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1.
Polychlorinated biphenyls in Chinese surface soils   总被引:18,自引:0,他引:18  
Polychlorinated biphenyl (PCB) concentrations in surface soil samples (0-20 cm) from 52 sites (4 background, 39 rural, and 9 urban) across China in 2005 are presented. The average concentration of total PCBs among all the sites was 515 pg/g dry weight (dw), approximately one-tenth of that in global background soil in 1998. Differences of less than 1 order of magnitude were found between all background and rural sites, indicating a generally uniform distribution of PCBs in Chinese background/rural surface soil. While the major PCB homologue group in global background soil is hexa-PCB followed by penta-PCB, the major PCB homologue group in Chinese background/rural soil is tri-PCB followed by di-PCB, indicating a rather fresh signature in comparison to the much weathered PCBs in global surface soil. The correlation between sigmaPCBs and also each PCB homologue group per soil organic carbon (SOC) content in background/rural soil with longitude from 80 degrees to 122 degrees East was studied. The results indicated the strong influence of PCBs concentrations in Chinese background/rural soil by proximity to source region and SOC content, and also provided evidence for urban fractionation effect of PCBs in soil in the city of Shanghai and the longitudinal fractionation of PCBs in Chinese background/ rural soil from east to west. This work is the first comprehensive and spatial study of its kind for PCBs in Chinese surface soil on a national scale, and the data presented in this study can provide baseline information for establishing a long-term PCBs monitoring program in China.  相似文献
2.
The influence of pH on the degradation of refractory organics (benzoic acid, BA) in UV(254 nm)/Peroxymonosulfate (UV/PMS) system was investigated. The degradation of BA was significantly enhanced at the pH range of 8-11, which could not be explained only by the generally accepted theory that SO(4)(?-) was converted to HO(?) at higher pH. A hypothesis was proposed that the rate of PMS photolysis into HO(?) and SO(4)(?-) increased with pH. The hypothesis was evidenced by the measured increase of apparent-molar absorption coefficient of PMS (ε(PMS), 13.8-149.5 M(-1)·cm(-1)) and photolysis rate of PMS with pH, and further proved by the increased quasi-stationary concentrations of both HO(?) and SO(4)(?-) at the pH range of 8-10. The formation of HO(?) and SO(4)(?-) in the UV/PMS system was confirmed mainly from the cooperation of the photolysis of PMS, the decay of peroxomonosulfate radical (SO(5)(?-)) and the conversion of SO(4)(?-) to HO(?) by simulation and experimental results. Additionally, the apparent quantum yield for SO(4)(?-) in the UV/PMS system was calculated as 0.52 ± 0.01 at pH 7. The conclusions above as well as the general kinetic expressions given might provide some references for the UV/PMS applications.  相似文献
3.
几种真菌多糖的提取及生物活性   总被引:7,自引:0,他引:7  
介绍了真菌多糖中几种比较典型的香菇多糖、灵芝多糖和茯苓多糖的化学结构、分离提取方法和生物活性。  相似文献
4.
原料乳中嗜冷菌计数及产脂肪酶特性的研究   总被引:7,自引:1,他引:6  
任静  张兰威  王芳 《食品科学》2006,27(5):208-211
本文主要对乳中的嗜冷菌数的检测方法进行了初步研究.同时,考虑到嗜冷菌能在乳中产生大量的耐热性脂肪酶,力求在脂肪酶活与菌数之间建立联系.即对不同时间测得的酶活与菌数之间的关系进行初步探讨.  相似文献
5.
本文研究了白藜芦醇与黑木耳多糖对ABTS+自由基清除的协同作用。采用ABTS+自由基清除实验与Chou-Talalay联合指数(CI)方法相结合,对白藜芦醇和黑木耳多糖单独和复配的清除效果、联合指数(CI)及剂量减少指数(DRI)进行分析评价,结果显示:单独白藜芦醇和黑木耳多糖的IC50值分别为3.56 mg/L、61.46 mg/L,复配(质量比1:1)后的IC50值为2.50 mg/L,表明复配物对ABTS+自由基有明显的清除作用;联合指数(CI)分析,从清除率5%至97%相互作用指数都小于1,且随着清除率的增加,联合指数(CI)也随之降低;剂量减少指数(DRI)分析,从清除率5%至97%剂量减少指数都大于1,且随着清除率的增加,剂量减少指数(DRI)也随之增加,证实在质量比1:1时,白藜芦醇与黑木耳多糖之间存在着显著协同抗氧化效应。  相似文献
6.
