全文获取类型
收费全文 | 208篇 |
免费 | 3篇 |
国内免费 | 4篇 |
专业分类
化学 | 106篇 |
力学 | 9篇 |
数学 | 41篇 |
物理学 | 59篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 3篇 |
2013年 | 7篇 |
2012年 | 19篇 |
2011年 | 12篇 |
2010年 | 11篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 14篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 1篇 |
1968年 | 3篇 |
1967年 | 1篇 |
1927年 | 1篇 |
1906年 | 1篇 |
排序方式: 共有215条查询结果,搜索用时 0 毫秒
71.
William Sims Bainbridge 《The Journal of mathematical sociology》2013,37(2-3):179-192
A simple but effective neural network algorithm illustrates common principles of this new class of computational tools. Designed for use in a range of simulation studies, this minimum intelligent neural device is capable of learning which of a complex set of stimuli to avoid, and large numbers of these devices can be assembled in programs to explore the development of prejudice and of various interaction strategies. Neural nets are error‐reduction algorithms with the potential to perform a wide range of useful tasks, including modeling theories of the social consequences of human error. 相似文献
72.
Sven?Bachmann Spyridon?Michalakis Bruno?NachtergaeleEmail author Robert?Sims 《Communications in Mathematical Physics》2012,309(3):835-871
Gapped ground states of quantum spin systems have been referred to in the physics literature as being ‘in the same phase’ if there exists a family of Hamiltonians H(s), with finite range interactions depending continuously on \({s\in [0,1]}\), such that for each s, H(s) has a non-vanishing gap above its ground state and with the two initial states being the ground states of H(0) and H(1), respectively. In this work, we give precise conditions under which any two gapped ground states of a given quantum spin system that ’belong to the same phase’ are automorphically equivalent and show that this equivalence can be implemented as a flow generated by an s-dependent interaction which decays faster than any power law (in fact, almost exponentially). The flow is constructed using Hastings’ ‘quasi-adiabatic evolution’ technique, of which we give a proof extended to infinite-dimensional Hilbert spaces. In addition, we derive a general result about the locality properties of the effect of perturbations of the dynamics for quantum systems with a quasi-local structure and prove that the flow, which we call the spectral flow, connecting the gapped ground states in the same phase, satisfies a Lieb-Robinson bound. As a result, we obtain that, in the thermodynamic limit, the spectral flow converges to a co-cycle of automorphisms of the algebra of quasi-local observables of the infinite spin system. This proves that the ground state phase structure is preserved along the curve of models H(s), 0 ≤ s ≤ 1. 相似文献
73.
We study many-body properties of quantum harmonic oscillator lattices with disorder. A sufficient condition for dynamical localization, expressed as a zero-velocity Lieb-Robinson bound, is formulated in terms of the decay of the eigenfunction correlators for an effective one-particle Hamiltonian. We show how state-of-the-art techniques for proving Anderson localization can be used to prove that these properties hold in a number of standard models. We also derive bounds on the static and dynamic correlation functions at both zero and positive temperature in terms of one-particle eigenfunction correlators. In particular, we show that static correlations decay exponentially fast if the corresponding effective one-particle Hamiltonian exhibits localization at low energies, regardless of whether there is a gap in the spectrum above the ground state or not. Our results apply to finite as well as to infinite oscillator systems. The eigenfunction correlators that appear are more general than those previously studied in the literature. In particular, we must allow for functions of the Hamiltonian that have a singularity at the bottom of the spectrum. We prove exponential bounds for such correlators for some of the standard models. 相似文献
74.
Kadwani P Modsching N Sims RA Leick L Broeng J Shah L Richardson M 《Optics letters》2012,37(10):1664-1666
We report a novel, Tm-doped photonic crystal fiber (PCF) actively Q-switched oscillator that provides ~8.9 kW peak power with 435 μJ, 49 ns pulses at 10 kHz repetition rate at 2 μm wavelength. This fiber has a mode-field area >1000 μm2, the largest of any flexible PCF providing diffraction-limited beam quality to the best of our knowledge. As an application, the oscillator is used as pump to generate >350 nm broadening in ~50 m of SMF-28 fiber. 相似文献
75.
76.
