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741.
Eleonora Truzzi Lucia Marchetti Stefania Benvenuti Valeria Righi Maria Cecilia Rossi Vito Gallo Davide Bertelli 《Molecules (Basel, Switzerland)》2021,26(18)
Essential oils (EOs) are more and more frequently adulterated due to their wide usage and large profit, for this reason accurate and precise authentication techniques are essential. This work aims at the application of qNMR as a versatile tool for the quantification of vegetable oils potentially usable as adulterants or diluents in EOs. This approach is based on the quantification of both 1H and 13C glycerol backbone signals, which are actually present in each vegetable oil containing triglycerides. For the validation, binary mixtures of rosemary EO and corn oil (0.8–50%) were prepared. To verify the general feasibility of this technique, other different mixtures including lavender, citronella, orange and peanut, almond, sunflower, and soy seed oils were analyzed. The results showed that the efficacy of this approach does not depend on the specific combination of EO and vegetable oil, ensuring its versatility. The method was able to determine the adulterant, with a mean accuracy of 91.81 and 89.77% for calculations made on 1H and 13C spectra, respectively. The high precision and accuracy here observed, make 1H-qNMR competitive with other well-established techniques. Considering the current importance of quality control of EOs to avoid fraudulent practices, this work can be considered pioneering and promising. 相似文献
742.
Laurent Desvillettes François Golse Valeria Ricci 《Journal of statistical physics》2008,131(5):941-967
We propose a mathematical derivation of Brinkman’s force for a cloud of particles immersed in an incompressible viscous fluid.
Specifically, we consider the Stokes or steady Navier-Stokes equations in a bounded domain Ω⊂ℝ3 for the velocity field u of an incompressible fluid with kinematic viscosity ν and density 1. Brinkman’s force consists of a source term 6π
ν
j where j is the current density of the particles, and of a friction term 6π
ν
ρ
u where ρ is the number density of particles. These additional terms in the motion equation for the fluid are obtained from the Stokes
or steady Navier-Stokes equations set in Ω minus the disjoint union of N balls of radius ε=1/N in the large N limit with no-slip boundary condition. The number density ρ and current density j are obtained from the limiting phase space empirical measure
, where x
k
is the center of the k-th ball and v
k
its instantaneous velocity. This can be seen as a generalization of Allaire’s result in [Arch. Ration. Mech. Anal. 113:209–259,
[1991]] who considered the case of periodically distributed x
k
s with v
k
=0, and our proof is based on slightly simpler though similar homogenization arguments. Similar equations are used for describing
the fluid phase in various models for sprays. 相似文献
743.
Clemenza Massimiliano Bonesini Maurizio Carpinelli Massimo Cremonesi Oliviero Fiorini Ettore Gorini Giuseppe Hillier Adrian Ishida Katsu Menegolli Alessandro Mocchiutti Emiliano Oliva Piernicola Prata Marco Rendeli Marco Rignanese Luigi Pio Rossella Massimo Sipala Valeria Soldani Mattia Tortora Ludovico Vacchi Andrea Vallazza Erik 《Journal of Radioanalytical and Nuclear Chemistry》2019,322(3):1357-1363
Journal of Radioanalytical and Nuclear Chemistry - The implementation in the RIKEN-RAL negative muons facility of a new muon beamline monitoring and novel digital data acquisition system for gamma... 相似文献
744.
Yannick T. Guntern James R. Pankhurst Jan Vvra Mounir Mensi Valeria Mantella Pascal Schouwink Raffaella Buonsanti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(36):12762-12769
The tunable chemistry linked to the organic/inorganic components in colloidal nanocrystals (NCs) and metal–organic frameworks (MOFs) offers a rich playground to advance the fundamental understanding of materials design for various applications. Herein, we combine these two classes of materials by synthesizing NC/MOF hybrids comprising Ag NCs that are in intimate contact with Al‐PMOF ([Al2(OH)2(TCPP)]) (tetrakis(4‐carboxyphenyl)porphyrin (TCPP)), to form Ag@Al‐PMOF. In our hybrids, the NCs are embedded in the MOF while still preserving electrical contact with a conductive substrate. This key feature allows the investigation of the Ag@Al‐PMOFs as electrocatalysts for the CO2 reduction reaction (CO2RR). We show that the pristine interface between the NCs and the MOFs accounts for electronic changes in the Ag, which suppress the hydrogen evolution reaction (HER) and promote the CO2RR. We also demonstrate a minor contribution of mass‐transfer effects imposed by the porous MOF layer under the chosen testing conditions. Furthermore, we find an increased morphological stability of the Ag NCs when combined with the Al‐PMOF. The synthesis method is general and applicable to other metal NCs, thus revealing a new way to think about rationally tailored electrocatalytic materials to steer selectivity and improve stability. 相似文献
745.
