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91.
The rates and products of cleavage of methyl (2-chloro-4-nitrophenyl) phosphate (2) promoted by a dinuclear Zn(II) complex (3) of 1,3-bis-N,N'(1,5,9-triazacyclododecyl)propane along with 1 equiv of ethoxide were investigated in ethanol solution containing small amounts of water (8 mM or=1.6 x 10(17) times relative to the background hydroxide reaction, suggesting that complex 3 promotes the hydrolysis at least 1000 times more effectively than ethanolysis. 相似文献
92.
Two metastable states of a multilayer Ge/p-Ge1−x
Six heterosystem with wide (∼ 35 nm) potential wells (Ge) are observed in strong magnetic fields B at low temperatures. In the first state, the Hall resistivity exhibits an inflection near the value ρxy=h/e
2 scaled to one Ge layer. The longitudinal magnetoresistivity ρxx(B) possesses a minimum in the range of fields where this inflection occurs. The temperature evolution of the inflection in
ρxy(B), the minimum of ρ xx(B), and the value of ρxy at the inflection indicates a weakly expressed state of the quantum Hall effect with a uniform current distribution over
the layers. In the second metastable state, an unusually wide plateau near h/2e
2 with a very weak field dependence is observed in ρxy(B). Estimates show that in these samples the Fermi level lies below but close to the top of the inflection in the bottom of
the well. For this reason, the second state can be explained by separation of a hole gas in the Ge layers into two sublayers,
and the saturation of ρxy(B) near h/2e
2 can be explained by the formation of a quantum Hall insulator state.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 290–297 (25 August 1999) 相似文献
93.
A A Neverov P J Montoya-Pelaez R S Brown 《Journal of the American Chemical Society》2001,123(2):210-217
The metal ions Zn(2+), Co(2+), and La(3+) strongly catalyze the methanolysis of the activated amides acetylimidazole (1) and its ligand-exchange-inert Co(III) complex, (NH(3))(5)Co(III)-AcIm (2). Studies of the kinetics of methanolysis are performed with pH measurement and control, and the metal ions are soluble in the medium throughout the pH regions where ionization of the M(x+)(CH(3)OH)(y) occurs. Zn(2+) and Co(2+) act as Lewis acids toward 1, catalyzing attack of external methoxide on a 1:M(2+) complex at values only 100-fold lower than the diffusion limit, the k(OR) values being 5.6 x 10(7) M(-1) s(-1) and 2.5 x 10(7) M(-1) s(-1), while that for CH(3)O(-) attack on 2 is 4.69 x 10(7) M(-1) s(-1). Since neither Zn(2+) nor Co(2+) promotes the methanolysis of 2, these metals appear to be acting through transient binding to the distal N of 1, which activates the C=O of the complex to external CH(3)O(-) attack. La(3+) catalyzes the methanolysis of both 1 and 2, which occurs by a mechanism that is fundamentally different from that exhibited by Zn(2+) and Co(2+) in that the active species appears to be a bis-methoxy-bridged dimer (La(3+))(2)(CH(3)O(-))(2)(CH(3)OH)(x)() that interacts directly with the C=O unit of the substrate. 相似文献
94.
Bogoliubskii A. S. Gudina S. V. Neverov V. N. Turutkin K. V. Podgornykh S. M. Shelushinina N. G. Yakunin M. V. Mikhailov N. N. Dvoretsky S. A. 《Physics of the Solid State》2022,64(3):107-117
Physics of the Solid State - The effects observed in the Shubnikov–de Haas oscillation regime in the HgCdTe/HgTe/HgCdTe heterostructure with a wide (20.3 nm) HgTe quantum well with an... 相似文献
95.
Zhumagulov Ya. V. Kashurnikov V. A. Krasavin A. V. Lukyanov A. E. Neverov V. D. 《JETP Letters》2019,109(1):45-50
JETP Letters - The phase diagram of the two-dimensional two-orbital Hubbard model, which is widely used to describe high-temperature iron-based superconductors, is calculated in the electron doping... 相似文献
96.
