全文获取类型
收费全文 | 1889篇 |
免费 | 327篇 |
国内免费 | 113篇 |
专业分类
化学 | 88篇 |
晶体学 | 8篇 |
力学 | 268篇 |
综合类 | 24篇 |
数学 | 877篇 |
物理学 | 967篇 |
无线电 | 97篇 |
出版年
2024年 | 5篇 |
2023年 | 14篇 |
2022年 | 38篇 |
2021年 | 44篇 |
2020年 | 49篇 |
2019年 | 40篇 |
2018年 | 35篇 |
2017年 | 48篇 |
2016年 | 64篇 |
2015年 | 40篇 |
2014年 | 77篇 |
2013年 | 156篇 |
2012年 | 81篇 |
2011年 | 77篇 |
2010年 | 91篇 |
2009年 | 107篇 |
2008年 | 128篇 |
2007年 | 117篇 |
2006年 | 127篇 |
2005年 | 105篇 |
2004年 | 86篇 |
2003年 | 76篇 |
2002年 | 89篇 |
2001年 | 92篇 |
2000年 | 90篇 |
1999年 | 70篇 |
1998年 | 62篇 |
1997年 | 56篇 |
1996年 | 36篇 |
1995年 | 24篇 |
1994年 | 29篇 |
1993年 | 29篇 |
1992年 | 24篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2329条查询结果,搜索用时 15 毫秒
271.
Shan-tao Liao 《Frontiers of Mathematics in China》2006,1(1):1-52
Let M
n
be an n-dimensional compact C
∞-differentiable manifold, n ≥ 2, and let S be a C
1-differential system on M
n
. The system induces a one-parameter C
1 transformation group φ
t
(−∞ < t < ∞) over M
n
and, thus, naturally induces a one-parameter transformation group of the tangent bundle of M
n
. The aim of this paper, in essence, is to study certain ergodic properties of this latter transformation group.
Among various results established in the paper, we mention here only the following, which might describe quite well the nature
of our study.
(A) Let M be the set of regular points in M
n
of the differential system S. With respect to a given C
∞ Riemannian metric of M
n
, we consider the bundle
of all (n−2) spheres Q
x
n−2, x∈M, where Q
x
n−2 for each x consists of all unit tangent vectors of M
n
orthogonal to the trajectory through x. Then, the differential system S gives rise naturally to a one-parameter transformation group ψ
t
#
(−∞<t<∞) of
. For an l-frame α = (u
1, u
2,⋯, u
l
) of M
n
at a point x in M, 1 ≥ l ≥ n−1, each u
i
being in
, we shall denote the volume of the parallelotope in the tangent space of M
n
at x with edges u
1, u
2,⋯, u
l
by υ(α), and let
. This is a continuous real function of t. Let
α is said to be positively linearly independent of the mean if I
+
*(α) > 0. Similarly, α is said to be negatively linearly independent of the mean if I
−
*(α) > 0.
A point x of M is said to possess positive generic index κ = κ
+
*(x) if, at x, there is a κ-frame
,
, of M
n
having the property of being positively linearly independent in the mean, but at x, every l-frame
, of M
n
with l >
κ does not have the same property. Similarly, we define the negative generic index κ
−
*(x) of x. For a nonempty closed subset F of M
n
consisting of regular points of S, invariant under φ
t
(−∞ < t < ∞), let the (positive and negative) generic indices of F be defined by
Theorem
κ
+
*(F)=κ
−
*(F).
(B) We consider a nonempty compact metric space x and a one-parameter transformation group ϕ
t
(−∞ < t < ∞) over X. For a given positive integer l ≥ 2, we assume that, to each x∈X, there are associated l-positive real continuous functions
of −∞ < t < ∞. Assume further that these functions possess the following properties, namely, for each of k = 1, 2,⋯, l,
for each x∈X, each −∞ < s < ∞, and each −∞ < t < ∞.
Theorem
With X, etc., given above, let μ
be a normal measure of X that is ergodic and invariant under ϕ
t
(−∞
< t < ∞). Then, for a certain permutation k→p(k) of k= 1, 2,⋯, l, the set W of points x of X such that all the inequalities
(I
k
)
(II
k
)
(k=2, 3,⋯, l) hold is invariant under ϕ
t
(−∞
< t < ∞) and is μ-measurable with μ-measure1.
In practice, the functions h
xk
(t) will be taken as length functions of certain tangent vectors of M
n
. This theory, established such as in this paper, is expected to be used in the study of structurally stable differential
systems on M
n
.
