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排序方式: 共有502条查询结果,搜索用时 15 毫秒
91.
92.
Ivana Tatárová René Fáber Renaud Denoyel Milan Polakovič 《Journal of chromatography. A》2009,1216(6):941-947
The quantitative characterization of pore structure of Sartobind Q, a strongly basic membrane anion exchanger that is formed by cross-linked cellulose support and a hydrogel layer on its pore surface, was made combining the results obtained by several experimental techniques: liquid impregnation, batch size-exclusion, inverse size-exclusion chromatography, and permeability. Mercury intrusion and nitrogen sorption porosimetry were carried out for a dry cellulose support membrane in order to get additional information for building a model of the bimodal pore structure. The model incorporated the distribution of the total pore volume between transport and gel-layer pores and the partitioning of solutes of different molecular weights was expressed through the cylindrical pore model for the transport pores and random plane model for the gel layer. The effect of composition of liquid phase on the pore structure was investigated in redistilled water, phosphate and Tris–HCl buffers containing up to 1 M NaCl. Evident differences in the bimodal pore structure were observed here when both the specific volume and size of the hydrogel layer pores significantly decreased with the ionic strength of liquid phase. 相似文献
93.
Renaud Lavalley Gustav Amberg Henrik Alfredsson 《European Journal of Mechanics - B/Fluids》2001,20(6):771
The present work investigates thermocapillary flow in a cylindrical configuration using large Prandtl number liquids. The flow is studied using coordinated simulations and experimental optical methods such as PIV and flow visualization. In this way, properties of the oscillatory state can be obtained in great detail. Considerable attention is given to the search for the parameters influencing the onset of the instability. It is found that the onset of oscillations can be correlated using a thermocapillary Reynolds number. The oscillations take the form of a standing wave close to the onset, which is replaced by a travelling wave for stronger forcing. The selection of azimuthal wave number of the oscillatory mode is determined from geometrical parameters, and resembles the wave number selection in vortex ring instabilities. Throughout we obtain good agreement between experiments and simulations using a mathematical model with an undeformed adiabatic free surface. 相似文献
94.
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
95.
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
96.
97.
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
98.
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
99.
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
100.
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