全文获取类型
收费全文 | 15700篇 |
免费 | 2242篇 |
国内免费 | 1212篇 |
专业分类
化学 | 8909篇 |
晶体学 | 478篇 |
力学 | 1328篇 |
综合类 | 39篇 |
数学 | 289篇 |
物理学 | 4047篇 |
无线电 | 4064篇 |
出版年
2024年 | 73篇 |
2023年 | 363篇 |
2022年 | 439篇 |
2021年 | 684篇 |
2020年 | 914篇 |
2019年 | 641篇 |
2018年 | 569篇 |
2017年 | 620篇 |
2016年 | 850篇 |
2015年 | 854篇 |
2014年 | 920篇 |
2013年 | 1119篇 |
2012年 | 847篇 |
2011年 | 970篇 |
2010年 | 899篇 |
2009年 | 885篇 |
2008年 | 1017篇 |
2007年 | 1089篇 |
2006年 | 939篇 |
2005年 | 830篇 |
2004年 | 701篇 |
2003年 | 630篇 |
2002年 | 434篇 |
2001年 | 353篇 |
2000年 | 278篇 |
1999年 | 216篇 |
1998年 | 184篇 |
1997年 | 129篇 |
1996年 | 131篇 |
1995年 | 77篇 |
1994年 | 87篇 |
1993年 | 62篇 |
1992年 | 56篇 |
1991年 | 56篇 |
1990年 | 39篇 |
1989年 | 34篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
981.
In this paper we consider the transmission problem of viscoelastic waves. That is, we study the wave propagations over materials consisting of elastic and viscoelastic components. We show that for this types of materials the dissipation produced by the viscoelastic part is strong enough to produce exponential decay of the solution, no matter how small is its size. We also show that the linear model is well posed. 相似文献
982.
The results of FEM investigation of the triaxial stress state in multilayer structural elements subjected to axial and bending loads are presented. The distribution regularities of the stiffness and stresses or strains depending on the geometric and mechanical characteristics of layers and their position in the cross section of beams and bars are examined. The optimization of these elements is carried out using the dependences of the Bareisis—Paulauskas method and the Optim-98 computer program created by the present authors. As the optimization criteria, the strength, stiffness, mass, and cost of the structural elements are considered. 相似文献
983.
Using the nano-moiré method, we measure the near tip nanoscopic deformation on the [111] plane of single crystal silicon with
a loaded quasi-cleavage crack running in the [110] direction. The measured strain distribution ahead of the crack tip agrees
with the linear elastic fracture mechanics prediction up to 10 nm from the crack tip. Dislocations of Peierls type are detected
and they extend from the crack tip over a length of hundreds of Burgers vectors. 相似文献
984.
Michael Bildhauer Martin Fuchs Victor Osmolovskii 《Mathematical Methods in the Applied Sciences》2002,25(2):149-178
We consider the problem of minimizing among functions u:?d?Ω→?d, u∣?Ω=0, and measurable subsets E of Ω. Here fh+, f? denote quadratic potentials defined on Ω¯×{symmetric d×d matrices}, h is the minimum energy of fh+ and ε(u) is the symmetric gradient of the displacement field u. An equilibrium state û, Ê of J(u,E) is called one‐phase if E=?? or E=Ω, two‐phase otherwise. For two‐phase states, σ∣?E∩Ω∣ measures the effect of the separating surface, and we investigate the way in which the distribution of phases is affected by the choice of the parameters h??, σ>0. Additional results concern the smoothness of two‐phase equilibrium states and the behaviour of inf J(u,E) in the limit σ↓0. Moreover, we discuss the case of additional volume force potentials, and extend the previous results to non‐zero boundary values. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
985.
