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排序方式: 共有237条查询结果,搜索用时 15 毫秒
201.
Applicability of a theoretical model, based on the fundamental governing equations of fluid motion is investigated to predict two-phase bubbly air-water flow structure through vertical columns. The model predictions are compared to experimental data for a wide range of flow parameters. The relative importance of various modes of interfacial momentum transfer, under different flow conditions, is also examined. It is found that correct estimation of the interfacial momentum transfer is necessary for agreement between the predictions and experimental data. The present study shows that the flow structure for air-water flows through vertical columns depends on the inlet flow conditions. This model predicts the experimentally observed trends well. In most cases the experimental data of local liquid velocity and gas volume fraction agree well with the calculated values. 相似文献
202.
203.
In the design of die casting dies, the object is to produce sound casting as cheaply and rapidly as possible. At the same time consideration must be given to suitable die size, locations of gating system, and selection of an appropriate die casting machine. Foundries in many cases encounter difficulties to ensure shortened lead-time in designing a new die for new product. A lot of estimations have to be done which use fundamentally based on previous experience and application of various mathematical and empirical equations. In this work, main die design procedures and related equations are presented in a logical way. A computer program is developed to estimate main die elements based on the geometry input of casting shape. After initial inputs have been given, the system does full calculations, optimizes selections, and lists main die element sizes. The program can present die characteristics and casting machine characteristics. From both characteristics the optimum die elements were optimized. Optimum filling time and gating dimensions among other elements of die are estimated. Cooling time, cooling channel locations, and flow rates relations are estimated and presented. 相似文献
204.
Tenascin is a large extracellular matrix glycoprotein which is widely distributed in normal, hyperplastic and neoplastic tissues. Its function is unknown but it has been associated with the epithelial-stromal interactions, such as cell adhesion and movement which take place, e.g. in morphogenesis, cellular proliferation and neoplasia. In this study, we investigated tenascin expression in 70 benign, dysplastic and malignant melanocytic tumors by using immunohistochemistry and monoclonal anti-tenascin 143DB7C8 antibody on paraffin sections. In all types of benign nevi, both intradermal, compound and junctional, there was a moderate expression of tenascin at the dermoepidermal junction and in the papillary dermis. In dysplastic nevi, the fibrotic areas in the papillary dermis also showed a moderate staining for tenascin. Invasive malignant melanomas showed the strongest expression of tenascin. In addition to the staining at the dermo-epidermal junction and in the papillary dermis, there was a variable expression of tenascin in the reticular dermis. Intracytoplasmic tenascin was detected both in primary melanomas and melanoma metastases. In conclusion, we have shown that tenascin expression is moderately increased in benign and dysplastic melanocytic tumors and greatly increased in malignant melanomas and melanoma metastases. The function of tenascin may be related to the cellular-stromal interactions and it is possibly associated with the proliferation and spread of the melanocytic tumors. 相似文献
205.
Amar Farouk Merah Samer Samarah Azzedine Boukerche Abdelhamid Mammeri 《Mobile Networks and Applications》2013,18(6):788-802
Behavioral patterns prediction in the context of Vehicular Ad hoc Networks (VANETs) has been receiving increasing attention due to the enabling of on-demand, intelligent traffic analysis and real-time responses to traffic issues. One of these patterns, sequential patterns, is a type of behavioral pattern that describes the occurrence of events in a timely and ordered fashion. In the context of VANETs, these events are defined as an ordered list of road segments traversed by vehicles during their trips from a starting point to their final intended destination. In this paper, a new set of formal definitions depicting vehicular paths as sequential patterns is described. Also, five novel communication schemes have been designed and implemented under a simulated environment to collect vehicular paths; such schemes are classified under two categories: RSU (Road Side Unit)-based and Vehicle-based. After collection, extracted frequent paths are obtained through data mining, and the probability of these frequent paths is measured. In order to evaluate the effectiveness and efficiency of the proposed schemes, extensive experimental analysis has been realized. 相似文献
206.
Farouk T. Awadalla Fathi Habashi Michel Pag 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1990,47(2):183-186
Chrysotile asbestos (Grade 7RF66) sorbs phosphate ion from aqueous solution of phosphoric acid, basic disodium phosphate, ammonium dibasic phosphate, sodium pyrophosphate, or sodium tripolyphosphate. The amount sorbed varies from 0·2 to 2·5% P2O5. The fiber treated with ammonium dibasic phosphate has appreciably low toxicity that is comparable to chrysophosphate obtained by the reaction of chrysotile asbestos with POCl3 gas, provided the latter is washed thoroughly with water to remove watersoluble ingredients. 相似文献
207.
