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951.
A weighted-integral based scheme (WIBS) and a weighted essentially non-oscillatory (WENO)-WIBS are constructed, where the integral of the unknown function with a set of linearly independent test functions are recorded on every cell. The time evolutions of these recordings are computed with TVD Runge–Kutta method. At the boundary of every two cells, the function values are interpolated from the recordings of the neighboring cells to calculate flux and volumetric integral in the weak form. 相似文献
952.
A new contrast enhancement algorithm for image is proposed combining genetic algorithm (GA) with wavelet neural network (WNN).
In-complete Beta transform (IBT) is used to obtain non-linear gray transform curve so as to enhance global contrast for an
image. GA determines optimal gray transform parameters. In order to avoid the expensive time for traditional contrast enhancement
algorithms, which search optimal gray transform parameters in the whole parameters space, based on gray distribution of an
image, a classification criterion is proposed. Contrast type for original image is determined by the new criterion. Parameters
space is, respectively, determined according to different contrast types, which greatly shrink parameters space. Thus searching
direction of GA is guided by the new parameter space. Considering the drawback of traditional histogram equalization that
it reduces the information and enlarges noise and background blur in the processed image, a synthetic objective function is
used as fitness function of GA combining peak signal-noise-ratio (PSNR) and information entropy. In order to calculate IBT
in the whole image, WNN is used to approximate the IBT. In order to enhance the local contrast for image, discrete stationary
wavelet transform (DSWT) is used to enhance detail in an image. Having implemented DSWT to an image, detail is enhanced by
a non-linear operator in three high frequency sub-bands. The coefficients in the low frequency sub-bands are set as zero.
Final enhanced image is obtained by adding the global enhanced image with the local enhanced image. Experimental results show
that the new algorithm is able to well enhance the global and local contrast for image while keeping the noise and background
blur from being greatly enlarged. 相似文献
953.
Circular meshes are quadrilateral meshes all of whose faces possess a circumcircle, whereas conical meshes are planar quadrilateral
meshes where the faces which meet in a vertex are tangent to a right circular cone. Both are amenable to geometric modeling
– recently surface approximation and subdivision-like refinement processes have been studied. In this paper we extend the
original defining property of conical meshes, namely the existence of face/face offset meshes at constant distance, to circular
meshes. We study the close relation between circular and conical meshes, their vertex/vertex and face/face offsets, as well
as their discrete normals and focal meshes. In particular we show how to construct a two-parameter family of circular (resp.,
conical) meshes from a given conical (resp., circular) mesh. We further discuss meshes which have both properties and their
relation to discrete surfaces of negative Gaussian curvature. The offset properties of special quadrilateral meshes and the
three-dimensional support structures derived from them are highly relevant for computational architectural design of freeform
structures. Another aspect important for design is that both circular and conical meshes provide a discretization of the principal
curvature lines of a smooth surface, so the mesh polylines represent principal features of the surface described by the mesh.
相似文献
954.
David Iglesias Juan C. Marrero David Martín de Diego Eduardo Martínez 《Journal of Nonlinear Science》2008,18(3):221-276
This paper studies the construction of geometric integrators for nonholonomic systems. We develop a formalism for nonholonomic
discrete Euler–Lagrange equations in a setting that permits to deduce geometric integrators for continuous nonholonomic systems
(reduced or not). The formalism is given in terms of Lie groupoids, specifying a discrete Lagrangian and a constraint submanifold
on it. Additionally, it is necessary to fix a vector subbundle of the Lie algebroid associated to the Lie groupoid. We also
discuss the existence of nonholonomic evolution operators in terms of the discrete nonholonomic Legendre transformations and
in terms of adequate decompositions of the prolongation of the Lie groupoid. The characterization of the reversibility of
the evolution operator and the discrete nonholonomic momentum equation are also considered. Finally, we illustrate with several
classical examples the wide range of application of the theory (the discrete nonholonomic constrained particle, the Suslov
system, the Chaplygin sleigh, the Veselova system, the rolling ball on a rotating table and the two wheeled planar mobile
robot).
This work was partially supported by MEC (Spain) Grants MTM 2006-03322, MTM 2007-62478, MTM 2006-10531, project “Ingenio Mathematica”
(i-MATH) No. CSD 2006-00032 (Consolider-Ingenio 2010) and S-0505/ESP/0158 of the CAM. 相似文献
955.
距离空间中的神经网络插值与逼近 总被引:4,自引:1,他引:3
已有的关于插值神经网络的研究大多是在欧氏空间中进行的,但实际应用中的许多问题往往需要用非欧氏尺度进行度量.本文研究一般距离空间中的神经网络插值与逼近问题,即先在距离空间中构造新的插值网络,然后在此基础上构造近似插值网络,最后研究近似插值网络对连续泛函的逼近. 相似文献
956.
利用Hermite变换和Jacobi椭圆函数展开法研究(2+1)-维广义随机Kadomtsev-Petviashvili方程,并给出了它的随机椭圆周期解及随机孤立波解. 相似文献
957.
FFTs on the Rotation Group 总被引:1,自引:0,他引:1
Peter J. Kostelec Daniel N. Rockmore 《Journal of Fourier Analysis and Applications》2008,14(2):145-179
We discuss an implementation of an efficient algorithm for the numerical computation of Fourier transforms of bandlimited
functions defined on the rotation group SO(3). The implementation is freely available on the web. The algorithm described herein uses O(B
4) operations to compute the Fourier coefficients of a function whose Fourier expansion uses only (the O(B
3)) spherical harmonics of degree at most B. This compares very favorably with the direct O(B
6) algorithm derived from a basic quadrature rule on O(B
3) sample points. The efficient Fourier transform also makes possible the efficient calculation of convolution over SO(3) which has been used as the analytic engine for some new approaches to searching 3D databases (Funkhouser et al., ACM Trans.
Graph. 83–105, [2003]; Kazhdan et al., Eurographics Symposium in Geometry Processing, pp. 167–175, [2003]). Our implementation is based on the “Separation of Variables” technique (see, e.g., Maslen and Rockmore, Proceedings of
the DIMACS Workshop on Groups and Computation, pp. 183–237, [1997]). In conjunction with techniques developed for the efficient computation of orthogonal polynomial expansions (Driscoll et
al., SIAM J. Comput. 26(4):1066–1099, [1997]), our fast SO(3) algorithm can be improved to give an algorithm of complexity O(B
3log 2
B), but at a cost in numerical reliability. Numerical and empirical results are presented establishing the empirical stability
of the basic algorithm. Examples of applications are presented as well.
First author was supported by NSF ITR award; second author was supported by NSF Grant 0219717 and the Santa Fe Institute. 相似文献
958.
959.
The procedures studied in this paper originate from a problem posed at the International Mathematical Olympiad in 1986. We present several approaches to the IMO problem and its generalizations. In this context we introduce a “signed mean value procedure” and study “relaxation procedures on graphs”. We prove that these processes are always finite, thus confirming a conjecture of Akiyama, Hosono and Urabe [J. Akiyama, K. Hosono, M. Urabe, Some combinatorial problems. Discrete Mathematics 116 (1993) 291-298]. Moreover, we indicate relations to sorting and to an iterative method used in circle packing. 相似文献
960.