首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2825篇
  免费   377篇
  国内免费   417篇
化学   304篇
晶体学   19篇
力学   350篇
综合类   79篇
数学   1903篇
物理学   964篇
  2024年   5篇
  2023年   20篇
  2022年   32篇
  2021年   53篇
  2020年   57篇
  2019年   55篇
  2018年   57篇
  2017年   70篇
  2016年   68篇
  2015年   65篇
  2014年   97篇
  2013年   303篇
  2012年   114篇
  2011年   140篇
  2010年   122篇
  2009年   134篇
  2008年   190篇
  2007年   196篇
  2006年   184篇
  2005年   144篇
  2004年   148篇
  2003年   170篇
  2002年   147篇
  2001年   148篇
  2000年   141篇
  1999年   117篇
  1998年   135篇
  1997年   92篇
  1996年   79篇
  1995年   61篇
  1994年   66篇
  1993年   34篇
  1992年   26篇
  1991年   21篇
  1990年   28篇
  1989年   15篇
  1988年   14篇
  1987年   13篇
  1986年   12篇
  1985年   3篇
  1984年   23篇
  1983年   2篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1978年   2篇
  1972年   1篇
  1971年   2篇
  1959年   1篇
  1936年   2篇
排序方式: 共有3619条查询结果,搜索用时 234 毫秒
61.
Information processing and two types of memory in an analog neural network model with time delay that produces chaos similar to the human and animal EEGs are considered. There are two levels of information processing in this neural network: the level of individual neurons and the level of the neural network. Similar to the state of brain, the state of chaotic neural network is defined. It is characterized by two types of memories (memory I and memory II) and correlation structure between the neurons. In normal (unperturbed) state, the neural network generates chaotic patterns of averaged neuronal activities (memory I) and patterns of oscillation amplitudes (memory II). In the presence of external stimulation, the activity patterns change, showing changes in both types of memory. As in experiments on stimulation of the brain, the neural network model shows synchronization of neuronal activities due to stimulus measured by Pearson's correlation coefficient. An increase in neural network asymmetry (increase of the neural network excitability) leads to the phenomenon similar to the epilepsy. Modeling of brain injury, Parkinson's disease, and dementia is performed by removing and weakening interneuron connections. In all cases, the chaotic neural network shows a decrease of the degree of chaos and changes in both types of memory similar to those observed in experiments with healthy human subjects and patients with Parkinson's disease and dementia. © 2005 Wiley Periodicals, Inc. Complexity 11:39–52, 2005  相似文献   
62.
ANTIFUZZYVECTORSPACES(Ⅱ)ChenYongnian(DepartmentofMathematics,XinjiangNormalUniversity,830054,Xinjiang,P.R.China)ANTIFUZZYVECT...  相似文献   
63.
Let B^α = {B^α(t),t E R^N} be an (N,d)-fractional Brownian motion with Hurst index α∈ (0, 1). By applying the strong local nondeterminism of B^α, we prove certain forms of uniform Hausdorff dimension results for the images of B^α when N 〉 αd. Our results extend those of Kaufman for one-dimensional Brownian motion.  相似文献   
64.
The leading logarithmic corrections to the critical behavior of a dilute uniaxial (Ising) ferromagnet in the disordered phase are derived using renormalization group methods. The values of the exponents in the logarithmic terms differ from those given by previous authors.  相似文献   
65.
The famous 1960's construction of Golod and Shafarevich yields infinite dimensional nil, but not nilpotent, algebras. However, these algebras have exponential growth. Here, we construct an infinite dimensional nil, but not locally nilpotent, algebra which has polynomially bounded growth.

  相似文献   

66.
在研究小波变换及布朗分形模型的基础上,定义了水平分维数,垂直分维数,对角分维数,并将它们作为纹理特征量来实现纹理的分割.实验结果表明,这些特征量能够很好地反映纹理特征,从而分割时不需有关图象中纹理类别的先验信息,较以往方法在准确度和计算复杂程度上都有很大提高.  相似文献   
67.
Let X(t) be an N parameter generalized Lévy sheet taking values in ℝd with a lower index α, ℜ = {(s, t] = ∏ i=1 N (s i, t i], s i < t i}, E(x, Q) = {tQ: X(t) = x}, Q ∈ ℜ be the level set of X at x and X(Q) = {x: ∃tQ such that X(t) = x} be the image of X on Q. In this paper, the problems of the existence and increment size of the local times for X(t) are studied. In addition, the Hausdorff dimension of E(x, Q) and the upper bound of a uniform dimension for X(Q) are also established.  相似文献   
68.
This article provides an introduction to A. Bak's theory of group-valued functors on categories with structure and dimension and applies this theory to the algebraic K-theory functors nonstable K 1 and K 2.  相似文献   
69.
We show that the problem of deciding whether anN-free ordered set has dimension at most 3 is NP-complete.Both authors supported by Office of Naval Research contract N00014-85K-0494.  相似文献   
70.
We define a classical probability analogue of Voiculescu's free entropy dimension that we shall call the classical probability entropy dimension of a probability measure on Rn. We show that the classical probability entropy dimension of a measure is related with diverse other notions of dimension. First, it can be viewed as a kind of fractal dimension. Second, if one extends Bochner's inequalities to a measure by requiring that microstates around this measure asymptotically satisfy the classical Bochner's inequalities, then we show that the classical probability entropy dimension controls the rate of increase of optimal constants in Bochner's inequality for a measure regularized by convolution with the Gaussian law as the regularization is removed. We introduce a free analogue of the Bochner inequality and study the related free entropy dimension quantity. We show that it is greater or equal to the non-microstates free entropy dimension.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号