全文获取类型
收费全文 | 1061篇 |
免费 | 52篇 |
国内免费 | 36篇 |
专业分类
化学 | 7篇 |
晶体学 | 3篇 |
力学 | 6篇 |
综合类 | 29篇 |
数学 | 884篇 |
物理学 | 220篇 |
出版年
2024年 | 2篇 |
2023年 | 35篇 |
2022年 | 53篇 |
2021年 | 52篇 |
2020年 | 48篇 |
2019年 | 27篇 |
2018年 | 19篇 |
2017年 | 26篇 |
2016年 | 32篇 |
2015年 | 19篇 |
2014年 | 39篇 |
2013年 | 45篇 |
2012年 | 15篇 |
2011年 | 32篇 |
2010年 | 23篇 |
2009年 | 72篇 |
2008年 | 79篇 |
2007年 | 62篇 |
2006年 | 68篇 |
2005年 | 31篇 |
2004年 | 35篇 |
2003年 | 38篇 |
2002年 | 61篇 |
2001年 | 42篇 |
2000年 | 35篇 |
1999年 | 57篇 |
1998年 | 36篇 |
1997年 | 27篇 |
1996年 | 16篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1149条查询结果,搜索用时 62 毫秒
201.
We present an elementary theory of optimal interleaving schemes for correcting cluster errors in two-dimensional digital data. It is assumed that each data page contains a fixed number of, say n, codewords with each codeword consisting of m code symbols and capable of correcting a single random error (or erasure). The goal is to interleave the codewords in the m×n array such that different symbols from each codeword are separated as much as possible, and consequently, an arbitrary error burst with size up to t can be corrected for the largest possible value of t. We show that, for any given m, n, the maximum possible interleaving distance, or equivalently, the largest size of correctable error bursts in an m×n array, is given by if n?⌈m2/2⌉, and t=m+⌊(n-⌈m2/2⌉)/m⌋ if n?⌈m2/2⌉. Furthermore, we develop a simple cyclic shifting algorithm that can provide a systematic construction of an m×n optimal interleaving array for arbitrary m and n. This extends important earlier work on the complementary problem of constructing interleaving arrays that, given the burst size t, minimize the interleaving degree, that is, the number of different codewords in a 2-D (or 3-D) array such that any error burst with given size t can be corrected. Our interleaving scheme thus provides the maximum burst error correcting power without requiring prior knowledge of the size or shape of an error burst. 相似文献
202.
Tuvi Etzion 《组合设计杂志》2007,15(1):15-34
The main goal of this article is to present several connections between perfect codes in the Johnson scheme and designs, and provide new tools for proving Delsarte conjecture that there are no nontrivial perfect Codes in the Johnson scheme. Three topics will be considered. The first is the configuration distribution which is akin to the weight distribution in the Hamming scheme. We prove that if there exists an e‐perfect code in the Johnson scheme then there is a formula which connects the number of vectors at distance i from any codeword in various codes isomorphic to . The second topic is the Steiner systems embedded in a perfect code. We prove a lower bound on the number of Steiner systems embedded in a perfect code. The last topic is the strength of a perfect code. We show two new methods for computing the strength of a perfect code and demonstrate them on 1‐perfect codes. We further discuss how to settle Delsarte conjecture. © 2006 Wiley Periodicals, Inc. J Combin Designs 15: 15–34, 2007 相似文献
203.
引进一个关于Goppa几何码(代数几何码)最小距离界的一个新方法.应用Maharaj的思想(即用显示基来近似表达Riemann-Roch空间)到Goppa几何码的最小距离的界上去.通过厄米特曲线上的代数几何码的一类例子,来证明标准的几何码的下界在某些情形下可以被显著地改进.进一步地,我们给出了这些码的最小距离上界,并说明了我们的下界非常接近这个上界. 相似文献
204.
205.
本文用Lang-Weil的一个经典结果证明了在一定维数限制下充分大域上平面代数曲线上MDS码的主猜想成立。 相似文献
206.
The optoelectronic and structural properties of p-type a-SiOx:H films have been studied. The deposition parameters e.g. chamber pressure and diborane to silane ratio are optimized to get a film with dark conductivity (σd) 7.9×10−6 S cm−1 and photoconductivity 9.3×10−6 S cm−1 for an optical gap (E04) of 1.94 eV. The decrease of optical gap accompanied by the increase of conductivity is due to less oxygen incorporation in the film, which is substantiated by the decrease of the intensity of SiO absorption spectra. The properties are very much effected by the chamber pressure and diborane to silane ratio. 相似文献
207.
A robust profilometer is proposed to measure 3-D object shapes based on a regularized phase tracker that is capable of demodulating fringe patterns with a high noise presence and broad bandwidth due to the object shape. As shown herein, the technique acts as an adaptive filter and is capable of giving the detected phase continuously so that no further unwrapping process is required. Experimental results of real surface profiles are presented. 相似文献
208.
B. Aneva 《Physics letters. [Part B]》1999,450(4):327
Chaos quantization conditions, which relate the eigenvalues of a Hermitian operator (the Riemann operator) with the non-trivial zeros of the Riemann zeta function are considered, and their geometrical interpretation is discussed. 相似文献
209.
J. Domscheit S. Trmnen B. Aengenvoort H. Hübel R. A. Bark M. Bergstrm A. Bracco R. Chapman D. M. Cullen C. Fahlander S. Frattini A. Grgen G. B. Hagemann A. Harsmann B. Herskind H. J. Jensen S. L. King S. Lenzi D. Napoli S. W.
degrd C. M. Petrache H. Ryde U. J. van Severen G. Sletten P. O. Tjm C. Ur 《Nuclear Physics A》1999,660(4):1211-392
High-spin states in 163Lu have been investigated using the Euroball spectrometer array. The previously known superdeformed band has been extended at low and high energies, and its connection to the normal-deformed states has been established. From its decay the mixing amplitude and interaction strength between superdeformed and normal states are derived. In addition, a new band with a similar dynamic moment of inertia has been found. The experimental results are compared to cranking calculations which suggest that the superdeformed bands in this mass region correspond to shapes with a pronounced triaxiality (γ≈±20°). 相似文献
210.
Lin Ziyang Jue Shi Xiang Ying L. P. Shi Wang Jian Z. X. Liang Z. R. Qiu 《Physics letters. A》2000,270(6):207-330
We observed an azo-isomerization-induced Freedericksz transition of the 5CB liquid crystal doped with 1% double-azo. In experiment, we found that the Freedericksz transition threshold occurred at optical intensity level of 0.3 mW/mm2 for the 12.5 μm-thickness planar alignment doped 5CB, which is four orders of magnitude lower as that for the pure 5CB. Using optical phase retardation, we measured the relations between the Freedericksz transition threshold and the pump beam polarization. The maximum twist angle of liquid crystal molecules under different pump beam intensity is given. The experiment indicated that trans–cis isomerization plays an important role in the decrease of the Freedericksz transition threshold. 相似文献