全文获取类型
收费全文 | 1541篇 |
免费 | 66篇 |
国内免费 | 2篇 |
专业分类
化学 | 1051篇 |
晶体学 | 6篇 |
力学 | 19篇 |
数学 | 213篇 |
物理学 | 320篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 54篇 |
2021年 | 49篇 |
2020年 | 40篇 |
2019年 | 43篇 |
2018年 | 29篇 |
2017年 | 28篇 |
2016年 | 77篇 |
2015年 | 50篇 |
2014年 | 62篇 |
2013年 | 64篇 |
2012年 | 125篇 |
2011年 | 145篇 |
2010年 | 109篇 |
2009年 | 64篇 |
2008年 | 99篇 |
2007年 | 133篇 |
2006年 | 76篇 |
2005年 | 64篇 |
2004年 | 53篇 |
2003年 | 37篇 |
2002年 | 27篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1935年 | 1篇 |
1905年 | 3篇 |
1904年 | 2篇 |
排序方式: 共有1609条查询结果,搜索用时 15 毫秒
841.
Sergio?Orlandini Simone?MeloniEmail author Giovanni?Ciccotti 《Journal of statistical physics》2011,145(4):812-830
We describe a combined Restrained MD/Parallel Tempering approach to study the difference in free energy as a function of a
set of collective variables between two states in presence of metastabilities in the manifold orthogonal to the one spanned
by the chosen collective variables. We illustrate the method by an extended study of the relative stability of the amorphous
vs crystalline Si nanoparticles embedded in a-SiO2 of size ranging between 0.8 and 1.8 nm as a function of temperature [S. Orlandini, S. Meloni, and L. Colombo in Phys. Rev.
B 83:235303, 2011]. The results show that the method permits to get over the hidden metastabilities. Finally, we try to identify the missing
collective variables from the Restrained MD/Parallel Tempering trajectories and analyze whether the collective variable used
to control the amorphous-to-crystalline transition is adequate to describe the mechanism of crystallization of some of the
nanoparticles considered. 相似文献
842.
We consider the trace map associated with the silver ratio Schr?dinger operator as a diffeomorphism on the invariant surface associated with a given coupling constant and prove that the non-wandering set of this map is hyperbolic if the coupling is sufficiently large. As a consequence, for this values of the coupling constant, the local and global Hausdorff dimension and the local and global box counting dimension of the spectrum of this operator all coincide and are smooth functions of the coupling constant. 相似文献
843.
Simone Dantas Celina M. H. de Figueiredo Martin Charles Golumbic Sulamita Klein Fr��d��ric Maffray 《Annals of Operations Research》2011,188(1):133-139
The chain graph sandwich problem asks: Given a vertex set V, a mandatory edge set E 1, and a larger edge set E 2, is there a graph G=(V,E) such that E 1?E?E 2 with G being a chain graph (i.e., a 2K 2-free bipartite graph)? We prove that the chain graph sandwich problem is NP-complete. This result stands in contrast to (1) the case where E 1 is a connected graph, which has a linear-time solution, (2) the threshold graph sandwich problem, which has a linear-time solution, and (3) the chain probe graph problem, which has a polynomial-time solution. 相似文献
844.
Adriani O Barbarino GC Bazilevskaya GA Bellotti R Boezio M Bogomolov EA Bongi M Bonvicini V Borisov S Bottai S Bruno A Cafagna F Campana D Carbone R Carlson P Casolino M Castellini G Consiglio L De Pascale MP De Santis C De Simone N Di Felice V Galper AM Gillard W Grishantseva L Jerse G Karelin AV Koldashov SV Krutkov SY Kvashnin AN Leonov A Malakhov V Malvezzi V Marcelli L Mayorov AG Menn W Mikhailov VV Mocchiutti E Monaco A Mori N Nikonov N Osteria G Palma F Papini P Pearce M Picozza P 《Physical review letters》2011,106(20):201101
Precision measurements of the electron component in the cosmic radiation provide important information about the origin and propagation of cosmic rays in the Galaxy. Here we present new results regarding negatively charged electrons between 1 and 625 GeV performed by the satellite-borne experiment PAMELA. This is the first time that cosmic-ray e? have been identified above 50 GeV. The electron spectrum can be described with a single power-law energy dependence with spectral index -3.18 ± 0.05 above the energy region influenced by the solar wind (> 30 GeV). No significant spectral features are observed and the data can be interpreted in terms of conventional diffusive propagation models. However, the data are also consistent with models including new cosmic-ray sources that could explain the rise in the positron fraction. 相似文献
845.
We numerically demonstrate that properly designed plasmonic covers can be used to enhance the performance of near-field scanning optical microscopy (NSOM) systems based on the employment of apertureless metallic tip probes. The covering material, exhibiting a near-zero value of the real permittivity at the working frequency, is designed in such a way to dramatically reduce the undesired scattering due to the strongly plasmonic behavior of the tip. Though the light scattering by the tip end is necessary for the correct operation of NSOMs, the additional scattering due to the whole probe affects the signal-to-noise ratio and thus the resolution of the acquired image. By covering the whole probe but not the very tip, we show that unwanted scattering can be effectively reduced. A realistic setup, working at mid-IR frequencies and employing silicon carbide covers, has been designed and simulated to confirm the effectiveness of the proposed approach. 相似文献
846.