M. Bildhauer M. Fuchs V. G. Osmolovskii 《Mathematical Methods in the Applied Sciences》2002,25(4):289-308
We consider the problem of minimizing 0<p<1, h∈?, σ>0, among functions u:?d?Ω→?d, u∣?Ω=0, and measurable characteristic functions χ:Ω→?. Here ?+h, ??, denote quadratic potentials defined on the space of all symmetric d×d matrices, h is the minimum energy of ?+h and ε(u) denotes the symmetric gradient of the displacement field. An equilibrium state û, χ?, of I [·,·,h, σ] is termed one‐phase if χ?≡0 or χ?≡1, two‐phase otherwise. We investigate the way in which the distribution of phases is affected by the choice of the parameters h and σ. Copyright 2002 John Wiley & Sons, Ltd. 相似文献
986.
This paper investigates the two-dimensional sliding frictional contact of a piezoelectric half-plane in the plane strain state under the action of a rigid flat or a triangular punch. It is assumed that the punch is a perfect electrical conductor with a constant electric potential. By using the Fourier integral transform technique and the superposition theorem, the problem is reduced to a pair of coupled Cauchy singular integral equations and then is numerically solved to determine the unknown contact pressure and surface electric charge distribution. The effects of the friction coefficient and electro-mechanical loads on the normal contact stress, normal electric displacement, in-plane stress and in-plane electric displacement are discussed in detail. It is found that the friction coefficient has a significant effect on the electro-mechanical sliding frictional contact behaviors of the piezoelectric materials. 相似文献
987.
The recycling of urban solid wastes is a critical point for the “closing supply chains” of many products, mainly when their value cannot be completely recovered after use. In addition to environmental aspects, the process of recycling involves technical, economic, social and political challenges for public management. For most of the urban solid waste, the management of the end-of-life depends on selective collection to start the recycling process. For this reason, an efficient selective collection has become a mainstream tool in the Brazilian National Solid Waste Policy. In this paper, we study effective models that might support the location planning of sorting centers in a medium-sized Brazilian city that has been discussing waste management policies over the past few years. The main goal of this work is to provide an optimal location planning design for recycling urban solid wastes that fall within the financial budget agreed between the municipal government and the National Bank for Economic and Social Development. Moreover, facility planning involves deciding on the best sites for locating sorting centers along the four-year period as well as finding ways to meet the demand for collecting recyclable materials, given that economic factors, consumer behavior and environmental awareness are inherently uncertain future outcomes. To deal with these issues, we propose a deterministic version of the classical capacity facility location problem, and both a two-stage recourse formulation and risk-averse models to reduce the variability of the second-stage costs. Numerical results suggest that it is possible to improve the current selective collection, as well as hedge against data uncertainty by using stochastic and risk-averse optimization models. 相似文献
988.
989.
Composite materials have been used in the design of the aircrafts structures because their low weight and high mechanical strength. However, structures made in composite material are exposed to dynamical and/or static loading environments. Therefore, a major research effort is undertaken in the development of tools numerical for analysis and design of composite structures. This paper presents a numerical formulation of the composite structures using the Finite Element Method (FEM). The damped composite structures, using inserted viscoelastic devices, and undamped composite structures are formulated by FEM. Viscoelastic materials are applied as continuous layers inserted on composite structures. The intrinsic damping of the composite material is included in the studies, too. The First‐order (FSDT) and Higher‐order Shear Deformation (HSDT) theories are formulated. They are distinguished by order of the approximation functions used in the mechanical displacements field. Both theories are computationally implemented using the Serendipity finite element. This is a rectangular finite element with 8 nodes, 5 or 11 degrees of freedom per node. The results are compared with papers predictions. The advantages and disadvantages of using each theory in the modeling of composite (thin or thick) and thick sandwiches structures, including the intrinsic and the viscoelastic damping, are discusses. 相似文献
990.
Jarosław Łazuka 《Mathematical Methods in the Applied Sciences》2020,43(17):10115-10137
This paper is devoted to the investigation of the solution to the Cauchy problem for a system of partial differential equations describing thermoelasticity of nonsimple materials in a three-dimensional space. The model of linear dynamical thermoelasticity of nonsimple materials is considered as the system of partial differential equations of fourth order. In this paper, we proposed a convenient evolutionary method of approach to the system of equations of nonsimple thermoelasticity. We proved the Lp−Lq time decay estimates for the solution to the Cauchy problem for linear thermoelasticity of nonsimple materials. 相似文献