全文获取类型
收费全文 | 645篇 |
免费 | 50篇 |
国内免费 | 105篇 |
专业分类
系统科学 | 109篇 |
丛书文集 | 17篇 |
理论与方法论 | 3篇 |
现状及发展 | 85篇 |
综合类 | 583篇 |
自然研究 | 3篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2016年 | 18篇 |
2015年 | 34篇 |
2014年 | 45篇 |
2013年 | 27篇 |
2012年 | 50篇 |
2011年 | 46篇 |
2010年 | 34篇 |
2009年 | 40篇 |
2008年 | 35篇 |
2007年 | 58篇 |
2006年 | 52篇 |
2005年 | 31篇 |
2004年 | 33篇 |
2003年 | 36篇 |
2002年 | 20篇 |
2001年 | 16篇 |
2000年 | 24篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1985年 | 1篇 |
排序方式: 共有800条查询结果,搜索用时 15 毫秒
81.
基于多元图图形几何特征的模式识别新方法 总被引:1,自引:1,他引:0
在简要比较统计模式识别和句法模式识别优缺点的基础上,进一步介绍了模式识别研究领域中的表示问题和基于几何特征的模式识别方法研究现状,并提出了具有探索性意义的基于多元图图形几何特征可视化模式识别新问题. 相似文献
82.
The ability to improve out-of-sample forecasting performance by combining forecasts is well established in the literature. This paper advances this literature in the area of multivariate volatility forecasts by developing two combination weighting schemes that exploit volatility persistence to emphasise certain losses within the combination estimation period. A comprehensive empirical analysis of the out-of-sample forecast performance across varying dimensions, loss functions, sub-samples and forecast horizons show that new approaches significantly outperform their counterparts in terms of statistical accuracy. Within the financial applications considered, significant benefits from combination forecasts relative to the individual candidate models are observed. Although the more sophisticated combination approaches consistently rank higher relative to the equally weighted approach, their performance is statistically indistinguishable given the relatively low power of these loss functions. Finally, within the applications, further analysis highlights how combination forecasts dramatically reduce the variability in the parameter of interest, namely the portfolio weight or beta. 相似文献
83.
Harald Hruschka 《Journal of forecasting》2017,36(3):230-240
We analyze multicategory purchases of households by means of heterogeneous multivariate probit models that relate to partitions formed from a total of 25 product categories. We investigate both prior and post hoc partitions. We search model structures by a stochastic algorithm and estimate models by Markov chain Monte Carlo simulation. The best model in terms of cross‐validated log‐likelihood refers to a post hoc partition with two groups; the second‐best model considers all categories as one group. Among prior partitions with at least two category groups a five‐group model performs best. Effects on average basket value differ for the model with five prior category groups from those for the best‐performing model in 40% and 24% of the investigated categories for features and displays, respectively. In addition, the model with five prior category groups also underestimates total sales revenue across all categories by about 28%. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
84.
Manabu Asai 《Journal of forecasting》2013,32(5):469-480
The paper considers the return and range model with dynamic conditional correlations (DCC). The paper suggests the new specifications for the asymmetric effects on log‐volatilities and dynamic correlations, combined with long‐run dependences. The new DCC model can be estimated by the quasi‐maximum likelihood method. Empirical analysis on Nikkei 225, Hang Seng and Straits Times indices shows the daily, weekly and monthly pattern of asymmetric effects. For the period including the global financial crisis, the new DCC model provides plausible one‐step‐ahead forecasts of the VaR thresholds, and yields positive economic values of switching from other DCC models. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
85.
This paper employed sequential minimal optimization (SMO) to develop default prediction model in the US retail market. Principal components analysis is used for variable reduction purposes. Four standard credit scoring techniques—naïve Bayes, logistic regression, recursive partitioning and artificial neural network—are compared to SMO, using a sample of 195 healthy firms and 51 distressed firms over five time periods between 1994 and 2002. The five techniques perform well in predicting default particularly one year before financial distress. Furthermore, the prediction still remains sound even 5 years before default. No single methodology has the absolute best classification ability, as the model performance varies in terms of different time periods and variable groups. External influences have greater impacts on the naïve Bayes than other techniques. In terms of similarity with Moody's ranking, SMO excelled over other techniques in most of the time periods. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
86.
This paper proposes a new mixture GARCH model with a dynamic mixture proportion. The mixture Gaussian distribution of the error can vary from time to time. The Bayesian Information Criterion and the EM algorithm are used to estimate the number of parameters as well as the model parameters and their standard errors. The new model is applied to the S&P500 Index and Hang Seng Index and compared with GARCH models with Gaussian error and Student's t error. The result shows that the IGARCH effect in these index returns could be the result of the mixture of one stationary volatility component with another non‐stationary volatility component. The VaR based on the new model performs better than traditional GARCH‐based VaRs, especially in unstable stock markets. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
87.
We propose a simple and flexible framework for forecasting the joint density of asset returns. The multinormal distribution is augmented with a polynomial in (time‐varying) non‐central co‐moments of assets. We estimate the coefficients of the polynomial via the method of moments for a carefully selected set of co‐moments. In an extensive empirical study, we compare the proposed model with a range of other models widely used in the literature. Employing a recently proposed as well as standard techniques to evaluate multivariate forecasts, we conclude that the augmented joint density provides highly accurate forecasts of the ‘negative tail’ of the joint distribution. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
88.
In this paper, we investigate the performance of a class of M‐estimators for both symmetric and asymmetric conditional heteroscedastic models in the prediction of value‐at‐risk. The class of estimators includes the least absolute deviation (LAD), Huber's, Cauchy and B‐estimator, as well as the well‐known quasi maximum likelihood estimator (QMLE). We use a wide range of summary statistics to compare both the in‐sample and out‐of‐sample VaR estimates of three well‐known stock indices. Our empirical study suggests that in general Cauchy, Huber and B‐estimator have better performance in predicting one‐step‐ahead VaR than the commonly used QMLE. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
89.
程艳 《科技情报开发与经济》2005,15(11):147-148
公共选择与公益物品是经济学关注的焦点问题,众多的经济学家就此提出了相关的可行性方案。结合公益物品的特性并借鉴管理学的拓展模型,主要考察其中的3种政府提供公共物品的方式:政府介入模式、自治型公共事业组织模式和多元组织模式。并用管理学中非传递对称双线性效用值理论剖析了在特定情景下各种方案的优势、机会成本和相关的代价。 相似文献
90.