全文获取类型
收费全文 | 2197篇 |
免费 | 471篇 |
国内免费 | 116篇 |
专业分类
化学 | 425篇 |
晶体学 | 11篇 |
力学 | 155篇 |
综合类 | 39篇 |
数学 | 223篇 |
物理学 | 1931篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 47篇 |
2021年 | 61篇 |
2020年 | 66篇 |
2019年 | 38篇 |
2018年 | 39篇 |
2017年 | 74篇 |
2016年 | 106篇 |
2015年 | 54篇 |
2014年 | 124篇 |
2013年 | 165篇 |
2012年 | 146篇 |
2011年 | 154篇 |
2010年 | 124篇 |
2009年 | 150篇 |
2008年 | 151篇 |
2007年 | 166篇 |
2006年 | 145篇 |
2005年 | 125篇 |
2004年 | 120篇 |
2003年 | 96篇 |
2002年 | 83篇 |
2001年 | 75篇 |
2000年 | 63篇 |
1999年 | 49篇 |
1998年 | 59篇 |
1997年 | 38篇 |
1996年 | 43篇 |
1995年 | 25篇 |
1994年 | 38篇 |
1993年 | 25篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有2784条查询结果,搜索用时 78 毫秒
951.
Factors influencing the signal-to-noise ratio (SNR) of lensless ghost interference with thermal incoherent light are investigated.Our result shows that the SNR of lensless ghost interference is related to the transverse length of the object,the position of the object in the imaging system and the transverse size of the light source.Furthermore,the effects of these factors on the SNR are discussed in detail by numerical simulations. 相似文献
952.
Generation-channel interference of high-order harmonics of an anharmonic oscillator driven by bi-chrime laser fields and its mechanism
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)
A method to describe the generation channels of high-order harmonics is proposed.According to this method,the mechanism of generation-channel interference of high-order harmonics is revealed clearly.We take the anharmonic oscillator driven by bi-chrome fields as an example to illustrate that this method can be used to understand the effect of generation-channel interference. 相似文献
953.
基于快速层次交替最小二乘非负张量Tucker分解的干涉高光谱图像光谱信息压缩方法 总被引:1,自引:0,他引:1
提出一种基于快速层次交替最小二乘非负张量Tucker分解的高光谱图像光谱信息压缩算法。首先,将干涉高光谱图像光程差方向的三维信息采用三维光程差方向提升小波变换(3D OPT-LDWT)进行分解,将三维小波子带系数看作三阶非负张量,采用快速层次交替最小二乘非负张量Tucker分解(FHALS-NTD)算法对进行分解,得到核心张量和模式矩阵。对每个模式矩阵进行量化,对核心张量采用比特平面重要系数编码算法进行编码,得出最终的压缩码流。结果表明,此压缩算法可以稳定可靠地工作。与传统压缩算法比较,平均信噪比提高了1.23 dB。有效的提高了干涉高光谱图像压缩性能。 相似文献
954.
Interference of dissociating wave packets in the I2 molecule driven by femtosecond laser pulses
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)
The interference between two dissociating wave packets of the I2 molecule driven by femtosecond laser pulses is theoretically studied by using the time-dependent quantum wave packet method.Both the internuclear distanceand velocity-dependent density functions are calculated and discussed.It is demonstrated that the interference pattern is determined by the phase difference and the delay time between two pump pulses.With two identical pulses with a delay time of 305 fs and a FWHM of 20 fs,more interference fringes can be observed,while with two pump pulses with a delay time of 80 fs and a FWHM of 20 fs,only a few interference fringes can be observed. 相似文献
955.
光学合成孔径成像技术及发展现状 总被引:1,自引:0,他引:1
956.
The electromagnetic shielding of Ni films deposited on cenosphere particles by magnetron sputtering method 总被引:2,自引:0,他引:2
Ni-coated cenosphere particles were successfully fabricated by an ultrasonic-assisted magnetron sputtering equipment. Their surface morphology and microstructure were analyzed using field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). FE-SEM results indicate that the Ni films coated by magnetron sputtering are uniform and compact. Ni film uniformity was related with the sputtering power and a large uniform film could be achieved at lower sputtering power. XRD results imply that the Ni film coated on cenospheres was a face-centered cubic (fcc) structure and the crystallization of film sample increases with increasing the sputtering power. The electromagnetic interference (EMI) shielding effectiveness (SE) of Ni-coated cenosphere particles were measured to be 4-27 dB over a frequency range 80-100 GHz, higher than those of uncoated cenosphere particles. The higher sputtering power and Ni film thickness are the higher EMI SE of the specimens. Ni-coated cenosphere particles are most promising alternative candidates for millimeter wave EMI shielding due to their lightweight, low cost, ease of processing, high floating time, good dispersion and tunable conductivities as compared with typical electromagnetic wave countermeasure materials. 相似文献
957.
The hyperfine structure of energy levels of copper atom and its transition probabilities were considered. The resonance and metastable levels of the copper atom are split into hyperfine structures, due to the magnetic dipole moment and the electric quadrupole moment. In this paper, a succinct introduction to the relevant theory of the hyperfine spectral structure and experimental observations of elemental copper vapor laser is presented. 相似文献
958.
In this paper, we report the use of differential detection in optical code-division multiple access (OCDMA) systems which use encoders and decoders based on unbalanced codes and utilize bipolar modulation/differential detection to demonstrate a significant improvement in system performance. Differential detection has been reported earlier also requiring a large number of one-chips in the code for (balanced codes) or with unbalanced codes with very long temporal dimensions requiring a large number of delay elements (either the delay lines in the ladder-type structures or the gratings in the multiple fiber gratings) making the encoder/decoder structures. We use single pulse per row codes to design our system and carry out the simulations for showing the results. The improved BER performance is achieved that can be traded for increasing the number of codes. Using optical simulation tool, the OCDMA system has been simulated for four users. The results of this system utilizing differential detection and another system that uses the same coding scheme but employing direct detection, for the same number of interfering users, are shown for comparison. The BER and the power penalty plots are shown for the two systems. Also, it is shown that performance degradation occurs due to the linear and non-linear effects of the fiber medium. The BER worsens more rapidly with link length for direct detection case, whereas for differential detection with an initial improvement of 8 dB, the increase in BER is insignificantly small for a link length of 500 km. 相似文献
959.
960.
干涉、衍射实验中衍射物位置的估算 总被引:5,自引:0,他引:5
从光源的空间相干性和实际光源的边缘衍射特性两个方面分析给出了干涉、衍射实验中衍射物到光源的距离的估算公式,分析了双缝干涉和泊松亮斑两个实验实例. 相似文献