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71.
This paper considers the design of a nonlinear observer‐based output‐feedback controller for oil‐field drill‐string systems aiming to eliminate (torsional) stick–slip oscillations. Such vibrations decrease the performance and reliability of drilling systems and can ultimately lead to system failure. Current industrial controllers regularly fail to eliminate stick–slip vibrations under increasingly challenging operating conditions caused by the tendency towards drilling deeper and inclined wells, where multiple vibrational modes play a role in the occurrence of stick–slip vibrations. As a basis for controller synthesis, a multi‐modal model of the torsional drill‐string dynamics for a real rig is employed, and a bit–rock interaction model with severe velocity‐weakening effect is used. The proposed model‐based controller design methodology consists of a state‐feedback controller and a (nonlinear) observer. Conditions, guaranteeing asymptotic stability of the desired equilibrium, corresponding to nominal drilling operation, are presented. The proposed control strategy has a significant advantage over existing vibration control systems as it can effectively cope with multiple modes of torsional vibration. Case study results using the proposed control strategy show that stick–slip oscillations can indeed be eliminated in realistic drilling scenarios in which industrial controllers fail to do so. Moreover, key robustness aspects of the control system involving the robustness against uncertainties in the bit–rock interaction and changing operational conditions are evidenced. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
72.
The development of crystalline phases in lithium oxynitride glass-ceramics was examined, with particular emphasis placed on the effect of the nitrogen source (AlN or Si3 N4 ) on the formation and stability of a β-quartz solid-solution ( ss ) phase. Oxynitride glasses derived from the Li-Si-Al-O-N system were heat-treated at temperatures up to 1200°C to yield glass-ceramics in which β-quartz( ss ) and β-spodumene( ss ) of approximate composition Li2 OAl2 O3 4SiO2 formed as major phases and in which X-phase (Si3 Al6 O12 N2 ) and silicon oxynitride (Si2 N2 O) were present as minor phases. The nitrogen-containing β-quartz( ss ) phase that was prepared with AlN was stable at 1200°C; however, the use of Si3 N4 as the nitrogen source was significantly less effective in promoting such thermal stabilization. Lattice parameter measurements revealed that AlN and Si3 N4 had different effects on the crystalline structures, and it was proposed that the enhanced thermal stability of the β-quartz( ss ) phase that was prepared with AlN was due to both the replacement of oxygen by nitrogen and the positioning of excess Al3+ ions into interstitial sites within the β-quartz( ss ) crystal lattice. 相似文献
73.
A global NDVI and EVI reference data set for land-surface phenology using 13 years of daily SPOT-VEGETATION observations 总被引:1,自引:0,他引:1
Astrid Verhegghen Sophie Bontemps Pierre Defourny 《International journal of remote sensing》2014,35(7):2440-2471
Time series of vegetation indices (VIs) obtained by remote sensing are widely used to study phenology on regional and global scales. The aim of the study is to design a method and to produce a reference data set describing the seasonal and inter-annual variability of the land-surface phenology on a global scale. Specific constraints are inherent in the design of such a global reference data set: (1) the high diversity of vegetation types and the heterogeneous conditions of observation, (2) a near-daily resolution is needed to follow the rapid changes in phenology, (3) the time series used to depict the baseline vegetation cycle must be long enough to be representative of the current vegetation dynamic and encompass anomalies, and (4) a spatial resolution consistent with a land-cover-specific analysis should be privileged. This study focuses on the SPOT (Satellite Pour l’Observation de la Terre)-VEGETATION sensor and its 13-year time series of reflectance values. Five steps addressing the noise and the missing data in the reflectance time series were selected to process the daily multispectral reflectance observations. The final product provides, for every pixel, three profiles for 52 × 7-day periods: a mean, a median, and a standard deviation profile. The mean and median profiles represent the reference seasonal pattern for variation of the vegetation at a specific location whereas the standard deviation profile expresses the inter-annual variability of VIs. A quality flag at the pixel level demonstrated that the reference data set can be considered as a reliable representation of the vegetation phenology in most parts of the Earth. 相似文献
74.
Astrid Roetzel Aris Tsangrassoulis Udo Dietrich Sabine Busching 《Renewable & Sustainable Energy Reviews》2010,14(3):1001-1013
According to IPCC (Intergovernmental Panel on Climate Change), the largest use of energy in commercial buildings is space heating in colder climates and air conditioning in hot climates. In Europe, the Directive on the energy performance of buildings EPBD (European Energy Performance of Buildings Directive) [1] provides a framework for national building performance regulations and calculation procedures. However, there are often large discrepancies between calculated and measured energy performance of buildings. One main reason is the behaviour of occupants, which is often not reflected in calculation models.This paper presents a literature review of various parameters influencing the effectiveness of occupant controlled natural ventilation. Additionally possibilities to implement these influences into calculation procedures/building simulation and adaptive thermal comfort evaluation are discussed. 相似文献
75.
