首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   186篇
  免费   36篇
化学   18篇
物理学   204篇
  2021年   1篇
  2019年   2篇
  2018年   1篇
  2014年   2篇
  2013年   2篇
  2011年   2篇
  2010年   8篇
  2009年   33篇
  2008年   28篇
  2007年   31篇
  2006年   16篇
  2005年   12篇
  2004年   5篇
  2003年   4篇
  2002年   10篇
  2001年   12篇
  2000年   3篇
  1999年   8篇
  1998年   6篇
  1997年   3篇
  1996年   3篇
  1995年   7篇
  1994年   4篇
  1993年   6篇
  1992年   4篇
  1991年   3篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1986年   1篇
  1980年   1篇
排序方式: 共有222条查询结果,搜索用时 31 毫秒
41.
We have studied both analytically and numerically the transient active mode locking in the case of a modulation frequency detuning. Analytical results for pulse width and position, extending previous works, are obtained within the frame of the stationary theory by assuming that a short pulse restores its shape after each round trip. Numerical evaluation leads to relaxation oscillations and change of the short-pulse shape. The results of both approaches agree with each other only for small detunings, when laser is operated in the steady state. For larger detunings the laser dynamics change dramatically, and the three operation modes observed earlier in experiments were demonstrated numerically: sequences of damped relaxation oscillations, deep periodic spiking and chaotic spiking. The periodic spiking can be used to increase the intensity of mode-locked pulses.  相似文献   
42.
43.
The adsorption structure and hydrogen-bonded complexes of alkane and alkene derivatives self-assembled on HOPG were studied by scanning tunneling microscopy (STM) and Molecular Mechanics (MM) simulations. The effect of different interior -CHCH- conformations and functional groups in molecules on the structure and stability of self-assembled monolayers was considered. It was found that octadecanol and trans-oleic acid could form stable structure on HOPG and their high-resolution images could be obtained by STM. Octadecanol exhibited two kinds of packing by alkyl-alkyl and adsorbate-substrate interactions. The interior trans-CHCH- group in trans-oleic acid had a slight influence on the self-assembly configuration. However, owing to the cis-double bond in the interior of cis-oleyamine molecule, the ordered monolayer could not be easily imaged by STM at ambient conditions. The adsorption conformations of three kinds of molecules on HOPG surface were optimized by MM simulation, respectively. The analysis of hydrogen-bond interactions by computation stimulation also revealed that the stability of cis-oleyamine on HOPG was the worst. These results demonstrated that molecular self-assembly and its stability could be significantly tailored by changing the molecular structure.  相似文献   
44.
An actively mode-locked fiber ring laser based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is demonstrated to operate stably with a simple configuration. By forward injecting an easily-generated external pulse train, the mode-locked fiber laser can generate an optical-pulse sequence with pulsewidth about 6 ps and average output power about 7.9 mW. The output pulses show an ultra-low RMS jitter about 70.7 fs measured by a RF spectrum analyzer. The use of the proposed forward-injection configuration can realize the repetition-rate tunability from 1 to 15 GHz for the generated optical-pulse sequences. By employing a wavelength-tunable optical band-pass filter in the laser cavity, the operation wavelength of the designed SOA-based actively mode-locked fiber laser can be tuned continuously in a wide span between 1528 and 1565 nm. The parameters of external-injection optical pulses are studied experimentally to optimize the mode-locked fiber laser.  相似文献   
45.
The compounds Ru(CCCCFc)(PP)Cp [PP = dppe (1), dppm (2)], have been obtained from reactions between RuCl(PP)Cp and FcCCCCSiMe3 in the presence of KF (1) or HCCCCFc and K[PF6] (2), both with added dbu. The dppe complex reacts with Co2(CO)6(L2) [L2 = (CO)2, dppm] to give 3, 4 in which the Co2(CO)4(L2) group is attached to the outer CC triple bond. The PPh3 analogue of 3 (5) has also been characterised. In contrast, tetracyanoethene reacts to give two isomeric complexes 6 and 7, in which the cyano-olefin has added to either CC triple bond. The reaction of RuCl(dppe)Cp with HCCCCFc, carried out in a thf/NEt3 mixture in the presence of Na[BPh4], gave [Ru{CCC(NEt3)CHFc}(dppe)Cp]BPh4 (8), probably formed by addition of the amine to an (unobserved) intermediate butatrienylidene [Ru(CCCCHFc)(dppe)Cp]+. The reaction of I2 with 8 proceeds via an unusual migration of the alkynyl group to the Cp ring to give [RuI(dppe){η-C5H4CCC(NEt3)CHFc}]I3 (9). Single-crystal X-ray structural determinations of 1, 2 and 4-9 are reported.  相似文献   
46.
A detailed experimental analysis of the amplitude noise in high-repetition-rate picosecond pulse trains generated by spectral filtering of a frequency-modulated Er-Yb:glass laser is reported. Two distinct sources of noise are identified, and stabilization techniques for noise suppression are proposed and experimentally demonstrated. Intensity noise suppression of ∼20 dB, corresponding to less than 2% residual amplitude fluctuations of the pulse train, has been achieved at repetition rates of 2.5 GHz and 5 GHz with pulse durations of ∼50 ps. Received: 28 July 1999 / Revised version: 13 September 1999 / Published online: 20 October 1999  相似文献   
47.
Multiwavelength dispersion-tuned actively mode-locked erbium-doped fibre ring laser is demonstrated by incorporating a section of highly nonlinear fibre (HNLF) in the laser cavity. The HNLF and the time gate element (modulator) in the fibre laser successfully suppress the gain competition in the erbium-doped fibre, and thus enable multiwavelength operation. Simultaneous generation of 10 GHz pulses up to eight different wavelengths is achieved. Wavelength, spacing and modes number tuning are investigated by changing fibre cavity length, dispersion, and erbium-doped fibre amplifier power, respectively.  相似文献   
48.
We report on a diode-pumped passively mode-locked Nd:Gd0.64Y0.36VO4 laser with a Cr4+:YAG saturable absorber. Q-switched mode locking (QML) with 90% modulation depth was obtained. The peak power of the mode-locked pulse near the maximum of the Q-switched envelope was estimated to be about 1.7 MW at the pump power of 12 W. Besides QML, continuous-wave mode locking was also experimentally realized, for the first time to our knowledge, in the laser under a strong intracavity pulse energy fluence. The mode-locked pulse width is about 2.96 ps at a repetition rate of 161.3 MHz.  相似文献   
49.
A widely tunable cw diode-pumped room-temperature Tm:GdVO4 laser is built. Output power of 2.8 W and a slope effic/ency of 22% pumped by a 18 W Fibre-coupled diode laser at 795nm have been obtained. Continuous tunability from 1820nm to 1946nm is achieved. In addition, the factors that contribute to the efficiency of oscillation are studied.  相似文献   
50.
A two-dimensional array of dodecagonal photonic quasicrystal (12PQC) is fabricated on the surface of current injected GaN-based LEDs to out-couple guided modes. The spatially-resolved surface light extraction mapping of 12PQC is observed and compared with that of triangular lattice photonic crystal (3PC) by microscopic electrical luminescence and scanning near-field microscopy. The higher enhancement factor of 12PQC is obtained to be larger than that of 3PC. It is shown that 12PQC is more favourable and efficient for light extraction of guided lights.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号