全文获取类型
收费全文 | 1257篇 |
免费 | 81篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 22篇 |
综合类 | 1篇 |
化学工业 | 357篇 |
金属工艺 | 13篇 |
机械仪表 | 21篇 |
建筑科学 | 40篇 |
矿业工程 | 1篇 |
能源动力 | 54篇 |
轻工业 | 218篇 |
水利工程 | 6篇 |
石油天然气 | 3篇 |
无线电 | 69篇 |
一般工业技术 | 219篇 |
冶金工业 | 71篇 |
原子能技术 | 14篇 |
自动化技术 | 234篇 |
出版年
2024年 | 2篇 |
2023年 | 23篇 |
2022年 | 81篇 |
2021年 | 94篇 |
2020年 | 46篇 |
2019年 | 49篇 |
2018年 | 42篇 |
2017年 | 42篇 |
2016年 | 54篇 |
2015年 | 45篇 |
2014年 | 54篇 |
2013年 | 81篇 |
2012年 | 90篇 |
2011年 | 100篇 |
2010年 | 83篇 |
2009年 | 72篇 |
2008年 | 66篇 |
2007年 | 56篇 |
2006年 | 53篇 |
2005年 | 24篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 24篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1343条查询结果,搜索用时 15 毫秒
121.
Federico Pallottino Paolo Menesatti Corrado Costa Graziella Paglia Flavio R. De Salvador Daniele Lolletti 《Food and Bioprocess Technology》2010,3(1):155-159
According to FAO statistics, in 2000, Italy was the second largest hazelnut (Corylus avellana, L. 1753) producer in the world. The price of the stock depends on the nut quality (kernel/nut ratio, nut and seed defect,
percentage of peeling, and taste panel scores). The evaluation of peeling efficiency after toasting is generally conducted
by trained operators in sight on 100 kernels. This work tests two alternative objective methods of after toasting peeling
evaluation based on image analysis. Eleven hazelnut cultivars were analyzed and results were compared with the ones assessed
by trained operators. Images were analyzed with two statistical approaches: fixed values of RGB thresholding and trained K
Nearest Neighbors (KNN). Root mean squared error (RMSE), estimating the comparison between operators and the two image analysis-based
techniques, shows better results for KNN (6.6) with respect to fixed threshold (15.9). 相似文献
122.
Isabel Daz Federico Mohino Teresa Blasco Enrique Sastre Joaqun Prez-Pariente 《Microporous and mesoporous materials》2005,80(1-3):33-42
Ordered mesoporous materials functionalized with alkyl sulfonic acid groups have been proved to be efficient catalysts for esterification. In this paper we report on the synthesis and characterization of new materials containing simultaneously alkyl groups (vinyl, chloromethyl), that have been sulfonated in a post-synthesis step, and methyl groups. Different techniques have been used to characterize the obtained materials: XRD, TEM, elemental analysis, nitrogen adsorption, TGA, 29Si and 13C MAS NMR. Finally, the influence of the different synthesis parameters and functional groups on the behavior of the catalysts in the reaction of esterification of glycerol with lauric and oleic acids has been studied. The catalytic performance of the resulting HSO3-ethyl-MCM-41, HSO3-ethyl/methyl-MCM-41 and HSO3-methyl-MCM-41 new materials is also compared to those of HSO3-phenyl/methyl-MCM-41 and HSO3-propyl/methyl-MCM-41 synthesized previously. It has been demonstrated that an optimum balance among parameters such as nature of the organic group which support the sulfonic acid, distance between the sulfonic group and the silica surface, average pore size of the material, etc., allows to obtain catalysts with improved activity and selectivity for these reactions. 相似文献
123.
