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排序方式: 共有535条查询结果,搜索用时 203 毫秒
101.
Robert J. Messinger Tan Vu Huynh Renaud Bouchet Vincent Sarou-Kanian Michaël Deschamps 《Magnetic resonance in chemistry : MRC》2020,58(11):1118-1129
Magic-angle-spinning (MAS) enhances sensitivity and resolution in solid-state nuclear magnetic resonance (NMR) measurements. MAS is obtained by aerodynamic levitation and drive of a rotor, which results in large centrifugal forces that may affect the physical state of soft materials, such as polymers, and subsequent solid-state NMR measurements. Here, we investigate the effects of MAS on the solid-state NMR measurements of a polymer electrolyte for lithium-ion battery applications, poly(ethylene oxide) (PEO) doped with the lithium salt LiTFSI. We show that MAS induces local chain ordering, which manifests itself as characteristic lineshapes with doublet-like splittings in subsequent solid-state 1 H, 7 Li, and 19 F static NMR spectra characterizing the PEO chains and solvated ions. MAS results in distributions of stresses and hence local chain orientations within the rotor, yielding distributions in the local magnetic susceptibility tensor that give rise to the observed NMR anisotropy and lineshapes. The effects of MAS were investigated on solid-state 7 Li and 19 F pulsed-field-gradient (PFG) diffusion and 7Li longitudinal relaxation NMR measurements. Activation energies for ion diffusion were affected modestly by MAS. 7Li longitudinal relaxation rates, which are sensitive to lithium-ion dynamics in the nanosecond regime, were essentially unchanged by MAS. We recommend that NMR researchers studying soft polymeric materials use only the spin rates necessary to achieve the desired enhancements in sensitivity and resolution, as well as acquire static NMR spectra after MAS experiments to reveal any signs of stress-induced local ordering. 相似文献
102.
Renaud Belin Monique Tillard Laure Monconduit 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):267-268
In iron tridecazinc, the FeZn13 unit cell contains two Zn12 icosahedra which are Fe‐centred and two Zn2 dumb‐bells coordinated by eight icosahedra. Zn12 icosahedra form chains along the c axis by vertex‐sharing, and are further interlinked through octahedra‐sharing and vertex‐to‐vertex bonds. 相似文献
103.
104.
Johanne Penafiel Laurent Maron Sjoerd Harder 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(1):203-208
Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal–alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca2+. The role of the metal was evaluated by a study using the metal‐free catalysts: [Ph2N−][Me4N+] and [Ph3C−][Me4N+]. These “naked” amides and carbanions can act as catalysts in the conversion of activated double bonds (CO and CN) in the hydroamination of Ar NCO and R NCN R (R=alkyl) by Ph2NH. For the intramolecular hydroamination of unactivated CC bonds in H2CCHCH2CPh2CH2NH2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study. 相似文献
105.
Sharon Curtis Justin Renaud John L. Holmes Paul M. Mayer 《Journal of the American Society for Mass Spectrometry》2010,21(11):1944-1946
A brief search in Sci Finder for oxalic acid and oxalates will reward the researcher with a staggering 129,280 hits. However,
the generation of alkali metal and silver anions via collision-induced dissociation of the metal oxalate anion has not been
previously been reported, though Tian and coworkers recently investigated the dissociation of lithium oxalate [18]. The exothermic
decomposition of alkali metal oxalate anion to carbon dioxide in the collision cell of a triple quadrupole mass spectrometer
leaves no place for the electron to reside, resulting in a double electron-transfer reaction to produce an alkali metal anion.
This reaction is facilitated by the negative electron affinity of carbon dioxide and, as such, the authors believe that metal
oxalates are potentially unique in this respect. The observed dissociation reactions for collision with argon gas (1.7−1.8
× 10−3 mbar) for oxalic acid and various alkali metal oxalates are discussed and summarized. Silver oxalate is also included to
demonstrate the propensity of this system to generate transition-metal anions, as well. 相似文献
106.
