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21.
Silviu Jipa Traian Zaharescu Radu Setnescu Laura Monica Gorghiu Crinela Dumitrescu Călin Oros 《Polymer Bulletin》2006,57(4):545-552
Summary The kinetic study on thermal degradation of stabilised low density polyethylene by chemiluminescence investigations was performed.
Four hindered amine light stabilisers, additive compounds, were used as thermal protector on polymer substrate. The experiments
were carried out on the samples consisting of polyetylene and 0.25% (w/w) of hindered amine. Three temperatures (180, 190
and 200 °C) were selected for this assay allowing the calculation of the activation energy required for thermal oxidation
of polyethylene matrix. A discussion on mechanistic aspects concerning the antioxidant efficiency of studied compounds is
also presented. 相似文献
22.
Time series analysis using RBF networks with FIR/IIR synapses 总被引:6,自引:0,他引:6
Iulian B. Ciocoiu 《Neurocomputing》1998,20(1-3):57-66
Radial basis functions networks (RBF) with dynamic synapses are introduced. The novelty aspect consists in replacing the standard scalar values of the output weights by discrete-time FIR/IIR filters. LMS-type learning algorithms are derived and simulation results for prediction of chaotic time series are reported. 相似文献
23.
Nonequilibrium Operation of Arsenic Diffused Long-Wavelength Infrared HgCdTe Photodiodes 总被引:1,自引:0,他引:1
Priyalal S. Wijewarnasuriya P.Y. Emelie Arvind D’Souza Gregory Brill Maryn G. Stapelbroek Silviu Velicu Yuanping Chen Chris Grein Sivalingam Sivananthan Nibir K. Dhar 《Journal of Electronic Materials》2008,37(9):1283-1290
We demonstrated a device with a unique planar architecture using a novel approach for obtaining low arsenic doping concentrations
in long-wavelength (LW) HgCdTe on CdZnTe substrates. HgCdTe materials were grown by molecular beam epitaxy (MBE). We fabricated
a p-on-n structure that we term P
+/π/N
+ where the symbol “π” is to indicate a drastically reduced extrinsic p-type carrier concentration (on the order of mid 1015 cm−3); P
+ and N
+ denote a higher doping density, as well as a higher energy gap, than the photosensitive base π-region. Fabricated devices
indicated that Auger suppression is seen in the P
+/π/N
+ architecture at temperatures above 130 K and we obtained a saturation current on the order of 3 mA on 250-μm-diameter devices at 300 K with Auger suppression. Data shows that about a 50% reduction in dark current is achieved at 300 K
due to Auger suppression. The onset of Auger suppression voltage is 450 mV at 300 K and 100 mV at 130 K. Results indicate
that a reduction of the series resistance could reduce this further. A principal challenge was to obtain low p-type doping levels in the π-region. This issue was overcome using a novel deep diffusion process, thereby demonstrating successfully
low-doped p-type HgCdTe in MBE-grown material. Near-classical spectral responses were obtained at 250 K and at 100 K with cut-off wavelengths
of 7.4 μm and 10.4 μm, respectively. At 100 K, the measured non-antireflection-coated quantum efficiency was 0.57 at 0.1 V under backside illumination.
Received November 7, 2007; accepted March 19, 2008 相似文献
24.
Daniela Cristina Culita Claudia Maria Simonescu Rodica Elena Patescu Silviu Preda Nicolae Stanica Cornel Munteanu Ovidiu Oprea 《Journal of Inorganic and Organometallic Polymers and Materials》2017,27(2):490-502
Three novel magnetic adsorbents were synthesized through the immobilization of di-, tri-, and tetraamine onto the surface of silica coated magnetite nanoparticles. The adsorbents were characterized by XRD patterns, FTIR spectroscopy, elemental and thermogravimetric analysis, magnetic measurements, SEM/TEM, EDX spectroscopy, and N2 adsorption/desorption isotherms. Their capacity to remove copper ions from aqueous solutions was investigated and discussed comparatively. The equilibrium data were analyzed using Langmuir and Freundlich isotherms. The kinetics was evaluated using the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The best interpretation for the equilibrium data was given by the Langmuir isotherm for the tri- and tetraamine functionalized adsorbents, while for the diamine functionalized adsorbent the Freundlich model seemed to be better. The kinetic data were well fitted to the pseudo-second-order model. The overall rate of adsorption was significantly influenced by external mass transfer and intraparticle diffusion. It was observed that the adsorption capacity at room temperature decreased as the length of polyamine chain immobilized on the adsorbent surface increased, the maximum adsorption capacities being 52.3 mg g?1 for 1,3-diaminopropan functionalized adsorbent, 44.2 mg g?1 for diethylenetriamine functionalized adsorbent, and 39.2 mg g?1 for triethylenetetramine functionalized adsorbent. The sorption process proved to be highly dependent of pH. The results of the present work recommend these materials as potential candidates for copper removal from aqueous solutions. 相似文献
25.
