全文获取类型
收费全文 | 468篇 |
免费 | 128篇 |
国内免费 | 27篇 |
专业分类
化学 | 62篇 |
晶体学 | 2篇 |
力学 | 42篇 |
综合类 | 4篇 |
数学 | 12篇 |
物理学 | 501篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 9篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 20篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 26篇 |
2013年 | 28篇 |
2012年 | 24篇 |
2011年 | 50篇 |
2010年 | 27篇 |
2009年 | 30篇 |
2008年 | 28篇 |
2007年 | 36篇 |
2006年 | 15篇 |
2005年 | 22篇 |
2004年 | 26篇 |
2003年 | 13篇 |
2002年 | 32篇 |
2001年 | 19篇 |
2000年 | 37篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有623条查询结果,搜索用时 358 毫秒
61.
激光二极管抽运(Tm,Ho)∶YLF激光器光谱特性实验分析 总被引:2,自引:0,他引:2
Ho∶YLF晶体的5I7和5I8斯塔克能级分裂数较多,形成2047~2070nm宽的增益谱带,对于可调谐2μm激光及宽带激光放大器研究具有重要意义。理论上分析了(Tm,Ho)∶YLF晶体的能级结构,并对晶体掺杂浓度和长度进行了优化。实验研究了激光二极管抽运微片Tm(原子数分数0.06),Ho(原子数分数0.004)∶YLF激光谱线可调谐特性,调谐范围2.0656~2.0671μm。利用(Tm,Ho)∶YLF晶体的宽增益谱特性,将其作为激光二极管抽运激光放大器,成功地将2.048μm(Tm,Ho)∶GdVO4激光功率放大了2.5倍。实验上测量了(Tm,Ho)∶YLF晶体在强抽运条件下480~492nm及530~550nm可见波段的上转换蓝绿光荧光谱。 相似文献
62.
Spectral Characteristics of Miniature Two-Longitudinal-Mode Optically Pumped FIR Laser 总被引:1,自引:0,他引:1
Xiaorong Zou Xizhang Luo Jiayin Qin 《International Journal of Infrared and Millimeter Waves》1998,19(11):1561-1570
With the assumption that the pump source was two-longitudinal-mode, the semiclassical density matrix equation of a three-energy-level system was solved. By means of iteration method, the spectral characteristics of miniature two-longitudinal-mode optically pumped NH3 far-infrared cavity laser, which was pumped by CO2-9R(16) line, were calculated numerically. The influences of operating parameters on laser spectrum were studied intensively. 相似文献
63.
A series of measurements on the high pressure (up to 18 bar) coaxial e-beam pumped Ar/Xe laser has been made at high power loading (up to 25 MW/cm~2) for various Xe mole fraction in Ar. We found that the optimum laser gas composition in our system was 0.4% Xe in Ar which was independent of the total gas pressure. At the optimum gas composition the output energy increased with increasing total gas pressure up to 16 bar, but the intrinsic efficiency reached a maximum at the total gas pressure of 8 bar. It was also found that at the optimum power deposition for both the 2.63μm and 2.65μm transitions the ratio of the integrated optical energy to that of the 1.73μm transition had a minimum in most cases at the optimum gas mixture for various gas pressures. This ratio increased with increasing gas pressure. The experimental results suggested that besides the 2-body Xe quenching at high Xe fraction and electron collision mixing at high power depositions the heavy particle quenching from Ar at high gas press 相似文献
64.
65.
The paper presents a new way of side pumping double-clad fibers. Elaborated asymmetric polished couplers are presented. By using these couplers in pumping power set-ups of double-clad fiber very good pumping efficiency a very good efficiency was attained. The experimental and numerical optimizations of designed couplers are presented. 相似文献
66.
We demonstrate a 1047 nm Nd:LiYF4 (Nd:YLF) laser by directly pumping into the upper lasing level with a tunable Ti:Sapphire laser. The results obtained for direct upper laser level pumping at 863, 872 and 880 nm of Nd:YLF were compared with traditional 806 nm pump band excitation. Highly efficient 1047 nm continuous-wave (CW) laser emission under direct pumping at 880 nm in an 8 mm thick, 1.0 at.% Nd:YLF crystal is obtained. The slope efficiency is improved from 55.6% for traditional pumping at 806 nm to 76.3% for direct pumping at 880 nm. 相似文献
67.
An analytical and numerical study of peristaltic transport of a Johnson-Segalman fluid in an endoscope 下载免费PDF全文
In the present study, we discuss the peristaltic flow of a Johnson-Segalman fluid in an endoscope. Perturbation, homotopy, and numerical solutions are found for the non-linear differential equation. The comparative study is also made to check the validity of the solutions. The expressions for pressure rise frictional forces, pressure gradient, and stream lines are presented to interpret the behavior of various physical quantities of the Johnson-Segalman fluid. 相似文献
68.
A.?N.?Soldatov N.?A.?YudinEmail author A.?V.?Vasilieva Yu.?P.?Polunin 《Russian Physics Journal》2008,51(12):1334-1343
The effect of the design features of the gas-discharge tube on the processes proceeding in the discharge circuit of a metal-vapor
laser has been investigated. The position of electrodes in the gas-discharge tube has been found to significantly affect the
processes at work in the discharge circuit and the energy characteristics of the laser. For instance, gas-discharge tubes
with electrodes placed in the hot region of the discharge channel are typified by high metastable-population rates at the
leading edge of the excitation pulse, whereas with electrodes positioned in cold buffer regions, the leading edge of the voltage
pulse across the resistive component of the tube impedance is seen to peak. Conditions for running-wave generation in the
active media of lasers on self-terminated transitions of metal atoms and the running-wave use efficiency for laser pumping
are discussed, considering a strontium-vapor laser as an illustration. It is shown that the running wave is generated as the
result of the breakdown in the anode end of the gas-discharge tube and is maintained by the energy stored in the capacitive
component of the impedance of the gas-discharge tube. The lasing pulse duration under running-wave excitation corresponds
to the time it takes an ionization wave to propagate from the anode to the cathode of the gas-discharge tube, with pumping
efficiency being ~6–8% for a strontium-vapor laser. The average lasing power varies within 10–15% depending on whether the
totally reflecting cavity mirror is placed near the anode or the cathode of the tube.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 79–87, December, 2008. 相似文献
69.
70.
理论和实验研究了LD泵浦Nd∶Gd0.42Y0.58VO4/Cr4+∶YAG被动调Q锁模激光器.在分析Cr4+∶YAG晶体能级结构和调Q锁模物理过程的基础上,通过数值模拟给出了Cr4+∶YAG调Q锁模的参量要求,然后进行了实验验证.实验中Cr4+∶YAG的初始透过率T0分别为86.3%、95%,输出镜的透过率T分别为10%、20%,在其他条件不变的情况下构成四种不同的组合,均实现了激光器的调Q锁模运转.实验结果表明,降低Cr4+∶YAG的初始透过率T0或提高输出镜透过率T有利于获得较好的锁模效果,与理论分析一致. 相似文献