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排序方式: 共有174条查询结果,搜索用时 15 毫秒
71.
Mauro C. Ribeiro Muthu K. Gnanamani Israel R. Azevedo Raimundo C. Rabelo-Neto Gary Jacobs Burtron H. Davis Fabio B. Noronha 《Topics in Catalysis》2014,57(6-9):550-560
Mn and Cr doped CeSi mixed oxides were used as supports for Co and tested for CO hydrogenation. Co/CeSi was found to be more active and significantly more selective to n-alcohols/olefins. An increasing selectivity to n-alcohols and decreasing selectivity to olefins as a function of time on stream was also observed, suggesting a trade-off between those two products. Addition of Mn led to similar behavior, although at slightly lower conversions. Addition of Cr, however, considerably suppressed n-alcohol formation, while it kept selectivities to olefins within a 20–30 % range over more than 250 h of testing, indicating either higher alcohol dehydration activity, or that the presence of Cr ions lowered the hydrogenating activity of Co. The present work indicates that enhanced contact area between Co and the reducible support is likely a key factor for enhancing selectivity to alcohols. 相似文献
72.
Seyed Ali Hosseini Aligholi Niaei Dariush Salari Raimundo K. Vieira Shamil Sadigov Seyed Reza Nabavi 《Journal of Industrial and Engineering Chemistry》2013,19(1):166-171
Optimization of 2-propanol oxidation over CuMnmCo2?mO4 nanospinels was carried out by a split design method. 15-term model was proposed to fit the experimental data. The model revealed that both whole plot and subplot variables have significant effects on conversion of 2-propanol. The model predicted the interaction of subplot and whole plot variables as well as their importance. The maximum conversion of 2-propanol was observed over CuMn2O4 (x1 = 0.33, x2 = 0, x3 = 0.67) at calcination and reaction temperatures of 800 °C (z1 = 1) and 300 °C (z2 = 1), respectively. The predicted response and the response obtained from experiment for optimum conditions were 93.36 and 96, respectively. 相似文献
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74.
Ligia Gargallo Angel Leiva Marcela Urzúa Luz Alegría Beatriz Miranda Deodato Radi 《Polymer International》2004,53(11):1652-1657
Monolayer formation by poly[(maleic anhydride)‐alt‐(stearyl methacrylate)] (MA‐alt‐StM) on aqueous subphases, with and without chitosan, was studied by the Langmuir technique. Chitosan (CS) modified considerably the shape of the MA‐alt‐StM isotherms on water. To explain this behavior, the surface activity properties of chitosan at the air–solution interface were studied. The variations of the interfacial tension, γint, with chitosan concentration and temperature, were also determined. The results were discussed in terms of the modification of the air–water interface owing to the presence of chitosan in the subphase and the surface activity. It was found that the standard free energy of adsorption, , values were dependent on the degree of acetylation (DA) over the DA range being studied. Copyright © 2004 Society of Chemical Industry 相似文献
75.
Summary Dynamic mechanical properties of poly(dimethylphenyl methacrylátes) were studied considering the different positions of the methyl groups on the phenyl ring. In all cases a clear relaxation can be observed which is associated to the polymer glass transition temperature (Tg). Nevertheless, at lower temperatures, viscoelastic activity is negligible. A correlation between the steric hindrance due to the methyl groups and the temperature at which the relaxation is detected, was established. 相似文献
76.
Marcela Urzúa Claudia Sandoval Fernando Gonzlez‐Nilo Angel Leiva Ligia Gargallo Deodato Radi 《应用聚合物科学杂志》2006,102(3):2512-2519
The phase behavior of blends containing N‐alkylitaconamic acid‐co‐styrene copolymers (NAIA‐co‐S) with poly(N‐vinyl‐2‐pyrrolidone) (PVP) of two different weight average molecular weights (M w ), poly(2‐vinylpyridine) (P2VPy) and poly(4‐vinylpyridine) (P4VPy), was analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. Copolymers containing 80% S are miscible with PVP10, PVP24, and P4VPy over the whole range of composition. In the case of blends with P2VPy, miscibility is observed only for the first three members of the series, i.e., NEIA‐co‐S, NPIA‐co‐S, and NBIA‐co‐S. For copolymers containing hexyl to dodecyl moieties, phase separation is observed in blends with P2VPy. Copolymers containing 50% S are miscible over the whole range of composition irrespective of the homopolymer and the length of the side chain of the itaconamic moiety of the copolymer. This behavior is interpreted in terms of steric hindrance, in the sense that the copolymers with long side chains are not able to interact with the nitrogen of P2VPy because of the position in the aromatic ring. The interactions between copolymers and homopolymers are discussed in terms of specific interactions like hydrogen bonds between the itaconamic moiety and the different functional groups of the homopolymers, together with the hydrophobic interaction, which cannot be disregarded. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2512–2519, 2006 相似文献
77.
