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941.
E. P. M. Leiva C. Vázquez M. I. Rojas M. M. Mariscal 《Journal of Applied Electrochemistry》2008,38(8):1065-1073
In this work, the structural and energetic properties of two typical catalytic surfaces, Na/Pt(111) and O/Pt(111), are studied
by means of quantum mechanical calculations and Monte Carlo Grand Canonical simulations. The simulations were performed with
electrostatic potentials at different truncation schemes. In order to elucidate the modification of catalyst surfaces produced
by the backspillover of ionic species onto Pt(111), the electrostatic field at the interface due to the electric double layer
was also analyzed. 相似文献
942.
S. Zisekas G. Karagiannakis C. Kokkofitis M. Stoukides 《Journal of Applied Electrochemistry》2008,38(8):1143-1149
The reaction of NH3 decomposition was studied on Ag in a proton conducting double chamber cell-reactor. The proton conductor was a strontia-ceria-ytterbia
(SCY) perovskite of the form SrCe0.95Yb0.05O3−α. The reaction was studied at 350–700 °C and atmospheric total pressure. The proton transference number (PTN) was calculated
by simultaneous measurement of the imposed current and the proton flux and it was found to vary between 0.5 and 0.7. The effects
of imposed current, temperature and inlet gas composition on the reaction rate and the PTN, were examined. Although the faradaic
efficiency (Λ) remained near unity in all experiments, reaction rate enhancements (ρ) as high as 57 were achieved. An up to
90% decrease in the activation energy of the reaction was observed when protons were electrochemically “pumped” away from
the catalyst. 相似文献
943.
Morphology of carbon black (CB)‐filled rubber was studied with AFM and SEM and the classification of filler agglomerates, based on their internal structure and filler–matrix interactions, has been proposed. It varies according to the activity of CB and the kind of rubber. It has been shown that fracture of rubber starts either inside filler agglomerates (de‐cohesion) or in a filler–matrix interphase (de‐adhesion) initiating wear of the material. Microscopic observations correlate well with TGA and EPR data of wear debris collected during friction of rubber. The increase of thermal stability of CB and the appearance of additional spin signals, respectively, for elongated samples or debris, are proposed to be associated with de‐cohesion or de‐adhesion of the agglomerates. New approach to the fracture of rubber called “fatal agglomerate concept” is presented. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
944.
A. Celaya Sanfiz T. W. Hansen F. Girgsdies O. Timpe E. Rödel T. Ressler A. Trunschke R. Schlögl 《Topics in Catalysis》2008,50(1-4):19-32
This work presents a detailed investigation of the preparation of MoVTeNbO x catalysts by hydrothermal synthesis. Phase-pure synthesis of M1 has been achieved applying the metals in a molar ratio Mo/V/Te/Nb = 1/0.25/0.23/0.12. Raman, UV/Vis spectroscopy, and SEM/EDX analysis show that the elements are inhomogeneously distributed in the initial suspension that is formed after mixing the metal salts in an aqueous medium. Iso- and heteropoly anions of molybdenum, free telluric acid as well as supra-molecular polyoxometalate clusters are observed in the solution, whereas all metals have been found in the precipitate. Complete rearrangement of molecular building blocks under hydrothermal conditions is essential for formation of phase-pure materials. Optimized synthesis conditions with respect to temperature and time result in the formation of a precursor consisting of nano-structured M1 characterized by an extended periodic organization in the [001] direction and a fairly homogeneous distribution of the elements. Residual ammonium containing supra-molecular species in the precursor result in the formation of phase mixtures during the subsequent crystallization by heat treatment in inert gas. Phase-pure M1 exhibits a distinct degree of flexibility with respect to the chemical composition that becomes obvious by incorporating Nb not exclusively into pentagonal bi-pyramidal units, but also into octahedral coordinated positions as shown by EXAFS. Anisotropic growth of the needle-like M1 crystals has been observed during the final heat treatment performed at 873–923 K in inert atmosphere disclosing a potential method to control the catalytic properties of MoVTeNbO x catalysts. 相似文献
945.
