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61.
Berquier Jean-Marc Nael Pascal Jupille Jacques Jacquiod Catherine 《Journal of Sol-Gel Science and Technology》2000,19(1-3):83-87
Fourier Transform Infrared transmission spectroscopy is used to characterize surfactant-templated silica films on glass. The calcination process is followed in situ and evidence for the removal of the surfactant along the Hoffman reaction is given. Once calcined, the surface of the pores of the mesoporous films is proven by deuteration experiment to be hydroxylated. Bands are attributed to isolated and hydrogen-bonded silanols. Silylation reaction with hexamethyldisilazane only occurs with isolated silanol groups. 相似文献
62.
63.
Sabine Devautour‐Vinot Eriyakkadan S. Sanil Amine Geneste Vanessa Ortiz Pascal G. Yot Jong‐San Chang Guillaume Maurin 《化学:亚洲杂志》2019,14(20):3561-3565
Post‐synthesis modification of MIL‐101(Cr)‐NO2 was explored in order to decorate the organic backbone by propyl‐sulfonic groups, with the aim to incorporate mobile and acidic protons for solid‐state proton electrolyte applications. The resulting solid switched from insulating towards proton superconductive behavior under humidity, while the conductivity recorded at 363 K and 95 % relative humidity reached 4.8×10?3 S cm?1. Propitiously, the impregnation of the material by strong acidic molecules (H2SO4) further boosted the proton conductivity performances up to the remarkable σ value of 1.3×10?1 S cm?1 at 363 K/95 % RH, which reaches the performances of the best proton conductive MOF reported so far. 相似文献
64.
Phenyliodine(III) bis(trifluoroacetate) (PIFA) in conjunction with a Lewis acid promotes C-C coupling of Bodipy monomers leading to mixtures of various oligomers. When a single position is blocked with an iodo or phenyl group, formation of the dimer is favored. These dimers display two successive oxidation and two reduction waves separated on average by 260 and 130 mV, respectively, corresponding to each Bodipy subunit. 相似文献
65.
First quasi-classical trajectory calculations have been carried out for the S((3)P) + OH(X?(2)Π) → SO(X?(3)Σ(-)) + H((2)S) reaction on an ab initio global potential energy surface for the ground electronic state, X?(2)A', of HSO. Cross sections, computed for collision energies up to 1 eV, show no energy threshold and decrease with the increasing collision energy. Rate constants have been calculated in the 5-500 K temperature range. The thermal rate constant is in good agreement with approximate quantum results, while a disagreement is found at 298 K with the experimental data. Product energy distributions have also been reported at four collision energies from 0.001 to 0.5 eV. The shapes of the rovibrational and angular distributions suggest the formation of an intermediate complex that is more and more long-lived as the collision energy increases. 相似文献
66.
[reaction: see text] The cobalt-catalyzed hydrohydrazination reaction of dienes and enynes is presented. Allylic and propargylic hydrazines were obtained in synthetically useful yields (allylic amines, 60-90%; propargylic amines, 47-83%) and good chemo- and regioselectivity. 相似文献
67.
Layer-by-layer (LbL) thin film assembly occurs via the alternate adsorption of positively and negatively charged macromolecular species. We investigate here the control of LbL film growth through the electric potential of the underlying substrate. We employ optical waveguide lightmode spectroscopy (OWLS) to obtain in situ kinetic measurements of poly(allylamine hydrochloride)/poly(sodium 4-styrenesulfonate) (PAH/PSS) and poly(L-lysine)/dextran sulfate (PLL/DXS) multilayer film formation in the presence of an applied voltage difference (deltaV) between the adsorbing substrate, an indium tin oxide- (ITO-) coated waveguiding sensor chip, and a parallel platinum counterelectrode. We find initial layer adsorption to be significantly enhanced by an applied potential for both polyelectrolyte systems: the mass and thickness of (positively charged) PAH and PLL layers on ITO are about 60% and 500% larger, respectively, at deltaV = 2 V than at open circuit potential (OCP), in apparent violation of electrostatics. A kinetic analysis reveals the initial attachment rate constant to decrease with voltage, in agreement with electrostatics. To reconcile these results, we propose a more coiled and loosely bound adsorbed polymer conformation at higher applied potential. Following 10 adsorption steps, the mass and thickness of a PAH/PSS film grown under deltaV = 2 V are about 15% less than those of a comparable film grown under OCP, reflecting a lower degree of complexation between adsorbing polyanions and more highly coiled adsorbed polycations. Following 14 adsorption steps, the mass and thickness of a PLL/DXS film grown under deltaV = 2 V are about 70% greater than those of a comparable film grown under OCP, reflecting the increased charge overcompensation in the initial layer. We find the scaling of film mass () with the number of adsorption steps (n) to be linear in the PAH/PSS system and exponential (i.e., approximately eyn) in the PLL/DXS system, irrespective of applied voltage. We observe to decrease with applied voltage and to exhibit a crossover to a smaller value around n = 5. Extrapolation reveals PLL/DXS multilayer films to be suppressed by increased voltage in the limit of large n: the mass of films grown at OCP and deltaV = 1 V would surpass that of a film grown under deltaV = 2 V at about the 23rd and 18th adsorption steps, respectively. The formation kinetics of PLL/DXS, but not PAH/PSS, change qualitatively under voltage: PLL adsorption is slow to reach a plateau, possibly due to the formation of secondary structure, and a decrease in film mass occurs toward the end of each DXS adsorption step, suggesting spontaneous removal of some PLL/DXS complexes from the film. 相似文献
68.
