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891.
Time domain integral equation solvers for transient scattering from electrically large objects have benefitted significantly from acceleration techniques like the plane wave time domain (PWTD) algorithm; these techniques reduce the asymptotic CPU and memory cost. However, PWTD breaks down when used in the analysis of structures that have subwavelength features or features whose length scales are orders of magnitude smaller than the smallest wavelength in the incident pulse. Instances of these occurring in electromagnetics range from antenna topologies, to feed structures, etc. In this regime, it is the geometric constraints that dictate the computational complexity, as opposed to the wavelength of interest. In this work, we present an approach for efficient analysis of such sub-wavelength source/observer distributions in time domain. The methodology that we seek to exploit is the recently developed algorithm based on Cartesian expansions for accelerating the computation of potentials of the form Rν. In this paper, we present an efficient methodology for computing these polynomials for two different scenarios; where the size of the domain spans the distance travelled by light in (i) one time step and (ii) multiple time steps. These algorithms are cast within the framework of both uniform and non-uniform distributions. Results that demonstrate the efficiency and convergence of the proposed algorithm are presented. 相似文献
892.
We consider the quasilinear systems of difference equations with periodic coefficients in linear terms. We obtain estimates for the attraction domain of the zero solution and establish inequalities for the norms of solutions. The results are stated in terms of Lyapunov-type matrix series. 相似文献
893.
894.
We describe a new fluorescence imaging device for clinical cancer photodetection in hollow organs in which the tumor/normal
tissue contrast is derived from the fluorescence lifetime of endogenous or exogenous fluorochromes. This fluorescence lifetime
contrast gives information about the physicochemical properties of the environment which are different between normal and
certain diseased tissues. The excitation light from a CW laser is modulated in amplitude at a radio frequency by an electrooptical
modulator and delivered by an optical fiber through an endoscope to the hollow organ. The image of the tissue collected by
the endoscope is separated in two spectral windows, one being the backscattered excitation light and the other the fluorescence
of the fluorochrome. Each image is then focused on the photocathode of image intensifiers (II) whose optical gain is modulated
at the same frequency as the excitation intensity, resulting in homodyne phase-sensitive images. By acquiring stationary phase-sensitive
frames at different phases between the excitation and the detection, it is possible to calculate in quasi-real time the apparent
fluorescence lifetime of the corresponding tissue region for each pixel. A result obtained by investigating the endogenous
fluorochromes present in the mucous membrane of an excised human bladder is presented to illustrate this method and most of
the optical parameters which are of major importance for this photodetection modality have been evaluated. 相似文献
895.
896.
用等效矩形波导近似,结合一级微扰理论,研究了双模椭圆芯光纤的传播特性,得到了双模运行的V值范围和Ex21模与Ex11模之间的双折射、模间色散随归一化频率和椭圆比的变化关系曲线 相似文献
897.
In this paper we introduce two kinds of parallel Schwarz domain decomposition me thods for general, selfadjoint, second order parabolic equations and study the dependence of their convergence rates on parameters of time-step and space-mesh. We prove that the, approximate solution has convergence independent of iteration times at each time-level. And the L~2 error estimates are given. 相似文献
898.
N. Fujii 《Journal of Optimization Theory and Applications》1988,59(3):407-422
In the present paper, the lower semicontinuity of certain classes of functionals is studied when the domain of integration, which defines the functionals, is not fixed. For this purpose, a certain class of domains introduced by Chenais is employed. For this class of domains, a basic lemma is proved that plays an essential role in the derivations of the lower-semicontinuity theorems. These theorems are applied to the study of the existence of the optimal domain in domain optimization problems; a boundary-value problem of Neumann type or Dirichlet type is the main constraint in these optimization problems.The author wishes to express his sincere thanks to the reviewer for his valuable comments, which made the paper more readable; the reviewer also pointed out that Lemma 2.1 in the text is a direct corollary to a lemma by Chenais (Ref. 9). He thanks Prof. Y. Sakawa of Osaka University for encouragement. 相似文献
899.
凹角型区域椭圆边值问题的自然边界归化 总被引:3,自引:0,他引:3
In this paper, the natural boundary reduction for some elliptic boundary value problems with concave angle domains and their natural boundary methods are investigated. The natural integral equations and the Poisson integral formulae are given. The finite element methods of the natural integral equations are discussed in details. The convergences of the approximate solutions and their error estimates are obtained. Finally, some numerical examples are presented to show that our methods are effective. 相似文献
900.
1.引言 正交函数基底在函数逼近、图像压缩和模式识别等领域中起着重要的作用.在二维区域中,通常采用分离变量法构造张量积形式的基底.然而,这种方法本质上只适用于规则的矩形区域.如何构造非规则区域,如三角形上的正交基底,是一个值得研究的课题[1][2][3][4][5].在一维情形下,通过求解Sturm—Liouville特征方程可以得到一组完备的正交基底.通过求解相应区域的特征方程,我们可以将这种方法推广到高维的基底构造.以三角区域为例,我们可以通过求解形式如下的特征方程来构造正交基底函数: 相似文献