全文获取类型
收费全文 | 552篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 347篇 |
晶体学 | 4篇 |
力学 | 10篇 |
数学 | 74篇 |
物理学 | 132篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 15篇 |
2014年 | 7篇 |
2013年 | 28篇 |
2012年 | 30篇 |
2011年 | 32篇 |
2010年 | 13篇 |
2009年 | 17篇 |
2008年 | 27篇 |
2007年 | 26篇 |
2006年 | 21篇 |
2005年 | 15篇 |
2004年 | 14篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1990年 | 8篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 12篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1969年 | 5篇 |
1968年 | 5篇 |
1966年 | 4篇 |
1962年 | 3篇 |
排序方式: 共有567条查询结果,搜索用时 296 毫秒
41.
H. Lavi?ka V. Poto?ek T. Kiss E. Lutz I. Jex 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,64(1):119-129
We analyze a special class of 1-D quantum walks (QWs) realized using optical multi-ports.
We assume non-perfect multi-ports showing errors in the connectivity, i.e. with a small
probability the multi-ports can connect not to their nearest neighbor but to another
multi-port at a fixed distance – we call this a jump. We study two cases of QW with jumps
where multiple displacements can emerge at one timestep. The first case assumes
time-correlated jumps (static disorder). In the second case, we choose the positions of
jumps randomly in time (dynamic disorder). The probability distributions of position of
the QW walker in both instances differ significantly: dynamic disorder leads to a
Gaussian-like distribution, while for static disorder we find two distinct behaviors
depending on the parity of jump size. In the case of even-sized jumps, the distribution
exhibits a three-peak profile around the position of the initial excitation, whereas the
probability distribution in the odd case follows a Laplace-like discrete distribution
modulated by additional (exponential) peaks for long times. Finally, our numerical results
indicate that by an appropriate mapping a universal functional behavior of the variance of
the long-time probability distribution can be revealed with respect to the scaled average
of jump size. 相似文献
42.
Formation of back corona and its effect on the voltage–current characteristics, etc., have been analysed by several authors. It has also been examined how the harmful effect of back corona can be reduced, for example by the application of pulse energisation. However, to find an optimal solution, modelling of the back corona effect is necessary. Different back corona models were created to estimate the time of its development, the change in current–voltage characteristics, the decrease in particle charge and finally, the collection efficiency of the ESP with back corona. In this paper the authors present an improved numerical ESP model that is capable of determining the parameters of back corona in such cases, when pulse energisation is applied for the power supply of the electrostatic precipitator. Based on the modular structure of the model, different modules calculate the distribution of gas velocity, electric field intensity, particle charging and particle movement. All these parameters are important to determine the properties of back corona while it feeds back on these parameters; therefore iteration is necessary to obtain reliable result. The harmful effects of back corona can be characterised with the help of the evaluation of calculated results. 相似文献
43.
The semiarcs are generalizations of semiovals. Estimates on the sizes of semiarcs, some characterization theorems of semiarcs with large collinear subsets, of semiarcs contained in the union of three concurrent lines and the complete classification of strong semiovals in PG(2, q), q odd, are given. 相似文献
44.
The effects of noise on phase synchronization (PS) of coupled chaotic oscillators are explored. In contrast to coupled periodic oscillators, noise is found to enhance phase synchronization significantly below the threshold of PS. This constructive role of noise has been verified experimentally with chaotic electrochemical oscillators of the electrodissolution of Ni in sulfuric acid solution. 相似文献
45.
Experiments were carried out on arrays of chaotic electrochemical oscillators to which global coupling, periodic forcing, and feedback were applied. The global coupling converts a very weakly coupled set of chaotic oscillators to a synchronized state with sufficiently large values of coupling strength; at intermediate values both intermittent and stable chaotic cluster states occur. Cluster formation and synchronization were also obtained by applying feedback and forcing to a moderately coupled base state. The three cases differ, however, in other details. The feedback and forcing also produce periodic cluster states and more than two clusters. Configurations of two (chaotic) clusters and two, three, or four (periodic) clusters were observed. (c) 2002 American Institute of Physics. 相似文献
46.