Translated from Qualitative Theory of Differentiable Dynamical Systems, Beijing, China: Science Press, 1996, by Dr. SUN Wen-xiang, School of Mathematical Sciences, Peking University, Beijing 100871,
China. The Chinese version of this paper was published in Acta Scientiarum Naturalium Universitatis Pekinensis, 1963, 9: 241–265, 309–326 相似文献
(i*) | h k (x, t) = h xk (t) is a continuous function of the Cartesian product X×(−∞, ∞). |
(ii*) |
272.
In this Letter, exponential synchronization of a complex network with nonidentical time-delayed dynamical nodes is considered. Two effective control schemes are proposed to drive the network to synchronize globally exponentially onto any smooth goal dynamics. By applying open-loop control to all nodes and adding some intermittent controllers to partial nodes, some simple criteria for exponential synchronization of such network are established. Meanwhile, a pinning scheme deciding which nodes need to be pinned and a simply approximate formula for estimating the least number of pinned nodes are also provided. By introducing impulsive effects to the open-loop controlled network, another synchronization scheme is developed for the network with nonidentical time-delayed dynamical nodes, and an estimate of the upper bound of impulsive intervals ensuring global exponential stability of the synchronization process is also given. Numerical simulations are presented finally to demonstrate the effectiveness of the theoretical results. 相似文献
273.
We highlight the potentiality of a special Information Theory (IT) approach in order to unravel the intricacies of nonlinear dynamics, the methodology being illustrated with reference to the logistic map. A rather surprising dynamic feature→plane-topography map becomes available. 相似文献
274.
提出了一种发现和学习不可复位动态系统的预测状态表示的新算法.在证明系统的任意landmark均可作为系统的初始状态的基础上,利用发现的landmark确定系统在任意时间步所处的经历,然后采用蒙特卡罗方法估计任意经历下任意检验发生的概率,解决了在不可复位动态系统中,经历下检验发生的概率难以获取问题,进而发现和学习不可复位动态系统的预测状态表示.实验结果表明,本文算法获得的系统的预测状态表示在预测精度上明显优于suffix-history算法,验证了所提算法的有效性. 相似文献
275.
In this paper, we consider the unilateral obstacle problem, trying to find the numerical solution and coincidence set. We construct an equivalent format of the original problem and propose a method with a second-order in time dissipative system for solving the equivalent format. Several numerical examples are given to illustrate the effectiveness and stability of the proposed algorithm. Convergence speed comparisons with existent numerical algorithm are also provided and our algorithm is fast. 相似文献
276.
277.
Pullback exponential attractors for nonautonomous dynamical system in space of higher regularity 下载免费PDF全文
Yongjun Li Tinggang Zhao Hongqing Wu Jinying Wei 《Journal of Applied Analysis & Computation》2016,6(1):242-253
Under what condition, a process which exists a $(E,E)$-pullback exponential attractor implies the existence of $(E,V)$- pullback exponential attractor when $V$ embedded in $E$? We answer this question in this paper. As an application of this result, we prove the existence of pullback exponential attractor for a nonlinear reaction-diffusion equation with a polynomial growth nonlinearity in $L^q(\Omega)(\forall q\geq 2)$ and $H_0^1(\Omega)$. 相似文献
278.
Juan Luis García Guirao Raquel García Rubio 《Journal of Mathematical Analysis and Applications》2010,362(2):350-354
The aim of the present paper is to study the structure of the nonwandering set of points Ω() for the skew-product maps of the unit square , (x,y)→(f(x),g(x,y)), with base f having closed set of periodic points. For every and every point (x,y) with x periodic of period px by f and y not chain recurrent of Fpx|Ix, where , we prove that (x,y)Ω(F). On the other hand we construct a map with an isolated fixed point x0 of f and y0Ω(F|Ix0) such that (x0,y0)Ω(F0). 相似文献
279.
针对反问题中出现的第一类算子方程Au=f,其中A是实Hilbert空间H上的一个无界线性算子利用动力系统方法和正则化方法,求解上述问题的正则化问题的解:u'(t)=-A~*(Au(t)-f)利用线性算子半群理论可以得到上述正则化问题的解的半群表示,并证明了当t→∞时,所得的正则化解收敛于原问题的解. 相似文献
280.
S. Kharibegashvili 《Applicable analysis》2013,92(12):2508-2525
We study the well-posedness of an initial-boundary value problem corresponding to the zeroth approximation of I. Vekua's hierarchical models for elastic cusped prismatic shells. The mathematical model is described by a two-dimensional order-degenerating hyperbolic system. We formulate the problem in the weak setting and prove the uniqueness and existence theorems. We show that the sequence of corresponding explicit Galerkin approximations converges to the exact solution in an appropriate weighted Lebesgue space. 相似文献