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151.
Cámpora J del Mar Conejo M Reyes ML Mereiter K Passaglia E 《Chemical communications (Cambridge, England)》2003,(1):78-79
A simple procedure for the preparation of cationic arene complexes of Ni(II) of composition [Ni(eta 6-ArX)(eta 3-C3H5)]+[BAr'4]- (X = OH, H) is reported. These compounds are shown to behave as highly active catalysts for the polymerization of 1,3-butadiene and styrene. 相似文献
152.
This work describes the conditions, in terms of dimensions and geometry, to guide a dc glow discharge preferentially through a microchannel in simple networks. Two- and three-channel microfluidic structures were studied. A preference towards a wider channel, in a two-channel network, was observed when the difference in width was at least 18% and the length was at least 10 mm. In a three-channel structure, a change in glow discharge intensity was observed when the network was downscaled from a pathlength of 2 to 0.5 cm. While the intensity within the path with fewer turns decreased with a reduction in size, the intensity of the path with greater number of turns increased. 相似文献
153.
M. Soledad Ureta-Zañartu Claudia Yáñez Gloria Reyes José Ramón Gancedo José F. Marco 《Journal of Solid State Electrochemistry》1998,2(3):191-197
The activity of Pt-Ir deposits on titanium for the reduction of the nitrate ion in 0.5 M perchloric acid was studied. The
electrodes were characterized by SEM-EDAX, XPS and cyclic voltammetry. The activity of the electrodes for the nitrate reduction
depended on the Pt-Ir ratio. Repetitive cyclic voltammograms produced an enrichment of the electrode surface with Ir and a
decrease of the catalytic activity. A synergistic effect in the electrodes with low iridium content is discussed.
Received: 2 June 1997 / Accepted: 28 August 1997 相似文献
154.
Alonso-Lebrero JL Domínguez-Jiménez C Tejedor R Brieva A Pivel JP 《Journal of photochemistry and photobiology. B, Biology》2003,70(1):31-37
The effect of a hydrophilic extract of the fern Polypodium leucotomos (PLE) has been investigated in terms of photoprotection against UV-induced cell damage. PLE efficiently preserved human fibroblast survival and restored their proliferative capability when the cells were exposed to UVA light. This effect was specific and dose-dependent. Photoprotection was not restricted to fibroblasts, as demonstrated by its effect on survival and proliferation of the human keratinocyte cell line HaCat. Finally, treatment of the cells with PLE prevented UV-induced morphological changes in human fibroblasts, namely disorganisation of F-actin-based cytoskeletal structures, coalescence of the tubulin cytoskeleton and mislocalization of adhesion molecules such as cadherins and integrins. Our in vitro results demonstrate the photoprotective effect of PLE on human cells and support its use in the preventive treatment of sunburning and skin pathologies associated with UV-mediated damage. 相似文献
155.
Kar S Sarkar B Ghumaan S Roy D Urbanos FA Fiedler J Sunoj RB Jimenez-Aparicio R Kaim W Lahiri GK 《Inorganic chemistry》2005,44(24):8715-8722
The bis-bidentate bridging function of gbha2- with N,O-/N,O- coordination was observed for the first time in the complex (mu-gbha)[Ru(III)(acac)2]2 (1). Density functional theory calculations of 1 yield a triplet ground state with a large (deltaE > 6000 cm(-1)) singlet-triplet gap. Intermolecular antiferromagnetic coupling was observed (J approximately -5.3 cm(-1)) for the solid. Complex 1 undergoes two one-electron reduction and two one-electron oxidation steps; the five redox forms [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2) were characterized by UV-vis-NIR spectroelectrochemistry (NIR = near infrared). The paramagnetic intermediates were also investigated by electron paramagnetic resonance (EPR) spectroscopy. The monoanion with a comproportionation constant K(c) of 2.7 x 10(8) does not exhibit an NIR band for a Ru(III)/Ru(II) mixed-valent situation; it is best described as a 1,4-diazabutadiene radical anion containing ligand gbha*3-, which binds two ruthenium(III) centers. A Ru(III)-type EPR spectrum with g1 = 2.27, g2 = 2.21, and g3 = 1.73 is observed as a result of antiferromagnetic coupling between one Ru(III) and the ligand radical. The EPR-active monocation (K(c) = 1.7 x 10(6)) exhibits a broad (deltanu(1/2) = 2600 cm(-1)) intervalence charge-transfer band at 1800 nm, indicating a valence-averaged (Ru3.5)2 formulation (class III) with a tendency toward class II (borderline situation). 相似文献
156.
Gloria Borda Hugo Rojas Julie Murcia J. L. G. Fierro Patricio Reyes Marcelo Oportus 《Reaction Kinetics and Catalysis Letters》2007,92(2):369-376
Hydrogenation of citral over Ir supported on SiO2, Nb2O5 and Ir/Nb2O5-SiO2 catalysts reduced at 473 K (LT) and 773 K (HT) was studied. High selectivity to unsaturated alcohol was found, the main reaction
products being geraniol and nerol. The LT catalysts show higher conversion levels, the one with a higher Nb content displays
highest conversion. 相似文献
157.
