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51.
Sondes Bauer Sergey Lazarev Alan Molinari Andreas Breitenstein Philipp Leufke Robert Kruk Horst Hahn Tilo Baumbach 《Journal of synchrotron radiation》2014,21(2):386-394
A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high‐energy diffraction with the in situ synchrotron high‐resolution X‐ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target–substrate separation distance. Ba0.5Sr0.5TiO3 grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X‐ray reflectivity, in situ two‐dimensional reciprocal space mapping of symmetric X‐ray diffraction and acquisition of time‐resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two‐dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba0.5Sr0.5TiO3 grown on MgO could be determined from the acquisition of time‐resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth. 相似文献
52.
Lars Radtke Axel Larena-Avellaneda Tilo Kölbel Eike Sebastian Debus Alexander Düster 《PAMM》2014,14(1):493-494
In this paper, we propose a technique for simulating the fluid-structure interaction in blood vessels. A partitioned approach is used, which allows for an independent discretization of the fluid domain and the structural domain. We choose the finite volume method to solve the Navier-Stokes equations and the p-version of the finite element method (p-FEM) to solve the equations of geometrically nonlinear structural dynamics. The solution strategy can be seen as a first approach towards a comprehensive study of the hemodynamics in vascular substitutes with the goal of improving their long term functionality. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
53.
Matthias Vogelgesang Tomas Farago Thilo F. Morgeneyer Lukas Helfen Tomy dos Santos Rolo Anton Myagotin Tilo Baumbach 《Journal of synchrotron radiation》2016,23(5):1254-1263
Real‐time processing of X‐ray image data acquired at synchrotron radiation facilities allows for smart high‐speed experiments. This includes workflows covering parameterized and image‐based feedback‐driven control up to the final storage of raw and processed data. Nevertheless, there is presently no system that supports an efficient construction of such experiment workflows in a scalable way. Thus, here an architecture based on a high‐level control system that manages low‐level data acquisition, data processing and device changes is described. This system is suitable for routine as well as prototypical experiments, and provides specialized building blocks to conduct four‐dimensional in situ, in vivo and operando tomography and laminography. 相似文献
54.
After many unsuccessful efforts, the structure of solid CD4 III finally has been solved. In this paper, we examine if the known tunneling spectra are consistent with the orientational potentials at the two sites with different symmetries. To this end, we study the rotational kinetic energy of the molecules, construct appropriate pocket states for the tunneling problem, and set up a model potential. Approximate energy levels are obtained from the Ritz variational principle. The agreement between the experimentally determined tunneling frequencies and the calculations is rather good, corroborating the findings of the structural analysis. A continuation of this paper will deal with the partly deuterated methanes. 相似文献
55.
Tilo D. Schachel Haidy Metwally Vlad Popa Lars Konermann 《Journal of the American Society for Mass Spectrometry》2016,27(11):1846-1854
Infusion of NaCl solutions into an electrospray ionization (ESI) source produces [Na(n+1)Cl n ]+ and other gaseous clusters. The n?=?4, 13, 22 magic number species have cuboid ground state structures and exhibit elevated abundance in ESI mass spectra. Relatively few details are known regarding the mechanisms whereby these clusters undergo collision-induced dissociation (CID). The current study examines to what extent molecular dynamics (MD) simulations can be used to garner insights into the sequence of events taking place during CID. Experiments on singly charged clusters reveal that the loss of small neutrals is the dominant fragmentation pathway. MD simulations indicate that the clusters undergo extensive structural fluctuations prior to decomposition. Consistent with the experimentally observed behavior, most of the simulated dissociation events culminate in ejection of small neutrals ([NaCl] i , with i?=?1, 2, 3). The MD data reveal that the prevalence of these dissociation channels is linked to the presence of short-lived intermediates where a relatively compact core structure carries a small [NaCl] i protrusion. The latter can separate from the parent cluster via cleavage of a single Na-Cl contact. Fragmentation events of this type are kinetically favored over other dissociation channels that would require the quasi-simultaneous rupture of multiple electrostatic contacts. The CID behavior of NaCl cluster ions bears interesting analogies to that of collisionally activated protein complexes. Overall, it appears that MD simulations represent a valuable tool for deciphering the dissociation of noncovalently bound systems in the gas phase. 相似文献
56.
