首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   185篇
  免费   21篇
  国内免费   3篇
电工技术   5篇
综合类   11篇
化学工业   100篇
机械仪表   6篇
建筑科学   7篇
矿业工程   5篇
能源动力   6篇
轻工业   6篇
石油天然气   13篇
武器工业   3篇
无线电   18篇
一般工业技术   11篇
冶金工业   6篇
自动化技术   12篇
  2022年   1篇
  2021年   2篇
  2020年   5篇
  2019年   8篇
  2018年   1篇
  2017年   6篇
  2016年   7篇
  2015年   7篇
  2014年   12篇
  2013年   13篇
  2012年   12篇
  2011年   14篇
  2010年   6篇
  2009年   8篇
  2008年   10篇
  2007年   7篇
  2006年   7篇
  2005年   8篇
  2004年   11篇
  2003年   15篇
  2002年   16篇
  2001年   9篇
  2000年   6篇
  1999年   8篇
  1998年   1篇
  1997年   2篇
  1996年   3篇
  1995年   1篇
  1993年   2篇
  1989年   1篇
排序方式: 共有209条查询结果,搜索用时 15 毫秒
181.
Eu(3+)-β-二酮、三正辛胺三元配合物的合成与光谱特性   总被引:2,自引:0,他引:2  
张颂培  李建宇  姜晓琳  李云天  陈鹃 《化学试剂》2003,25(3):137-138,144
合成了铕(Ⅲ)的二苯甲酰甲烷、三正辛胺的三元配合物Eu(3+·(DBM)3·[N(C8H(17))3]2,通过元素分析确定了配合物的组成,并通过红外光谱对配合物进行了表征。结合红外光谱、荧光光谱讨论了配合物的成键特性、配体传能机制以及协同配体N(C8H(17))3引入对激发光谱的影响。荧光光谱表明配合物可吸收247~400nm的宽带紫外光,发射Eu(3+)的5D0→7F2对应的612nm红色荧光。适于用作农膜转光剂。  相似文献   
182.
本文研究了丙酸与异丁醇在十二烷基磺酸铁催化剂作用下的酯化反应,考察了反应时间、催化剂用量、醇酸摩尔比等因素对丙酸异丁酯收率的影响。实验结果表明反应的最佳反应条件为:丙酸用量为 0.1 mol,醇酸摩尔比为1.2,十二烷基磺酸铁用量为2g(约2.5 mmol),反应时间为30 min,酯收率达93.5%,催化剂重复使用5次仍保持较高活性。无污染产生,具有绿色合成的特点。产品经折光率、红外光谱进行了表征。  相似文献   
183.
The effects of compatibilization on the toughening of polypropylene (PP) by melt blending with styrene/ethylene‐butylene/styrene tri‐block copolymer (SEBS) in a twin‐screw extruder were investigated. The compatibilizers used were SEBS functionalized with maleic anhydride (SEBS‐g‐MA), PP functionalized with acrylic acid (PP‐g‐AA), and bifunctional compound p‐phenylenediamine (PPD). The effects of the compatibilization were evaluated through the mechanical properties as well as through the determination of the phase morphology of the blends by scanning electron microscopy. Reactive compatibilized blends show up to a 30‐fold increase in impact strength compared with neat PP; likely the result of the reaction of the bifunctional compound (PPD) with the acid acrylic and maleic anhydride groups, this increase in strength rendered both morphological and mechanical stability to these blends. The addition of PPD to the blends significantly changed their phase morphologies, leading to larger average diameters of the dispersed particles, probably as a result of the morphological stabilization at the initial processing steps during extrusion, with the occurrence of chemical reactions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3466–3479, 2002  相似文献   
184.
Extraction and back‐extraction of valeric acid in a fixed bed packed with Amberlite XAD‐4 resin impregnated with trin‐butyl phosphate were experimentally studied at 25 °C. The effects of the feed flow rate, acid concentration in the feed solution and extractant concentration in the impregnated resin on the breakthrough curves, were investigated. The bed saturation capacity was larger under the conditions of higher extractant concentration in the resin phase and higher acid concentration in the feed solution. A dynamic model that considers intraparticle diffusion and external liquid film diffusion as limiting steps in mass transfer rates was successfully applied. The intraparticle effective diffusivities (10?9 dm2 s?1) were from one to three orders of magnitude lower than the diffusivities in the external liquid film (10?8–10?6 dm2 s?1). A fast and complete back‐extraction of valeric acid from the saturated bed was carried out with sodium hydroxide solutions. The operational life of the impregnated resin was also studied. Copyright © 2005 Society of Chemical Industry  相似文献   
185.
