全文获取类型
收费全文 | 7494篇 |
免费 | 682篇 |
国内免费 | 154篇 |
专业分类
系统科学 | 1147篇 |
丛书文集 | 55篇 |
教育与普及 | 38篇 |
理论与方法论 | 283篇 |
现状及发展 | 880篇 |
研究方法 | 3篇 |
综合类 | 5924篇 |
出版年
2024年 | 16篇 |
2023年 | 25篇 |
2022年 | 63篇 |
2021年 | 50篇 |
2020年 | 48篇 |
2019年 | 22篇 |
2018年 | 755篇 |
2017年 | 769篇 |
2016年 | 475篇 |
2015年 | 115篇 |
2014年 | 114篇 |
2013年 | 105篇 |
2012年 | 380篇 |
2011年 | 1056篇 |
2010年 | 924篇 |
2009年 | 589篇 |
2008年 | 634篇 |
2007年 | 868篇 |
2006年 | 110篇 |
2005年 | 137篇 |
2004年 | 193篇 |
2003年 | 208篇 |
2002年 | 99篇 |
2001年 | 31篇 |
2000年 | 45篇 |
1999年 | 80篇 |
1998年 | 62篇 |
1997年 | 45篇 |
1996年 | 49篇 |
1995年 | 51篇 |
1994年 | 41篇 |
1993年 | 37篇 |
1992年 | 34篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 24篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 3篇 |
1967年 | 1篇 |
排序方式: 共有8330条查询结果,搜索用时 15 毫秒
211.
Thomas Durt 《Foundations of Science》2011,16(4):315-318
As was mentioned by Nicolas Lori in his (Found Sci, 2010) commentary, the definition of Information in Physics is something about which not all authors agreed. According to physicists
like me Information decreases when Entropy increases (so entropy would be a negative measure of information), while many physicists,
seemingly the majority of them, are convinced of the contrary (even in the camp of Quantum Information Theoreticians). In
this reply I reproduce, and make more precise, some of my arguments, that appeared here and there in my (2010) paper, in order to clarify the presentation of my personal point of view on the subject. 相似文献
212.
This paper aims to contribute to the literature on the explanatory power of behavior models with heterogeneous agents. The
authors present a new nonlinear structural stock market model which is a nonlinear deterministic process buffeted by dynamic
noise. An exogenous noise is introduced to the model with the assumption of IID normal innovations of the fundamental value
in order to investigate how noisy dynamics interacts with deterministic process. The market is composed of two typical trader
types: the rational fundamentalists and the boundedly rational traders governed by greed and fear. The interaction between
noise and deterministic element determines the evolution process of the system as key parameters are changed. The authors
find the model is able to generate time series that exhibit dynamical and statistical properties closely resembling those
of the S&P500 index, such as volatility clustering, fat tails (leptokurtosis), autocorrelation in square and absolute return,
larger amplitude, crashes and bubbles. The authors also investigate the nonlinear dependence structure in our data. The results
indicate that the GARCH-type model cannot completely account for all nonlinearity in our simulated market, which is thus consistent
with the results from real markets. It seems that the nonlinear structural model is more powerful to give a satisfied explanation
to market behavior than the traditional stochastic approach. 相似文献
213.
214.
This paper considers the optimal investment strategy for an insurer under the criterion of mean-variance. The risk process
is a compound Poisson process and the insurer can invest in a risk-free asset and multiple risky assets. This paper obtains
the optimal investment policy using the stochastic linear quadratic (LQ) control theory with no-shorting constraint. Then
the efficient strategy (optimal investment strategy) and efficient frontier are derived explicitly by a verification theorem
with the viscosity solution of Hamilton-Jacobi-Bellman (HJB) equation. 相似文献
215.
This paper considers a class of stochastic variational inequality problems. As proposed by Jiang and Xu (2008), by using the
so-called regularized gap function, the authors formulate the problems as constrained optimization problems and then propose
a sample average approximation method for solving the problems. Under some moderate conditions, the authors investigate the
limiting behavior of the optimal values and the optimal solutions of the approximation problems. Finally, some numerical results
are reported to show efficiency of the proposed method. 相似文献
216.
