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81.
The paper deals with detection of range spread targets embedded in K-distributed clutter with unknown parameters. A two-step detection algorithm based on multiple-pulse cell-averaging scheme and using lookup tables is proposed. First, the threshold factors that maintain a constant probability of false alarm for various clutter parameters are offline computed and stored. Then, at the detection stage, the most appropriate threshold factor is selected through the estimation of actual environment parameters. We assume that the target energy is spread over a finite number of cells, according to the multiple dominant scattering (MDS) centers model. Next, an expression for the overall reflected target energy, following the multiple-pulse integration, is derived. Finally, we proposed a specific binary hypothesis test by taking into account the number of primary cells, the target energy profile and the number of pulses. The performances analysis of the proposed detector is carried out using Monte Carlo simulations for different clutter parameters and various MDS models. The obtained results are then compared to those of the order statistics-based generalized likelihood ratio test (OS-GLRT). Simulations indicate that the performances of the proposed detector are closely related to the radar resolution, the target energy profile and the number of integrated pulses. 相似文献
82.
83.
Nabila Labraoui Mourad Gueroui Makhlouf Aliouat Jonathan Petit 《Telecommunication Systems》2013,54(1):3-17
Data aggregation is considered as one of the fundamental distributed data processing procedures for saving the energy and minimizing the medium access layer contention in wireless sensor networks. However, sensor networks are likely to be deployed in an untrusted environment, which make them vulnerable against several attacks. A compromised node may forge arbitrary aggregation value and mislead the base station into trusting a false reading. Secure in-network aggregation can detect such manipulation. But, as long as such subversive activity is, reliable aggregation result can not be obtained. In contrast, the collection of individual sensor node values is robust and solves the problem of availability, but in an inefficient way. Our work seeks to bridge this gap in secure data collection. We propose a framework that enhances availability with efficiency close to that of in-network aggregation avoiding over-reliance on sensors. To achieve this, we design a scheme that is built on one core concept: no trust is supposed in any sensor. Therefore, we design a two hierarchical levels of monitoring to ensure the integrity and the accuracy of aggregate result, only when necessary, i.e. only when malicious activities are detected. Relying on this new type of monitoring mechanism, the framework has the ability to recover from aggregator failure without neglecting energy efficiency, providing thus much higher availability than other security protocols. 相似文献
84.
Lhadi Nouri Jack Legrand Nabila Benmalek Faiza Imerzoukene Ahmed-Reda Yeddou Farid Halet 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2008,142(1):78-86
The mixing at a molecular scale (micromixing) plays an important role on selectivity, yield and quality of final products of a large range of competing fast chemical reactions. In this study, we have compared, by the use of iodide–iodate reaction tests, the micromixing in two reactors, the first one is the standard batch stirred reactor and the second is the torus reactor. Various conditions of agitation and feed locations were used for this study. A comparative analysis of the micromixedness ratio (α) in the two reactors was carried out on the basis of the local rate of specific energy dissipation. 相似文献
85.
86.
Ahmed M. Shafeek Hamdy Salah Nabila Shehata A.B. Saddek 《Egyptian Journal of Petroleum》2018,27(3):277-284
This paper studied the influence of the different water types on clinker properties. It concern with cement plants which are using the water for cooling the clinker (El-Minia white cement plant). The water types are Nile, ground and deionized water. The cooling was mad suddenly for clinker by three water types at the same time. The paper discusses the physical and chemical analysis and algal detection of all water types. It also discusses the chemical and physical analysis for kiln feed, clinker. The analysis of water showed that the concentration of dissolved salts in groundwater is higher than Nile water. The concentration of algae gave opposite direction; the algae concentration in Nile water is higher than groundwater. While the deionized is completely free from dissolved salts and algae. The cement tests for clinker which treated by the different water types showed that the cement strength was reducing when used the Nile water with high algae count. From another side, the high concentration of dissolved salts in groundwater does not affect on strength. The water contained the algae prevent the complete crystallization of calcium silicate for clinker. The results also showed that the best type of water, which improved cement compressive strength ranged according to algae count by the sequence deionized water > groundwater > Nile water. 相似文献
87.
