全文获取类型
收费全文 | 1022篇 |
免费 | 84篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 216篇 |
金属工艺 | 6篇 |
机械仪表 | 23篇 |
建筑科学 | 35篇 |
矿业工程 | 1篇 |
能源动力 | 51篇 |
轻工业 | 193篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 77篇 |
一般工业技术 | 148篇 |
冶金工业 | 217篇 |
原子能技术 | 6篇 |
自动化技术 | 119篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 18篇 |
2021年 | 30篇 |
2020年 | 24篇 |
2019年 | 26篇 |
2018年 | 30篇 |
2017年 | 31篇 |
2016年 | 36篇 |
2015年 | 27篇 |
2014年 | 55篇 |
2013年 | 56篇 |
2012年 | 60篇 |
2011年 | 50篇 |
2010年 | 54篇 |
2009年 | 36篇 |
2008年 | 53篇 |
2007年 | 44篇 |
2006年 | 45篇 |
2005年 | 25篇 |
2004年 | 39篇 |
2003年 | 18篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 79篇 |
1997年 | 48篇 |
1996年 | 35篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1976年 | 10篇 |
1971年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1108条查询结果,搜索用时 97 毫秒
81.
The use of online analytical processing (OLAP) systems as data sources for data mining techniques has been widely studied and has resulted in what is known as online analytical mining (OLAM). As a result of both the use of OLAP technology in new fields of knowledge and the merging of data from different sources, it has become necessary for models to support imprecision. We, therefore, need OLAM methods which are able to deal with this imprecision. Association rules are one of the most used data mining techniques. There are several proposals that enable the extraction of association rules on DataCubes but few of these deal with imprecision in the process. The main problem observed in these proposals is the complexity of the rule set obtained. In this paper, we present a novel association rule extraction method that works over a fuzzy multidimensional model which is capable of representing and managing imprecise data. Our method deals with the problem of reducing the complexity of the result obtained by using fuzzy concepts and a hierarchical relation between them. 相似文献
82.
Maria Concepcion Serrano Eun Ji Chung Guillermo. A. Ameer 《Advanced functional materials》2010,20(2):192-208
When elastomers were first proposed as useful materials for regenerative medicine a few decades ago, their high versatility and suitability for a diverse and wide range of in vivo applications could not have been predicted. Due to their ability to recover after deformation, these materials were first introduced in tissue engineering in an attempt to mimic the mechanical properties of the extracellular matrix. Furthermore, elastomeric characteristics have been described as important criteria for cell interaction by modulating cellular behavior. From soft to hard tissues, elastomers have demonstrated degradation, mechanical, and biocompatibility requirements in accordance with the target tissue. In this feature article, biodegradable synthetic polyester elastomers that have been reported in the literature are discussed, with special focus on those that show promise for in vivo tissue replacement. Their satisfactory performance in vivo shows the promise of elastomers for use in regenerative medicine. However, further investigation is required to demonstrate the prospect of elastomer‐based therapies in clinical trials. 相似文献
83.
Marissa Vargas‐Ramirez Antonio Romero‐Serrano Rodolfo Morales Miguel Angeles‐Hernandez Federico Chavez‐Alcala Javier Castro‐Arellano 《国际钢铁研究》2001,72(5-6):173-181
A mathematical model earlier proposed has been improved to predict the kinetics of multicomponent reactions in the hot metal pretreatment through the injection of reactive fluxes. It is assumed that there are two reaction zones along the flux injection operation: a transitory reaction between the rising particles and the bulk metal, and the permanent reaction between the metal and the top slag. A criterion to estimate the fraction of solids which will react with molten iron in a three‐phase jet (gas‐solid‐liquid) was considered; this fraction of solids carries out the transitory reaction. The model also takes into account the thermodynamic changes produced in the metal and slag due to the chemical reactions. Calculated results of the model are in good agreement with experimental results for the desulfurization of hot metal through the injection of CaO‐SiO2‐CaF2‐FeO‐Na2O reagents at 1400 ‐ 1450 °C. Two kinds of hot metal were tested, one with a low carbon mass content of 3 % and the other with a high carbon mass content of 4.5 %. 相似文献
84.
Anders Olsson Jan Oscarsson Erik Serrano Bo Källsner Marie Johansson Bertil Enquist 《Holz als Roh- und Werkstoff》2013,71(3):319-333
Machine strength grading of structural timber is based upon relationships between so called indicating properties (IPs) and bending strength. However, such relationships applied on the market today are rather poor. In this paper, new IPs and a new grading method resulting in more precise strength predictions are presented. The local fibre orientation on face and edge surfaces of wooden boards was identified using high resolution laser scanning. In combination with knowledge regarding basic wood material properties for each investigated board, the grain angle information enabled a calculation of the variation of the local MOE in the longitudinal direction of the boards. By integration over cross-sections along the board, an edgewise bending stiffness profile and a longitudinal stiffness profile, respectively, were calculated. A new IP was defined as the lowest bending stiffness determined along the board. For a sample of 105 boards of Norway spruce of dimension 45 × 145 × 3,600 mm³, a coefficient of determination as high as 0.68–0.71 was achieved between this new IP and bending strength. For the same sample, the coefficient of determination between global MOE, based on the first longitudinal resonance frequency and the board density, and strength was only 0.59. Furthermore, it is shown that improved accuracy when determining the stiffness profiles of boards will lead to even better predictions of bending strength. The results thus motivate both an industrial implementation of the suggested method and further research aiming at more accurately determined board stiffness profiles. 相似文献
85.
