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排序方式: 共有347条查询结果,搜索用时 15 毫秒
181.
An adaptive Kalman filter is proposed to estimate the states of a system where the system noise is assumed to be a multivariate generalized Laplace random vector. In the presence of outliers in the system noise, it is shown that improved state estimates can be obtained by using an adaptive factor to estimate the dispersion matrix of the system noise term. For the implementation of the filter, an algorithm which includes both single and multiple adaptive factors is proposed. A Monte-Carlo investigation is also carried out to access the performance of the proposed filters in comparison with other robust filters. The results show that, in the sense of minimum mean squared state error, the proposed filter is superior to other filters when the magnitude of a system change is moderate or large.  相似文献   
182.
The continuous quadratic variation of asset return plays a critical role for high-frequency trading. However, the microstructure noise could bias the estimation of the continuous quadratic variation. Zhang et al. (2005 Zhang, L., Mykland, P., Ait-Sahalia, Y. (2005). A tale of two time scales: determining integrated volatility with noisy high-frequency data. J. Amer. Statist. Assoc. 100(472):13941411.[Taylor & Francis Online], [Web of Science ®] [Google Scholar]) proposed a batch estimator for the continuous quadratic variation of high-frequency data in the presence of microstructure noise. It gives the estimates after all the data arrive. This article proposes a recursive version of their estimator that outputs variation estimates as the data arrive. Our estimator gives excellent estimates well before all the data arrive. Both real high-frequency futures data and simulation data confirm the performance of the recursive estimator.  相似文献   
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185.
This article proposes an extension of the log periodogram regression in perturbed long memory series that accounts for the added noise, while also allowing for correlation between signal and noise, a common situation in many economic and financial series. Consistency (for d < 1) and asymptotic normality (for d < 3/4) are shown with the same bandwidth restriction as required for the original log periodogram regression in a fully observable series, with the corresponding gain in asymptotic efficiency and faster convergence over competitors. Local Wald, Lagrange Multiplier, and Hausman type tests of the hypothesis of no correlation between the latent signal and noise are also proposed.  相似文献   
186.
Approximate normality and unbiasedness of the maximum likelihood estimate (MLE) of the long-memory parameter H of a fractional Brownian motion hold reasonably well for sample sizes as small as 20 if the mean and scale parameter are known. We show in a Monte Carlo study that if the latter two parameters are unknown the bias and variance of the MLE of H both increase substantially. We also show that the bias can be reduced by using a parametric bootstrap procedure. In very large samples, maximum likelihood estimation becomes problematic because of the large dimension of the covariance matrix that must be inverted. To overcome this difficulty, we propose a maximum likelihood method based upon first differences of the data. These first differences form a short-memory process. We split the data into a number of contiguous blocks consisting of a relatively small number of observations. Computation of the likelihood function in a block then presents no computational problem. We form a pseudo-likelihood function consisting of the product of the likelihood functions in each of the blocks and provide a formula for the standard error of the resulting estimator of H. This formula is shown in a Monte Carlo study to provide a good approximation to the true standard error. The computation time required to obtain the estimate and its standard error from large data sets is an order of magnitude less than that required to obtain the widely used Whittle estimator. Application of the methodology is illustrated on two data sets.  相似文献   
187.
The nonparametric density function estimation using sample observations which are contaminated with random noise is studied. The particular form of contamination under consideration is Y = X + Z, where Y is an observable random variableZ is a random noise variable with known distribution, and X is an absolutely continuous random variable which cannot be observed directly. The finite sample size performance of a strongly consistent estimator for the density function of the random variable X is illustrated for different distributions. The estimator uses Fourier and kernel function estimation techniques and allows the user to choose constants which relate to bandwidth windows and limits on integration and which greatly affect the appearance and properties of the estimates. Numerical techniques for computation of the estimated densities and for optimal selection of the constant are given.  相似文献   
188.
按照国家民航体制改革方案,我国民用机场下放地方政府、实行企业化管理;位于经济不发达地区的西北民用机场在属地化之后,面临着市场、资金、管理及发展等诸多困境,如何在新的形势下摆脱困境谋求发展,成为摆在国家、地方政府和机场经营者面前的重要课题;发展西北民用机场,应明确机场定位,充分整合各种资源,与地方经济互动发展;同时,鼓励机场之间的联合,引进资金和管理,转换机场经营思路,并争取国家、地方政府的资金和政策支持。  相似文献   
189.
口译理解过程中的心理噪音及其对口译教学的启示   总被引:2,自引:0,他引:2  
口译译员在双语交际过程中扮演着中间人的角色。由于其身份的必要性和工作的特殊性,国内外出版的口译论著和译著中在论及口译理解时都要求译员做到:听力好;精通讲话者所用的语言;熟悉讲话者所属国的文化背景;了解讲话者所属国在发音和用词方面的特点;了解讲话的主题并且具备广博的学识。然而,在口译实践过程中,我们发现,仅做到这些,有时仍然难以胜任工作。究其原因,祸首乃口译理解过程中的“心理噪音”。本文用口译实例阐述了由于译员缺乏心理期待或作出错误预测而造成的“心理噪音”在口译理解过程中产生的负面影响,用认知心理学、语用学和巴黎释意派理论分析其作用的原因,并探讨了在口译教学过程中如何设计有针对性地训练和练习。  相似文献   
190.
分析了我国客运需求的主要影响因素,提出基本需求和活动需求概念,研究了我国客运需求函数的一般表达式和实证形式。认为各客运方式的需求应依赖于其竞争的状态,各客运方式将主要集中在典型竞争因素上开展竞争,其各自的市场需求份额将趋于一个较合理的比例。用AHP定量方法并结合定性方法推算出了这一比例。  相似文献   
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