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排序方式: 共有674条查询结果,搜索用时 31 毫秒
661.
Nonlinear Dynamics - The paper studies bifurcations and complex dynamics in a class of nonautonomous oscillatory circuits with a flux-controlled memristor and harmonic forcing term. It is first... 相似文献
662.
663.
Dr. Jacopo Perego Dr. Andrea Daolio Dr. Charl X. Bezuidenhout Dr. Sergio Piva Dr. Giacomo Prando Benjamin Costarella Prof. Pietro Carretta Prof. Luciano Marchiò Dr. Dominik Kubicki Prof. Piero Sozzani Prof. Silvia Bracco Prof. Angiolina Comotti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(10):e202317094
Engineering coordinated rotational motion in porous architectures enables the fabrication of molecular machines in solids. A flexible two-fold interpenetrated pillared Metal-Organic Framework precisely organizes fast mobile elements such as bicyclopentane (BCP) (107 Hz regime at 85 K), two distinct pyridyl rotors and E-azo group involved in pedal-like motion. Reciprocal sliding of the two sub-networks, switched by chemical stimuli, modulated the sizes of the channels and finally the overall dynamical machinery. Actually, iodine-vapor adsorption drives a dramatic structural rearrangement, displacing the two distinct subnets in a concerted piston-like motion. Unconventionally, BCP mobility increases, exploring ultra-fast dynamics (107 Hz) at temperatures as low as 44 K, while the pyridyl rotors diverge into a faster and slower dynamical regime by symmetry lowering. Indeed, one pillar ring gained greater rotary freedom as carried by the azo-group in a crank-like motion. A peculiar behavior was stimulated by pressurized CO2, which regulates BCP dynamics upon incremental site occupation. The rotary dynamics is intrinsically coupled to the framework flexibility as demonstrated by complementary experimental evidence (multinuclear solid-state NMR down to very low temperatures, synchrotron radiation XRD, gas sorption) and computational modelling, which helps elucidate the highly sophisticated rotor-structure interplay. 相似文献
664.
A possible application of a novel double-iterated Kalman filter (DIKF) as an algorithm for molecular structure determination is investigated in this work. Unlike traditional optimization algorithms, the DIKF does not exploit experimental nuclear magnetic resonance (NMR) constraints in a penalty function to be minimized but used them to filter the atomic coordinates. Furthermore, it is a nonlinear Bayesian estimator able to handle the uncertainty in the experimental data and in the computed structures, represented as covariance matrices. The algorithm presented applies all constraints simultaneously, in contrast with DIKF algorithms for structure determination found in literature, which apply the constraints one at a time. The performances of both paradigms are tested and compared with those obtained by a commonly used optimization algorithm (based on the conjugate gradient method). Besides providing estimates of the conformational uncertainty directly in the final covariance matrix, DIKF algorithms appear to generate structures with a better stereochemistry and be able to work with realistically imprecise constraints, while time performances are strongly affected by the heavy matricial calculations they require. © 1996 by John Wiley & Sons, Inc. 相似文献
665.
The thermal conductivities of five potassium borosilicate samples which had undergone thermal treatment for different periods of time, were measured between 1 and 10 K. The results showed that, initially, as the particles grow bigger, thermal conductivity decreases until it reaches a minimum corresponding to an average dimension of 900 Å, thereafter increasing. An attempt was made to analyse the results in terms of a resonant scattering theory, which proved to be insufficient. As an alternative, a phenomenological model taking into account Kapitza's resistance was developed. This effect being important mainly during the first stage of the thermal treatment when the boundaries between phases are not yet well defined, it could explain the existence of a minimum of the thermal conductivity. 相似文献
666.
667.
Giacomo Pugliese Dr. Francesco Vaghi Giovanni Lonardi Prof. Giulia Licini Dr. Manuel Orlandi 《European journal of organic chemistry》2023,26(17):e202201492
Co-Salox complexes are suitable catalysts for the reduction of prochiral α,β-unsaturated esters. These ligands can be prepared in a single step from available and inexpensive materials, thus representing an easily accessible alternative to previously reported Co-catalysts. NaBH4 is employed as reducing agent in the presence of EtOH as proton source, leading to the stereoselective formation of chiral esters, amides, and nitriles in up to 99 % yield and 96.5 : 3.5 er. The concentration of the reductant counter cation (Na+) and the solvent polarity have been shown to correlate with reactivity and enantioselectivity, suggesting that a relatively complex mechanistic manifold is in place. 相似文献
668.
669.
Elisa Passaglia Serena Coiai Mauro Aglietto Giacomo Ruggeri Marco Rubertà Francesco Ciardelli 《Macromolecular Symposia》2003,198(1):147-160
Previous studies carried out in our laboratory on the functionalization of ethylene polymers (homo and copolymers) through free radical processes, using mechanical mixers and/or extruders with diethylmaleate (DEM) and dicumyl peroxide (DCP), have shown that the presence of branched α-olefin blocks favours degradation versus functionalization and crosslinking whereas these last are more effective with linear ethylene blocks. In this contest the present paper reports about attempts to extend the same processes to propylene polymers by benefitting of the indications of previous results. In particular the one step functionalization of EPM with two or more different groups was carried through the use of different monomers. Moreover the procedure was extended to polypropylene thus obtaining a significant functionalization degree flanked by a remarkable decrease of molecular weight. 相似文献
670.
Dr. Matteo Corrieri Dr. Lucia De Crescentini Prof. Fabio Mantellini Dr. Giacomo Mari Dr. Stefania Santeusanio Prof. Gianfranco Favi 《European journal of organic chemistry》2023,26(21):e202300242
An oxidative cyclization of electron-rich α-arylhydrazones promoted by phenyliodine bis(trifluoroacetate) (PIFA) has been accomplished. This metal-free, chemoselective transformation allows to obtain synthetically and medicinally important N-amino-1H-indoles, obviating the need for pre-functionalization of substrates. 相似文献