全文获取类型
收费全文 | 995篇 |
免费 | 118篇 |
国内免费 | 1篇 |
专业分类
综合类 | 2篇 |
化学工业 | 408篇 |
金属工艺 | 7篇 |
机械仪表 | 41篇 |
建筑科学 | 29篇 |
矿业工程 | 1篇 |
能源动力 | 31篇 |
轻工业 | 329篇 |
水利工程 | 14篇 |
石油天然气 | 8篇 |
无线电 | 21篇 |
一般工业技术 | 123篇 |
冶金工业 | 30篇 |
原子能技术 | 1篇 |
自动化技术 | 69篇 |
出版年
2024年 | 5篇 |
2023年 | 26篇 |
2022年 | 77篇 |
2021年 | 99篇 |
2020年 | 51篇 |
2019年 | 64篇 |
2018年 | 61篇 |
2017年 | 66篇 |
2016年 | 51篇 |
2015年 | 37篇 |
2014年 | 68篇 |
2013年 | 62篇 |
2012年 | 76篇 |
2011年 | 86篇 |
2010年 | 63篇 |
2009年 | 43篇 |
2008年 | 37篇 |
2007年 | 37篇 |
2006年 | 26篇 |
2005年 | 15篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有1114条查询结果,搜索用时 15 毫秒
911.
912.
This study investigates the aqueous photocatalytic degradation of small polar organic compounds (SPOCs) that bear hydrogen-bonding capabilities but do not readily adsorb to the TiO2 catalyst. The effect of pH on the TiO2 surface hydroxyl speciation and surface acid/base equilibria was used to elucidate the possible role of hydrogen-bonding interactions in the degradation of acetone and isopropanol in aqueous TiO2 photocatalytic systems. The kinetic parameters describing the decomposition of these two model compounds were obtained by gas chromatographic analysis of their photoreaction systems and interpreted on the grounds of the Brönsted acid/base properties of the TiO2 surface speciation and solute hydrogen-bonding numerical scales. The results showed that the fastest initial degradation rates of acetone and isopropanol occurred in a pH range where the optimal conditions for adsorption through hydrogen bonding to the TiO2 surface and optimum concentration of hydroxyl radicals (OH) coincide. The fastest degradation constants were observed at pH 6.04 and 8.61 for acetone and isopropanol, respectively. The hypothesis of hydrogen bonding to surface hydroxyl groups presented in this study challenges the common assumption that these model compounds do not adsorb to surface sites, and that their oxidative pathways of degradation only occur via homogeneous-phase reaction with free OH radicals. 相似文献
913.
Schnettler B Shene C Rubilar M Miranda H Sepúlveda J Denegri M Lobos G 《Archivos latinoamericanos de nutrición》2010,60(4):380-390
In view of the interest in the role of foodstuffs in improving wellbeing and health, the object of this study is to distinguish consumer typologies in Temuco, La Araucanía Region, Chile, according to their preferences for different functional ingredients, flavouring, colouring and price in yoghurt. A semi-structured survey was applied to 400 supermarket customers. The respondents ordered eight alternative yoghurts according to their preferences, with different functional ingredients (fibre, antioxidants), flavourings (sugar, sweetener), colouring (natural, artificial) and three price options, for a conjoint analysis with fractional factorial design. Variables affecting knowledge of "functional food" were evaluated using a binomial logit model. It was determined by conjoint analysis that in general a preference existed for yoghurt containing fibre, sweetener, natural colouring, and at the lowest price. Three typologies were distinguished by analysis of hierarchical conglomerates: the majority segment (48.8%) displayed a greater preference for fibre; the second (41.7%) also preferred fibre, but gave first priority to artificial colouring and preferred a higher price. The minority (9.5%) was the only segment to prefer antioxidants. The typologies differed significantly in satisfaction with their food-related life, knowledge of the function of fibre and presence of cancer and obesity in some member of the respondent's family. The binomial logit model was significant (P < 0.01), indicating that if the consumer has a job or has had access to information on functional foods, the probability increased of knowledge of what these mean. There was thus majority acceptance of yoghurt enriched with fibre and with added sweetener. 相似文献
914.
