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61.
This paper reviews some of the progress made on wellbore stability modeling during the last two decades. First we demonstrate the improvement made on mud-pressure predictions by moving from analytic elastic solutions to finite element elastoplastic modeling. We show this progress, presenting a finite element model based on a generalized plane strain formulation for analyzing efficiently the three-dimensional problem of stability in deviated wellbores. On a more research oriented work, we present results from two advanced theories capable of modeling localization of deformation in shear bands, which causes borehole breakouts. The first theory is based on a more established approach, the Cosserat continuum. The second theory, called gradient elastoplasticity, is being developed to resolve some of the drawbacks of gradient plasticity theories. Gradient elastoplasticity is a unified theory where both elastic and plastic parts are of gradient type. We demonstrate that both theories, in addition to localization, can also model the scale effect observed in thick-walled cylinder tests. 相似文献
62.
Antonios E. Goulas Antonios Kokkinos Michael G. Kontominas 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1995,201(1):74-78
Food-grade PVC and PVDC/PVC films containing 28.3% dioctyladipate (DOA) and 5.0% acetyltributylcitrate (ATBC) plasticizers, respectively, were brought into contact with olive oil and were irradiated with -radiation [60Co] at doses equal to 4 kGy and 9 kGy corresponding to cold pasteurization. Irradiation was carried out at 8–10 °C and samples were subsequently stored at 4–5 °C. Contaminated oil samples were analysed for DOA and ATBC at intervals between 7 h and 97 h of contact, using an indirect GC method. Identical nonirradiated (control) samples were also analysed for DOA and ATBC content. Results showed no statistically significant differences in migrated amounts of DOA and ATBC between irradiated and non-irradiated samples. Neither were differences observed between samples irradiated at 4 kGy and 9 kGy. This was supported by identical IR spectra recorded for irradiated and non-irradiated samples and leads to the conclusion that at such intermediate radiation doses (9 kGy) the migration characteristics of both PVC and PVDC/PVC films are not affected. The amount of DOA that migrated into olive oil was dependent on time, reaching equilibrium after approximately 47 h of contact (302.8 mg/l). The amount of ATBC that migrated into olive oil was non-detectable (<1 mg/1) for all samples stored at 4–5 °C after 97 h. In non-irradiated samples (PVDC/PVC in contact with oil) stored at 20 °C, small amounts of migrated ATBC were determined (3.3 and 5.1 mg/l after 29 h and 94 h of contact respectively). Furthermore, in thermally treated samples heated to 80 °C for 30 min and 60 min, the respective amounts of migrated ATBC determined were 2.9 mg/l and 19.3 mg/l. 相似文献
63.
Vassilios Vonikakis Rigas Kouskouridas Antonios Gasteratos 《Multimedia Tools and Applications》2018,77(8):9211-9231
This paper presents a comparison framework for algorithms that can diminish the effects of illumination in images. Its main objective is to reveal the positive and negative characteristics of such algorithms, allowing researchers to select the most appropriate one for their target application. The proposed framework utilizes artificial illumination degradations on real images, which are then processed by the tested algorithms. The results are evaluated by an ensemble of performance metrics, highlighting the various characteristics of the algorithms across a range of different image attributes. The proposed framework represents a useful tool for the selection of illumination compensation algorithms due to a) its quantitative nature, b) its multifaceted analysis and c) its easy reproducibility. The validity of the proposed framework is tested by applying it to the enhancement results of four illumination compensation algorithms, which are used as preprocessing in two classic computer vision applications. The improvements brought about by the algorithms are in accordance with the predictions of the proposed framework. 相似文献
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66.
Ra Won-Sang Whang Ick-Ho Shin Hyo-Sang Tsourdos Antonios 《International Journal of Control, Automation and Systems》2017,15(4):1969-1974
International Journal of Control, Automation and Systems - This paper proposes an efficient aimpoint tracking filter for high-range resolution FMCW radar seekers. A modified probabilistic data... 相似文献
67.
In this work, we present an overview of recently developed methods for control and optimization of complex process systems described by multiscale models. We primarily discuss methods developed in the context of our previous research work and use examples of thin film growth processes to motivate the development of these methods and illustrate their application. 相似文献
68.
George Tsilomelekis Antonios Christodoulakis Soghomon Boghosian 《Catalysis Today》2007,127(1-4):139-147
The structural and catalytic properties of MoO3 catalysts supported on ZrO2, Al2O3, TiO2 and SiO2 with Mo surface densities, ns, in the range of 0.5–18.5 Mo/nm2 were studied for the oxidative dehydrogenation (ODH) of ethane by in situ Raman spectroscopy and catalytic activity measurements at temperatures of 400–540 °C. The molecular structure of the dispersed surface species evolves from isolated monomolybdates (MoO4 and MoO5, depending on the support) at low loadings to associated MoOx units in polymolybdate chains at high loadings and ultimately to bulk crystalline phases for loadings exceeding the monolayer coverage of the supports used. The nature of the oxide support material and of the Mo–O–support bond has a significant influence on the catalytic behaviour of the molybdena catalysts with monolayer coverage. The dependence of reactivity on the support follows the order ZrO2 > Al2O3 > TiO2 > SiO2. The oxygen site involved in the anchoring Mo–O–support is of relevance for the catalytic activity. 相似文献
69.
Antonios Gouglidis Ioannis Mavridis Vincent C. Hu 《International Journal of Information Security》2014,13(2):97-111
The cloud is a modern computing paradigm with the ability to support a business model by providing multi-tenancy, scalability, elasticity, pay as you go and self-provisioning of resources by using broad network access. Yet, cloud systems are mostly bounded to single domains, and collaboration among different cloud systems is an active area of research. Over time, such collaboration schemas are becoming of vital importance since they allow companies to diversify their services on multiple cloud systems to increase both uptime and usage of services. The existence of an efficient management process for the enforcement of security policies among the participating cloud systems would facilitate the adoption of multi-domain cloud systems. An important issue in collaborative environments is secure inter-operation. Stemmed from the absence of relevant work in the area of cloud computing, we define a model checking technique that can be used as a management service/tool for the verification of multi-domain cloud policies. Our proposal is based on NIST’s (National Institute of Standards and Technology) generic model checking technique and has been enriched with RBAC reasoning. Current approaches, in Grid systems, are capable of verifying and detect only conflicts and redundancies between two policies. However, the latter cannot overcome the risk of privileged user access in multi-domain cloud systems. In this paper, we provide the formal definition of the proposed technique and security properties that have to be verified in multi-domain cloud systems. Furthermore, an evaluation of the technique through a series of performance tests is provided. 相似文献
70.