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331.
This paper presents a combined method for modeling the mode-I and II crack growth behavior in thick-section fiber reinforced polymeric composites having a nonlinear material response. The experimental part of this study includes crack growth tests of a thick composite material system manufactured using the pultrusion process. It consists of alternating layers of E-glass unidirectional roving and continuous filament mats in a polymeric matrix. Integrated micromechanical and cohesive finite element (FE) models are used to simulate the crack growth response in eccentrically loaded single-edge-notch, (tension), ESE(T) and notched butterfly specimens. Micromechanical constitutive models for the mat and the roving layers are used to generate the effective nonlinear material behavior from the in situ fiber and matrix responses. The validity of the numerical modeling approach before the onset of crack growth is investigated using an infrared thermal method. Cohesive FE models are calibrated and used to simulate the complete crack growth behavior for different crack configurations. The proposed integrated framework of multi-scale material models with cohesive fracture models is shown to be an effective method for predicting the structural and material responses including failure load and crack growth in thick-section fiber reinforced polymeric composites. 相似文献
332.
Säilynoja E Koskinen M Salonen J Holmlund P Södergärd A Koskinen M 《Journal of materials science. Materials in medicine》1999,10(12):703-705
The electron beam radiation induced grafting method was used to attach a reactive polyacrylamide (PAA) layer (20 wt %) on the surface of a biodegradable poly-L-lactide-co--caprolactone (PLLA-co-CL). The biocompatibility of graft–polymer obtained was studied by cytotoxicity test and no signs of toxicity were observed. Heparin and sol–gel-produced silica-gel coatings were successfully attached on the top of the polymeric material produced. The amount of heparin immobilized directly on the surface can be controlled by reaction conditions: reaction time, temperature and pH of the incubation solution. By using acidic conditions, up to 98 µg cm-2 of heparin was immobilized on the surface. The sol–gel-produced silica-gel layer formed by dipping technique was 30 µm thick and the cracking of the layer was minimal after bending several times to 90°. © 1999 Kluwer Academic Publishers 相似文献
333.
Aryloxycarbonylphenyl acrylates and methacrylates were prepared by reacting 4‐acryloyloxybenzoyl chloride and 4‐methacryloyloxybenzoyl chloride with different phenols. They were homopolymerized using benzoyl peroxide as the initiator at 65°C in dimethylformamide. The polymers were characterized by IR and 1H–NMR spectra and size exclusion chromatography. Differential scanning calorimetry and polarizing optical microscopy studies revealed that the phenyl esters of poly(4‐acryloyloxybenzoic acid) and poly(4‐methacryloyloxybenzoic acid) did not show any liquid crystalline properties, but, the para‐aryl–substituted phenyl esters did exhibit mesophase properties in the temperature range of 98–265°C depending on the nature of the aryl substituent. Polymethacrylates exhibit higher Tg, and lower Tm and Ti than the polyacrylates having the same pendant mesogen. Thermogravimetric analyses have shown that the initial decomposition temperatures of the polymers are above 230°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 465–474, 2000 相似文献
334.
335.
Reversible and irreversible degradation in fuel cells during Open Circuit Voltage durability testing
In this study reversible and irreversible voltage loss in a polymer electrolyte membrane fuel cell undergoing an open circuit voltage (OCV) durability test was studied. OCV durability testing is thought to promote chemical degradation of the electrolyte membrane material via radical attack and degradation of the catalyst layer. The results for degradation under constant relative humidity showed that voltage degradation rates measured in the first 20–50 h after polarization curve measurement consisted of a reversible, or transient, and irreversible component. A steady voltage decay rate became evident after 50 h of operation. Comparison to the voltage decay rates obtained from polarization curves showed that the steady voltage decay rate was representative of irreversible voltage loss due to irreversible changes in materials as shown by crossover and active surface area measurements. This study highlights the necessity of understanding the difference between reversible and irreversible voltage decay rates since the reversible decay rates were found to be much higher than irreversible decay rates. 相似文献
336.
