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排序方式: 共有141条查询结果,搜索用时 109 毫秒
1.
Olga Bori Timo J. Tolmunen Erik Kollberg Margaret A. Frerking 《International Journal of Infrared and Millimeter Waves》1992,13(6):799-814
The S-parameters of several different quantum well double barrier diodes have been measured. A technique has been developed for measuring whisker contacted diodes with and HP 8510B automatic network analyzer. Special coaxial mounts using K-connectors were designed to enable measurements up to 20 GHz. The voltage-dependent conductance and capacitance were derived from the measured reflection coefficient of each device. The C/V characteristics were observed to exhibit an anomalous increase at voltages corresponding the the negative differential resistance region (NDR). These are the first reported S-parameter measurements in the negative differential resistance region of quantum well double barrier diodes. A theory is presented that explains, in part, the observed results. 相似文献
2.
In distinction from the well-known double-negation embeddings of the classical logic we consider some variants of single-negation embeddings and describe some classes of superintuitionistic first-order predicate logics in which the classical first-order calculus is interpretable in such a way. Also we find the minimal extensions of Heyting's logic in which the classical predicate logic can be embedded by means of these translations. 相似文献
3.
4.
Renata Ga<parová Daniel Zbojek Margita Lácová Katarína Král'ová Anton Gatial Branislav Horváth Alžbeta Krutošíková 《Central European Journal of Chemistry》2005,3(4):622-646
The reactions of substituted furo[3,2-b]pyrrole-5-carboxhydrazides 1 with 5-arylfuran-2-carboxaldehydes 2, 4,5-disubstituted furan-2-carboxaldehydes 3 and thiophene-2-carboxaldehyde 4 has been studied. The advantage of microwave irradiation on some of these reactions was reflected in the reduced reaction
time and increased yields. Reactions of 1 with 4-substituted 1,3-oxazol-5(4H)-ones 11 led to diacylhydrazines 13 or to imidazole derivatives 14 depending on the temperature. 1,2,4-Triazole-3-thione 17 was synthesized by two-step reaction of 1 with phenylisothiocyanate and subsequent base-catalyzed cyclization of thiosemicarbazide 16. The effects of hydrazones 5–10 on inhibition of photosynthetic electron transport in spinach chloroplasts and chlorophyll content in the antialgal suspensions
of Chlorella vulgaris were investigated. 相似文献
5.
Branislav Dugovi
Lubor Fiera MichalK. Cyranski Christian Hametner Nada Prnayov Marin Obranec 《Helvetica chimica acta》2005,88(6):1432-1443
The regio‐ and stereoselectivity of cycloadditions of the nitrone 1a and the chiral, sugar‐derived nitrones 13a and 13b with 3‐(prop‐2‐enoyl)‐1,3‐oxazolidin‐2‐one ( 2 ) depends on the nature of the Lewis acid catalyst used. Addition of Lewis acid reverses the regioselectivity of the cycloaddition, and improves the anti‐diastereoselectivity in the case of chiral nitrones. The sterically favored isoxazolidin‐5‐yl‐substituted adducts 3, 4 , and 14 – 17 are produced as the major products in the absence of Lewis acid, while the electronically favored regioisomers with isoxazolidin‐4‐yl substituents ( 5, 6 , and 18 – 21 , respectively) are obtained as major products in the [Ti(OiPr)2Cl2] catalyzed reactions. The reactions of nitrone 13b with 2 in the presence of other Lewis acids such as ZnCl2, ZnBr2, ZnI2 and MgI2/I2 gave both regioisomeric pairs of the diastereoisomers, favoring the 4‐substituted congeners. The diastereoisomeric isoxazolidines 3a – 6a were reduced with NaBH4 in THF/H2O with subsequent desilylation to yield the separable diols 9 – 12 . Reduction of the diastereoisomeric isoxazolidines 19a and 18a afforded the chiral alcohols 23 and 22 , the latter of which was analyzed by X‐ray crystallography. 相似文献
6.
Differential calculus on quantized simple lie groups 总被引:1,自引:0,他引:1
Branislav Jurčo 《Letters in Mathematical Physics》1991,22(3):177-186
Differential calculi, generalizations of Woronowicz's four-dimensional calculus on SU
q
(2), are introduced for quantized classical simple Lie groups in a constructive way. For this purpose, the approach of Faddeev and his collaborators to quantum groups was used. An equivalence of Woronowicz's enveloping algebra generated by the dual space to the left-invariant differential forms and the corresponding quantized universal enveloping algebra, is obtained for our differential calculi. Real forms for q are also discussed. 相似文献
7.
Branislav Jurčo 《Letters in Mathematical Physics》1991,21(1):51-58
The coherent states for the simplest quantum groups (q-Heisenberg-Weyl, SU
q
(2) and the discrete series of representations of SU
q
(1, 1)) are introduced and their properties investigated. The corresponding analytic representations, path integrals, and q-deformation of Berezin's quantization on , a sphere, and the Lobatchevsky plane are discussed. 相似文献
8.
The partial order 〈E(R)∪{?},?〉, where E(R) is the set of isomorphic subgraphs of the Rado graph R, is investigated. The order types of maximal chains in this poset are characterized as the order types of compact sets of reals having the minimum non-isolated. 相似文献
9.
Ida‐Marie Hyvik Branislav Jansik Kasper Kristensen Poul Jrgensen 《Journal of computational chemistry》2013,34(15):1311-1320
Using the three‐level energy optimization procedure combined with a refined version of the least‐change strategy for the orbitals—where an explicit localization is performed at the valence basis level—it is shown how to more efficiently determine a set of local Hartree–Fock orbitals. Further, a core–valence separation of the least‐change occupied orbital space is introduced. Numerical results comparing valence basis localized orbitals and canonical molecular orbitals as starting guesses for the full basis localization are presented. The results show that the localization of the occupied orbitals may be performed at a small computational cost if valence basis localized orbitals are used as a starting guess. For the unoccupied space, about half the number of iterations are required if valence localized orbitals are used as a starting guess compared to a canonical set of unoccupied Hartree–Fock orbitals. Different local minima may be obtained when different starting guesses are used. However, the different minima all correspond to orbitals with approximately the same locality. © 2013 Wiley Periodicals, Inc. 相似文献
10.
2,2′-Diiodo-1,1′-binaphthalene undergoes a tandem Heck reaction with methyl acrylate to afford methyl 2-(7H-dibenzo[c,g]fluoren-7-ylidene)acetate. As a consequence, the target macrocyclic diazene with binaphthalene unit attached via acrylamide linker was prepared by the stepwise building of acrylamide at a binaphthalene moiety, including the Doebner modification of the Knoevenagel condensation, and completed by oxidative macrocyclisation of aniline end-groups. Despite being an equimolar mixture of monomer and dimer, it exhibited remarkable changes in CD spectra due to reversible (E/Z) isomerisation of N=N diazene bonds upon irradiation at 365/465 nm. Although the dimer isomerises from (E) to (Z) isomer 7.4 times faster than the monomer, the latter’s contribution to the change in ellipticity at 307 nm in the photostationary state is 2.4 times greater. 相似文献