全文获取类型
收费全文 | 1669篇 |
免费 | 227篇 |
国内免费 | 86篇 |
专业分类
化学 | 496篇 |
晶体学 | 7篇 |
力学 | 183篇 |
综合类 | 39篇 |
数学 | 751篇 |
物理学 | 506篇 |
出版年
2024年 | 1篇 |
2023年 | 28篇 |
2022年 | 43篇 |
2021年 | 93篇 |
2020年 | 91篇 |
2019年 | 66篇 |
2018年 | 54篇 |
2017年 | 93篇 |
2016年 | 85篇 |
2015年 | 53篇 |
2014年 | 119篇 |
2013年 | 138篇 |
2012年 | 83篇 |
2011年 | 94篇 |
2010年 | 82篇 |
2009年 | 88篇 |
2008年 | 108篇 |
2007年 | 91篇 |
2006年 | 74篇 |
2005年 | 66篇 |
2004年 | 59篇 |
2003年 | 45篇 |
2002年 | 39篇 |
2001年 | 44篇 |
2000年 | 34篇 |
1999年 | 31篇 |
1998年 | 28篇 |
1997年 | 27篇 |
1996年 | 24篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 1篇 |
排序方式: 共有1982条查询结果,搜索用时 31 毫秒
991.
This article considers the robust regulation problem for a class of constrained linear switched systems with bounded additive disturbances. The proposed solution extends the existing robust tube based model predictive control (RTBMPC) strategy for non-switched linear systems to switched systems. RTBMPC utilizes nominal model predictions, together with tightened sets constraints, to obtain a control policy that guarantees robust stabilization of the dynamic systems in presence of bounded uncertainties. In this work, similar to RTBMPC for non-switched systems, a disturbance rejection proportional controller is used to ensure that the closed loop trajectories of the switched linear system are bounded in a tube centered on the nominal system trajectories. To account for the uncertainty related to all sub-systems, the gain of this controller is chosen to simultaneously stabilize all switching dynamics. The switched system RTBMPC requires an on-line solution of a Mixed Integer Program (MIP), which is computationally expensive. To reduce the complexity of the MIP, a sub-optimal design with respect to the previous formulation is also proposed that uses the notion of a pre-terminal set in addition to the usual terminal set to ensure stability. The RTBMPC design with the pre-terminal set aids in determining the trade-off between the complexity of the control algorithm with the performance of the closed-loop system while ensuring robust stability. Simulation examples, including a Three-tank benchmark case study, are presented to illustrate features of the proposed MPC. 相似文献
992.
传统函数型回归模型变量选择方法,忽略了对稀疏函数型数据的讨论.提出了稀疏函数型数据情形下函数型回归模型的变量选择方法,基于条件期望对稀疏函数型自变量进行函数型主成分分析,并以估计的正交特征函数作为基函数对模型进行展开.这种方法可以有效解决对稀疏函数型变量的选择.作为实证分析,选取2002年到2011年全国34个气象观测站的年降水量,月度平均气温,光照时长,湿度,最高气温和最低气温数据,分别比较讨论了密集和稀疏情形下,原始样本和Bootstrap样本的函数型回归模型变量选择的结果,结果显示新方法具有较好的选择效果. 相似文献
993.
在传染病模型建模中,采用合理的非线性发生率所得到的动力学性态与实际更加接近,并且在实际的疾病防治过程中,由于受到医院各种医疗资源的影响,染病类的恢复率也会有一定的限制.建立了具有非线性发生率和恢复率函数的SIS传染病模型并分析了其动力学性态,分析这个模型,得到了无病平衡点和地方病平衡点的存在性和稳定性的条件,以及出现Hopf分支的条件.通过数值模拟,给出系统随两个分支参数变化的分支曲线图及系统的相图. 相似文献
994.
