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T. I. Gubina V. I. Labunskaya A. N. Pankratov S. A. Trushin V. G. Kharchenko 《Chemistry of Heterocyclic Compounds》1993,29(12):1393-1398
The kinetics of the conversion of di-, tri-, and tetraalkylfurans to the corresponding thiophenes were investigated. A correlation between the reactivities and structures of the investigated furans was established. Quantum-chemical calculations of the objects of the recyclization were made. The calculated and experimental data on the reactivities of the investigated compounds were compared. The most likely pathway of the protonation of furans in their recyclization was determined on the basis of calculations of the total energies of the protonated forms.For Communication 2 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1614–1620, December, 1993. 相似文献
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J. Henningsen S. A. Trushin T. Møgelberg M. Hammerich 《Applied physics. B, Lasers and optics》1995,61(3):291-299
A tunable source is described, giving extensive coverage of a spectral region around 2000 cm–1. A frequency self-calibration routine allows for the recording of Doppler-limited absorption profiles with an absolute accuracy of better than 10 MHz. The applicability of the source is demonstrated through measurements on the12C16O,12C17O, and12C18O isotopomers. Collision-broadening parameters and line strengths are determined, some of the data showing evidence of motional narrowing. Sensitivity limits are determined for linear absorption measurements as well as for photoacoustic absorption, and the feasibility of monitoring all three isotopomers with ppm sensitivity is demonstrated.Work supported by the Danish Science Research Council under grants no. 11-6866, 11-0116, and 11-0920 相似文献
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T.-J. Wang Z. Major I. Ahmad S. A. Trushin F. Krausz S. Karsch 《Applied physics. B, Lasers and optics》2010,100(1):207-214
A scheme for the generation of an ultra-broadband, near-infrared beam from a Ti:sapphire source is proposed with the aim to
serve as seed pulse of a petawatt-field synthesizer (Major et al. in Rev. Laser Eng. 37:431, 2009). The idler beam of a noncollinear optical parametric amplifier, pumped at the second harmonic of the Ti:sapphire output,
displays the required bandwidth, albeit with an inherent angular chirp owing to the noncollinear geometry. We propose a scheme
for the compensation of this angular dispersion which consists of a diffraction grating, a telescope and a deformable mirror.
The suitability of this scheme is discussed quantitatively and preliminary experimental findings are shown. 相似文献
28.
In the group-6 metal hexacarbonyls a number of metal-to-ligand charge-transfer (MLCT) and ligand-field (LF or d → d) states can be excited in the near UV. The latter are repulsive. In equilibrium geometry, most of them are higher than the MLCT states. We probed the dynamics of photodissociation of M(CO)6 → M(CO)5 + CO (M = Cr; some data also for M = Mo) with improved time resolution (10–40 fs), pumping at different wavelengths (mainly 270–345 nm) and probing by nonresonant photoionization. The initial relaxation (e.g. within 12.5 fs from T1u excited at 270 nm) is assigned to direct crossing over to the repulsive surface, from where the subsequent dissociation is also remarkably fast (18 fs in this example). That is, there is no detour via the lowest excited singlet state, in contrast to the usual assumption. Also with 318 and 345 nm excitation a direct MLCT → LF relaxation seems to occur before dissociation. The product M(CO)5 is generated in the S1 state, also at pump wavelengths (345 nm) with barely sufficient energy. It relaxes to S0 through a Jahn–Teller induced conical intersection along pseudorotation coordinates, which stimulates a coherent oscillation in S0 in this vibration. A higher-frequency oscillation, assigned to totally symmetric MC stretch vibrations, is already found in the Franck–Condon region; it persists (with different wavenumbers) also during dissociation and over the subsequent product states. This vibration is transverse to the valley of dissociation, which is barrierless. The wavelength-independent mechanism also implies that there is no triplet contribution (which was previously supposed at long wavelengths) to photochemical dissociation of the hexacarbonyls. 相似文献
29.
We used Monte Carlo method to generate the configurations of disassembly of hot nucleus Au* based on the Atomic Mass Table and the conservation of mass and charge number.The resulted charge distribution of fragments was then used to calculate the conditional moments.The logarithm correlation between second and third moments of experimental charge distribution is very well reproduced by theory.It seems that no connection to the critical phenomenon of concerned system exists. 相似文献
30.
In this paper a simplified method for the calculation of average Coulomb energy in statistical model of the disassembly processes of hot nuclei is proposed.The effect of freeze-out volume is studied based on the assumption of Gaussion-like distribution.It is indecated that the centre and dispersion of Gaussion-like distribution somewhat reflect the location and the renge of liquid-gas coexistence phase. 相似文献