A Horizontal Visibility Graph (HVG) is defined in association with an ordered set of non-negative reals. HVGs realize a methodology in the analysis of time series, their degree distribution being a good discriminator between randomness and chaos Luque et al. [B. Luque, L. Lacasa, F. Ballesteros, J. Luque, Horizontal visibility graphs: exact results for random time series, Phys. Rev. E 80 (2009), 046103]. We prove that a graph is an HVG if and only if it is outerplanar and has a Hamilton path. Therefore, an HVG is a noncrossing graph, as defined in algebraic combinatorics Flajolet and Noy [P. Flajolet, M. Noy, Analytic combinatorics of noncrossing configurations, Discrete Math., 204 (1999) 203-229]. Our characterization of HVGs implies a linear time recognition algorithm. Treating ordered sets as words, we characterize subfamilies of HVGs highlighting various connections with combinatorial statistics and introducing the notion of a visible pair. With this technique, we determine asymptotically the average number of edges of HVGs. 相似文献
847.
Weyand S Shimamura T Beckstein O Sansom MS Iwata S Henderson PJ Cameron AD 《Journal of synchrotron radiation》2011,18(1):20-23
Secondary active transporters move molecules across cell membranes by coupling this process to the energetically favourable downhill movement of ions or protons along an electrochemical gradient. They function by the alternating access model of transport in which, through conformational changes, the substrate binding site alternately faces either side of the membrane. Owing to the difficulties in obtaining the crystal structure of a single transporter in different conformational states, relatively little structural information is known to explain how this process occurs. Here, the structure of the sodium-benzylhydantoin transporter, Mhp1, from Microbacterium liquefaciens, has been determined in three conformational states; from this a mechanism is proposed for switching from the outward-facing open conformation through an occluded structure to the inward-facing open state. 相似文献
848.
Jana Padežnik Gomilšek Alojz Kodre Iztok Arčon Simone de Panfilis Darko Makovec 《Journal of synchrotron radiation》2011,18(4):557-563
The approximate barium X‐ray atomic absorption in the energy region of L‐edges is reconstructed from the absorption spectrum of an aqueous solution of BaCl2. The result is corroborated by comparison with pure atomic absorption spectra of neighbour elements Xe and Cs. The application of the atomic absorption signal as a proper EXAFS background is demonstrated and discussed in the analysis of Ba hexaferrite nanoparticles with a very weak structural signal. The essential gain is found in the decrease of uncertainty intervals of structural parameters and their correlations. A simple analytical model of the absorption background for the practical EXAFS analysis is demonstrated. 相似文献
849.
Marques SM Petushkov VN Rodionova NS da Silva JC 《Journal of photochemistry and photobiology. B, Biology》2011,102(3):218-223
This paper presents the main results of RP-HPLC-MS and microscale NMR analysis performed on Accompanying similar to Luciferin (AsLn(x)), compounds present in extracts of the bioluminescent earthworm Fridericia heliota that display similarities with Fridericia's luciferin, the substrate of the bioluminescent reaction. Three isomers of AsLn were discovered, AsLn(1), AsLn(2) and AsLn(3), all of which present a molecular weight of 529 Da. Their UV-Vis absorption spectra show maxima at 235 nm for AsLn(1), 238 and 295 nm for AsLn(2) and 241 and 295nm for AsLn(3). MS(n) fragmentation patterns suggest the existence of carboxylic acid and hydroxyl moieties, and possibly chemical groups found in other luciferins like pterin or benzothiazole. The major isomer, AsLn(2), presents an aromatic ring and alkene and alkyl moieties. These luciferin-like compounds can be used as models that could give further insights into the structure of this newly discovered luciferin. 相似文献
850.
Rotella C Napolitano S Vandendriessche S Valev VK Verbiest T Larkowska M Kucharski S Wübbenhorst M 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13533-13538
We studied the adsorption kinetics of supported ultrathin films of dye-labeled polystyrene (l-PS) by combining dielectric spectroscopy (DS) and the interface-specific nonlinear optical second harmonic generation (SHG) technique. While DS is sensitive to the fraction of mobile dye moieties (chromophores), the SHG signal probes their anisotropic orientation. Time-resolved measurements were performed above the glass transition temperature on two different sample geometries. In one configuration, the l-PS layer is placed in contact with the aluminum surface, while in the other one, the deposition is done on a strongly adsorbed layer of neat PS. From the time dependence of the dielectric strength and SHG signal of the l-PS layer in contact with the metal, we detected two different kinetics regimes. We interpret these regimes in terms of the interplay between adsorption and orientation of the adsorbing labeling moieties. At early times, dye moieties get adsorbed adopting an orientation parallel to the surface. When adsorption proceeds to completeness, the kinetics slows down and the dye moieties progressively orient normal to the surface. Conversely, when the layer of l-PS layer is deposited on the strongly adsorbed layer of neat PS, both the dielectric strength and the SHG signal do not show any variation with time. This means that no adsorption takes place. 相似文献