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   3045篇
  免费   292篇
  国内免费   133篇
化学   148篇
晶体学   1篇
力学   765篇
综合类   42篇
数学   1940篇
物理学   574篇
  2024年   1篇
  2023年   44篇
  2022年   45篇
  2021年   70篇
  2020年   121篇
  2019年   92篇
  2018年   77篇
  2017年   93篇
  2016年   91篇
  2015年   84篇
  2014年   124篇
  2013年   229篇
  2012年   135篇
  2011年   191篇
  2010年   155篇
  2009年   204篇
  2008年   189篇
  2007年   195篇
  2006年   180篇
  2005年   171篇
  2004年   147篇
  2003年   147篇
  2002年   89篇
  2001年   89篇
  2000年   83篇
  1999年   66篇
  1998年   70篇
  1997年   45篇
  1996年   48篇
  1995年   21篇
  1994年   41篇
  1993年   19篇
  1992年   25篇
  1991年   24篇
  1990年   12篇
  1989年   14篇
  1988年   4篇
  1987年   8篇
  1986年   3篇
  1985年   7篇
  1984年   3篇
  1983年   3篇
  1982年   1篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1976年   2篇
  1957年   1篇
  1936年   1篇
排序方式: 共有3470条查询结果,搜索用时 19 毫秒
1.
针对三维非稳态对流扩散反应方程,构造了一种高精度紧致有限差分格式,对空间的离散采用四阶紧致差分方法,对时间的离散采用Taylor级数展开和余项修正技术,所提格式在时间上的精度为二阶、在空间上的精度为四阶。利用Fourier稳定性分析法证明了该格式是无条件稳定的。最后给出数值算例验证了理论结果。  相似文献   
2.
柳键  万谧宇  周辉  江玮璠 《运筹与管理》2022,31(12):227-233
考虑自有平台和第三方平台两种分时租赁方式,将汽车质量划分为性能质量和环境质量,构建销售模式、纯分时租赁模式和混合模式下的产品线策略模型,研究制造商产品线策略与商业模式之间的相互作用。研究发现,同品牌产品间竞争和合并效应是分时租赁模式影响产品线策略的两个关键因素。同品牌产品间竞争的加剧和合并效应的增大都会激励企业选择性能更好的车型而忽略其环境表现。分时租赁模式能同时改进利润与产品环境表现,但存在条件:当消费者价格敏感性较低时,使用成本高且合并效应小是实现同时改进的条件;当消费者价格敏感较高时,使用成本低且合并效应小则是同时改进的条件。  相似文献   
3.
An independent set game is a cooperative game dealing with profit sharing in the maximum independent set problem. A population monotonic allocation scheme is a rule specifying how to share the profit of each coalition among its participants such that every participant is better off when the coalition expands. In this paper, we provide a necessary and sufficient characterization for independent set games admitting population monotonic allocation schemes. Moreover, our characterization can be verified efficiently.  相似文献   
4.
In this paper, we propose an effective spectral method based on dimension reduction scheme for fourth order problems in polar geometric domains. First, the original problem is decomposed into a series of one‐dimensional fourth order problems by polar coordinate transformation and the orthogonal properties of Fourier basis function. Then the weak form and the corresponding discrete scheme of each one‐dimensional fourth order problem are derived by introducing polar conditions and appropriate weighted Sobolev spaces. In addition, we define the projection operators in the weighted Sobolev space and give its approximation properties, and further prove the error estimation of each one‐dimensional fourth order problem. Finally, we provide some numerical examples, and the numerical results show the effectiveness of our algorithm and the correctness of the theoretical results.  相似文献   
5.
We solve a combinatorial question concerning eigenvalues of the universal intertwining endomorphism of a subset representation.  相似文献   
6.
In this paper, we propose an efficient numerical method for a distributed order fractional subdiffusion problem using nonpolynomial spline approach. The solvability, stability, and convergence of the scheme are established rigorously, and it is shown that the spatial convergence order improves some previous work done. Simulation is then conducted to verify the accuracy of the proposed scheme as well as to compare with earlier work.  相似文献   
7.
研究了含分数阶Caputo导数的非线性振动系统响应的数值计算方法。首先,由Caputo分数阶导数算子的叠加关系,得到含分数阶导数项非线性振动系统状态方程的标准形式。其次,基于Caputo导数与Riemann-Liouville导数和Grunwald-Letnikov导数间的关系,推导计算了Caputo导数的一般数值迭代格式。本文方法不要求状态方程中各分数阶导数阶数相等,弱化了已有算法中对分数阶导数阶数的限制,并可推广到多自由度的情形。随后,选择若干有解析解的算例验证了本文方法的正确性。最后,以多吸引子共存的分数阶Duffing振子系统为例,比较Caputo和GL两种算法所得结果,说明了用GL算法求解存在的问题。  相似文献   
8.
Erosion and sediments transport processes have a great impact on industrial structures and on water quality. Despite its limitations, the Saint‐Venant‐Exner system is still (and for sure for some years) widely used in industrial codes to model the bedload sediment transport. In practice, its numerical resolution is mostly handled by a splitting technique that allows a weak coupling between hydraulic and morphodynamic distinct softwares but may suffer from important stability issues. In recent works, many authors proposed alternative methods based on a strong coupling that cure this problem but are not so trivial to implement in an industrial context. In this work, we then pursue 2 objectives. First, we propose a very simple scheme based on an approximate Riemann solver, respecting the strong coupling framework, and we demonstrate its stability and accuracy through a number of numerical test cases. However, second, we reinterpret our scheme as a splitting technique and we extend the purpose to propose what should be the minimal coupling that ensures the stability of the global numerical process in industrial codes, at least, when dealing with collocated finite volume method. The resulting splitting method is, up to our knowledge, the only one for which stability properties are fully demonstrated.  相似文献   
9.
A new supplier price break and discount scheme taking into account order frequency and lead time is introduced and incorporated into an integrated inventory planning model for a serial supply chain that minimizes the overall incurred cost including procurement, inventory holding, production, and transportation. A mixed-integer linear programming (MILP) formulation is presented addressing this multi-period, multi-supplier, and multi-stage problem with predetermined time-varying demand for the case of a single product. Then, the length of the time period is considered as a variable. A new MILP formulation is derived when each period of the model is split into multiple sub-periods, and under certain conditions, it is proved that the optimal solution and objective value of the original model form a feasible solution and an upper bound for the derived model. In a numerical example, three scenarios of the derived model are solved where the number of sub-period is set to 2, 3, and 4. The results further show the decrease of the optimal objective value as the length of the time period is shortened. Sufficient evidence demonstrates that the length of the time period has a significant influence on supplier selection, lot sizing allocation, and inventory planning decisions. This poses the necessity of the selection of appropriate length of a time period, considering the trade-off between model complexity and cost savings.  相似文献   
10.
In this article, a compact finite difference method is developed for the periodic initial value problem of the N‐coupled nonlinear Klein–Gordon equations. The present scheme is proved to preserve the total energy in the discrete sense. Due to the difficulty in obtaining the priori estimate from the discrete energy conservation law, the cut‐off function technique is employed to prove the convergence, which shows the new scheme possesses second order accuracy in time and fourth order accuracy in space, respectively. Additionally, several numerical results are reported to confirm our theoretical analysis. Lastly, we apply the reliable method to simulate and study the collisions of solitary waves numerically.  相似文献   
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