Salvatore Federico Shoji Imatani Walter Herzog 《International Journal of Engineering Science》2008,46(2):164-181
We demonstrate that for the class of anisotropic hyperelastic materials with stiffening behaviour (i.e., the stiffness increases for increasing strain), it is possible to find an approximation by means of the linear superposition of an anisotropic quadratic potential, generated by the true linear elasticity tensor of the target material, and a suitable correction potential that is isotropic and hyperelastic. The proposed method can be implemented into commercially available Finite Element software by use of featured options only. This approach is intended to provide the solution to a stress-strain problem, based entirely on energetic considerations, which ensures the convexity of the potentials, and provides a simple material characterisation procedure. 相似文献
124.
Laser Flash is considered the standard technique for measuring the thermal diffusivity of solids. The interaction between
TBC and the laser energy is studied because very low thermal effusivity and thermal diffusivity of TBC can produce very high
temperature increase on the surface and temperature gradient within the sample. In such a case, microstructural modifications
of TBC can be generated. In this work, such phenomena are studied experimentally on free standing TBC samples. 相似文献
125.
José Luis García-Gutiérrez Gustavo A. Fuentes Maria Eugenia Hernández-Terán Ponciano García Florentino Murrieta-Guevara Federico Jiménez-Cruz 《Applied Catalysis A: General》2008,334(1-2):366-373
This work presents the results obtained in the development of Mo/γ-Al2O3 catalysts and their evaluation in the oxidative desulfurization (OD) process of diesel fuel using hydrogen peroxide as the oxidizing reagent. The catalysts were prepared by equilibrium adsorption using several molybdenum precursors and aluminas with different acidity values. They were characterized by Raman spectroscopy. The effect of the reaction time, reaction temperature, nature of solvent, concentration of solvent and hydrogen peroxide, content of molybdenum and phosphate in the catalysts were investigated. The results showed that the activity for sulfur elimination depends mainly on the presence of hepta- and octamolybdates species on the catalyst support and the use of a polar aprotic solvent. Likewise, the presence of phosphate markedly increases the sulfur elimination. In this way, it is possible to reduce sulfur level in diesel fuel from about 320 to less than 10 ppmw at 333 K and atmospheric pressure. Additionally, on the basis of the results obtained a mechanistic proposal for this reaction is described, as an oxidation mechanism by nucleophilic attack of the sulfur atom on peroxo species of hepta- and octamolybdates, but a mechanism involving the singlet oxygen presence can be discarded. 相似文献
126.
Federico Rossi Mauro Rustici Claudio Rossi Enzo Tiezzi 《International journal of molecular sciences》2007,8(9):943-949
In this work we present results about the deuterium isotope effect on the global kinetics of a Belousov-Zhabotinsky reaction in batch conditions. A nonlinear dependence of the Induction Period upon the percentage of deuterated reactants was found. The isotopic effect on the bromination reaction of malonic acid was evaluated. 相似文献
127.
The focus of this work is the study of the thermal aging of high‐performance fibers used in the making of fire protective garments. Accelerated thermal aging tests were carried out on fabric samples made up of a blend of Kevlar® (poly p‐phenylene terephthalamide) and PBI (poly benzimidazole) staple fibers, as well as on yarns pulled from this fabric, by means of exposure to elevated temperatures, comprised between 190°C and 320°C. All samples underwent loss of breaking force retention. The material thermal life, defined as the time required for the fibers to attain a 50% reduction of the original breaking force, ranged between a dozen of days at the lowest exposure temperature, to less than an hour at the highest. Breaking force data were fitted using the Arrhenius model following two different approaches, namely the extrapolated thermal life value and the shift factors yielded by the time‐temperature superposition (TTS). The Arrhenius model seemed to describe appropriately the overall aging process, as inferred from the excellent fit obtained when using both approaches, although activation energies provided from both approaches are different. To follow the chemical evolution of the material with thermal aging, Fourier‐transform infrared (FTIR) analyses were conducted. The qualitative analysis of the FTIR spectra showed little evidence of chemical changes between the aged and the nonaged samples, indicating either that the aging process carries on without significant modification of the chemical structure of the fibers, or that FTIR is not an appropriate method to spot such a modification. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
128.
