全文获取类型
收费全文 | 5007篇 |
免费 | 682篇 |
国内免费 | 322篇 |
专业分类
化学 | 698篇 |
晶体学 | 17篇 |
力学 | 345篇 |
综合类 | 71篇 |
数学 | 2148篇 |
物理学 | 2732篇 |
出版年
2024年 | 13篇 |
2023年 | 31篇 |
2022年 | 398篇 |
2021年 | 391篇 |
2020年 | 169篇 |
2019年 | 117篇 |
2018年 | 126篇 |
2017年 | 116篇 |
2016年 | 165篇 |
2015年 | 122篇 |
2014年 | 222篇 |
2013年 | 301篇 |
2012年 | 212篇 |
2011年 | 240篇 |
2010年 | 205篇 |
2009年 | 263篇 |
2008年 | 312篇 |
2007年 | 293篇 |
2006年 | 274篇 |
2005年 | 276篇 |
2004年 | 202篇 |
2003年 | 223篇 |
2002年 | 196篇 |
2001年 | 141篇 |
2000年 | 110篇 |
1999年 | 108篇 |
1998年 | 98篇 |
1997年 | 101篇 |
1996年 | 73篇 |
1995年 | 39篇 |
1994年 | 50篇 |
1993年 | 40篇 |
1992年 | 55篇 |
1991年 | 36篇 |
1990年 | 31篇 |
1989年 | 32篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 19篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1973年 | 5篇 |
1969年 | 4篇 |
排序方式: 共有6011条查询结果,搜索用时 15 毫秒
71.
The measure of uncertainty is adopted as a measure of information. The measures of fuzziness are known as fuzzy information measures. The measure of a quantity of fuzzy information gained from a fuzzy set or fuzzy system is known as fuzzy entropy. Fuzzy entropy has been focused and studied by many researchers in various fields. In this paper, firstly, the axiomatic definition of fuzzy entropy is discussed. Then, neural networks model of fuzzy entropy is proposed, based on the computing capability of neural networks. In the end, two examples are discussed to show the efficiency of the model. 相似文献
72.
Quantization consists in studying the L
r
-error induced by the approximation of a random vector X by a vector (quantized version) taking a finite number n of values. We investigate this problem for Gaussian random vectors in an infinite dimensional Banach space and in particular, for Gaussian processes. A precise link proved by Fehringer(4) and Dereich et al.
(3) relates lower and upper bounds for small ball probabilities with upper and lower bounds for the quantization error, respectively. We establish a complete relationship by showing that the same holds for the direction from the quantization error to small ball probabilities. This allows us to compute the exact rate of convergence to zero of the minimal L
r
-quantization error from logarithmic small ball asymptotics and vice versa. 相似文献
73.
74.
Using the thermodynamical approach and the method of York, the back-reaction of anti-de Sitter Schwarzschild black hole in thermal equilibrium with conformal spin-2 field is studied. It is found that both approaches give identical results. 相似文献
75.
76.
Periodica Mathematica Hungarica - Let X 1,X 2,... be a sequence of independent and identically distributed random variables, and put % MATHTYPE!MTEF!2!1!+-%... 相似文献
77.
Vladimir E. Bondarenko 《Complexity》2005,11(2):39-52
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
78.
Pierre Gaspard 《Journal of statistical physics》2004,117(3-4):599-615
A concept of time-reversed entropy per unit time is introduced in analogy with the entropy per unit time by Shannon, Kolmogorov, and Sinai. This time-reversed entropy per unit time characterizes the dynamical randomness of a stochastic process backward in time, while the standard entropy per unit time characterizes the dynamical randomness forward in time. The difference between the time-reversed and standard entropies per unit time is shown to give the entropy production of Markovian processes in nonequilibrium steady states. 相似文献
79.
In this paper we consider the problem of estimating an unknown joint distribution which is defined over mixed discrete and continuous variables. A nonparametric kernel approach is proposed with smoothing parameters obtained from the cross-validated minimization of the estimator's integrated squared error. We derive the rate of convergence of the cross-validated smoothing parameters to their ‘benchmark’ optimal values, and we also establish the asymptotic normality of the resulting nonparametric kernel density estimator. Monte Carlo simulations illustrate that the proposed estimator performs substantially better than the conventional nonparametric frequency estimator in a range of settings. The simulations also demonstrate that the proposed approach does not suffer from known limitations of the likelihood cross-validation method which breaks down with commonly used kernels when the continuous variables are drawn from fat-tailed distributions. An empirical application demonstrates that the proposed method can yield superior predictions relative to commonly used parametric models. 相似文献
80.