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71.
Direct observation of tunneling and nonlinear self-trapping in a single bosonic Josephson junction 总被引:1,自引:0,他引:1
Albiez M Gati R Fölling J Hunsmann S Cristiani M Oberthaler MK 《Physical review letters》2005,95(1):010402
We report on the first realization of a single bosonic Josephson junction, implemented by two weakly linked Bose-Einstein condensates in a double-well potential. In order to fully investigate the nonlinear tunneling dynamics we measure the density distribution in situ and deduce the evolution of the relative phase between the two condensates from interference fringes. Our results verify the predicted nonlinear generalization of tunneling oscillations in superconducting and superfluid Josephson junctions. Additionally, we confirm a novel nonlinear effect known as macroscopic quantum self-trapping, which leads to the inhibition of large amplitude tunneling oscillations. 相似文献
72.
We introduce the notion of electronic enthalpy for first-principles structural and dynamical calculations of finite systems under pressure. An external pressure field is allowed to act directly on the electronic structure of the system studied via the ground-state minimization of the functional E+PV(q), where V(q) is the quantum volume enclosed by a charge isosurface. The Hellmann-Feynman theorem applies, and assures that the ionic equations of motion follow an isoenthalpic dynamics. No pressurizing medium is explicitly required, while coatings of environmental ions or ligands can be introduced if chemically relevant. We apply this novel approach to the study of group-IV nanoparticles during a shock wave, highlighting the significant differences in the plastic or elastic response of the diamond cage under load, and their potential use as novel nanostructured impact-absorbing materials. 相似文献
73.
Light propagation in uniform arrays of photonic crystal waveguides is studied. We demonstrate that, in stark contrast to the case of conventional waveguide arrays, diffraction can be tailored both in magnitude and sign by varying only the spacing between adjacent waveguides. Diffraction management in ultracompact arrays of straight photonic crystal waveguides is demonstrated by solving Maxwell's equations through the time-domain finite-element method. 相似文献
74.
We discuss the ground state of a pyrochlore lattice of threefold orbitally degenerate S=1/2 magnetic ions. We derive an effective spin-orbital Hamiltonian and show that the orbital degrees of freedom can modulate the spin exchange, removing the infinite spin-degeneracy characteristic of pyrochlore structures. The resulting state is a collection of spin-singlet dimers, with a residual degeneracy due to their relative orientation. This latter is lifted by a magnetoelastic interaction, induced in the spin-singlet phase space, that forces a tetragonal distortion. Such a theory provides an explanation for the helical spin-singlet pattern observed in the B spinel MgTi2O4. 相似文献
75.
Piazza R Pierno M Vignati E Venturoli G Francia F Mallardi A Palazzo G 《Physical review letters》2003,90(20):208101
Solubilization of membrane proteins requires surfactants, whose structural properties play a crucial role in determining the protein phase behavior. We show that ionization of a pH-sensitive surfactant, lauryldymethylamino-N-oxide, bound to the bacterial photosynthetic Reaction Center, induces protein phase segregation in micrometric "droplets." Liquid-liquid phase separation takes place in a narrow pH range, is promoted by increasing temperature, and vanishes by adding salt. After a fast initial droplet growth, the nearly arrested kinetics at a later stage leaves the system in a finely divided, long-lasting emulsified state. 相似文献
76.
Benati L Calestani G Leardini R Minozzi M Nanni D Spagnolo P Strazzari S 《Organic letters》2003,5(8):1313-1316
[reaction: see text] The radical chain reaction of benzenethiol with alkynylthiol esters provides a new, valuable protocol for the tin-free generation of acyl radicals that arise from intramolecular substitution at sulfur by the initial sulfanylvinyl radicals. 相似文献
77.
We analyze the role and influence of a tradition of research linked to the concept of
primary matter
in nineteenth-century studies on the nature of the elements.The suggestion of William Prout
(1785-1850) in 1816 that the atomic weights of pure chemical elements are whole numbers and
multiples of the atomic weight of hydrogen, taken as unity, was met with serious confutations,which
in turn prompted several attempts to save Prouts hypothesis.We discuss these attempts in detail
and the objections raised against them, for instance by Dmitry Ivanovich Mendeleev (1834-1907).
