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排序方式: 共有72条查询结果,搜索用时 636 毫秒
61.
62.
S. P. Sovilj V. M. Vasić D. Lj. Stojić B. Stojčeva-Radovanović Ljubica T. Petkovska 《光谱学快报》2013,46(5):1107-1122
The effect of the substituents, solvent polarities and hydrogen ion concentration on the electronic structure and UV/VIS absorption spectra of some Schiff bases, derivatives of N-(R-benzylidene)benzidine (R = o-NO2 and o-OH, p-OH) and N-(R-furfurylidene)benzidine (R = H and 5 - NO2), have been studied. The spectral shifts obtained in various organic solvents were discussed on the basis of the specific solute - solvent interactions through the formation of hydrogen bonds between hydrogen-bond donor (HBD) solvents and the benzidine nitrogen atom of the Schiff bases. Some interpretations of the electronic aspects of this type of hydrogen bonding were discussed as well as the stabilization effects due to the solvation. Finally, the pK values of the compounds were determined. 相似文献
63.
One of the characteristic examples of the inability of the classical linear frequency response (FR) method to identify the correct kinetic mechanism is adsorption of some substances (p-xylene, 2-butane, propane or n-hexane) on silicalite-1. The linear FR resulted with bimodal FR characteristic functions, which fitted equally well to three different kinetic models: nonisothermal micropore diffusion, two independent isothermal diffusion processes, and an isothermal diffusion-rearrangement process. We show that the second order frequency response functions (FRFs), obtained from the nonlinear FR, can be used for discrimination among these three mechanisms. Starting from the nonlinear models, we derive the theoretical expressions for the first and second order FRFs corresponding to these three mechanisms and show that different shapes of the second order FRFs are obtained for each mechanism. This would enable identification of the real mechanism from nonlinear FR data. 相似文献
64.
epan S. Miljanic Bojan B. Radak Ljubica T. Petkovska 《Journal of Chemical Sciences》1991,103(3):405-408
Spectra of coincidence of CH3F IR absorption with CO2-laser emission at pressures of 2, 10 and 60 Torr were recorded by the use of a photoacoustic detection method in the whole
range of CO2-laser emission. The spectra show that CH3F absorbs many CO2-laser lines in the range 1084–1071 cm−1 with the strongest absorption at 1046.80cm−1, laser line P(20). Absorption is predominantly due to the fundamental of v3, which is well spread over the whole laser emission range. The intensities of all absorptions rise with increasing pressure,
but some absorptions change their relative intensity with respect to one another. In addition, the fine structure of the line
spectrum, characteristic of lower pressure samples, disappears as pressure is increased. 相似文献
65.
Ljubica T. Petkovska Bojan B. Radak epan S. Miljani Raymond T. Bailey Francis R. Cruickshank David Pugh 《Journal of Chemical Sciences》1991,103(3):401-404
Spectra of coincidence of SO2 IR absorption with CO2-laser emission at pressure of 50,100 and 450 Torr were recorded by the use of a photoacoustic detection method in the whole
range of CO2-laser emission. The spectra show that SO2 absorbs many CO2-laser lines in the range 1084–1071 cm−1 with the strongest absorption at 1082.29cm−1, laser line R(26). The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative
intensity with respect to one another. In addition, the fine structure of line spectra, characteristic of lower pressure samples,
disappear as pressure is increased. 相似文献
66.
Ivo Piantanida Mladen Žinić Saška Marczi Ljubica Glavaš‐Obrovac 《Journal of Physical Organic Chemistry》2007,20(4):285-295
Novel bis‐4,9‐diazapyrenium dication has shown reversible pH dependent formation of 4,9‐ diazapyrenium pseudobase in water characteristic for most 4,9‐diazapyrenium derivatives. The compound has formed non‐covalent complexes with nucleotides in water, whose stability is controlled dominantly by aromatic stacking interactions. No cooperativity between two 4,9‐diazapyrenium subunits was observed in binding of nucleotides. Novel bis‐4,9‐diazapyrenium dication formed mono‐intercalative complexes with studied double stranded DNA and RNA. Additional interactions of non‐intercalated part were found to depend significantly on the polynucleotide secondary structure, yielding strong DNA over RNA preference. Appearance of ICD band of 3 was found to be specific for DNA polynucleotides and together with observed destabilisation of double stranded RNA is attributed to the aggregation of compound in one of the RNA grooves. All bis‐4,9‐diazapyrenium dications prepared till now have shown considerable antiproliferative activity against five human tumour cell lines, which suggested mechanism of action by interacting with cell DNA. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
67.
Ljubica Davidović Branislav Sazdović 《The European Physical Journal C - Particles and Fields》2018,78(7):600
We investigate whether the symmetry transformations of a bosonic string are connected by T-duality. We start with a standard closed string theory. We continue with a modified open string theory, modified to preserve the symmetry transformations possessed by the closed string theory. Because the string theory is conformally invariant world-sheet field theory, in order to find the transformations which preserve the physics, one has to demand the isomorphism between the conformal field theories corresponding to the initial and the transformed field configurations. We find the symmetry transformations corresponding to the similarity transformation of the energy-momentum tensor, and find that their generators are T-dual. Particularly, we find that the general coordinate and local gauge transformations are T-dual, so we conclude that T-duality in addition to the well-known exchanges, transforms symmetries of the initial and its T-dual theory into each other. 相似文献
68.
Michael P. Brown Susan J. Cooper Aileen A. Frew Ljubica Manojlović-Muir Kenneth W. Muir Richard J. Puddephatt Mary A. Thomson 《Journal of organometallic chemistry》1980,198(2):C33-C35
The complex [Pt2Me2(μ-H)(μ-dppm)2][PF6] (I, dppm = Ph2PCH2PPh2) has been prepared and characterised by 1H and 31P NMR spectroscopy and by a full molecular structure determination by X-ray methods. The complex undergoes only slow reductive elimination of methane induced by added tertiary phosphine at 70°C. 相似文献
69.
Ljubica Vrhovac Dragoljub Filipovi Milica Misi-vukovi Jovan Veli
kovi 《国际化学动力学杂志》1992,24(10):861-869
Data from previous articles on the initial polymerization rates of a series of monoalkyl substituted phenyl methacrylates were found to depend strongly on the size and position of the monoalkyl substituent in the phenyl ring. In order to investigate the possibility of correlation of all the rate data obtained, all those for phenyl methacrylate and ten other alkylphenyl substituted methacrylate monomers were fitted into empirical linear free energy relationships (LFER). Assuming steady-state kinetics and separating out the initiator decomposition contribution to the initial overall rate Rp, it was demonstrated that k′ = kp/kt½ can be successfully correlated with LFER equations containing predominantly steric parameters. The steric influence is more pronounced in the o- than in the p-substitution, due to the proximity of the o-substituent to the reaction propagation site. The results are corroborated by the existence of an isokinetic relationship of ΔH? vs. ΔS?, providing the proportionality of electronic effects, however small, and the predominating steric effects. The treatment is based on the assumption that the initiator efficiency ? equals 1 and that the termination rate constants kt are equal for monomers of similar structure, what might represent an approximation of the true situation in the system investigated. © John Wiley & Sons, Inc. 相似文献
70.