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101.
Staircaselike hysteresis loops of the magnetization of a LiY0.998Ho0.002F4 single crystal are observed at subkelvin temperatures and low field sweep rates. This behavior results from quantum dynamics at avoided level crossings of the energy spectrum of single Ho3+ ions in the presence of hyperfine interactions. Enhanced quantum relaxation in constant transverse fields allows the study of the relative magnitude of tunnel splittings. At faster sweep rates, nonequilibrated spin-phonon and spin-spin transitions, mediated by weak dipolar interactions, lead to magnetization oscillations and additional steps. 相似文献
102.
Jan Pelant Mihail G. Tkachenko Vladimir V. Tkachuk Richard G. Wilson 《Proceedings of the American Mathematical Society》2003,131(10):3257-3265
We prove in ZFC that there exists a Tychonoff pseudocompact scattered AP-space of uncountable tightness. We give some sufficient and necessary conditions for a -space to be AP as well as a characterization of AP-property in linearly ordered topological spaces.
103.
A. M. Tkachuk 《Nonlinear Oscillations》2005,8(2):256-263
For a system of difference equations, we establish conditions for the existence and stability of invariant sets, substantiate
the reduction principle, and study the behavior of an invariant set under small perturbations.
__________
Translated from Neliniini Kolyvannya, Vol. 8, No. 2, pp. 258–264, April–June, 2005. 相似文献
104.
105.
T. V. Shokol O. A. Lozinskii T. M. Tkachuk T. A. Volovnenko V. P. Khilya 《Chemistry of Heterocyclic Compounds》2010,46(6):675-680
The corresponding 9-azolyl-8-imino-4H,8H-pyrano[2,3-f]chromen-4-ones have been synthesized by the condensation of 7-hydroxy-3-(5-methoxycarbonyl-2-methylfuran-3-yl)-8-formylchromones
with 2-aza-hetarylacetonitriles. Acid hydrolysis of the products led to the furyl analogs of 9-azolyl-α-pyrono-[2,3-f]isoflavones. 相似文献
106.
P. N. Tkachuk 《Physics of the Solid State》2000,42(11):2014-2016
The effect of chlorine impurity on the fundamental reflection spectrum and the electronic band structure of cadmium telluride crystals has been studied. At the impurity concentration N Cl>5.0×1019 cm?3, a peak appears in the reflectance spectra. This peak is due to electron transitions at the X point of the Brillouin zone from the upper split valence band to Cl levels lying 0.05 eV above the Γ minimum of the conduction band. The other features in the reflectance spectra and band structure are explained as being due to the effect of spin-orbit splitting at the X point and to indirect electronic transitions from the Cl levels to the Γ minimum. 相似文献
107.
L. L. Gur’eva A. I. Tkachuk E. A. Dzhavadyan G. A. Estrina N. F. Surkov I. V. Sulimenkov B. A. Rozenberg 《Polymer Science Series A》2007,49(9):987-999
The thermodynamics, kinetics, and mechanism of the anionic polymerization of a number of acrylamide monomers has been studied with the use of isothermal and scanning calorimetry, liquid chromatography, 1H NMR and IR spectroscopy, mass spectrometry, and chemical analysis of functional groups. It has been demonstrated that the polymerization system shows the living character and the interchain exchange reactions are absent. It has been shown that N,N-diethanolacrylamide and N,N-diethanol(meth)acrylamide are uninvolved in anionic polymerization. The causes of this phenomenon have been ascertained. The products of the anionic polymerization of acrylamides are hyperbranched copolymers containing heterochain and carbochain fragments. Macromolecules contain end amide and acrylamide groups; in some macromolecules, end tert-butoxide groups of the used polymerization initiator are detected. For the products of the anionic polymerization of the acrylamide monomers under study, the temperatures of glass transition and melting have been measured. 相似文献
108.
Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta0.33V0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV2. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase. 相似文献
109.
Pozharskii AF Povalyakhina MA Degtyarev AV Ryabtsova OV Ozeryanskii VA Dyablo OV Tkachuk AV Kazheva ON Chekhlov AN Dyachenko OA 《Organic & biomolecular chemistry》2011,9(6):1887-1900
It has been shown that the 1-NMe(2) group in the 2-substituted 1,8-bis(dimethylamino)naphthalenes (proton sponges) can intramolecularly donate a hydride ion to an appropriate electron-accepting ortho-substituent such as diarylcarbenium ion, β,β'-dicyanovinyl or methyleneiminium group. This produces the 1-N(+)(Me)=CH(2) functionality and triggers a number of further transformations (tert-amino effect) including peri-cyclization, ortho-cyclization or hydrolytic demethylation. In each particular case, the course of the reaction is determined by the nature of the ortho-substituent and the most potent nucleophile presenting in the reaction mixture. For 2,7-disubstituted 1,8-bis(dimethylamino)naphthalenes, two types of tandem tert-amino effect with the involvement of both peri-NMe(2) groups have been registered. The conclusion was made that proton sponges are generally more active in the tert-amino reactions than the corresponding monodimethylaminoarenes. This is ascribed both to higher electron donor ability of proton sponges and markedly shortened distance between electrophilic C(α)-atom in the ortho-substituent and hydrogen atoms of the nearest NMe(2) group. Most conversions observed proceed in good to high yields and are useful for the preparation of derivatives of benzo[h]quinoline, quino[7,8:7',8']quinoline, 2,3-dihydroperimidine, N,N,N'-trimethyl-1,8-diaminonaphthalene and proton sponge itself. 相似文献
110.
Oleg V. Shishkin Irina S. Konovalova Roman I. Zubatyuk Gennady V. Palamarchuk Svitlana V. Shishkina Angelina V. Biitseva Igor V. Rudenko Volodymyr A. Tkachuk Mikhail Yu. Kornilov Olga V. Hordiyenko Jerzy Leszczynski 《Structural chemistry》2013,24(4):1089-1097
Results of the X-ray diffraction studies of 1-imino-1H-isoindol-3-amine and its derivatives reveal unusual distribution of bond lengths within the NH2–C=N amidine fragment in the considered crystals. In the crystal phase, single C–N bond is shorter or at most has the same length as double C=N bond, while in isolated molecules both these bonds have expected lengths, according to the calculations by MP2/6-311G(d,p) and MP2/cc-pvtz methods. It is demonstrated that so unusually strong polarization of the amidine fragment is induced by polar environment in solid state. This effect stabilizes the amino-imino tautomer of 1-imino-1H-isoindol-3-amine, which becomes more stable than the diimino tautomer possessing the lowest energy in the gas phase. 相似文献