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991.
Improved maximum-likelihood estimation for the common shape parameter of several Weibull populations
The biasness problem of the maximum-likelihood estimate (MLE) of the common shape parameter of several Weibull populations is examined in detail. A modified MLE (MMLE) approach is proposed. In the case of complete and Type II censored data, the bias of the MLE can be substantial. This is noticeable even when the sample size is large. Such a bias increases rapidly as the degree of censorship increases and as more populations are involved. The proposed MMLE, however, is nearly unbiased and much more efficient than the MLE, irrespective of the degree of censorship, the sample sizes, and the number of populations involved. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
992.
Modelling coupled water and heat transport in a soil–mulch–plant–atmosphere continuum (SMPAC) system
This paper presents a physically based model coupling water and heat transport in a soil–mulch–plant–atmosphere continuum (SMPAC) system, in which a transparent polyethylene mulch is applied to a winter wheat crop. The purpose of the study is to simulate profiles of soil water content and temperature for different stages of wheat growth. The mass and energy balance equations are constructed to determine upper boundary conditions of governing equations. Energy parameters are empirically formulated and calibrated from three-month field observed data. Resistance parameters in the SMPAC system are calculated. The mass and energy equations are solved by an iterative Newton–Raphson technique and a finite difference method is used to solve the governing equations. Water-consuming experiments are performed within the growing period of wheat. The results show that the model is quite satisfactory, particularly for high soil water content, in simulating the water and temperature profiles during the growth of the winter wheat. 相似文献
993.
We consider the number Kn of clusters at a distance level dn ∈ (0, 1) of n independent random variables uniformly distributed in [0, 1], or the number Kn of connected components in the random interval graph generated by these variables and dn, and, depending upon how fast dn → 0 as n → ∞, determine the asymptotic distribution of Kn, with rates of convergence, and of related random variables that describe the cluster sizes. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004 相似文献
994.
Adsorption probabilities for neopentane on Pt(111) were measured directly using supersonic molecular-beam techniques at coverages ranging from zero to monolayer saturation, incident translational energies between 18 and 110 kJ mol−1 and incident angles between 0° and 60° at a surface temperature of 105 K. The adsorption probability was found to increase with coverage up to near monolayer saturation at all incident translational energies and incident angles. The coverage dependence of the adsorption probability predicted by a modified Kisliuk model with enhanced trapping into the second layer exhibits good quantitative agreement with the experimental values. The angular dependence of the adsorption probability decreases with increasing coverage, suggesting that the effective corrugation of the gas–surface interaction potential increases with the adsorbate coverage. The initial adsorption probability into the second layer onto the covered surface decreases from 0.95 to 0.75 with increasing energy over the energy range studied, and exhibits total energy scaling. A comparison with second-layer trapping data of simpler molecules onto covered Pt(111) indicates that the structural complexity of adsorbed neopentane molecules facilitates collisional energy transfer during adsorption. 相似文献
995.
Deepu John Varughese 《Tetrahedron letters》2006,47(38):6795-6797
Non-traditional methods (grinding, water-based biphasic reactions, microwave chemistry) were used for the preparation of Schiff bases from several amines and 2-nitrobenzaldehydes. These nitro compounds were allowed to react with triethyl phosphite under microwave irradiation for the generation of nitrenes that underwent insertion reactions to form indazoles. This procedure constitutes an energy-efficient, greener chemistry version of the Cadogan reaction for nitrene-based formation of nitrogen heterocycles. 相似文献
996.
Based on the vectorial Rayleigh diffraction integrals, a nonparaxial propagation equation of vectorial plane waves diffracted at a circular aperture is derived. The nonparaxial far-field expression, Fresnel and Fraunhofer diffraction formulae are given and treated as special cases of our general expression. The theoretical formulation permits us to study and compare the transversal and axial intensity distributions of diffracted plane waves both analytically and numerically. Illustrative numerical examples are given. It is shown that the vectorial nonparaxial approach has to be used if the aperture size is comparable with or less than the wavelength, and the knowledge of both transversal and axial intensity distributions is required to provide a comprehensive comparison of the paraxial and nonparaxial results. 相似文献
997.
用EHMO-CO方法研究了卤代聚苯胺的能带结构及其掺杂导电机理,结果表明,在掺杂态卤代聚苯胺中形成单极化子晶格;取代主要通过改变带宽影响电导率,由掺杂而大幅度地提高了电导率是因为大大缩小了带隙,并进一步证实了外层d轨道的成键作用。 相似文献
998.
Mino Yang 《Journal of Molecular Spectroscopy》2006,239(1):108-114
Intensity pattern of the vibronic transitions of a molecular dimer consisting of two molecules interacting through the Coulombic coupling is theoretically studied using a reduced density-matrix approach. The monomeric molecules are assumed to be electronic two-state systems. A single vibration mode with a high frequency and a continuous distribution of low-frequency phonons represented by the Ohmic spectral density are coupled to the electronic transition of the respective molecules. The spin-Boson model is employed to include the effect of electron-vibration and electron-phonon couplings. The intermolecular Coulombic coupling is assumed to be weak (inducing the Förster type of energy transfer process). It is found that, in addition to the well-known excitonic shifts, the intensity of the vibronic side bands reduces with the intermolecular coupling strength in the J-aggregate type of dimer while it increases in the H-aggregate type. When the vibronic bands are blurred by the broadening resulting from the coupling of the electrons to the continuous distribution of the phonons, the absorption line shape shows a wide range of variation depending on the strength of the intermolecular coupling. 相似文献
999.
黎野平 《数学年刊A辑(中文版)》2007,(1)
对一类有短的动量松弛时间的多维等熵流体动力学半导体模型的极限问题进行了讨论.首先构造非线性问题的有初始层的近似解,进而,在归结问题的解存在且有合适的正则性的假设下,证明了原非线性问题的局部古典解的存在性,并且证明了这个解在归结问题解的存在时间区间内收敛到形式近似解. 相似文献
1000.
A canonical decomposition of two factor spaces obtained from the same variables observed on two populations is considered to obtain statistics of use in the comparison of these spaces. In particular, statistics are derived to test for a common factor space. The asymptotic distributions of these statistics are obtained in a variety of cases using perturbation methods. The methods are applied to a numerical example and results of a simulation are given to indicate the accuracy of the asymptotic results. 相似文献