全文获取类型
收费全文 | 584篇 |
免费 | 81篇 |
国内免费 | 13篇 |
专业分类
化学 | 73篇 |
晶体学 | 1篇 |
力学 | 13篇 |
综合类 | 20篇 |
数学 | 507篇 |
物理学 | 64篇 |
出版年
2023年 | 2篇 |
2022年 | 38篇 |
2021年 | 29篇 |
2020年 | 16篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 31篇 |
2013年 | 36篇 |
2012年 | 36篇 |
2011年 | 39篇 |
2010年 | 33篇 |
2009年 | 38篇 |
2008年 | 40篇 |
2007年 | 49篇 |
2006年 | 33篇 |
2005年 | 31篇 |
2004年 | 29篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
排序方式: 共有678条查询结果,搜索用时 31 毫秒
71.
Finding the critical factor and possible “Newton’s laws” in financial markets has been an important issue. However, with the development of information and communication technologies, financial models are becoming more realistic but complex, contradicting the objective law “Greatest truths are the simplest.” Therefore, this paper presents an evolutionary model independent of micro features and attempts to discover the most critical factor. In the model, information is the only critical factor, and stock price is the emergence of collective behavior. The statistical properties of the model are significantly similar to the real market. It also explains the correlations of stocks within an industry, which provides a new idea for studying critical factors and core structures in the financial markets. 相似文献
72.
73.
Abstract We analyze the efficiency of the international management of the Bay of Biscay anchovy. While a sharing agreement between France and Spain has been in place since 1992, the fish stock collapsed in 2005 and the fishery closed from 2005 to spring 2010. We consider differences in production technologies between both countries and calibrate our model using data from 1987 to 2009. Our results suggest two sources of rent dissipation under the existing sharing agreement: inefficient quota allocation and production inefficiencies due to inflexible national regulations. We discuss several alternatives to improve management. 相似文献
74.
We constructed an agent-based stock market model which concisely describe investors? heterogeneity and adaptability by introducing price sensitivity and feedback time. Under different parameters, the peak and fat-tail property of return distribution is produced and the obtained statistic values coincide with empirical results: the center peak exponents range from ?0.787 to ?0.661, and the tail exponents range from ?4.29 to ?2.37. Besides, long-term correlation in volatility is examined by DFA1 method, and the obtained exponent α is 0.803, which also coincides with the exponent of 0.78 found in real market. 相似文献
75.
WUXIONGWEI XUWENSHENG CHENSHUPING 《高校应用数学学报(英文版)》1998,13(1):68-76
In this paper, optimal investment and consumption decisions for an optimal choiceproblem in infinite borizon are considered, for an investor who has available a bank account anda stock whose price is a log normal diffusion. The bank pays at an interest rate r for any de-posit, and takes at a larger rate / for any loan. As in the paper of Xu Wensheng and ChenShuping in JAMS(B), where an analogous problem in finite horizon is studied, optimal strategies are obtained via Hamilton-Jacobi-Bellman (ladE) equation which is derived from dynamic c1-programming principle. For the specific HARA case, i.e. U(t,c)=e^-βtc^1-R/1-R, this paper getsthe optimal consumption and optimal investment in the form of c^‘1 =β -^-g/Rwi and π^‘1= b -- γ / Rσ^2wr, with γ1,=max{γ,min{γ‘,b--Rσ^2‘} },^-g=(1--R)[γ (b-γ)^2/2Rσ^2]. This result coincides with the classical one under condition γ‘ ≡γ. 相似文献
76.
Nicholas J. Cavenagh Catherine Greenhill Ian M. Wanless 《Random Structures and Algorithms》2008,33(3):286-309
Let L be chosen uniformly at random from among the latin squares of order n ≥ 4 and let r,s be arbitrary distinct rows of L. We study the distribution of σr,s, the permutation of the symbols of L which maps r to s. We show that for any constant c > 0, the following events hold with probability 1 ‐ o(1) as n → ∞: (i) σr,s has more than (log n)1?c cycles, (ii) σr,s has fewer than 9 cycles, (iii) L has fewer than n5/2 intercalates (latin subsquares of order 2). We also show that the probability that σr,s is an even permutation lies in an interval and the probability that it has a single cycle lies in [2n‐2,2n‐2/3]. Indeed, we show that almost all derangements have similar probability (within a factor of n3/2) of occurring as σr,s as they do if chosen uniformly at random from among all derangements of {1,2,…,n}. We conjecture that σr,s shares the asymptotic distribution of a random derangement. Finally, we give computational data on the cycle structure of latin squares of orders n ≤ 11. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2008 相似文献
77.
The next order conditions across a three-dimensional curved shock near stagnationpoint have been established,including the effects of heat conduction,viscosity and the shockstructure.These shock conditions involve the local shock curvature in addition to its localinclination.Explicit results have been obtained for the correctional formulations in themass flux across the shock,the stagnation enthalpy,the tangential component of velocityand the normal component of momentum flux. 相似文献
78.
计算股市的基本方程、理论和原理(Ⅰ)——基本方程 总被引:3,自引:0,他引:3
本文采用网络模型和类似于固体力学的方法论来研究计算股市。建立四个基本的联立方程,即:利率-流通量方程;股票买入、卖出方程;股价变化率方程;以及利率、股价及股价变化率方程。文中着重讨论利率-流通量方程的解及其简单应用,包括时间离散化时股市网络用Banach收缩映射定理证明最终趋向平衡状态,以及银行减息引起资金流动按指数型式衰减等。 相似文献
79.
Computational study of a column generation algorithm for bin packing and cutting stock problems 总被引:4,自引:0,他引:4
François Vanderbeck 《Mathematical Programming》1999,86(3):565-594
This paper reports on our attempt to design an efficient exact algorithm based on column generation for the cutting stock
problem. The main focus of the research is to study the extend to which standard branch-and-bound enhancement features such
as variable fixing, the tightening of the formulation with cutting planes, early branching, and rounding heuristics can be
usefully incorporated in a branch-and-price algorithm. We review and compare lower bounds for the cutting stock problem. We
propose a pseudo-polynomial heuristic. We discuss the implementation of the important features of the integer programming
column generation algorithm and, in particular, the implementation of the branching scheme. Our computational results demonstrate
the efficiency of the resulting algorithm for various classes of bin packing and cutting stock problems.
Received October 18, 1996 / Revised version received May 14, 1998?Published online July 19, 1999 相似文献
80.
乐碧宏 《宁波大学学报(理工版)》2005,18(1):122-125
证券风险的计量准确与否,是证券组合理论能否有效运用的前提,在现有研究成果的基础上,结合我国证券市场的特点,选取“流通市值”作为影响我国证券风险的第二个因素,建立了证券风险计量模型,并使用统计软件对模型的适用性进行了检验. 相似文献