全文获取类型
收费全文 | 1414篇 |
免费 | 262篇 |
国内免费 | 61篇 |
专业分类
化学 | 82篇 |
晶体学 | 5篇 |
力学 | 465篇 |
综合类 | 9篇 |
数学 | 474篇 |
物理学 | 702篇 |
出版年
2024年 | 3篇 |
2023年 | 22篇 |
2022年 | 22篇 |
2021年 | 32篇 |
2020年 | 41篇 |
2019年 | 31篇 |
2018年 | 38篇 |
2017年 | 41篇 |
2016年 | 76篇 |
2015年 | 45篇 |
2014年 | 84篇 |
2013年 | 105篇 |
2012年 | 79篇 |
2011年 | 109篇 |
2010年 | 86篇 |
2009年 | 84篇 |
2008年 | 83篇 |
2007年 | 72篇 |
2006年 | 85篇 |
2005年 | 81篇 |
2004年 | 78篇 |
2003年 | 63篇 |
2002年 | 56篇 |
2001年 | 53篇 |
2000年 | 37篇 |
1999年 | 40篇 |
1998年 | 39篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 21篇 |
1994年 | 6篇 |
1993年 | 17篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1737条查询结果,搜索用时 15 毫秒
131.
Previous studies suggesting that people predict chaotic sequences better than chance have not discriminated between sensitivity to nonlinear determinism and facilitation using autocorrelation. Since prediction accuracy declines with increases in the look-ahead window in both cases, a decline in prediction accuracy does not imply chaos sensitivity. To overcome this problem, phase-randomized surrogate time series are used as a control. Such series have the same linear properties as the original chaotic sequence but contain no nonlinear determinism, i.e. chaos. In the experimental task, using a chaotic Hénon attractor, participants viewed the previous eight days temperatures and then predicted temperatures for the next four days, over 120 trials. The control group experienced a sample from a corresponding phase-randomized surrogate series. Both time series were linearly transformed to provide a realistic temperature range. A transformation of the correlation between observed and predicted values decreased over days for the chaotic time series, but remained constant and high for the surrogate series. The interaction between the days and series factors was statistically significant, suggesting that people are sensitive to chaos, even when the autocorrelation functions and power spectra of the control and experimental series are identical. Implications for the psychological assessment of individual differences in human prediction are discussed. 相似文献
132.
Gaetan?KerschenEmail author Alexander?F.?Vakakis Young?S.?Lee D.?Michael?Mcfarland Jeffrey?J.?Kowtko Lawrence?A.?Bergman 《Nonlinear dynamics》2005,42(3):283-303
The purpose of this study is to highlight and explain the vigorous energy transfers that may take place in a linear oscillator
weakly coupled to an essentially nonlinear attachment, termed a nonlinear energy sink. Although these energy exchanges are
encountered during the transient dynamics of the damped system, it is shown that the dynamics can be interpreted mainly in
terms of the periodic orbits of the underlying Hamiltonian system. To this end, a frequency-energy plot gathering the periodic
orbits of the system is constructed which demonstrates that, thanks to a 1:1 resonance capture, energy can be irreversibly
and almost completely transferred from the linear oscillator to the nonlinear attachment. Furthermore, it is observed that
this nonlinear energy pumping is triggered by the excitation of transient bridging orbits compatible with the nonlinear attachment being initially at rest, a common feature in most practical applications. A parametric
study of the energy exchanges is also performed to understand the influence of the parameters of the nonlinear energy sink.
Finally, the results of experimental measurements supporting the theoretical developments are discussed.
This study was carried out while the author was a postdoctoral fellow at the National Technical University of Athens and at
the University of Illinois at Urbana-Champaign. 相似文献
133.
NONLINEAROSCILIATIONANALYSISBYANORTHOGONALFUNCTIONMETHODSunPi,hong(孙丕忠)TangPiangang(唐乾刚)SunShixian(孙世贤)(NationUniversityofDef... 相似文献
134.
