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61.
del Carmen Fernández-Alonso M Cañada FJ Jiménez-Barbero J Cuevas G 《Journal of the American Chemical Society》2005,127(20):7379-7386
The existence of stabilizing carbohydrate-aromatic interactions is demonstrated from both the theoretical and experimental viewpoints. The geometry of experimentally based galactose-lectin complexes has been properly accounted for by using a MP2/6-31G(d,p) level of theory and by considering a counterpoise correction during optimization. In this case, the stabilizing interaction energy of the fucose-benzene complex amounts to 3.0 kcal/mol. The theoretical results obtained herein indicate that the carbohydrate-aromatic interactions are stabilizing interactions with an important dispersive component and that electronic density between the sugar hydrogens and the aromatic ring indeed exists, thus giving rise to three so-called nonconventional hydrogen bonds. Experimental evidence of the intrinsic tendency of aromatic moieties to interact with certain sugars has also been shown by simple NMR experiments in water solution. Benzene and phenol specifically interact with the clusters of C-H bonds of the alpha face of methyl beta-galactoside, without requiring the well-defined three-dimensional shape provided by a protein receptor, therefore resembling the molecular recognition features that are frequently observed in many carbohydrate-protein complexes. 相似文献
62.
L. Gerardo Zepeda Eleuterio Burgueño‐Tapia Nury Pérez‐Hernández Gabriel Cuevas Pedro Joseph‐Nathan 《Magnetic resonance in chemistry : MRC》2013,51(4):245-250
Complete assignment of the 1H NMR chemical shift and coupling constant values of perezone (1), O‐methylperezone (2) and 6‐hydroxyperezone (3) was carried out by total‐line‐shape‐fitting calculations using the PERCH iterative spectra analysis software (PERCH Solutions Ltd., Kuopio, Finland). The resulting simulated spectra for the three compounds showed strong similarity to their corresponding experimental spectra. Particularly, all vicinal, allylic and homoallylic coupling constant values for the side chain of the three compounds were very similar, thus revealing that the conformation of these three molecules in solution is indeed almost identical. This fact is in agreement with extended side chain conformations over folded chain conformations because 1, 2 and 3 undergo completely different intramolecular cycloaddition reactions. In addition, results of double pulsed field gradient spin echo NOESY 1D experiments performed on perezone (1) were unable to provide evidence for folded conformers. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
63.
We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk “poor conductors” in which Fermi energy EF is located in the region of localized states not so far from the Anderson mobility edge Ec. We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model.Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems.We identify three distinct phases: ‘critical’ superconductive state formed at EF = Ec, superconducting state with a strong pseudo-gap, realized due to pairing of weakly localized electrons and insulating state realized at EF still deeper inside a localized band. The ‘critical’ superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gapped state is the presence of two independent energy scales: superconducting gap Δ, that is due to many-body correlations and a new “pseudo-gap” energy scale ΔP which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive Tc. Two gap nature of the pseudo-gapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudo-gapped superconducting state demonstrates anomalous behavior of the optical spectral weight. The insulating state is realized due to the presence of local pairing gap but without superconducting correlations; it is characterized by a hard insulating gap in the density of single electrons and by purely activated low-temperature resistivity ln R(T) ∼ 1/T.Based on these results we propose a new “pseudo-spin” scenario of superconductor-insulator transition and argue that it is realized in a particular class of disordered superconducting films. We conclude by the discussion of the experimental predictions of the theory and the theoretical issues that remain unsolved. 相似文献
64.
65.
Gracia C Isidro-Llobet A Cruz LJ Acosta GA Alvarez M Cuevas C Giralt E Albericio F 《The Journal of organic chemistry》2006,71(19):7196-7204
Kahalalide compounds are peptides that are isolated from a Hawaiian herbivorous marine species of mollusc, Elysia rufescens, and its diet, the green alga Bryopsis sp. Kahalalide F and its synthetic analogues are the most promising compounds of the Kahalalide family because they show antitumoral activity. Linear solid-phase syntheses of Kahalalide F have been reported. Here we describe several new improved synthetic routes based on convergent approaches with distinct orthogonal protection schemes for the preparation of Kahaladide analogues. These strategies allow a better control and characterization of the intermediates because more reactions are performed in solution. 相似文献
66.
