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71.
The influence of high temperature annealing and heavy current treatments of porous Pt electrodes is investigated with scanning electron microscopy. The results are discussed on the basis of the kinetic behaviour of these electrodes, known from the literature or deduced from our still unpublished results.It is demonstrated that both the structure and the catalytic activity are influenced by the treatments. 相似文献
72.
Fernando A. Oliveira Neri Alves José A. Giacometti Carlos J. L. Constantino Luiz H. C. Mattoso Ana M. O. A. Balan Aldo E. Job 《应用聚合物科学杂志》2007,106(2):1001-1006
This work describes the preparation and characterization of composite materials obtained by the combination of natural rubber (NR) and carbon black (CB) in different percentages, aiming to improve their mechanical properties, processability, and electrical conductivity, aiming future applications as transducer in pressure sensors. The composites NR/CB were characterized through optical microscopy (OM), DC conductivity, thermal analysis using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), thermogravimetry (TGA), and stress–strain test. The electrical conductivity varied between 10?9 and 10 S m?1, depending on the percentage of CB in the composite. Furthermore, a linear (and reversible) dependence of the conductivity on the applied pressure between 0 and 1.6 MPa was observed for the sample with containing 80 wt % of NR and 20% of CB. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
73.
Rinaldo Gregorio Luiz Francisco Malmonge Guilherme Fontes Leal Ferreira Wilson Nunes Dos Santos Luiz Henrique Capparelli Mattoso 《应用聚合物科学杂志》2003,87(5):752-758
The real (ε′) and imaginary (ε″) components of the complex permittivity of blends of PVDF [poly(vinylidene fluoride)] with POMA [poly(o‐methoxyaniline)] doped with toluenosulfonic acid (TSA) containing 1, 2.5, and 5 wt % POMA–TSA were determined in the frequency interval between 102 and 3 × 106 Hz and in the temperature range from ?120 up to 120°C. It was observed that the values of ε′ and ε″ had a greater increase with the POMA–TSA content and with a temperature in the region of frequencies below 10 kHz. This effect decreased with frequency and it was attributed to interfacial polarization. This polarization was caused by the blend heterogeneity, formed by conductive POMA–TSA agglomerates dispersed in an insulating matrix of PVDF. The equation of Maxwell–Garnett, modified by Cohen, was used to evaluate the permittivity and conductivity behavior of POMA–TSA in the blends. A strong decrease was observed in POMA–TSA conductivity in the blend, which was bigger the lower the POMA–TSA content in the blend. This decrease could have been caused either by the POMA dedoping during the blend preparation process or by its dispersion into the insulating matrix. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 752–758, 2003 相似文献
74.
Erika Carneiro Riqueza Alcino Palermo de Aguiar Luiz Claudio Santa Maria Mônica Regina Marques Palermo de Aguiar 《Polymer Bulletin》2002,48(4-5):407-414
Summary
The preparation of a chelating ion-exchange network based on acrylonitrile was carried out by chemical modification with hydroxylamine.
The beads of resin were synthesized by aqueous suspension copolymerization of acrylonitrile (AN), styrene (STY) and divinylbenzene
(DVB). The influence of diluent used in the suspension polymerization on the structure of the resulting copolymers was evaluated.
The diluents employed were heptane (HEP), toluene (TOL) and anisole (ANI). It was found that the AN incorporation into copolymer
structure was dependent on the diluent used. Conversion of nitrile groups into the amidoxime was conducted by treatment with
hydroxylamine under alkaline solution. The resins were characterized by apparent density, surface area, average pore diameter,
elemental analysis (CHN), FTIR and optical microscopy. Based on the results obtained, it was possible to control the porosity
by diluent employed in the synthesis and to modify chemically a resin containing nitrile groups by hydroxylamine reaction.
Received: 6 October 2001/Revised version: 2 April 2002/ Accepted: 11 April 2002 相似文献
75.
Luiz C.A Oliveira 《Carbon》2004,42(11):2279-2284
In this work, hydrogen peroxide reactions, i.e. H2O2 decomposition and oxidation of organics in aqueous medium, were studied in the presence of activated carbon. It was observed that the carbon pre-treatment with H2 at 300, 500, 700 and 800 °C resulted in an increase in activity for both reactions. The carbons were characterized by BET nitrogen adsorption, thermogravimetric analyses (TG), temperature programmed reduction (TPR), electron paramagnetic resonance (EPR), iodometric titration and determination of the acid/basic sites. TPR experiments showed that activated carbon reacts with H2 at temperatures higher than 400 °C. The treatment produces a slight increase in the surface area. EPR analyses indicate the absence of unpaired electrons in the carbon. Iodometric titrations and TG analyses suggested that the treatment with H2 generates reduction sites in the carbon structure, with concentration of approximately 0.33, 0.53, 0.59, 0.65 and 0.60 mmol/g for carbons treated at 25, 300, 500, 700 and 800 °C, respectively. It was also observed the appearance of basic sites which might be related to the reduction sites. It is proposed that these reducing sites in the carbon can activate H2O2 to generate HO* radicals which can lead to two competitive reactions, i.e. the hydrogen peroxide decomposition or the oxidation of organics in water. 相似文献
76.
