全文获取类型
收费全文 | 1951篇 |
免费 | 47篇 |
国内免费 | 81篇 |
专业分类
化学 | 378篇 |
晶体学 | 3篇 |
力学 | 69篇 |
综合类 | 3篇 |
数学 | 1322篇 |
物理学 | 304篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 18篇 |
2021年 | 20篇 |
2020年 | 42篇 |
2019年 | 49篇 |
2018年 | 31篇 |
2017年 | 58篇 |
2016年 | 60篇 |
2015年 | 37篇 |
2014年 | 123篇 |
2013年 | 166篇 |
2012年 | 166篇 |
2011年 | 120篇 |
2010年 | 94篇 |
2009年 | 133篇 |
2008年 | 125篇 |
2007年 | 117篇 |
2006年 | 82篇 |
2005年 | 58篇 |
2004年 | 75篇 |
2003年 | 54篇 |
2002年 | 50篇 |
2001年 | 44篇 |
2000年 | 24篇 |
1999年 | 40篇 |
1998年 | 28篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 25篇 |
1994年 | 25篇 |
1993年 | 20篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1974年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有2079条查询结果,搜索用时 31 毫秒
991.
Sílvia C. Hirata 《Physics letters. A》2010,374(26):2661-4613
By using the mathematical formalism of absolute and convective instabilities we study the nature of unstable three-dimensional disturbances of viscoelastic flow convection in a porous medium with horizontal through-flow and vertical temperature gradient. Temporal stability analysis reveals that among three-dimensional (3D) modes the pure down-stream transverse rolls are favored for the onset of convection. In addition, by considering a spatiotemporal stability approach we found that all unstable 3D modes are convectively unstable except the transverse rolls which may experience a transition to absolute instability. The combined influence of through-flow and elastic parameters on the absolute instability threshold, wave number and frequency is then determined, and results are compared to those of a Newtonian fluid. 相似文献
992.
993.
We present a high order multivariate approximation scheme for scattered data sets. Each data point is represented as a Taylor series, and the high order derivatives in the Taylor series are treated as random variables. The approximation coefficients are then chosen to minimize an objective function at each point by solving an equality constrained least squares. The approximation is an interpolation when the data points are given as exact, or a nonlinear regression function when nonzero measurement errors are associated with the data points. Using this formulation, the gradient information on each data point can be used to significantly reduce the approximation error. All parameters of the approximation scheme can be computed automatically from the data points. An uncertainty bound of the approximation function is also produced by the scheme. Numerical experiments demonstrate that although this method is more computationally intensive than traditional methods, it produces more accurate approximation functions. 相似文献
994.
995.
在函数单向S-粗集生成的一元F-粗积分的基础上,结合元素迁移的概率特征,提出了依概率p-粗积分的概念,给出了依概率p-粗积分上下关系链定理和依概率p-粗积分关系链定理,讨论了依概率p-粗积分和F-粗积分及牛顿积分间的关系. 相似文献
996.
Andreas Tsanakas 《Insurance: Mathematics and Economics》2008,42(2):520-528
A distortion-type risk measure is constructed, which evaluates the risk of any uncertain position in the context of a portfolio that contains that position and a fixed background risk. The risk measure can also be used to assess the performance of individual risks within a portfolio, allowing for the portfolio’s re-balancing, an area where standard capital allocation methods fail. It is shown that the properties of the risk measure depart from those of coherent distortion measures. In particular, it is shown that the presence of background risk makes risk measurement sensitive to the scale and aggregation of risk. The case of risks following elliptical distributions is examined in more detail and precise characterisations of the risk measure’s aggregation properties are obtained. 相似文献
997.
Opportunities to make sequential decisions and adjust activities as a season progresses and more information becomes available characterise the farm management process. In this paper, we present a discrete stochastic two-stage utility-efficient programming model of organic dairy farms, which includes risk aversion in the decision maker’s objective function as well as both embedded risk (stochastic programming with recourse) and non-embedded risk (stochastic programming without recourse). Historical farm accountancy data and subjective judgements were combined to assess the nature of the uncertainty that affects the possible consequences of the decisions. The programming model was used within a stochastic dominance framework to examine optimal strategies in organic dairy systems in Norway. 相似文献
998.
We consider a class of rearrangement invariant Banach Function Spaces recently appeared in a paper by the same authors, containing at the same time some Lorentz spaces Γ(ν), classical Lebesgue spaces and small Lebesgue spaces. We discuss the main properties coming directly from the norm, and, for certain values of the involved parameters, we prove some estimates of the norm of the associate space. 相似文献
999.
1000.
Enlistment at the earliest viable age maximizes the country’s wartime army size and thereby the country’s attack-deterrence capacity. Injuries and death generate a loss of quantity and quality of life that reduces the benefit from early-age enlistment. The benefit from any age of recruitment is also affected by the rise and decline of the individual’s military performance and civilian productivity and by the changes in the individual’s adjustment costs over his lifecycle. The simulations of an optimization model incorporating these cost and benefit elements suggest that if the intensity of the rise and decline of the individual’s military performance is sufficiently larger than the intensity of the rise and decline of his civilian productivity, there exists an interior optimal enlistment age that is greater than the commonly practiced 18. In such a case, most of the simulation results are closely scattered around 21 despite large parameter changes. 相似文献