全文获取类型
收费全文 | 1198篇 |
免费 | 40篇 |
国内免费 | 2篇 |
专业分类
化学 | 14篇 |
综合类 | 1篇 |
数学 | 114篇 |
物理学 | 65篇 |
无线电 | 1046篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 23篇 |
2021年 | 18篇 |
2020年 | 26篇 |
2019年 | 29篇 |
2018年 | 20篇 |
2017年 | 18篇 |
2016年 | 21篇 |
2015年 | 21篇 |
2014年 | 47篇 |
2013年 | 74篇 |
2012年 | 53篇 |
2011年 | 54篇 |
2010年 | 42篇 |
2009年 | 46篇 |
2008年 | 53篇 |
2007年 | 80篇 |
2006年 | 70篇 |
2005年 | 68篇 |
2004年 | 59篇 |
2003年 | 55篇 |
2002年 | 66篇 |
2001年 | 49篇 |
2000年 | 51篇 |
1999年 | 38篇 |
1998年 | 31篇 |
1997年 | 27篇 |
1996年 | 23篇 |
1995年 | 24篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
排序方式: 共有1240条查询结果,搜索用时 0 毫秒
171.
随着互联网络技术的飞速发展,网络聊天日益进入了人们的生活,聊天室也受到了越来越多网民的欢迎,它为网友提供了实时性交流的渠道.提出了用ASP开发基于B/S模式的聊天室系统,并对系统的设计与实现加以详细的阐述,并给出了部分关键代码. 相似文献
172.
Kostas A. Tsagkaris George Dimitrakopoulos Panagiotis Demestichas 《Wireless Networks》2009,15(3):391-405
The ceaseless evolution of wireless communications is reflected nowadays on the introduction of Beyond-3G (B3G) systems, characterized
by the coexistence and cooperation of various Radio Access Technologies (RATs), over a common infrastructure. Major facilitator
of this convergence is the advent of cognitive networks, which deploy elements (base stations and mobile terminals) that are
able to proactively adapt to environmental stimuli, so that to optimize their performance. Part of the adaptation action takes
place in cognitive base stations that own several reconfigurable transceivers, which are controlled by appropriate management
functionality and may dynamically change their operating parameters. Each reconfiguration set includes a specific RAT, carrier
frequency, as well as demand volume to be allocated per transceiver. Accordingly, proper evaluation of the various candidate
reconfiguration sets appears to be of high significance. To this effect, in this paper we consider a cognitive network segment
with transceivers operating at 3G RAT/carrier and we solve the DAMC problem (Demand Allocation into Multiple Carriers problem),
which aims at evaluating and selecting the optimum policy to allocate the demand into the available 3G carrier frequencies.
Optimality is expressed in terms of minimizing the total transmitted/received power per base station, thus deciding for the
reconfigurations with the least impact on network interference. Indicative simulation scenarios and results are also presented
for the validation and verification of the proposed functionality.
相似文献
Panagiotis DemestichasEmail: |
173.
174.
175.
176.
Natural disasters increase in number and severity. Studies have shown the failure of the catastrophe insurance market by listing many causes or through developing economic models (Charpentier and Le Maux, 2014; Kousky and Cooke, 2012; Ibragimov et al., 2009). However, they have not considered the effect of the following factors on market equilibrium: advanced disaster-resistant technologies used by insureds, alternative financial innovations employed by insurers, and various disaster policies that are implemented by governments. To fill this gap, this study examines how these three factors affect the market equilibrium by changing the supply of, and demand for insurance and determines which factor(s) contributes to the market equilibrium. Furthermore, we derive the formula of position size which gives criteria for selecting index-based contracts. Overall annual numbers and insured losses of catastrophes are collected by peril type and by occurrence region listed in Sigma, which is issued by Swiss Re annually. The comparative static equilibrium analysis demonstrates that the improvement of market equilibrium is significant at low level of loss correlation in all cases. The empirical findings give insurers good references for business and geographical diversification in portfolio of catastrophe insurance policies. 相似文献
177.
Widely cited evidence for scaling (self-similarity) of the returns of stocks and other securities is inconsistent with virtually all currently-used models for price movements. In particular, state-of-the-art models provide for ubiquitous, irregular, and oftentimes high-frequency fluctuations in volatility (“stochastic volatility”), both intraday and across the days, weeks, and years over which data is aggregated in demonstrations of self-similarity of returns. Stochastic volatility renders these models, which are based on variants and generalizations of random walks, incompatible with self-similarity. We show here that empirical evidence for self-similarity does not actually contradict the analytic lack of self-similarity in these models. The resolution of the mismatch between models and data can be traced to a statistical consequence of aggregating large amounts of non-stationary data. 相似文献
178.
We first present prima facie evidence for the predictions generated by the mixture of distributions hypothesis, using daily German stock returns and their corresponding daily trading volumes and number of trades. These last two variables are used as proxies for the stochastic rate of information arrival when one wishes to explain GARCH effects by adhering to the mixture of distributions hypothesis. We show that there is no need for these proxies when the stochastic rate of information arrival follows an inverted gamma distribution. Daily trading volume and the daily number of trades, however, empirically provide an explanation for the occurrence of conditional heteroskedasticity of the GARCH form. We estimate several specifications where daily trading volume is included in the conditional variance equation additively and multiplicatively. The new multiplicative specification clearly outperforms the additive specification. 相似文献
179.
Luitgard A. M. Veraart 《Applied Mathematical Finance》2013,20(4):359-372
Abstract This paper is concerned with optimal market making in the foreign exchange market. The market maker's holdings in the different currencies are modelled as stochastic processes that are influenced by both the stochastic exchange rates and the stochastic customer buy and sell orders. The market maker can control their own bid and ask price quotes and, additionally, can buy and sell at other market participants' quotes. The resulting stochastic control problem consists of a controlled diffusion problem for the optimal quotes and a singular control problem for optimal trades at other market participants' quotes. A Markov chain approximation is used to derive optimal strategies. 相似文献
180.
In this work we study how optical amplifiers can deeply improve the performance of the passive optical networks (PONs), permitting a large number of optical network units (ONUs), transmitting at high bit rate. These high-capacity networks are called SUPERPONs, and we show how to achieve a network with 8,192 ONUs with a transmission in the downstream direction up to 10 Gbit/s. 相似文献