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261.
Corrosion of uranium and its alloys with low content (0.5–5.0 at %) of Zr, Nb, and Ru in water and bicarbonate aqueous solutions is studied; the effect of hydrogen peroxide, the main product of radiation processes, on the corrosion rate is elucidated. The rate of the primary corrosion process U +(2 +n)H2O=UO2·nH2O+ 2H2↑ is measured by electrochemical methods in anaerobic and aerobic conditions for uranium metal and its alloys containing 0.5 to 5.0 at % of Zr, Nb, and Ru. It is shown that the corrosion rates for the alloys are lower than that of reactor-grade uranium; however, the difference is rather close to the measurement error. The corrosion mechanism is studied; U(III) is shown to be rather unstable in neutral solutions when uranium(III) hydroxide is precipitated and no significant amount of U(III) and UH3 is present among the products of the metallic uranium corrosion in water. The kinetics of the second corrosion stage U(IV) + O2→U(VI) is studied by spectrophotometric method. It is shown that the reaction of U(IV) oxidation by atmospheric oxygen is similar in weakly acid solutions (pH 1.5–4.0) and in bicarbonate media: in particular, it has an induction period for uranium (IV) accumulation, after which the reaction accelerates; it is formally a first-order reaction with respect to uranium. The reaction mechanisms differ in the two media: in weakly acid solutions, after the appearance of U(VI), the reproportionation reaction proceeds; thus formed U(V) interacts with O2 faster than U(IV). In the bicarbonate medium, the acceleration of the reaction is due to the formation of a [U(IV)ΣU(VI)] complex whose reactivity is higher than that of uranium (IV). In the absence of bicarbonate, of great importance is the formation of a copolymer of U(IV) and U(VI), which at pH≥4 prevents formation of U(V). It is shown that on the introduction of hydrogen peroxide to aqueous solutions, the metallic uranium surface becomes transpassive, which increases the rate of corrosion process by at least an order of magnitude,. The introducing of oxidants and platinum mesh lowers the hydrogen accumulation at 120–150°C and, hence, the hydrogen-explosion danger of the uranium-water-corrosion-products system. Methods of deposition of metal oxide (Tc, Ru, Mo, W) films onto uranium surfaces by immersing uranium metal into Tc(VII), Ru(VI), or Mo and W heteropoly compound solutions are studied. Original Russian Text ? V.F. Peretrukhin, A.G. Maslennikov, A.Yu. Tsivadze, C.H. Delegard, A.B. Yusov, V.P. Shilov, A.A. Bessonov, K.E. German, A.M. Fedoseev, L.P. Kazanskii, N.Yu. Budanova, A.V. Kareta, A.V. Gogolev, K.N. Gedgovd, G.S. Bulato, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 3, pp. 229–251.  相似文献   
262.
U(III) was precipitated from solution as a yellowish-brown precipitate under the action of NH4OH or Na2B4O7 solutions at pH ~7.5. The electronic spectra showed the presence of substantial amounts of U(OH)3 in the precipitate, decreasing within a few minutes. Therefore, pure U(OH)3 can hardly be obtained. A brown precipitate is formed when a U(III) solution is added to an NH4F solution. An X-ray phase analysis shows that anhydrous UF3 is the only crystalline compound in the precipitate. The synthesis of U(III) phosphate was unsuccessful, because uranium was completely oxidized to U(IV). Thus, preparation of U(III) phosphate compounds from aqueous solutions is hardly possible.  相似文献   
263.
Reaction of amino acids (glycine and serine) and amino sugar (glucosamine) with atomic tritium generated by thermal dissociation of molecular tritium on a tungsten filament was studied. A frozen aqueous solutions and a freeze-dried mixture of these compounds was bombarded with tritium atoms is a special vacuum unit. The relative yield of the labeled compounds was determined as influenced by the reaction conditions (residual pressure in the system and bombardment time) and target type (frozen solution and freeze-dried mixture). Formation of labeled products is almost independent of the tritium pressure. The ratio of the formation rates of labeled serine and glycine in the frozen solution and freeze-dried mixture bombarded with atomic tritium for 45–270 s was 1.66±0.15 and 1.44±0.13, respectively. At shorter reaction time (15 s), the ratio increases to 3.5±0.2 and 2.0±0.4, respectively. The formation rate of [3H]glucosamine in the mixture is higher at a shorter bombardment time. The radioactivity ratio of labeled glucosamine and glycine formed in frozen solutions and freeze-dried mixture in 15 s was 26.0±2.3 and 6.8±0.6, respectively. At longer reaction time, the relative yield of [3H]glucosamine sharply decreases owing to stronger radiolysis of labeled glucosamine on exposure to tritium beam.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 281–283.Original Russian Text Copyright © 2005 by Badun, Ksenofontov, Lukashina, Pozdnyakova, Fedoseev.  相似文献   
264.
