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11.
We give a lower bound for the number of vertices of a generald-dimensional polytope with a given numberm ofi-faces for eachi = 0,..., d/2 – 1. The tightness of those bounds is proved using McMullen's conditions. Form greater than a small constant, those lower bounds are attained by simpliciali-neighbourly polytopes. 相似文献
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Antoine Royer 《Foundations of Physics》1992,22(5):727-736
For a wave packet evolving quantum mechanically, the rates of change of the expectations and uncertainties of the position and momentum are exactly the same as if Wigner's function instantaneously obeyed a classical Liouville equation (whatever the Hamiltonian). This extension of Ehrenfest's theorem should be useful for dealing with the evolution and manipulation of quantum states. 相似文献
14.
Doried?GhaderEmail author Vinod?Ashokan Michel Abou?Ghantous Antoine?Khater 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(4):180
A model calculation is presented for the spin wave scattering and coherent transport at the ferrimagnetically ordered cobalt-gadolinium alloy nanojunction between cobalt leads. The structural model for the amorphous alloy nanojunction [Co1/2Gd1/2]3 is considered as an ordered alloy hcp structure of three (0001) atomic planes between the leads. To analyze the spin dynamics and spin wave scattering at the nanojunction boundary, the phase field matching method (PFMT) is implemented over the ground state of the system, in the Heisenberg Hamiltonian representation. The coherent reflection and transmission probabilities of spin waves from the cobalt leads incident onto the nanojunction boundary are calculated, and numerical results are presented for the coherent SW transport across the nanojunction over the entire range of their frequencies. The results are especially valid in the interval between nanometric SW wavelengths greater than the nanojunction width and macroscopic wavelengths. They demonstrate in particular, the possibility of the resonance assisted maxima for the SW transmission spectra owing to the interactions between the incident spin waves and the localized spin resonances on the nanojunction. This effect is general and may be observed at different characteristic frequencies and corresponding incident angles. 相似文献
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Coron A Vanhamme L Antoine JP Van Hecke P Van Huffel S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,152(1):26-40
Suppressing the solvent peak is important in many applications of biomedical NMR spectroscopy in order to quantify the metabolites with a great accuracy. Among the postprocessing methods proposed in the literature, many deal with the concept of filtering. However, several proposals lack a theoretical perspective and some have not been explicitly applied to quantification problems. The present article is intended to bridge this gap: five methods are analyzed from a theoretical perspective. Subsequently the different methods are applied to the same set of data, and then the latter are quantified using the model fitting method AMARES. With our set, the scheme proposed by T. Sundin et al. (J. Magn. Reson. 139(2), 189-204 (1999)) proved to be the most reliable method. 相似文献
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In this article, we propose new Monte Carlo techniques for moving a diffusive particle in a discontinuous media. In this framework, we characterize the stochastic process that governs the positions of the particle. The key tool is the reduction of the process to a Skew Brownian motion (SBM). In a zone where the coefficients are locally constant on each side of the discontinuity, the new position of the particle after a constant time step is sampled from the exact distribution of the SBM process at the considered time. To do so, we propose two different but equivalent algorithms: a two-steps simulation with a stop at the discontinuity and a one-step direct simulation of the SBM dynamic. Some benchmark tests illustrate their effectiveness. 相似文献
18.
Fluorescence tomography of diffuse media can yield optimal three-dimensional imaging when multiple projections over 360 degrees geometries are captured, compared with limited projection angle systems such as implementations in the slab geometry. We demonstrate how it is possible to perform noncontact, 360 degrees projection fluorescence tomography of mice using CCD-camera-based detection in free space, i.e., in the absence of matching fluids. This approach achieves high spatial sampling of photons propagating through tissue and yields a superior information content data set compared with fiber-based 360 degrees implementations. Reconstruction feasibility using 36 projections in 10 degrees steps is demonstrated in mice. 相似文献
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BACKGROUND: Supracricoid partial laryngectomy (SCPL) results in laryngeal preservation in more than 95% of patients with T2 glottic carcinoma. Postsurgical glottic function is characterized by an absence of vocal cords, and phonation quality is a key post-SCPL quality-of-life factor. OBJECTIVE: This investigation was designed to enhance post-SCPL vocal function, study anatomic function of the post-SCPL larynx, and correlate anatomic findings with perceptual and instrumented measurements of voice. METHOD: Twenty-five patients were included. All had undergone SCPL with cricoepiglottopexy for T2 glottic carcinoma. All patients were evaluated by laryngostroboscopic examination, voice sample recording, and instrumented voice analysis with the aim of gaining further insight into postoperative larynx function. Laryngostroboscopic parameters such as laryngeal occlusion, epiglottic length, arytenoid movement, and vibratory area were assessed. The perceptual evaluation was based on the GRBAS scale. Acoustic and aerodynamic parameters were recorded, including fundamental frequency (F0), intensity, jitter, shimmer, signal-to-noise ratio (SNR), oral airflow (OAF), maximum phonation time (MPT), and estimated subglottic pressure (ESGP). Nonparametric tests were used to compare laryngostroboscopic parameters with instrumented measurements and perceptual evaluations of voice quality. RESULTS: Correlations were established among occlusion, epiglottic length, and general grade of dysphonia. Oral air flow (P = 0.006) was found to be correlated with occlusion. Voice roughness was correlated with the presence of a clearly identifiable vibratory area (P = 0.003), whereas these vibratory areas were correlated with shimmer (P = 0.041), OAF (P = 0.001), and SNR (P = 0.001). The number of preserved arytenoids was not identified as a voice quality factor (P = 0.423). CONCLUSION: This study highlighted correlations between the laryngostroboscopic examination results and the perceptive and instrumented measurements of voice. Glottis occlusion and epiglottis length were found to be key factors for postoperative voice quality. These results should help to advance technical development on surgical techniques to enhance voice results. 相似文献
20.
Stable polar oxide surfaces must be simultaneously electrostatically compensated and in thermodynamic equilibrium with the environment. As a paradigm, the MgO(111)-p(2x2) reconstructed surface is shown to involve combinations of Mg-covered terminations with peculiar insulating electronic structure, favored in O-poor conditions, and the O-terminated octopole, stabler in more O-rich environments. Such a picture, which could not have been foreseen by either experiments or simulations separately, goes beyond the Wolf model and reconciles the theory with the experimental data taken in variable thermodynamic conditions. 相似文献