Nancy Alvarado Irma Fuentes Luz Alegría Claudia Sandoval Galder Kortabería Arantxa Eceiza Ligia Gargallo Angel Leiva Deodato Radić 《应用聚合物科学杂志》2015,132(34)
Poly(diethylaminoethyl methacrylamide) (PEAM), a dendronized polymer, was synthesized according to classical procedures. Monomers and polymers were characterized by spectroscopic measurements. The results obtained were in agreement with the expected chemical structure. The phase behavior of blends of PEAM with diclofenac (DCF), ibuprofen (IBU) , and paracetamol (PCM) were studied by different experimental techniques. FT‐IR, UV‐Vis, DSC , and TGA measurements suggested important interactions between the blended components. Thermogravimetric analysis (TGA) indicated the temperature at which the dendronized polymer released a small molecule. AFM measurements and molecular dynamics (MD) simulations were used to better understand the nature of the interactions and to estimate the distance between the components of the blends to explain the interaction involved. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42450. 相似文献
78.
Molecular and microbiological analysis of caecal microbiota in rats fed with diets supplemented either with prebiotics or probiotics 总被引:2,自引:0,他引:2
Montesi A García-Albiach R Pozuelo MJ Pintado C Goñi I Rotger R 《International journal of food microbiology》2005,98(3):281-289
The potential health-improving effects of both a prebiotic and a probiotic infant formula have been evaluated in a rat model. Two groups of 10 rats were fed with either prebiotics containing fructo-oligosaccharides or probiotics containing viable Bifidobacterium lactis and Streptococcus thermophilus. The composition of their caecal microbiota was analyzed both by classical plate count of the main bacterial groups and by PCR amplification of a V3 fragment of 16S rRNA genes and denaturing gradient gel electrophoresis (DGGE). Both diets induced a significant reduction of clostridia and Bacteroides spp. compared to a control diet, whereas prebiotics were also able to reduce the number of coliforms and to increase the presence of bifidobacteria. DGGE analysis showed a significant increase of 16S rRNA gene fragments in rats fed with either probotics or prebiotics. Nineteen bands were sequenced and most of them showed similarity to cultured bacteria. Detection of Bifidobacterium spp. by this technique using genus-specific primers only permitted these bacteria to be detected in prebiotics-fed rats, whereas the use of Lactobacillus group-specific primers gave similar results in rats fed with any diet, in agreement with the plate count results. 相似文献
79.
80.
Study of the dielectric relaxation of poly(phenylpropyl acrylate) and poly(phenylpropyl methacrylate): effect of slight differences in chemical structure
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Pilar Ortiz‐Serna María J Sanchis Belén Redondo‐Foj Marta Carsí Ricardo Díaz Calleja Angel Leiva Ligia Gargallo Deodato Radić 《Polymer International》2015,64(12):1733-1740
A comparative study of the dielectric relaxational behaviour of two structurally close polymers, containing aromatic side groups, was carried out in order to analyse how slight differences in the chemical structure affect the molecular responses to perturbation field. Specifically, poly(phenylpropyl acrylate) (P3Ph1PA) and poly(phenylpropyl methacrylate) (P3Ph1PM) were studied using differential scanning calorimetry and dielectric relaxation spectroscopy in the frequency range 10?2–106 Hz and temperature window of ?80 to 120 °C. Both techniques show one glass–rubber transition for P3Ph1PA and two for P3Ph1PM, which evidence the great effect of the methyl groups on the segmental motions of the polymer. Phenomenological analysis of the data was carried out in order to establish the strength, width and fragility parameters of the glass–rubber transitions. In the case of P3Ph1PA, the strength is found to be larger than for P3Ph1PM, pointing out that the methyl group disturbs the mobility. Conductive processes dominate the dielectric spectra at high temperatures and low frequencies. © 2015 Society of Chemical Industry 相似文献