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991.
Poly(vinyl chloride) (PVC) and its blends with polybutadiene-acrylonitrile (NBR) (containing 21.7 weight-percent acrylonitrile (AN), a heterogeneous two-phase system; and containing 41.6 weight-percent of AN, a homogeneous one-phase system) and with polyethylene-vinyl acetate (EVA) (containing 45 weight-percent of vinyl acetate (VA), a heterogenous two-phase system; and containing 65 weight-percent VA, a homogeneous one-phase system) were UV-irradiated (at 3500 Å UV-light (solar spectrum)). After UV irradiation the kinetics measurements were made of the formation of hydroperoxy (OOH) and carbonyl (CO) groups and the changes of mechanical properties: tensile strength, elongation to break, and impact energy. As a result of the photooxidative degradation of PVC blends, decreases of mechanical properties were observed. The effects are more severe in PVC/NBR blends, which contain unsaturated bonds (polybutadiene segments) than in the case of PVC/EVA. The phase structure plays an evident role on the UV degradation only of PVC/NBR blends. The photostability of PVC blends can be slightly improved by introducing Tinuvin P or Ni-chelates photostabilizers. 相似文献
992.
Christopher J.G. Plummer André Luciani Tuan-Quoc Nguyen László Garamszegi Marlene Rodlert Jan-Anders E. Månson 《Polymer Bulletin》2002,49(1):77-84
Summary
When the effects of physical aging below T
g are erased, the rheological response of a series of aliphatic hyperbranched polyesters is Newtonian and the melt viscosity
scales roughly linearly with M
w at high M
w, indicating entanglement to be absent. The rheological behavior is also highly sensitive to the nature of the terminal groups,
suggesting the overall behavior to be close to that of an assembly of compact coreshell "particles". There are therefore strong
parallels between the physical behavior of the hyperbranched polyesters in question and that of their ideal dendrimer analogues.
Received: 14 April 2002 /Revised: 1 July 2002 / Accepted: 1 July 2002 相似文献
993.
The performance of powder coatings on hot-dip galvanized steel has been studied by testing in 5 years field exposure in marine and industrial atmospheres, as well as in accelerated tests. The aim was to assess the quality of such coating systems in corrosive environments and to establish criteria for how to obtain good quality. The test data demonstrates that polyester powder coatings are a good alternative to wet paint as top coat on hot-dip galvanized steel. The phosphate layer is identified as the most crucial step to ensure high quality. Recommendations for how to obtain good quality are provided. 相似文献
994.
Dorota Johansson Björn Bergenståhl Eva Lundgren 《Journal of the American Oil Chemists' Society》1995,72(8):939-950
The influence of low concentrations (0.1-5%) of fat crystals on the stability of water-in-soybean oil emulsions was examined
by light scattering and sedimentation experiments. Both the initial flocculation/coalescence rate and long-term stability
against water separation were determined. The initial flocculation/coalescence rate increased upon addition of small amounts
of fat crystals. When the crystal concentration was increased above a critical concentration (specific to a system), a decrease
in the flocculation/coalescence rate occurred. The increased flocculation/coalescence rate is likely the effect of bridging
of water droplets by fat crystals. Fat crystal wetting by water is an important criterion for this phenomenon to occur. Emulsion
stabilization for crystal concentrations above critical is caused by a mechanical screening of water droplets. The presence
of considerable amounts of crystals in oil also lowered the density difference between droplet and medium, and enhanced viscosity.
The degree of increase in viscosity depended upon the emulsifier. Both a decrease in density difference and an increase in
viscosity play a role in hindering flocculation/coalescence of droplets. In long-term studies of water separation, all concentrations
of fat crystals stabilized the water-in-oil emulsions. The droplet size of these emulsions increased until the critical droplet
size was approached where the screening effect of crystals on the droplets no longer stabilized the emulsions. The stabilizing
effect for emulsions with monoolein was continuously improved by increasing the amount of crystals up to 5%. For lecithin-stabilized
emulsions, an optimal effect was achieved for fact crystal concentrations of 1–2%. 相似文献
995.
CCPE: Methodology for a Combined Evaluation of Cognitive and Physical Ergonomics in the Interaction between Human and Machine 下载免费PDF全文
Evaluation methods of today often focus on cognitive ergonomics (such as mental workload or usability) or physical ergonomics (such as physical workload or body posture). This article describes an analytical methodology of a joint systematic search for potential deficiencies in the human–machine interaction; such as high physical and mental workload, use errors, usability problems, and physical ergonomic errors. The purpose with the joint search is to achieve a more holistic evaluation approach and make the evaluation cost more effective than when using separate evaluation methods for cognitive and physical ergonomic aspects. The methodology is task‐based, which makes it possible to use both with focus on the device design, as in development projects; as well as with focus on the procedure, in the operative organization. © 2012 Wiley Periodicals, Inc. 相似文献
996.
