全文获取类型
收费全文 | 400篇 |
免费 | 116篇 |
国内免费 | 49篇 |
专业分类
化学 | 118篇 |
晶体学 | 1篇 |
力学 | 15篇 |
综合类 | 3篇 |
数学 | 9篇 |
物理学 | 193篇 |
无线电 | 226篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 14篇 |
2021年 | 18篇 |
2020年 | 31篇 |
2019年 | 10篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 28篇 |
2015年 | 20篇 |
2014年 | 37篇 |
2013年 | 27篇 |
2012年 | 34篇 |
2011年 | 34篇 |
2010年 | 28篇 |
2009年 | 17篇 |
2008年 | 37篇 |
2007年 | 29篇 |
2006年 | 35篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 7篇 |
2002年 | 16篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有565条查询结果,搜索用时 10 毫秒
51.
A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb 下载免费PDF全文
This paper reports that two identical external-cavity-diode-laser
(ECDL) based spectrometers are constructed at 634 nm referencing on
the hyperfine B-X transition R(80)8-4 of 127I2. The lasers
are stabilized on the Doppler-free absorption signals using the
third-harmonic detection technique. The instability of the
stabilized laser is measured to be 2.8×10-12 (after
1000 s) by counting the beat note between the two lasers. The
absolute optical frequency of the transition is, for the first time,
determined to be 472851936189.5 kHz by using an optical frequency
comb referenced on the microwave caesium atomic clock. The
uncertainty of the measurement is less than 4.9 kHz. 相似文献
52.
This paper studies a simple asymmetrically evolved community
network with a combination of preferential attachment and random
properties. An important issue about community networks is to
discover the different utility increments of two nodes, where the
utility is introduced to investigate the asymmetrical effect of
connecting two nodes. On the other hand, the connection of two nodes
in community networks can be classified as two nodes belonging to the
same or to different communities. The simulation results show that the
model can reproduce a power-law utility distribution P(u)~u-σ, σ = 2 + 1/p, which can be obtained by
using mean-field approximation methods. Furthermore, the model
exhibits exponential behaviour with respect to small values of a
parameter denoting the random effect in our model at the low-utility
region and a power-law feature with respect to big values of this
parameter at the high-utility region, which is in good agreement with
theoretical analysis. This kind of community network can reproduce
a unique utility distribution by theoretical and numerical analysis. 相似文献
53.
A new method of fabricating all-fiber broadband-rejection filter based on long period fiber grating (LPFG) is proposed. The principle in the method is to make periodic asymmetrical deformation in the core of fiber without microbends by electrode discharging so as to induce periodic refractive index changes. Two kinds of filters whose rejection peak wavelength at 1550 nm and 1310 nm are obtained. The insertion loss is less than 0.6 dB and 1.4 dB respectively. The 20 dB bandwidth ranges from 10 nm to 39 nm. The backward reflection loss is extremely small (less than -70 dB). Such devices can be used as isolation filters in 1310/1550 nm WDM system and other fields. 相似文献
54.
Pingyu Zhu Qilin Zheng Shichuan Xue Chao Wu Xinyao Yu Yang Wang Yingwen Liu Xiaogang Qiang Junjie Wu Ping Xu 《Frontiers of Physics》2020,15(6):61501
One of the most important multipartite entangled states, Greenberger–Horne–Zeilinger state (GHZ), serves as a fundamental resource for quantum foundation test, quantum communication and quantum computation. To increase the number of entangled particles, significant experimental efforts should been invested due to the complexity of optical setup and the difficulty in maintaining the coherence condition for high-fidelity GHZ state. Here, we propose an ultra-integrated scalable on-chip GHZ state generation scheme based on frequency combs. By designing several microrings pumped by different lasers, multiple partially overlapped quantum frequency combs are generated to supply as the basis for on-chip polarization-encoded GHZ state with each qubit occupying a certain spectral mode. Both even and odd numbers of GHZ states can be engineered with constant small number of integrated components and easily scaled up on the same chip by only adjusting one of the pump wavelengths. In addition, we give the on-chip design of projection measurement for characterizing GHZ states and show the reconfigurability of the state. Our proposal is rather simple and feasible within the existing fabrication technologies and we believe it will boost the development of multiphoton technologies. 相似文献
55.