During machining, unstable self-excited vibrations known as regenerative chatter can occur, causing excessive tool wear or failure, and a poor surface finish on the machined workpiece. Consequently it is desirable to predict, and hence avoid the onset of this instability. Regenerative chatter is a function of empirical cutting coefficients, and the structural dynamics of the machine-tool system. There can be significant uncertainties in the underlying parameters, so the predicted stability limits do not necessarily agree with those found in practice. In the present study, fuzzy arithmetic techniques are applied to the chatter stability problem. It is first shown that techniques based upon interval arithmetic are not suitable for this problem due to the issue of recursiveness. An implementation of fuzzy arithmetic is then developed based upon the work of Hanss and Klimke. The arithmetic is then applied to two techniques for predicting milling chatter stability: the classical approach of Altintas, and the time-finite element method of Mann. It is shown that for some cases careful programming can reduce the computational effort to acceptable levels. The problem of milling chatter uncertainty is then considered within the framework of Ben-Haim's information-gap theory. It is shown that the presented approach can be used to solve process design problems with robustness to the uncertain parameters. The fuzzy stability bounds are then compared to previously published data, to investigate how uncertainty propagation techniques can offer more insight into the accuracy of chatter predictions. 相似文献
77.
The phenomena of the onsets of liquid entrainment and gas entrainment were investigated experimentally for the case of a flat plane with a circular outlet branch of diameter d (=6.35 mm) at the plane centre. This flat plane was situated in a large tank containing a stratified mixture of air and water under pressure (317 kPa for most experiments and 520 kPa for a few experiments) and at room temperature. The plane was inclined through various angles (θ) in increments of 30°, from the outlet branch orientation being vertically upward through the horizontal to vertically downward. For both onsets the vertical distance between the centre of the outlet branch and the undisturbed gas–liquid interface (h) was measured for various angles of inclination and Froude numbers. Both onsets were observed visually through a large viewing part of the test section. It was found that for both onsets there is a range of inclination angles where the onset h depended on θ and a range where the onset h essentially did not depend on θ. The data were correlated in terms of onset h/d, Froude number, and θ where there was dependence of onset h on the angle of inclination. 相似文献
78.
Dyes in Liquid Crystals: Experimental and Computational Studies of a Guest–Host System Based on a Combined DFT and MD Approach
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mark T. Sims Dr. Laurence C. Abbott Dr. Stephen J. Cowling Prof. Dr. John W. Goodby Dr. John N. Moore 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):10123-10130
Practical applications of guest–host liquid crystal systems are critically dependent on the alignment of the guest species within the liquid crystal host. UV/Vis absorption spectroscopy shows that the 1,5‐dihydroxy‐2,6‐bis‐(4‐propylphenyl)‐9,10‐anthraquinone dye aligns within the E7 nematic host, giving an experimental dichroic ratio of 9.40 and dye order parameter of 0.74. This alignment was modelled by using a combination of density functional theory (DFT) and molecular dynamics (MD) computational approaches that do not require the input of experimental data. Time‐dependent DFT calculations show that the electronic transition dipole moment is highly aligned with the long molecular axis of the dye. Fully atomistic MD simulations show that the long axis of the dye is less highly aligned within the E7 host, indicating that this contribution limits the overall dye alignment and, thereby, the potential practical applications of this particular system. Importantly, this study demonstrates an experimental and combined DFT and MD computational approach that may be applied generally to guest–host systems, providing a potential route to their rational design. 相似文献
79.
Ana?Maria?Gonzalez Wendy?E?Leadbeater Michael?Burg Karen?Sims Tetsuya?Terasaki Conrad?E?Johanson Edward?G?Stopa Brian?P?Eliceiri Andrew?BairdEmail author 《BMC neuroscience》2011,12(1):4
Background
Because the choroid plexus (CP) is uniquely suited to control the composition of cerebrospinal fluid (CSF), there may be therapeutic benefits to increasing the levels of biologically active proteins in CSF to modulate central nervous system (CNS) functions. To this end, we sought to identify peptides capable of ligand-mediated targeting to CP epithelial cells reasoning that they could be exploited to deliver drugs, biotherapeutics and genes to the CNS. 相似文献80.
Houssam Abdul-Rahman Bruno Nachtergaele Robert Sims Günter Stolz 《Letters in Mathematical Physics》2016,106(5):649-674
We consider the dynamics of the quantum XY chain with disorder under the general assumption that the expectation of the eigenfunction correlator of the associated one-particle Hamiltonian satisfies a decay estimate typical of Anderson localization. We show that, starting from a broad class of product initial states, entanglement remains bounded for all times. For the XX chain, we also derive bounds on the particle transport which, in particular, show that the density profile of initial states that consist of fully occupied and empty intervals only have significant dynamics near the edges of those intervals, uniformly for all times. 相似文献