全文获取类型
收费全文 | 241篇 |
免费 | 15篇 |
专业分类
化学工业 | 95篇 |
金属工艺 | 4篇 |
机械仪表 | 9篇 |
建筑科学 | 16篇 |
矿业工程 | 1篇 |
能源动力 | 12篇 |
轻工业 | 28篇 |
水利工程 | 3篇 |
石油天然气 | 3篇 |
无线电 | 4篇 |
一般工业技术 | 30篇 |
冶金工业 | 28篇 |
原子能技术 | 1篇 |
自动化技术 | 22篇 |
出版年
2024年 | 3篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 25篇 |
2012年 | 20篇 |
2011年 | 21篇 |
2010年 | 14篇 |
2009年 | 25篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2002年 | 4篇 |
2000年 | 1篇 |
排序方式: 共有256条查询结果,搜索用时 15 毫秒
251.
The potential of ETS-10 as a Lewis acid catalyst was investigated using the MPV reaction at one atmosphere total pressure
and 273 K. ETS-10 was hypothesized to be a potential Lewis acid catalyst as it has titanium in octahedral symmetry, which
is the symmetry shown in zeolite Beta to be the most active site for the Lewis acid catalyzed Meerwein–Ponndorf–Verley (MPV) reaction. The MPV reaction is a hydrogen transfer reaction that can be used for obtaining information about the structure
and performance of catalysts by comparing the product selectivities and catalytic activities. Due to their similar structures,
the catalytic activity of ETS-10 was compared to zeolite Beta samples that were space-grown (flight, fewer defects) and to
their earth-grown terrestrial controls. The higher tr-alcohol selectivity (i.e., trans-4-tert-butylcyclohexanol, ∼80% vs. 40%) observed over ETS-10 was attributed to a larger volume being available in the pores of ETS-10
compared to the zeolite Beta samples. By-product formation (i.e., 4-tert-butylcyclohexene) was significantly less over ETS-10
(∼5%) in comparison with the zeolite Beta samples (flight and control; ∼35%). These results reaffirm the octahedral symmetry
as the Lewis active site for the MPV reaction, and illustrate that ETS-10 is a good catalyst for MPV type reactions. 相似文献
252.
In this study, optimum conditions for the extraction of black carrot anthocyanins were determined by response surface methodology. Central composite design of extraction factors (pH 2.5–6.5, temperature 4–72 °C, solvent/solid ratio 5:1–25:1 v/w, ethanol/water ratio 0:100–100:0?v/v) was generated as two replicates. Total phenolic content, total monomeric anthocyanin content, polymeric color, total antioxidant activity, and anthocyanin composition determined by high-performance liquid chromatography were used as responses. Except for color analysis, higher temperature, solid/solvent ratio, and ethanol concentration were observed to increase the extraction yield. However, polymeric color results were found to have minimum values at lower pH and solid/solvent ratio, lower or moderate temperature, and higher ethanol concentration. Optimum extraction conditions were found as follows: 50 °C, pH 3.5, solvent solid ratio 10:1 (v/w), and ethanol/water ratio 75:25 (v/v) when all responses were considered. The validation of the optimum conditions for black carrot extraction was performed at specified values. 相似文献
253.
Productivity monitoring, which involves frequent monitoring and analysis of on-going construction activities, helps in assessing a project's performance and in enabling identification of opportunities for improvement. It often involves finding answers for dynamic user queries that require data to be fused from different combinations of heterogeneous data sources having different levels of detail, representations and reference systems. Digital elements of these sources are expanding exponentially, and yet fusing and processing them manually remains a challenging problem. In this paper, the authors present a formal approach for capturing dynamic user queries and identifying applicable sets of data sources from a given set of available data sources to answer such queries. This approach is an important step to enable automated and efficient multi-source data fusion. 相似文献
254.
In this study, α‐amylase was immobilized on glutaraldehyde activated silanized calcium carbonate nanoparticles by a using covalent binding method. The surface modified nano calcium carbonate (CaCO3) were characterized using FTIR and SEM. Immobilization yield was found as 199.43 mg/g of calcium carbonate nanoparticles. The maximum activity was observed at pH 6.5. The immobilized enzyme had a higher activity at elevated temperature (50–90°C) than the free one. Reuse studies demonstrated that the immobilized enzyme could reuse 25 times while retaining 18.2% of its activity. Free enzyme lost its activity completely within 15 days. Vmax values for the free and immobilized enzymes were calculated as 10 and 0.35 mg/mL/min, respectively. 相似文献
255.
It has been well documented that excess concentrations of boron (B) causes toxic effects on many of the environmental systems. Although Chlorella sp. has been studied to remove pollutants from water, its capacity to remove B has not been investigated yet. Boron removal levels of newly isolated Chlorella sp. were investigated in BG 11 media with stimulators as triacontanol (TRIA) and/or sodium bicarbonate (NaHCO3) and without them, to test if they could increase the removal efficiency by increasing biomass. The assays were performed to determine the effect of different medial compositions, B concentrations, pH and biomass concentrations onto removal efficiency. Boron removal was investigated at 5-10 mg/L range at pH 8 in different medial compositions and maximum removal yield was found as 32.95% at 5.45 mg/L B in media with TRIA and NaHCO3. The effect of different pH values on the maximum removal yield was investigated at pH 5-9, and the optimum pH was found again 8. The interactive effect of biomass concentration and B removal yield was also investigated at 0.386-1.061 g wet weight/L biomass. The highest removal yield was found as 38.03% at the highest biomass range. This study highlights the importance of using new isolate Chlorella sp. as a new biomaterial for B removal process of waters containing B. 相似文献
256.