Jansson ET Trkulja CL Olofsson J Millingen M Wikström J Jesorka A Karlsson A Karlsson R Davidson M Orwar O 《Analytical chemistry》2012,84(13):5582-5588
We have developed a microfluidic flow cell where stepwise enzymatic digestion is performed on immobilized proteoliposomes and the resulting cleaved peptides are analyzed with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The flow cell channels consist of two parallel gold surfaces mounted face to face with a thin spacer and feature an inlet and an outlet port. Proteoliposomes (50-150 nm in diameter) obtained from red blood cells (RBC), or Chinese hamster ovary (CHO) cells, were immobilized on the inside of the flow cell channel, thus forming a stationary phase of proteoliposomes. The rate of proteoliposome immobilization was determined using a quartz crystal microbalance with dissipation monitoring (QCM-D) which showed that 95% of the proteoliposomes bind within 5 min. The flow cell was found to bind a maximum of 1 μg proteoliposomes/cm(2), and a minimum proteoliposome concentration required for saturation of the flow cell was determined to be 500 μg/mL. Atomic force microscopy (AFM) studies showed an even distribution of immobilized proteoliposomes on the surface. The liquid encapsulated between the surfaces has a large surface-to-volume ratio, providing rapid material transfer rates between the liquid phase and the stationary phase. We characterized the hydrodynamic properties of the flow cell, and the force acting on the proteoliposomes during flow cell operation was estimated to be in the range of 0.1-1 pN, too small to cause any proteoliposome deformation or rupture. A sequential proteolytic protocol, repeatedly exposing proteoliposomes to a digestive enzyme, trypsin, was developed and compared with a single-digest protocol. The sequential protocol was found to detect ~65% more unique membrane-associated protein (p < 0.001, n = 6) based on peptide analysis with LC-MS/MS, compared to a single-digest protocol. Thus, the flow cell described herein is a suitable tool for shotgun proteomics on proteoliposomes, enabling more detailed characterization of complex protein samples. 相似文献
915.
de Vasconcellos LM Oliveira FN Leite Dde O de Vasconcellos LG do Prado RF Ramos CJ Graça ML Cairo CA Carvalho YR 《Journal of materials science. Materials in medicine》2012,23(2):357-364
A porous implant material with adequate pore structure and the appropriate mechanical properties for bone ingrowth has long
been sought. This article presents details of the development, characterization and in vivo evaluations of powder metallurgy-processed
titanium samples exhibiting a dense core with an integrated porous surface for biomedical applications. A space-holder method
was applied to investigate the effects of different percentages and particle sizes of the urea on bone neoformation in 30
rabbits. The samples were previously characterized using scanning electron microscopy and mechanical testing. After 8 and
12 weeks of implantation, bone ingrowth was histologically and histometrically analyzed and push-out testing was performed.
This study demonstrated that the association of a dense core integrated with the greatest number of interconnected pores of
the smallest size is a promising biomaterial for bone tissue engineering. This sample exhibits appropriate mechanical properties
combined with increased bone ingrowth, providing enhanced resistance to displacement. 相似文献
916.
Juliê Marra André Gustavo Paleari Ana Carolina Pero Raphael Freitas de Souza Débora Barros Barbosa Marco Antonio Compagnoni 《International Journal of Adhesion and Adhesives》2009,29(4):391-395
Bond failures at the acrylic teeth and denture base resin interface are still a common clinical problem in prosthodontics. The effect of methyl methacrylate (MMA) monomer on the bond strength of three types of denture base resins (Acron MC, Lucitone 550 and QC-20) to two types of acrylic teeth (Biotone and Trilux) was evaluated. Twenty specimens were produced for each denture base resin/acrylic tooth combination and were randomly divided into control (acrylic teeth received no surface treatment) and experimental groups (MMA was applied to the surface of the acrylic teeth for 180 s) and were submitted to shear tests (1 mm/min). Data (MPa) were analyzed using three-way ANOVA/Student's test (α=0.05). MMA increased the bond strength of Lucitone denture base resins and decreased the bond strength of QC-20. No difference was detected for the bond strength of Acron MC base resin after treatment with MMA. 相似文献
917.
