全文获取类型
收费全文 | 2610篇 |
免费 | 456篇 |
国内免费 | 86篇 |
专业分类
化学 | 362篇 |
晶体学 | 6篇 |
力学 | 412篇 |
综合类 | 55篇 |
数学 | 420篇 |
物理学 | 1897篇 |
出版年
2023年 | 12篇 |
2022年 | 42篇 |
2021年 | 33篇 |
2020年 | 38篇 |
2019年 | 43篇 |
2018年 | 44篇 |
2017年 | 112篇 |
2016年 | 140篇 |
2015年 | 97篇 |
2014年 | 211篇 |
2013年 | 173篇 |
2012年 | 158篇 |
2011年 | 204篇 |
2010年 | 162篇 |
2009年 | 160篇 |
2008年 | 178篇 |
2007年 | 179篇 |
2006年 | 160篇 |
2005年 | 157篇 |
2004年 | 113篇 |
2003年 | 109篇 |
2002年 | 92篇 |
2001年 | 80篇 |
2000年 | 83篇 |
1999年 | 64篇 |
1998年 | 49篇 |
1997年 | 41篇 |
1996年 | 32篇 |
1995年 | 39篇 |
1994年 | 29篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 18篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1968年 | 1篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有3152条查询结果,搜索用时 15 毫秒
931.
Image processing, in particular image enhancement techniques have been the focal point of considerable research activity in the last decade. With the aid of an existing image enhancement technique, adaptive unsharp masking (AUM), we propose a novel kernel to be used in AUM filtering in order to enhance discontinuities which occur on the edges of targets of interest in infrared (IR) images. The proposed method uses an adaptive filter approach where an objective function is minimized by using descent algorithms. The output IR image has better sharpness and contrast adjustment for the detection of targets in terms of objective quality metrics. Hence, the proposed method ensures that the edges of the targets in IR images are sharper and that the quality of contrast adjustment has its optimum level in terms of peak signal-to-noise ratios. 相似文献
932.
933.
Somayeh Motamed Lida Torkzadeh Arsham Borumand Saeid Neda Mohtashamnia 《Mathematical Logic Quarterly》2011,57(2):166-179
In this paper, the notion of the radical of a filter in BL‐algebras is defined and several characterizations of the radical of a filter are given. Also we prove that A/F is an MV‐algebra if and only if Ds(A) ? F. After that we define the notion of semi maximal filter in BL‐algebras and we state and prove some theorems which determine the relationship between this notion and the other types of filters of a BL‐algebra. Moreover, we prove that A/F is a semi simple BL‐algebra if and only if F is a semi maximal filter of A. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim 相似文献
934.
We present the design and analysis of a wideband and tunable optical Hilbert transformer (OHT) using a tunable waveguide-based finite-impulse response (FIR) filter structure by using the digital filter design method and the Remez algorithm. The tunable Nth-order waveguide-based FIR filter, which simply consists of N delay lines, N tunable couplers, N tunable phase shifters and a combiner, can be tuned, by thermally adjusting the tunable couplers and tunable phase shifters, to tune the bandwidth of an OHT using silica-based planar lightwave circuit (PLC) technology. To demonstrate the effectiveness of the method, the simulation results have an excellent agreement with the theoretical predictions. The tunable OHT can function as a wideband and tunable 90° phase shifter and thus has many potential applications. The two unique features of wideband characteristic (up to ~ 2 THz) and tunable bandwidth (THz tuning range) of the proposed OHT cannot be obtained from the existing OHTs. 相似文献
935.
Mohammed Nazrul Islam K. Vijayan Asari Mohammad S. Alam 《Optics Communications》2011,284(6):1532-1539
This paper proposes a novel pattern recognition system for invariance to noise and distortions. The technique first generates a synthetic discriminant function of the target image from its different distorted versions. It then takes four different phase-shifted versions of the reference image, which are individually joint transform correlated with the given input scene. Thus the proposed algorithm produces a single cross-correlation signal corresponding to each potential target. Also a fringe-adjusted filter is designed to generate a delta-like correlation peak with high discrimination between the signal and the noise. The pattern recognition system is also designed for the identification of multiple targets belonging to multiple reference objects simultaneously in a given input scene. The proposed technique is investigated using computer simulation including real-life images in different complex environments. 相似文献
936.
The analytical form for the reconstructed field of a hologram illuminated by a reference beam coded with a multicolored aperture array filter is derived. Experiments showed that the colored aperture array filter improved the quality of the reconstructed image by reducing the intensity of crosstalk images. Some parameters of the aperture array configuration that influence image quality were investigated. This technique presented here can be applied to full-color holographic displays and dot matrix holographic printers, etc. 相似文献
937.
Muhammad Faryad 《Optics Communications》2011,284(24):5678-5687
The excitation of multiple surface-plasmon-polariton (SPP) waves—of different linear polarization states, phase speeds and spatial profiles—guided by the interface of a metal film and a rugate filter in the Kretschmann configuration was investigated. A plane wave of either of the two linear polarization states was made incident on the metal-capped rugate filter of finite thickness and the absorptances were calculated using a stable algorithm. The excitation of SPP waves was inferred by the presence of those peaks in the absorptance curves that were independent of the thickness of the rugate filter. The absorptance peaks representing the excitation of s-polarized SPP waves are narrower than those representing p-polarized SPP waves. For efficient excitation of multiple SPP waves, the metal film's thickness should be close to the penetration depth of the metal. The solution of a canonical boundary-value problem of SPP-wave propagation guided by a metal film, with a semi-infinite homogeneous dielectric material on one side and a semi-infinite rugate filter on the other side, reinforced the results obtained for the Kretschmann configuration. The thin metal film in the Kretschmann configuration may lead to coupling of its two interfaces. 相似文献
938.
939.
940.