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Metal Science and Heat Treatment - 相似文献
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Alexandre Chmel Alexy Krivda Ekatherina Mazurina Victor Shashkin Valery Zhizhenkov 《Journal of the American Ceramic Society》1993,76(6):1563-1567
The gel-to-glass transition in SiO2 xerogels prepared by inorganic sol-gel synthesis was studied. The evolution of the molecular structure is traced using the infrared and lowfrequency Raman spectroscopy methods. The elastic moduli of the samples as well as the pore wall moduli at various stages of heat treatment are determined from the data on Brillouin scattering. The formation of monolithic glass on the macroscopic level manifests itself within a narrow temperature range by the dramatic increase of Young's modulus to the accepted value for fused silica. This phenomenon coincides with structural transformations on the molecular scale: (i) the definite correlation radius (the long-range order sphere) appears; (ii) local distortions of the silica network relax. The presence of structural defects influences the kinetics of vitreous SiO2 formation during xerogel heat treatment. 相似文献
5.
Tz. Boiadjieva D. Kovacheva K. Petrov S. Hardcastle A. Sklyarov M. Monev 《Journal of Applied Electrochemistry》2004,34(3):315-321
The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg2SO4, which is reached at current density of about 20 A dm–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a
3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a
2.67 Å, c
4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)2. After 50 min sputtering, Zn and a mixture of Cr, Cr2O3 and Cr7C3 were found. The presence of organic C and O, probably from inclusions of PEG, were also detected. 相似文献
6.
V. S. Matveev G. A. Budnitskii G. P. Mashinskaya L. B. Aleksandrova N. M. Sklyarov 《Fibre Chemistry》1997,29(6):381-384
The following conclusions can be drawn from an analysis of the data reported in the present article: SVM and Armos fibres
are now the most promising for use in bulletproof materials; increasing the elongation to 5–6% while preserving the strength
at the level of 400–450 kgf/mm
2
allows increasing the efficiency of use of fibres for bulletproofing; the method proposed here allows rapidly and efficiently
conducting comparative tests and initial selection of materials and the pack structure of the energy-absorbing polymer support;
new types of bulletproof fabrics must be developed to increase the efficiency of manifestation of the energy-absorbing properties
of fibres.
Translated from Khimicheskie Volokna, No. 6, pp. 37–40, November–December, 1997. 相似文献
7.
The reactivity of O-, T- and R-phases of the high pressure-high temperature (HPHT) polymerized C60 towards gaseous fluorine in the temperature range of 50-250 °C was investigated. The reaction products were characterized by FTIR, powder X-ray diffraction, SEM, EDX, and VTP-EIMS to determine the bulk stoichiometries, bonding patterns, phase compositions, crystalline structures and thermal decomposition behavior of the fluorinated polymers. At 1 h isothermal treatment duration, fluorinated products with various bulk stoichiometries were obtained from different polymer phases with the R-phase showing the highest fluorine uptake. At 250 °C, all C60 polymers showed partial decomposition to unfluorinated C60 monomer under fluorine atmosphere. At 200 °C, the fluorination of R-phase yielded a pure fluoropolymer most likely having a {C60Fx}n (x = 36-44) composition. The same fluoropolymer was presumably obtained from O- and T-phases in lower yields. The linear chain structure was suggested for this new fluorocarbon polymer in agreement with the molecular mechanics modeling calculations. 相似文献
8.
Pavel P. Fedorov Alexander A. Alexandrov Valery V. Voronov Mariya N. Mayakova Alexander E. Baranchikov Vladimir K. Ivanov 《Journal of the American Ceramic Society》2021,104(6):2836-2848
Phase formation in the SrF2–LaF3 system was studied at temperatures ranging from 300°C to 450°C using nitrate flux. The solubility of LaF3 in SrF2 decreases with decreasing temperature. The equilibrium width of the solid solution region Sr1−xLaxF2+x at 400°C, it is 44.6 ± 0.4 mol% LaF3 (x = 0.446), at 350°C — 38.3 ± 0.7 mol% LaF3 (x = 0.383), and decreases almost to zero at 300°C. 相似文献
9.
In this paper we study the single machine common due date assignment and scheduling problem with the possibility to perform a rate-modifying activity (RMA) for changing the processing times of the jobs following this activity. The objective is to minimize the total weighted sum of earliness, tardiness and due date costs. Placing the RMA to some position in the schedule can decrease the objective function value. Several properties of the problem are considered which in some cases can reduce the complexity of the solution algorithm. 相似文献
10.
The theory of adiabatic invariants has a long history, and very important implications and applications in many different
branches of physics, classically and quantally, but is rarely founded on rigorous results. Here we treat the general time-dependent
one-dimensional harmonic oscillator, whose Newton equation q + ω2(t)q = 0 cannot be solved in general. We follow the time-evolution of an initial ensemble of phase points with sharply defined
energy Eo at time t = 0 and calculate rigorously the distribution of energy E1 after time t = T, which is fully (all moments, including the variance μ2) determined by the first moment Ē1. For example, μ2 = E2o[(Ē1/Eo)2 — (ω(T)/ω(0))2]/2, and all higher even moments are powers of μ2, whilst the odd ones vanish identically. This distribution function does not depend on any further details of the function
ω(t) and is in this sense universal. In ideal adiabaticity Ē1 = ω(T)Eo/ω(0), and the variance μ,2 is zero, whilst for finite T we calculate Ē1, and μ2 for the general case using exact WKB-theory to all orders. We prove that if ω(t)is of class
m (all derivatives up to and including the order m are continuous) μ, ∝ T−(m + 1)) whilst for the class
°° it is known to be exponential μ ∝ exp(—aT). 相似文献