全文获取类型
收费全文 | 349篇 |
免费 | 14篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 127篇 |
金属工艺 | 2篇 |
机械仪表 | 8篇 |
建筑科学 | 7篇 |
能源动力 | 5篇 |
轻工业 | 35篇 |
水利工程 | 5篇 |
无线电 | 39篇 |
一般工业技术 | 54篇 |
冶金工业 | 32篇 |
原子能技术 | 1篇 |
自动化技术 | 45篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 18篇 |
2013年 | 19篇 |
2012年 | 14篇 |
2011年 | 23篇 |
2010年 | 19篇 |
2009年 | 15篇 |
2008年 | 18篇 |
2007年 | 15篇 |
2006年 | 8篇 |
2005年 | 13篇 |
2004年 | 8篇 |
2003年 | 15篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1964年 | 6篇 |
1963年 | 2篇 |
1962年 | 4篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1958年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有363条查询结果,搜索用时 15 毫秒
271.
Tapio Pahikkala Sampo Pyysalo Jorma Boberg Jouni Järvinen Tapio Salakoski 《Machine Learning》2009,74(2):133-158
In the application of machine learning methods with natural language inputs, the words and their positions in the input text
are some of the most important features. In this article, we introduce a framework based on a word-position matrix representation
of text, linear feature transformations of the word-position matrices, and kernel functions constructed from the transformations.
We consider two categories of transformations, one based on word similarities and the second on their positions, which can
be applied simultaneously in the framework in an elegant way. We show how word and positional similarities obtained by applying
previously proposed techniques, such as latent semantic analysis, can be incorporated as transformations in the framework.
We also introduce novel ways to determine word and positional similarities. We further present efficient algorithms for computing
kernel functions incorporating the transformations on the word-position matrices, and, more importantly, introduce a highly
efficient method for prediction. The framework is particularly suitable to natural language disambiguation tasks where the
aim is to select for a single word a particular property from a set of candidates based on the context of the word. We demonstrate
the applicability of the framework to this type of tasks using context-sensitive spelling error correction on the Reuters
News corpus as a model problem. 相似文献
272.
This paper introduces an embedded fuzzy expert system for Adaptive Weighted Fair Queueing (AWFQ) located in the network traffic router to update weights for output queues. WFQ algorithm allows differentiated service for traffic classes according to Quality of Service (QoS) requirements. Link sharing and packet scheduling methods are the most critical factors when guaranteeing QoS. There are many different scheduling mechanisms but adequate and adaptive QoS aware scheduling solutions are still in a phase of development due to the rapid growth of multimedia in the Internet. The proposed AWFQ model in this work simplifies the link sharing to two service classes: one for UDP and another for TCP. The implementation of the model is based on adaptive change of weight coefficients that determine the amount of allowed bandwidth for the service class. New weight coefficients are calculated periodically on routers according to developed embedded fuzzy expert system. It is shown through simulations that the AWFQ model is more stable and reacts faster to different traffic states than the traditional WFQ scheduler. The embedded expert system adjusts the weights of AWFQ with two parameters that are based on the share of the UDP and TCP input traffic data rate and the change of the share of the UDP and TCP input data rate. 相似文献
273.
Adamov A Viidanoja J Kärpänoja E Paakkanen H Ketola RA Kostiainen R Sysoev A Kotiaho T 《The Review of scientific instruments》2007,78(4):044101
This article presents the combination of an aspiration-type ion mobility spectrometer with a mass spectrometer. The interface between the aspiration ion mobility spectrometer and the mass spectrometer was designed to allow for quick mounting of the aspiration ion mobility spectrometer onto a Sciex API-300 triple quadrupole mass spectrometer. The developed instrumentation is used for gathering fundamental information on aspiration ion mobility spectrometry. Performance of the instrument is demonstrated using 2,6-di-tert-butyl pyridine and dimethyl methylphosphonate. 相似文献
274.