The adsorption of the cationic dyes Rhodamine B (RB) and Crystal Violet (CV) on polyacrylamide/poly(acrylic acid) (poly(AAm/AAc), 25:25 % weightwise) and polyacrylamide/poly(sodium acrylate) (poly(AAm/AAcNa), 25:25 % weightwise) hydrogels was studied, employing the Langmuir and Freundlich isotherms. The results of swelling tests at pH 5.5 indicate that poly(AAm/AAcNa) hydrogel shows maximum percentage swelling (%S) was 4400 %. Moreover, the results show that the adsorption capacity is pH‐ and concentration‐dependent. At pH >5 adsorption of RB and CV increases due to ionization of ? COOH and ? COONa groups of (poly(AAm/AAc) and (poly(AAm/AAcNa) and interactions with the cationic groups of the dyes. However, at pH lower than 5, adsorption is still high, which can be explained by considering the formation of hydrogen bonds between the amino groups of the dyes and the ? COOH groups of the polymeric hydrogels. Moreover, the kinetics of adsorption follows a first‐order equation. Furthermore, scanning electron microscopy (SEM) micrographs of polymeric hydrogels doped with CV and RB have morphological differences from the pure form. Our data show that Rhodamine B adsorbs more efficiently on both polyacrylamide/poly(acrylic acid) and polyacrylamide/poly(sodium acrylate) hydrogels than CV. Copyright © 2004 Society of Chemical Industry 相似文献
88.
Carbamoylethylation of wood pulp was carried out at different conditions including acrylamide concentration, time of impregnation, and medium of the reaction (aqueous and nonaqueous). Mechanical properties of paper sheets prepared from the carbamoyethylated cellulose were examined. Carbamoyethylated paper sheets showed improved double-fold breaking length and burst factor irrespective of the reaction medium. Tear strength remained practically unaltered with aqueous carbamoylethylation but decreased in the case of non-aqueous carbamoylethylation. Water retention value (WRV) decreased by carbamoylethylation especially when the latter was performed in nonaqueous medium. 相似文献
89.
Acrylamide monomer (AAm) was grafted onto poly(vinyl chloride) (PVC) films using γ‐radiation to produce high performance functional membranes which can be employed as ion‐exchangers. The preparation and characterization of the synthetic membranes are investigated. To elucidate their possible applications, some selected properties have been studied. In addition, thermal properties have been studied using thermogravimetric analysis and differential scanning calorimetry; X‐ray diffraction has been used to determine changes in polymer morphology. The selectivity of such membranes towards different radionuclides has also been investigated. On the basis of these investigations, the applicability of the prepared membranes is determined and discussed. The prepared PVC‐g‐PAAm has a great tendency to remove 60Co from a radioactive liquid waste containing both 60Co and 137Cs. © 2002 Society of Chemical Industry 相似文献
90.
Bernard Besnault Nabila Berkane Marc Helier Philippe Lartigue Christian Pichot 《电信纪事》1984,39(5-6):199-208
The first part of this paper compares the frequency responses of a horn type and of a dipole type simulators. The field in the test volume is computed using a wire model for the simulators, and its values over a wide frequencies range are compared. The radiation of the horn type simulator is more homogeneous with regard to frequency variations. This is due to the compact shape of this type of simulator. This compactness can lead to a strong and unwanted coupling between the object and the structures of the simulator. In the second part of the paper, the interaction between the simulator and the object is investigated by means of an integral representation of the field, applied to a two dimensional model of the simulator. The latter is considered as a non-uniform guiding structure. The currents on the object along with their rise time and their shape are then used to probe the coupling phenomena. 相似文献