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671.
Jozef Rychlý Lyda Matisová-Rychlá Vladimír Bukovský Martina Pleteníková Milan Vrška 《Macromolecular Symposia》2005,231(1):178-192
Lignin-containing papers from different sources and of different age were irradiated by the visible light and the progress of the degradation reaction was followed by non-isothermal chemiluminescence method. Kinetic data obtained for papers degraded in oxygen were compared with double fold endurance test and carbonyl groups concentration. The effect of lignin on degradation of cellulose after deacidification treatment of the paper by methoxymagnesium methylcarbonate (MMMC) was ascertained and a mechanism of co-oxidation of lignin and cellulose in originally alkaline conditions was outlined. 相似文献
672.
Nguyen TL Dils B Carl SA Vereecken L Peeters J 《The journal of physical chemistry. A》2005,109(43):9786-9794
In this work, the C(2)F(4)(X(1)A(g)) + O((3)P) reaction was investigated experimentally using molecular beam-threshold ionization mass spectrometry (MB-TIMS). The major primary products were observed to be CF(2)O (+ CF(2)) and CF(3) (+ CFO), with measured approximate yields of % versus %, respectively, neglecting minor products. Furthermore, the lowest-lying triplet and singlet potential energy surfaces for this reaction were constructed theoretically using B3LYP, G2M(UCC, MP2), CBS-QB3, and G3 methods in combination with various basis sets such as 6-31G(d), 6-311+G(3df), and cc-pVDZ. The primary product distribution for the multiwell multichannel reaction was then determined by RRKM statistical rate theory and weak-collision master equation analysis. It was found that the observed production of CF(3) (+ CFO) can only occur on the singlet surface, in parallel with formation of ca. 5 times more CF(2)O(X) + CF(2)(X(1)A(1)). This requires fast intersystem crossing (ISC) from the triplet to the singlet surface at a rate of ca. 4 x 10(12) s(-1). The theoretical calculations combined with the experimental results thus indicate that the yield of triplet CF(2)(?(3)B(1)) + CF(2)O formed on the triplet surface prior to ISC is < or =35%, whereas singlet CF(2)(X(1)A(1)) + CF(2)O is produced with yield > or =60%, after ISC. In addition, the thermal rate coefficients k(O + C(2)F(4)) in the T = 150-1500 K range were computed using multistate transition state theory and can be expressed as k(T) = 1.67 x 10(-16) x T(1.48) cm(3) molecule(-1) s(-1); they are in agreement with the available experimental results in the T = 298-500 K range. 相似文献
673.
[carbohydrate structure: see text] Hydrogen bond mediated NMR J couplings offer additional structural information. The interpretation of these usually small (h)J couplings are, however, not necessarily straightforward. In the present case of a carbohydrate system, a four-bond classical W coupling, (4)J(HO4,H5), is more reasonable on the basis of, in particular, density functional theory calculations of spin-spin coupling constants at the UB3LYP/6-311G** level of theory. 相似文献
674.
Pavol Valko Marcel Miglierini Jozef Sitek Milan Hucl Anna Grusková 《Hyperfine Interactions》1990,61(1-4):1113-1116
Annealing time and temperature dependence of Y, Ba, Cu, Fe nitrade mixture towards new phases creation was revealed by Mössbauer spectroscopy. The observed changes can be assigned to chemical decomposition of corresponding nitrades and creation of intermedial and final Y1Baz(Cuo.o3Feo. o3)3Ox phase. 相似文献
675.
Jozef Sitek Marcel Miglierini Jozef Lipka Pavol Valko Ignác Tóth 《Hyperfine Interactions》1990,60(1-4):777-779
The present work provides an analysis of crystallization processes in amorphous metallic alloys Fe80Si4Cr1.0B14 and Fe67Co18B14Si1. Crystallization of the first sample started at the temperature of 648 K. The fully crystalline state was observed after
annealing at 748 K. We identified four sextets. One corresponds to crystalline Fe2B and the three others to FeSi solid solution with 10 at .% of Si. Crystallization of Fe67Co18B14Si1 started at the temperature of 623 K. We identified two crystalline phases. The first may have its origin as (Fe1−xCox)3B, the second one may correspond to a Fe−Co solid solution with a different Co content. 相似文献
676.
Kövér KE Batta G Kowalewski J Ghalebani L Kruk D 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(2):273-281
Conventional relaxation parameters (T1(-1), T2(-1), and NOE), obtained at different temperatures and magnetic fields, are reported for the hydroxymethyl (C6) carbon in methyl-beta-D-glucopyranoside in a D2O/DMSO cryosolvent. These data are interpreted with the Lipari-Szabo model. In addition, two-field measurements of longitudinal and spin-locked relaxation rates related to the cross-correlated carbon-proton dipole-dipole interactions for the same carbon are reported. The complete data set consisting the conventional and cross-correlated relaxation parameters is interpreted using a new "hybrid" approach, in which the Lipari-Szabo model for the auto-correlated spectral densities is combined with the two-site jump model for the cross-correlated spectral densities, with the global correlation time as a common parameter. The two-site jump rates thus obtained are in reasonable agreement with the ultrasonic relaxation measurements, and have reasonable temperature dependence. 相似文献
677.
Hermans I Vereecken L Jacobs PA Peeters J 《Chemical communications (Cambridge, England)》2004,(9):1140-1141
The mechanism of the recently proposed catalytic oxidation of hydrocarbons by oxygen in the presence of N-hydroxyphthalimide (NHPI) was established by quantum chemical calculations, consistent with experiments. 相似文献
678.
Gonda J 《Angewandte Chemie (International ed. in English)》2004,43(27):3516-3524
Among the reactions available to synthetic chemists for the construction of new C--C bonds, the Claisen rearrangement is one of the most powerful, elegant, and well-characterized methods. A genuinely new variant, the Bellus-Claisen rearrangement came to light a quarter of a century ago: The reaction of an allylic ether, thioether, or amine with a ketene leads through a [3,3] sigmatropic bond reorganization of a zwitterionic intermediate to an E unsaturated ester, thioester, or amide. When applied to cyclic allylic substrates, a ring-enlargement by four carbon atoms in one step provides medium-ring unsaturated E-configured lactones, thiolactones, and lactams. The scope of the Bellus-Claisen rearrangement and the optimum reaction conditions will be discussed in this Minireview. 相似文献
679.
Jozef Džurina 《Czechoslovak Mathematical Journal》2004,54(1):107-117
In this paper we present some new oscillatory criteria for the n-th order neutral differential equations of the form
The results obtained extend and improve a number of existing criteria. 相似文献
680.
Gorecka E Pociecha D Mieczkowski J Matraszek J Guillon D Donnio B 《Journal of the American Chemical Society》2004,126(49):15946-15947
The polycatenar bent-shaped molecules are able to form columnar phases with column stratum built of few molecules, arranged in coplanar or conelike geometry. In the latter case, the phase becomes axially polar, with electric spontaneous polarization reorientable in the electric field by flipping the cone axis. The phase is antiferroelectric; in the plane perpendicular to columns, the ferroelectric hexagonal order exists, but the columns are broken along the z direction and the polarization direction alternates between the blocks. 相似文献