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71.
Vassil B. Delchev 《Monatshefte für Chemie / Chemical Monthly》2010,16(4):1153-1157
Abstract
In this research we studied the mechanisms of photoinduced conformational transformation of hydroxy forms of (deoxy)uridine, which have been found to be accessible in aqueous solution. The mechanisms were compared with those for the oxo forms of (deoxy)uridine studied recently. The mechanisms of photoinduced proton detachment in oxo and hydroxy forms of (deoxy)uridine were also studied. These mechanisms are driven by the repulsive 1πσ* state. 相似文献72.
The anodic oxidation of tungsten has been studied in 1 M Na2SO4 solutions containing 0–0.25 M NaF. Steady-state currents measured in the passivation and passivity ranges increase significantly
with increasing fluoride concentration, indicating enhanced dissolution of the oxide film. The electrochemical impedance response
is dominated by the processes in the barrier layer and at its interface with the electrolyte. The presence of a pseudo-inductive
loop in the impedance spectra at intermediate frequencies indicates point defect interaction during film growth and dissolution
processes. A kinetic model including the recombination reaction between oppositely charged point defects at the film/solution
interface as well as a kinetic scheme for tungsten dissolution through the film mediated by cation vacancies is proposed.
It is found to reproduce satisfactorily the steady-state currents and the impedance spectra in the potential range 0.2–2 V.
Such a model for the conduction mechanism in the barrier layer is believed to be an essential part of a modelling approach
to the formation of a nanoporous overlayer on tungsten in fluoride-containing solutions. 相似文献
73.
George B. Mullen Patricia A. Swift David M. Marinyak Stanley D. Allen Jeffrey T. Mitchell C. Richard Kinsolving Vassil St. Georgiev 《Helvetica chimica acta》1988,71(4):718-732
The synthesis and antifungal activity of a novel series of 3-aryl-5-[(aryloxy)alkyl]-3-[(1H-imidazol-1-yl)-methyl]-2-methylisoxazolidines and related compounds, are discussed. The synthesis of the title compounds was accomplished via a 1,3-dipolar cycloaddition of α-substituted ketonitrones with l-alkenyl phenyl ethers (Scheme 2 and 3). The compounds were evaluated for in vitro antifungal activity in solid agar cultures against a broad variety of yeast and systemic mycoses and dermatophytes. While antifungal activity was evident throughout the series, in general, derivatives having halogen atom(s) in either or both aryl rings demonstrated the highest potency, especially against Trichophyton rubrum and Candida albicans. The dichloro analog 20 (PR 967-248) was found to possess the most useful activity. Its minimum inhibitory concentration (MIC) values ranged between 0.2 and 2.0 μg/ml, as compared to 0.2–20.0 μg/ml for the standard drug ketoconazole (4). 相似文献
74.
Robert A. Mack Patrick J. Carroll Vassil St. Georgiev 《Journal of heterocyclic chemistry》1988,25(2):603-606
The isolation of a stable intermediate product and the mechanism of a novel 3(2H)-furanone-2(5H)-furanone rearrangement that led to the facile preparation of a new class of γ-lactone amides 2 and 4 are discussed. 相似文献
75.
A novel rearrangement of 2(5H)-furanones is described. When refluxed in aq. Ethanolic solution in the presence of excess KOH, the 2,5-dihydro-2-oxofuran-3-carboxamides 6 underwent a novel rearrangement to the corresponding 4,5-dihydro-4-oxo-2-(phenylamino)-3-furancarboxylic acids 1 in moderate-to-excellent yields. 相似文献
76.
Grace A. Bennett Patricia A. Swift George B. Mullen Jeffrey T. Mitchell Stanley D. Allen Wendy E. Jones C. Richard Kinsolving Vassil St. Georgiev 《Helvetica chimica acta》1988,71(7):1622-1629
The synthesis and antifungal activity of a novel series of 1-[(3,5-bisaryl-2-methylisoxazolidin-3-yl)methyl]-1H-1,2,4-triazoles 6 and 7 (i.e. 8 – 19 ) are discussed. The preparation of 8 – 19 was straightforward and highlighted by a regiospecific 1,3-dipolar cycloaddition of α-substituted (E)-ketonitrones 4 with appropriate atyrene derivatives 5 that led to a cis/trans-diastereoisomeric mixture of the corresponding triazoles (Scheme). The title compounds were evaluated for in vitro antifungal activity in solid agar cultures against a broad array of yeast and systemic mycoses and dermatophytes. The in vivo activity was determined in an immune-compromised mouse model of systemic candidiasis. While the in vitro activity was evident throughout the series, it was moderate in potency. However, some of the triazole derivatives demonstrated a potent in vivo activity comparable to that of the standard drug ketoconazole. Analogue 12 (PR 988-399) emerged as the best overall compound demonstrating potent antifungal activity in both in vitro and in vivo assays. 相似文献
77.
All singly-even self-dual [40,20,8] binary codes which have an automorphism of prime order
are obtained up to equivalence. There are two inequivalent codes with an automorphism of order 7 and 37 inequivalent codes with an automorphism of order 5. These codes have highest possible minimal distance and some of them are the first known codes with weight enumerators prescribed by Conway and Sloane. 相似文献
78.
Vassil B. Delchev Hans Mikosch Georgi St. Nikolov 《Monatshefte für Chemie / Chemical Monthly》2001,132(3):339-348
Summary. The mechanism of the keto-enol interconversion of pentane-2,4-dione (trivial name: acetylacetone, acac) was examined at the restricted Hartree-Fock (HF) level and the DFT correlation functional BLYP method using the 6-311G** basis, both included in the program GAUSSIAN 98. Two initial enol forms are considered: the omega and sickle forms, related
by a rotation of 180° around the OC*CC bond. The study is restricted to the through-space transfer of the hydroxyl proton
to C(2). The two geometry-optimized enol forms are planar; the geometry optimization of the diketone forms leads to the same
non-planar structure, regardless of the starting enol geometry. The transition state of the through-space omega-enol→diketone
conversion has also a non-planar structure, indicating that the hydroxyl proton moves outside of the CCC plane. The BLYP-calculated
energy barrier of the forward (omega-enol→diketone) conversion is 245 kJ·mol−1, that of the reverse (diketone→omega-enol) conversion 222 kJ·mol−1; thus, an almost symmetric barrier, which is not thermally accessible, is defined. The energy barrier for the sickle-enol→diketone
conversion is considerably lower (187 kJ·mol−1), to access the sickle form from the more stable omega form, a rotation is needed (energy barrier: 88 kJ·mol−1). The HF-calculated barriers are 1.3–1.4 times higher than those obtained with the BLYP method.
Received July 6, 2000. Accepted (revised) September 8, 2000 相似文献
79.
We prove that the moduli spaces
of polarized Abelian threefolds with polarizations of types D=(1,1,2),(1,2,2),(1,1,3) or (1,3,3) are unirational. The result is based on the study of families of simple coverings of elliptic curves of degree 2 or 3 and on the study of the corresponding period mappings associated with holomorphic differentials with trace 0. In particular we prove the unirationality of the Hurwitz space
which parametrizes simply branched triple coverings of an elliptic curve Y with determinants of the Tschirnhausen modules isomorphic to A-1. Dedicated to the memory of Fabio BardelliMathematics Subject Classification (2000) Primary: 14K10; Secondary: 14H10, 14H30, 14D07 相似文献