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61.
N.K. Vitanov I.P. Jordanov Z.I. Dimitrova 《Communications in Nonlinear Science & Numerical Simulation》2009,14(5):2379-2388
We discuss a nonlinear model of the spatial–time interaction among populations which reproduction and intensity of interaction depend on their spatial density. For the particular case of two populations with constant growth rates and competition coefficients we obtain analytical nonlinear waves of kink kind. The kinks are connected to propagation of the deviations from the stationary densities corresponding to fixed points in the phase space of the population densities. The kinks are coupled, i.e. the changes of the densities of the two populations are synchronous. Coupled kink solutions are obtained also for the general case of variable growth rates and variable coefficients of interactions. 相似文献
62.
Mekenyan O Dimitrov S Dimitrova N Dimitrova G Pavlov T Chankov G Kotov S Vasilev K Vasilev R 《SAR and QSAR in environmental research》2006,17(1):107-120
The role of metabolism in prioritising chemicals according to their potential adverse health effects is extremely important given the fact that innocuous parents can be transformed into toxic metabolites. Our recent efforts in simulating metabolic activation of chemicals are reviewed in this work. The application of metabolic simulators to predict biodegradation (microbial degradation pathways), bioaccumulation (fish liver metabolism), skin sensitisation (skin metabolism), mutagenicity (rat liver S-9 metabolism) are discussed. The ability of OASIS approach to predict metabolism (toxicokinetics) and toxicity (toxicodynamics) of chemicals resulting from their metabolic activation in a single modelling platform is an important advantage of the method. It allows prioritisation of chemicals due to predicted toxicity of their metabolites. 相似文献
63.
Dimitrova Y 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(2):427-437
The vibrational characteristics (vibrational frequencies, infrared intensities and Raman activities) for the hydrogen-bonded system of Vitamin C (L-ascorbic acid) with five water molecules have been predicted using ab initio SCF/6-31G(d,p) calculations and DFT (BLYP) calculations with 6-31G(d,p) and 6-31++G(d,p) basis sets. The changes in the vibrational characteristics from free monomers to a complex have been calculated. The ab initio and BLYP calculations show that the complexation between Vitamin C and five water molecules leads to large red shifts of the stretching vibrations for the monomer bonds involved in the hydrogen bonding and very strong increase in their IR intensity. The predicted frequency shifts for the stretching vibrations from Vitamin C taking part in the hydrogen bonding are up to -508 cm(-1). The magnitude of the wavenumber shifts is indicative of relatively strong OH...H hydrogen-bonded interactions. In the same time the IR intensity and Raman activity of these vibrations increase upon complexation. The IR intensity increases dramatically (up to 12 times) and Raman activity increases up to three times. The ab initio and BLYP calculations show, that the symmetric OH vibrations of water molecules are more sensitive to the complexation. The hydrogen bonding leads to very large red shifts of these vibrations and very strong increase in their IR intensity. The asymmetric OH stretching vibrations of water, free from hydrogen bonding are less sensitive to the complexation than the hydrogen-bonded symmetric OH stretching vibrations. The increases of the IR intensities for these vibrations are lower and red shifts are negligible. 相似文献
64.
Mirjana?Bo?i? Milena?Davidovi? Teodora?L.?Dimitrova Salvador?Miret-Artés ángel?S.?Sanz Antoine?Weis 《Journal of Russian Laser Research》2010,31(2):117-128
We study experimentally and theoretically the influence of light polarization on the interference patterns behind a diffracting
grating. Different states of polarization and configurations are considered. The experiments are analyzed in terms of electromagnetic
energy (EME) flow lines, which can be eventually identified with the paths followed by photons. This gives rise to a novel
trajectory interpretation of the Arago–Fresnel laws for polarized light, which we compare with interpretations based on the
concept of “which-way” (or “which-slit”) information. 相似文献
65.
A new rubidium pentaborate is synthesized under hydrothermal conditions. Its crystal structure is studied by the heavy-atom method without any a priori knowledge of chemical formula. The chemical formula is Rb[B5O6(OH)4] · 0.5H2O, sp. gr. $\bar P1$ , lattice parameters a = 7.679(4) Å, b = 9.253(6) Å, c = 12.053(9) Å, α = 98.55(5)°, β = 106.80(5)°, γ = 91.71°, R = 0.0573, R w = 0.0638, S = 1.07. The anionic part of the structure consists of a chain of fundamental building blocks 5:[4Δ + 1T] built by four B triangles bound to one B tetrahedron, which are common to Na, K, Rb, and Cs pentaborates. This new pentaborate is closely related to the mineral larderellite (NH4)[B5O6(OH)4] · H2O but possesses an original structure, which manifests itself in the different morphology of the new pentaborate and the absence of perfect cleavage. The Dornberger-Schiff OD theory allows one to describe in detail the structural relationships, predict possible hypothetical structures, and write the OD groupoid. 相似文献
66.
