全文获取类型
收费全文 | 1115篇 |
免费 | 63篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 27篇 |
化学工业 | 304篇 |
金属工艺 | 25篇 |
机械仪表 | 59篇 |
建筑科学 | 32篇 |
矿业工程 | 8篇 |
能源动力 | 48篇 |
轻工业 | 119篇 |
水利工程 | 8篇 |
石油天然气 | 15篇 |
无线电 | 84篇 |
一般工业技术 | 171篇 |
冶金工业 | 128篇 |
原子能技术 | 12篇 |
自动化技术 | 142篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 25篇 |
2021年 | 52篇 |
2020年 | 37篇 |
2019年 | 44篇 |
2018年 | 42篇 |
2017年 | 52篇 |
2016年 | 52篇 |
2015年 | 33篇 |
2014年 | 45篇 |
2013年 | 96篇 |
2012年 | 58篇 |
2011年 | 60篇 |
2010年 | 68篇 |
2009年 | 71篇 |
2008年 | 45篇 |
2007年 | 42篇 |
2006年 | 35篇 |
2005年 | 34篇 |
2004年 | 24篇 |
2003年 | 16篇 |
2002年 | 23篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 35篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1182条查询结果,搜索用时 15 毫秒
51.
Marcelo A. V. Souza Luiz Claudio de Santa Maria Marcos A. S. Costa Wang S. Hui Luciana C. Costa Hiram C. Araujo Filho Sandro C. Amico 《Polymer Bulletin》2011,67(2):237-249
Phosphinic-derivative poly(styrene-co-divinylbenzene)-based on PS–DVB copolymers with different porosity degrees have been prepared by aromatic electrophilic substitution reaction using PCl3/AlCl3 followed by base-promoted hydrolysis. The phosphorylation reaction was analyzed by infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG/DTG). In addition, the phosphorous content of the phosphorylated copolymers was determined by spectrophotometry using the method based on sodium molybdate reactant so that the extension of that modification could be assessed. The performance of the phosphorylated resins in the extraction of Pb2+ from aqueous solutions in a batch system was also evaluated. The Pb2+ content was determined by atomic absorption spectrometry (AAS). These materials presented excellent extraction capacity under the contact time of 30 min and pH 6. 相似文献
52.
Adriano Pinto Mariano Caliane Bastos Borba Costa Dejanira de Franceschi de Angelis Francisco Maugeri Filho Daniel Ibraim Pires Atala Maria Regina Wolf Maciel Rubens Maciel Filho 《Chemical Engineering Research and Design》2010,88(5-6):562-571
Factorial design and response surface techniques were used in combination with mathematical modelling and computational simulation to optimise an innovative industrial bioprocess, the production of biobutanol employing the flash fermentation technology. A parametric analysis performed by means of a full factorial design at two levels determined the influence of operating variables on butanol yield and productivity. A second set of simulations were carried out based on the central composite rotatable design. This procedure generated simplified statistical models that describe butanol yield and productivity as functions of the significant operating variables. From these models, response surfaces were obtained and used to optimise the process. For a range of substrate concentration from 130 to 180 g/l, the optimum operating ranges ensure butanol productivity between 7.0 and 8.0 g/l h, butanol yield between 19 and 22%, substrate conversion above 90% and final butanol concentration around 25 g/l. 相似文献
53.
Mónica B. Alvarado‐Huallanco Francisco Maugeri‐Filho 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2010,85(12):1654-1662
BACKGROUND: Fructosyltransferase synthesizes fructo‐oligosaccharides from sucrose. Data used in this work were obtained by an enzyme produced by Rhodotorula sp., a microorganism isolated from fruit samples from the Brazilian Atlantic Forest, which was immobilized in an inorganic support, consisting of a niobium and graphite alloy. RESULT: All essays were conducted using enzymes at two purification grades, highly and partially purified enzymes, as comparison. The results were not significantly different between the two enzyme grades, mainly concerning the final fructo‐oligossacharides yield, which were around 46%. Concerning the kinetics, the enzyme follows the Michaelis–Menten equation with inhibition by sucrose (above 60%). Also, a competitive inhibition by glucose was observed on sucrose, kestose and nystose uptakes. The immobilization of the enzyme was by ion exchange on the surface of the particles, since the support is a charged and compact solid, with negligible porosity. The mathematic model includes mass balances, considering the resistance to external mass transfer. A parameter sensitivity analysis and parameter fitting were performed by simulations and the model was validated by comparison with experimental data. CONCLUSION: The model fitted experimental data well, with deviations lower than 5% concerning FOS concentrations, indicating that it can be used in the design and control of bioreactors, either using purified or partially purified enzyme. Copyright © 2010 Society of Chemical Industry 相似文献
54.