Investigation of CO oxidation and NO reduction on three-way monolith catalysts with transient response techniques 总被引:1,自引:0,他引:1
Teuvo Maunula Juha Ahola Tapio Salmi Heikki Haario Matti Härkönen Marjo Luoma Veikko J. Pohjola 《Applied catalysis. B, Environmental》1997,12(4):91-308
The kinetics of CO oxidation and NO reduction reactions over alumina and alumina-ceria supported Pt, Rh and bimetallic Pt/Rh catalysts coated on metallic monoliths were investigated using the step response technique at atmospheric pressure and at temperatures 30–350°C. The feed step change experiments from an inert flow to a flow of a reagent (O2, CO, NO and H2) showed that the ceria promoted catalysts had higher adsorption capacities, higher reaction rates and promoting effects by preventing the inhibitory effects of reactants, than the alumina supported noble metal catalysts. The effect of ceria was explained with adsorbate spillover from the noble metal sites to ceria. The step change experiments CO/O2 and O2/CO also revealed the enhancing effect of ceria. The step change experiments NO/H2 and H2/NO gave nitrogen as a main reduction product and N2O as a by-product. Preadsorption of NO on the catalyst surface decreased the catalyst activity in the reduction of NO with H2. The CO oxidation transients were modeled with a mechanism which consistent of CO and O2 adsorption and a surface reaction step. The NO reduction experiments with H2 revealed the role of N2O as a surface intermediate in the formation of N2. The formation of NN bonding was assumed to take place prior to, partly prior to or totally following to the NO bond breakage. High NO coverage favors N2O formation. Pt was shown to be more efficient than Rh for NO reduction by H2. 相似文献
275.
Narendra Kumar Jose Ignacio Villegas Tapio Salmi Dmitry Yu. Murzin Teemu Heikkil 《Catalysis Today》2005,100(3-4):355-361
Aluminium sulphate, sodium aluminate, aluminium oxide and pseudo-boehmite were used as sources of aluminium in the synthesis of SAPO-5. The samples were characterized using XRD, SEM, XRF, FTIR and nitrogen adsorption. The formation of SAPO-5 phase, morphology, surface area and catalytic properties were found to be influenced by the source of aluminium used in the synthesis. The sample synthesized using pseudo-boehmite as a source of aluminium showed most phase pure silicoaluminophosphate, whereas syntheses using aluminium phosphate or sodium aluminate only formed quartz and berlinite. The FT-IR spectra exhibited the presence of Brønsted and Lewis acid sites in the Pt-SAPO-5, SAPO-5, Pt-H-mordenite and H-mordenite catalysts. Modification of SAPO-5 and mordenite by Pt impregnation did not influence the structures of these catalytic materials. The Pt-H-mordenite and H-mordenite catalysts with stronger Brønsted acidity exhibited higher conversion of n-butane and yield to isobutane than Pt-SAPO-5 and SAPO-5 catalysts with weak acid sites. Introduction of Pt in SAPO-5 and mordenite played a positive role in the isomerization of n-butane to isobutane. 相似文献
276.
Kinetic modeling strategy for an exothermic multiphase reactor system: Application to vegetable oils epoxidation using Prileschajew method
下载免费PDF全文
![点击此处可从《American Institute of Chemical Engineers》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jun L. Zheng Johan Wärnå Tapio Salmi Fabrice Burel Bechara Taouk Sébastien Leveneur 《American Institute of Chemical Engineers》2016,62(3):726-741
Epoxidation of cottonseed oil by peroxyformic acid (PFA) was studied in a semibatch calorimeter. This liquid–liquid reaction system is composed of different exothermic steps. Thus, a kinetic modeling strategy to diminish the number of parameters to estimate was developed by investigating each reaction system: PFA synthesis and decomposition, ring‐opening and epoxidation. A thermal study was conducted by determining heat capacity of the different organic species, and by analyzing the evolution of global heat‐transfer coefficient with the reaction extent. The epoxidation reaction was performed in a semibatch reactor under isoperibolic mode within an initial temperature range of 50–70°C, an organic phase of 30–34 wt %, a formic acid molar flow rate of 0.02–0.05 mol/min and an addition time of 25–50 min. The interfacial mass transfer was supposed to be faster than the intrinsic reaction kinetics suppressing the use of mass transfer correlation. Nonlinear regression was used to estimate the kinetic and thermal parameters. The kinetic parameters of epoxidation of the three different fatty acids, namely oleic, linoleic, and its intermediate were estimated. The reaction enthalpy of epoxidation was estimated to ?230 ± 3.8 kJ/mol, and the reaction enthalpy of ring‐opening was measured to be ?90 kJ/mol by Tian–Calvet calorimeter. © 2015 American Institute of Chemical Engineers AIChE J, 62: 726–741, 2016 相似文献
277.