In this paper, the dynamic behaviors of a discrete epidemic model with a nonlinear incidence rate obtained by Euler method
are discussed, which can exhibit the periodic motions and chaotic behaviors under the suitable system parameter conditions.
Codimension-two bifurcations of the discrete epidemic model, associated with 1:1 strong resonance, 1:2 strong resonance, 1:3
strong resonance and 1:4 strong resonance, are analyzed by using the bifurcation theorem and the normal form method of maps.
Moreover, in order to eliminate the chaotic behavior of the discrete epidemic model, a tracking controller is designed such
that the disease disappears gradually. Finally, numerical simulations are obtained by the phase portraits, the maximum Lyapunov
exponents diagrams for two different varying parameters in 3-dimension space, the bifurcation diagrams, the computations of
Lyapunov exponents and the dynamic response. They not only illustrate the validity of the proposed results, but also display
the interesting and complex dynamical behaviors. 相似文献
217.
J. D. R. de Raadt 《Systemic Practice and Action Research》2011,24(6):509-521
Starting from the crisis in our communities—research has indicated it to be widely spread—the author explores the scientific
tradition preceding the rise of modernism in order to draw out a more humane way of thinking that may help our contemporary
societies. He discerns between two types of Renaissance humanism, one characterised by its cleverness, the other by its compassion
and desire to restore dignity to the lives of people struggling to escape the clutches of medievalism. The father of the latter
is Erasmus of Rotterdam and we follow the development of his conception of a social humanism as it branches out, through the
work of his successors, into every scientific discipline, both natural and human. These disciplines are united by an embracing
systemic idea of philosophy that unites the mind with the heart and which Erasmus called “Philosophia Christi”. We examine
the two main pillars upon which this philosophy is built, love for our neighbour and education as the only legitimate instrument
to change society, and the extraordinary impact it had on science and on communities living in the seventeenth century. We
contrast this with the idea of power, the chosen instrument of modernity to transform society, and trace some of its tragic
outcomes. We conclude by discussing the incorporation of an Erasmian type of social humanism into systems education and the
future development of such programmes. 相似文献
218.
利用摄动法对NLS方程和Zakharov方程作展开.应用Jacobi椭圆函数展开法求得了零级近似方程的准确解,并在Lamé方程和Lamé函数的基础上分别求得一级近似方程和二级近似方程的准确解.这样,就求得此类非线性演化方程的多级准确解. 相似文献
219.
CONG YanQing WU ZuCheng LI YuQiong 《科学通报(英文版)》2007,52(10):1432-1435
The most reactive hydroxyl radical (OH) was generated by electrochemical approach with safe water as the complete atom source. The direct evidence for OH formation was obtained by electron spin resonance method. The powerful OH electrochemically generated could effectively degrade organic pollutants and reduce the toxicity of wastewater. Electrochemical disinfection by OH was considerably efficient even without the aid of active chlorine. Bacteria inactivation of 99.99% was achieved for contact time of 30 min and current density of 5 mA·cm^-2, In comparison with active chlorine, OH is rather attractive as a promising environmentally benign disinfectant and opens a new route for microbial inactivation. 相似文献
220.
ZHANG Xuejun 《武汉大学学报:自然科学英文版》2007,12(1):5-8
T6 et al presented a bilinear-map-based traitor tracing scheme(TSZ scheme) with revocation, but it is a symmetric scheme because it does not provide non-repudiation. In this paper, an improved TSZ scheme was proposed by using oblivious polynomial evaluation (OPE) protocol and service parameters. Under the recondition of general sameness capabilities of both TSZ and improved TSZ scheme, the new scheme adds some advantages such as providing multi-service capability, user's non-repudiation and data provider's no-framing innocent users. Furthermore, it is also proved to be semantically secure under the decisional bilinear Diffie-Hellman (DBDH problem) assumption. 相似文献