首先通过臭氧氧化作用把钛白废酸中的二价铁转化成三价铁,然后采用萃取法去除其中的三价铁。考察了络合剂(盐酸)浓度、萃取剂、萃取相比等对三价铁萃取率的影响,并初步探索了反萃法回收萃取剂及萃取剂的循环利用。结果表明:当盐酸浓度为3.4 mol/L时,几乎可完全络合溶液中的三价铁;在萃取剂磷酸三丁酯中加入苯作为稀释剂,可有效降低磷酸三丁酯的粘度,消除萃取过程中的乳化现象;磷酸三丁酯萃取三价铁的传质过程很快,2-3 min即达平衡;当萃取相比O/W(萃取剂与钛白废酸体积之比)=0.6∶1时,三价铁萃取率可达97%以上。当反萃相比W/O=4∶1时,三价铁反萃率接近100%。磷酸三丁酯经过5次萃取-反萃循环后,三价铁的萃取率没有明显下降。去除三价铁后的钛白废酸,经蒸馏浓缩到质量分数70%左右,再与浓硫酸混合后可用于钛白粉的生产,蒸馏过程中回收的盐酸循环使用。反萃出来的三价铁可作为生产铁红的原料。  相似文献   
186.
三相相转移催化合成对硝基苯甲醚的研究   总被引:3,自引:0,他引:3  
合成制备了聚苯乙烯支载聚乙二醇 ,并以之作为三相相转移催化剂用于对硝基氯苯合成对硝基苯甲醚 ,考察了催化剂、NaOH、CH3OH等的用量对反应转化率的影响 ,得到了适宜的合成工艺条件为 :n(PCNB)∶n(CH3OH)∶n(NaOH)∶n(PTC) =1∶3∶3∶(0 0 3~ 0 0 5) ,反应温度约 78~ 80℃ ,反应时间 9~ 1 0h。在该条件下 ,对硝基氯苯转化率大于 99 5 % ,收率大于 95 % ,产品经气相色谱检测纯度达 99 7% ,聚苯乙烯支载聚乙二醇催化剂可重复使用 5次以上 ,反应母液经除盐后 ,配碱套用对反应无不良影响  相似文献   
187.
This article presents a novel multi‐mode microstrip resonator. Using the even‐odd‐mode method, its resonance characteristics are analyzed and the design graphs are given. Each mode equivalent circuit is a λ/4 stepped impedance resonator (SIR), so the proposed resonator has a compact size and the higher harmonics can be tuned in a wide range. Stub–stub coupling is introduced to split two identical modes and produce two transmission zeros (TZs). Then a tri‐band filter operating at 1.5, 2.4, and 3.8 GHz is designed using the proposed resonator. The three center frequencies and bandwidths can be independently controlled. By tuning the impedance and length ratios of the stubs, wide upper stopband is achieved. Finally, the designed filter is fabricated and measured, and the measured results agree well with the simulated ones. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:559–564, 2016.  相似文献   
188.
采用H2O2-三氟乙酸作为氧化剂将盘锦催化裂化柴油中的硫化物(主要为苯并噻吩类)氧化成相应的砜,同时又用功率超声作用于该过程。然后根据相似相容原理用合适的溶剂将这些砜萃取除去。最佳的操作条件为:反应温度70℃;氧化剂与油的体积比为1:10;氧化时间60min;萃取剂为N,N-胺(DMF);萃取剂油比为1:1。加入功率超声后,可使反应时间由60min缩短为10min,同时也使脱硫率提高了10个百分点。  相似文献   
189.
BACKGROUND: The extractants used in solvent extraction processes undergo degradation under thermal, chemical and radiolytical stresses. In the case of uranium plants, trin‐octylamine, used as an extractant, slowly degrades into di‐n‐octylamine. Such degradation causes a gradual depletion of the uranium extraction isotherms and as a result, of the efficiency of uranium recovery from feed solutions. The present work highlights a new route to delay this depletion of the extraction efficiency, merely by optimizing the flow‐sheets involved in the process. Five flow‐sheets have been compared for uranium recovery from acidic sulfate media by a solution of 0.146 mol L−1 trin‐octylamine in kerosene modified with 5% w/w 1‐tridecanol and stripping with a 199 g L−1 Na2CO3 solution. These five flow‐sheets include the classical counter‐current flow‐sheet with four mixers–settlers in extraction and three mixers–settlers in stripping and four unusual combined solvent extraction flow‐sheets with two independent extraction stripping loops and with one or two feed inlets. RESULTS: Computer simulation supplied evidence of the strong influence of the studied flow‐sheets on the sturdiness of the process. More precisely, the unusual combined solvent extraction flow‐sheets appeared to be significantly more efficient than the classical counter‐current one and it is shown that an advantage of this can be to delay the negative impact of gradual degradation of trin‐octylamine on uranium recovery efficiency from acidic sulfate media. CONCLUSION: The replacement of classical counter‐current flow‐sheets with a unique extraction‐stripping loop in unusual combined flow‐sheets with two or more independent extraction‐stripping loops and with one or more feed inlets is a fruitful approach to delay the periodic addition of fresh trin‐octylamine necessary for counter‐balancing the progressive degradation of the extraction solvent and, as a result, to delay the gradual depletion of the efficiency of uranium recovery. Copyright © 2009 Society of Chemical Industry  相似文献   
190.
详细阐述本安三元配气装置的原理、特点及使用方法,该装置主要用于精确控制气体流量和控制气体的浓度,提高本安火花试验的精确度。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号