全文获取类型
收费全文 | 864篇 |
免费 | 111篇 |
国内免费 | 59篇 |
专业分类
化学 | 130篇 |
晶体学 | 15篇 |
力学 | 62篇 |
综合类 | 25篇 |
数学 | 381篇 |
物理学 | 421篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 25篇 |
2020年 | 24篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 24篇 |
2016年 | 18篇 |
2015年 | 13篇 |
2014年 | 42篇 |
2013年 | 67篇 |
2012年 | 30篇 |
2011年 | 42篇 |
2010年 | 44篇 |
2009年 | 65篇 |
2008年 | 56篇 |
2007年 | 66篇 |
2006年 | 56篇 |
2005年 | 47篇 |
2004年 | 37篇 |
2003年 | 44篇 |
2002年 | 40篇 |
2001年 | 45篇 |
2000年 | 24篇 |
1999年 | 33篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1034条查询结果,搜索用时 31 毫秒
991.
提出了基于稳定性准则的半周期延迟-非线性反馈控制混沌的方法,即SC(stability criterion)半周期延迟非线性反馈控制法.通过对混沌系统的适当分离,得到一个特殊的非线性函数,并利用混沌输出信号与其半周期延迟信号的非线性函数之和,构造了连续反馈输入干扰.该方法继承了延迟反馈控制方法及稳定性准则控制方法的优点,实现了有效的自控制过程;并克服了延迟反馈方法的限制,能将嵌入混沌吸引子中的自对称直接不稳周期轨稳定.控制过程可随时开始,具有简便、灵活性.数值模拟结果显示了SC半周期延迟-非线性反馈方法控制的有效性.
关键词:
稳定性准则
混沌控制
半周期延迟
非线性反馈 相似文献
992.
I. Rahimov 《随机分析与应用》2013,31(5):925-940
Abstract We consider a model of age-dependent branching stochastic process that takes into account the incubation period of the life of individuals. We demonstrate that such processes may be treated as a two-type branching process with a periodic mean matrix. In the case when the Malthusian parameter does not exist study of the process requires additional restrictions on the life and incubation time distributions which define so called subexponential family (Athreya, K. 1972. Branching Processes, Springer, New York). We obtain certain new properties of subexponential distributions, in particular, describe a subclass, which is closed with respect to convolution. Using these results we derive asymptotic behavior of the first and second moments and of the probability of nonextinction. We also prove a limit theorem for the process conditioned on nonextinction. 相似文献
993.
《随机分析与应用》2013,31(3):739-753
Abstract We consider an M x /G/1 queueing system with a random setup time, where the service of the first unit at the commencement of each busy period is preceded by a random setup time, on completion of which service starts. For this model, the queue size distributions at a random point of time as well as at a departure epoch and some important performance measures are known [see Choudhury, G. An M x /G/1 queueing system with setup period and a vacation period. Queueing Sys. 2000, 36, 23–38]. In this paper, we derive the busy period distribution and the distribution of unfinished work at a random point of time. Further, we obtain the queue size distribution at a departure epoch as a simple alternative approach to Choudhury4. Finally, we present a transform free method to obtain the mean waiting time of this model. 相似文献
994.
Long Yuhua 《Journal of Difference Equations and Applications》2013,19(10):1499-1518
By making use of minimax theory and geometrical index theory, some results on the existence and multiplicity of subharmonic solutions with prescribed minimal period to discrete Hamiltonian systems are obtained. 相似文献
995.
