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   52294篇
  免费   232篇
  国内免费   551篇
系统科学   1227篇
丛书文集   280篇
教育与普及   290篇
理论与方法论   518篇
现状及发展   31248篇
研究方法   643篇
综合类   16673篇
自然研究   2198篇
  2013年   805篇
  2012年   607篇
  2011年   2630篇
  2009年   610篇
  2008年   798篇
  2007年   880篇
  2006年   944篇
  2005年   1139篇
  2004年   2228篇
  2003年   1860篇
  2002年   1535篇
  2001年   1152篇
  2000年   690篇
  1999年   813篇
  1998年   640篇
  1997年   758篇
  1996年   510篇
  1994年   681篇
  1993年   687篇
  1992年   790篇
  1991年   695篇
  1990年   759篇
  1989年   592篇
  1988年   571篇
  1987年   563篇
  1986年   651篇
  1985年   793篇
  1984年   701篇
  1983年   624篇
  1982年   751篇
  1981年   803篇
  1980年   882篇
  1979年   1308篇
  1978年   1183篇
  1977年   1199篇
  1976年   1036篇
  1975年   1013篇
  1974年   875篇
  1973年   1120篇
  1972年   1208篇
  1971年   1174篇
  1970年   1251篇
  1969年   1170篇
  1968年   1138篇
  1967年   981篇
  1966年   821篇
  1965年   662篇
  1964年   476篇
  1958年   497篇
  1957年   446篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
61.
This paper undertakes an in-sample and rolling-window comparative analysis of dependence, market, and portfolio investment risks on a 10-year global index portfolio of developed, emerging, and commodity markets. We draw our empirical results by fitting vine copulas (e.g., r-vines, c-vines, d-vines), IGARCH(1,1) RiskMetrics value-at-risk (VaR), and portfolio optimization methods based on risk measures such as the variance, conditional value-at-risk, conditional drawdown-at-risk, minimizing regret (Minimax), and mean absolute deviation. The empirical results indicate that all international indices tend to correlate strongly in the negative tail of the return distribution; however, emerging markets, relative to developed and commodity markets, exhibit greater dependence, market, and portfolio investment risks. The portfolio optimization shows a clear preference towards the gold commodity for investment, while Japan and Canada are found to have the highest and lowest market risk, respectively. The vine copula analysis identifies symmetry in the dependence dynamics of the global index portfolio modeled. Large VaR diversification benefits are produced at the 95% and 99% confidence levels by the modeled international index portfolio. The empirical results may appeal to international portfolio investors and risk managers for advanced portfolio management, hedging, and risk forecasting.  相似文献   
62.
Online search data provide us with a new perspective for quantifying public concern about animal diseases, which can be regarded as a major external shock to price fluctuations. We propose a modeling framework for pork price forecasting that incorporates online search data with support vector regression model. This novel framework involves three main steps: that is, formulation of the animal diseases composite indexes (ADCIs) based on online search data; forecast with the original ADCIs; and forecast improvement with the decomposed ADCIs. Considering that there are some noises within the online search data, four decomposition techniques are introduced: that is, wavelet decomposition, empirical mode decomposition, ensemble empirical mode decomposition, and singular spectrum analysis. The experimental study confirms the superiority of the proposed framework, which improves both the level and directional prediction accuracy. With the SSA method, the noise within the online search data can be removed and the performance of the optimal model is further enhanced. Owing to the long-term effect of diseases outbreak on price volatility, these improvements are more prominent in the mid- and long-term forecast horizons.  相似文献   
63.
The use of correlation between forecasts and actual returns is commonplace in the literature, often used as a measurement of investors' skill. A prominent application of this is the concept of the information coefficient (IC). Not only can the IC be used as a tool to rate analysts and fund managers but it also represents an important parameter in the asset allocation and portfolio construction process. Nevertheless, a theoretical understanding of it has typically been limited to the partial equilibrium context where the investing activities of each agent have no effect on other market participants. In this paper we show that this can be an undesirable oversimplification and we demonstrate plausible circumstances in which conventional empirical measurements of IC can be highly misleading. We suggest that improved understanding of IC in a general equilibrium setting can lead to refined portfolio decision making ex ante and more informative analysis of performance ex post. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
64.
65.
66.
67.
68.
69.
70.
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