Vladescu A Kiss A Braic M Cotrut CM Drob P Balaceanu M Vasilescu C Braic V 《Journal of nanoscience and nanotechnology》2008,8(2):733-738
In recent years, the smart materials have attracted much attention due to their unusual properties such as shape memory effect and pseudoelasticity, being widely used for biomedical implants. These materials contain certain amounts of nickel, titanium and others which are not adequate for surgical implants and prosthesis. In the work reported here, two types of nonostructured multilayer coatings (TiN/ZrN, ZrN/Zr) used to prevent the ions release from shape memory alloys were investigated. For comparison, the TiN and ZrN monolayers were also examined. The films were deposited onto nickel-titanium based alloy (Ti-Ni-Nb) and Ni substrates by vacuum arc deposition technique under various deposition conditions. The concentrations of dissolved ions in Ringer solution for uncoated and coated Ni samples were determined to examine the benefic barrier effect of these coatings for ions release from shape memory alloys. In order to have a more complete characterization of the investigated coatings, other properties such as elemental and phase composition, morphology, texture, microhardness, and adhesion were studied. For all coatings, the concentrations of dissolved ions were lower that those measured in the case of the uncoated specimens. The nanostructured multilayer films exhibited the best mechanical and anticorrosive properties. 相似文献
26.
M. V. Popa E. Vasilescu P. Drob M. Anghel C. Vasilescu I. Mirza‐Rosca A. Santana Lopez 《工业材料与腐蚀》2002,53(1):51-55
The passivity of titanium, binary Ti‐15Mo and ternary Ti‐15Mo‐5Al alloys in hydrochloric acid solutions was studied by potentiostatic, potentiodynamic, linear polarization and electrochemical impedance spectroscopy (EIS) techniques. The anodic passivity of binary Ti‐15Mo and ternary Ti‐15Mo‐5Al titanium alloys differs from that of the base metal in hydrochloric acid solutions. The corrosion potentials of both alloys are nobler than of the titanium because the beneficial effect of molybdenum. The critical passivation current density for binary Ti‐15Mo alloy is higher than of titanium; this fact can be explained by the instability of the constituent phases in hydrochloric acid solutions. Ternary Ti‐15Mo‐5Al alloy exhibits two critical passivation current densities (icr1 and icr2) with higher values than of the base metal and two critical passivation potentials (Ecr1 and Ecr2); at the first critical passivation potential (Ecr1) the porous titanium trioxide (Ti3O5) is formed and at the second critical passivation potential (Ecr2) this oxide is converted to a still higher valence oxide, the compact and protective titanium dioxide (TiO2). The dissolution current densities in the passive range of alloys are higher than of the base metal due the dissolution of the alloying elements in this potential range. The alloys are more resistant than titanium presenting lower corrosion rates. A three time constants equivalent circuit was fitted: one time constant is for the double layer capacity (Cdl) and for the passive film (Rp); another time constant is for the charge transfer reactions visualised by a constant phase element (CPE) and a resistance (R1); the third time constant is for diffusion processes through the passive film represented by a resistance (R2) and a Warburg element (W). 相似文献
27.