Lucimara Lopes da Silva Pedro de Alcântara Pessôa Filho Everson Alves Miranda 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2010,85(7):962-967
BACKGROUND: The use of the volatile salt ammonium carbamate in protein downstream processing has recently been proposed. The main advantage of using volatile salts is that they can be removed from precipitates and liquid effluents through pressure reduction or temperature increase. Although previous studies showed that ammonium carbamate is efficient as a precipitant agent, there was evidence of denaturation in some enzymes. In this work, the effect of ammonium carbamate on the stability of five enzymes was evaluated. RESULTS: Activity assays showed that α‐amylase (1,4‐α–D‐glucan glucanohydrolase, EC 3.2.1.1), lysozyme (1,4‐β‐N‐acetylmuramoylhydrolase, EC 3.2.1.17) and lipase (triacyl glycerol acyl hydrolase, EC 3.1.1.3) did not undergo activity loss in ammonium carbamate solutions with concentrations from 1.0 to 5.0 mol kg?1, whereas cellulase complex (1,4‐(1,3:14)‐β‐D‐glucan 4‐glucano‐hydrolase, EC 3.2.1.4) and peroxidase (hydrogen peroxide oxidoreductase, EC 1.11.1.7) showed an average activity loss of 55% and 44%, respectively. Precipitation assays did not show enzyme denaturation or phase separation for α‐amylase and lipase, while celullase and peroxidase precipitated with some activity reduction. Analysis of similar experiments with ammonium and sodium sulfate did not affect the activity of enzymes. CONCLUSION: Celullase and peroxidase were denatured by ammonium carbamate. While more systematic studies are not available, care must be taken in designing a protein precipitation with this salt. The results suggest that the generally accepted idea that salts that denature proteins tend to solubilize them does not hold for ammonium carbamate. Copyright © 2010 Society of Chemical Industry 相似文献
55.
Ismael Prieto-Fernández J. Carlos Luengo-Garcia Manuela Alonso-Hidalgo Belen Folgueras-Diaz 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2013,35(1):97-103
The use of nonconventional on-line measurements of moisture and ash content in coal is presented. The background research is briefly reviewed. The possibilities of adjusting microwave-based moisture measurements using natural radioactive techniques, and vice versa, are proposed. The results obtained from the simultaneous analysis of moisture and ash content as well as the correlation improvements are shown. 相似文献
56.
57.
An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insulators.Ageing process can cause degradation of the cement used in this type of insulator and this fact can affect its dielectric performance under heavy rain.This paper presents results of an investigation based on power frequency high voltage tests performed on 800 kV porcelain multicone type insulators,removed from service after having operated for more than 20 years,as well a non-used one that had been stored on site for long time.The insulators were tested in different arrangements:each section at a time and the two sections assembled in series,as actually used insulator columns.The tests were carried out under artificial rain ranging from 1 mm/min to 5 mm/min.The results have confirmed a reduction of up to 30% in the insulator power frequency flashover voltage under 5 mm/min rain conditions and gave important information to the utility about radial cracks that were observed in many insulators and about the discharge mechanisms along the insulators under rain. 相似文献
58.
Guimes Rodrigues Filho Leandra Cardoso Toledo Daniel Alves Cerqueira Rosana Maria Nascimento de Assunção Carla da Silva Meireles Harumi Otaguro Sizue Ota Rogero Ademar Benévolo Lugão 《Polymer Bulletin》2007,59(1):73-81
Summary In this article, cellulose acetate produced through the homogeneous acetylation of sugar cane bagasse cellulose was used to
produce membranes, using poly(ethyleneglycol) 600 (PEG 600) as an admixture. The membranes were characterized using water
flux measurements (Payne’s cup), differential scanning calorimetry (DSC) and neutral red uptake (cytotoxicity). The results
showed that PEG 600 acts as a crystallinity inductor and/or pore former in the cellulose acetate matrix. The induction of
crystallinity is important for this system since it had not been reported on the literature yet. The results also demonstrated
that the studied membranes present a nontoxic behavior. 相似文献
59.
R.D. Toledo Filho J.P. Gonçalves E.M.R. Fairbairn 《Cement and Concrete Research》2007,37(9):1357-1365
The Brazilian ceramic industry generates large amounts of calcined-clay waste. This paper examines the factors that influence its potential for use as a partial replacement of Portland cement. Superplasticized mortars of equal workability containing ground crushed waste calcined-clay brick (GCWCCB) in the proportions of 10, 20, 30 and 40% as a cement replacement were analyzed through mechanical tests, pore structure characterization and durability tests. The results indicated the optimal percentages of substitution lies between 10% to 20%. The potential reduction of CO2 emissions could be as high as 10% of current Brazilian cement industry emissions if this approach were to be fully implemented, and it could be eligible for “Clean Development Mechanism” credits under Kyoto protocol. 相似文献
60.
Rachel Passos de Oliveira Santos Daniele Oliveira Castro Adhemar Coll Ruvolo‐Filho Elisabete Frollini 《应用聚合物科学杂志》2014,131(12)
This investigation focuses on the preparation of bio‐based composites from recycled poly (ethylene terephthalate) (PET) and sisal fibers (3 cm, 15 wt %), via thermopressing process. Plasticizers derived from renewable raw materials are used, namely, glycerol, tributyl citrate (TBC) and castor oil (CO), to decrease the melting point of the recycled PET (Tm ∼ 265°C), which is sufficiently high to initiate the thermal decomposition of the lignocellulosic fiber. All used materials are characterized by thermogravimetric analysis and differential scanning calorimetry, and the composites are also characterized via dynamic mechanical thermal analysis. The storage modulus (30°C) and the tan δ peak values of CT [PET/sisal/TBC] indicate that TBC also acts as a compatibilizing agent at the interface fiber/PET, as well as a plasticizer. To compare different processing methods, rheometry/thermopressing and compression molding are used to prepare the recycled PET/sisal/glycerol/CO composites. These two different methods of processing show no significant influence on the thermal properties of these composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40386. 相似文献