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11.
12.
The evolution with β of the distributions of the spacing ‘s’ between nearest-neighbour levels of unfolded spectra of random matrices from the β-Hermite ensemble (β-HE) is investigated by Monte Carlo simulations. The random matrices from the β-HE are real symmetric and tridiagonal where β, which can take any positive value, is the reciprocal of the temperature in the classical electrostatic interpretation of eigenvalues. The distribution of eigenvalues coincide with those of the three classical Gaussian ensembles for β=1, 2, 4. The use of the β-HE ensemble results in an incomparable speed up and efficiency of numerical simulations of all spectral characteristics of large random matrices. Generalized gamma distributions are shown to be excellent approximations of the nearest-neighbor spacing (NNS) distributions for any β while being still simple. They account both for the level repulsion in ∼sβ when s→0 and for the whole shape of the NNS distributions in the range of ‘s’ which is accessible to experiment or to most numerical simulations. The exact NNS distribution of the GOE (β=1) is in particular significantly better described by a generalized gamma distribution than it is by the Wigner surmise while the best generalized gamma approximation coincides essentially with the Wigner surmise for β>∼2. They describe too the evolution of the level repulsion between that of a Poisson distribution and that of a GOE distribution when β increases from 0 to 1. The distribution of ln (s), related to the electrostatic interaction energy between neighbouring charges, is accordingly well approximated by a generalized Gumbel distribution for any β?0. The distributions of the minimum NN spacing between eigenvalues of matrices from the β-HE, obtained both from as-calculated eigenvalues and from unfolded eigenvalues are Brody distributions which are classically used to characterize the spectral fluctuations of various physical systems. 相似文献
13.
Yi-Ching Yao 《Annals of the Institute of Statistical Mathematics》1987,39(1):377-383
Summary The problem of testing for constant hazard against a change-point alternative is considered. It is shown that this problem
is related to another one in quality control. Based on this relationship, a test is proposed. The main advantages of this
test are its computational simplicity and the ready availability of small and large sample distribution theory. 相似文献
14.
F. Burstein M. Borisover I. Lapides S. Yariv 《Journal of Thermal Analysis and Calorimetry》2008,92(1):35-42
In the present research we studied the effect of the solvent used, whether it was polar water or a non-polar organic solvent
(n-hexane or n-hexadecane), on the basal-spacing and bulk structure of the sorbate-sorbent complexes obtained by the secondary adsorption
of nitrobenzene and m-nitrophenol by two types of organo-montmorillonites. X-ray measured basal spacings before and after thermal treatments up
to 360°C. The organo-clays were synthesized, with 41 and 90% replacement of the exchangeable Na+ by hexadecyltrimethylammonium (HDTMA), with mono-and bilayers of HDTMA cations in the interlayer space, labelled OC-41 and
OC-90, respectively. After heating at 360°C both organo-clays showed spacing at 1.25–1.28 nm, due to the presence of interlayer-charcoal,
indicating that in the preheated organo-clays the HDTMA was located in the interlayer.
The thermo-XRD-analysis of Na-clay complexes showed that from organic solvents both sorbates were adsorbed on the external
surface but from water they were intercalated. m-Nitrophenol complexes of both organo-clays obtained in aqueous suspensions contain water molecules. Spacings of nitrobenzene
complexes of OC-41 and OC-90 and those of nitrophenol complexes of OC-41 showed that the adsorbed molecules were imbedded
in cavities in the HDTMA layers. Adsorption of m-nitrophenol by OC-90 from water and n-hexane resulted in an increase of basal spacing (0.21 and 0.29 nm, respectively) suggesting the existence of a layer of nitrophenol
molecules sandwiched between two parallel HDTMA layers. 相似文献
15.