In this article, the Multiple Scales Method is used to analyze the chaotic behavior and different types of fixed points in ferroresonance of voltage transformers considering core loss. This phenomenon has nonlinear chaotic dynamics and includes subharmonic, quasi‐periodic, and also chaotic oscillations. In this article, the chaotic behavior and various ferroresonant oscillations modes of the voltage transformer is studied. This phenomenon consists of different types of bifurcations such as Period Doubling Bifurcation (PDB), Saddle Node Bifurcation (SNB), Hopf Bifurcation (HB) and chaos. The dynamic analysis of ferroresonant circuit is based on bifurcation theory. The bifurcation and phase plane diagrams are illustrated using a continuous method and linear and nonlinear models of core loss. To analyze ferroresonance phenomenon, the Lyapunov exponents are calculated via Multiple Scales Method obtaining Feigenbaum numbers. The bifurcation diagrams illustrate the variation of the control parameter. Therefore, the chaos is created and increased in the system. © 2013 Wiley Periodicals, Inc. Complexity 18: 34‐45, 2013 相似文献
996.
The purpose of this note is to correct an error in Baltrunas et al. (2004) [1], and to give a more detailed argument to a formula whose validity has been questioned over the years. These details close a gap in the proof of Theorem 4.1 as originally stated, the validity of which is hereby strengthened. 相似文献
997.
本文提供反例说明现有文献中关于n维分段线性映射非光滑周期加倍分叉现象的结论不成立,进而给出该结论的正确表述,并重新给予证明. 相似文献
998.
P. Schobinger-Papamantellos K.H.J. BuschowJ. Rodríguez-Carvajal 《Journal of magnetism and magnetic materials》2011,323(21):2592-2607
The temperature magnetic phase diagrams of the dimorphic HoSi compound were studied by neutron diffraction. The sample comprises 35.5% CrB- (Cmcm) and 64.5% FeB-type (Pnma) of structure. Both phases order antiferromagnetically below TN=25 K and undergo first-order magnetic transitions at Tic=16.5 K. Their T-phase diagrams comprise a low temperature (LT) 2.7 K−Tic and a high temperature (HT) range Tic−TN with distinct wave vectors.The LT magnetic ordering of the CrB-type HoSi with the wave vector q1=(1/2, 0, 1/2) corresponds to a uniaxial magnetic structure, with the Ho moments along the shortest axis c. At 2.7 K the ordered moment value is 8.6(2) μB/Ho atom. The HT ordering, described by the wave vector q2=(q2x, 0, q2z) with a T-variable length, corresponds to an amplitude modulated structure.The magnetic ordering of the FeB-type HoSi requires two symmetry independent vectors q3=(0, q3y, q3z) for the LT- and q4=(q4x, q4y, 0) for the HT range. Both vectors correspond to sine wave modulated structures with the Ho magnetic moments confined along the shortest axis b. The q3 vector has an almost invariable length vs. T close to ≈(0, 9/17, 1/11). At 2.7 K the amplitude of the wave is 10.9(1) μB/Ho atom. At Ticq3 jumps to the wave vector q4=(q4x, q4y, 0) with a T-variable length. At 17 K q4=(0.092(1), 0.538(3), 0). Around Tic there is a narrow coexistence range of the q3 and q4 competing phases. Various models are discussed and compared with the isomorphic RSi (R=rare earth) compounds counterparts of HoSi, a comparison that has led us to briefly review the magnetic structures available in the literature for this interesting class of compounds. 相似文献
999.
1000.
Numerical analysis of plasmon polarition refractive index fiber sensors with hollow core and a long period grating 总被引:1,自引:0,他引:1
The main principle of this design is based on the efficient energy transfer between the waveguide mode (WM) and the co-directional SPP provided by a properly designed fiber long period grating (LPG). This LPG is imprinted into a waveguide fiber layer of a specially designed hollow core optical fiber. The simulations are based on the finite element method (FEM) algorithm in electromagnetics and coupled mode theory for gratings. Compared to the previous proposed structure using a fiber Bragg grating (FBG), this novel kind of sensor can greatly enhance the refractive index sensitivity, e.g., from 5.93 nm/RIU (with FBG) to 817 nm/RIU (with LPG) at the sensing refractive index of 1.40. The other advantage is that the working conditions can be performed for the well-developed telecom wavelength windows 1500-1600 nm. 相似文献