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71.
Shufang Wang Yuanhui Ma Yanji Wang Wei Xue Xinqiang Zhao 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(11):1466-1471
BACKGROUND: A single‐step conversion of nitrobenzene (NB) to p‐aminophenol (PAP) through catalytic hydrogenation is a widely used synthesis route for PAP. The main shortcoming of this route is the use of sulfuric acid for rearrangement of the phenylhydroxylamine (PHA) intermediate. In this paper, S2O82?/ZrO2 (PSZ) solid acid and Pt‐S2O82?/ZrO2 (Pt‐PSZ) bifunctional catalysts were prepared for the synthesis of PAP in non‐acid medium. RESULTS: Calcination temperature has a substantial effect on the acidity, structure and activity for PHA rearrangement of PSZ. The highest PAP yield was 33.8% over PSZ calcined at 823 K when the reaction was carried out in water at 423 K. A high PAP yield of 23.9% was achieved by a single‐step reaction of nitrobenzene over Pt‐PSZ bifunctional catalysts. CONCLUSION: PSZ solid acid exhibits high activity for PHA rearrangement. Perfect tetragonal ZrO2 and much stronger acid sites play important roles in catalytic activity. Inhibiting the hydrogenation activity by reducing the amount of Pt loading on Pt‐PSZ can improve the competition of PHA rearrangement on acid sites with hydrogenation of PHA on metal active sites, resulting in better selectivity to PAP. Copyright © 2008 Society of Chemical Industry 相似文献
72.
Influence of Pt particle size on catalytic combustion of xylenes on carbon aerogel-supported Pt catalysts 总被引:3,自引:0,他引:3
M.N. Padilla-Serrano F.J. Maldonado-Hdar C. Moreno-Castilla 《Applied catalysis. B, Environmental》2005,61(3-4):253-258
Pt catalysts supported on a carbon aerogel with different Pt particle sizes were studied in the combustion of o-xylene and m-xylene. Results found show that the activity of the catalysts increased with larger Pt particle size. In addition, the catalysts were activated during consecutive combustion runs and during time on stream. This activation depends on the Pt particle size and type of xylene isomer. Activation was due to the increase in Pt particle size during reaction. The lower activity of catalysts with smaller Pt particle size was due to the stronger PtO bonds formed during xylene combustion by the smaller Pt particles. 相似文献
73.
Francesco Donsì Stefano Cimino Almerinda Di Benedetto Raffaele Pirone Gennaro Russo 《Catalysis Today》2005,105(3-4):551-559
The oxidative dehydrogenation of ethane is carried out in short contact time reactors over Pt and LaMnO3 based catalysts supported on a large number of different ceramic substrates (45, 60 and 80 ppi foam monoliths and 200, 400, 600, 900 and 1200 cpsi honeycomb monoliths). Experimental results, obtained under the same conditions at varying the C2H6/O2 ratio, showed that the highest performance in terms of ethylene selectivity and yield is always attained on LaMnO3 catalysts. Furthermore, the results are significantly influenced by the morphology and cell density of the support, with 45 and 60 ppi foams and 400 and 600 cpsi honeycombs giving the best performance. The experimental results are explained by means of geometrical and fluid dynamic considerations on the support, and by means of a 2D mathematical model, which clearly indicates an optimal intermediate cell density for maximising ethylene selectivity and yield. 相似文献
74.
Recent research on annotation interfaces provides provocative evidence that anchored, annotation-based discussion environments
may lead to better conversations about a text. However, annotation interfaces raise complicated tradeoffs regarding screen
real estate and positioning. It is argued that solving this screen real estate problem requires limiting the number of annotations
displayed to users. In order to understand which annotations have the most learning value for students, this paper presents
two complementary studies examining the effects of annotations on students performing a reading-to-write task. The first study
used think-aloud protocols and a within-subjects methodology, finding that annotations appeared to provoke students to reflect
more critically upon the primary text. This effect was particularly strong when students encountered pairs of annotations
presenting different viewpoints on the same section of text. Student interviews suggested that annotations were most helpful
when they caused the reader to consider and weigh conflicting viewpoints. The second study used a between-subjects methodology
and a more naturalistic task to provide complementary evidence that annotations encourage more reflective responses to a text.
This study found that students who received annotated materials both perceived themselves and were perceived by instructors
as less reliant on unreflective summary strategies than students who received the same content but in a different format.
These findings indicate that the learning value of an annotation lies in its ability to provoke students to consider and weigh
new perspectives on the primary text. When selected effectively, annotations provide a critical scaffolding that can support
students’ critical thinking and argumentation activities. Collaborative digital libraries and applications for the Web 2.0
should be designed with this learning framework in mind. 相似文献
75.
Ahmad Nozad Golikand Elaheh Lohrasbi Mohammad Ghannadi Maragheh Mehdi Asgari 《Journal of Applied Electrochemistry》2008,38(6):869-874
The effect of carbon surface oxidation on platinum supported carbon particles (Pt/C) with nitric acid was investigated by
cyclic voltammetry, electrochemical impedance spectroscopy, polarization experiments and chronoamperometry. Cyclic voltammograms,
polarization curves and electrochemical impedance spectra showed that the treated catalyst had much larger active surface
area and higher ionic conductivity than the untreated catalyst, and provided enhanced performance for oxygen reduction. The
formation of acidic groups was examined by IR spectra. The Pt/C surface oxidation had a large effect on the performance of
a gas diffusion electrode for oxygen reduction reaction. 相似文献
76.
The polymerization of α‐methylstyrene (AMS) catalyzed by Maghnite‐H+ (Mag‐H) was investigated. Mag‐H is a montmorillonite sheet silicate clay, exchanged with protons. It was found that the cationic polymerization of AMS is initiated by Mag‐H at ambient temperature in bulk and in solution. The effect of the amount of Mag‐H, the temperature, and the solvent was studied. The polymerization rate increased with increase in the temperature and the proportion of catalyst, and it was larger in nonpolar solvents. These results indicated the cationic nature of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from Mag‐H. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
77.
The temperature programmed (palladium) hydride decomposition appeared very effective method for diagnosing the extent of alloying in Pd-Pt/SiO2 catalysts. Introduction of Pt to Pd catalysts moves the TPHD peak gradually towards lower temperatures and the shift in hydride decomposition peak is accompanied by a decrease in the amount of released hydrogen. The catalysts prepared the direct redox method showed much better alloy homogeneity than the samples prepared by coimpregnation. The results of probing with other techniques, i.e. catalytic probing with hydrodechlorination of CCl2F2 and XRD, were in line with TPHD data. The catalytic probing showed the presence of synergistic effect, a clear indication of Pd-Pt mixing. XRD data of post-reaction samples showed carbon incorporation into Pd-rich phase, whereas separate Pt-rich phase did not experience any bulk carbiding. 相似文献
78.
79.
The effects of H2O and NH3 on the kinetics of the liquid phase hydrogenation of tetralin to decalin at 6.9 MPa and 330°C over commercial P---Ni---Mo/alumina catalysts in the presence of H2S have been investigated. H2O functioned as a mild kinetic inhibitor to an extent sensitive to the H2S level. Quasi in situ XPS was used to investigate the catalyst structure after exposure to H20/H2S. 相似文献
80.
Pt NaY and Pt In NaY adsorption properties have been compared by using probes like H2, C4H10, 2-C4H8 and microcalorimetry. It appears that the addition of In to Pt does not change the initial heat of H2 chemisorption but decreases the initial heat of butane and butene chemisorption. 相似文献