全文获取类型
收费全文 | 98283篇 |
免费 | 4486篇 |
国内免费 | 3556篇 |
专业分类
化学 | 39217篇 |
晶体学 | 1072篇 |
力学 | 7961篇 |
综合类 | 302篇 |
数学 | 34286篇 |
物理学 | 23487篇 |
出版年
2024年 | 55篇 |
2023年 | 386篇 |
2022年 | 749篇 |
2021年 | 760篇 |
2020年 | 910篇 |
2019年 | 894篇 |
2018年 | 11045篇 |
2017年 | 10847篇 |
2016年 | 6988篇 |
2015年 | 1913篇 |
2014年 | 1603篇 |
2013年 | 1926篇 |
2012年 | 5678篇 |
2011年 | 12415篇 |
2010年 | 7033篇 |
2009年 | 7445篇 |
2008年 | 8094篇 |
2007年 | 10032篇 |
2006年 | 1503篇 |
2005年 | 2363篇 |
2004年 | 2407篇 |
2003年 | 2635篇 |
2002年 | 1697篇 |
2001年 | 840篇 |
2000年 | 754篇 |
1999年 | 569篇 |
1998年 | 516篇 |
1997年 | 474篇 |
1996年 | 481篇 |
1995年 | 355篇 |
1994年 | 298篇 |
1993年 | 253篇 |
1992年 | 165篇 |
1991年 | 191篇 |
1990年 | 159篇 |
1989年 | 134篇 |
1988年 | 133篇 |
1987年 | 121篇 |
1986年 | 103篇 |
1985年 | 79篇 |
1984年 | 71篇 |
1983年 | 64篇 |
1982年 | 68篇 |
1981年 | 56篇 |
1980年 | 62篇 |
1979年 | 50篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
Marvin D. Troutt M. Diane Pettypool 《The Journal of the Operational Research Society》1989,40(6):571-579
We first demonstrate that mixed strategies are relevant in decision analysis for a maximin decision-maker quite apart from any game-theory considerations. This rectifies the apparent misconception that results from MS/OR textbooks which discuss mixed strategies only in the game-theory setting. Next we show an example of an implementable mixed strategy, by which we mean a mixed decision strategy which does not require randomization for its implementation. This application is to portfolio construction. 相似文献
862.
Nicholas A. ZainoJr. John D'Errico 《The Journal of the Operational Research Society》1989,40(4):379-388
In decision and risk analysis, it is common to use discrete probability distributions to approximate uncertain events with continuous outcomes. This paper discusses how these approximations may be selected. A class of approximations based on a modification to Taguchi's work on tolerance analysis is shown to be optimal under assumptions of independent uncertainties with normally distributed outcomes. The approximation procedure is shown to be robust in many other situations and is extremely easy to use in practice. We also show how the approximation may be integrated into the process of subjective probability estimation by a ‘subject-matter expert’. 相似文献
863.
Karen Aardal Örjan Jonsson Henrik Jönsson 《The Journal of the Operational Research Society》1989,40(1):65-73
In a practical situation it is often difficult to determine the value of the shortage costs for use in in ventory-control systems. However, in cost-minimization problems including service-level constraints, shortage costs are implicitly prevailing. With the purpose of exploring these relations, a continuous review (Q, r) stock-control system is considered, where the order points and lot sizes are computed simultaneously. Instead of explicitly expressing the shortage cost in the objective function, it is taken into consideration through a service-level constraint. The shadow price of this constraint can in some sense be interpreted as the shortage cost corresponding to the requested service level. By changing the value of the service level, interesting relations between shortage costs and service levels can be viewed for different sets of other inventory parameters. In order to investigate the sensitivity for probabilistic variations in the input data, two different probability distributions are used to describe the lead-time demand. 相似文献
864.
865.
866.
867.
868.
Fabrication of tunable colloid crystals from amine-terminated polyamidoamine dendrimers 总被引:1,自引:0,他引:1
Mingzhu Li Jingxia Wang Lin Feng Bingbing Wang Xinru Jia Lei Jiang Yanlin Song Daoben Zhu 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,290(1-3):233-238
A pH-responsive colloidal crystal was assembled using core-shell composite spheres, poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) spheres covered by generation 4 amine-terminated polyamidoamine dendrimers. The light reflection of the colloidal crystal film can be tuned at different pH due to different protonation level of the dendrimers. The method shows a facile way to fabricate diffraction-based chemical and biological sensors by exploiting the effect of photonic crystal cooperated with tunable nanoparticles. 相似文献
869.
870.
合成了香兰素缩赖氨酸希夫碱配体(HL)和15种香兰素缩赖氨酸希夫碱的稀土配合物REL(NO3)2.3H2O(RE=Y,La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu),并通过元素分析、摩尔电导、热重分析、红外光谱、紫外光谱、核磁共振方法对配合物的组成和结构进行了表征。采用紫外光谱和荧光光谱方法初步研究了Nd,Tb,Yb,Lu这4种希夫碱配合物与DNA的相互作用,实验结果显示,随着DNA的加入,配合物在280 nm处的紫外吸收峰不断增强,同时配合物在418 nm左右的荧光发射峰随DNA浓度的增大均逐渐减小,说明配合物和DNA是以静电模式结合。 相似文献