全文获取类型
收费全文 | 79篇 |
免费 | 1篇 |
专业分类
化学 | 44篇 |
数学 | 14篇 |
物理学 | 22篇 |
出版年
2023年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2013年 | 10篇 |
2012年 | 7篇 |
2011年 | 3篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1993年 | 2篇 |
1989年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1966年 | 1篇 |
1939年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有80条查询结果,搜索用时 15 毫秒
31.
Debate continues over which active species plays the role of oxidative agent during the Fenton reaction-the HO˙ radical or oxo iron [Fe(IV)O](2+). In this context, the present study investigates the oxidation of p-chlorophenol by [Fe(IV)O(H(2)O)(5)](2+) using DFT calculations, within gas-phase and micro-solvated models, in order to explore the possible role of oxo iron as a reactant. The results show that the chlorine atom substitution of p-chlorophenol by oxo iron is a highly stabilising step (ΔH = -83 kcal mol(-1)) with a free energy barrier of 5.8 kcal mol(-1) in the micro-solvated model. This illustrates the high oxidising power of the [Fe(IV)O(H(2)O)(5)](2+) complex. On the other hand, the breaking of the Fe-O bond, leading to the formation of hydroquinone, is observed to be the rate-determining step of the reaction. The rather large free energy barrier corresponding to this bond cleavage amounts to 10.2 and 9.3 kcal mol(-1) in the gas-phase and micro-solvated models, respectively. Elsewhere, the lifetime of the HO˙ radical has previously been shown to be extremely small. These facts, combined with observations of oxo iron under certain experimental conditions, suggest that oxo iron is a highly plausible oxidative species of the reaction. In addition, a trigonal bipyramidal iron complex, coordinated either by hydroxyl groups and/or by water molecules, has been found in all described mechanisms. This structure appears to be a stable intermediate; and to our knowledge, it has not been characterised by previous studies. 相似文献
32.
Jae-Hun Kim Chang-Woo Park Euntai Kim Mignon Park 《Chaos, solitons, and fractals》2005,24(5):1353-1361
This paper presents a fuzzy model-based adaptive approach for synchronization of chaotic systems which consist of the drive and response systems. Takagi–Sugeno (T–S) fuzzy model is employed to represent the chaotic drive and response systems. Since the parameters of the drive system are assumed unknown, we design the response system that estimates the parameters of the drive system by adaptive strategy. The adaptive law is derived to estimate the unknown parameters and its stability is guaranteed by Lyapunov stability theory. In addition, the controller in the response system contains two parts: one part that can stabilize the synchronization error dynamics and the other part that estimates the unknown parameters. Numerical examples, including Duffing oscillator and Lorenz attractor, are given to demonstrate the validity of the proposed adaptive synchronization approach. 相似文献
33.
Won-Ki Lee Chang-Ho Hyun Heejin Lee Euntai Kim Mignon Park 《Chaos, solitons, and fractals》2007,34(5):1590-1598
This paper presents a model reference adaptive control approach for the synchronization of a discrete-time chaotic systems using output tracking control. The reference model system is chosen using the output of master system and Takagi–Sugeno (T–S) fuzzy model is employed to represent the discrete-time chaotic slave system. Design the control input so that the controlled slave system achieves asymptotic synchronization with the reference system given that two systems start from different initial conditions, different parameters and/or different type of model. Using a gradient algorithm, the ideal controller gains which can stabilize the error equation are estimated. Simulation examples of two cases are given to demonstrate the validity of our proposed adaptive method. 相似文献
34.
Alcaide B Almendros P Luna A Cembellín S Arnó M Domingo LR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(41):11559-11566
N-Bromosuccinimide (NBS) smoothly promotes the ring expansion of lactam-tethered allenols to efficiently afford cyclic α- or β-ketoamides with good yields and high chemo-, regio-, and diastereoselectivity, through controlled C-C bond cleavage of the β- or γ-lactam nucleus. Interestingly, in contrast to the rearrangement reactions of 2-azetidinone-tethered allenols, which lead to the corresponding tetramic acid derivatives (β-keto lactam adducts) as the sole products, the reactions of 2-indolinone-tethered allenols under similar conditions give quinoline-2,3-diones (α-keto lactam adducts) as the exclusive or major products. To rationalize the experimental observations, theoretical studies have been performed. 相似文献
35.
Sebastian Aniţa Viorel Arnăutu Răzvan Ştefănescu 《Numerical Functional Analysis & Optimization》2013,34(3-4):183-198
We investigate an optimal harvesting problem for age-structured population dynamics with logistic term and periodic vital rates. We use first-order necessary optimality conditions in order to derive an algorithm to approximate the optimal harvesting effort. We present corresponding numerical experiments. 相似文献
36.
We prove an asymptotic behavior result for an age-dependent population dynamics with logistic term and periodic vital rates. We investigate next an optimal harvesting problem related to a periodic age-structured model with logistic term. Existence of an optimal control and necessary optimality conditions are established. A conceptual algorithm to approximate the optimal pair is derived and some numerical experiments are presented. 相似文献
37.
Vaillant C Audit B Thermes C Arnéodo A 《The European physical journal. E, Soft matter》2006,19(3):263-277
The understanding of the long-range correlations (LRC) observed in DNA sequences is still an open and very challenging problem.
In this paper, we start reviewing recent results obtained when exploring the scaling properties of eucaryotic, eubacterial
and archaeal genomic sequences using the space-scale decomposition provided by the wavelet transform (WT). These results suggest
that the existence of LRC up to distances ∼ 20-30kbp is the signature of the nucleosomal structure and dynamics of the chromatin
fiber. Actually the LRC are mainly observed in the DNA bending profiles obtained when using some structural coding of the
DNA sequences that accounts for the fluctuations of the local double-helix curvature within the nucleosome complex. Because
of the approximate planarity of nucleosomal DNA loops, we then study the influence of the LRC structural disorder on the thermodynamical
properties of 2D elastic chains submitted locally to mechanical/topological constraint as loops. The equilibrium properties
of the one-loop system are derived numerically and analytically in the quite realistic weak-disorder limit. The LRC are shown
to favor the spontaneous formation of small loops, the larger the LRC, the smaller the size of the loop. We further investigate
the dynamical behavior of such a loop using the mean first passage time (MFPT) formalism. We show that the typical short-time
loop dynamics is superdiffusive in the presence of LRC. For displacements larger than the loop size, we use large-deviation
theory to derive a LRC-dependent anomalous-diffusion rule that accounts for the lack of disorder self-averaging. Potential
biological implications on DNA loops involved in nucleosome positioning and dynamics in eucaryotic chromatin are discussed. 相似文献
38.
We study a problem in fluid dynamics that has three competing instabilities and reduce it to a third-order nonlinear ordinary differential equation which exhibits chaotic solutions. 相似文献
39.
40.
We study the influence of a structural disorder on the thermodynamical properties of 2D-elastic chains submitted to mechanical/topological constraint as loops. The disorder is introduced via a spontaneous curvature whose distribution along the chain presents either no correlation or long-range correlations (LRC). The equilibrium properties of the one-loop system are derived numerically and analytically for weak disorder. LRC are shown to favor the formation of small loop, larger the LRC, smaller the loop size. We use the mean first passage time formalism to show that the typical short time loop dynamics is superdiffusive in the presence of LRC. Potential biological implications on nucleosome positioning and dynamics in eukaryotic chromatin are discussed. 相似文献