J. P. Valcárcel M J. A. Palacios J. J. Alvarado-Gil 《Journal of Materials Science》1999,34(9):2113-2119
Using photothermal techniques and the Open Photoacoustic Cell (OPC) we measure thermophysical properties, such as thermal diffusivity, thermal conductivity, and heat capacity per unit volume of 5 polymer foils, poly(ethylene terephthalate) PET, of different molecular weights. It is shown that the physical properties influence strongly the thermal ones, and that photoacoustics can be used as a monitoring technique in the application of polymers. 相似文献
86.
Mona Ibrahim Karine Groenen Serrano Laure Noe Ccile Garcia Marc Verelst 《Electrochimica acta》2009,55(1):155-158
Nanoparticles of magnetites (Fe3O4) are synthesized with a new process based on electro-precipitation in ethanol medium. A mechanism pathway is proposed consisting of a Fe(OH)3 precipitation followed by the reduction of iron hydroxide to magnetite in the presence of hydroxyl ions which are generated at the cathode. 相似文献
87.
Bioaccumulation of palladium, platinum and rhodium from urban particulates and sediments by the freshwater isopod Asellus aquaticus. 总被引:1,自引:0,他引:1
The three-way catalytic converters introduced to oxidize and reduce gaseous automobile emissions represent a source of platinum group elements (PGEs), in particular platinum, palladium and rhodium, to the urban environment. Abrasion of automobile exhausts leads to an increase of the concentration of PGEs in environmental matrices such as vegetation, soil and water bodies. The bioaccumulation of Pd, Pt and Rh by the freshwater isopod Asellus aquaticus was studied in natural ecosystems and under laboratory conditions. Owing to the low concentration level (ng g(-1)) of PGEs in the animals studied. analyses were performed with a quadrupole inductively coupled plasma mass spectrometry (ICP-MS) and hafnium, copper, yttrium, rubidium, strontium and lead were monitored for spectral interference correction. Asellus aquaticus collected in an urban river showed a content (mean +/- s) of 155.4 +/- 73.4, 38.0 +/- 34.6, and 17.9 +/- 12.2 ng g(-1) (dry weight) for Pd, Pt and Rh, respectively. The exposure of Asellus aquaticus to PGE standard solutions for a period of 24h give bioaccumulation factors of Bf: 150, 85, and 7 for Pd, Pt and Rh, respectively. Exposure of Asellus aquaticus to environmental samples for different exposure periods demonstrated that PGE bioaccumulation is time dependent. and shows a higher accumulation for the materials with a higher PGE content. While all three elements have the same uptake rate for exposure to catalyst materials, for exposure to environmental materials they havc a different uptake rate which can be attributed to transformations of the PGE species in the environment. 相似文献
88.
E Valiente MS Botella R Martín J Serrano J Verdú O Caballero 《Canadian Metallurgical Quarterly》1997,25(139):460-464
INTRODUCTION: Global amnesia (AG) is a dysfunction of memory, in which there is a sudden incapacity to remember recent events and assimilate new information. The aetiology is currently under discussion. The main hypotheses under consideration are an ischemic mechanism and an epileptic mechanism. OBJECTIVE: To study the cerebral blood flow in patients with temporary global amnesia (AGT) or permanent global amnesia (AGP) using functional neuroimaging techniques. MATERIAL AND METHODS: Four patients were studied. Two had severe alterations of fixation memory which had been present for months. The other two had a sudden loss of recent memory, although space-person orientation and immediate memory remained normal. In all cases the cerebral blood flow (FSC), was assessed by single photon emission tomography (SPECT), using Tc-HMPAO as the radio tracer. RESULTS: We describe 4 patients, 2 men and 2 women aged between 42 and 64.2 with AGT and the others with AGP. On SPECT there was temporal hypoperfusion in all 4 patients. In 2 cases there was associated parietal hypoperfusion and in 1 case there was frontal hypoperfusion. CONCLUSIONS: These findings suggest that AGT and AGP are of vascular origin and that SPECT is a useful diagnostic technique in patients with AG. 相似文献
89.
M. A. Uguina D. P. Serrano R. Sanz J. L. G. Fierro M. L pez-Granados R. Mariscal 《Catalysis Today》2000,61(1-4):263-270
The deactivation of the TS-1 zeolite during styrene oxidation with H2O2 has been investigated by a series of kinetic experiments and further characterisation of the spent catalysts. A decline of the TS-1 activity with time has been observed, especially during the first hours of reaction. TG and TPD–MS analyses of the spent catalysts show that the main products occluded within the zeolite pores are styrene, phenylacetaldehyde and benzaldehyde. The presence of styrene oligomeric compounds has also been detected, although it is postulated they are formed mainly in the solution outside the zeolite pores. Diffusional hindrances due to the high degree of occupancy of the TS-1 pores, as well as, a strong adsorption of styrene, phenylacetaldehyde and benzaldehyde on the Ti sites are proposed as the main reasons for the TS-1 deactivation. These phenomena are enhanced at lower reaction temperatures, which cause a faster initial deactivation. Likewise, longer reaction times favour preferential chemisorption of aldehydes versus styrene. 相似文献
90.