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81.
S. P. Gromov A. I. Vedernikov Yu. V. Fedorov O. A. Fedorova E. N. Andryukhina N. E. Shepel' Yu. A. Strelenko D. Johnels U. Edlund J. Saltiel M. V. Alfimov 《Russian Chemical Bulletin》2005,54(7):1569-1579
In the presence of Ba2+ ions, (benzothiazolyl)ethenylbenzocrown ether forms the stable sandwich complex 2L⋅Ba2+ with an unusual structure, in which the benzothiazole fragments are arranged one above the other. Irradiation of the sandwich
complex with visible light induces stereoselective [2+2] cycloaddition giving rise to two “head-to-head” isomers of biscrown-cyclobutane.
The addition of dibasic dicarboxylic acids that additionally stabilize the sandwich complex in a favorable conformation affects
the isomer ratio of the cyclobutanes formed. The conformational equilibria for the sandwich complex and cyclobutanes were
studied by 1H NMR spectroscopy.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1524–1533, July, 2005. 相似文献
82.
83.
D. A. Ivanov N. Kh. Petrov M. V. Alfimov A. I. Vedernikov S. P. Gromov 《High Energy Chemistry》2014,48(4):253-259
Photolysis of aqueous solutions of styryl dye 1 in the presence of cucurbit[8]uril (CB[8]) has been studied by optical spectroscopic methods for the molar ratios n = c CB[8]/c 1 in the range of 0 ≤ n ≤ 6. It has been found that the inclusion complexes (1)2@CB[8] dominate in the solution at n ≤ 0.5, whereas the complexes 1@CB[8] dominate at n ≥ 1. The stability constants have been determined for the 1: 1 (log K 1 = 6.2 (L mol?1)) and 2: 1 (log β = 11.9 (L2 mol?2)) complexes. The fluorescence decay kinetics of dye 1 in the presence of CB[8] is two-exponential, with the average lifetime increasing substantially at n ≥ 1. It has been shown that the system can operate in the cyclic mode as an assembler (or supramolecular catalyst) in the photodimerization reaction of dye 1 to form cyclobutane derivative 2. The stability constant of the complex 2@CB[8] (log K 3 = 5.9 (L mol?1)) and the quantum yield of cycloaddition (? ≈ 0.07 at n ≈ 0.5) have been determined. 相似文献
84.
Ivanov DA Petrov NKh Nikitina EA Basilevsky MV Vedernikov AI Gromov SP Alfimov MV 《The journal of physical chemistry. A》2011,115(17):4505-4510
The photophysical properties of aqueous solution of styryl dye, 4-[(E)-2-(3,4-dimethoxyphenyl)ethenyl]-1-ethylpyridinium perchlorate (dye 1), in the presence of cucurbit[7]uril (CB[7]) was studied by means of fluorescence spectroscopy methods. The production of 1:1 host-guest complexes in the range of CB[7] concentrations up to 16 μM with K = 1.0 × 10(6) M(-1) has been observed, which corresponds to appearance of the isosbestic point at 396 nm in the absorption spectra and a 5-fold increase in fluorescence intensity. The decay of fluorescence was found to fit to double-exponential functions in all cases; the calculated average fluorescence lifetime increases from 145 to 352 ps upon the addition of CB[7]. Rotational relaxation times of dye 1 solutions 119 ± 14 ps without CB[7] and 277 ± 35 ps in the presence of CB[7] have been determined by anisotropy fluorescence method. The comparison of the results of quantum-chemical calculations and experimental data confirms that in the host cavity dye 1 rotates as a whole with CB[7]. 相似文献
85.