The finite difference method was used to solve differential equations of motion of free vibration of composite plates with different boundary conditions. The effects of shear deformation and rotary inertia on the natural frequencies of laminated composite plates are investigated in this paper. Four cases are studied: neglecting both shear deformation and rotary inertia, considering only rotary inertia, considering only shear deformation, and considering both. Solutions were obtained for symmetric and angle-ply laminated plates. The factors that affect natural frequencies of different composite plates, such as span-to-depth ratio, aspect ratio, angle-ply, and lamination sequence were also investigated. Results were found to agree well with exact and approximate solutions reported in literature. Shear deformation showed a considerable effect on the natural frequencies for composite plates, whereas the rotary inertia effect was found to be negligible. 相似文献
337.
This study investigates the influence of using micro-encapsulated phase change material (MEPCM) on the thermal and hydraulic performance of micro-channel heat sinks used for heat dissipation of high power electronic devices. A three-dimensional, one-phase, laminar flow model of a rectangular channel using water slurry of MEPCM with temperature dependent physical properties was developed. The results showed a significant increase in the heat transfer coefficient under certain conditions for heat flux rates of 100 W/cm2 and 500 W/cm2 that is mainly dependant on the channel inlet and outlet temperatures and the selected MEPCM melting temperature. Lower and more uniform temperatures across the electronic device can be achieved at less pumping power compared to using water only as the cooling fluid. 相似文献
338.
L. Srinivasa Rao M. Srinivasa Reddy M. Rami Reddy N. Veeraiah 《Journal of Alloys and Compounds》2008,464(1-2):472-482
Li2O–MoO3–B2O3 glasses containing different amounts of V2O5, ranging from 0 to 1.5 mol%, were prepared. The dielectric properties (viz., constant ′, loss tan δ, AC conductivity σac over a wide range of frequency and temperature) have been studied as a function of the concentration of vanadium ions. The variation of AC conductivity with the concentration of V2O5 passes through a maximum at 0.8 mol% V2O5. In the high-temperature region, the AC conduction seems to be connected with the mixed conduction, viz., electronic and ionic conduction. The dielectric relaxation effects exhibited by these glasses have been analyzed quantitatively by pseudo Cole–Cole plot method and the spreading of relaxation times has been established. Further analysis of these results has been carried out with the aid of the data on ESR, IR and optical absorption spectra. 相似文献
339.
Acrylate and methacrylate monomers with the photodimerizable α,β-unsaturated ketone moiety, such as 4-cinnamoylphenyl, 4-(4-methoxycinnamoyl)phenyl, 4-(4-nitrocinnamoyl)phenyl, or 4-(4-chlorocinnamoyl)phenyl, were prepared and homopolymerized using benzoyl peroxide as the initiator at 70°C in methyl ethyl ketone. The poly(meth)acrylates were characterized by ultraviolet, infrared, 1H-nuclear magnetic resonance (NMR), and 13C-NMR spectra, and gel permeation chromatography. Their thermal properties were studied by thermogravimetric analyses in air and nitrogen, and differential scanning calorimetry. The photocrosslinking properties of the polymers were investigated as thin films and in solution in the presence and absence of sensitizer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2111–2120, 1998 相似文献
340.
4-Acetyl-3-hydroxyphenylacrylate (AHAH) was synthesized and polymerized in 2-butanone using benzoyl peroxide as initiator. Poly(4-acetyl-3-hydroxyphenyl-acrylate) (PAHAH) was characterized by infrared and nuclear magnetic resonance techniques. The molecular weight of the polymer was determined by gel permeation chromatography. Cu(II) and Ni(II) chelates of PAHAH were synthesized. The diffuse reflectance spectra and magnetic moments of the polychelates show distorted planar and octahedral structures for poly[Ni(AHA)2] and poly[Cu(AHA)2(OH2)2] complexes, respectively. The thermal properties of the polychelates are also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 177–182, 1998 相似文献