Walysson Ferreira de Paiva Ingredy Bastos Braga João Vitor de Assis Sandra Milena Bonilla Castañeda Ángel Gabriel Sathicq Valeria Palermo Gustavo Pablo Romanelli Ricardo Natalino Marcio José da Silva Felipe Terra Martins Gustavo Senra Gonçalves de Carvalho Giovanni Wilson Amarante Sergio Antonio Fernandes 《Tetrahedron》2019,75(27):3740-3750
The application of immobilizing calixarene onto the surface of silica using a sol-gel method, as an efficient heterogeneous catalyst (CX4SO3HSi(n)) for multicomponent Povarov reaction has been described. Catalytic activity of the CX4SO3HSi(n) for the synthesis of julolidines under greener and environmentally benign conditions in simple and efficient method was explored. Notably, only 0.5 mol% of the catalyst is sufficient to catalyze the Povarov solvent-free reaction under microwave-assistance. Besides, this protocol allows the construction of four new C–C bonds and two C–N bonds in a single step. To the best of our knowledge, this consists the first silica support calix[4]arene as a heterogeneous catalyst for multicomponent synthesis of julolidines. 相似文献
746.
Barra Valeria Afkhami Shahriar Kondic Lou 《The European physical journal. E, Soft matter》2019,42(1):1-23
The European Physical Journal E - The phenomena on the capillarity-driven migration of small objects are full of interest for both scientific and engineering communities, and a critical review is... 相似文献
747.
Stefano Lanciotti Mariangela Bellusci Iolanda Francolini Valeria Ruggeri Antonella Piozzi 《Macromolecular Symposia》2006,234(1):211-216
Vinyl polymers such as poly(ethylene-co-vinyl alcohol) (EVAL) and polyallylamine (PALA) both commercially available were chemically modified by introduction of carboxylic and sulfonate groups to obtain polymeric materials with improved haemocompatibility. The introduction of carboxyl groups was carried out by reaction of EVAL's hydroxy groups with acrylonitrile followed by basic hydrolysis of CN groups. Amino groups of PALA were transformed into sulfonate groups by reaction with pyridine-SO3 complex. Influence of reagents molar ratio, temperature and reaction time on the carboxylation degree was evaluated. In particular, yields of 86% (EVAL-CN 0.52) and 30% (EVALCOOH 0.16) were obtained for the cyanoethylation and the hydrolysis reaction of the CN groups, respectively, whereas a sulfonation of 24% of the PALA amino groups was found. The functionalised polymers were characterized by physicochemical measurements. Preliminary biological tests proved the importance of strong acidic groups on the anticoagulant properties of the polymeric materials. 相似文献
748.
Degli Esposti A Fattori V Sabatini C Casalbore-Miceli G Marconi G 《Physical chemistry chemical physics : PCCP》2005,7(21):3738-3743
A series of triphenylamine (TPA) based compounds is investigated by means of density functional theory and cyclic voltammetry. Using the Nicholson's formalism, the measured deltaE(p) are correlated with B3LYP/6-31G* calculated reorganisation energies (lambda), elucidating the trend followed by the electron transfer rate of these compounds. Besides the direct dependency upon the dimension of the cationic fragment contributing to the hole stabilisation, the lambdas are tuned by the symmetry local to the TPA units, as evidenced by the structural relaxation of the cations. MDTAB shows the interesting combination of low ionisation potential (IP) and low lambda. This can make this compound interesting for practical applications in organic light emitting diode (OLEDs) devices, due to the direct correlation of the IP and lambda with the hole transfer efficiency to the anode, along with the hole mobility. 相似文献
749.
This paper describes the synthesis and use of beta-hydroxylamino imides derived from D-glyceraldehyde possessing a number of reactive sites that operate synergistically or alternatively to bring about highly regio- and diastereoselective transformations to give an optically pure aziridine-2-imide, a dihydro pyrimidine-2,4-dione, or a lactone. Both the syntheses, via the diastereoselective 1,4-conjugate addition of O-benzyl hydroxylamine to alpha,beta-unsaturated imides, and transformations can be simply tuned by choosing between different Lewis acids. 相似文献
750.
The pK(a) values of ionisation of a set of phenols ortho, meta and para substituted are studied by spectrophotometry and (13)C NMR spectroscopy. A dual substituent analysis of equilibrium and NMR results, according to the Swain and Lupton procedure, is presented. The results of this analysis allow the assignment of the contribution of field and resonance contributions, both on equilibrium constants and chemical shifts. 相似文献