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91.
Matteo Villani Guillermo Albareda Carlos Destefani Xavier Cartoix Xavier Oriols 《Entropy (Basel, Switzerland)》2021,23(4)
Without access to the full quantum state, modeling quantum transport in mesoscopic systems requires dealing with a limited number of degrees of freedom. In this work, we analyze the possibility of modeling the perturbation induced by non-simulated degrees of freedom on the simulated ones as a transition between single-particle pure states. First, we show that Bohmian conditional wave functions (BCWFs) allow for a rigorous discussion of the dynamics of electrons inside open quantum systems in terms of single-particle time-dependent pure states, either under Markovian or non-Markovian conditions. Second, we discuss the practical application of the method for modeling light–matter interaction phenomena in a resonant tunneling device, where a single photon interacts with a single electron. Third, we emphasize the importance of interpreting such a scattering mechanism as a transition between initial and final single-particle BCWF with well-defined central energies (rather than with well-defined central momenta). 相似文献
92.
Federico Liberatore Giovanni Righini Matteo Salani 《4OR: A Quarterly Journal of Operations Research》2011,9(1):49-82
The Vehicle Routing Problem with Time Windows consists of computing a minimum cost set of routes for a fleet of vehicles of
limited capacity visiting a given set of customers with known demand, with the additional constraint that each customer must
be visited in a specified time window. We consider the case in which time window constraints are relaxed into “soft” constraints,
that is penalty terms are added to the solution cost whenever a vehicle serves a customer outside of his time window. We present
a branch-and-price algorithm which is the first exact optimization algorithm for this problem. 相似文献
93.
A frequency selective acoustic transducer (FSAT) is proposed for directional sensing of guided waves. The considered FSAT design is characterized by a spiral configuration in wavenumber domain, which leads to a spatial arrangement of the sensing material producing output signals whose dominant frequency component is uniquely associated with the direction of incoming waves. The resulting spiral FSAT can be employed both for directional sensing and generation of guided waves, without relying on phasing and control of a large number of channels. The analytical expression of the shape of the spiral FSAT is obtained through the theoretical formulation for continuously distributed active material as part of a shaped piezoelectric device. Testing is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The discrete array approximates the continuous spiral FSAT geometry, and provides the flexibility to test several configurations. The experimental results demonstrate the strong frequency dependent directionality of the spiral FSAT and suggest its application for frequency selective acoustic sensors, to be employed for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health. 相似文献
94.
Luca Pasquini Elsa Callini Matteo Brighi Federico Boscherini Amelia Montone Torben R. Jensen Chiara Maurizio Marco Vittori Antisari Ennio Bonetti 《Journal of nanoparticle research》2011,13(11):5727-5737
We report on the hydrogen storage behaviour of Mg nanoparticles (NPs) (size range 100 nm–1 μm) with metal-oxide core–shell
morphology synthesized by inert gas condensation and decorated by transition metal (TM) (Pd or Ti) clusters via in situ vacuum
deposition. The structure and morphology of the as-prepared and hydrogenated NPs is studied by electron microscopy, X-ray
diffraction including in situ experiments and X-ray absorption spectroscopy, in order to investigate the relationships with
the hydrogen storage kinetics measured by the volumetric Sieverts method. With both Pd and Ti, the decoration deeply improves
the hydrogen sorption properties: previously inert NPs exhibit complete hydrogenation with fast transformation kinetics, good
stability and reversible gravimetric capacity that can attain 6 wt%. In the case of Pd-decoration, the occurrence of Mg–Pd
alloying is observed at high temperatures and in dependence of the hydrogen pressure conditions. These structural transformations
modify both the kinetics and thermodynamics of hydride formation, while Ti-decoration has an effect only on the kinetics.
The experimental results are discussed in relation with key issues such as the amount of decoration, the heat of mixing between
TM and Mg and the binding energy between TM and hydrogen. 相似文献
95.
We study the community structure of the multi-network of commodity-specific trade relations among world countries over the 1992-2003 period. We compare structures across commodities and time by means of the normalized mutual information index (NMI). We also compare them with exogenous community structures induced by geography and regional trade agreements. We find that commodity-specific community structures are very heterogeneous and much more fragmented than that characterizing the aggregate ITN. This shows that the aggregate properties of the ITN may result (and be very different) from the aggregation of very diverse commodity-specific layers of the multi-network. We also show that commodity-specific community structures, especially those related to the chemical sector, are becoming more and more similar to the aggregate one. Finally, our findings suggest that geography-induced partitions of our set of countries are much more correlated with observed community structures than partitions induced by regional-trade agreements. This result strengthens previous findings from the empirical literature on trade. 相似文献
96.
Natashia L. Boland Andrew C. Eberhard Faramroze G. Engineer Matteo Fischetti Martin W. P. Savelsbergh Angelos Tsoukalas 《Mathematical Programming Computation》2014,6(3):255-279
The feasibility pump (FP) has proved to be an effective method for finding feasible solutions to mixed integer programming problems. FP iterates between a rounding procedure and a projection procedure, which together provide a sequence of points alternating between LP feasible but fractional solutions, and integer but LP infeasible solutions. The process attempts to minimize the distance between consecutive iterates, producing an integer feasible solution when closing the distance between them. We investigate the benefits of enhancing the rounding procedure with a clever integer line search that efficiently explores a large set of integer points. An extensive computational study on benchmark instances demonstrates the efficacy of the proposed approach. 相似文献
97.
98.
In this paper we construct new Beauville surfaces with group either PSL(2, p e ), or belonging to some other families of finite simple groups of Lie type of low Lie rank, or an alternating group, or a symmetric group, proving a conjecture of Bauer, Catanese and Grunewald. The proofs rely on probabilistic group theoretical results of Liebeck and Shalev, on classical results of Macbeath and on recent results of Marion. 相似文献
99.
Ranking fuzzy numbers is often a necessary step in many mathematical models, and a large number of ranking methods have been proposed to perform this task. However, few comparative studies exist and nowadays it is still unknown how similar ranking methods are in practice, i.e., how likely they are to induce the same ranking. In this study, by means of numerical simulations, we try to answer this question. We shall discover that there are some very similar methods as well as some outliers. We end the paper interpreting the results and giving some recommendations on the use of ranking methods. 相似文献
100.