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2.
V. V. Nikitenko A. I. Martynenko S. A. Ostrovsky V. V. Rusak V. V. Kryuchkov D. A. Topchiev 《Russian Chemical Bulletin》1993,42(2):378-380
3-Methyl-l-vinylpyrazole (M3VP) and 5-methyl-1-vinylpyrazole (M5VP) were isolated as individual substances by vacuum rectification of their mixture (M3VP: M5VP 60 40). For each of them the kinetics of free-radical polymerization in MeOH were measured at low conversions. In both cases the rate of polymerization is proportional to 0.5 order with respect to the initiator (AIBN) concentration. On the other hand, a first order of reaction with respect to monomer concentration is observed only when the latter is relatively low (3M). At higher initial concentrations of monomers the order of reaction becomes less than unity. The overall rate of polymerization for M5VP was higher than for M3VP, whereas the initiation rate remained constant in the whole range of monomer concentrations and did not depend on the exact structure of the monomer. The difference in the rates of polymerization observed for M3VP and M5VP is probably connected with the difference in the key parameterk
p/k
t
1/2
for each of the two isomers. It is concluded that the correct kinetic information about homo- and co-polymerization of M3VP and M5VP cannot be obtained without their adequate separation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 413–415, February, 1993. 相似文献
3.
Recent advances in time-dependent density functional theory (TDDFT) have led to computational methods that can predict properties of photoexcited molecules with satisfactory accuracy at comparably moderate cost. We apply these methods to study the photophysics and photochemistry of 4-(dimethyl)aminobenzonitrile (DMABN). DMABN is considered the paradigm of photoinduced intramolecular charge transfer (ICT), leading to dual fluorescence in polar solvents. By comparison of calculated emission energies, dipole moments, and vibrational frequencies with recent results from transient spectroscopy measurements, a definitive assignment of the electronic and geometric structure of the two lowest singlet excited states of DMABN is possible for the first time. We investigate the mechanism of the ICT reaction by means of minimum energy path calculations. The results confirm existing state-crossing models of dual fluorescence. Our study suggests that analytical TDDFT derivative methods will be useful to predict and classify emissive properties of other donor-acceptor systems as well. 相似文献
4.
It has been shown that under high-power laser UV irradiation (I = 108–1010 W/cm2, λ = 266 nm, τp = 30 ps) water becomes ionized by a two-photon mechanism to form some free radicals including the hydrated electron e?aq. 相似文献
5.
Dmitrij Bondarev Jiří Zedník Ivana Šloufová Ahmed Sharf Marek Procházka Jiří Pfleger Jiří Vohlídal 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):3073-3081
High‐regioregular poly{3‐[6‐(1‐methylimidazolium‐3‐yl)hexyl]thiophene‐2,5‐diyl bromide}, PMHT‐Br, has been prepared by reaction of high‐regioregular (above 92%) poly[3‐(6‐bromohexyl)thiophene‐2,5‐diyl] with 1‐methylimidazole. PMHT‐Br is soluble in water and water miscible solvents such as methanol, DMSO and shows solvatochromism; λmax (nm): 423 (H2O); 435 (MeOH); 452 (DMSO). Increased absorption band broadening observed for aqueous solution as well as NMR spectra in D2O suggests a micelle‐like structure of PMHT‐Br molecules in these solutions: poly(3‐hexylthiophene) core and 1‐methylimidazolium bromide shell. Despite the disturbing effect of ionic groups, the solid‐state PMHT‐Br shows absorption maximum at 520 nm, the band edge at 660 nm (ca. 1.9 eV), and fluorescence emission with maximum at 635 nm, in a good agreement with the polymer regioregularity. Fluorescence emission maxima: λem (nm): 598 (H2O); 562 (MeOH); 574 (DMSO), occur in a vicinity of corresponding adsorption band edges. Plot of electrical conductivity of PMHT‐Br (measured under the dynamic vacuum conditions, 5 × 10?5 Pa) versus 1/T shows a break at about 70 °C same as the temperature dependence of λmax of the solid PMHT‐Br. These breaks indicate an increase in the mobility of polymer segments and ions within PMHT‐Br; however, a thermal analysis did not provide solid evidence for it. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3073–3081, 2010 相似文献
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7.
Bark T von Zelewsky A Rappoport D Neuburger M Schaffner S Lacour J Jodry J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(19):4839-4845
The hexadentate, and ditopic ligand 2,5-bis([2,2']bipyridin-6-yl)pyrazine yields a chiral, tetrameric, square-shaped, self-assembled species upon complexation with Fe2+ ions. The racemate of this complex was resolved with antimonyl tatrate as the chiral auxiliary. The purity of the enantiomer was determined by NMR spectroscopy, by using a chiral, diamagnetic shift reagent, and by circular dichroism (CD). The CD spectrum was also calculated by time-dependent density functional theory, and the correlation that was found between CD spectrum and configuration was confirmed by X-ray cristallography. When a "chiralised" version of the ligand was used instead, the corresponding iron complex was obtained in diastereomerically pure form. 相似文献
8.
A. V. Topchiev A. I. Petel'man V. I. Smetanyuk B. A. Krentsel' 《Russian Chemical Bulletin》1959,8(7):1301-1303
Summary The yield of highly crystalline polypropylene was considerably increased by polymerization of propylene on a chromium oxide catalyst in the presence of small amounts of i-(C4H9)3Al. 相似文献
9.
D. A. Topchiev Yu. A. Malkanduev N. N. Kaptsov V. D. Oppengeim V. A. Kabanov 《Russian Chemical Bulletin》1988,37(4):654-656
1. | Studies of the kinetics of radical polymerization of DAC in aqueous solutions in conditions of deep degrees of conversion of monomer into polymer with a combination of dilatometric, calorimetric, and PMR spectral methods showed that in the conditions selected, poly-merization is accompanied by autoacceleration whose onset corresponds to certain values of the concentration of the polymer formed and is in all probability due to the formation of a fluctuation linkage network of the polymer in the reaction solution. |
2. | The quantitative dependence of the values of the characteristic concentrations of the polymer corresponding to the onset of autoacceleration on the degree of polymerization of the polymer formed at the onset of autoacceleration was established. |
10.
Kęstutis Kubilius Dmitrij Melichov 《Methodology and Computing in Applied Probability》2016,18(3):785-804
In this paper exact confidence intervals for the Orey index of Gaussian processes are obtained using concentration inequalities for Gaussian quadratic forms and discrete observations of the underlying process. The obtained result is applied to Gaussian processes with the Orey index which not necessarily have stationary increments. 相似文献