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   1646篇
  免费   111篇
  国内免费   46篇
电工技术   407篇
综合类   81篇
化学工业   434篇
金属工艺   138篇
机械仪表   46篇
建筑科学   29篇
矿业工程   17篇
能源动力   103篇
轻工业   76篇
水利工程   11篇
石油天然气   12篇
武器工业   7篇
无线电   74篇
一般工业技术   227篇
冶金工业   69篇
原子能技术   46篇
自动化技术   26篇
  2024年   11篇
  2023年   13篇
  2022年   22篇
  2021年   33篇
  2020年   35篇
  2019年   25篇
  2018年   52篇
  2017年   43篇
  2016年   48篇
  2015年   40篇
  2014年   96篇
  2013年   125篇
  2012年   165篇
  2011年   165篇
  2010年   135篇
  2009年   136篇
  2008年   104篇
  2007年   143篇
  2006年   100篇
  2005年   70篇
  2004年   43篇
  2003年   47篇
  2002年   21篇
  2001年   36篇
  2000年   26篇
  1999年   20篇
  1998年   10篇
  1997年   5篇
  1996年   8篇
  1995年   8篇
  1994年   4篇
  1993年   1篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   4篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
排序方式: 共有1803条查询结果,搜索用时 0 毫秒
51.
以苯胺、邻硝基氯苯为原料,采用直接缩合法引入相转移催化剂合成邻硝基二苯胺。对影响反应的各种因素进行了研究,通过正交实验确定了缩合反应最佳工艺条件:邻硝基氯苯:K2CO3:PEG=1:0.55:0.015,反应温度为185℃,反应时间为2h。反应收率为99.1%。该方法是邻硝基二苯胺的最佳合成工艺。  相似文献   
52.
聚醚增韧酚醛树脂及其泡沫的研究   总被引:5,自引:3,他引:5  
本文介绍了两类聚醚改性剂-PEG和活性聚醚增韧酚醛树脂及其泡沫的方法和工艺。对一系列不同分子量PEG和活性聚醚改性酚醛树脂的力学性能进行了比较,同时研究了各种改性酚醛泡沫的尺寸稳定性、压缩强度及表观密度等;并对几种改性酚醛泡沫和未改性酚醛泡沫进行了电子显微镜扫描泡孔结构的研究和红外分析;结果表明,树脂中导入活性聚醚的柔性链段,可使酚醛树脂及其泡沫的韧性及综合性能得到明显的改善,其中尤以分子量为1000活性聚醚改性树脂及其泡沫的各种性能为优。  相似文献   
53.
Polyethylene glycol (PEG) glucosides (PEGG) and the PEGG esters of lauric acid were analyzed by atmospheric-pressure ionization MS (API-MS) with electrospray ionization. Straightforward mass characterization of the complex mixtures could be achieved without prior chromatographic separation. The constituents were identified on the basis of quasi-molecular ions. Individual components could be observed as protonated molecular ions [M+H]+ and/or as their NH4 +, Na+, or K+ adducts in positive ion mode. The mass spectrometric investigation showed that mixtures of PEGG consisted of monoglucoside, diglucoside, polyglucoside, and free PEG. The esterification product is a mixture of two types of nonionic surfactants: PEG-laurates and PEGG-laurates. The reasons for distortion of the quasi-molecular ion intensities and the stabilization of adduct ions were discussed. The rapid and highly sensitive API-MS analysis technique proposed here is well suited for direct characterization of complex mixtures and suitable for development as a routine analytical method.  相似文献   
54.
以聚乙二醇(PEG)为模板制备了纳米氧化铜。以一种高分子材料为包覆材料自组装制备了纳米铝/氧化铜(Al/CuO)复合材料。采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能谱仪(EDS)、X射线衍射(XRD)等对材料的结构形貌进行了表征。利用热重分析法(TG)和差示扫描量热法(DSC)对比研究了自组装法(含包覆材料)与超声共混法(不含包覆材料)制得样品的热性能。研究了不同Al与CuO摩尔比下Al/CuO复合材料的放热量。结果表明,纳米铝与CuO发生铝热反应的放热峰约为576.4℃,放热量达1 093J/g。含有包覆材料的复合材料比不含包覆材料的复合材料具有更大的放热量。在纳米铝与CuO摩尔比为1.0∶1.2时铝热反应放热量最大,可达1 093J/g。  相似文献   
55.
