全文获取类型
收费全文 | 234篇 |
免费 | 53篇 |
国内免费 | 46篇 |
专业分类
化学 | 58篇 |
晶体学 | 2篇 |
力学 | 2篇 |
综合类 | 2篇 |
数学 | 2篇 |
物理学 | 134篇 |
综合类 | 133篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 18篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 24篇 |
2011年 | 22篇 |
2010年 | 15篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 15篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有333条查询结果,搜索用时 9 毫秒
61.
62.
We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO3. Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm, the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained. This system is compatible with standard telecommunication optical fibers, and will be useful for continuous variable long-distance quantum communication and distributed quantum computing. 相似文献
63.
LD双端端面泵浦的高功率连续单频Nd:YVO4激光器 总被引:1,自引:1,他引:1
通过研究Nd:YVO4晶体在不同Nd3+掺杂浓度下对泵浦激光的吸收特性,以及激光晶体因吸收泵浦光而产生的热效应,在理论上分析了大功率泵浦情况下全固体化单频Nd:YVO4激光器中激光晶体Nd3+掺杂浓度对激光输出特性的影响,得出了激光器的输出功率、泵浦阈值以及斜效率与晶体掺杂浓度的对应关系.在实验上对晶体掺杂浓度分别为0.2 at%、0.3 at%和0.5 at%的大功率全固体化单频Nd:YVO4激光器的输出功率进行了比较,实验结果和理论预测基本吻合.当Nd:YVO4晶体的Nd3+掺杂浓度为0.3 at%,在44.3 W泵浦光功率下,我们在实验室得到18 W单频连续1.064 μm激光输出,激光器的斜效率为49.4%. 相似文献
64.
金孙均 王友宝 苏俊 颜胜权 李云居 郭冰 李志宏 曾晟 连钢 白希祥 柳卫平 山口英齐 久保野茂 胡钧 D.Kahl 郑孝顺 文俊永 寺西高 王宏伟 石山博信 岩佐直人 小松原哲郎 李二涛 张健 《原子核物理评论》2015,32(3):274-279
在日本东京大学CRIB 次级束装置上,用长气体靶开展了22Na+ α共振散射的厚靶实验研究。针对长气体靶实验中的两体运动学重构问题,提出了一套包括构建空间复杂几何关系、计算能量损失以及反应运动学的逐事件分析方法;对22Na+α共振散射的实验数据进行了重构分析,得到了Ec.m. = 4.2 ~ 5.4 MeV 区间22Na( α,α ) 的激发函数,从实验的激发函数中观测到了复合核26Al 5 个较为明显的共振峰。鉴于26Al 共振态的衰变模式比较复杂,本工作发现的26Al新共振态的能级性质有待进一步的理论分析。The 22Na+α resonant scattering is studied via a conventional thick target inverse kinematic method with an extended gas target. A data analysis method is proposed for the two-body reaction kinematic reconstruction, in which the spatial geometry, the reaction kinematics and the energy losses are considered. The experimental data of 22Na+ αresonant scattering have been thus reconstructed, and the excitation function is obtained in the energy interval of Ec.m. =4.2~5.4 MeV. Five resonant states in 26Al are observed in the experimental excitation function. Since several decay modes coexist for the observed 26Al resonant states, multi-channel theoretical analysis is thus needed to reveal their structure and decay features. 相似文献
65.
New experimental measurement of natSe(n, γ) cross section between 1 eV to 1 keV at the CSNS Back-n facility 下载免费PDF全文
Xin-Rong Hu 《中国物理 B》2022,31(8):80101-080101
The 74Se is one of 35 p-nuclei, and 82Se is a r-process only nucleus, and their (n, γ) cross sections are vital input parameters for nuclear astrophysics reaction network calculations. The neutron capture cross section in the resonance range of isotopes and even natural selenium samples has not been measured. Prompt γ-rays originating from neutron-induced capture events were detected by four C6D6 liquid scintillator detectors at the Back-n facility of China Spallation Neutron Source (CSNS). The pulse height weighting technique (PHWT) was used to analyze the data in the 1 eV to 100 keV region. The deduced neutron capture cross section was compared with ENDF/B-VIII.0, JEFF-3.2, and JENDL-4.0, and some differences were found. Resonance parameters were extracted by the R-matrix code SAMMY in the 1 eV-1 keV region. All the cross sections of natSe and resonance parameters are given in the datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00019. 相似文献
66.
应用光纤布喇格光栅传感器监测地下管道腐蚀的新方法研究 总被引:2,自引:3,他引:2
地下管线工作环境恶劣,腐蚀是引起它破坏和失效的主要原因之一.本文提出了一种应用光纤光栅传感器监测管道腐蚀的新方法.输送石油和天然气等一些物质的管道内部存在的压力会使管道发生膨胀,进而导致管道外壁产生环向变形.假定管道为无限长,管道内部压力导致的管道外壁轴向应变可忽略不计,当管线发生腐蚀时,会导致管壁变薄,管道内部的压力又可以看作基本不变,这样就会增大管道外壁的环向应变.当管道内部压力保持恒定时,管道壁厚与应变之间存在一定的反比例关系,本文方法就是将封装好的光纤光栅传感器粘贴在管道外壁,通过监测外壁环向变形来判断管道腐蚀的情况和程度.通过理论值、模拟值和试验值三者的对比分析来说明了这种新方法是可行的,并且值得被广泛应用,为埋地管道的防灾减灾提供了一种对策. 相似文献
67.
Angular distributions of the ^7Li(^6Li, ^6Li)^7Li elastic scattering and the ^7Li(^6Li, ^7Lig.s.)^6Li, ^7Li(^6Li, ^7Li0.48)^6Li transfer reactions at Ec.m. = 23.7 MeV are measured with the Q3D magnetic spectrograph. The optical potential of ^6Li + ^7Li is obtained by fitting the elastic scattering differential cross sections. Based on the distorted wave Born approximation (DWBA) analysis, spectroscopic factors of ^7Li =^6Li n are determined to be 0.73 ± 0.05 and 0.90 ± 0.09 for the ground and first exited states in ^7Li, respectively. Using the spectroscopic factors, the cross sections of the ^6 Li(n, γ0,1)^7 Li direct neutron capture reactions and the astrophysical ^6Li(n, γ)^7 Li reaction rates are derived. 相似文献
68.
69.
Distributed Measurement of Birefringence by P-OTDR Assisted with Piezoelectric Polarization Controller 下载免费PDF全文
We propose a new polarization sensitive optical time domain reflectometry (P-OTDR) setup assisted with a piezoelectric polarization controller (PPC). The input state of polarization can be changed by varying the voltage of PPC without any rotatable instrument, and only one optical receiver is used to detect the backward beam. We measure a single mode fibre and get the distribution of birefringence along the SMF. 相似文献
70.
We consider a passive and active hybrid interferometer for phase estimation, which can reach the sub-shot-noise limit in phase sensitivity with only the cheapest coherent sources. This scheme is formed by adding an optical parametric amplifier before a Mach-Zehnder interferometer. It is shown that our hybrid protocol can obtain a better quantum Cramer-Rao bound than the pure active(e.g., SU(1,1)) interferometer, and this precision can be reached by implementing the parity measurements. Furthermore, we also draw a detailed comparison between our scheme and the scheme suggested by Caves[Phys. Rev. D 23 1693(1981)], and it is found that the optimal phase sensitivity gain obtained in our scheme is always larger than that in Caves' scheme. 相似文献