全文获取类型
收费全文 | 194篇 |
免费 | 25篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 2篇 |
综合类 | 14篇 |
化学工业 | 98篇 |
金属工艺 | 17篇 |
机械仪表 | 9篇 |
建筑科学 | 6篇 |
矿业工程 | 6篇 |
能源动力 | 4篇 |
轻工业 | 19篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
无线电 | 13篇 |
一般工业技术 | 23篇 |
冶金工业 | 2篇 |
原子能技术 | 5篇 |
自动化技术 | 1篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 14篇 |
2012年 | 14篇 |
2011年 | 10篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 9篇 |
2007年 | 15篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 8篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有226条查询结果,搜索用时 953 毫秒
41.
离子色谱法测定城市生活垃圾渗沥水中阴离子 总被引:1,自引:0,他引:1
介绍了离子色谱法测定城市生活垃圾渗沥水中的阴离子(氯离子、亚硝酸根离子、硝酸根离子、磷酸根离子和硫酸根离子).避免了样品中复杂组分对分析体系的干扰及对色谱系统的污染,该方法快速、灵敏、准确.当以10mmol/LNa2CO3作淋洗液,流速为1.0mL/min时,分离效果良好,阴离子的检出限分别为0.18,0.45,0.67,1.02和0.85mg/L,回收率为95.85%~106.5%. 相似文献
42.
This work deals with poly(ethylene oxide), PEO–MX (M=Li, K and Cs) amorphous electrolytes with −X–X−, [CF3SO2NCH2(CH2OCH2)2CH2NSO2CF3]2− (EDSA) and [CF3SO2NCH2CH2(CH2OCH2)3CH2CH2NSO2CF3]2− (TTSA) disulfonamide anions. These dianions have X− end-groups identical to anions [CF3SO2N(CH2)2OCH3]− (MESA) and [CF3SO2N(CH2)3OCH3]− (MPSA), one of which (MPSA) was reported to yield chelate-like associated species (presumably LiX2− triplets) at concentrations above EO/Li=20 in PEO. This feature of LiMPSA, evidenced through glass transition temperature (Tg) measurements, does not apply to Li2EDSA and Li2TTSA. Though none of these lithium salts form crystalline intermediate compounds with PEO, the limit of solubility of LiMESA (EO/Li=16) does not allow a clarification of this point for this salt. At lower concentrations, however, a conductivity comparison with the potassium and caesium salts shows that the apparent degree of dissociation (=CLi+/CLi) of LiMESA is comparable to that of LiMPSA. As opposed to both these salts and to some extent to Li2EDSA, a much greater dissociation takes place for Li2TTSA, the anion of which contains an inner, third ether group in its structure. 相似文献
43.
Dams and reservoirs are known to disturb river‐water composition, among other impacts, with potential implications for downstream river ecosystems and water uses. Existing studies have emphasized the variable influence of dams on water composition according to the element, its speciation (dissolved vs. particulate), reservoir properties (residence times), reservoir functions (e.g., hydropower, irrigation), and management (water releases). A now common approach to analyzing hydrological, geochemical, and biological controls on element export from unregulated rivers is to study hydrochemical signatures such as concentration‐flow relationships. We investigated a case study to analyze hydrochemical signatures of a regulated river (Sélune River, western France) upstream and downstream of a chain of two hydropower dams, assuming that the dams disturbed the river's signatures, and that those disturbances would provide information about processes occurring in the reservoirs. Both seasonal and event‐scale signatures were analyzed over two contrasting hydrological years and a range of storm events. The dams induced a chemostatic downstream response to storm events whenever elements were diluted or concentrated upstream. Dams did not disturb the seasonality of major anions but did modify silica and phosphorus concentration‐flow relationships, especially during low flow. Such changes in dynamics of river‐water composition may affect downstream biological communities. This study presents an initial state of the hydrochemical signature of the downstream river, before the removal of the two dams. 相似文献
44.
为了研究低磷酸盐—低氢氧化钠水处理工艺下侵蚀性阴离子对碳钢的腐蚀 ,通过高压釜静态试验 ,计算在不同浓度下碳钢的腐蚀速度 ,测定溶液中总铁离子浓度以及对表面的 EPMA(Electron probe microanalysis,电子探针微量分析 )分析。结果表明 :高温下 ,Cl-、SO42 -是引起碳钢腐蚀的主要原因。它们能阻碍膜的形成。随着离子浓度的增大 ,当 CCl- >0 .4m g/L 时 ,碳钢的腐蚀速率明显增加 ,蚀孔增多 ,耐蚀性能降低 相似文献
45.
Electrochemical reduction of 1-chloro-10-methyltribenzotriquinacene in benzonitrile, acetonitrile and N,N-dimethylformamide (DMF) is compared. A two-electron DISP1 mechanism was found in C6H5CN at glassy carbon and mercury electrodes with C-Cl bond cleavage as the rate determining step. In CH3CN and DMF the hydrogen atom abstraction from solvent molecules by a radical formed in bond cleavage results in the one-electron process. In the above-mentioned solvents an analysis of a potential dependence of the transfer coefficient, obtained from convoluted voltammetric curves at mercury electrode, showed the concerted mechanism. A change from the stepwise process in C6H5CN to the concerted one in CH3CN and DMF is explained by acceleration of bond cleavage in the radical anion due to stronger solvation of product chloride anions by CH3CN and DMF. 相似文献
46.
