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81.
Electrochemical characterization of 8-hydroxyquinoline-5-sulphonate/aluminium(III) aqueous solutions
Denis Badocco Annalisa Dean Valerio Di Marco Paolo Pastore 《Electrochimica acta》2007,52(28):7920-7926
8-Hydroxyquinoline-5-sulphonate/Al(III) aqueous solutions were studied both by potentiometric titrations and voltammetric measurements, in order to obtain the number, the stoichiometry and the stability constants of the complexes formed at equilibrium, and to evaluate the redox and (electro)kinetic properties of the free ligand and of the metal/ligand complexes. The complexes formed in 0.2 m (Na)Cl aqueous solution (stability log beta values ± standard deviation) are AlL+ (8.95 ± 0.05), AlL2− (17.43 ± 0.03) and AlL33− (24.58 ± 0.05), where “L” denotes the free ligand in the completely deprotonated form (L2−, pKa1 = 3.910 ± 0.008, pKa2 = 8.319 ± 0.004). AlL33− is the predominant Al(III) species in a very wide range of pH, metal and ligand concentrations and metal-to-ligand ratios. The free ligand shows an oxidation wave at 0.62 V versus SCE. The proposed oxidation mechanism includes a first reversible one-electron oxidation of the ligand, followed by a coupling reaction and by a second reversible one-electron oxidation, and finally by a decomposition reaction. The addition of Al(III) lowers the intensity of the oxidation wave due to the formation of the redox-inactive complex AlL33−. A residual low signal was attributed to the free ligand produced by the complex dissociation, AlL33− = AlL2− + L2−. All the kinetic parameters involved in the ligand oxidation and in the complex disruption were calculated on the basis of the agreement between experimental and simulated linear sweep and cyclic voltammetries. Correctness of the mechanisms proposed was further confirmed “a posteriori” by the agreement between potentiometric and linear sweep voltammetric results. The low residual signal observed in the presence of fully formed complex was attributed to the free ligand produced by the complex dissociation, having a kinetic constant estimated 0.2 s−1. 相似文献
82.
Moracci Marco; Capalbo Luisa; Ciaramella Maria; Rossi Mose 《Protein engineering, design & selection : PEDS》1996,9(12):1191-1195
The Sulfolobus solfataricus, strain MT4, ß-glycosidase(Ssßgly) is a thermophilic member of glycohydrolasefamily 1. To identify active-site residues, glutamic acids 206and 387 have been changed to isosteric glutamine by site-directedmutagenesis. Mutant proteins have been purified to homogeneityusing the Schistosoma japonicum glutathione S-transferase (GST)fusion system. The proteolytic cleavage of the chimeric proteinwith thrombin was only obtainable after the introduction ofa molecular spacer between the GST and the Ssß-glydomains. The Glu387 Gin mutant showed no detectable activity,as expected for the residue acting as the nucleophile of thereaction. The Glu206 Gin mutant showed 10- and 60-fold reducedactivities on aryl-galacto and aryl-glucosides, respectively,when compared with the wild type. Moreover, a significant Kmdecrease with plo-nitrophenyl-ß-D-glucoside was observed.The residual activity of the Glu206 Gln mutant lost the typicalpH dependence shown by the wild type. These data suggest thatGlu206 acts as the general acid/base catalyst in the hydrolysisreaction. 相似文献
83.
Ressler Thorsten Wienold Julia Jentoft Rolf E. Neisius Thomas Günter Marco M. 《Topics in Catalysis》2002,18(1-2):45-52
The potentials of X-ray absorption spectroscopy (XAS) (quantitative phase composition and average valence together with a short-range order structure analysis) combined with a time-resolution in the second range make time-resolved (TR-) XAS a powerful tool for investigating the reactivity of solids in catalysis and solid-state chemistry. General aspects of TR-XAS investigations are discussed (i.e., instrumentation, data analysis). In addition, some experiments illustrate how the kinetics of solid-state reactions in heterogeneous catalysis can be elucidated from TR-XAS studies. 相似文献
84.