Emmanuelle Lipka Sa?d Yous Christophe Furman Pascal Carato Carole Deghaye Jean-Paul Bonte Claude Vaccher 《Chromatographia》2012,75(7-8):337-345
In the present study, baseline separation of the enantiomers of 16 β-carboline derivatives was successfully achieved using both capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) techniques in short run times (<15?min) and thus permit the determination of enantiomeric excess. In HPLC methodology, cellulose chiral stationary phase (Chiralcel OD-H) was used with a binary mobile phase constituted of n-hexane/ethanol 85/15 leading to a resolution factor of 12.6 in 15?min. Preparative HPLC allowed to obtain pure enantiomers of two compounds. In CE, chiral selectivity was developed with an in-capillary stacking strategy using anionic (highly sulfated-γ) cyclodextrins 5% (w/v) as chiral selectors and a 60?mM phosphate buffer (pH 2.5) resulting in a resolution of 10.26 in 14?min of analysis. The analytical characteristics of the two developed methods were studied in terms of repeatability, limits of detection and limits of quantification showing their suitability to be extended to all the other molecules. 相似文献
69.
Direct electrochemical determination of arsenate (AsV) in neutral pH waters is considered impossible due to electro-inactivity of AsV. AsIII on the other hand is readily plated as As0 on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of AsV to AsIII was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to MnII. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of AsV in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (∼1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of −1.3 V. Deposition of As0 from dissolved AsV caused elemental Mn to be re-oxidised to MnII in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited AsV is subsequently quantified using an ASV scan. AsIII interferes and should be quantified separately at a more positive deposition potential of −0.9 V. Combined inorganic As is quantified after oxidation of AsIII to AsV using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM AsV using a deposition time of 180 s. 相似文献
70.
Pascal Salaün Kristopher B. Gibbon-Walsh Georgina M.S. Alves Helena M.V.M. Soares Constant M.G. van den Berg 《Analytica chimica acta》2012
The oxidation potentials of As0/AsIII and Sb0/SbIII on the gold electrode are very close to each other due to their similar chemistry. Arsenic concentration in seawater is low (10–20 nM), Sb occurring at ∼0.1 time that of As. Methods are shown here for the electroanalytical speciation of inorganic arsenic and inorganic antimony in seawater using a solid gold microwire electrode. Anodic stripping voltammetry (ASV) and chronopotentiometry (ASC) are used at pH ≤ 2 and pH 8, using a vibrating gold microwire electrode. Under vibrations, the diffusion layer size at a 5 μm diameter wire is 0.7 μm. The detection limits for the AsIII and SbIII are below 0.1 nM using 2 min and 10 min deposition times respectively. AsIII and SbIII can be determined in acidic conditions (after addition of hydrazine) or at neutral pH. In the latter case, oxidation of As0 to AsIII was found to proceed through a transient AsIII species. Adsorption of this species on the gold electrode at potentials where SbIII diffused away is used for selective deposition of AsIII. Addition of EDTA removes the interfering effect of manganese when analysing AsIII. Imposition of a desorption step for SbIII analysis is required. Total inorganic arsenic (iAs = AsV + AsIII) can be determined without interference from Sb nor mono-methyl arsenious acid (MMA) at 1.6 < pH < 2 using Edep = −1 V. Total inorganic antimony (iSb = SbV + SbIII) is determined at pH 1 using Edep = −1.8 V without interference by As. 相似文献