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91.
de Castro RA Canotilho J Barbosa RM Redinha JS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(5):1194-1200
The molecular structure of conformational isomorphs given by X-ray diffraction for racemic and enantiomeric atenolol were optimized at the HF/6-31G* level of theory and the infrared spectra of the structure were calculated. These spectra are used to characterize the differences between the various atenolol conformers. The spectra of the (R,S)- and S-atenolol solid forms were recorded and the bands corresponding to the functional groups identified with the aid of the calculated spectra, fitting analysis, temperature effect and H/D isotopic exchange. Particular attention was paid to the stretch vibration modes of the functional groups present in the atenolol. 相似文献
92.
Study of adsorption of tetraethylammonium ions on Bi single crystal planes from solutions in ethanol
The adsorption of tetraethylammonium (TEA+) ions on the (001) and planes of the bismuth single crystal from solutions in ethanol has been investigated by impedance measurement method. The
experimental data were obtained in 0.02 M mixed-electrolyte solutions and the calculations performed with electrode potential
as the independent electrical variable. The Gibbs energy of adsorption of TEA+ ions has been calculated using the simple virial adsorption isotherm, and it was found that the adsorption of TEA+ cations is weaker than the adsorption of halide anions. The electrosorption valency evaluated has a nearly constant value
in the potential region studied. It was concluded that the formed effective surface dipole is significantly screened by the
solvent molecules and the metal electron gas. The analysis of the impedance spectra was performed by fitting the experimental
data to the various equivalent circuits. It was found that the behaviour of TEA+ ions at Bi(hkl)∣ethanol interface can be described with the equivalent circuit, corresponding to the classical Frumkin–Melik-Gaikazyan
model. The results obtained indicate that only weak interaction between TEA+ ions and bismuth surface takes place, and there is no remarkable partial charge transfer from the adsorbed ions to the Bi
surface atoms. 相似文献
93.
Simões A 《Journal of computational chemistry》2007,28(1):62-72
In this paper, I will look at the rather convoluted discovery process which gave birth to the concept of the shared electron pair bond as developed by G.N. Lewis, to be subsequently appropriated by the American founders of quantum chemistry, and highlight the complex relations between conceptual development and the different contexts in which ideas are created and presented. I will show how the successive installments of Lewis's model of the chemical bond were supported by and gained credence from an epistemological background in which Lewis explored the relations of chemistry to physics. Furthermore, they were shaped by the changing public contexts in which the successive metamorphoses of the ideas took place and their epistemological background was outlined and explored. The complexities which are always associated with a discovery process can therefore be illuminated if one pays attention to different interactive realms-the conceptual, epistemological, and the presentational one. 相似文献
94.
Villo L Danilas K Metsala A Kreen M Vallikivi I Vija S Pehk T Saso L Parve O 《The Journal of organic chemistry》2007,72(15):5813-5816
A chemoenzymatic synthesis of deoxy sugar esters is described. The synthesis is based on the O-alkylation of carboxylic acid with 2-bromo-5-acetoxypentanal. The method allows treatment of hydroxy carboxylic acids without protection of alcoholic hydroxyl groups. Several stereoisomeric deoxy sugar esters were resolved (up to ee or de > 98%) using a lipase-catalyzed acetylation of hemiacetals that in certain cases afforded deoxy sugar derivatives in the form of aldehydes. The stereochemistry of the reactions was determined by the NMR spectra of mandelic acid derivatives. 相似文献
95.
T. von Egidy P. Figuera J. Galin F. Goldenbaum Ye. S. Golubeva M. Hasinoff D. Hilscher A. S. Iljinov U. Jahnke M. Krause W. Kurcewicz X. Ledoux B. Lott L. Maier M. Manrique de Lara G. Pausch L. Pienkowski B. Quednau W. Schott W. U. Schröder J. Tõke 《The European Physical Journal A - Hadrons and Nuclei》2000,8(2):197-204
Inclusive neutron energy spectra were measured by time of flight using 1.22 GeV antiprotons from LEAR, CERN, as projectiles
and targets from natural Al, Cu, Ag, Ho, Ta, Au, Pb, Bi, U. The sum of two Maxwellian distributions was fitted to the spectra
obtained at several forward and backward angles yielding neutron multiplicities Mi and slope or temperature parameters T
i for the low-energy (evaporative, i=1) and high-energy (pre-equilibrium,i=2) parts, respectively. M
1 increases with A, proportional to the nuclear volume, and M
2 is growing with A
, proportional to the nuclear radius. The T parameters are nearly independent of A. The results are compared with previous multiplicity measurements with a neutron detector, intranuclear cascade calculations and neutron spectra from stopped antiproton annihilation on nuclei. With
the measured proton spectra also the ratio of emitted neutrons to protons was determined for Au.