C. R. Apesteguía S. M. Trevizán T. F. Garetto J. F. Plaza de los Reyes J. M. Parera 《Reaction Kinetics and Catalysis Letters》1982,20(1-2):1-6
Chemisorption of H2S on Al2O3, Al2O3–Cl and Pt/Al2O3–Cl has been studied by gravimetry and IR spectroscopy. The influence of the amount of Cl on the H2S adsorption equilibrium value and the nature of the adsorption sites at low and high coverages are discussed.
H2S Al2O3, Al2O3–Cl Pt/Al2O3–Cl . Cl H2S, .相似文献
158.
Summary Pt/SiO2 and Pt-Fe/SiO2 catalysts having a Pt loading ranging from 0.5 to 3.0 wt.% and a fixed amount of Fe in the bimetallic series, 1.0 wt.% have
been prepared by the impregnation procedure, followed by calcinations and reduction in H2 flow at 773 K. The samples were characterized by N2 adsorption at 77 K, H2 chemisorption at 298 K, TEM, TPR and XPS. The hydrogenation of citral at 363 K and 8.3 bar over a series of Pt/SiO2 and Pt-Fe/SiO2 catalysts was studied. Thus, the selectivity towards the unsaturated alcohol (geraniol + nerol) decreases at high loads of
monometallic Pt. An effect of polarization of the C=O bond due to the presence of Fe3+ species leads to catalysts active and highly selective to the hydrogenation of the carbonyl bond. Characterization results
showed that Pt is present as Pto and Fe mainly asFe3+. 相似文献
159.
Kar S Chanda N Mobin SM Datta A Urbanos FA Puranik VG Jimenez-Aparicio R Lahiri GK 《Inorganic chemistry》2004,43(16):4911-4920
Paramagnetic diruthenium(III) complexes (acac)(2)Ru(III)(mu-OC(2)H(5))(2)Ru(III)(acac)(2) (6) and [(acac)(2)Ru(III)(mu-L)Ru(III)(acac)(2)](ClO(4))(2), [7](ClO(4))(2), were obtained via the reaction of binucleating bridging ligand, N,N,N',N'-tetra(2-pyridyl)-1,4-phenylenediamine [(NC(5)H(4))(2)-N-C(6)H(4)-N-(NC(5)H(4))(2), L] with the monomeric metal precursor unit (acac)(2)Ru(II)(CH(3)CN)(2) in ethanol under aerobic conditions. However, the reaction of L with the metal fragment Ru(II)(bpy)(2)(EtOH)(2)(2+) resulted in the corresponding [(bpy)(2)Ru(II) (mu-L) Ru(II)(bpy)(2)](ClO(4))(4), [8](ClO(4))(4). Crystal structures of L and 6 show that, in each case, the asymmetric unit consists of two independent half-molecules. The Ru-Ru distances in the two crystallographically independent molecules (F and G) of 6 are found to be 2.6448(8) and 2.6515(8) A, respectively. Variable-temperature magnetic studies suggest that the ruthenium(III) centers in 6 and [7](ClO(4))(2) are very weakly antiferromagnetically coupled, having J = -0.45 and -0.63 cm(-)(1), respectively. The g value calculated for 6 by using the van Vleck equation turned out to be only 1.11, whereas for [7](ClO(4))(2), the g value is 2.4, as expected for paramagnetic Ru(III) complexes. The paramagnetic complexes 6 and [7](2+) exhibit rhombic EPR spectra at 77 K in CHCl(3) (g(1) = 2.420, g(2) = 2.192, g(3) = 1.710 for 6 and g(1) = 2.385, g(2) = 2.177, g(3) = 1.753 for [7](2+)). This indicates that 6 must have an intermolecular magnetic interaction, in fact, an antiferromagnetic interaction, along at least one of the crystal axes. This conclusion was supported by ZINDO/1-level calculations. The complexes 6, [7](2+), and [8](4+) display closely spaced Ru(III)/Ru(II) couples with 70, 110, and 80 mV separations in potentials between the successive couples, respectively, implying weak intermetallic electrochemical coupling in their mixed-valent states. The electrochemical stability of the Ru(II) state follows the order: [7](2+) < 6 < [8](4+). The bipyridine derivative [8](4+) exhibits a strong luminescence [quantum yield (phi) = 0.18] at 600 nm in EtOH/MeOH (4:1) glass (at 77 K), with an estimated excited-state lifetime of approximately 10 micros. 相似文献
160.
Gina Pecchi Patricio Reyes M. Graciela Jiliberto T. López J. L. G. Fierro 《Journal of Sol-Gel Science and Technology》2006,37(3):169-174
Platinum-supported catalysts prepared by impregnation of mixed CeO2/Al2O3 and CeO2/ZrO2 oxides using the sol-gel method were characterized and used in the combustion of ethyl acetate. In each series, the effect
of CeO2 loading (3 and 5 wt%) was studied. Characterization data from the studied catalysts (specific area measurements, hydrogen
chemisorption, programmed temperature reduction (TPR), X-ray diffraction (XRD), photoelectron spectra (XPS) and transmission
electron microscopy (TEM)) revealed significant changes in porosity and metal dispersion in each series. The catalytic activity
of the solids, evaluated in the total combustion of ethyl acetate, exhibited a positive effect with the addition of Ce in
the zirconia series whereas no significant changes was observed in the alumina series. 相似文献