Two types of endocyclic enol-acetal forming β-elimination were investigated on synthetic model compounds. In both types the 4-O-methanesulfonyl residue was chosen as leaving group. The a,e-β-elimination was proved on 2,3-benzyl ether protected D -glucopyranosiduronate derivatives I, and the a, a-β-elimination on the analogous substituted D -galactopyranosiduronates XVII. Using a small excess of KOH in methanol at 25°, a quick elimination of a molecule of methanesulfonic acid was observed, and as reaction product the 4,5-unsaturated 4-deoxyhexopyranosiduronate derivative II was obtained. Only an unimportant stereoselectivity was found between the a,e- and a,a-mesylate β-eliminations. The 4,5-unsaturated 4-deoxyhexopyranosiduronates show a strong UV. maximum at 238 nm, and Cotton effects in the ORD. spectra. This stable ring system with an endocyclic enol-acetal linkage is present in a half-chair (H) conformation. The structure of the unsaturated deoxyhexopyranosiduronate obtained was established by structure- and stereo-correlation with a 2-deoxy-L -xylose derivative, showing that a ring contraction during the β-elimination does not occur. 相似文献
47.
48.
Tamura R Takeuchi T Aoki C Takeuchi S Kiss T Yokoya T Shin S 《Physical review letters》2004,92(14):146402
Ca 2p-3d resonant photoemission spectroscopy of a Cd6Ca crystalline approximant unambiguously demonstrates that the low-lying unoccupied 3d levels of calcium are lowered below the Fermi energy by the formation of the approximant, as suggested from electronic structure calculations [Phys. Rev. Lett. 87, 206408 (2001)]]. Moreover, the Ca 3d partial density of states (DOS) obtained near the Fermi energy is in reasonable agreement with theoretical Ca 3d DOS. These results verify the unconventional picture that the origin of the pseudogap in the Cd-based quasicrystals is due to hybridization of the Ca 3d band with the Cd 5p band. 相似文献
49.
Christmann U Dau H Haumann M Kiss E Liebisch P Rehder D Santoni G Schulzke C 《Dalton transactions (Cambridge, England : 2003)》2004,(16):2534-2540
The EXAFS region of vanadium K-edge XAS spectra of native vanadate-dependent bromoperoxidase (isoenzyme I) from Ascophyllum nodosum in the presence of the substrate bromide can be fitted to three shells (at 1.62, 1.73-1.78 and 1.99-2.07 A) in the first coordination sphere of vanadium plus two more distant shells at 4.1A, possibly corresponding to bromide, and 4.7 A due to light scatterers stemming from the protein pocket. Bromide does not directly bind to the vanadium centre. The XANES and the EXAFS features for the enzyme are essentially reproduced by model complexes of the general composition [VO(H(2)O)(n)(ONO)] (n= 1 or 2) where ONO is the dianion of a Schiff base from bromosalicylaldehydes (Brsal; with the Br substituent in the position 3, 4, 5 or 6) and amino acids. The 3-Brsal derivatives exhibit an outer sphere shell at 3.8 A, which is traced back to intermolecular contacts. The data obtained from EXAFS are compared to those obtained from single crystal X-ray diffraction of [VO(H(2)O)(2)(4-Brsal-gly)] and [VO(H(2)O)(2)(6-Brsal-gly)] (gly = glycinate). In the complex [VOBr(2)(ONO)']] ((ONO)' is the Schiff base from o-anisole and o-hydroxyaniline), the V-Br distance is 2.44 A. 相似文献
50.
Gyürky Gy. Fülöp Zs. Somorjai E. Kiss G. Rolfs C. 《The European Physical Journal A - Hadrons and Nuclei》2004,20(2):355-358
The absolute strengths of the
keV resonance in the
reaction and of the
keV resonance in the
reaction have been measured to
meV and
meV, respectively, in good agreement with previous values. These resonances can be used to measure the absolute acceptance of the recoil separator ERNA to a precision of about 10%.Received: 12 December 2003, Revised: 10 February 2004, Published online: 3 August 2004PACS:
24.30.-v Resonance reactions - 25.40.Lw Radiative capture - 26.20. + f Hydrostatic stellar nucleosynthesis 相似文献