Precipitates prepared by addition of ammonia or NaOH into solutions containing Al and REE(III) (La, Nd) or Al and Am(III) were studied by thermogravimetry, UV-Vis and IR spectroscopy, X-ray diffraction analysis, and measurement of the dissolution rate. It was shown that the properties of the precipitates containing Al and the second element noticeably differ from the properties of straight aluminum hydroxide precipitate. In the IR spectra, new vibrational bands appear. In the electronic spectra, small shifts of Nd(III) and Am(III) absorption bands relative to the bands of the individual f-element hydroxides are observed. The rates of dissolution of the precipitates in HCl solutions noticeably differ. With increasing pH of coagulation to 13-14, a part of aluminum is captured with the precipitate. However, this fraction is small. In the precipitates obtained from 0.1-1 M NaOH, the interaction of f elements with aluminum is practically lacking.  相似文献   
265.
A self-consistent kinetic model is used to treat the effect of striation of the positive column of gas discharge in low-pressure inert gases. The model is based on the solution of the kinetic Boltzmann equation for the electron energy distribution function, of the unsteady-state equation of drift and diffusion for ions, and of the Poisson equation for electric field. Spatial distributions of the electron and ion density are obtained, as well as of the electric field in the positive column of striated discharge. The model is used to explain the kinetic mechanism of origination of the effect of striation in low-pressure inert gases. The obtained distributions are independent of the initial conditions, and the solution gives a self-consistent “resonance” length of strata and the value and form of modulation of electric field.  相似文献   
266.
The dispersion and resonance characteristics of whispering-gallery modes in a resonator with a small height-to-radius ratio are investigated theoretically and experimentally. It is shown that the calculated mode frequencies and azimuthal indexes match the experimental data obtained in the millimeter-wave range for resonators fabricated from certain materials. A maximum is revealed in the dependence of frequency intervals between neighboring modes on the azimuthal index at large values of the latter.  相似文献   
267.
The kinetics and stoichiometry of the reaction of Np(VI) with H2O2 in carbonate solutions were studied by spectrophotometry. In the range 1–0.02 M Na2CO3, the reaction 2Np(VI) + H2O2 = 2Np(V) + O2 occurs, as Δ[Np(VI)]/Δ[H2O2] ≈ 2. In Na2CO3 + NaHCO3 solutions, the stoichiometric coefficient decreases, which is caused by side reactions. The reduction at low (1 mM) concentrations of Np(VI) and H2O2 follows the first-order rate law with respect to Np(VI), which suggests the formation of a Np(VI) peroxide-carbonate complex, followed by intramolecular charge transfer. Addition of Np(V) in advance decreases the reaction rate. An increase in the H2O2 concentration leads to the reaction deceleration owing to formation of a complex with two peroxy groups. In a 1 M Na2CO3 solution containing 1 mM H2O2, the first-order rate constant k increases with a decrease in [Np(VI)] from 2 to 0.1 mM. For solutions with [Np(VI)] = [H2O2] = 1 mM, k passes through a minimum at [Na2CO3] = 0.5–0.1 M. The activation energy in a 0.5 M Na2CO3 solution is 48 kJ mol−1.  相似文献   
268.
Fedoseev  A. M.  Shilov  V. P.  Budantseva  N. A.  Yusov  A. B.  Delegard  C. H. 《Radiochemistry》2002,44(4):361-365
Reaction of Cr(III) hydroxides and mixed Fe(III)-Cr(III) and Ni(II)-Cr(III) hydroxides with persulfate ion in alkaline solutions was studied by spectrophotometry. The Cr(VI) yield (at oxidant deficiency) corresponds to the S2O8 2 - : Cr(VI) molar ratio close to 1.5. The initial reaction rate V 0 is described by the kinetic equation -d[Cr(III)]/d = k[Cr(III)][S2O8 2 -][NaOH]. The activation energy is 53 kJ mol- 1 within the 41.5-95°C range. V 0 is higher than the rate of thermal decomposition of persulfate ion, i.e., Cr(III) reacts directly with S2O8 2 -. Oxidation of NiCr2O4·nH2O and mixed Fe(III)-Cr(III) hydroxides proceeds faster than oxidation of pure Cr(III) hydroxide. This is due to the catalytic effect of Fe(III) and Ni(II). Additions of Co(II) and Cu(II) also accelerate the process. Pu(IV) in alkali solution under the action of persulfate is converted into a more soluble oxidized species, which can be reduced back to Pu(IV) with appropriate reductants.  相似文献   
269.
270.
Extraction of trace amounts of Pu(IV), U(VI), Th(IV), Am(III), and REEs(III) from nitric acid solutions with o-methyleneoxyphenyldiphosphine dioxides with phenyl (I) and butyl (II) substituents at the phosphoryl group is studied. The stoichiometry of extractable complexes in dichloroethane is determined. Changing the butyl substituents for phenyl ones increases the effective extraction constants of Pu(IV), Th(IV), and Am(III) and decreases that of U(VI). In extraction from 3 M HNO3, the Pu(IV)/U(VI) and Th(IV)/U(VI) partition coefficients are higher with reagent I, and the Pu(IV)/Am(III) and U(VI)/Am(III) partition coefficients, with reagent II.  相似文献   
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