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1.
2.
P. K. Kashkarov B. V. Kamenev M. G. Lisachenko O. A. Shalygina V. Yu. Timoshenk M. Schmidt J. Heitmann M. Zacharias 《Physics of the Solid State》2004,46(1):104-108
The photoluminescence spectra and kinetics of both erbium-doped and undoped multilayer structures of quasi-ordered silicon
nanocrystals in a silicon dioxide matrix were studied. It was shown that the optical excitation energy of silicon nanocrystals
2–3 nm in size can be practically completely transferred to Er3+ ions in the oxide surrounding the nanocrystals, with its subsequent radiation at 1.5 μm. Possible reasons for the high excitation
efficiency of the Er3+ ions are discussed, and the conclusion is drawn that the F?rster mechanism is dominant in the energy transfer processes occurring
in these structures.
__________
Translated from Fizika Tverdogo Tela, Vol. 46, No. 1, 2004, pp. 105–109.
Original Russian Text Copyright ? 2004 by Kashkarov, Kamenev, Lisachenko, Shalygina, Timoshenko, Schmidt, Heitmann, Zacharias. 相似文献
3.
We propose a three-field formulation for efficiently solving a two-dimensional Stokes problem in the case of nonstandard boundary conditions. More specifically, we consider the case where the pressure and either normal or tangential components of the velocity are prescribed at some given parts of the boundary. The proposed computational methodology consists in reformulating the considered boundary value problem via a mixed-type formulation where the pressure and the vorticity are the principal unknowns while the velocity is the Lagrange multiplier. The obtained formulation is then discretized and a convergence analysis is performed. A priori error estimates are established, and some numerical results are presented to highlight the perfomance of the proposed computational methodology.
4.
H. Zacharias 《Applied Physics A: Materials Science & Processing》1988,47(1):37-54
In this article the application of tunable dye lasers to desorption phenomena is illuminated. These lasers provide radiation continuously tunable from 105 nm in the vacuum ultraviolet to about 10 m in the mid-IR. By employing either laser induced fluorescence (LIF) or resonance enhanced multiphoton ionization (REMPI) spectroscopy almost all diatomic and many polyatomic molecules can be probed with the sensitivity required to detect desorbing molecules under UHV conditions. The spectral resolution of the lasers is sufficiently high that rotational state selectivity is achieved. Recent developments permit in addition the velocity distributions of molecules to be determined with internal quantum state resolution. Therefore very detailed information about the molecular dynamics has been obtained. In most experiments so far reactive recombinations off surfaces have been investigated. In this paper special emphasis will be given to the recombination of hydrogen on copper and palladium surfaces. For these systems very detailed data about the internal state populations at various surface temperatures have been obtained. The rotational cooling previously observed in molecular beam scattering has also been established for desorption. Strong vibrational excitation has been observed, which in the case of desorption from copper may be associated with the recombination dynamics, whereas for desorption of D2 from Pd(100) a molecular precursor state might be responsible. By measuring the velocity distribution in each quantum state, the complete energetics of the desorbing molecules has been determined. Some first experiments on laser induced desorption with state selective detection of the desorbing molecules will also be discussed. Finally, making use of the polarization analysis of the signal, alignment effects in the desorption can be observed, permitting observation of molecular dynamics with a magnifying glass.Heisenberg fellow of the Deutsche Forschungsgemeinschaft 相似文献
5.
Besma Lajmi Mourad Hidouri Mongi Ben Amara 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):i156-i158
The crystal structure of tripotassium pentairon hexaphosphate has been determined by single‐crystal X‐ray diffraction. The structure contains one Fe atom on a center of symmetry, one K, two Fe and two P atoms on twofold axes, and one Fe, two P and one K atom in general positions. The K3Fe5(PO4)6 structure consists of a complex three‐dimensional framework of corner‐sharing between iron polyhedra, and corner‐ and edge‐sharing between PO4 tetrahedra and iron polyhedra (FeO5 and FeO6). This linkage between iron and phosphorus forms intersecting channels containing the K atoms. 相似文献
6.