The crystal structures of the hydrides of austenitic and martensitic Ti0.64Zr0.36Ni alloy have been investigated by conjoint X-ray diffraction (XRD)-neutron diffraction (ND) analysis. Austenitic Ti0.64Zr0.36Ni alloy with cubic CsCl-type structure preserves its metal sublattice structure after deuteration. It forms a Ti0.64Zr0.36NiD1.5 deuteride with D-atoms occupying half of the octahedrally coordinated 3d sites. On the contrary, the monoclinic TiNi-type structure of martensitic Ti0.64Zr0.36Ni alloy is modified after deuterium absorption. At and , two deuterides coexist with orthorhombic CrB-type structure for the metal sublattice and compositions Ti0.64Zr0.36NiD (β-deuteride) and Ti0.64Zr0.36NiD2.6 (γ-deuteride). For the β-monodeuteride, deuterium atoms are tetrahedrally coordinated by (Ti,Zr) atoms. For the γ-deuteride, D-atoms fully occupy tetrahedrally coordinated (Ti,Zr)3Ni 8f sites and partially occupy pyramidal (Ti,Zr)3Ni2 4c sites. At higher pressures, deuterium solution occurs in the γ-phase with a partial occupancy of octahedrally coordinated (Ti,Zr)2Ni4 4a sites. 相似文献
67.
Gómez J García-Herbosa G Cuevas JV Arnaiz A Carbayo A Muñoz A Falvello L Fanwick PE 《Inorganic chemistry》2006,45(6):2483-2493
Coordination of N,N' bidentate ligands aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N 1 (Ar = 4-CH3-C6H4, 1a; 4-CH3O-C6H4, 1b; 2,6-(CH3)2-C6H3, 1c; 4-CF3-C6H4, 1d) to the moieties [Ru(bipy)2]2+, [Ru(eta5-C5H5)L]+ (L = CH3CN, CO), or [Ru(eta6-arene)Cl]2+ (arene = benzene, p-cymene) occurs under diastereoselective or diastereospecific conditions. Detailed stereochemical analysis of the new complexes is included. The coordination of these secondary amine ligands activates their oxidation to imines by molecular oxygen in a base-catalyzed reaction and hydrogen peroxide was detected as byproduct. The amine-to-imine oxidation was also observed under the experimental conditions of cyclic voltammetry measurements. Deprotonation of the coordinated amine ligands afforded isolatable amido complexes only for the ligand (1-methyl-1-pyridin-2-yl-ethyl)-p-tolyl-amine, 1e, which doesn't contain hydrogen atoms in a beta position relative to the N-H bond. The structures of [Ru(2,2'-bipyridine)2(1b)](PF6)2, 2b; [Ru(2,2'-bipyridine)(2)(1c)](PF6)2, 2c; trans-[RuCl2(COD)(1a)], 3; and [RuCl2(eta6-C6H6)(1a)]PF6, 4a, have been confirmed by X-ray diffraction studies. 相似文献
68.
[structure: see text]. The synthesis of two tamandarin B analogues in which the N,O-Me2Tyr5 unit was replaced by N-Me-phenylalanine (N-MePhe5) and (S)-2-(methylamino)-3-(naphthalen-2-yl)propanoic acid (N-MeNaphth5) is described. The choice of the macrocyclization site was crucial to achieve satisfactory macrolactamization. Coupling between norstatine (Nst1) and threonine (Thr6) afforded only a 15% yield, while lactamization between proline (Pro4) and the aromatic moiety could be achieved in 65% yield. 相似文献
69.
Weighted pseudo-almost periodic solutions of a class of semilinear fractional differential equations
Ravi P. Agarwal Bruno de Andrade Claudio Cuevas 《Nonlinear Analysis: Real World Applications》2010,11(5):3532-3554
We study the existence and uniqueness of a weighted pseudo-almost periodic (mild) solution to the semilinear fractional equation , , where is a linear operator of sectorial negative type. This article also deals with the existence of these types of solutions to abstract partial evolution equations. 相似文献
70.
Gloria Ruiz-Gómez Andrés Francesch Carmen Cuevas Manuel Serrano-Ruiz María José Iglesias Fernando López-Ortiz 《Tetrahedron》2012,68(4):995-1004
The dearomatizing anionic cyclization of N-alkyl-N-benzyldi(1-naphthyl)phosphinamide 1d followed by trapping with a series of carbonyl reagents and α,β-unsaturated ketones under optimized conditions provided new tetrahydro-1H-naphtho[1,2-c][1,2]-azaphosphole 1-oxides from moderate to high yields and diastereoselectivities. In addition, two doubly dearomatized compounds as a result of double dearomatization on the two naphthalene rings of 1d have been isolated at first time. Three functionalized azaphospholes have been evaluated on three different human tumor cell lines showing growth inhibition factors (GI50) at a micromolar scale. One of these heterocycles has also shown cytostatic properties. 相似文献