The work presents density (ρ) and viscosity (η) data of binary system polyethylene glycol 600 (PEG) + dimethyl sulfoxide (DMSO) over the entire concentration range at T =(298.15,303.15,308.15,313.15 and 318.15) K and atmospheric pressure.On the basis of density and viscosity values,the excess properties of PEG (1) + DMSO (2) mixtures,including excess molar volume (VEm),viscosity deviation (△η),excess free energies of activation (△G*E),and isobaric thermal expansion coefficient (αp),were calculated.At the same time,in order to conjecture the density viscosity under different conditions,the density and viscosity data were fitted with the corresponding formula.The calculated results of VEm,△η,and △G*E were fitted with the Redlich-Kister equation to derive coefficients and estimate the standard deviations (σ) between the experimental and calculated values.Moreover,the intermolecular interaction of PEG with DMSO was discussed on the basis of FTIR and UV-Vis spectral results of PEG (1) + DMSO (2) mixtures.The results indicated that there were the hydrogen bonding and interactions of hvdroxvl hydrogen atoms in PEG with oxygen atoms in DMSO.  相似文献   
56.
以6-氯嘌呤衍生物为原料,使用PEG1000-DAIL为催化剂,在相应的醇溶剂中回流反应合成了一系列6-烷氧基嘌呤衍生物。聚乙二醇酸性双子离子液体(PEG1000-DAIL)作为催化剂具有优良的催化性能,反应条件温和,多次重复使用能保持很高的催化活性,损失量小,避免了资源的浪费。  相似文献   
57.
将聚乙二醇单甲醚(mPEG)醛化改性后,通过西佛碱反应接枝到自制的O-季铵化壳聚糖的NH2上,硼氢化钠还原制得N-mPEG接枝O-季铵化壳聚糖(QACS-mPEG),反相悬浮法制备二乙烯基砜交联QACS-mPEG微球。用FTIR、1 H NMR、EA和SEM对产物进行表征,并且以酮洛芬为模型药物研究微球的载药性能及释放行为。结果表明,mPEG和季铵盐基团的引入提高了N-mPEG-O-季铵化壳聚糖微球的载药量,为4.31mg/mg;载药N-mPEG-O-季铵化壳聚糖微球在模拟肠液的缓释效果优于胃液,微球释药具有pH响应性。  相似文献   
58.
Chronoflex, a polyurethane, is a suitable material for use in polymeric tracheobronchial stents. A controlled release layer on the stent is required for effective localized delivery of cancer drugs to the tumor cells. This paper reports on the investigation of coating Chronoflex with acrylated oligomers by argon plasma assisted UV graft polymerization. Coatings of poly(ethylene glycol) diacrylate (PEGDA) with molecular weight 700 or a 50 : 50 mixture of PEGDA with poly(propylene glycol) diacrylate (PPGDA) with molecular weight 900 which were tens of micrometers thick were shown to have good adhesion to Chronoflex. No photoinitiator was added. Formulations containing photoinitiator or a trifunctional crosslinker which increases strength and decreases water swelling showed poor adhesion to Chronoflex. The degree of water swelling of grafted PEGDA coating reached about 709%, making it suitable for use as a hydrogel coating for controlled drug release on Chronoflex. Adding PPGDA to PEGDA was shown to decrease the degree of water swelling. Hence, removal of the photoinitiator, use of oligomeric diacrylate with high molecular weight per acrylate group and a clean Chronoflex surface are found to be important factors for ensuring adhesion between the thick hydrogel coating and Chronoflex.  相似文献   
59.
工艺条件对ZrO2粒度的影响   总被引:2,自引:0,他引:2  
武志胜 《纤维复合材料》2005,22(4):33-35,49
以工业ZrOCl2·8H2O和分析纯Nh3·H2O为主要原料,采用化学沉淀法制备了ZrO2纳米粒子,研究了不同阶段添加表面活性剂聚乙二醇(PEG)对ZrO2粉体颗粒尺寸的影响机理.通过测定ZrO2粉体比表面积计算出其粒度在10~40nm之间.  相似文献   
60.
Chun Zhang  Douglas E. Hirt 《Polymer》2005,46(22):9257-9264
Dansyl cadaverine and polyethylene glycol (PEG) derivatives were grafted on the surface of EAA film and in its subsurface region through formation of amides and esters, respectively. A two-step reaction was conducted. First, EAA film was activated with PCl5 at room temperature. Second, the acid chloride was reacted with dansyl cadaverine or a PEG derivative to form a modified film. ATR-FTIR spectroscopy and fluorometry were employed to analyze the modified films after each step. It was found that dichloromethane yielded the highest grafting efficiency, with the dansyl cadaverine penetrating throughout the ATR-FTIR analysis region (∼400 nm) in a few minutes. As the grafting depth increased with time, so did the amount of fluorescence intensity of grafted dansyl cadaverine. ATR-FTIR spectra for PEG grafting indicated that the acid chloride peak decreased with time, while the ester peak increased. However, hydrolysis occurred at later times, consuming the acid chloride groups within the film. A marked decrease of static water contact angle was observed for EAA grafted with PEG99 (PEG that contains 99 ethylene glycol repeat units), almost 40° lower than that of neat EAA (∼99°). For other PEG-grafted films, the surface hydrophilicity was also improved.  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