M.M. Antonijevi? M.D. Dimitrijevi? V.L.J. Dimitrijevi? S.M. Mili? 《Electrochimica acta》2005,50(20):4160-4167
This work gives an investigation of pyrite behaviour during anodic oxidation in solutions of four inorganic acids: sulphuric, hydrochloric, phosphoric and perichloric acid. In wider range of concentrations, the influence of acids on following parameters was investigated: rate of establishment and corrosion potential value, Tafel's slope, corrosion current and electrodic reaction order. Based on potentiodynamic and chronoamperometric investigations, it was found out that pyrite oxidation is developed in three regions conditionally named active, passive and transpassive region. It was also found out that pyrite is intensively dissolved at potentials higher than 0.75 V versus SCE and that oxidation rate of pyrite is the highest in hydrochloric acid solutions (≥1 M HCl). By comparison of obtained results, it was concluded that there are no distinctive differences in pyrite behaviour during anodic oxidation in solutions of investigated acids. 相似文献
47.
Leaching optimization and dissolution behavior of alkaline anions in bauxite residue 总被引:1,自引:0,他引:1
Xiao-fei LI Yu-zhen YE Sheng-guo XUE Jun JIANG Chuan WU Xiang-feng KONG William Hartley Yi-wei LI 《中国有色金属学会会刊》2018,28(6):1248-1255
Bauxite residue is a highly alkaline waste containing soluble alkaline anions, which can cause environmental concerns. The optimal leaching conditions, distribution of alkaline anions, types of pivotal alkaline anions and their dissolution behaviors were investigated based on the combination of single factors-orthogonal experiments and leaching stage experiment. Using a two-stage leaching, 86% of the soluble alkaline anions
were leached with a L/S ratio of 2 mL/g, at 30 °C, over 23 h. During the first stage of leaching, approximately 88% of alkaline anions were leached from the dissolution of free alkali (NaOH, carbonate, bicarbonate, NaAl(OH)4) with the rest originating from the dissolution of alkaline minerals (calcite, cancrinite and hydrogarnet). Supernatant alkalinity was 69.78 mmol/L with
accounting for 75%. Furthermore, carbonate leaching was controlled by solid film diffusion using the Stumm Model with an apparent activation energy of 10.24 kJ/mol. 相似文献
48.
Effects of sulfate, phosphate, silicate and humic acid (HA) on the removal of As(III) in the KMnO4–Fe(II) process were investigated in the pH range of 4–9 with permanganate and ferrous sulfate applied at selected dosage. Sulfate decreased the removal of arsenic by 6.5–36.0% at pH 6–9 and the decrease in adsorption did not increase with increasing concentration of sulfate from 50 to 100 mg/L. In the presence of 1 mg/L phosphate, arsenic removal decreased gradually as pH increased from 4 to 6, and a sharp drop occurred at pH 7–9. The presence of 10 mg/L silicate had negligible effect on arsenic removal at pH 4–5 whereas decreased the arsenic removal at pH 6–9 and the decrease was more significant at higher pH. The presence of HA dramatically decreased the arsenic removal over the pH range of 6–9 and HA of higher concentration resulted in greater drop in arsenic removal. The effects of the competing anions on arsenic removal in the KMnO4–Fe(II) process were highly dependent on pH and the degree of these four anions influencing As(III) removal decreased in the following order, phosphate > humic acid > silicate > sulfate. Sulfate differed from the other three anions because sulfate decreased the removal of arsenic mainly by competitive adsorption while phosphate, silicate and HA decreased the removal of As(III) by competitive adsorption and sequestering the formation of ferric hydroxide derived from Fe(II). 相似文献
49.
E.E. Abd El Aal 《Corrosion Science》2006,48(2):343-360
The anodic behaviour of Zn electrode in 1 × 10−2 M Na2B4O7 solutions in the absence and presence of various concentrations of Na2SO4, Na2S2O3 or Na2S as aggressive agent was studied by galvanostatic polarization technique. In the absence of sulphur-containing anions in solution, the polarization curves are characterized by one distinct arrest corresponding to Zn(OH)2 and/or ZnO, after which the potential increases linearly with time due to the formation of barrier oxide film before reaching the oxygen evolution reaction. The duration time of the arrest decreases with increasing current density while the rate of oxide film formation increases. On the other hand, the duration time of the arrest increases with the number of anodic cyclization while the rate of oxide film formation decreases. Additions of low concentration of the aggressive anions have no effect on the passive film formed on the metal surface. The potential starts to oscillate within the oxygen evolution region with increases in the concentration of these aggressive anions. Further increases in the concentration of these aggressive anions are associated with impaired Zn passivity that might indicate pitting attack. The aggressiveness of the sulphur species decreases in the order: . The effect of raising pH of the solution on the anodic behaviour of Zn electrode in the presence of anions was also investigated. It was found that the raising the pH of the solution affecting on the rate of oxide film formation and the breakdown potential value. 相似文献
50.
Analysis of literature indicates that the strength of superacids is mainly determined by unusual chemical properties of weakly
solvated protons while the extent of dissociation of superacids is rather low and is less important. A higher chemical activity
of protons in very concentrated acids and in such water-free superacids as liquid HF or 100% H2SO4 results from a weaker solvation of these species with the molecules of superacids which are less basic than water. In contrast,
solvation by superacids of the negatively charged anions is stronger than in water solutions. These conclusions are illustrated
by the ab initio quantum chemical calculations performed for self-dissociation of anhydrous liquid hydrofluoric acid.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献