Sergey P. Gromov Valery B. Nazarov Vitaly G. Avakyan Marina V. Fomina Artem I. Vedernikov Lyudmila G. Kuz’mina Tat’yana G. Vershinnikova Natalia A. Lobova Vladimir Yu. Rudyak Michael V. Alfimov Judith A.K. Howard 《Journal of photochemistry and photobiology. A, Chemistry》2011,217(1):87-99
The spontaneous and photoinduced protonation of 4-(2-naphthyl)pyridine (1) in solutions and in complexes with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) were studied by absorption and fluorescence spectroscopy. The structure and stability of the complexes (log K = 1.5–2.3) of 1, its protonated form 2, and quaternized derivative, 1-methyl-4-(2-naphthyl)pyridinium perchlorate (3), with β-CD and HP-β-CD were studied by 1H NMR. It was shown that irrespective of the solution pH, compound 1 resides in the cyclodextrin cavity. HP-β-CD better binds the neutral form of 1 than β-CD, while naphthylpyridinium salts have approximately equal binding affinity to both cyclodextrins. The structures of salt 3 and pseudorotaxane complex 1@β-CD were determined by X-ray diffraction analysis. According to spectral data, pKa of 1 in water is 5.12, which promotes protonation of nitrogen both in the ground state and in the excited state. As a consequence, the fluorescence spectrum exhibits only the protonated form with a lifetime of 15 ns. The addition of HP-β-CD to a solution of 1 results in inclusion complex 1@HP-β-CD; simultaneously pKa of 1 decreases to 4.62 and non-protonated form fluorescence (NFF) of 1 with a lifetime of 1.25 ns appears. Thus, the residence of 1 in the HP-β-CD cavity hampers its protonation in the excited state. From comparison of the initial regions of fluorescence of 1 in solution and in the HP-β-CD complex after pulse excitation, a mechanism for appearance of short-lived NFF of 1 was proposed. Quantum chemical simulation of the protonation and complexation of 1 in the presence of water was performed. On the basis of results, reversible photoinduced mechanical motion of 1 in the HP-β-CD cavity was suggested. 相似文献
86.
Siberian Mathematical Journal - Given $ r\in\{2,3,5\} $ , we study the structure of finite non- $ r $ -decomposable groups whose every non- $ r $ -decomposable maximal subgroup is a $... 相似文献
87.
G. A. Vedernikov V. N. Karnyushin R. I. Soloukhin 《Journal of Applied Mechanics and Technical Physics》1975,16(2):155-162
Dynamics of the operation of a CO2-laser during excitation by a non independent discharge is investigated within the framework of a comparatively simple theoretical model. 相似文献
88.
Ushakov E. N. Gromov S. P. Kuz"mina L. G. Vedernikov A. I. Avakyan V. G. Howard J. A. K. Alfimov M. V. 《Russian Chemical Bulletin》2004,53(7):1549-1562
The structure of the E,E isomer of a butadienyl dye of the benzothiazole series containing a 15-crown-5 fragment was established by X-ray diffraction analysis. The stacking motif of the dye molecules in the crystal structure is, apparently, attributable to intermolecular -interactions between the large conjugated fragments. The possibility of [2+2] photocycloaddition occurring in the crystal is discussed. Reversible geometrical photoisomerization of the dye and its complex with Mg2+ in acetonitrile solution was studied by spectrophotometry and 1H NMR spectroscopy. Photoirradiation of the complex of the E,E isomer with Mg2+ leads predominantly to isomerization of the C=C bond adjacent to the benzothiazole fragment. Regioselective E,EZ,E photoisomerization occurs via a singlet mechanism with a quantum yield of about 0.45. The quantum yield of reverse Z,EE,E photoisomerization is approximately 0.52. The structures of different geometrical isomers of the dye complex with Mg2+ were calculated by the quantum-chemical density functional theory (DFT). 相似文献
89.
Fedorova O. A. Vedernikov A. I. Baronova I. E. Eshcheulova O. V. Fedorchuk E. A. Gloe K. Gromov S. P. 《Russian Chemical Bulletin》2004,53(2):396-403
A simple and convenient procedure was developed for the synthesis of formyl derivatives of benzodiazacrown ethers and benzocryptands by condensation of 3,4-bis(2-iodoethoxy)benzaldehyde with ,-oligooxaalkanediamines or diazacrown ethers in the presence of alkali metal carbonates under high-dilution conditions in various organic solvents and their mixtures with water. In the reactions giving rise to diazacrown ethers, alkali metal cations exhibit the negative template effect resulting in a decrease in the yield of the target product if the size of the cation matches well the size of the cavity of the crown ether formed. An N,N"-bis(carboxymethyl) derivative was prepared from the formyl derivative of benzodiaza-18-crown-6. 相似文献
90.
Chmutova G. A. Kurbangalieva A. R. Vedernikov A. N. 《Russian Journal of General Chemistry》2001,71(5):780-785
The relative stability of tautomeric forms of 1-methyl-substituted heteropyrazolones (O, S, Se) and their gas-phase acidity were estimated by DFT calculations with various basis sets and methods of geometry optimization. The electron correlation effects make an appreciable contribution to the Gibbs free energies of their tautomers and anions, especially those containing the heavy atoms. The qualitative pattern of tautomerism in pyrazolones is essentially similar to that obtained by semiempirical and nonempirical RHF calculations: The most stable is the CH form. For hetero analogs, consideration of electron correlations effects increases the relative stability of SH (SeH) forms. The series of relative acidity of the compounds depending on the heteroatom is preserved (Se O). 相似文献