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71.
Fouling is a major limitation for the application of membrane bioreactors (MBRs) in municipal wastewater treatment; the critical flux concept represents a valid tool for process optimisation in planning fouling control strategies. The paper presents the results obtained on a large pilot MBR equipped with a plate-and-frame ultrafiltration membrane. The experimental assessment of flux criticality was carried out by flux-stepping tests showing the positive impact of liquid temperature on the value of the critical threshold. The reliability of short-term tests was then verified over a long period by determining the time of sustainability, t(sust), of six different sub-critical fluxes ranging between 17 and 30Lm(-2)h(-1). An exponential fitting was observed in terms of fouling rate both before and after t(sust), though fouling after t(sust) is likely to be ascribed not only to cake formation. Finally, a new mathematical formulation was proposed according to the local flux approach to model the sub-critical TMP transients. The model involves both bound and free forms of EPS and, once experimentally calibrated, it provided a fair prediction of the TMP jump. 相似文献
72.
A new one-dimensional mixed-culture biofilm model was derived based on a hypothesis that each particulate component would have different space occupancy within biofilm. Contrary to conventional density-based modeling approaches, in this model the volume change of the biofilm is described with the space occupancies of the particulate components, new model parameters introduced here. The unique feature of this model is that internal pore development during biofilm growth can be predicted implicitly so that the changes of effective diffusivities of soluble components depending on internal porosity are readily implemented in the model. Simulation studies revealed that the presented biofilm model could reasonably describe several important aspects of biofilm growth phenomena. In a mixed-culture biofilm system where heterotrophs and autotrophs were involved, the overall biofilm growth pattern was governed by microbial competition depending on influent composition. In a thick heterotrophic biofilm, a simulated biomass distribution and internal porosity profile showed higher total biomass concentration, lower active cell fraction, and lower internal porosity in the bottom layers of the biofilm, which are well coincident with the experimental data reported previously. All these phenomena can be explained by the proceeding of biofilm consolidation, which happens due to the inter-conversions of the particulate components having different space-occupancy values. The presented biofilm model suggests that the space occupancy of EPS may be a key model parameter to decide the overall biofilm growth pattern by regulating the extent of biofilm consolidation. 相似文献
73.
74.
乳酸菌胞外多糖的研究进展 总被引:5,自引:1,他引:5
本文总结了菌种、培养基成分、温度、pH值、发酵时间等因素对乳酸菌EPS产量的影响;探讨了提高乳酸菌EPS的生物合成量的方法,旨在加深乳酸菌EPS的研究和推动其应用. 相似文献
75.
聚苯板保温材料在三峡工程中的研究与应用 总被引:4,自引:0,他引:4
为防止因气温骤降引起大坝混凝土表面裂缝,应对坝体进行表面保温。根据设计要求并结合三峡二期工程保温材料实际运用情况,通过一系列试验比选,最终选择聚苯板作为三峡工程三期大坝、厂房永久暴露面保温材料。经使用验证,采用聚苯板作为保温材料保温效果良好,施工工艺简便,满足坝体跟进保温要求,且因耐久性好可多年保温,具有较好的经济性。 相似文献
76.
77.
A mathematical model is established to simulate the formation of extracellular polymeric substances (EPS), soluble microbial products (SMP), and internal storage products (XSTO) in aerobic granular sludge. The sensitivity of these microbial products concentrations toward the key model parameters is analyzed. Independent experiments are conducted to find required parameter values and to test its predictive ability. The model is evaluated by using one‐cycle operating experimental results of a lab‐scale aerobic granule‐based sequencing batch reactor (SBR) and batch experimental results. Results show that the model is able to describe the microbial product dynamics in aerobic granules and provide further insights into a granule‐based SBR. The effect of the initial substrate and biomass concentrations on the formation of microbial products in aerobic granular sludge can therefore be analyzed by model simulation. A higher substrate concentration results in a greater concentration of EPS, SMP, and XSTO. An accumulation of biomass in the bioreactor leads to an increased production rate of EPS, SMP, and XSTO. © 2009 American Institute of Chemical Engineers AIChE J, 2010 相似文献
78.
Critical assessment of extracellular polymeric substances extraction methods from mixed culture biomass 总被引:3,自引:0,他引:3
Extracellular polymeric substances (EPS) have a presumed determinant role in the structure, architecture, strength, filterability, and settling behaviour of microbial solids in biological wastewater treatment processes. Consequently, numerous EPS extraction protocols have recently been published that aim to optimize the trade off between high EPS recovery and low cell lysis. Despite extensive efforts, the obtained results are often contradictory, even when analysing similar biomass samples and using similar experimental conditions, which greatly complicates the selection of an extraction protocol. This study presents a rigorous and critical assessment of existing physical and chemical EPS extraction methods applied to mixed-culture biomass samples (nitrifying, nitritation-anammox, and activated sludge biomass). A novel fluorescence-based method was developed and calibrated to quantify the lysis potential of different EPS extraction protocols. We concluded that commonly used methods to assess cell lysis (DNA concentrations or G6PDH activities in EPS extracts) do not correlate with cell viability. Furthermore, we discovered that the presence of certain chemicals in EPS extracts results in severe underestimation of protein and carbohydrate concentrations by using standard analytical methods. Keeping both maximum EPS extraction yields and minimal biomass lysis as criteria, it was identified a sonication-based extraction method as the best to determine and compare tightly-bound EPS fractions in different biomass samples. Protein was consistently the main EPS component in all analysed samples. However, EPS from nitrifying enrichments was richer in DNA, the activated sludge EPS had a higher content in humic acids and carbohydrates, and the nitritation-anammox EPS, while similar in composition to the nitrifier EPS, had a lower fraction of hydrophobic biopolymers. In general, the easily-extractable EPS fraction was more abundant in carbohydrates and humic substances, while DNA could only be found in tightly bound EPS fractions. In conclusion, the methodology presented herein supports the rational selection of analytical tools and EPS extraction protocols in further EPS characterization studies. 相似文献
79.
EPS板薄抹灰外墙外保温系统粘贴面砖施工探讨 总被引:1,自引:0,他引:1
文章结合工程实例对EPS板薄抹灰外墙外保温系统粘贴面砖无现行设计标准进行了探讨。 相似文献
80.
介绍消失模铸造的白区模样制备的工艺特点及对设备的性能要求,制模设备预发泡机、成型机、冷粘结的工作原理、技术特点与应用情况. 相似文献