Solid-phase extraction and HPLC determination of Ochratoxin A in cereals products on Chilean market 总被引:1,自引:0,他引:1
Mario Vega Katherine Muñoz Carolina Sepúlveda Mario Aranda Victor Campos Ricardo Villegas Orialis Villarroel 《Food Control》2009,20(7):631-634
Ochratoxin A (OTA) is a mycotoxin produced by different species of Aspergillus and Penicillium fungi. The presence of this mycotoxin in cereals-based products has relation with manufacturing practices, especially with storage conditions. An extraction procedure for OTA from wheat-based products was implemented in this study. The method uses an alkaline extraction with NaHCO3, purification with Sep-Pak® RP-18 cartridges; and quantitative analysis by high performance liquid chromatography with fluorescence detection. The presence of OTA was confirmed by the formation of Ochratoxin A methyl ester. The method shows good validation parameters with a rate of recovery rate over 95%, limits of detection and quantification of 0.6 and 2.1 μg kg?1, respectively. Once the method was validated; 31 samples including, flour, corn starches and rice were analyzed. About 70% of flour samples, 50% of rice and 63% of corn starch samples resulted positives for OTA. 相似文献
918.
Maria Angélica Hueb De Menezes Oliveira Carolina Paes Torres Jaciara Miranda Gomes‐Silva Michelle Alexandra Chinelatti Fernando Carlos Hueb De Menezes Regina Guenka Palma‐Dibb Maria Cristina Borsatto 《Microscopy research and technique》2010,73(5):572-577
Purpose: This study evaluated and compared in vitro the microstructure and mineral composition of permanent and deciduous teeth's dental enamel. Methods: Sound third molars (n = 12) and second primary molars (n = 12) were selected and randomly assigned to the following groups, according to the analysis method performed (n = 4): Scanning electron microscopy (SEM), X‐Ray diffraction (XRD) and Energy dispersive X‐ray spectrometer (EDS). Qualitative and quantitative comparisons of the dental enamel were done. The microscopic findings were analyzed statistically by a nonparametric test (Kruskal‐Wallis). The measurements of the prisms number and thickness were done in SEM photomicrographs. The relative amounts of calcium (Ca) and phosphorus (P) were determined by EDS investigation. Chemical phases present in both types of teeth were observed by the XRD analysis. Results: The mean thickness measurements observed in the deciduous teeth enamel was 1.14 mm and in the permanent teeth enamel was 2.58 mm. The mean rod head diameter in deciduous teeth was statistically similar to that of permanent teeth enamel, and a slightly decrease from the outer enamel surface to the region next to the enamel‐dentine junction was assessed. The numerical density of enamel rods was higher in the deciduous teeth, mainly near EDJ, that showed statistically significant difference. The percentage of Ca and P was higher in the permanent teeth enamel. Conclusions: The primary enamel structure showed a lower level of Ca and P, thinner thickness and higher numerical density of rods. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc. 相似文献
919.
Rodolfo de Andrade Schaffner Elson Oliveira Roberta Carolina Pelissari Rizzo Domingues Leandro da Conceição Carlos Itsuo Yamamoto Graciela Inêz Bolzon de Muniz Helton José Alves 《加拿大化工杂志》2024,102(2):738-747
Niobium pentoxide (Nb2O5) is a polymorphic ceramic with semiconductor characteristics applied in various fields of study. In this work, the Nb2O5 synthesis by the spray pyrolysis route was compared to the hydrothermal technique. The obtained materials were characterized by N2 physisorption (BET-N2), average particle size distribution by dynamic light scattering (DLS), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and X-ray fluorescence (XRF) spectroscopy. The material synthesized by the spray pyrolysis technique presented high specific area and pore volume, high crystallinity, homogeneity, and nanometric particles, thus representing a potential technique for the Nb2O5 synthesis. 相似文献
920.
Gustavo Luiz Venturelli Joana Laura Bischoff Mirella Christine Scariot Gabriela Barbosa Rossi Ana Carolina Maisonnave Arisi 《International Journal of Food Science & Technology》2019,54(4):1381-1389
Food authentication by quantitative polymerase chain reaction (qPCR) methods assures food quality. The aim was to evaluate three qPCR assays for DNA quantification after heat processing of common bean grains, genus-specific FAS assay for Phaseolus, species-specific LEC assay for common bean (Phaseolus vulgaris) and genetically modified (GM) event-specific FGM assay for Embrapa 5.1 event GM common bean. FAS assay showed high stability among Phaseolus genus samples. Common bean grains were heat-treated in autoclave (at 120 °C for 15–60 min) and target DNA copy number decreased as processing time increased. Even with DNA degradation, qPCR assays were capable to detect low DNA quantity, and the limit of detection was 100 copy number. Mean efficiency value of FGM assay was 92% in the presence of background DNA. Background DNA did not cause any interference, and 0.39% of GM material can be detected. These qPCR assays are able to quantify common bean in processed food. 相似文献