Ben van Berkel Caroline Bos Astrid Piber Hannes Pfau Luis Etchegorry Hans Peter Nuenning Kristina Madsen Malaica Cimenti Veronica Baraldi Nannang Santoso Albert Gnodde Ramon van der Heijden Jeorg Lonkwitz 《城市环境设计》2010,(1):28-31
国际投资广场是北京的一个新区域,它为现代商住混合的城市提供了一个高效而可持续发展的场所。
场地位于五六环之间的亦庄经济技术开发区的核心地带。在UNStudio的总体规划中,国际投资广场的布局带有一些对中国传统生活方式的隐喻,同时也表达了保持独立性与邻里在社交相平衡的当代生活观念。 相似文献
76.
Jiang Xu Astrid Avellan Hao Li Xitong Liu Vincent Noël Zimo Lou Yan Wang Rälf Kaegi Graeme Henkelman Gregory V. Lowry 《Advanced materials (Deerfield Beach, Fla.)》2020,32(17):1906910
Sulfidized nanoscale zerovalent iron (SNZVI) is a promising material for groundwater remediation. However, the relationships between sulfur content and speciation and the properties of SNZVI materials are unknown, preventing rational design. Here, the effects of sulfur on the crystalline structure, hydrophobicity, sulfur speciation, corrosion potential, and electron transfer resistance are determined. Sulfur incorporation extended the nano-Fe0 BCC lattice parameter, reduced the Fe local vacancies, and lowered the resistance to electron transfer. Impacts of the main sulfur species (FeS and FeS2) on hydrophobicity (water contact angles) are consistent with density functional theory calculations for these FeSx phases. These properties well explain the reactivity and selectivity of SNZVI during the reductive dechlorination of trichloroethylene (TCE), a hydrophobic groundwater contaminant. Controlling the amount and speciation of sulfur in the SNZVI made it highly reactive (up to 0.41 L m−2 d−1) and selective for TCE degradation over water (up to 240 moles TCE per mole H2O), with an electron efficiency of up to 70%, and these values are 54-fold, 98-fold, and 160-fold higher than for NZVI, respectively. These findings can guide the rational design of robust SNZVI with properties tailored for specific application scenarios. 相似文献
77.
78.
The effect of particle size on the zeta potential and rheology of nanoparticulate SiO2 dispersions stabilized with the polymer polyethylenimine (PEI) was investigated experimentally. The particle size and molecular weight of the polymer had only a small influence on the amount of PEI needed and the achieved zeta potential of the suspensions. The polymer concentration range within which a stable dispersion could be produced was very narrow for the smallest particle size. Higher-molecular-weight PEI was more suitable to stabilize small particle dispersions. Under optimum conditions, Newtonian flow behavior was achieved for dispersions of 20 nm particles with a solids content as high as 25 vol%. 相似文献
79.
The pressure-volume analogy between compressible fluids and macroscopic sand bodies (Ivsic et al. in Phys A, 277:47–61, 2000) is further extended using quantitative determination of corresponding empirical constants based on adapted van der Waals
state equation. The isothermal constants obtained by interpretation of triaxial sand tests at so called “critical state of
sand” are clearly related to the universal ideal gas properties and molar properties of mineral sands. The corresponding constants
for sand and gases or other volatile liquids have the same order of magnitude. The apparent bulk repulsion/attraction effects
in sand bodies are also discussed. 相似文献
80.
Laurence Mertens Trung D. T. Dang Annemie H. Geeraerd An Vermeulen Eva Van Derlinden Astrid M. Cappuyns Johan Debevere Frank Devlieghere Jan F. Van Impe 《Food and Bioprocess Technology》2012,5(6):2578-2585
The spoilage potential of Zygosaccharomyces bailii has been widely recognized within the food industry. However, few data are available on the growth characteristics of this yeast at low temperature and in the absence of chemical preservatives. In this study, the growth/no growth boundary of Z. bailii was defined at refrigeration temperature (7?°C) and at conditions relevant to high-sugar, low-pH foods (such as ketchup and salad dressing), i.e. pH?3.0?C5.0 (five levels), a w 0.93?C0.97 (five levels) and acetic acid concentration 0?C2.5% (v/v; six levels). Yeast growth was followed during 90?days by optical density measurements, and logistic regression models were used to describe the data. Acetic acid had a significant effect on the relation between a w and NaCl concentration and this interaction had important consequences for the model development. When data were modelled as a function of a w or NaCl concentration, a stimulatory effect by acetic acid was observed. In contrast, as a function of (toxic) Na+ ions, no evidence was found of such a phenomenon. These results indicate that in cases where the relationship between a w and solute concentration is not straightforward such as in the presence of acid preservatives, one must be critical towards the interpretation of data and correspondingly, the development of predictive models. On a practical note, the developed models, especially the one incorporating Na+ ions, may be used (1) to assess the stability of shelf-stable acidified foods stored under chilled conditions after opening or (2) to formulate new additive-free products intended for storage at 7?°C. 相似文献