全文获取类型
收费全文 | 40014篇 |
免费 | 4303篇 |
国内免费 | 3008篇 |
专业分类
化学 | 10735篇 |
晶体学 | 122篇 |
力学 | 3807篇 |
综合类 | 451篇 |
数学 | 21706篇 |
物理学 | 10504篇 |
出版年
2024年 | 78篇 |
2023年 | 376篇 |
2022年 | 480篇 |
2021年 | 664篇 |
2020年 | 1137篇 |
2019年 | 1119篇 |
2018年 | 1002篇 |
2017年 | 978篇 |
2016年 | 1162篇 |
2015年 | 1024篇 |
2014年 | 1649篇 |
2013年 | 3308篇 |
2012年 | 1798篇 |
2011年 | 2202篇 |
2010年 | 2101篇 |
2009年 | 2382篇 |
2008年 | 2644篇 |
2007年 | 2688篇 |
2006年 | 2282篇 |
2005年 | 2216篇 |
2004年 | 1881篇 |
2003年 | 1786篇 |
2002年 | 1665篇 |
2001年 | 1265篇 |
2000年 | 1202篇 |
1999年 | 1142篇 |
1998年 | 1060篇 |
1997年 | 912篇 |
1996年 | 772篇 |
1995年 | 680篇 |
1994年 | 566篇 |
1993年 | 433篇 |
1992年 | 419篇 |
1991年 | 334篇 |
1990年 | 257篇 |
1989年 | 170篇 |
1988年 | 176篇 |
1987年 | 153篇 |
1986年 | 158篇 |
1985年 | 147篇 |
1984年 | 131篇 |
1983年 | 68篇 |
1982年 | 132篇 |
1981年 | 122篇 |
1980年 | 80篇 |
1979年 | 85篇 |
1978年 | 59篇 |
1977年 | 40篇 |
1976年 | 34篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
1.引 言 本文的目的是用求解偏微分方程(PDE)的方法来消除离散三角形曲面的噪声,所使用的方程是热传导方程到曲面的推广.热传导方程应用于图像处理已有二十余年的历史,有关参考文献相当丰富(见[1,11,12,19]).众所周知,对于给定的初始图像ρ0,热传导方程 在τ时刻的解与用Gauss滤波器Gσ(x)= (当标准差σ=2τ,时)和ρ0作卷积的结果相同.容易看出Gρ和ρ0的卷积运算相当于对ρ0做加权平均,当标准离差σ变大时,该加权平均在一个较大的范围实现,这解释了热传导方程的滤波作用.近来热传导方程已推广到空间曲面[4,5]以及高维空间中的二维流形(见[3]),对 相似文献
62.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
63.
In this work we study nonnegativity and positivity of a discrete quadratic functional with separately varying endpoints. We introduce a notion of an interval coupled with 0, and hence, extend the notion of conjugate interval to 0 from the case of fixed to variable endpoint(s). We show that the nonnegativity of the discrete quadratic functional is equivalent to each of the following conditions: The nonexistence of intervals coupled with 0, the existence of a solution to Riccati matrix equation and its boundary conditions. Natural strengthening of each of these conditions yields a characterization of the positivity of the discrete quadratic functional. Since the quadratic functional under consideration could be a second variation of a discrete calculus of variations problem with varying endpoints, we apply our results to obtain necessary and sufficient optimality conditions for such problems. This paper generalizes our recent work in [R. Hilscher, V. Zeidan, Comput. Math. Appl., to appear], where the right endpoint is fixed. 相似文献
64.
65.
方程w"-w+f(t,w)=O的Dirichlet边值问题的正解存在性与多解性 总被引:1,自引:0,他引:1
姚庆六 《应用泛函分析学报》2002,4(1):4-9
考察了下列常微分方程的Dirichlet边值问题的正解[w″(t)-w(t) f(t,w(t))=0,0≤t≤1 w(0)=w(1)=0建立了n正解的存在性,其中n是一个任意的自然数。 相似文献
66.
Alexander Krasnosel'skii Dmitrii Rachinskii 《NoDEA : Nonlinear Differential Equations and Applications》2002,9(1):93-115
We consider autonomous systems with a nonlinear part depending on a parameter and study Hopf bifurcations at infinity. The
nonlinear part consists of the nonlinear functional term and the Prandtl--Ishlinskii hysteresis term. The linear part of the
system has a special form such that the close-loop system can be considered as a hysteresis perturbation of a quasilinear
Hamiltonian system. The Hamiltonian system has a continuum of arbitrarily large cycles for each value of the parameter. We
present sufficient conditions for the existence of bifurcation points for the non-Hamiltonian system with hysteresis. These
bifurcation points are determined by simple characteristics of the hysteresis nonlinearity. 相似文献
67.
According to an induced-matter approach, Liu and Wesson obtained the rest mass of a typical particle from the reduction of a 5D Klein–Gordon equation to a 4D one. Introducing an extra-dimension momentum operator identified with the rest mass eigenvalue operator, we consider a way to generalize the 4D Dirac equation to 5D. An analogous normal Dirac equation is gained when the generalization reduces to 4D. We find the rest mass of a particle in curved space varies with spacetime coordinates and check this for the case of exact solitonic and cosmological solution of the 5D vacuum gravitational field equations. 相似文献
68.
A simple simulation scheme that simultaneously describes the growth kinetics of SiO2 films at the nanometer scale and the SiOx/Si interface dynamics (its extent, and spatial/temporal evolution) is presented. The simulation successfully applies to experimental data in the region above and below 10 nm, reproduces the Deal and Grove linear-parabolic law and the oxide growth rate enhancement in the very thin film regime (the so-called anomalous region). According to the simulation, the oxidation is governed mainly by two processes: (a) the formation of a transition suboxide layer and (b) its subsequent drift towards the silicon bulk. We found that it is the superposition of these two processes that produces the crossover from the anomalous oxidation region behavior to the linear-parabolic law. 相似文献
69.
Koumei Tanaka 《Mathematical Methods in the Applied Sciences》2006,29(12):1451-1466
We consider a compressible viscous fluid with the velocity at infinity equal to a strictly non‐zero constant vector in ?3. Under the assumptions on the smallness of the external force and velocity at infinity, Novotny–Padula (Math. Ann. 1997; 308 :439– 489) proved the existence and uniqueness of steady flow in the class of functions possessing some pointwise decay. In this paper, we study stability of the steady flow with respect to the initial disturbance. We proved that if H3‐norm of the initial disturbance is small enough, then the solution to the non‐stationary problem exists uniquely and globally in time, which satisfies a uniform estimate on prescribed velocity at infinity and converges to the steady flow in Lq‐norm for any number q? 2. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
70.