全文获取类型
收费全文 | 282篇 |
免费 | 14篇 |
国内免费 | 11篇 |
专业分类
化学 | 121篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 55篇 |
物理学 | 125篇 |
出版年
2023年 | 3篇 |
2021年 | 2篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 22篇 |
2012年 | 17篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 19篇 |
2003年 | 10篇 |
2002年 | 2篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 5篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有307条查询结果,搜索用时 15 毫秒
141.
Ong SY Zhu P Poon YF Leung KH Fang WH Phillips DL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(9):2163-2171
We report time-resolved resonance Raman spectra for 2-fluorenylnitrene and its dehydroazepine products acquired after photolysis of 2-fluorenylnitrene in acetonitrile. The experimental Raman band frequencies exhibit good agreement with the calculated vibrational frequencies from UBPW91/cc-PVDZ density functional calculations for the singlet and triplet states of the 2-fluorenylnitrene as well as BPW91/cc-PVDZ calculations for the two dehydroazepine ring-expansion product species. The decay of the 2-fluorenylnitrene Raman signal and the appearance of the dehydroazepine products suggest the presence of an intermediate species (probably an azirine) that does not absorb very much at the 416 nm probe wavelength used in the time-resolved resonance Raman experiments. Comparison of the singlet 2-fluorenylnitrene species with the singlet 2-fluorenylnitrenium ion species indicates that protonation of the nitrene to give the nitrenium ion leads to a significant enhancement of the cyclohexadienyl character of the phenyl rings without much change of the C-N bond length. 相似文献
142.
Collision-induced photon emissions (CIE) were observed for keV CO2+·/He collisions from 190 to 1020 nm. The emissions were assigned to the Δν=0 band of the CO2+· B 2Σu+ → X 2Πg electronic transition and the Δν = +3, +2, +1, 0, −1, −2, −3 vibrational transition progression in the CO2+· A 2Πu → X 2Πg electronic transition. The other peaks arise from the emissions of excited O· fragment atoms and the target gas. The relative intensities of the CO2+· and O· emissions are independent of the ion translational energy above 3 keV, supporting the curve-crossing mechanism for collisional
excitation. Investigation of the relative intensities within the A 2Πu → X 2Πg emission of CO2+· indicates that the vibrational distribution is well described by the Franck-Condon principle at high collision energy, a
consequence of short collision time but not necessarily an indication of vertical transitions. Below 3 keV ion translational
energy, vibrational excitation in the A 2Πu electronic state was observed. The observation is consistent with the explanation that the reaction occurs at small impact
parameters, in which short-range, repulsive interactions between the projectile and the target result in direct translational-vibrational
excitation. 相似文献
143.
Levulinic acid and related γ-ketoacids react with diethylaminosulfur trifluoride to give γ-fluorobutyrolactones in good yield. The involvement of a bicyclic (3.2.1) mechanism is considered. 相似文献
144.
Magnetoresistivity measurements have been performed in fields up to 40 kOe on some concentrated amorphous LaGdAu alloys exhibiting characteristics of a spin-glass. The negative magnetoresistivity at low temperature is found to be roughly proportional to the square of the magnetization. The resistivity minima in these alloys are attributed to a mechanism of electron scattering from magnetic clouds coupled by RKKY interactions, in qualitative agreement with analysis of our remanent magnetization data. 相似文献
145.
Marta Falcone Lok Nga Poon Dr. Farzaneh Fadaei Tirani Prof. Marinella Mazzanti 《Angewandte Chemie (International ed. in English)》2018,57(14):3697-3700
Cleavage of dihydrogen is an important step in the industrial and enzymatic transformation of N2 into ammonia. The reversible cleavage of dihydrogen was achieved under mild conditions (room temperature and 1 atmosphere of H2) by the molecular uranium nitride complex, [Cs{U(OSi(OtBu)3)3}2(μ‐N)] 1, leading to a rare hydride–imide bridged diuranium(IV) complex, [Cs{U(OSi(OtBu)3)3}2(μ‐H)(μ‐NH)], 2 that slowly releases H2 under vacuum. This complex is highly reactive and quickly transfers hydride to acetonitrile and carbon dioxide at room temperature, affording the ketimide‐ and formate‐bridged UIV species [Cs{U(OSi(OtBu)3)3}2(μ‐NH)(μ‐CH3CHN)], 3 and [Cs{U(OSi(OtBu)3)3}2(μ‐HCOO)(μ‐NHCOO)], 4 . 相似文献
146.
Pak Wai Poon 《Proceedings of the American Mathematical Society》1998,126(4):1071-1080
We extend the technique used by Kordula and Müller to show that the stability radius of a quasi-Fredholm operator is the limit of as . If is an isolated point of the Apostol spectrum , then the above limit is non-zero if and only if is quasi-Fredholm.
147.
Three-dimensional location of fluorescent inhomogeneities in turbid media by scanning heterodyne holography 总被引:1,自引:0,他引:1
We describe and illustrate experimentally a method aimed at the three-dimensional (3-D) imaging of fluorescent inhomogeneities embedded in a turbid medium. The method utilizes incoherent scanning holography to capture 3-D information in a single two-dimensional scan and phase-sensitive heterodyne detection to reject multiply scattered light and to produce a single-sideband holographic record. The 3-D imaging capability of the method is illustrated by an example. 相似文献
148.
149.
V.J. Anderson E.M. Terentjev S.P. Meeker J. Crain W.C.K. Poon 《The European physical journal. E, Soft matter》2001,4(1):11-20
We study the phase ordering colloids suspended in a thermotropic nematic liquid crystal below the clearing point and the resulting aggregated structure. Small () PMMA particles are dispersed in a classical liquid crystal matrix, 5CB or MBBA. With the help of confocal microscopy we
show that small colloid particles densely aggregate on thin interfaces surrounding large volumes of clean nematic liquid,
thus forming an open cellular structure, with the characteristic size of inversely proportional to the colloid concentration. A simple theoretical model, based on the Landau mean-field treatment,
is developed to describe the continuous phase separation and the mechanism of cellular structure formation.
Received 13 March 2000 and Received in final form 6 June 2000 相似文献
150.