A commercial cation exchange resin Amberlite 200 has been modified after immersion in solutions of polyethyleneimine (PEI). The kinetic of fixation of the metallic ions have been determined. The modification of the surface of the resin deals with a change in the order of the affinities of the resins towards cations. The retention is the function of the formation and the stability of the complex. The conditions of modification (pH, PEI concentration and time of immersion) have been examined and the modification was confirmed by the determination of the exchange capacities, the distribution coefficient (P) and the selectivity factors (S). The obtained results revealed the effect of PEI on the exchange properties of the resin. The pH range selected (6-8) permitted a good adherence of PEI onto the resin surface. The quantity of the adsorbed PEI was increased by raising the initial concentration and the immersion period. The exchange capacity for copper ion passed from 2.6 mmol g−1, in the case of unmodified resin, to 3.9 mmol g−1 for the modified one. 相似文献
7.
8.
The thermal decompositions of-AlF3 · 3H2O, AlF3 · 3.5H2O, AlF3 · 1.5H2O,-AlF3 and hydroxyfluorides of aluminium were investigated. The literature data were complemented with X-ray results. The first stages of decomposition are described. The AlF3 hydrates and hydroxyfluorides were used as model systems in order to interpret the thermal behaviour of -AlF3 in more detail.
Zusammenfassung Die thermische Zersetzung von-AlF3 · 3H2O, AlF3 · 3,5H2O, AlF3 · 1,5H2O,-AlF3 und Hydroxyfluoriden des Aluminiums wurden untersucht und die in der Literatur beschriebenen Ergebnisse durch Röntgenuntersuchungen ergänzt. Die ersten Phasen der Zersetzung werden beschrieben. Die AlF3-Hydrate und Hydroxyfluoride des Aluminiums können als Modellsystem genutzt werden, um das thermische Verhalten von -AlF3 detailliert zu beschreiben.
-AlF3 · 2, AlF3 · 3,52, AlF3 · 1,52,-AlF3 . . . - lF3.相似文献
9.
U. Robra H. Zacharias K. H. Welge 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,16(3):175-188
The dynamics of the photodissociation of NO2 into NO(X 2ΠΩ″, ν″=0,J″)+O(3 P 0,1,2) is investigated near the thermodynamic threshold. Cooling the internal degrees of freedom by a supersonic beam expansion provides a nearly complete quantum state selection prior to the predissociation. Measurements of the wavelength dependent dissociation yield into specific product quantum states are reported. At certain wavelengths Λ″ doublet resolved rotational population distributions of the fragments are obtained. Up to an excess energy ofE exc=121 cm?1 about 42% of this energy is partitioned into the rotation of the NO molecules, and correspondingly 58% into the translational degree of freedom. The role of electronic and total parity is discussed. 相似文献
10.
Navamoney Arulsamy Chepuri R. K. Rao Panthappally S. Zacharias 《Transition Metal Chemistry》1991,16(6):606-609
Summary Condensations of Cu(L-ser)2 and Cu(L-thr)2 (where L-ser=L-serinato anion and L-thr=L-threoninato anion) with formaldehyde at pH 4.5 yield two new optically active products:bis[L-(oxazolidine-4-carboxylato)]-copper(II) monohydrate (1) andbis[L-(N-hydroxymethyl-5-methyloxazolidine-4-carboxylato)]copper(II) dihydrate (2), respectively. Cu(D-ser)2 and Cu(D-thr)2 also undergo similar reactions. The new products are different from the products obtained from Cu(DL-ser)2 and Cu(DL-thr)2, and a mechanism has been suggested to explain the stereospecificity of these conversions. Condensation of Cu(L-ser)2 with formaldehyde and ammonia at pH 4.5 yields the new product, [3N,7N-(1,3,5,7-tetraazabicyclo-[3.3.1]nonyl)di(hydroxymethyl)-acetato]copper(II), (3). The compexes have been characterized by analytical and by i.r. electronic and c.d. spectral data. Complexes (1) and (2) undergo a reversible CuII/CuI redox process in aqueous media at –0.18 Vversus s.c.e.; complex (3) exhibits irreversible CuII/CuI reduction at –0.49 V confirming the presence of a rigid pentamethylenediaza-bridged ligand system. 相似文献