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991.
A.L. SampaioD.C. Lobão L.C.S. NunesP.A.M. dos Santos L. Silva J.A.O. Huguenin 《Optics and Lasers in Engineering》2011,49(1):32-35
In this paper, we present a study of metallic surface roughness using the Hurst exponent calculated from speckle pattern. A set of samples was prepared using polishing techniques and the roughness was directly measured by means of an optical profilometer. To study the H exponent, an experiment was performed by illuminating the samples using an expanded laser beam and the surface image was captured by a CCD camera. We applied techniques of the Hurst exponent calculation, traditionally calculated from surface profile, in the digitalized speckle patterns generated by the rough surfaces. We showed a clear dependence of the H exponent on roughness of the samples. We demonstrated that this tool is very sensitive to defects in the surfaces and can be used for roughness control. 相似文献
992.
993.
Francisco Eduardo de Sousa Filho João Hermínio da Silva Antônio Álamo Feitosa Saraiva Deyvid Dennys S. Brito Bartolomeu Cruz Viana Bruno Tavares de Oliveira Abagaro Paulo de Tarso Cavalcante Freire 《Brazilian Journal of Physics》2011,41(4-6):275-280
X-ray diffraction was combined with X-ray energy-dispersion, Fourier-transform infrared, and Raman spectroscopies to study the fossilization of a Cretaceous specimen of the plant Brachyphyllum castilhoi, a fossil from the Ipubi Formation, in the Araripe Sedimentary Basin, Northeastern Brazil. Among the possible fossilization processes, which could involve pyrite, silicon oxide, calcium oxide, or other minerals, we were able to single out pyritization as the central mechanism producing the fossil, more than 100 million years ago. In addition to expanding the knowledge of the Ipubi Formation, this study shows that, when combined with other experimental techniques, Raman spectroscopy is a valuable tool at the paleontologist’s disposal. 相似文献
994.
T. TaveraN. Pérez A. RodríguezP. Yurrita S.M. OlaizolaE. Castaño 《Applied Surface Science》2011,258(3):1175-1180
The production of periodic structures in silicon wafers by four-beam is presented. Because laser interference ablation is a single-step and cost-effective process, there is a great technological interest in the fabrication of these structures for their use as antireflection surfaces. Three different laser fluences are used to modify the silicon surface (0.8 J cm−2, 1.3 J cm−2, 2.0 J cm−2) creating bumps in the rim of the irradiated area. Laser induced periodic surface structures (LIPSS), in particular micro and nano-ripples, are also observed. Measurements of the reflectivity show a decrease in the reflectance for the samples processed with a laser fluence of 2.0 J cm−2, probably caused by the appearance of the nano-ripples in the structured area, while bumps start to deteriorate. 相似文献
995.
M. ElMassalami D. da S. OliveiraH. Takeya 《Journal of magnetism and magnetic materials》2011,323(16):2133-2136
Based on extensive Mossbauer effect (ME) and magnetization measurements, the orthorhombic AlFe2B2 was characterized as a ferromagnet (FM) because this character is evident as an onset of a FM transition at Tc=320 K and characteristic magnetizations isotherms below Tc. At liquid helium temperatures, the magnetization saturates to μsat≈1μB per Fe atom; a value which is half the one reported for the iron metal indicating a relatively more filled 3d band. The ME analysis revealed a hyperfine field H(0) of 88(2) kOe, an isomer shift (relative to Fe) of 0.50(2) mm/s, and a quadrupole parameter of 0.02 mm/s: all parameters extrapolated to zero Kelvin. The itinerant character of the magnetic moment will be discussed. 相似文献
996.
Stability conditions of a quiescent, horizontally infinite fluid layer with adiabatic bottom subject to sudden cooling from above are studied. Here, at difference from Rayleigh-Bénard convection, the temperature base state is never steady. Instability limits are studied using linear analysis while stability is analyzed using the energy method. Critical stability curves in terms of Rayleigh numbers and convection onset times were obtained for several kinematic boundary conditions. Stability curves resulting from energy and linear approaches exhibit the same temporal growth rate for large values of time, suggesting a bound for the temporal asymptotic behavior of the energy method. 相似文献
997.
Andre L. Barbieri G.F. de Arruda Francisco A. Rodrigues Odemir M. Bruno Luciano da Fontoura Costa 《Physica A》2011,390(3):512-518
An entropy-based image segmentation approach is introduced and applied to color images obtained from Google Earth. Segmentation refers to the process of partitioning a digital image in order to locate different objects and regions of interest. The application to satellite images paves the way to automated monitoring of ecological catastrophes, urban growth, agricultural activity, maritime pollution, climate changing and general surveillance. Regions representing aquatic, rural and urban areas are identified and the accuracy of the proposed segmentation methodology is evaluated. The comparison with gray level images revealed that the color information is fundamental to obtain an accurate segmentation. 相似文献
998.
We study various properties of a nonperturbative partition function which can be associated with any spectral curve. When the spectral curve arises from a matrix model, this nonperturbative partition function is given by a sum of matrix integrals over all possible filling fractions, and includes all the multi-instanton corrections to the perturbative 1/N expansion. We show that the nonperturbative partition function, which is manifestly holomorphic, is also modular and background independent: it transforms as the partition function of a twisted fermion on the spectral curve. Therefore, modularity is restored by nonperturbative corrections. We also show that this nonperturbative partition function obeys the Hirota equation and provides a natural nonperturbative completion for topological string theory on local Calabi–Yau 3-folds. 相似文献
999.
We investigate the geometry of the moduli space of N vortices on line bundles over a closed Riemann surface Σ of genus g>1, in the little explored situation where 1≤N<g. In the regime where the area of the surface is just large enough to accommodate N vortices (which we call the dissolving limit), we describe the relation between the geometry of the moduli space and the complex geometry of the Jacobian variety of Σ. For N=1, we show that the metric on the moduli space converges to a natural Bergman metric on Σ. When N>1, the vortex metric typically degenerates as the dissolving limit is approached, the degeneration occurring precisely on the critical locus of the Abel–Jacobi map of Σ at degree N. We describe consequences of this phenomenon from the point of view of multivortex dynamics. 相似文献
1000.
Carla Cruz Maria Irene Falcão Helmuth R. Malonek 《Mathematical Methods in the Applied Sciences》2014,37(12):1723-1735
The use of a non‐commutative algebra in hypercomplex function theory requires a large variety of different representations of polynomials suitably adapted to the solution of different concrete problems. Naturally arises the question of their relationships and the advantages or disadvantages of different types of polynomials. In this sense, the present paper investigates the intrinsic relationship between two different types of monogenic Appell polynomials. Several authors payed attention to the construction of complete sets of monogenic Appell polynomials, orthogonal with respect to a certain inner product, and used them advantageously for the study of problems in 3D‐elasticity and other problems. Our goal is to show that, as consequence of the binomial nature of those generalized Appell polynomials, their inner structure is determined by interesting combinatorial relations in which the central binomial coefficients play a special role. As a byproduct of own interest, a Riordan–Sofo type binomial identity is also proved. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献