全文获取类型
收费全文 | 16926篇 |
免费 | 2205篇 |
国内免费 | 1779篇 |
专业分类
化学 | 2726篇 |
晶体学 | 46篇 |
力学 | 1228篇 |
综合类 | 280篇 |
数学 | 6241篇 |
物理学 | 2903篇 |
无线电 | 7486篇 |
出版年
2024年 | 54篇 |
2023年 | 191篇 |
2022年 | 272篇 |
2021年 | 315篇 |
2020年 | 495篇 |
2019年 | 370篇 |
2018年 | 376篇 |
2017年 | 554篇 |
2016年 | 616篇 |
2015年 | 565篇 |
2014年 | 1043篇 |
2013年 | 1232篇 |
2012年 | 1107篇 |
2011年 | 1262篇 |
2010年 | 946篇 |
2009年 | 1022篇 |
2008年 | 1162篇 |
2007年 | 1148篇 |
2006年 | 1067篇 |
2005年 | 939篇 |
2004年 | 864篇 |
2003年 | 801篇 |
2002年 | 671篇 |
2001年 | 554篇 |
2000年 | 475篇 |
1999年 | 431篇 |
1998年 | 385篇 |
1997年 | 324篇 |
1996年 | 288篇 |
1995年 | 243篇 |
1994年 | 208篇 |
1993年 | 147篇 |
1992年 | 141篇 |
1991年 | 108篇 |
1990年 | 94篇 |
1989年 | 62篇 |
1988年 | 59篇 |
1987年 | 38篇 |
1986年 | 37篇 |
1985年 | 34篇 |
1984年 | 41篇 |
1983年 | 15篇 |
1982年 | 34篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Propagation of the Hermite–Gaussian beams through misaligned optical system with a circular aperture
By means of expanding a hard-edged aperture into a finite sum of complex Gaussian functions, the approximate analytical formula of one kind of higher-order Gaussian beams called the Hermite–Gaussian beams (HGBs) passing through circular apertured and misaligned optical system is obtained in this paper. The result provides more convenience for studying its propagation than the usual way by using diffraction integral directly. Some numerical simulations are also given for illustrating the propagation properties of the HGBs through the circular apertured optical systems. 相似文献
52.
Zhao Hanzhong 《Acta Mechanica Solida Sinica》2002,15(2):156-162
A finite difference/boundary integral procedure to determine the acoustic reflected pressure from a fluid-loaded bi-laminated
plate is described. The bi-laminate is composed of a piezoelectric layer and an elastic layer in contact with the fluid, and
is held by an acoustically hard baffle. In the numerical model, the fluid pressure at fluid/solid interface is replaced by
a continuum of point sources weighted by the normal acceleration of the elastic plate, and the governing equation system is
solved in the solid domain. With the normal acceleration found, the reflected pressure in the fluid is determined by an integral
expression involving the Green's function. It is demonstrated that an appropriate applied voltage potential across the piezoelectric
layer has the effect of cancelling either the reflected or scattered pressure of the plate at any chosen field points in the
fluid.
Project supported by the National Natural Science Foundation of China (No. 10172039). 相似文献
53.
Mehdi Dehghan 《Numerical Methods for Partial Differential Equations》2002,18(2):193-202
Developement of numerical methods for obtaining approximate solutions to the three dimensional diffusion equation with an integral condition will be carried out. The numerical techniques discussed are based on the fully explicit (1,7) finite difference technique and the fully implicit (7,1) finite difference method and the (7,7) Crank‐Nicolson type finite difference formula. The new developed methods are tested on a problem. Truncation error analysis and numerical examples are used to illustrate the accuracy of the new algorithms. The results of numerical testing show that the numerical methods based on the finite difference techniques discussed in the present article produce good results. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 193–202, 2002; DOI 10.1002/num.1040 相似文献
54.
55.
56.
In asynchronous transfer mode (ATM) networks, fixed length cells of 53 bytes are transmitted. A cell may be discarded during transmission due to buffer overflow or a detection of errors. Cell discarding seriously degrades transmission quality. The quality degradation can be reduced by employing efficient forward error control (FEC) to recover discarded cells. In this paper, we present the design and implementation of decoding equipment for FEC in ATM networks based on a single parity check (SPC) product code using very‐large‐scale integration (VLSI) technology. FEC allows the destination to reconstruct missing data cells by using redundant parity cells that the source adds to each block of data cells. The functionality of the design has been tested using the Model Sim 5.7cXE Simulation Package. The design has been implemented for a 5 ° 5 matrix of data cells in a Virtex‐E XCV 3200E FG1156 device. The simulation and synthesis results show that the decoding function can be completed in 81 clock cycles with an optimum clock of 56.8 MHz. A test bench was written to study the performance of the decoder, and the results are presented. 相似文献
57.
一类积分不等式的推广 总被引:1,自引:0,他引:1
对一些基本的积分不等式进行了推广,给出了含有n个无关变元的更广泛的非线性积分不等式.利用所得的不等式讨论了某些非线性积分方程解的有界性. 相似文献
58.
The authors study the singular integrals under the Hormander condition and the measure not satisfying the doubling condition. At first, if the corresponding singular integral is bounded from L2 to itself, it is proved that the maximal singular integral is bounded from L∞to RBMO except that it is infinite μ-a.e. on Rd. A sufficient condition and a necessary condition such that the maximal singular integral is bounded from L2 to itself are also obtained. There is a small gap between the two conditions. 相似文献
59.
Continuity is obtained of some multilinear operators related to certain integral operators for the weighted Herz spaces with extreme exponents. The operators include the Littlewood–Paley and Marcinkiewicz operators. 相似文献
60.
We establish a relation between stable distributions in probability theory and the fractional integral. Moreover, it turns out that the parameter of the stable distribution coincides with the exponent of the fractional integral. It follows from an analysis of the obtained results that equations with the fractional time derivative describe the evolution of some physical system whose time degree of freedom becomes stochastic, i.e., presents a sum of random time intervals subject to a stable probability distribution. We discuss relations between the fractal Cantor set (Cantor strips) and the fractional integral. We show that the possibility to use this relation as an approximation of the fractional integral is rather limited. 相似文献