Electrochemical impedance spectroscopy (EIS) was used to study the fouling produced due to the adsorption of poly(vinyl sulfonic
acid) on polyethersulfone membrane during metal ion recovery by polymer-enhanced ultrafiltration (PEUF). A solution of PVSA
(40 mM in monomeric unit and pH 3.0, 4.5, and 6.0) was placed in a ultrafiltration cell, and then a stream of metal ions (2.0 mM
in Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+) was passed from reservoir to cell. Fouled membranes were studied by EIS at low and intermediate frequencies. Measurements
of hydrodynamic permeability and ATR-FTIR spectra were also obtained. Different relaxation processes were observed with characteristic
frequencies (f
0) ~ 78 kHz and f
0 ~ 3562 kHz for active layer and clean membrane, respectively, while the frequencies for the fouled membrane f
0 = ~79.4 and f
0 = ~2511.9 kHz (pH 3.0). The value of f
0 could not be defined at pH 6.0. The relaxation times obtained were in the order of ×10−5 and ×10−3 s approximately for all cases. Our results suggest that relaxation mechanisms, at intermediate frequencies, can mainly be
associated to polarization processes or to the migration of charge carriers. 相似文献
129.
Sánchez-García JA Ortega A Barceló-Santana FH Palacios-Alquisira J 《International journal of molecular sciences》2010,11(10):3906-3921
Maxillofacial prostheses is a dental medicine specialty aimed at restoring anatomical facial defects caused by cancer, trauma or congenital malformations through an artificial device, which is commonly attached to the skin with the help of an adhesive. The purpose of our research was to develop a pressure-sensitive adhesive (PSA) based on acrylic monomers, characterizing and determining its drying kinetics, that is to say the time it takes to lose 50 to 90% of its moisture. The adhesive synthesis was realized by means of emulsion polymerization; the composition of formulations was: (AA-MMA-EA) and (AA-MMA-2EHA) with different molar ratios. The formulation based on (AA-MMA-2EHA) with 50 w% of solids, presented good adhesive properties such as tack, bond strength, and short drying time. We propose this formulation as a PSA, because it offers an alternative for systemically compromised patients, by less irritation compared to organic solvent-based adhesives. 相似文献
130.
Zicarelli F Calabrò S Cutrignelli MI Infascelli F Tudisco R Bovera F Piccolo V 《Journal of the science of food and agriculture》2011,91(7):1213-1221
BACKGROUND: The aim of this trial was to evaluate the replacement of rumen fluid with faeces as inoculum in studying the in vitro fermentation characteristics of diets for ruminants using the in vitro gas production technique. Six iso‐protein diets with different forage/concentrate ratios were incubated with rumen fluid (RI) or faeces (FI) collected from sheep. RESULTS: Most of the fermentation parameters were influenced by diet and inoculum (P < 0.01). With both inocula, organic matter degradability (dOM), cumulative gas production (OMCV) and maximum fermentation rate (Rmax) increased as the amount of concentrate in the diet increased. Rmax was lower with FI vs RI (P < 0.01); dOM was higher with FI vs RI and the diet × inoculum interaction was significant. As expected, with both inocula, Rmax increased as the neutral detergent fibre content of the diet decreased. Significant correlations were obtained using both inocula between OMCV/dOM and gas/volatile fatty acid (VFA), while the correlation VFA/dOM was significant only with FI. The microbial biomass yield calculated by stoichiometric analysis for all diets was higher with FI vs RI. With FI the organic matter used for microbial growth showed an overall decreasing trend as the amount of concentrate in the diet increased. CONCLUSION: The results indicate that both faeces and rumen fluid from sheep have the potential to be used as inoculum for the in vitro gas production technique. Copyright © 2011 Society of Chemical Industry 相似文献