羧甲基玉米多孔淀粉的制备及性能研究   总被引:6,自引:0,他引:6  
徐忠  缪铭  王鹏  张海华 《食品科学》2005,26(10):116-120
以多孔淀粉为原料,采用一氯乙酸和乙醇溶剂来制取羧甲基多孔复合变性淀粉,并探讨了反应温度、反应时间、氢氧化钠用量、一氯乙酸用量、乙醇浓度等对羧甲基多孔淀粉的取代度的影响。以取代度为指标,通过单冈素和正交实验方法确定最佳工艺条件为:反应温度45℃、反应时间6h、氢氧化钠4.0g、一氯乙酸4.5g、乙醇浓度95%。同时对羧甲基多孔淀粉、原玉米淀粉和多孔淀粉的理化性质和糊的流变学性质进行了分析比较,结果表明羧甲基多孔淀粉的理化性质和糊的流变学性质均有所改善。  相似文献
7.
Microarc oxidation (MAO) was performed on titanium in an electrolyte containing calcium glycerphosphate (Ca-GP) and calcium acetate (CA) using a direct current power supply. It was found that the MAO method is suitable forming a ceramic coating containing Ca and P using titanium, and that films display a porous and rough structure on their surface. Samples with a Ca/P ratio of 1.71 were hydrothermally treated in water solution whose pH was adjusted to 7.0-11.0 by adding NaOH at 190 degrees C for 10 h in an autoclave. Hydroxyapatite crystals were precipitated on the film surface after the hydrothermal treatment, and the amount of hydroxyapatite precipitated increased with increasing pH of water solution. The oxide film composition was semiquantitatively analyzed with an electron probe microanalyzer. The microstructures on the sample surfaces were observed by scanning electron microscopy before and after the hydrothermal treatment. The topography of the oxide film was imaged with an atomic force microscope. Its cross section was observed by scanning electron microscopy after being coated with a thin Au film. The surface structures of the films were analyzed by X-ray diffraction.  相似文献
8.
大豆蛋白亚基组成与7S/11S对豆腐品质及产率的影响   总被引:5,自引:1,他引:4  
通过采用不连续的十二烷基磺酸钠-聚丙烯酰胺凝胶电泳技术,运用数学归一法对所选不同大豆品种中蛋白质的亚基组成及其比值(7S/11S)进行了测定,得出品种间差异对蛋白质亚基组成的变化影响较明显。然后将所选大豆品种分别制成豆腐制品,通过测定豆腐品质(出品率、硬度),将其与亚基组成及7S/11S分别进行相关分析,得出各亚基对豆腐品质参数的影响显著程度各不相同,其中α′和α亚基与豆腐出品率、硬度均呈现极显著负相关性;β亚基与二者之间呈显著负相关;A3酸性亚基与二者之间相关性均不显著;A1,2,4酸性亚基与出品率呈显著正相关性,且与硬度呈现极显著正相关;B碱性亚基与出品率呈显著正相关,而与硬度之间无显著相关性;7S/11S与二者均呈极显著负相关。最后采用聚类分析法,筛选出88079、310及东农42为较适合作为加工豆腐的专用品种。  相似文献
9.
食品安全隐患--苯并(a)芘的研究进展   总被引:5,自引:0,他引:5  
从当前倍受关注的食品安全问题出发,根据食品中的强致癌物质——笨并(a)芘(benzopyrene)的结构综合论述了其性质、来源、潜在的危害、检测方法,以及在研究苯并(a)芘过程中所面临的问题,为今后更好的研究苯并(a)芘,控制其在食品中的含量奠定一定的理论基础。  相似文献
10.
Most halogenated organic compounds (HOCs) are toxic and persistent, and their efficient destruction is currently a challenge. Here, we proposed a sulfite/UV (253.7 nm) process to eliminate HOCs. Monochloroacetic acid (MCAA) was selected as the target compound and was degraded rapidly in the sulfite/UV process. The degradation kinetics were accelerated proportionally to the increased sulfite concentration, while the significant enhancement by increasing pH only occurred in a pH range of 6.0-8.7. The degradation proceeded via a reductive dechlorination mechanism induced by hydrated electron (e(aq)(-)), and complete dechlorination was readily achieved with almost all the chlorine atoms in MCAA released as chloride ions. Mass balance (C and Cl) studies showed that acetate, succinate, sulfoacetate, and chloride ions were the major products, and a degradation pathway was proposed. The dual roles of pH were not only to regulate the S(IV) species distribution but also to control the interconversion between e(aq)(-) and H(?). Effective quantum efficiency (Φ) for the formation of e(aq)(-) in the process was determined to be 0.116 ± 0.002 mol/einstein. The present study may provide a promising alternative for complete dehalogenation of most HOCs and reductive detoxification of numerous toxicants.  相似文献
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