An efficient coefficient quantization scheme is described for minimizing the cost of implementing fixed parallel linear-phase
finite impulse response (FIR) filters in the modified Farrow structure introduced by Vesma and Saramaki for generating FIR
filters with an adjustable fractional delay. The implementation costs under consideration are the minimum number of adders
and subtracters when implementing these parallel subfilters as a very large-scale integration (VLSI) circuit. Two implementation
costs are under consideration to meet the given criteria. In the first case, all the coefficient values are implemented independently
of each other as a few signed-powers-of-two terms, whereas in the second case, the common subexpressions within all the coefficient
values included in the overall implementation are properly shared in order to reduce the overall implementation cost even
further. The optimum finite-precision solution is found in four steps. First, the number of filters and their (common odd)
order are determined such that the given criteria are sufficiently exceeded in order to allow some coefficient quantization
errors. Second, those coefficient values of the subfilters having a negligible effect on the overall system performance are
fixed to be zero valued. In addition, the experimentally observed attractive connections between the coefficient values of
the subfilters, after setting some coefficient values equal to zero, are utilized to reduce both the implementation cost and
the parameters to be optimized even more. Third, constrained nonlinear optimization is applied to determine for the remaining
infinite-precision coefficients a parameter space that includes the feasible space where the given criteria are met. The fourth
step involves finding in this space the desired finite-precision coefficient values for minimizing the given implementation
costs to meet the stated overall criteria. Several examples are included illustrating the efficiency of the proposed synthesis
scheme. 相似文献
278.
Sillanpää S Salminen JP Lehikoinen E Toivonen E Eeva T 《The Science of the total environment》2008,406(1-2):247-255
Carotenoids are synthesized by plants, therefore insects and birds must obtain them from their diet. They function in pigmentation and as antioxidants. We studied the carotenoid profiles in a model food chain (plant-insect-bird) in an air pollution gradient to find out whether heavy metal pollution affects the transfer of carotenoids across the trophic levels. Birch leaves showed higher beta-carotene and, one of the birch species (Betula pendula), higher total carotenoids levels in the polluted area. There was no difference in the lutein concentration of caterpillars' food source, birch leaves, between the study areas. Autumnal moth larvae accumulated lutein more efficiently than beta-carotene while sawfly larvae accumulated beta-carotene over lutein. Because of different antioxidant profiles in different leaf chewing insects their sensitivity to pollution stress may differ. The lutein concentration of plasma and feathers of Great tit nestlings did not differ along the pollution gradient. The lack of difference in lutein concentration of autumnal moth larvae along pollution gradient may partly explain the lutein concentrations of Great tit nestlings, since the abundance of autumnal moth larvae peak during the nestling phase of Great tit. The lutein concentration of autumnal moth larvae was positively associated to circulating plasma lutein level of Great tit indicating the importance of carotenoid rich diet during the nestling phase. In addition, the higher the plasma lutein concentration the more lutein was deposited to feathers, irrespective of the other possible functions of lutein in nestlings. We found that carotenoid levels differed between the polluted and the unpolluted area especially at lower levels of food chain: in birches and in caterpillars. 相似文献
279.
Manninen A Putkiranta M Rostedt A Saarela J Laurila T Marjamäki M Keskinen J Hernberg R 《Applied optics》2008,47(2):110-115
An experimental instrument for measuring a laser-induced fluorescence spectrum from a single aerosol particle is described. As a demonstration of instrument capabilities, the results of monodisperse 4.7 microm sodium chloride particles doped with fluorescent riboflavin, produced with an inkjet aerosol generator, are presented. The fluorescence of the aerosol particles is excited in the wide range from 210 to 419 nm using a pulsed, tunable optical parametric oscillator laser. The maximum of the fluorescence emission of separately measured particles is detected at 560 nm. The dependence of the fluorescence on the excitation wavelength is studied and fluorescence cross sections are estimated. Agreement between the measured fluorescence data and the literature data for riboflavin is observed. 相似文献
280.
Nanoimprint lithography has the potential to cost efficiently realize patterns with extremely narrow linewidth over a large area. A significant challenge to achieving this target is the fabrication of nanoimprint templates. The cost and writing time of conventional electron beam lithography for direct writing of the templates rapidly increases as the patterned area increases and the linewidth decreases. We have developed a novel process for creating narrow linewidth nanopatterns. This process is based on conformal deposition of thin films on seed nanopatterns. We have demonstrated the process by fabricating nanosized loops and lines. The linewidth of the structures can be tuned precisely, and in our experiments it could be reduced to 20?nm. The closed loop structures are interesting, since this geometry is crucially important in many leading edge research fields such as negative refractive index materials, ultrahigh density memory applications and quantum rings. The fabricated template was subsequently used as a template in soft-stamp UV nanoimprint lithography to successfully replicate the structures in UV-curable resist. 相似文献