Rgia Maria Cordeiro Brito Alzir Azevedo Batista Javier Ellena Eduardo E. Castellano Izaura Cirino Nogueira Digenes Luiz Gonzaga de Frana Lopes Jackson Rodrigues de Sousa Ícaro de Sousa Moreira 《Inorganic chemistry communications》2007,10(12):1515-1517
The cis-[Ru(dppb)(Me-bipy)(NCS)2], dppb = 1,4-bis (diphenylphosphino)butane, Me-bipy = 4,4′-dimethyl-2,2′-bipyridine, and NCS = thiocyanate, was synthesized and characterized by spectroscopic and electrochemical techniques and its structure was determined by crystal X-ray analysis. The crystal structure reveals that the coordination geometry around the Ru(II) center is distorted octahedron where two molecules of thiocyanate are bonded to the ruthenium through nitrogen atom in cis orientation. The half-wave formal potential value E1/2 = 0.8 V (versus Ag/AgCl) observed is considerable higher than that for the cis-[RuCl2(dppb)(Me-bipy)] complex, E1/2 = 0.6 V (versus Ag/AgCl), well illustrating the strong π-acceptor effect the NCS ligand toward the backbonding interaction with the Ru(II) metal center. The MLCT absorption bands of the thiocyanate complex present a higher molar absorptivity (about 12%) compared with the cis-[RuCl2(dppb)(Me-bipy)] complex, in the same experimental conditions. These properties make the complex potentially promising for the photosensitization process. 相似文献
77.
The vulcanization of natural rubber was studied with the sulfurating agents dipentamethylene thiuram tetrasulfide (DPTT) and tetramethylene thiuram disulfide (TMTD) in the presence of tetramethyl thiuram monosulfide (TMTM). This last accelerant affects the rate and efficiency of the vulcanization as well as the structures of crosslinks formed by the two sulphur donors. It may give rise to a polymerization between adjacent double bonds and generate a inhomogeneous crosslink distribution with an adverse effect on physical properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 491–499, 2002 相似文献
78.
Guadalupe Del C. Pizarro Oscar G. Marambio Manuel Jeria O Margarita Huerta Bernab L. Rivas 《应用聚合物科学杂志》2006,100(1):178-185
The free‐radical copolymerization of water‐soluble poly(1‐vinyl‐2‐pyrrolidone‐co‐hydroxyethylmethacrylate) was carried out with a feed monomer ratio of 75:25 mol %, and the total monomer concentration was 2.67M. The synthesis of the copolymer was carried out in dioxane at 70°C with benzoyl peroxide as the initiator. The copolymer composition was obtained with elemental analysis and 1H‐NMR spectroscopy. The water‐soluble polymer was characterized with elemental analysis, Fourier transform infrared, 1H‐ and 13C‐NMR spectroscopy, and thermal analysis. Additionally, viscosimetric measurements of the copolymer were performed. The thermal behavior of the copolymer and its complexes were investigated with differential scanning calorimetry (DSC) and thermogravimetry techniques under a nitrogen atmosphere. The copolymer showed high thermal stability and a glass transition in the DSC curves. The separation of various metal ions by the water‐soluble poly(1‐vinyl‐2‐pyrrolidone‐co‐hydroxyethylmethacrylate) reagent in the aqueous phase with liquid‐phase polymer‐based retention was investigated. The method was based on the retention of inorganic ions by this polymer in a membrane filtration cell and subsequent separation of low‐molar‐mass species from the polymer/metal‐ion complex formed. Poly(1‐vinyl‐2‐pyrrolidone‐co‐hydroxyethylmethacrylate) could bind metal ions such as Cr(III), Co(II), Zn(II), Ni(II), Cu(II), Cd(II), and Fe(III) in aqueous solutions at pHs 3, 5, and 7. The retention percentage for all the metal ions in the polymer was increased at pH 7, at which the maximum retention capacity could be observed. The interaction of inorganic ions with the hydrophilic polymer was determined as a function of the pH and filtration factor. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 178–185, 2006 相似文献
79.
Josianne Lefebvre Federico Galli Claudia L. Bianchi Gregory S. Patience Daria C. Boffito 《加拿大化工杂志》2019,97(10):2588-2593
X‐ray photoelectron spectroscopy (XPS) is a quantitative surface analysis technique used to identify the elemental composition, empirical formula, chemical state, and electronic state of an element. The kinetic energy of the electrons escaping from the material surface irradiated by an x‐ray beam produces a spectrum. XPS identifies chemical species and quantifies their content and the interactions between surface species. It is minimally destructive and is sensitive to a depth between 1–10nm. The elemental sensitivity is in the order of 0.1 atomic %. It requires ultra high vacuum ( Pa) in the analysis chamber and measurement time varies from minutes to hours per sample depending on the analyte. XPS dates back 50 years ago. New spectrometers, detectors, and variable size photon beams, reduce analysis time and increase spatial resolution. An XPS bibliometric map of the 10 000 articles indexed by Web of Science[1] identifies five research clusters: (i) nanoparticles, thin films, and surfaces; (ii) catalysis, oxidation, reduction, stability, and oxides; (iii) nanocomposites, graphene, graphite, and electro‐chemistry; (iv) photocatalysis, water, visible light, and ; and (v) adsorption, aqueous solutions, and waste water. 相似文献
80.
Summary The effect of di-n-butyl ether (DBE) in the synthesis of a highly active propylene polymerization catalyst was studied. Electron-donors having ester and phosphate groups (ethyl benzoate-EB, diisobutyl phthalate-DIBP and tri-n-butyl phosphate-TBP) were added as second internal bases (IB2) to the catalysts prepared by the reduction of TiCl4 with AlClEt2 (DEAC) in the presence of DBE as a first internal base (IB1). The crystalline forms were examined for all catalyst samples by X-ray method. Special attention has been paid to the -TiCl3 samples showing the best catalytic properties. These catalysts were evaluated in propylene polymerization in the absence and presence of external bases (EB, DIBP and DBE). The effects of internal and external bases on the catalyst activity and stereo-specificity are discussed. 相似文献