S. A. Vinogradova D. Yu. Pushcharovsky A. V. Arakcheeva O. V. Dimitrova 《Crystallography Reports》2002,47(1):24-28
The crystal structure of a newly synthesized compound Na2Ba2[B10O17(OH)2] has been determined (Syntex \(P\bar 1\) diffractometer, MoKα radiation, 1784 crystallographically nonequivalent reflections, anisotropic approximation, R = 1.7%). The parameters of the monoclinic unit cell are a = 11.455(7), b = 6.675(4), c = 9.360(7) Å, β = 93.68(5)°, Z = 2, sp. gr. C2. The structure consists of double pseudohexagonal layers built by BO4-tetrahedra and BO3-triangles forming three-membered rings of two mutually orthogonal orientations. The neighboring layers along the [001] direction are bound by Na-polyhedra and hydrogen bonds with participation of OH groups. The interlayer tunnels along the [100] direction are filled with columns of Ba-polyhedra. The crystallochemical characteristics of a number of synthetic Ba-borates (to which the structure of new decaborate is related) are considered in terms of borate building blocks singled out in the structure. 相似文献
67.
EPR and spectrophotometric study on the products of ligand‐exchange taking place on mixing bis(diethyldiselenocarbamato)copper(II), [Cu(Et2dsc)2], and bis(diethyldithiocarbamato)copper(II), [Cu(Et2dtc)2], solutions is reported. EPR spectra monitored at room temperature for one month period reveal a stable equilibrium among the parents (chromophores CuS4 and CuSe4) and the obtained mixed‐chelate [Cu(Et2dtc)(Et2dsc)] complex (chromophore CuS2Se2) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl4 and CHCl3 two new additional EPR spectra appear attributed to the mixed‐chelate complexes with the chromophores CuSSe3 and CuS3Se which are not observed with electronic spectroscopy. The intensities of all five EPR spectra decrease with the time. It is assumed that the new mixed‐chelates observed in CCl4 and CHCl3 are obtained in a reaction of [Cu(Et2dtc)(Et2dsc)] or [Cu(Et2dtc)2] with the ester of diselenocarbamic acid which is formed in a parallel reaction of [Cu(dsc)2]with CCl4 or CHCl3. 相似文献
68.
B. Galabov P. Bobadova-Parvanova S. Ilieva V. Dimitrova 《Journal of Molecular Structure》2003,630(1-3):101-112
The paper reviews results from computational studies by molecular orbital and density functional theories on several series of hydrogen bonded complexes. These studies aim at quantifying the reactivity of molecules for the complexation process. Excellent linear relationships are found between the electrostatic potential values at the sites of the electron donor and electron accepting atoms and the energy of hydrogen bond formation (ΔE). The series studied are: (a) complexes of R–CHO and R–CN molecules with hydrogen fluoride; (b) complexes of mono-substituted acetylene derivatives with ammonia; (c) (HCN)n hydrogen bonded cluster for n=2–7. All 22 studied complexes of carbonyl and nitrile compounds with hydrogen fluoride fall in the same dependence between the energy of hydrogen bond formation and the electrostatic potential at the atomic site of the carbonyl oxygen and nitrile nitrogen atoms, with linear regression correlation coefficient r=0.979. In the case of complexes of mono-substituted acetylene and diacetylene derivatives with NH3, the correlation coefficient for the dependence between the electrostatic potential at the acidic hydrogen atom and ΔE equals 0.996. For the series of hydrogen bonded (HCN)n clusters, the correlation coefficient for the relationship between the electrostatic potential at the end nitrogen atom and ΔE is r=0.9996. Similarly, the analogous relationship with the electrostatic potential at the end hydrogen atom has a regression coefficient equal to 0.9994. The dependencies found are theoretically substantiated by applying the Morokuma energy decomposition scheme. The results show that the molecular electrostatic potential at atomic sites can be successfully used to predict the ability of molecules to form hydrogen bonds. 相似文献
69.
The dehydrogenation of tetralin on two zeolite catalysts has been studied, the experiments were planned statistically according to the Orthogonal Central Composite Design. In order to determine the influence of coke deposits, the time-on-stream theory of catalyst decay is applied too.
. . .相似文献
70.
New sodium iron orthophosphate NaFe 4 2+ Fe 3 3+ [PO4]6 was synthesized by the hydrothermal method. The crystal structure (sp. gr. $P\bar 1$ ) was established by the heavy-atom method, with the exact chemical formula of the compound being unknown; R hkl = 0.0492, R whkl = 0.0544, S = 0.52. The new compound is analogous to iron phosphate Fe 3 2+ Fe 4 3+ [PO4]6 studied earlier. However, these two compounds differ in the Fe2+ and Fe3+ contents, because Na+ ions in the new compound are located at the centers of symmetry not occupied earlier. 相似文献