damping in exterior domains. 相似文献
182.
In this article we study the inverse problem of thermoacoustic tomography (TAT) on a medium with attenuation represented by a time-convolution (or memory) term, and whose consideration is motivated by the modeling of ultrasound waves in heterogeneous tissue via fractional derivatives with spatially dependent parameters. Under the assumption of being able to measure data on the whole boundary, we prove uniqueness and stability, and propose a convergent reconstruction method for a class of smooth variable sound speeds. By a suitable modification of the time reversal technique, we obtain a Neumann series reconstruction formula. 相似文献
183.
针对传统调频连续波(FMCW)雷达高度表模拟信号处理方法精度差、检测能力低、不够灵活等缺点,给出了一种基于快速傅里叶变换(FFT)的恒差拍FMCW雷达高度表数字信号处理器设计方案,实现了信号的全数字化处理,并通过仿真验证了方案的可行性和正确性。 相似文献
184.
J.S. Steinhoff 《Journal of Computational and Applied Mathematics》2010,234(6):1826-1833
A recently developed method is described to propagate short wave equation pulses over indefinite distances and through regions of varying indices of refraction, including multiple reflections. The method, “Wave Confinement”, utilizes a newly developed nonlinear partial differential equation (pde) that propagates basis functions according to the wave equation. These basis functions are generated as stable solitary waves where the discretized equation can be solved without any numerical dissipation. The method can also be used to solve for harmonic waves in the high frequency (Eikonal) limit, including multiple arrivals. The solution involves discretizing the wave equation on a uniform Eulerian grid and adding a simple nonlinear “Confinement” term. This term does not change the amplitude (integrated through each point on the pulse surface) or the propagation velocity, or arrival time, and yet results in capturing the waves as thin surfaces that propagate as thin nonlinear solitary waves and remain ∼2-3 grid cells in thickness indefinitely with no numerical spreading. A new feature described in this paper involves computing scattering of short pulses from complex objects such as complete aircraft. A simple “immersed surface” approach is used, that utilizes the same uniform grid as the propagation and avoids complex, body fitted or adaptive grid schemes.The new method should be useful in areas of wave propagation, from radar scattering and long distance communications to cell phone transmission. 相似文献
185.
In this work, exact and approximate non-reflecting boundary conditions (NRBCs) are implemented with the Partition of Unity Finite Element Method (PUFEM) to solve short wave scattering problems governed by the Helmholtz equation in two dimensions. By short wave problems, we mean situations in which the wavelength is a small fraction of the characteristic dimension of the scatterer. Various NRBCs are implemented and a comparison of their performance is carried out based on the accuracy of the results, ease of implementation and computational cost. The aim is to accurately model such problems in a reduced computational domain around the scatterer with fewer elements and without refining the mesh at each wave number. 相似文献
186.
In this paper, we study the nonlinear one-dimensional periodic wave equation with x-dependent coefficients u(x)ytt−(ux(x)yx)+g(x,t,y)=f(x,t) on (0,π)×R under the boundary conditions a1y(0,t)+b1yx(0,t)=0, a2y(π,t)+b2yx(π,t)=0 ( for i=1,2) and the periodic conditions y(x,t+T)=y(x,t), yt(x,t+T)=yt(x,t). Such a model arises from the forced vibrations of a nonhomogeneous string and the propagation of seismic waves in nonisotropic media. A main concept is the notion “weak solution” to be given in Section 2. For T is the rational multiple of π, we prove some important properties of the weak solution operator. Based on these properties, the existence and regularity of weak solutions are obtained. 相似文献
187.
Pengfei YAO 《数学年刊B辑(英文版)》2010,31(1):59-70
Decay of the energy for the Cauchy problem of the wave equation of variable coefficients with a dissipation is considered. It is shown that whether a dissipation can be localized near infinity depends on the curvature properties of a Riemannian metric given by the variable coefficients. In particular, some criteria on curvature of the Riemannian manifold for a dissipation to be localized are given. 相似文献
188.
Nikolaos L.Tsitsas 《计算数学(英文版)》2010,(6):864-878
Block matrices associated with discrete Trigonometric transforms (DTT's) arise in the mathematical modelling of several applications of wave propagation theory including discretizations of scatterers and radiators with the Method of Moments, the Boundary Element Method, and the Method of Auxiliary Sources. The DTT's are represented by the Fourier, Hartley, Cosine, and Sine matrices, which are unitary and offer simultaneous diagonalizations of specific matrix algebras. The main tool for the investigation of the aforementioned wave applications is the efficient inversion of such types of block matrices. To this direction, in this paper we develop an efficient algorithm for the inversion of matrices with U-diagonalizable blocks (U a fixed unitary matrix) by utilizing the U- diagonalization of each block and subsequently a similarity transformation procedure. We determine the developed method's computational complexity and point out its high efficiency compared to standard inversion techniques. An implementation of the algorithm in Matlab is given. Several numerical results are presented demonstrating the CPU-time efficiency and accuracy for ill-conditioned matrices of the method. The investigated matrices stem from real-world wave propagation applications. 相似文献
189.
Nasser-eddine Tatar 《Nonlinear Analysis: Theory, Methods & Applications》2010,72(6):3209-3215
In this paper we consider the evolution of sound in a compressible fluid with reflection of sound at the surface of the material. The boundary controller involves a derivative of non-integer order. It is proved that solutions blow up in finite time in the presence of a nonlinear source. 相似文献
190.