56.
第Ⅰ种非对称两态叠加多模叠加态光场的偶数阶等阶N次方Y压缩 总被引:17,自引:1,他引:17
本文利用多模压缩态理论,研究了第Ⅰ种非对称两态叠加多模叠加态光场|ΨⅠ(ab)Ⅰ>q的偶数阶等阶N次方Y压缩特性.结果发现:在压缩阶数N取偶数情况下,只要构成态|ΨⅠ(ab)Ⅰ>q的两个量子光场态的强度(即平均光子数)不相等,则当各模的初始相位φj(a)、φj(b)(j=1,2,3,…,q)、态间的初始相位差(θpq(bI)-θnq(aR))以及与上述的两个量子光场态相对应的各单模相干态光场的光子干涉项之和 =[Rj(a)Rj(b)cos(φj(a)-φj(b))]等满足一定条件时,态|ΨⅠ(ab)Ⅰ>q可呈现出周期性变化的、任意偶数阶的等阶N次方Y压缩效应.这一结果与现有文献报道的结果截然不同. 相似文献
57.
An optical frequency comb generator (OFCG) at 1064 nm with a modulation frequency of 2 GHz is developed for an accurate optical frequency link between iodine absorption lines near 532 nm. With the OFCG, we have measured frequency differences between seventeen 127I2 transitions with a measurement uncertainty of about 240 Hz (relatively 4.3×10−13), which is mainly contributed from the frequency repeatability of iodine-stabilized Nd:YAG lasers. The measured transitions provide an attractive frequency reference network and are excellent candidates for the practical realization of the meter. 相似文献
58.
本文提出了一种双光梳多外差大尺寸高精度绝对测距的新方法, 结合基于双光梳互相关的多外差距离测量和基于重复频率的梳间拍频距离测量, 在不需要依靠脉冲飞行时间先验判断以及扫描重复频率或扫描参考光路的前提下实现km量程高精度绝对测距. 文章在光梳基本原理和测距方案的基础上, 建立了基于双光梳的大尺寸距离测量链理论模型, 讨论了多外差最低谱线和光梳重复频率稳定度对测量结果的影响, 并进行了大量仿真计算; 仿真结果表明, 在理想相位解调精度的前提下, 该方法的测距误差优于± 50 pm, 且多外差最低谱线的频率偏差对测距造成的影响远低于多外差测量的测距分辨力, 验证了该方法能够用于开展大尺寸高精度绝对测距研究.
关键词:
激光测距
飞秒光梳
重复频率
多外差干涉 相似文献
59.
宽截止窄带高反射滤光膜设计 总被引:1,自引:1,他引:1
窄带高反射滤光膜在光通讯、光学探测仪器等领域有着重要应用.探讨了"基片|H(LH)m1aL(HL)m2βCr,M|空气"膜系结构的窄带高反射滤光膜系,讨论了金属Cr层厚度,以及两种不同的匹配膜系对滤光膜特性的影响,计算了Cr层内部的电场分布.结果表明,较厚的金属层可实现更宽的截止带宽,匹配层的加入有效地实现了宽截止带的深截止,使中心波长处导纳为较大值的匹配膜系可以更好地实现滤光膜宽截止、窄带高反射特性;匹配膜层使中心波长处Cr层内部的电场强度趋于零,有效地降低了整个膜系的吸收,提高了反射率. 相似文献
60.
在标量势和矢量势相等的条件下,严格求解了在广义非对称Hartmann势场中粒子运动的Klein Gordon方程;并利用束缚态边界条件,获得了束缚态能谱表达式和由超几何函数表示出的波函数. 相似文献