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21.
In order to screen for the bitter compounds generated from hop-derived precursors during the wort boiling process, an ethanolic hop extract was fractionated; the fractions obtained were thermally treated under model wort boiling conditions and, then, sensorially evaluated for their bitterness. Besides the isomerisation of the α-acids into the intensely bitter iso-α-acids, the bitterness of the fraction containing the β-acids was also found to be enhanced after wort boiling. To gain first insights into the β-acid-derived bitter compounds, the β-acid colupulone was isolated, thermally treated under wort boiling conditions and, then, investigated for bitter tasting degradation products by means of a taste dilution analysis (TDA). Besides the cohulupone, five previously unreported bitter-tasting colupulone degradation products, all of which exhibited a lingering, β-acid-like bitter taste with low recognition thresholds between 37.9 and 90.3 μmol/l, were isolated and their structures determined as two tricyclocolupone epimers, two dehydrotricyclocolupone epimers, and nortricyclocolupone, respectively, by means of LC–TOF–MS and 1D/2D-NMR spectroscopy. 相似文献
22.
快速跳频性能特征及其测试的研究 总被引:2,自引:0,他引:2
跳频转换时间、驻留时间、跳频速率是快速跳频的典型性能特征。文中介绍了这些性能特征的概念,从快速跳频系统的设计层面重点讲述了跳频转换时间、驻留时间、跳频速率之间的关系以及他们和硬件电路之间的联系,分析了影响快速跳频性能的主要因素,提出了提高快速跳频性能的途径。并对跳频转换时间等快速跳频性能特征的测试方法进行了研究,给出了使用下变频以及实时频谱分析仪的测试实例。 相似文献
23.
Stanley Makumire Tendamudzimu Harmfree Dongola Graham Chakafana Lufuno Tshikonwane Cecilia Tshikani Chauke Tarushai Maharaj Tawanda Zininga Addmore Shonhai 《International journal of molecular sciences》2021,22(4)
Parasitic organisms especially those of the Apicomplexan phylum, harbour a cytosol localised canonical Hsp70 chaperone. One of the defining features of this protein is the presence of GGMP repeat residues sandwiched between α-helical lid and C-terminal EEVD motif. The role of the GGMP repeats of Hsp70s remains unknown. In the current study, we introduced GGMP mutations in the cytosol localised Hsp70-1 of Plasmodium falciparum (PfHsp70-1) and a chimeric protein (KPf), constituted by the ATPase domain of E. coli DnaK fused to the C-terminal substrate binding domain of PfHsp70-1. A complementation assay conducted using E. coli dnaK756 cells demonstrated that the GGMP motif was essential for chaperone function of the chimeric protein, KPf. Interestingly, insertion of GGMP motif of PfHsp70-1 into DnaK led to a lethal phenotype in E. coli dnaK756 cells exposed to elevated growth temperature. Using biochemical and biophysical assays, we established that the GGMP motif accounts for the elevated basal ATPase activity of PfHsp70-1. Furthermore, we demonstrated that this motif is important for interaction of the chaperone with peptide substrate and a co-chaperone, PfHop. Our findings suggest that the GGMP may account for both the specialised chaperone function and reportedly high catalytic efficiency of PfHsp70-1. 相似文献
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27.
朱军 《数字社区&智能家居》2011,(17)
该文提出了一种基于RSSI测距技术的DV-Hop定位算法。该算法有效利用每跳的统计信息并结合RSSI测距技术,在不增加传感器节点的硬件开销的基础上有效提高定位精度和扩大定位范围。实验表明了提出的方法在不同的节点比例和节点数的情况下,定位误差和定位范围等性能与传统的定位算法相比有明显的提高,是一种有效的方法。 相似文献
28.
In this paper, two solid–liquid extraction techniques, supercritical fluid extraction (SFE) with and without modifiers and cyclically pressurized solid–liquid extraction with a Naviglio Extractor, were compared on the basis of extraction of acidic compounds contained in hops flowers. The hops extracts were analyzed by electro-kinetic capillary chromatography (MECK). The results showed that the technique using supercritical carbon dioxide was more effective for the isolation of β acids; the use of ethanol as a co-solvent, as reported in the literature, produced a heterogeneous extract, while cyclically pressurized solid–liquid extraction showed a greater extraction capacity for α acids. Consequently, both techniques are valid for the extraction of α and β acids from hops. By suitably varying the parameters of the two extractive procedures, it will be possible to obtain extracts for use in the production of beer and dietary supplements and drugs. Furthermore, based on the SFE CO2 extraction process, a mathematical model was applied to the examined process, and a numerical simulation was performed, leading to a model that provides direction for the optimization of further experiments. 相似文献
29.
Xanthohumol (XN), a component of hops, is lost in significant quantities in the conventional brewing process. In commercial beers less than 0.2 mg XN/L are found. In order to increase the yield of XN in the brewing process, the parameters of XN recovery were studied. During wort boiling, XN is largely isomerised to isoxanthohumol. Further losses are owing to the precipitation and absorption of XN to yeast cells and haze particles and by filtration. The use of XN-enriched hop products combined with a late hop dosage during wort boiling proved to be effective in increasing the XN content in beer. The yield was further raised by a low-pitching rate and the abnegation of beer stabilisation. The use of dark malts had a positive effect on the XN recovery. Investigations of roasted malt extracts revealed several high-molecular substances that are able to form complexes with XN. These complexes proved to be stable in the brewing process. Depending on the addition of roasted malt or special XN-enriched roasted malt extracts, dark beers with more than 10 mg XN/L were achieved. Results obtained led to a brewing technology that produced on an industrial scale pale wheat beer with more than 1 mg XN/L. 相似文献
30.
酒花浸膏的分离及α—酸异构化 总被引:1,自引:0,他引:1
用化学方法对啤酒花宫中的α-酸等有效物质进行分离提纯,对分离出的α-酸、β-酸进行了紫外学谱的测试,测试结果与文献值一致。并对α-酸进行异构化,提高了酒花这有有效分的利用率。 相似文献