In this work, we report the fabrication of sensors’ element for humidity or gases, prepared by in situ polymerization of aniline N-propansulfonic acid using ammonium persulfate in acidic medium. The polymer is being used in the form of powder or deposited in multiple layers onto the PET film. Various techniques including Fourier Transform infrared (FTIR), ultraviolet-–visible spectroscopy (UV–vis), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the as-prepared sensing materials. The film has been tested for humidity influence, where the significant variations in electrical characteristics were observed, suggesting its usefulness for humidity sensors. Also, for different organic and inorganic gases, a relatively low operating temperature and important sensitivity were observed that indicate its applicability as an active element for general gases sensors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47743. 相似文献
28.
Identifying pathways of exposure to highway pollutants in great crested newt (Triturus cristatus) road mitigation tunnels 下载免费PDF全文
Katie J. White William M. Mayes Silviu O. Petrovan 《Water and Environment Journal》2017,31(3):310-316
Road mitigation tunnels are increasingly deployed for amphibians but very little is known about chemical pollution in such schemes. We assessed pollution pressures associated with road runoff at a major great crested newt mitigation scheme in England. Sediments and waters in the mitigation system were analysed for major physico‐chemical parameters, trace metals and total petroleum hydrocarbons and compared to a nearby reference site. Seven out of eight tested metals including copper, zinc, lead and iron were in significantly greater concentrations in the tunnels than at a reference site and at environmentally significant concentrations. Water samples also exhibited elevated concentrations of aluminium and chromium and occasionally extreme alkaline pH associated with leaching of portlandite in tunnel cements. High conductivity values in waters and sediments corresponding with seasonal de‐icing salt application were also apparent. The study highlights the potential pollutant pressures for amphibians associated with large‐scale urban development and road mitigation schemes. 相似文献
29.
D.M. Gordin D. Busardo A. Cimpean C. Vasilescu D. Höche S.I. Drob V. Mitran M. Cornen T. Gloriant 《Materials science & engineering. C, Materials for biological applications》2013,33(7):4173-4182
In this study, a superelastic Ni-free Ti-based biomedical alloy was treated in surface by the implantation of nitrogen ions for the first time. The N-implanted surface was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy, and the superficial mechanical properties were evaluated by nano-indentation and by ball-on-disk tribological tests. To investigate the biocompatibility, the corrosion resistance of the N-implanted Ti alloy was evaluated in simulated body fluids (SBF) complemented by in-vitro cytocompatibility tests on human fetal osteoblasts. After implantation, surface analysis methods revealed the formation of a titanium-based nitride on the substrate surface. Consequently, an increase in superficial hardness and a significant reduction of friction coefficient were observed compared to the non-implanted sample. Also, a better corrosion resistance and a significant decrease in ion release rates have been obtained. Cell culture experiments indicated that the cytocompatibility of the N-implanted Ti alloy was superior to that of the corresponding non-treated sample. Thus, this new functional N-implanted titanium-based superelastic alloy presents the optimized properties that are required for various medical devices: superelasticity, high superficial mechanical properties, high corrosion resistance and excellent cytocompatibility. 相似文献
30.
Anne M. Itsuno Jamie D. Phillips Silviu Velicu 《Journal of Electronic Materials》2012,41(10):2886-2892
A unipolar mercury cadmium telluride (HgCdTe) NBνN infrared (IR) device architecture is analyzed by physics-based numerical device simulations. The device structure is predicted to suppress Shockley–Read–Hall (SRH) and Auger generation–recombination (G–R) processes, while also providing a simplified fabrication process by eliminating p-type doping requirements. The performance characteristics of mid- and long-wavelength infrared (MWIR: λ c?=?5?μm; LWIR: λ c?=?12?μm) NBνN devices are calculated and compared with those of nBn and double-layer planar heterostructure (DLPH) devices. Theoretical dark current density (J dark) values of the MWIR and LWIR NBνN devices are lower by an order of magnitude or more for temperatures between 50?K and 225?K. Calculated peak detectivity (D *) values of 6.01?× 1014?cm?Hz0.5/W to 2.36?×?1010?cm?Hz0.5/W for temperatures from 95?K to 225?K, and 2.37?×?1014?cm?Hz0.5/W to 2.27?×?1011?cm?Hz0.5/W for temperatures from 50?K to 95?K are observed for MWIR and LWIR NBνN structures, respectively. A component of the NBνN structure, embodied in a unipolar MWIR nBn device, is also fabricated to experimentally demonstrate selective carrier extraction. 相似文献