全文获取类型
收费全文 | 175篇 |
免费 | 34篇 |
国内免费 | 33篇 |
专业分类
化学 | 99篇 |
晶体学 | 1篇 |
力学 | 2篇 |
综合类 | 3篇 |
数学 | 13篇 |
物理学 | 124篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 12篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 21篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 18篇 |
2010年 | 12篇 |
2009年 | 16篇 |
2008年 | 6篇 |
2007年 | 15篇 |
2006年 | 16篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有242条查询结果,搜索用时 15 毫秒
111.
Atoms characterized by nonequivalent electronegativities form chemical bonds by exchanging electrical charge. The fraction of charge exchanged is dictated by the electronegativity differences among the system atoms. In the electronegativity equalization method, the charge distribution is estimated by forcing the system to relax to a common chemical potential, which corresponds to its configuration of energy minimum. By definition, this method cannot be applied to homonuclear bonds. A model is proposed to estimate the charge shared in molecular orbitals of homonuclear molecules. The model expands upon the electronegativity equalization method by adding formalism to describe the spin coupling characteristic of homonuclear bonds. Results are in excellent agreement with other quantum mechanical estimations of the charge distributions. © 2013 Wiley Periodicals, Inc. 相似文献
112.
113.
We evaluate the performance of a novel technique to equalize power variation between optical bursts using feed-forward control of semiconductor optical amplifier gain. The technique enables large dynamic range power equalization of incoming optical bursts with up to 10 dB power difference. Moreover, the technique can remove SOA-induced waveform distortion. We achieve more than 4 dB sensitivity improvement with equalized burst power. 相似文献
114.
近场扫描光学显微镜和近场光谱学的进展 总被引:2,自引:0,他引:2
在简要评介近场扫描光学显微镜的工作原理和有关技术问题的基础上,着重介绍了近场光谱学的最新发展,并讨论了对近场光谱结果的分析问题。 相似文献
115.
116.
117.
郑舒 《数学的实践与认识》2011,41(6)
盲均衡技术是不需要训练序列的自适应均衡技术.该项技术可以消除由于通信信道失真造成的码间干扰.本文的目的是对盲均衡技术作一介绍,包括对广泛应用的最大归一化累积量判据的介绍和讨论,并在此基础上提出了基于模拟退火技术的设计方法,最后,对这种盲均衡器骑行了仿真,并得出了相应的结论. 相似文献
118.
Recent years, although great efforts have been made to improve its performance, few Histogram equalization (HE) methods take human visual perception (HVP) into account explicitly. The human visual system (HVS) is more sensitive to edges than brightness. This paper proposes to take use of this nature intuitively and develops a perceptual contrast enhancement approach with dynamic range adjustment through histogram modification. The use of perceptual contrast connects the image enhancement problem with the HVS. To pre-condition the input image before the HE procedure is implemented, a perceptual contrast map (PCM) is constructed based on the modified Difference of Gaussian (DOG) algorithm. As a result, the contrast of the image is sharpened and high frequency noise is suppressed. A modified Clipped Histogram Equalization (CHE) is also developed which improves visual quality by automatically detecting the dynamic range of the image with improved perceptual contrast. Experimental results show that the new HE algorithm outperforms several state-of-the-art algorithms in improving perceptual contrast and enhancing details. In addition, the new algorithm is simple to implement, making it suitable for real-time applications. 相似文献
119.
120.
The electronegativity was defined by Pauling1 as a measure of the power of an atom in the molecule to attract electrons to itself. This concept of electronegativity has undergone radical changes. Recent calculations of electronegativity show2,3 that it is a complex quantity including an important atomic term depending on the charge and hybridization of the atom, and a molecular term depending on the length and the nature of the bonds in the molecule. In a molecular group of the type A-B, B is a halogen atom, say chlorine and A stands for different atoms of a subgroup of the periodic table. Since the nature of the bonds in the molecule AB and the electronegativity of halogen atom, B, is constant for a molecular group, the electronegativity, X, of atom A may be related to the dissociation energy and bond length which in its turn is related to the vibrational constant,ωe, and the reduced mass, μ, of the molecule AB. 相似文献