全文获取类型
收费全文 | 86589篇 |
免费 | 8706篇 |
国内免费 | 7808篇 |
专业分类
化学 | 29701篇 |
晶体学 | 846篇 |
力学 | 7177篇 |
综合类 | 1423篇 |
数学 | 30122篇 |
物理学 | 33834篇 |
出版年
2024年 | 112篇 |
2023年 | 676篇 |
2022年 | 1396篇 |
2021年 | 1536篇 |
2020年 | 1720篇 |
2019年 | 1927篇 |
2018年 | 1678篇 |
2017年 | 2115篇 |
2016年 | 2379篇 |
2015年 | 2112篇 |
2014年 | 3218篇 |
2013年 | 5955篇 |
2012年 | 3814篇 |
2011年 | 4216篇 |
2010年 | 3512篇 |
2009年 | 4958篇 |
2008年 | 5564篇 |
2007年 | 5606篇 |
2006年 | 5221篇 |
2005年 | 4548篇 |
2004年 | 4075篇 |
2003年 | 4051篇 |
2002年 | 3736篇 |
2001年 | 3178篇 |
2000年 | 3073篇 |
1999年 | 2768篇 |
1998年 | 2595篇 |
1997年 | 2165篇 |
1996年 | 1887篇 |
1995年 | 1706篇 |
1994年 | 1561篇 |
1993年 | 1295篇 |
1992年 | 1238篇 |
1991年 | 937篇 |
1990年 | 774篇 |
1989年 | 676篇 |
1988年 | 608篇 |
1987年 | 486篇 |
1986年 | 413篇 |
1985年 | 480篇 |
1984年 | 465篇 |
1983年 | 222篇 |
1982年 | 369篇 |
1981年 | 416篇 |
1980年 | 315篇 |
1979年 | 307篇 |
1978年 | 235篇 |
1977年 | 208篇 |
1976年 | 159篇 |
1974年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
Software Cold Test Simulation of Coupled Cavity Slow-Wave Structure in Millimeter Wave TWT 总被引:2,自引:0,他引:2
In this paper, the software cold-test simulation method to obtain RF dispersion, interaction impedance by MAFIA software is discussed considering effect of the conducting barrel in the millimeter-wave TWT. The dispersion simulation result is obtained more consistent with experiment data than the method that ignoring effect of the conducting barrel. By changing the structure parameter, high frequency characteristic will be affected. The change relationship of high frequency characteristic with structure parameter is obtained. The different calculation methods of the interaction impedance are discussed. These results are received and are consistent with experiment data. 相似文献
992.
For the purpose of testing the spherical uniformity based on i.i.d. directional data (unit vectors) zi, i=1,…,n, Anderson and Stephens (Biometrika 59 (1972) 613–621) proposed testing procedures based on the statistics Smax=maxu S(u) and Smin=minu S(u), where u is a unit vector and nS(u) is the sum of squares of u′zi's. In this paper, we also consider another test statistic Srange=Smax−Smin. We provide formulas for the P-values of Smax, Smin, Srange by approximating tail probabilities of the limiting null distributions by means of the tube method, an integral-geometric approach for evaluating tail probability of the maximum of a Gaussian random field. Monte Carlo simulations for examining the accuracy of the approximation and for the power comparison of the statistics are given. 相似文献
993.
Veli B. Shakhmurov 《Journal of Mathematical Analysis and Applications》2004,292(2):605-620
This study focuses on nonlocal boundary value problems (BVP) for degenerate elliptic differential-operator equations (DOE), that are defined in Banach-valued function spaces, where boundary conditions contain a degenerate function and a principal part of the equation possess varying coefficients. Several conditions obtained, that guarantee the maximal Lp regularity and Fredholmness. These results are also applied to nonlocal BVP for regular degenerate partial differential equations on cylindrical domain to obtain the algebraic conditions that ensure the same properties. 相似文献
994.
