全文获取类型
收费全文 | 2795篇 |
免费 | 257篇 |
国内免费 | 112篇 |
专业分类
化学 | 94篇 |
晶体学 | 1篇 |
力学 | 774篇 |
综合类 | 23篇 |
数学 | 1619篇 |
物理学 | 653篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 35篇 |
2021年 | 43篇 |
2020年 | 63篇 |
2019年 | 61篇 |
2018年 | 53篇 |
2017年 | 87篇 |
2016年 | 112篇 |
2015年 | 89篇 |
2014年 | 110篇 |
2013年 | 206篇 |
2012年 | 145篇 |
2011年 | 153篇 |
2010年 | 134篇 |
2009年 | 158篇 |
2008年 | 175篇 |
2007年 | 166篇 |
2006年 | 167篇 |
2005年 | 165篇 |
2004年 | 120篇 |
2003年 | 103篇 |
2002年 | 106篇 |
2001年 | 89篇 |
2000年 | 75篇 |
1999年 | 65篇 |
1998年 | 58篇 |
1997年 | 59篇 |
1996年 | 43篇 |
1995年 | 28篇 |
1994年 | 23篇 |
1993年 | 33篇 |
1992年 | 32篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1973年 | 3篇 |
排序方式: 共有3164条查询结果,搜索用时 15 毫秒
31.
储蓄——收入模型的转变点分析 总被引:1,自引:0,他引:1
本文利用线性回归模型分析改革开放以来我国居民储蓄与收入的关系 ,并引入转变点理论研究二者关系发生结构性转变的问题 ,最后讨论了影响储蓄增长的几个因素 .实证研究表明 ,90年代以来 ,随着经济环境的巨大变化 ,居民储蓄与收入的关系有所改变 ,储蓄的增长速度已经超过了收入的增长速度 .我们的研究还表明 ,当用时间跨度较大的样本时 ,结论虽符合长期趋势 ,但考虑到其可信度及从时效性角度看对近期宏观政策的现实指导意义 ,常规的回归分析应该加入转变点检验 ,以防忽略系统结构性转变 . 相似文献
32.
An adaptive pruning algorithm for the discrete L-curve criterion 总被引:1,自引:0,他引:1
Per Christian Hansen Toke Koldborg Jensen Giuseppe Rodriguez 《Journal of Computational and Applied Mathematics》2007
We describe a robust and adaptive implementation of the L-curve criterion. The algorithm locates the corner of a discrete L-curve which is a log–log plot of corresponding residual norms and solution norms of regularized solutions from a method with a discrete regularization parameter (such as truncated SVD or regularizing CG iterations). Our algorithm needs no predefined parameters, and in order to capture the global features of the curve in an adaptive fashion, we use a sequence of pruned L-curves that correspond to considering the curves at different scales. We compare our new algorithm to existing algorithms and demonstrate its robustness by numerical examples. 相似文献
33.
Dave Auckly 《Proceedings of the American Mathematical Society》2005,133(3):885-889
Vidussi was the first to construct knotted Lagrangian tori in simply connected four-dimensional manifolds. Fintushel and Stern introduced a second way to detect such knotting. This note demonstrates that similar examples may be distinguished by the fundamental group of the exterior.
34.
A Kind of direct methods is presented for the solution of optimal control problems with state constraints.These methods are sequential quadratic programming methods.At every iteration a quadratic programming which is obtained by quadratic approximation to Lagrangian function and Linear approximations to constraints is solved to get a search direction for a merit function.The merit function is formulated by augmenting the Lagrangian funetion with a penalty term.A line search is carried out along the search direction to determine a step length such that the merit function is decreased.The methods presented in this paper include continuous sequential quadratic programming methods and discreate sequential quadrade programming methods. 相似文献
35.
In this paper, numerical simulation of three-dimensional supersonic flow in a duct is presented. The flow field in the duct is complex and can find its applications in the inlet of air-breathing engines. A unique streamwise marching Lagrangian method is employed for solving the steady Euler equations. The method was first initiated by Loh and Hui (1990) for 2-D steady supersonic flow computations and then extended to 3-D computation by the present authors Loh and Liou (1992). The new scheme is shown to be capable of accurately resolving complicated shock or contact discontinuities and their interactions. In all the computations, a free stream of Mach numberM=4 is considered.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
36.
O. A. Brezhneva Yu. G. Evtushenko A. A. Tret’yakov 《Computational Mathematics and Mathematical Physics》2006,46(11):1896-1909
The theory of p-regularity is applied to optimization problems and to singular ordinary differential equations (ODE). The special variant of the method of the modified Lagrangian function proposed by Yu.G. Evtushenko for constrained optimization problems with inequality constraints is justified on the basis of the 2-factor transformation. An implicit function theorem is given for the singular case. This theorem is used to show the existence of solutions to a boundary value problem for a nonlinear differential equation in the resonance case. New numerical methods are proposed including the p-factor method for solving ODEs with a small parameter. 相似文献
37.
In this work we display a numerical comparison, under statistical and computational point of view, between semi-analytical Eulerian and Lagrangian dispersion models to simulate the ground-level concentration values of a passive pollutant released from a low height source. The Eulerian approach is based on the solution of the advection–diffusion equation by the Laplace transform technique. The Lagrangian approach is based on solution of the Langevin equation through the Picard’s Iterative Method. Turbulence inputs are calculated according to a parameterization capable of generating continuous values in all stability conditions and in all heights of the Planetary Boundary Layer (PBL). Numerical simulations and comparisons show a good agreement between predicted and observed concentrations values. The comparison reveals the main advantages and disadvantages between the models. 相似文献
38.
In this paper, we propose the treatment of complex reservoir operation problems via our newly developed tool of fuzzy criterion
decision processes. This novel approach has been shown to be a more flexible and useful analysis tool especially when it is
desirable to incorporate an expert’s knowledge into the decision models. Additionally, it has been demonstrated that this
form of decision models will usually result in an optimal solution, which guarantees the highest satisfactory degree. We provide
a practical exemplification procedure for the models presented as well as an application example. 相似文献
39.
Lagrangian relaxation is commonly used in combinatorial optimization to generate lower bounds for a minimization problem.
We study a modified Lagrangian relaxation which generates an optimal integer solution. We call it semi-Lagrangian relaxation
and illustrate its practical value by solving large-scale instances of the p-median problem.
This work was partially supported by the Fonds National Suisse de la Recherche Scientifique, grant 12-57093.99 and the Spanish
government, MCYT subsidy dpi2002-03330. 相似文献
40.