Received: 25 February 2000 / Accepted: 19 May 2000 相似文献
96.
Kõta Yoshioka 《Communications in Mathematical Physics》1999,205(3):501-517
Recently, Minahan, Nemeschansky, Vafa and Warner computed partition functions for N = 4 topological Yang–Mills theory on rational
elliptic surfaces. In particular they computed generating functions of Euler characteristics of SU(2)-instanton moduli spaces. In mathematics, they are expected to coincide with those of Gieseker compactifications. In this
paper, we compute Euler characteristics of these spaces and show that our results coincide with theirs. We also check the
modular property of Z
SU
(2) and Z
SO
(3) conjectured by Vafa and Witten.
Received: 8 June 1998 / Accepted: 1 February 1999 相似文献
97.
J. Rams N.V. Sochinskii V. Munõz J.M. Cabrera 《Applied Physics A: Materials Science & Processing》2000,71(3):277-279
CdTe epilayers have been grown by vapor phase epitaxy (VPE) on glass, MgO, sapphire, LiNbO3 and mica substrates. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show the good structural quality
of the epilayers. In these epilayers, a few optical modes were excited with a 1.33-μm laser. The measured propagation losses
were in the range between 5 dB/cm and less than 0.5 dB/cm. From dark-mode m-lines, the epilayer thickness was found to be
in the 1–3 μm range, in good accord with that obtained by SEM measurements. The refractive index obtained from the fitting
is also in good accord with that of bulk CdTe.
Received: 7 October 1999 / Accepted: 13 March 2000 / Published online: 5 July 2000 相似文献
98.
99.
We report theoretical results on the magnetic behavior of free standing nanowires of Ti. Four different structures of Ti nanowires-linear, ladder, dimerized, and zigzag-with nonmagnetic, ferromagnetic, and anti-ferromagnetic configurations were considered. Exploration of magnetism in these atomic chains leads to ferromagnetic behavior for all the structures: zigzag structure shows almost degenerate ferromagnetic and anti-ferromagnetic states though. The zigzag structure of Ti nanowires is favored of all for low values of nearest neighbor distances, whereas the dimerized structure is favored at larger atomic separations. Our work helps to resolve the controversy in the predicted ground state magnetic nature of zigzag chains of Ti as reported in recent previous works. The maximum value of magnetic moment (0.93 μB/atom) occurs in the ladder chains while the zigzag chains show the minimum value (0.17 μB/atom). Interestingly, all the structures in the magnetic configuration show metastable state except the dimerized structure. Ferromagnetic dimerized nanowires seem to be a potential candidate for use in spintronics. The projected density of states shows that dx2−y2 and dxy bands play a leading role in magnetism of linear and ladder structures, whereas there is no outstanding contribution from a particular d-orbital for zigzag and dimerized nanowires. The charge density plots suggest that linear and zigzag structures have metallic bonding whereas covalent bonding is predominant in the dimerized and ladder structures. The estimated diameters for the favored ferromagnetic configuration of these ultrathin nanowires lie in the range 1.9-3.4 Å and indicate the instability of the ladder structure, as also projected by the relative cohesive energy and relative break force values. 相似文献
100.
Anders Lindfors Anu Heikkilä Jussi Kaurola Tapani Koskela Kaisa Lakkala 《Photochemistry and photobiology》2009,85(5):1233-1239
UV radiation exerts several effects concerning life on Earth, and spectral information on the prevailing UV radiation conditions is needed in order to study each of these effects. In this paper, we present a method for reconstruction of solar spectral UV irradiances at the Earth's surface. The method, which is a further development of an earlier published method for reconstruction of erythemally weighted UV, relies on radiative transfer simulations, and takes as input (1) the effective cloud optical depth as inferred from pyranometer measurements of global radiation (300–3000 nm); (2) the total ozone column; (3) the surface albedo as estimated from measurements of snow depth; (4) the total water vapor column; and (5) the altitude of the location. Reconstructed daily cumulative spectral irradiances at Jokioinen and Sodankylä in Finland are, in general, in good agreement with measurements. The mean percentage difference, for instance, is mostly within ±8%, and the root mean square of the percentage difference is around 10% or below for wavelengths over 310 nm and daily minimum solar zenith angles (SZA) less than 70°. In this study, we used pseudospherical radiative transfer simulations, which were shown to improve the performance of our method under large SZA (low Sun). 相似文献