Mursaleen 《Journal of Mathematical Analysis and Applications》2004,293(2):523-531
The idea of almost convergence for double sequences was introduced by Moricz and Rhoades [Math. Proc. Cambridge Philos. Soc. 104 (1988) 283-294] and they also characterized the four dimensional strong regular matrices. In this paper we define and characterize the almost strongly regular matrices for double sequences and apply these matrices to establish a core theorem. 相似文献
995.
Michael Szydlo 《Journal of Number Theory》2004,104(1):75-99
Kodaira and Néron classified and described the geometry of the special fibers of the Néron model of an elliptic curve defined over a discrete valuation ring with a perfect residue field. Tate described an algorithm to determine the special fiber type by manipulating the Weierstrass equation. In the case of non-perfect residue fields, we discover new fiber types which are not on the Kodaira-Néron list. We describe these new types and extend Tate's algorithm to deal with all discrete valuation rings. Specifically, we show how to translate a Weierstrass equation into a form where the reduction type may be easily determined. Having determined the special fiber type, we construct the regular model of the curve with explicit blow-up calculations. We also provide tables that serve as a simple reference for the algorithm and which succinctly summarize the results. 相似文献
996.
Hong-jun Liu Wei Zhao Guo-fu Chen Yi-shan Wang Lian-jun Yu Chi Ruan Xue-feng Li 《Optics & Laser Technology》2004,36(4):3482-314
Experimental investigations of a type-I noncollinear phase-matched optical parametric amplification based on lithium triborate, which was pumped by a 5-ns second-harmonic pulses from a Q-switched Nd:YAG, seeded by a cw Ti:sapphire laser at 800 nm, was presented. The experiments generated 2-ns signal output pulses at 800 nm, the maximum signal output pulse energy reached 19 μJ, the corresponding parametric gain was 44 dB. Furthermore, the experiments demonstrate that the 65 nm-FWHM parametric fluorescence gain spectrum could also be observed. A quantitative account of the ultrabroadband parametric fluorescence gain spectrum was given with our theory. The experimental measurements are in agreement with theoretical calculations. 相似文献
997.
Juguan Gu Juguan Gu Daomu Zhao Zhangrong Mei Zhangrong Mei Haidan Mao Haibin Xu 《Optik》2004,115(11-12):529-532
By means of Collins diffraction integral formula in the paraxial approximation and based on the fact that a hard aperture function can be expanded into a finite sum of complex Gaussian functions, an approximate analytical expression for linearly polarized Bessel-Gaussian beams passing through a paraxial ABCD optical system with an annular aperture has been derived. The results provide more convenient for studying their propagation and transformation than the usual way by using diffraction integral directly. By using the analytical expression and the diffraction integral formula some numerical simulations are done to illustrate for the propagation characteristics of a linearly polarized Bessel-Gaussian beam through an optical system with an annular aperture. 相似文献
998.
戴菁 《宁波大学学报(理工版)》2003,16(3):317-319
介绍了供应链管理中的一个得力工具——条形码技术,对这一技术进行了剖析,分析了条形码技术的国际发展趋势以及在我国的应用现状,最后针对我国在实现条形码技术时所遇到的各种问题提出了一些建议。 相似文献
999.
We propose a minimum mean absolute error linear interpolator (MMAELI), based on theL
1 approach. A linear functional of the observed time series due to non-normal innovations is derived. The solution equation
for the coefficients of this linear functional is established in terms of the innovation series. It is found that information
implied in the innovation series is useful for the interpolation of missing values. The MMAELIs of the AR(1) model with innovations
following mixed normal andt distributions are studied in detail. The MMAELI also approximates the minimum mean squared error linear interpolator (MMSELI)
well in mean squared error but outperforms the MMSELI in mean absolute error. An application to a real series is presented.
Extensions to the general ARMA model and other time series models are discussed.
This research was supported by a CityU Research Grant and Natural Science Foundation of China. 相似文献
1000.
Xinghua Wang 《计算数学(英文版)》2003,(2)
The convergence problem of the family of Euler-Halley methods is considered under the Lipschitz condition with the L-average, and a united convergence theory with its applications is presented. 相似文献