Two different kinds of organoclays were prepared by mixing a pristine montmorillonite and a double‐chain ammonium salt in many different thermoplastic or elastomeric polymers. Independently of the chemical nature of the considered polymers, the obtained organoclays presented a basal spacing of 4 or 6 nm, when the mixing occurred in the absence or in the presence of a small amount of stearic acid (SA), respectively. X‐ray diffraction and Fourier transform infrared measurements support the hypothesis that these two kinds of organoclays correspond to paraffin‐type tilted and perpendicular bi‐layer intercalates, respectively. The co‐intercalation of SA molecules with the double‐chain amphiphile is suggested, to explain the observed expansion of the clay interlayer distance. The obtained results suggest an easy way to control the organoclay structure in polymer composites. Moreover, the authors on the basis of these results propose a criticism to the extensive literature that systematically explains most d basal spacing increase observed for clays in polymer with the penetration of apolar polymer chains in the clay interlayer space. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
16.
Simulation of crack spacing using a reinforced concrete model with an internal length parameter 总被引:3,自引:0,他引:3
Summary A gradient-enhanced smeared crack model and bond-slip interface elements are utilized in finite element simulations of reinforced
concrete. The crack model is rooted in an enhanced plasticity theory. It uses the Rankine failure surface dependent on an
equivalent inelastic strain measure as well as on its Laplacian. As a result, finitely sized fracture process zones and realistic
crack spacings are obtained. A reinforced concrete bar in uniaxial tension is analyzed to demonstrate the regularizing influence
of the internal length parameter in the model and to evaluate the influence of the model parameters on the energy dissipation
in multiple cracks. A comparison of numerical simulations with experimental results for a beam without shear reinforcement
in four-point bending concludes the analysis.
Received 4 November 1997; accepted for publication 23 April 1998 相似文献
17.
小间距隧道爆破开挖动力效应数值模拟研究 总被引:18,自引:0,他引:18
从爆破施工的特点入手,对小间距隧道在采用典型双侧导坑法时的爆破施工动力效应进行了数值模拟研究,给出了爆破施工在已有洞室周边产生的动力效应的一般规律,指出在爆破(后开挖洞室)开挖影响区以内,合理确定已有洞室二次衬砌施作时间的重要性,并给出了爆破施工对已有洞室稳定性影响较大的关键开挖位置。研究表明,爆破动载荷对小间距隧道围岩稳定性的影响主要表现为爆炸应力波造成围岩临空面的反射拉伸破坏,破坏较严重的是已有洞室的迎爆墙、拱脚、拱顶等部位。所得结论对小间距隧道爆破施工有一定的参考价值。 相似文献
18.
The chromatographic dimensionality was recently proposed as a measure of retention time spacing based on a power law (fractal) distribution. Using this model, a statistical overlap theory (SOT) for chromatographic peaks is developed that estimates the number of peak maxima as a function of the chromatographic dimension, saturation and scale. Power law models exhibit a threshold region whereby below a critical saturation value no loss of peak maxima due to peak fusion occurs as saturation increases. At moderate saturation, behavior is similar to the random (Poisson) peak model. At still higher saturation, the power law model shows loss of peaks nearly independent of the scale and dimension of the model. The physicochemical meaning of the power law scale parameter is discussed and shown to be equal to the Boltzmann-weighted free energy of transfer over the scale limits. The scale is discussed. Small scale range (small β) is shown to generate more uniform chromatograms. Large scale range chromatograms (large β) are shown to give occasional large excursions of retention times; this is a property of power laws where "wild" behavior is noted to occasionally occur. Both cases are shown to be useful depending on the chromatographic saturation. A scale-invariant model of the SOT shows very simple relationships between the fraction of peak maxima and the saturation, peak width and number of theoretical plates. These equations provide much insight into separations which follow power law statistics. 相似文献
19.
本文利用表面张力在液面上产生毛细波的现象,设计了一种原理上的比较新颖,操作上简单,相对误差为0.2%,可与公认的毛细上升法相比的测量方法。 相似文献
20.
R. L. Eubank 《Statistics & probability letters》1982,1(2):69-73
The relationships between two distributions having the same solutions for problems of optimal spacing selection for the asymptotically best linear unbiased estimator of a location or scale parameter or for problems of optimal stratification for estimation of a population mean are investigated. Easily checked necessary and sufficient conditions under which two distributions have identical solutions to these problems are given in terms of their quantile and density-quantile functions. As an application of these results a quantile domain analoque of a theorem due to Adatia and Chan (1981) on the equivalence of optimal grouping, spacing and stratification problems is obtained. 相似文献