Jeremy Steinhauer Lois M. L. Delcambre Marianne Lykke Marit Kristine Ådland 《International Journal on Digital Libraries》2014,14(3-4):167-179
We seek to improve information retrieval in a domain-specific collection by clustering user sessions from a click log and then classifying later user sessions in real time. As a preliminary step, we explore the main assumption of this approach: whether user sessions in such a site are related to the question that they are answering. Since a large class of machine learning algorithms use a distance measure at the core, we evaluate the suitability of common machine learning distance measures to distinguish sessions of users searching for the answer to same or different questions. We found that two distance measures work very well for our task and three others do not. As a further step, we then investigate how effective the distance measures are when used in clustering. For our dataset, we conducted a user study where we had multiple users answer the same set of questions. This data, grouped by question, was used as our gold standard for evaluating the clusters produced by the clustering algorithms. We found that the observed difference between the two classes of distance measures affected the quality of the clusterings, as expected. We also found that one of the two distance measures that worked well to differentiate sessions, worked significantly better than the other when clustering. Finally, we discuss why some distance metrics performed better than others in the two parts of our work. 相似文献
997.
Ingeborg Kaus Kjell Wiik Marit Dahle Morten Brustad Siv Aasland 《Journal of the European Ceramic Society》2007,27(16):4509-4514
Strontium silicate was found on the surface of La0.2Sr0.8Fe0.79Cr0.2Mg0.01O3 exposed to hydrogen containing humid atmospheres at 1000 °C and 30 bars. Silica originated from the furnace tube material and was transported via the gas phase as a gaseous silica hydrate. Fe and Sr were initially preferentially expelled from the perovskite grain boundaries to give Sr2SiO4 at the surface, along with a secondary Fe-rich phase and a LaCrO3-rich grain boundary region. Eventually, Fe and Sr were drawn from the grains, leaving a porous structure. This investigation highlights the importance of avoiding Si sources near Sr-rich membranes in humid atmospheres at high temperatures. 相似文献
998.
Kent B. Abbås 《Polymer》1981,22(6):836-841
Bisphenol A polycarbonate was repeatedly extruded in a capillary rheometer at high, constant shear stresses (0.15–0.95 MPa) and at temperatures between 275 and 320°C. Changes in molecular weight and molecular weight distribution were determined. Polymer degradation occurred to a much larger extent during extrustion than under static conditions; a difference explained by viscous heating effects. The chain scission reaction had an activation energy of 113 kJ mol?1 for static as well as dynamic conditions, which indicates similar degradation mechanisms in both cases. The molecular scission followed non-random kinetics. 相似文献
999.
Summary Acrylamide (AAm)-maleic acid (MA) hydrogels with different monomer ratios were prepared in an aqueous solution by radical polymerization using a new crosslinking agent, polyethyleneglycol (400) diacrylate (PEG (400) DA) and also using N, N’-methylenebisacrylamide (NMBA) for comparison purpose. The hydrogels were characterized by acid group content and FTIR spectroscopy. Their swelling and deswelling behavior were studied as a function of maleic acid content, pH and crosslinking agent. Incorporation of MA in hydrogels significantly increased their swelling ability and their equilibrium degree of swelling (EDS) values changed between 100–269 g water/g polymer in water while AAm polymers swollen less (22–23 g water/g polymer). The AAm hydrogels showed Fickian type diffusion but the all AAm-MA hydrogels showed non-Fickian type behavior. Their swelling degree increased with the increase of pH of the external medium and an instantaneous increase was observed near a pH value of 7.0. The use of PEG (400) DA instead of NMBA as a crosslinking agent also increased the swelling rate and capacity of the gel. The swelling constant (K) and the diffusion coefficient (D) of hydrogels were also increased. The swelling-deswelling cycles in acidic-basic solutions showed that they could be used as pH responsive gels without any decrease in swelling capacity. 相似文献
1000.
Ingeborg Kaus Kjell Wiik Bente Krogh Marit Dahle Karina H. Hofstad Siv Aasland 《Journal of the American Ceramic Society》2007,90(7):2226-2230
The chemical stability of SrFeO3 -based perovskites in H2 O- and CO2 -containing atmospheres at high temperatures and pressures has been examined. The extent of reaction as a function of p CO2 , p H2 O, temperature, and time has been determined. Either strontium carbonate or Sr(OH)2 ·H2 O was observed on sample surfaces after exposure. Observation of two different reaction-rate behaviors could be explained by the formation of different products. The stability of the perovskite has been found to increase when the activity of Sr is decreased. Chemical stability in H2 O/CO2 is important to understand in order to use these membrane materials for syngas production. 相似文献