L.A. Chernozatonskii V.S. Neverov A.B. Kukushkin 《Physica B: Condensed Matter》2012,407(17):3467-3471
An approximation of the positions of carbon atoms in a curved graphene sheet is suggested for calculation of X-ray diffraction (XRD) patterns of curved-graphene nanoparticles. The model is tested for carbon nanotubes and newly calculated carbon nanotoroids consisting of several hundreds of atoms. It is shown that the random distribution of carbon atoms with graphene surface-averaged density and the local graphene-like rearrangement of atoms in a curved lattice are sufficient for describing the XRD patterns of an ensemble of respective exact carbon nanoparticles of random isotropic orientation in the range of scattering wave vector's modulus q from several units to several tens of inverse nanometers. The model is of interest to a fast-routine identification of curved-graphene nanoparticles in carbonaceous materials. 相似文献
97.
98.
Kukushkin A. B. Neverov V. S. Lisitsa V. S. Shurygin V. A. Alekseev A. G. 《Physics of Atomic Nuclei》2020,83(7):1070-1082
Physics of Atomic Nuclei - The results of the analysis of the accuracy of measuring the flux density of all hydrogen isotopes from the first wall of the main vacuum chamber to the ITER tokamak... 相似文献
99.
The regularities of galvanostatic electrocarboxylation of CCl4 in Alk4NBr/MeCN in an undivided cell with sacrificial Zn anode were studied. The major product of the electrolysis is zinc trichloroacetate,
which is formed as a result of the reaction of the cathode-generated CCl3- anion with CO2. The further trichloroacetate reduction is prevented by cathode passivation. Therefore, small amounts of zinc dichloro- and
monochloroacetates are formed due to the chemical reduction of zinc trichloroacetate with Zn0 rather than the cathodic reduction. Zero-valence zinc is formed in minor amounts when Zn2+ ions are discharged at the cathode surface because of the low solubility of ZnBr2 in MeCN. The treatment of (Cl3CCOO)2Zn with H2SO4 in MeOH gives Cl3CCO2Me in 11% yield based on the starting CCl4. 相似文献
100.
The mechanism of cleavage of a series of seven O,O-dimethyl O-aryl phosphorothioates (6a-g) promoted by a C,N-palladacycle, (2-[N,N-dimethylamino(methyl)phenyl]-C(1),N)(pyridine) palladium(II) triflate (5:OTf) in methanol at 25 °C was investigated with the aim of identifying catalytically important intermediates. Complete (s)(s)pH/rate profiles (in methanol) were conducted for the cleavage of 6a-g in the presence of 0.08 mM 5. The log k(obs) for the catalyzed methanolysis of 6a increases linearly with (s)(s)pH with a plateau above the (s)(s)pK(a)(1) of 11.16 for formation of 5:(-)OCH3. The profiles for 6b-g are bell-shaped, depending on the apparent ionizations of two acidic groups, with the rate constant maximum of the bell and the (s)(s)pK(a)(1) values shifting to higher (s)(s)pH values as the (s)(s)pK(a)(HOAr) of the leaving group phenol increases. A Br?nsted plot of the log k(obs)(max) (the maximum rate constants for cleavage of 6a-g) vs (s)(s)pK(a)(HOAr) exhibits a downward break at ~ (s)(s)pK(a)(HOAr) 13, with the two wings having β(lg) values of 0.01 and -0.96. A model describing the kinetically important species involves a complex series of equilibria: 5:(HOCH(3)):pyr <=> 5:((-)OCH3):pyr + H(+) <=>(6) 5:((-)OCH3):6 + pyr <=> phosphorane 7 → product, where the rate limiting steps change from formation of 5:((-)OCH3):6 to formation of thiophosphorane 7 and then to product formation as the aryloxy leaving groups of 6 get progressively worse. Kinetic experiments indicate that the reaction of 5 with 6e, having a 4-chlorophenoxy leaving group, rapidly produces a transient intermediate, postulated to be the palladacycle-bound 5-coordinate thiophosphorane (7e) that exists long enough to obtain its UV/vis spectrum by stopped-flow spectrophotometry. Detailed analysis of the data sheds light on the origins of a previously reported anomalously large β(lg) of -1.93 for the descending wing of a Br?nsted plot (J. Am. Chem. Soc. 2010, 132, 16599). Finally, energetics analysis indicates that the binding of palladacycle to the transition state comprising attack of methoxide on 6e, [MeO(-) + 6e](++), stabilizes the latter by 34.9 kcal/mol, converting that transition state into an observable intermediate. 相似文献