A. Zebda L. Renaud M. Cretin F. Pichot C. Innocent R. Ferrigno S. Tingry 《Electrochemistry communications》2009,11(3):592-595
A Y-shaped microfluidic channel is applied for the first time to the construction of a glucose/O2 biofuel cell, based on both laminar flow and biological enzyme strategies. During operation, the fuel and oxidant streams flow parallel at gold electrode surfaces without convective mixing. At the anode, the glucose oxidation is performed by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from an interfering parasite reaction of O2 at the anode and offers the advantage of using different streams of oxidant and fuel for optimal performance of the enzymes. Electrochemical characterizations of the device show the influence of the flow rate on the output potential and current density. The maximum power density delivered by the assembled biofuel cell reached 110 μW cm?2 at 0.3 V with 10 mM glucose at 23 °C. The microfluidic approach reported here demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O2 biofuel cell device. 相似文献
107.
Baruah M Qin W Flors C Hofkens J Vallée RA Beljonne D Van der Auweraer M De Borggraeve WM Boens N 《The journal of physical chemistry. A》2006,110(18):5998-6009
Steady-state and time-resolved fluorescence techniques have been used to study the photophysical properties of the fluorescent BODIPY-derived dye 3-{2-[4-(dimethylamino)phenyl]ethenyl}-4,4-difluoro-8-(4-methoxyphenyl)-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene. This compound has been synthesized via a microwave-assisted condensation of p-N,N-dimethylaminobenzaldehyde with the appropriate 1,3,5,7-tetramethyl substituted borondipyrromethene unit. The fluorescence properties of the dye are strongly solvent dependent: increasing the solvent polarity leads to lower fluorescence quantum yields and lifetimes, and the wavelength of maximum fluorescence emission shifts to the red. The Catalán solvent scales are found to be the most suitable for describing the solvatochromic shifts of the fluorescence emission. These are dominated by polarity/polarizability effects, as confirmed by quantum-chemical calculations performed in the dielectric continuum approximation. Fluorescence decay profiles of the dye can be described by a single-exponential fit in most solvents investigated, while two decay times are found in alcohols. The dye undergoes a reversible protonation-deprotonation reaction in the acidic pH range with a pK(a) of 2.25 in acetonitrile solution. Fluorimetric titrations as a function of pH produce fluorescence emission enhancements at lower pH. The fluorescence excitation spectra show a hypsochromic shift from 600 nm for the neutral amine to 553 nm for the ammonium form, so that ratiometric measurements can be used to determine pK(a). 相似文献
108.
Totally dissipative measures for the shift and conformal σ-finite measures for the stable holonomies
In this paper we investigate some results of ergodic theory with infinite measures for a subshift of finite type. We give
an explicit way to construct σ-finite measures which are quasi-invariant by the stable holonomy and equivalent to the conditional measures of some σ-invariant measure. These σ-invariant measures are totally dissipative, σ-finite but satisfy a Birkhoff Ergodic-like Theorem. The constructions are done for the symbolic case, but can be extended
for uniformly hyperbolic flows or diffeomorphisms. 相似文献
109.
Hania Hebbache Thomas Jerphagnon Christian Bruneau Jean-Luc Renaud 《Journal of organometallic chemistry》2010,695(6):870-874
β-Aminoesters were prepared in two simple steps from β-ketoesters derivatives and primary amines under mild conditions. Their hydrogenation was performed at 50 °C in the presence of several organometallic catalysts under acidic conditions. The new β-N-substituted aminoesters were isolated in moderate to good yields. 相似文献
110.
Céline Perego Renaud Revel Olivier Durupthy Sophie Cassaignon Jean-Pierre Jolivet 《Solid State Sciences》2010,12(6):989-995
TiO2 is a material of great interest for many technological applications among which, as catalyst support. As this specific application requires a good thermal stability of the material, the phase transition between the two most commonly used titania polymorphs, anatase and rutile, has been extensively studied over the past decade. However not much importance has been given to the initial and final particles morphologies. In this study, anatase nanoparticles with an elongated shape were synthesized and their kinetic phase transformation was studied. The thermal treatments were conducted at temperatures ranging from 500 to 700 °C. The morphology evolution and the phase transition were characterized by X-ray diffraction and transmission electron microscopy. The phase transformation kinetics is best described by the interface nucleation models. The values of the measured kinetic parameters are significantly lower than those proposed in the literature for isotropic particles, with an activation energy of Ea = 345 kJ mol?1. The influence of morphology and, as a consequence, the influence of exposed faces on anatase particles, are presented and discussed. 相似文献