全文获取类型
收费全文 | 125篇 |
免费 | 32篇 |
国内免费 | 18篇 |
专业分类
化学 | 47篇 |
力学 | 2篇 |
综合类 | 3篇 |
数学 | 13篇 |
物理学 | 110篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2017年 | 11篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 18篇 |
2013年 | 8篇 |
2012年 | 6篇 |
2011年 | 14篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 4篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有175条查询结果,搜索用时 15 毫秒
71.
ABEEM/MM model has been applied to compute the various properties characterizing water clusters (H2O)
n
(n = 7−10), such as optimized geometries, the hydrogen bonds number, cluster interaction energies, stabilities, ABEEM charge
distributions, dipole moments, structural parameters, and so on, and to describe the transition reflected by the hexamer region
from two-dimensional (from dimer to pentamer) to three-dimensional structures (for clusters larger than the hexamer).
Supported by the National Natural Science Foundation of China (Grant No. 20373021) 相似文献
72.
以密度泛函理论和电负性均衡原理为基础,应用修正的电负性均衡方法,并自编程序,用最小二乘法,拟合确定了H,C,O,N,F和Cl以及S等各种类型原子的价态电负性、价态硬度和能量的相关参数;从电负性均衡原理的观点,利用这些参数确定了一些青霉素基团的电负性和电荷分布,并进行了讨论. 相似文献
73.
The possible genesis of negative atom condensed Fukui functions is discussed based on hardness kernel matrix relationships. The recent hypothesis that diagonal dominance of the hardness matrix is a requirement for positive Fukui functions is proven, and general considerations also predict the possibility of regions with numerically unstable Fukui functions, including discontinuities. 相似文献
74.
基于直方图均衡化的Robinson图像边缘检测算法 总被引:1,自引:0,他引:1
针对图像边缘检测,现有Robinson相关算法存在效率低、阈值设定随机性大、易出现伪边缘等问题,提出一种改进Robinson的图像边缘检测算法。该算法利用直方图均衡化对图像进行增强,然后将Robinson算子原有的八方向梯度依照两两垂直原则组合为八组,分别计算每组梯度的范数,并取其最大值作为该像素点的梯度。最后取整幅图像的灰度均值作为阈值来识别图像的边缘像素和背景像素。实验表明,相对于现有相关算法,该算法检测结果更加清晰完整,同时避免了传统算子人为设定阈值随机性大的问题。 相似文献
75.
Image contrast enhancement using adjacent-blocks-based modification for local histogram equalization
Infrared images usually have some non-ideal characteristics such as weak target-to-background contrast and strong noise. Because of these characteristics, it is necessary to apply the contrast enhancement algorithm to improve the visual quality of infrared images. Histogram equalization (HE) algorithm is a widely used contrast enhancement algorithm due to its effectiveness and simple implementation. But a drawback of HE algorithm is that the local contrast of an image cannot be equally enhanced. Local histogram equalization algorithms are proved to be the effective techniques for local image contrast enhancement. However, over-enhancement of noise and artifacts can be easily found in the local histogram equalization enhanced images. In this paper, a new contrast enhancement technique based on local histogram equalization algorithm is proposed to overcome the drawbacks mentioned above. The input images are segmented into three kinds of overlapped sub-blocks using the gradients of them. To overcome the over-enhancement effect, the histograms of these sub-blocks are then modified by adjacent sub-blocks. We pay more attention to improve the contrast of detail information while the brightness of the flat region in these sub-blocks is well preserved. It will be shown that the proposed algorithm outperforms other related algorithms by enhancing the local contrast without introducing over-enhancement effects and additional noise. 相似文献
76.
水声信道的严重双扩特性极大地限制了水声高速通信的稳健性。针对近程高速水声通信技术的需求,该文基于水声毫米波频段,提出了一种基于超奈奎斯特发射技术及高阶调制技术的单载波的水声毫米波通信技术。而超奈奎斯特发射技术以及高阶调制给接收机带来了极大的挑战:一是超奈奎斯特发射技术引入了严重的符号间干扰,二是高阶调制系统的符号检测对信道估计的精度要求很高。针对以上问题,该文提出了一种基于迭代信道估计技术的迭代软反馈DFE接收机技术。仿真实验表明:采用128QAM高阶调制时,在较为严重的多途衰落信道条件下,采用所提出的接收机可以在15 dB时实现无误码传输。信道水池试验证明:当通信带宽为300 kHz,通信符号率为300k符号/秒且采用64QAM调制时,在发射平台慢速运动的条件下可以实现900 kbps的净数据率,其相应的频谱利用率高达6 Bits/s/Hz。 相似文献
77.
针对目前分数间隔盲均衡算法存在的缺陷,提出了基于分数间隔的四二阶归一化累积量盲均衡算法.先对接收信号进行分数间隔采样,然后利用四二阶归一化累积量将盲均衡算法归结为无约束的极值问题,从而简化了算法,加快了收敛速度,降低了误码率.仿真验证了算法的有效性. 相似文献
78.
79.
80.
By using a coarse-grain representation of the molecular electronic density, we demonstrate that the value of the condensed
Fukui function at an atomic site is directly related to the polarization charge (Coulomb hole) induced by a test electron
removed (or added) from (at) the atom. The link between the formation of an electron-hole pair and the condensed Fukui function
provides insights on the possible negativity of the Fukui function which is interpreted in terms of two phenomena: overscreening
and over-strengthening. 相似文献