We pay particular attention to the use of spectroscopy as a method for proving the existence of
elementary forms of matter inside atoms. Leaders in this field of research were two English scientists,
the astrophysicist Norman Lockyer (1836-1920) and the chemist William Crookes (1832-
1919). Both of their approaches involved the idea of primary matter. However, while Crookess
approach proved to be incorrect, Lockyers ideas survived for several years and supported the discovery
of the electron by J.J.Thomson (1856-1940). 相似文献
78.
Local branching 总被引:1,自引:0,他引:1
The availability of effective exact or heuristic solution methods for general Mixed-Integer Programs (MIPs) is of paramount importance for practical applications. In the present paper we investigate the use of a generic MIP solver as a black-box ``tactical' tool to explore effectively suitable solution subspaces defined and controlled at a ``strategic' level by a simple external branching framework. The procedure is in the spirit of well-known local search metaheuristics, but the neighborhoods are obtained through the introduction in the MIP model of completely general linear inequalities called local branching cuts. The new solution strategy is exact in nature, though it is designed to improve the heuristic behavior of the MIP solver at hand. It alternates high-level strategic branchings to define the solution neighborhoods, and low-level tactical branchings to explore them. The result is a completely general scheme aimed at favoring early updatings of the incumbent solution, hence producing high-quality solutions at early stages of the computation. The method is analyzed computationally on a large class of very difficult MIP problems by using the state-of-the-art commercial software ILOG-Cplex 7.0 as the black-box tactical MIP solver. For these instances, most of which cannot be solved to proven optimality in a reasonable time, the new method exhibits consistently an improved heuristic performance: in 23 out of 29 cases, the MIP solver produced significantly better incumbent solutions when driven by the local branching paradigm.
Mathematics Subject Classification (2000):90C06, 90C10, 90C11, 90C27, 90C59 相似文献
79.
Solar System tests give nowadays constraints on the estimated value of the cosmological constant, which can be accurately
derived from different experiments regarding gravitational redshift, light deflection, gravitational time-delay and geodesic
precession. Assuming that each reasonable theory of gravitation should satisfy Solar System tests, we use these limits on
the estimated value of the cosmological constant to constrain extended theories of Gravity, which are nowadays studied as
possible theories for cosmological models and provide viable solutions to the cosmological constant problem and the explanation
of the present acceleration of the Universe. We obtain that the estimated values, from Solar System tests, for the parameters
appearing in the extended theories of Gravity are orders of magnitude bigger than the values obtained in the framework of
cosmologically relevant theories. 相似文献
80.
Giovanni Di Nicola Cristiano Di Nicola Matteo Moglie Marco Pacetti 《Journal of Thermal Analysis and Calorimetry》2012,108(2):621-625
This study presents a new formula for the surface tension prediction of alkenes. As a first step, an analysis of the available
data of the experimental surface tension data for alkenes was performed. The experimental data were collected, after a careful
literature survey, for the following pure fluids: propene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, and 1-pentadecene.
Then, the experimental data were regressed with the most reliable semi-empirical correlating methods based on the corresponding
state theory existing in the literature. As a final step, an analysis of the available data of the experimental surface tension
data for alkenes was performed starting from the two recently proposed equations for the prediction of the surface tension
of refrigerants based on the corresponding states principle. To minimize the deviation between the predicted data and the
experimental data and to find the optimal equation coefficients for experimental data regression, a (μ + λ)-evolution strategy
was adopted. The analysis showed that the equation that gave the best results for the prediction of the surface tension of
alkenes was the one with a very limited number of parameters. The finally proposed equation is very simple and gives a noticeable
improvement with respect to the existing equations. It is based on the corresponding state principle, containing the acentric
factor, the critical temperature, and pressure. 相似文献