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81.
Walter M Häkkinen H Lehtovaara L Puska M Enkovaara J Rostgaard C Mortensen JJ 《The Journal of chemical physics》2008,128(24):244101
We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we found perfect agreement in the calculated photoabsorption spectra. We discuss the strengths and weaknesses of the two methods as well as their convergence properties. We demonstrate different applications of the methods by calculating excitation energies and excited state Born-Oppenheimer potential surfaces for a set of atoms and molecules with the linear-response method and by calculating nonlinear emission spectra using the time-propagation method. 相似文献
82.
Vehkamäki H Määttänen A Lauri A Kulmala M Winkler P Vrtala A Wagner PE 《The Journal of chemical physics》2007,126(17):174707
In this paper we present a new form of the nucleation theorems applicable to heterogeneous nucleation. These heterogeneous nucleation theorems allow, for the first time, direct determination of properties of nanoclusters formed on pre-existing particles from measured heterogeneous nucleation probabilities. The theorems can be used to analyze the size (first theorem) and the energetics (second theorem) of heterogeneous clusters independent of any specific nucleation model. We apply the first theorem to the study of small water and n-propanol clusters formed at the surface of 8 nm silver particles. According to the experiments the size of the two-component critical clusters is found to be below 90 molecules, and only less than 20 molecules for pure water, less than 300 molecules for pure n-propanol. These values are drastically smaller than the ones predicted by the classical nucleation theory, which clearly indicates that the nucleating clusters are too small to be quantitatively described using a macroscopic theory. 相似文献
83.
Jalkanen JP Halonen M Fernández-Torre D Laasonen K Halonen L 《The journal of physical chemistry. A》2007,111(49):12317-12326
The adsorption of silver and gold atoms, and M2, M6, and M13 (M=Ag or Au) clusters on the (0001) graphite surface has been investigated computationally using the density functional theory (DFT) with periodic boundary conditions and plane wave basis functions. The surface has been modeled as a single carbon sheet. The role of dispersion forces has been studied with an empirical classical model. The results show that the clusters avoid hollow sites on the graphite surface, and that the metal atoms favor atop and bond sites. Large structural changes are observed in octahedral M6 and icosahedral M13 clusters on the graphite surface when compared with gas-phase geometries. The results also indicate that if accurate results are required, the dispersion forces between metal and carbon atoms should be included in the studied systems. 相似文献
84.
We present the first monolithically integrated silicon/glass liquid chromatography-electrospray ionization microchip for mass spectrometry. The microchip is fabricated by bonding a silicon wafer, which has deep reactive ion etched micropillar-filled channels, together with a glass lid. Both the silicon channel and the glass lid have a through-wafer etched sharp tip that produces a stable electrospray. The microchip is also compatible with laser induced fluorescence (LIF) detection, due to the glass lid. Separation of drugs in less than 5 minutes using either SiO(2) (normal phase) or C(18) coated (reversed-phase) pillars with good sensitivity was demonstrated with mass spectrometric detection as well as separation of fluorescent compounds with LIF detection. 相似文献
85.
Lauri Oksanen 《偏微分方程通讯》2013,38(9):1492-1518
We consider boundary measurements for the wave equation on a bounded domain M ? ?2 or on a compact Riemannian surface, and introduce a method to locate a discontinuity in the wave speed. Assuming that the wave speed consist of an inclusion in a known smooth background, the method can determine the distance from any boundary point to the inclusion. In the case of a known constant background wave speed, the method reconstructs a set contained in the convex hull of the inclusion and containing the inclusion. Even if the background wave speed is unknown, the method can reconstruct the distance from each boundary point to the inclusion assuming that the Riemannian metric tensor determined by the wave speed gives simple geometry in M. The method is based on reconstruction of volumes of domains of influence by solving a sequence of linear equations. For τ ∈C(?M) the domain of influence M(τ) is the set of those points on the manifold from which the distance to some boundary point x is less than τ(x). 相似文献
86.
87.
Anne-Marja Uusitalo Tuula T. Pakkanen Minna Krger-Laukkanen Lauri Niinist Kimmo Hakala Santeri Paavola Barbro Lfgren 《Journal of molecular catalysis. A, Chemical》2000,160(2):343-356
Heterogeneous metallocene catalysts were prepared by adsorbing rac-Et(Ind)2ZrCl2 on a modified silica surface in solution. The modification of silica was conducted in gas phase with atomic layer chemical vapor deposition (ALCVD) technique, where the silica, preheated at either 350 or 600°C, was allowed to react with vaporized trimethylaluminum (TMA) at 250°C. Modified carriers and heterogeneous catalysts were characterized with FTIR, 1H MAS (magic-angle spinning) NMR, 13C, and 29Si CP (cross-polarization) MAS NMR spectroscopies and elemental analyses. In the reaction of TMA with silica, a saturated surface was formed consisting of different (---O)4−nSi(CH3)n (n=1, 2 or 3) and ---AlCH3 groups. The ratio of ---SiMe to ---AlMe groups was approximately 1.5 in the TMA/SiO2 carriers. When the metallocene was adsorbed onto the carrier it seemed to react with the surface ---AlCH3 groups and possibly ---ZrCH3 groups were formed. Heterogeneous catalysts were tested in the polymerization of ethylene and propylene in the presence of methylalumoxane (MAO). And they produced similar polymer as the homogeneous rac-Et(Ind)2ZrCl2 catalyst, but with lower activity. A catalyst with the best activity was achieved from silica that was preheated at 600°C. Moreover, leaching of catalyst was examined whereupon a part of zirconium was observed to desorb from the carrier. 相似文献
88.
X-ray fluorescence spectrometry (XRF) was applied to determine aluminium in AlCl3- and Al2O3-modified silica catalyst supports that were prepared by gas-solid reactions in an atomic layer epitaxy (ALE) process using
aluminium chloride or aluminium chloride and water as adsorbates and silica as support. INAA and AAS were used as reference
methods to determine the aluminium content of the supports. The calibration of XRF results was done by plotting the Al/Si
intensity ratios against the aluminium content as determined by atomic absorption spectrometry (AAS) and verified by instrumental
neutron activation analysis (INAA). Correlation factors for the calibration graphs were 0.984 for AlCl3/SiO2 and 0.995 for Al2O3/ SiO2 samples in the aluminium content range 0–2.6 g Al per 100 g of sample.
Received: 19 October 1998 / Accepted: 14 December 1998 相似文献
89.
90.
Dr. Michael Georg Hoesl M. Sc. Stefan Oehm Dr. Patrick Durkin Dr. Elise Darmon Dr. Lauri Peil Dr. Hans‐Rudolf Aerni Prof. Dr. Juri Rappsilber Prof. Dr. Jesse Rinehart Prof. Dr. David Leach Prof. Dr. Dieter Söll Prof. Dr. Nediljko Budisa 《Angewandte Chemie (International ed. in English)》2015,54(34):9726-9726