This study has developed an electrochemical impedance spectroscopy (EIS) method for the in situ investigation of the influence of positive plate compression on the electrochemical behaviour of lead-acid batteries during charge/discharge cycling. The EIS data for a fully charged and fully discharged battery are internally consistent with the expected kinetics of a battery in the opposite states of charge, and demonstrate that EIS measurements may be recorded with a high level of reproducibility. Furthermore, this study has necessitated the development of a special cell incorporating horizontally orientated battery plates that can be subjected to elevated pressure through the stacking of lead bricks on top of the cell, as well as a physically robust reference electrode system that can withstand the application of pressure. For this purpose, a platinum-wire pseudo-reference electrode has been developed, and has been shown to exhibit sufficient electrode stability over the period of an EIS recording, enabling the measurement of reproducible and meaningful EIS data. Additionally, the influence of positive plate compression on the behaviour of the lead-acid battery has been investigated by using scanning electron microscopy (SEM). Clearly, the experimental data show that plate compression enhances significantly the kinetics and concomitant performance of the lead-acid battery, and this is related to the enhanced reactivity of the active material, as rationalized by using the agglomeration-of-spheres (AOS) model. 相似文献
85.
Claude Deslouis Bernard Tribollet Guiliano Mengoli Marco M. Musiani 《Journal of Applied Electrochemistry》1988,18(3):374-383
The electrochemical behaviour of a Cu rotating disc electrode in neutral aerated NaCl solution was investigated in the cathodic and anodic ranges and at the corrosion potential. In the cathodic range, where the reduction of oxygen takes place, reduction peaks allow the identification and quantitative evaluation of insoluble corrosion products (CuCl and Cu2O). In the anodic range Cu is dissolved, most likely as CuCl
2
–
. A new mechanism for the anodic dissolution is proposed after comparing our data with previously published mechanisms. Corrosion currents were found to decrease with time and to be a function of the rotation rate of the electrode. Both the mixed kinetics of the anodic partial reaction and diffusion through a porous layer seem to be relevant in controllingl
corr. 相似文献
86.
87.
Procopio Lorenzo M. Delgado Francisco Enríquez Marco Belabas Nadia 《Quantum Information Processing》2021,20(6):1-3
Quantum Information Processing - A Correction to this paper has been published: https://doi.org/10.1007/s11128-019-2234-5 相似文献
88.
Capponi Caterina Meniconi Silvia Lee Pedro J. Brunone Bruno Cifrodelli Marco 《Water Resources Management》2020,34(2):501-514
Water Resources Management - The pressure damping occurring in pressurized pipes with a leak during transients has been examined as a diagnostic tool – the so-called transient damping method... 相似文献
89.
90.
Ingrid R. Marques Camila Silveira Monique J. L. Leite Artur M. Piacentini Cristiano Binder Marta E. R. Dotto Alan Ambrosi Marco Di Luccio Cristiane da Costa 《应用聚合物科学杂志》2021,138(24):50558
The modification of the surface characteristics after treatment with plasma in polymeric materials, such as the aging phenomenon, calls the attention of research in the area of nonthermal plasma technology. In this work, a direct treatment with dielectric-barrier discharge plasma was used on the surfaces of ultrafiltration membranes. The measurements of the contact angle with water, attenuated total reflectance accessory, zeta potential, atomic force microscopy and scanning electron microscopy-MEV were performed on the surfaces to verify changes after plasma treatment and to understand the occurrence and timing of the plasma aging effect. In the analysis of the membrane performance, hydraulic permeation and protein retention tests were performed. The results showed an improvement in wettability and hydrophilic properties in the post-treated membranes. The study of reversibility/aging of the post-plasma surface is important for research that deals with the modification of polymeric membranes. Changes in surface morphology, topography and wettability of the membranes were observed up to seven days after treatment, with a tendency to return to the initial characteristics of the membranes. 相似文献