Classical scheduling problem assumes that machines are available during the scheduling horizon. This assumption may be justified in some situations but it does not apply if maintenance requirements, machine breakdowns or other availability constraints have to be considered. In this paper, we treat a two-machine job shop scheduling problem with one availability constraint on each machine to minimise the maximum completion time (makespan). The unavailability periods are known in advance and the processing of an operation cannot be interrupted by an unavailability period (non-preemptive case). We present in our approach properties dealing with permutation dominance and the optimality of Jackson's rule under availability constraints. In order to evaluate the effectiveness of the proposed approach, we develop two mixed integer linear programming models and two schemes for a branch and bound method to solve the tackled problem. Computational results validate the proposed approach and prove the efficiency of the developed methods. 相似文献
208.
A. M. Sanad I. Kashif A. M. Abou-Al-Azm M. A. Khaled H. Farouk 《Journal of Materials Science》1986,21(1):230-234
A glass system was prepared according to the formula 75 mol % B2O3-(25 –x) mol % BaO –x mol % Fe2O3, wherex = 0, 1, 2.5, 5, 7.5 and 10. The glasses were subjected to heat treatment at 550° C for 2, 6, 12, 18 and 24 h. The glasses were also irradiated using-rays at a dose of 4.805 × 104 rad h–1 for 12, 18 and 24 h. An X-ray diffraction technique was used to identify the separated crystalline phases. The electrical conductivity and activation energy of untreated, heat-treated and irradiated samples were measured and calculated. The rate and the dimensions of crystallization were also calculated by using the Avrami equation. It was found that-Fe2O3 is the separated phase when a sample containing 7.5 mol% Fe2O3 is heat treated for 24h;-Fe2O3 and Fe2O3 are the separated phases when the sample containing 10 mol% Fe2O3 is heat treated for 6, 12 and 18 h, with the addition of BaO when the sample is heat treated for 24 h. A miminum value for the electrical conductivity of glass samples was found to occur around an Fe2O3/BaO ratio of 0.425. The rate of crystallization in the sample containing 10 mol% Fe2O3 is 1.30607 × 10–3 and the geometry of crystallizationn is 1.2238, which indicates that the crystallization was in one dimension. 相似文献
209.
Amin Mesmoudi Mohand-Saïd Hacid Farouk Toumani 《Distributed and Parallel Databases》2016,34(3):347-378
In the era of bigdata, with a massive set of digital information of unprecedented volumes being collected and/or produced in several application domains, it becomes more and more difficult to manage and query large data repositories. In the framework of the PetaSky project (http://com.isima.fr/Petasky), we focus on the problem of managing scientific data in the field of cosmology. The data we consider are those of the LSST project (http://www.lsst.org/). The overall size of the database that will be produced is expected to exceed 60 PB (Lsst data challenge handbook, 2012). In order to evaluate the performances of existing SQL On MapReduce data management systems, we conducted extensive experiments by using data and queries from the area of cosmology. The goal of this work is to report on the ability of such systems to support large scale declarative queries. We mainly investigated the impact of data partitioning, indexing and compression on query execution performances. 相似文献
210.
A new approach for workshop design 总被引:1,自引:1,他引:0
Naim Yalaoui Halim Mahdi Lionel Amodeo Farouk Yalaoui 《Journal of Intelligent Manufacturing》2011,22(6):933-951
In this paper we solve a combined group technology problem with a facility layout problem (FLP). This new approach is called
T-FLP. We have developed a hybrid algorithm containing three main steps. The first one, called MPGV (Machine Part Grouping with
Volume) is a decomposition method that can create families of product and machine groups based on a volume data matrix. The
second one consists on assigning machines to fixed locations, using as a constraint, the solution of the MPGV. This problem
is solved as a Quadratic Assignment Problem (QAP). In the third step, we make a global evaluation of all the solutions. A
loop on cells is performed using a minimum and maximum number of cells. This loop can choose the appropriate number of cells
based on the best solution of a global evaluation. The hybrid algorithm is implemented with two different rules for taking
into account the constraint of the MPGV solution. This has generated two methods called YMAY1 and YMAY2. In the MPGV we use
a data oriented genetic algorithm. The QAP is solved with an Ant Colony Optimization mixed with a Guided Local Search (ACOGLS).
This method has been used to solve a real industrial case. For estimating the efficiency of our method, we have compared our
results with an optimal solution obtained by complete enumeration (an exact method). 相似文献