Bednars'ka L. M. Horelenko Yu. K. Kovbuz M. O. Hertsyk O. M. Kotur B. Ya. Nosenko V. K. 《Materials Science》2003,39(2):291-294
Alloying of amorphous Fe-Me-Si-B metallic compositions with nickel and molybdenum results in a decrease in the values of saturation magnetization in fields with a magnetic intensity of 0.72 MA/m. The same alloying additions decrease the temperature of formation of new magnetic Fe3B-type phases, which are stable up to 873 ± 5 K. 相似文献
946.
V. N. Gurin M. M. Korsukova S. P. Nikanorov A. P. Nechitailov L. I. Derkachenko Z. I. Uspenskaya I. N. Zimkin 《Technical Physics Letters》2003,29(6):464-466
Ionic substances under normal conditions are stoichiometric compounds with phase diagrams featuring no homogeneity regions.
Crystals grown under nonequilibrium conditions, in particular, under significant centrifugal acceleration, are characterized
by nonstoichiometric compositions (e.g., K2−x
Br1.07). In this way, it is possible to obtain nonequilibrium nonstoichiometric ionic compounds possessing certain homogeneity regions.
Nonstoichiometric crystals of KCl, KBr, and KI grown under various accelerations ranging within (1.3–100.0)×103
g exhibit insignificant variations in the lattice constants and a significant increase in micro-hardness with acceleration. 相似文献
947.
S. A. Ktitorov 《Technical Physics Letters》2003,29(11):956-958
Conditions for reconstructing the relaxation time distribution function from the frequency dependence of dielectric losses
have been studied using an approach analogous to that employed in the communication theory (Kotel’nikov-Shannon theorem). 相似文献
948.
The parametric X-ray (PXR) yield due to 500-MeV electrons in a 2-mm-thick diamond crystal with a mosaicity angle of ~0.2 mrad has been studied. It is shown that the mosaic crystal structure leads to a significant (about fourfold) increase in the PXR yield doe to the contribution of diffracted bremsstrahlung radiation. Advantages of using mosaic crystals for the generation of intense X-ray beams are discussed. 相似文献
949.
A (time-dependent) model for an electrochemical cell, comprising a dilute binary electrolytic solution between two flat electrodes,
is formulated. The method of matched asymptotic expansions (taking the ratio of the Debye length to the cell width as the
small asymptotic parameter) is used to derive simplified models of the cell in two distinguished limits and to systematically
derive the Butler–Volmer boundary conditions. The first limit corresponds to a diffusion-limited reaction and the second to
a capacitance-limited reaction. Additionally, for sufficiently small current flow/large diffusion, a simplified (lumped-parameter)
model is derived which describes the long-time behaviour of the cell as the electrolyte is depleted. The limitations of the
dilute model are identified, namely that for sufficiently large half-electrode potentials it predicts unfeasibly large concentrations
of the ion species in the immediate vicinity of the electrodes. This motivates the formulation of a second model, for a concentrated
electrolyte. Matched asymptotic analyses of this new model are conducted, in distinguished limits corresponding to a diffusion-limited
reaction and a capacitance-limited reaction. These lead to simplified models in both of which a system of PDEs, in the outer
region (the bulk of the electrolyte), matches to systems of ODEs, in inner regions about the electrodes. Example (steady-state)
numerical solutions of the inner equations are presented. 相似文献
950.
O. L. Perevozchikova V. G. Tul'chinskii A. V. Kharchenko 《Cybernetics and Systems Analysis》2003,39(4):501-508
A statistical learning model is considered within the framework of the theory of uniform convergence of frequencies of errors in the case where the convergence is violated as a result of increasing the informativeness of training examples. Drawbacks of nonconstructive refinements of Vapnik-Chervonenkis estimates based on an assumption on the distribution law of violations are shown. A new approach to obtaining constructive estimates for mass data sets is proposed. 相似文献