全文获取类型
收费全文 | 4017篇 |
免费 | 703篇 |
国内免费 | 167篇 |
专业分类
化学 | 740篇 |
晶体学 | 39篇 |
力学 | 426篇 |
综合类 | 90篇 |
数学 | 678篇 |
物理学 | 2914篇 |
出版年
2024年 | 2篇 |
2023年 | 30篇 |
2022年 | 119篇 |
2021年 | 96篇 |
2020年 | 85篇 |
2019年 | 87篇 |
2018年 | 89篇 |
2017年 | 170篇 |
2016年 | 192篇 |
2015年 | 144篇 |
2014年 | 284篇 |
2013年 | 250篇 |
2012年 | 231篇 |
2011年 | 274篇 |
2010年 | 225篇 |
2009年 | 332篇 |
2008年 | 273篇 |
2007年 | 267篇 |
2006年 | 251篇 |
2005年 | 215篇 |
2004年 | 177篇 |
2003年 | 160篇 |
2002年 | 144篇 |
2001年 | 118篇 |
2000年 | 104篇 |
1999年 | 97篇 |
1998年 | 82篇 |
1997年 | 64篇 |
1996年 | 53篇 |
1995年 | 63篇 |
1994年 | 50篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3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4887条查询结果,搜索用时 15 毫秒
111.
The high-sensitivity electron bombarded active pixel sensor (EBAPS) not only has the characteristics of high gain and high sensitivity of vacuum imaging devices, but also has the digital characteristics of solid-state imaging devices, which greatly improves the level of night vision imaging. A natural color low-level-light EBAPS imaging system was built based on three-color liquid crystal tunable filter (LCTF). According to the characteristics of low-level-light images, the color enhancement processing such as grayscale stretching, white balance, and color correction was performed on the color images obtained by the system. The experimental results show that the system can realize the natural low-illumination color imaging that reflects the color characteristics of the scene itself, which can effectively improve the observation effect of the characteristics of the target scene at night, and can realize the color imaging under 5×10−4 lx illumination. © 2022 Editorial office of Journal of Applied Optics. All rights reserved. 相似文献
112.
Learnable three-dimensional Gabor convolutional network with global affinity attention for hyperspectral image classification
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hai-Zhu Pan 《中国物理 B》2022,31(12):120701-120701
Benefiting from the development of hyperspectral imaging technology, hyperspectral image (HSI) classification has become a valuable direction in remote sensing image processing. Recently, researchers have found a connection between convolutional neural networks (CNNs) and Gabor filters. Therefore, some Gabor-based CNN methods have been proposed for HSI classification. However, most Gabor-based CNN methods still manually generate Gabor filters whose parameters are empirically set and remain unchanged during the CNN learning process. Moreover, these methods require patch cubes as network inputs. Such patch cubes may contain interference pixels, which will negatively affect the classification results. To address these problems, in this paper, we propose a learnable three-dimensional (3D) Gabor convolutional network with global affinity attention for HSI classification. More precisely, the learnable 3D Gabor convolution kernel is constructed by the 3D Gabor filter, which can be learned and updated during the training process. Furthermore, spatial and spectral global affinity attention modules are introduced to capture more discriminative features between spatial locations and spectral bands in the patch cube, thus alleviating the interfering pixels problem. Experimental results on three well-known HSI datasets (including two natural crop scenarios and one urban scenario) have demonstrated that the proposed network can achieve powerful classification performance and outperforms widely used machine-learning-based and deep-learning-based methods. 相似文献
113.
114.
Dong-Ping Zhang Jianda Shao Hongji Qi Ming Fang Kui Yi Zhengxiu Fan 《Optics & Laser Technology》2006,38(8):654-657
Optical filters composed of Ag, Al2O3, and ZnSe films were prepared on BK7 substrates by evaporation. By employing spectrophotometer, microscope, scanning electron microscope (SEM), and energy dispersive spectrum (EDS) analysis, the moisture-dependent stability of the samples was tested. The experimental results revealed that filter failure often occurs initially at defect sites. Small sputtering particles and pinhole are found to be two types of defects that induced the optical coating filter failure. The mechanisms of the defect-induced failure of the filters also are discussed in the article. 相似文献
115.
116.
117.
Via a cascaded structure, the peak-to-trough ratio is considerably improved for sampled fiber Bragg gratings (SFBGs) based on multiple-phase-shift (MPS) technique. This cascaded filter is composed of two identical SFBGs which are inserted with the increasing or decreasing arrangement of phase shifts. With this inverse arrangement of MPS in grating design, the phase fluctuation of individual SFBG can be compensated, and as a result an excellent phase matching condition is realized. In this way, the peak-to- trough ratio in reflection spectra is improved from 6 to 12 dB when multiplication factor m = 4, and from 5dBto 10dBwhenm=8. 相似文献
118.
119.
120.
中性密度滤光片的典型结构是在K9玻璃上镀金属膜,来实现对激光的有效吸收.由于损伤阈值较低,严重限制了其在高能激光系统中的应用.实验研究了较高激光能量密度下滤光片的损伤形貌和损伤机理.损伤形貌的变化特征是:随着激光能量密度的增加,滤光片先出现损伤点,后以损伤点为中心产生裂纹,且裂纹长度逐渐变长,最终连接成线状和块状,导致大面积的薄膜脱落.建立了缺陷吸收激光能量升温致中性密度滤光片表面薄膜损伤的模型,计算了薄膜表面的温度和应力分布,讨论了薄膜表面不均匀温升造成的径向、环向和轴向热应力分布.理论分析显示:环向应力是造成薄膜沿径向产生裂纹的主要原因.当激光能量密度大于约2.2 J/cm2,杂质粒子半径大于140 nm且相邻杂质粒子之间的距离小于10 μ m时,裂纹才能大量连接起来引起薄膜的大面积脱落. 相似文献