全文获取类型
收费全文 | 6135篇 |
免费 | 614篇 |
国内免费 | 468篇 |
专业分类
化学 | 2037篇 |
晶体学 | 99篇 |
力学 | 739篇 |
综合类 | 39篇 |
数学 | 2394篇 |
物理学 | 1909篇 |
出版年
2024年 | 5篇 |
2023年 | 66篇 |
2022年 | 134篇 |
2021年 | 175篇 |
2020年 | 180篇 |
2019年 | 142篇 |
2018年 | 134篇 |
2017年 | 201篇 |
2016年 | 236篇 |
2015年 | 179篇 |
2014年 | 236篇 |
2013年 | 585篇 |
2012年 | 354篇 |
2011年 | 365篇 |
2010年 | 303篇 |
2009年 | 418篇 |
2008年 | 436篇 |
2007年 | 388篇 |
2006年 | 343篇 |
2005年 | 284篇 |
2004年 | 238篇 |
2003年 | 208篇 |
2002年 | 178篇 |
2001年 | 134篇 |
2000年 | 153篇 |
1999年 | 131篇 |
1998年 | 124篇 |
1997年 | 119篇 |
1996年 | 96篇 |
1995年 | 103篇 |
1994年 | 90篇 |
1993年 | 62篇 |
1992年 | 38篇 |
1991年 | 39篇 |
1990年 | 41篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 16篇 |
1986年 | 31篇 |
1985年 | 37篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1976年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有7217条查询结果,搜索用时 15 毫秒
61.
基于错误概率达到最小的原则,该文在罐子模型序贯试验中构造了一种渐近最优设计。在这种设计下,不仅能使病员以较多机会分配到较好的处理,而且能使估计量的统计效率在一定意义下达到最优。 相似文献
62.
This study investigates the robust output tracking problem for a class of uncertain linear systems. The uncertainties are assumed to be time invariant and to satisfy the matching conditions. According to the selected nominal parameters, an optimal solution with a prescribed degree of stability is determined. Then, an auxiliary input via the use of an adapting factor, connected to the nominal optimal control, is introduced to guarantee the robustness and prescribed degree of stability for the output tracking control of the uncertain linear systems. This method is very simple and effective and can reject bounded uncertainties imposed on the states. A maglev vehicle model example is given to show its effectiveness. 相似文献
63.
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
64.
JINJIANG YUAN 《运筹学学报》1998,(3)
1.IntroductionGraphsconsideredinthispaperarefiniteandsimple.FOragraphG,V(G)andE(G)denoteitssetofvenicesandedges,respectively.AbijectionwillbecalledalabellingofG.Letpbeapositiverealnumber.ForagivenlabellingTofagraphG,definethegndiscrepencya.(G,ac)ofTasTheobjectiveoftheminimum-p--sumproblemistofindalabelling7ofagraphGsuchthatac(G,T)isassmallaspossible.ThelabellingTminimizinga.(G,7)iscalledanoptimalHsumlabellingofG.Theminimumvalueiscalledtheminimum-psumofG.ItisshowninI31thattheminimum-… 相似文献
65.
66.
用方差定义的激光束横向尺寸,有着普适、简单和便于利用光学元件并行运算功能的特点.本文提出一种借助改变柱形容器内吸收液浓度来直接测量各种波长激光束横向尺寸的理论和方法. 相似文献
67.
A striking size dependence of the mean-square displacement of diffusing particles in the two-dimensional lattice gas of hard squares has been observed by Monte Carlo simulation. It is shown that the size effect is due to the formation of a stable cage structure in small lattices when the particle concentration is high. The formation of cages is governed by a new type of percolation problem related to bootstrap percolation. 相似文献
68.
N.P. Somasiri W.K. Toh X. Chen I.D. Robertson A.A. Rezazadeh 《International Journal of Infrared and Millimeter Waves》2002,23(12):1777-1785
This paper describes numerical modelling of a dual band multi-layered microstrip patch antenna operating at 35GHz on an in-house semi-insulating GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies will be compared to check the accuracy of the different numerical modelling techniques. 相似文献
69.
Smooth Solutions to Optimal Investment Models with Stochastic Volatilities and Portfolio Constraints
Pham 《Applied Mathematics and Optimization》2002,46(1):55-78
Abstract. This paper deals with an extension of Merton's optimal investment problem to a multidimensional model with stochastic volatility
and portfolio constraints. The classical dynamic programming approach leads to a characterization of the value function as
a viscosity solution of the highly nonlinear associated Bellman equation. A logarithmic transformation expresses the value
function in terms of the solution to a semilinear parabolic equation with quadratic growth on the derivative term. Using a
stochastic control representation and some approximations, we prove the existence of a smooth solution to this semilinear
equation. An optimal portfolio is shown to exist, and is expressed in terms of the classical solution to this semilinear equation.
This reduction is useful for studying numerical schemes for both the value function and the optimal portfolio. We illustrate
our results with several examples of stochastic volatility models popular in the financial literature. 相似文献
70.
本文用对数正态分布对物理显影中常用的Au、Ag及Ag_2s胶体催化剂的颗粒大小的实验分布进行了拟合。理论分布与实验分布的比较表明:本实验条件下制备的十二组胶体溶液其颗粒大小都服从了对数正态分布,并且不依赖于胶体的组成、大小及制备方法。因此,它们很可能遵从了同样的成核成长规律。 相似文献