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221.
Diffusion-limited cluster aggregation and gelation of hard spheres is simulated using off-lattice Monte Carlo simulations.
A comparison is made of the wall-particle correlation function with the particle-particle correlation function over a range
of volume fractions, both for the initial system of randomly distributed spheres and for the final gel state. For randomly
distributed spheres the correlation functions are compared with theoretical results using the Ornstein-Zernike equation and
the Percus-Yevick closure. At high volume fractions (φ > 40%) gelation has little influence on the correlation function, but
for φ < 10% it is a universal function of the distance normalized by correlation length (ξ) of the bulk. The width of the
depletion layer is about 0.5ξ. The concentration increases as a power law from the wall up to r ≈ ξ, where it reaches a weak maximum before decreasing to the bulk value. 相似文献
222.
Probabilistically induced domain decomposition methods for elliptic boundary-value problems 总被引:1,自引:0,他引:1
Juan A. Acebrn Maria Pia Busico Piero Lanucara Renato Spigler 《Journal of computational physics》2005,210(2):421-438
Monte Carlo as well as quasi-Monte Carlo methods are used to generate only few interfacial values in two-dimensional domains where boundary-value elliptic problems are formulated. This allows for a domain decomposition of the domain. A continuous approximation of the solution is obtained interpolating on such interfaces, and then used as boundary data to split the original problem into fully decoupled subproblems. The numerical treatment can then be continued, implementing any deterministic algorithm on each subdomain. Both, Monte Carlo (or quasi-Monte Carlo) simulations and the domain decomposition strategy allow for exploiting parallel architectures. Scalability and natural fault tolerance are peculiarities of the present algorithm. Examples concern Helmholtz and Poisson equations, whose probabilistic treatment presents additional complications with respect to the case of homogeneous elliptic problems without any potential term and source. 相似文献
223.
Predicting the vibro-acoustic behaviour of a structure is usually done by using the well established finite element (FE) method and boundary element method. This paper presents a vibro-acoustic prediction case performed on a metal box using less accurate but simplified methods: sub-structuring for the calculation of the dynamic response of the structure, and a monopole distribution for the radiated noise calculation. Both are less accurate but faster methods than previous ones. An experimental validation was performed. It led to the conclusion that these methods give precise results and are sufficient for the pre-design of structures in the low frequency domain. However, this conclusion must be moderated by the fact that in spite of the simplicity of the structure, the FE model had to be adjusted to the experiments to yield to a result close to the experiments. 相似文献
224.
225.
Zolfira Zakirova 《Czechoslovak Journal of Physics》2005,55(11):1541-1544
We study the six-dimensional pseudo-Riemannian spaces with two time-like coordinates that admit non-homothetic infinitesimal
projective transformations. The metrics are manifestly obtained and the projective group properties are determined. We also
find a generic definition of projective motion in the 6-dimensional rigid h-space.
Presented at the International Colloquium “Integrable Systems and Quantum Symmetries”, Prague, 16–18 June 2005. 相似文献
226.
The present work deals with the electrochemical formation of superlattice structures on n-type (1 0 0) InP in HCl solutions. The superlattices consist of a stack of two layers with alternating high and low porosity on n-type material obtained by changing the anodizing current or the potential periodically in HCl solutions. The superlattice structures were characterized by scanning electron microscopy. The pore morphology and structure depend strongly on the electrochemical conditions. For anodization with low currents (e.g., 1 or 10 mA) or at low potentials (e.g., 1.5 VAg/AgCl), a porous layer with a facet-like structure was formed. For higher currents or potentials, such as 50 or 100 mA or 3 VAg/AgCl, respectively, a tree-like structure with random and/or tangled branches was observed. Finally, samples anodized at 5 VAg/AgCl, show a porous layer with a regular array of straight pores. The morphology and structure of the stacks of the porous layers can be controlled in the nanometer range, depending on the electrochemical conditions. 相似文献
227.
S. Caravati G.P. Brivio S. Pagliara G. Galimberti C. Giannetti 《Surface science》2006,600(18):3901-3905
Recent advances in both the experimental resolution and in the computational capabilities motivate new studies of surface properties. In particular, a detailed comparison between theoretical and experimental data is expected to provide a better insight into surface and image states. In this work we present a joint effort analyzing such features of the Cu(1 1 1) and Cu(0 0 1) surfaces. The experiments are performed by using both linear and non-linear angle-resolved photoemission. From the theoretical point of view, we make use of the Green function embedding technique within density functional theory. We are able to account for the image states by suitably modifying the effective potential in the Kohn-Sham equation and the generalized boundary conditions on the Green function. Comprehensive theoretical and experimental results on the effective mass and the binding energy of the Shockley state and the first image states are reported. 相似文献
228.
We propose an extension of the well-known flat-island approximation in (1 + 1) dimensions which, while keeping simple analytical relations, allows one to better describe the strain field on the facets of steeper islands, and on the wetting layer between them. The results of atomistic molecular dynamics simulations using the Tersoff potential are used as a benchmark. The simple continuum approach is also shown to predict the correct trend of the strain gradients characterizing closely-spaced interacting islands, which has been recently observed to produce lateral motion of large Ge dots on Si(0 0 1). 相似文献
229.
Based on the property analysis of interferential multispectral images, a novel compression algorithm of partial set partitioning in hierarchical trees (SPIHT) with classified weighted rate-distortion optimization is presented.After wavelet decomposition, partial SPIHT is applied to each zero tree independently by adaptively selecting one of three coding modes according to the probability of the significant coefficients in each bitplane.Meanwhile the interferential multispectral image is partitioned into two kinds of regions in terms of luminous intensity, and the rate-distortion slopes of zero trees are then lifted with classified weights according to their distortion contribution to the constructed spectrum.Finally a global ratedistortion optimization truncation is performed.Compared with the conventional methods, the proposed algorithm not only improves the performance in spatial domain but also reduces the distortion in spectral domain. 相似文献
230.
We design and analyze compound selectivity sets of antagonists with differential selectivity against seven biogenic amine G-protein coupled receptors. The selectivity sets consist of a total of 267 antagonists and contain a spectrum of in part closely related molecular scaffolds. Each set represents a different selectivity profile. Using these com- pound sets, a systematic computational analysis of structure-selectivity relationships is carried out with different 2D similarity methods including fingerprints, recursive partitioning, clustering, and dynamic compound mapping. Screening calculations are performed in a background database containing nearly four million molecules. Fingerprint searching and compound mapping are found to enrich target-selective antagonists over family-selective ones. Dynamic compound mapping effectively discriminates database compounds from GPCR antagonists and consistently retains target-selective antagonists during the final dimension extension levels. Furthermore, the widely used MACCS key fingerprint displays a strong tendency to distinguish between target- and family-selective GPCR antagonists. Taken together, the results indicate that different types of 2D similarity methods are capable of distinguishing closely related molecules having different selectivity. The reported compound benchmark system is made freely available in order to enable selectivity-oriented analyses using other computational approaches. 相似文献