全文获取类型
收费全文 | 235篇 |
免费 | 4篇 |
专业分类
化学 | 171篇 |
力学 | 6篇 |
数学 | 21篇 |
物理学 | 41篇 |
出版年
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 11篇 |
2011年 | 17篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 15篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有239条查询结果,搜索用时 218 毫秒
71.
We report on fundamental and intracavity frequency-doubled emission in a miniature Nd:YVO4 (3×3×1 mm) laser. A maximum slope efficiency of ηs=58.6%, with optical efficiency of η0=53.0% at 780 mW pump power was realized in a TEM00 output beam. To obtain the optimum pump-beam focusing conditions we applied a new formalism in which the pump-beam propagation in the active medium was described by its M2 factor. A good agreement between theoretical predictions and experimental results was observed. In second-harmonic regime, obtained by a KTP crystal, 230 mW green power that corresponds to 54% nonlinear conversion efficiency was reached. 相似文献
72.
73.
74.
75.
Broadband quasi-phase-matched second-harmonic generation in MgO-doped periodically poled LiNbO_3 at the communications band 总被引:2,自引:0,他引:2
A novel scheme for broadband second-harmonic generation was developed with type I quasi phase matching by use of an off-digital nonlinear optical coefficient d(31) . This was achieved by matching of the group velocities of the second harmonic and the fundamental, while the phase velocities were quasi phase matched. The desired group-velocity dispersion could be obtained with LiNbO(3) doped with 5 mol. % of MgO. Efficient second-harmonic generation with a bandwidth of 52 nm was obtained for the fundamental wavelength centered at 1566 nm in MgO-doped periodically poled LiNbO(3) , compared with a bandwidth of 1.3 nm for the conventional scheme using d(33) . Efficient frequency doubling of an ultrafast pulse is expected without group-velocity walk-off or pulse distortion. 相似文献
76.
M. Tsuchiya K. Igarashi R. Yatsu K. Taira K.Y. Koay M. Kishi 《Optical and Quantum Electronics》2001,33(7-10):751-766
We report our studies on a fiber-optic soliton compressor for generation of sub-100 femtosecond (fs) optical pulses out of picosecond (ps) diode laser pulses. The soliton compressor is rather simple and composed of a 15 ~ 20 m-long step-like dispersion profiled fiber (SDPF) in conjunction with a single Er-doped fiber amplifier (EDFA). Careful design of such a SDPF compressor was performed, leading to demonstration of 20-fs class compression performance, and experimental investigation was carried out in detail on the optical pulse propagation in the compression processes. In addition, nonlinear fiber loops were applied to suppression of pulse pedestals, resulting successfully in high quality optical pulses of the 100-fs range. 相似文献
77.
V. Lupei A. Lupei N. Pavel T. Taira A. Ikesue 《Applied physics. B, Lasers and optics》2001,73(7):757-762
A high-resolution spectroscopic and emission-decay investigation of highly concentrated Nd:YAG single crystals and ceramics
shows that the state of the Nd3+ ions and their interaction in these materials are similar and can be used for construction of efficient solid-state lasers
directly pumped in the emitting level. This possibility is demonstrated by continuous-wave emission of concentrated Nd:YAG
crystals with up to 3.5 at. % Nd and ceramics with up to 6.8 at. % Nd under resonant 885-nm end pump.
Received: 28 May 2001 / Final version: 17 August 2001 / Published online: 10 October 2001 相似文献
78.
Aida Taira Toma Takahiro Kanada Satoshi 《Journal of Solid State Electrochemistry》2020,24(6):1415-1425
Journal of Solid State Electrochemistry - It is well known that reducing particle size and/or hollowing the particles improves the electrochemical performance, especially the rate capability, of... 相似文献
79.
Encapsulation of ion pairs in small spaces that are isolated from the medium is expected to result in amplified interactions between the ions. Yet, sequestration of ion pairs in self-assembled capsules is complicated by competition of the acids and bases for binding directly to the assembly components. We describe here a hydrogen-bonded capsule 1.2(8).1 that accommodates two γ-picolines and two acids as ion pairs. The supramolecular structure of the discrete 14-component assembly is characterized by NMR spectroscopy. The structure reveals the acids in the tapered ends of the capsule and γ-picoliniums near the glycoluril spacers in the capsule's center. Similar acid-base ion pairs are also obtained with 4-ethylpyridine, γ-picoline with difluoroacetic acid, and γ-picoline with trifluoromethanesulfonic acid. The (1)H NMR spectrum of the γ-picoline/trifluoroacetic acid ion pair shows a signal at δ = 18.7 ppm, indicating the acidic proton is in contact with both the picoline nitrogen and the trifluoroacetate oxygen. Further details about the unusual structures of ion pairs in small spaces are reported. 相似文献
80.
Hiroki Ishikawa Naohiro Uemura Ryo Taira Kento Sano Yasushi Yoshida Takashi Mino Yoshio Kasashima Masami Sakamoto 《Tetrahedron》2019,75(29):3911-3916
A new class of flavonoids bearing cyclic polyethers involving a phenyl ring was conveniently provided by the intramolecular photochemical dimerization of 2-chromonecarboxylic esters. Irradiation of 2-chromonecarboxylate with a polyether tethered at both ends promoted intramolecular [2 + 2] cyclobutane formation leading to 14- to 27-membered cyclic polyethers. The efficiency depended on the substituted position of the phenyl ring, with ortho- and meta-substituted derivatives giving cycloadducts in good chemical yields and quantum efficiencies, whereas the para-derivatives were inert toward photolysis. X-ray crystallographic analysis revealed that the stereochemistry of the macrocyclic cycloadducts exhibited C2-symmetry. 相似文献