Maria Cristina Patria 《Meccanica》1991,26(2-3):135-141
An exact solution is given for the steady flow of a Newtonian fluid occupying the halfspace past the plane z=0 uniformly rotating about a fixed normal axis (Oz). This solution is obtained in a velocity field of the form considered by Berker [2] and can be deduced as a limiting case, as h+, of the solution to the problem relative to the strip 0zh imposing at z=h either the adherence boundary conditions or the free surface conditions. Furthermore, the stability of this flow, subject to periodic disturbances of finite amplitude, is studied using the energy method and the result is compared with those corresponding to stability of flows in the strip 0zh.
Sommario In questa nota si mostra che-oltre alla calssica soluzione di von Karman [1] — esiste, per opportuni valori del gradiente di pressione all'infinito, una soluzione esatta per il moto stazionario di un fluido Newtoniano posto nel semispazio limitato dal piano z=0 uniformemente rotante attorno ad un asse ad esso perpendicolare (Oz). Tale soluzione, ottenuta sulla scia del lavoro di Berker [2], si può dedurre anche come limite, per h+, della soluzione del problema relativo alla striscia 0zh quando sul piano z=h si assegnano o le condizioni di aderenza o le condizioni di frontiera libera. Si studia poi la stabilità di tale moto rispetto a perturbazioni spazialmente periodiche di ampiezza finita col metodo dell'energia e si confronta il risultato ottenuto con quelli relativi alla stabilità dei moti nella striscia 0zh.相似文献
135.
给出了硅微机械谐振陀螺仪的结构,介绍了硅微机械谐振陀螺仪的工作原理,详细推导并给出了陀螺仪的输出频率和标度因数非线性的计算公式;基于影响谐振陀螺仪标度因数的参数,分析了由谐振器的振幅和梳齿静电驱动力引起的硅微机械谐振陀螺仪的非线性特性,给出了振动幅度与谐振频率关系的表达式.实验结果表明,陀螺仪的整体性能主要取决于谐振器振动幅度的稳定性. 相似文献
136.
137.
一阶非线性项、四阶色散项的Boussinesq类方程 总被引:1,自引:0,他引:1
推导了由一阶色散项O(β2)表示的Bousinesq类方程,方程中保留了一阶非线性项O(α)及四阶色散项O(β8),其中α=A/h0,β=h0/L,A为特征波高,L为特征波长,h0为特征水深从理论上证明了Bousinesq改善型方程对色散性精度的提高,阐明了此类方程对色散项所保留的精度为O(β8),而并非是此类方程推导之初的假设为O(β2)这一点,将改变人们传统的认识 相似文献
138.
一类强非线性机械基础系统的亚谐振动解析解 总被引:3,自引:0,他引:3
建立了机械基础动力系统的强非线性动力学模型,利用能量法对该系统的周期解进行了解析研究,确定了系统动态参数满足周期解的条件、系统的周期解以及解的稳定性判别式。发现了亚谐振动,并给出了系统在满足周期解条件下的一组参数对应的主振动、1/3亚谐振动和1/5亚谐振动。最后利用数值积分方法计算了系统在给定条件下的主振动及亚谐振动解,考察了解析解的正确性。 相似文献
139.
Basic features of plastic strains: From micro-mechanics to incrementally nonlinear models 总被引:1,自引:0,他引:1
Most rate-independent constitutive relations for granular materials are based on the existence of a regular flow rule. This assumption states that once the mechanical state of a material point belongs to the yield surface, then the direction of the plastic strains is independent of the loading direction. In this paper, the notion of a regular flow rule is shown to exist only for two-dimensional and axisymmetric loading conditions. By considering our incrementally nonlinear constitutive model, it is established that this notion disappears as soon as more general loading conditions are applied, as also predicted from discrete element simulations. Moreover, a sound micro-mechanical interpretation of the vanishing of a regular flow rule in three-dimensional loading conditions is given from a multi-scale perspective using the micro-directional model. This model highlights the great influence of the loading history on the shape of the plastic Gudehus response-envelope. 相似文献
140.