无证书密码体制结合了基于身份密码体制和传统公钥密码体制的优点,受到了密码和信息安全研究者的极大关注.对梁景玲等提出的消息可恢复的无证书签名方案和侯红霞等提出的无证书短签名方案进行安全性分析,发现两个方案都不能抵抗公钥替换攻击.通过修改签名者密钥生成算法,增加对用户公钥的有效性验证,提高了梁等方案的安全性.通过在签名阶段将用户公钥绑定进HaSh函数,弥补了侯等方案的安全缺陷. 相似文献
995.
相位恢复在多个不同领域均被提出,如量子力学、光学成像等.相位恢复即具有多种应用背景,亦具有丰富的数学内涵,因而近期该问题吸引了多个不同领域专家的关注,如计算数学、数据科学、最优化、代数几何等.本文将主要介绍相位恢复中的理论基础问题,特别是最少观测次数问题,并介绍求解相位恢复的模型性能,以及求解算法等.本文也介绍了一些当前相位恢复中研究的热点方向. 相似文献
996.
Othman Cherkaoui Dekkaki Noha El Khattabi Nadia Raissi 《Mathematical Methods in the Applied Sciences》2022,45(1):468-482
The ecological consciousness has driven developed societies to explore alternatives to the growing need for energy and the consequent increase in waste production. The adjustment towards the waste recovery and their transformation into energy, by various processes, is then necessary. However, so far, the domain has not benefited much from a mathematical modeling approach. The main contribution of this work consists of building a bioeconomic model describing the problem of a potential investor who aims to maximize his net profit generated by selling the produced energy from the household waste transformation. We first study the evolution of a waste stock, the energy quantity produced, and the capital dedicated to the transformation process in a giving landfill and recovery center. Then we insert decision variables to this dynamic which are both the investment and the part of waste to be treated. This leads to an optimal control problem which we solve by the deductive method. The resulted solution is then illustrated by some numerical simulations. This investment policy would be to support the decision makers to go towards investment in this activity. 相似文献
997.
998.
999.
Nanocomposite hydrogels were prepared by cross-linking of aqueous solutions of sulfonated polyacrylamide/sodium montmorillonite with chromium triacetate. The gelation process and effects of clay content and ionic strength on swelling behavior were investigated. X-ray diffraction patterns indicated that exfoliated type of microstructure was formed. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the nanocomposite (NC) gels decreased with increasing clay content up to 1000 ppm, but it increased by further increase of Na+-montmorillonite concentration. It was also found that with increasing the clay content, the viscous energy dissipation properties of the nanocomposite gels increased. The swelling ratio of nanocomposite gels in tap water decreased as the concentration of the clay increased. However, nanocomposite gels showed higher resistance against syneresis in electrolyte solutions as compared with unfilled gels. Therefore, they are potentially good candidates for enhanced oil recovery applications. 相似文献
1000.
In 1963 Smolyak introduced an approach to overcome the exponential scaling with respect to the number of variables of the direct product size [S. A. Smolyak Soviet Mathematics Doklady, 4, 240 (1963)]. The main idea is to replace a single large direct product by a sum of selected small direct products. It was first used in quantum dynamics in 2009 by Avila and Carrington [G. Avila and T. Carrington, J. Chem. Phys., 131, 174103 (2009)]. Since then, several calculations have been published by Avila and Carrington and by other groups. In the present study, and to push the limit to larger and more complex systems, this scheme is combined with the use of an on-the-fly calculation of the kinetic energy operator and a Block-Davidson procedure to obtain eigenstates in our home-made Fortran codes, ElVibRot and Tnum-Tana. This was applied to compute the tunneling splitting of malonaldehyde in full dimensionality (21D) using the potential of Mizukami et al. [W. Mizukami, S. Habershon, and D.P. Tew, J. Chem. Phys. 141, 1443–10 (2014)]. Our tunneling splitting calculations, 21.7±0.3 cm−1 and 2.9±0.1 cm−1, show excellent agreement with the experimental values, 21.6 cm−1 and 2.9 cm−1 for the normal isotopologue and the mono-deuterated one, respectively. 相似文献