Przystawik A Radcliffe P Diederich T Döppner T Tiggesbäumker J Meiwes-Broer KH 《The Journal of chemical physics》2007,126(18):184306
Photoelectron spectra of neutral silver trimers, grown in ultracold helium nanodroplets, are recorded after ionization with laser pulses via a strong optical resonance of this species. Varying the photon energy reveals that direct vertical two-photon ionization is hindered by a rapid relaxation into the lower edge of a long-living excited state manifold. An analysis of the ionization threshold of the embedded trimer yields an ionization potential of 5.74+/-0.09 eV consistent with the value found in the gas phase. The asymmetrical form of the electron energy spectrum, which is broadened toward lower kinetic energies, is attributed to the influence of the matrix on the photoionization process. The lifetime of the excited state was measured in a two-color pump-probe experiment to be 5.7+/-0.6 ns. 相似文献
57.
Sequences of residence times (RTs) associated with the escape from metastable states are observed in many fields. Here we study analytically and numerically the correlations among RTs for a bistable stochastic system driven by dichotomous noise. Our theory predicts an oscillatory behavior of the correlations with respect to the lag between RTs. Correlations vanish at all lags if the switching rate matches the hopping rate of the unperturbed system. It is also shown that RT correlations may reveal features of the driving which are not present in the single-RT statistics. 相似文献
58.
Hydrogen in N-methylacetamide: positions and dynamics of the hydrogen atoms using neutron scattering
Bordallo HN Argyriou DN Barthès M Kalceff W Rols S Herwig KW Fehr C Juranyi F Seydel T 《The journal of physical chemistry. B》2007,111(27):7725-7734
This work reports neutron diffraction and incoherent neutron scattering experiments on N-methylacetamide (NMA), which can be considered the model building block for the peptide linkage of polypeptides and proteins. Using the neutron data, we have been able to associate the onset of a striking negative thermal expansion (NTE) along the a-axis with a dynamical transition around 230 K, consistent with our calorimetric experiments. Observation of the NTE raises the question of possible proton transfer in NMA, which, from our data alone, still cannot be settled. We can only speculate that intermolecular repulsive forces increase as the O...H distance decreases upon cooling, and that around 230 K the lattice relaxes without observation of an actual proton transfer. However, the existence of a nonharmonic potential, reflected by the behavior of the phonon vibrations together with the observation of NTE, could be justified by the "vibrational" polaron theory in which a dynamic localization of the vibrational energy is created by coupling an internal molecular mode to a lattice phonon. More generally, this work shows that neutron powder diffraction techniques can be very powerful for investigating structural deformations in small peptide systems. 相似文献
59.
Victor E. Asadchikov Andrey V. Butashin Alexey V. Buzmakov Alexander N. Deryabin Vladimir M. Kanevsky Igor A. Prokhorov Boris S. Roshchin Yuri O. Volkov Denis A. Zolotov Atefeh Jafari Pavel Alexeev Angelica Cecilia Tilo Baumbach Dimitrios Bessas Andreas N. Danilewsky Ilya Sergueev Hans‐Christian Wille Raphaël P. Hermann 《Crystal Research and Technology》2016,51(4):290-298
We report on the growth and characterization of sapphire single crystals for X‐ray optics applications. Structural defects were studied by means of laboratory double‐crystal X‐ray diffractometry and white‐beam synchrotron‐radiation topography. The investigations confirmed that the main defect types are dislocations. The best quality crystal was grown using the Kyropoulos technique. Therein the dislocation density was 102–103 cm−2 and a small area with approximately 2*2 mm2 did not show dislocation contrast in many reflections. This crystal has suitable quality for application as a backscattering monochromator. A clear correlation between growth rate and dislocation density is observed, though growth rate is not the only parameter impacting the quality. 相似文献
60.
First principles computational studies have been carried out on the gas phase and surface polymerisation of formaldehyde. Any gas phase polymerisation in dark conditions is shown to occur by way of neutral species, as opposed to earlier suggestions that a charged species may be involved. The resulting paraformaldehyde chains are shown to be stable only when fully bonded at both chain ends, as opposed to some of the earlier suggested mechanisms. Polymerisation is shown to be thermodynamically favourable in the gas phase, but kinetically limited. Derived rate constants are insufficient to account for experimental results, in agreement with prior studies suggesting that gas phase polymerisation actually occurs on surfaces rather than directly in the gas phase. The TiO(2) (110) surface is employed as a model surface to study formaldehyde adsorption and possible polymerisation mechanisms. Formaldehyde monomers are shown to weakly bind by way of coordinate bonding through the carbonyl group to surface Ti. A particularly strong dimerisation configuration is also found where the two ends of paraformaldehyde are terminated by a surface Ti and surface O, consistent with the earlier observation that paraformaldehyde chains are only stable when saturated at both ends. 相似文献