全文获取类型
收费全文 | 1157篇 |
免费 | 143篇 |
国内免费 | 107篇 |
专业分类
化学 | 46篇 |
力学 | 93篇 |
综合类 | 20篇 |
数学 | 917篇 |
物理学 | 331篇 |
出版年
2023年 | 5篇 |
2022年 | 32篇 |
2021年 | 41篇 |
2020年 | 23篇 |
2019年 | 26篇 |
2018年 | 22篇 |
2017年 | 39篇 |
2016年 | 59篇 |
2015年 | 23篇 |
2014年 | 47篇 |
2013年 | 76篇 |
2012年 | 55篇 |
2011年 | 65篇 |
2010年 | 49篇 |
2009年 | 70篇 |
2008年 | 67篇 |
2007年 | 60篇 |
2006年 | 67篇 |
2005年 | 63篇 |
2004年 | 53篇 |
2003年 | 38篇 |
2002年 | 48篇 |
2001年 | 43篇 |
2000年 | 37篇 |
1999年 | 40篇 |
1998年 | 21篇 |
1997年 | 24篇 |
1996年 | 33篇 |
1995年 | 15篇 |
1994年 | 24篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 4篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 5篇 |
排序方式: 共有1407条查询结果,搜索用时 15 毫秒
181.
Questions of asymptotic inference are discussed for a point process model in which the conditional intensity function increases monotonically between events and drops by determined (nonrandom) amounts after each event. Parameter estimates are shown to be consistent and, except under the null hypothesis of a Poisson process, normally distributed. Under the null hypothesis, however, the Hessian matrix is not asymptotically constant, and the limiting distribution of the likelihood ratio statistics is not χ2, but has a form related to that of the Cramer-von Mises ω2 statistic for the test of goodness of fit. 相似文献
182.
Let FX,Y(x,y) be a bivariate distribution function and Pn(x), Qm(y), n, m = 0, 1, 2,…, the orthonormal polynomials of the two marginal distributions FX(x) and FY(y), respectively. Some necessary conditions are derived for the co-efficients cn, n = 0, 1, 2,…, if the conditional expectation E[Pn(X) ∥ Y] = cnQn(Y) holds for n = 0, 1, 2,…. Several examples are given to show the application of these necessary conditions. 相似文献
183.
Richard A Davis 《Journal of multivariate analysis》1983,13(2):273-286
The aim of this paper is to examine the weak limiting behavior of upper and lower extremes from stationary sequences satisfying dependence conditions similar to D and D′ introduced by Leadbetter (Z. Wahrsch. Verw. Gebiete28 (1974), 289–303). By establishing the convergence in distribution of an associated sequence of point processes, the joint limiting distribution of any collection of upper and lower extremes can be determined. Sufficient and, in some cases, necessary conditions for the asymptotic independence of the upper and lower extremes are also given. 相似文献
184.
PAN Jiazhu & WU Guangxu LMAM School of Mathematical Sciences Peking University Beijing China 《中国科学A辑(英文版)》2005,48(9):1169-1181
We study the tail probability of the stationary distribution of nonparametric non- linear autoregressive functional conditional heteroscedastic (NARFCH) model with heavy- tailed innovations.Our result shows that the tail of the stationary marginal distribution of an NARFCH series is heavily dependent on its conditional variance.When the innovations are heavy-tailed,the tail of the stationary marginal distribution of the series will become heavier or thinner than that of its innovations.We give some specific formulas to show how the increment or decrement of tail heaviness depends on the assumption on the con- ditional variance function.Some examples are given. 相似文献
185.
We introduce in this paper the concept of “impulse evolutionary game”. Examples of evolutionary games are usual differential
games, differentiable games with history (path-dependent differential games), mutational differential games, etc. Impulse
evolutionary systems and games cover in particular “hybrid systems” as well as “qualitative systems”. The conditional viability
kernel of a constrained set (with a target) is the set of initial states such that for all strategies (regarded as continuous
feedbacks) played by the second player, there exists a strategy of the first player such that the associated run starting
from this initial state satisfies the constraints until it hits the target. This paper characterizes the concept of conditional
viability kernel for “qualitative games” and of conditional valuation function for “qualitative games” maximinimizing an intertemporal
criterion. The theorems obtained so far about viability/capturability issues for evolutionary systems, conditional viability
for differential games and about impulse and hybrid systems are used to provide characterizations of conditional viability
under impulse evolutionary games. 相似文献
186.
S.?CairesEmail author J.?A.?Ferreira 《Statistical Inference for Stochastic Processes》2005,8(2):151-184
We prove the strong consistency of estimators of the conditional distribution function and conditional expectation of a future
observation of a discrete time stochastic process given a fixed number of past observations. The results apply to conditionally
stationary processes (a class of processes including Markov and stationary processes) satisfying a strong mixing condition,
and they extend and bring together the work of several authors in the area of non-parametric estimation. One of our goals
is to provide further justification for the growing practical application of non-parametric estimators in non-stationary time
series and in other `non-i.i.d.' settings. Some arguments as to why such estimators should work very generally in practice,
often in a nearly `optimal' way, are given. Two numerical illustrations are included, one with simulated data and the other
with oceanographic data.
An erratum to this article is available at . 相似文献
187.
One of the difficulties that arise in the statistical analysis of autoregressive schemes is the very complex nature of the domain of the regression parameters. In the present paper we study an alternative parametrization of autoregressive models of finite order, namely the parametrization by the partial autocorrelations. These are shown to vary freely from −1 to +1 and to be in a one-to-one, continuously differentiable correspondence with the regression parameters. Properties of the asymptotic normal distribution of the maximum likelihood estimates are discussed, and we present a new deduction of Quenouille's result on the asymptotic independence of some of the estimated partial autocorrelations. 相似文献
188.
For continuous time birth-death processes on {0,1,2,…}, the first passage time T+n from n to n + 1 is always a mixture of (n + 1) independent exponential random variables. Furthermore, the first passage time T0,n+1 from 0 to (n + 1) is always a sum of (n + 1) independent exponential random variables. The discrete time analogue, however, does not necessarily hold in spite of structural similarities. In this paper, some necessary and sufficient conditions are established under which T+n and T0,n+1 for discrete time birth-death chains become a mixture and a sum, respectively, of (n + 1) independent geometric random variables on {1,2,…};. The results are further extended to conditional first passage times. 相似文献
189.
190.
水上交通事故严重程度影响因素的识别对从根本上减少严重事故件数、降低事故危害和损失具有重要意义。在历史事故报告的基础上,构建并量化事故影响因素集,提出以极限学习机(ELM)为一般事故、严重事故的二分类器,以遗传算法(GA)为因素搜索算法的GA-ELM因素识别模型。对发生在我国水域的737件水上交通事故进行实证研究,并与以支持向量机(SVM)为分类器的GA-SVM模型进行对比分析。结果表明,GA-ELM模型识别出时段、人为致因、环境致因等9个事故严重程度影响因素,较GA-SVM模型结果更为精简,且分类精度较不做因素识别时分别提高8.2%、7.1%。此外,GA-ELM大大缩短运算时间。由此可见,GA-ELM可为水上交通事故严重程度影响因素识别提供一个较好的方法。 相似文献