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   103篇
  免费   12篇
  国内免费   10篇
化学   87篇
力学   2篇
综合类   1篇
数学   13篇
物理学   22篇
  2023年   3篇
  2022年   2篇
  2021年   5篇
  2020年   6篇
  2019年   1篇
  2017年   1篇
  2016年   5篇
  2015年   8篇
  2014年   1篇
  2013年   2篇
  2012年   3篇
  2011年   12篇
  2010年   8篇
  2009年   9篇
  2008年   3篇
  2007年   1篇
  2006年   6篇
  2005年   5篇
  2004年   17篇
  2003年   8篇
  2002年   6篇
  2001年   4篇
  2000年   2篇
  1999年   4篇
  1997年   1篇
  1996年   1篇
  1993年   1篇
排序方式: 共有125条查询结果,搜索用时 15 毫秒
111.
无机固体酸催化合成乙酸乙酯   总被引:10,自引:0,他引:10  
介绍了利用一水硫酸氢钠、六水三氯化铁、五水四氯化锡、十二水合硫酸铁铵和水合硫酸铁催化乙醇和乙酸制备乙酸乙酯的方法。  相似文献   
112.
水中苯胺类化合物的分光光度法测定   总被引:24,自引:0,他引:24  
提出3种测定水中苯胺类化合物的分光光度法,在氢氧化钠介质(PH=12.2)中,邻甲氰基苯酚、8-羟基喹啉和1-萘酚均可与苯胺形成偶氮化合物,它们的最大吸收波长分别位于452、482和497nm处,与传统的N-(1-萘基)乙二胺光度法相比,这3种方法测定苯胺更方便,快速、灵敏,线性范围更宽;它们的检出下限分别为8.6、10、14μg/L;线性范围分别为0-5.6、0-4.8和0-3.2mg/L。这3种方法用于测定环境水样中的苯胺类化合物,均获得了满意的结果。  相似文献   
113.
In this paper the auther begins with some known results about η_λ(=the least cardinal K such that K→(λ)~<∞), proving this theorem: If λ is not Ramsey cardinal and η_λ exists, then for every a<η_λ there is a weakly compact cardinal γ, such that λ<γ_α<η_λandγ_α<γ_βwhenever a<β<η_λ, therefore η_λ is the limit of the sequence(γ_α:a<η_λ), i.e. η_λ=limγ_α. The theorem is mainly based on the theory of models with indiscernibles.  相似文献   
114.
NdFeO3纳米晶的合成及气敏性能   总被引:7,自引:1,他引:7  
以Nd2O3,Fe(NO3)3·9H2O,硝酸(1∶1)为原料,在柠檬酸体系中用溶胶凝胶法合成了具有钙钛矿结构的稀土复合氧化物NdFeO3;用XRD和TEM对产物的组成、颗粒大小、形貌进行了表征;结果表明:产物为纳米颗粒,平均粒径为28nm左右,且颗粒均匀。还采用静态配气法测试了材料的气敏性能,发现NdFeO3对H2S有很高的灵敏度,且抗干扰能力强,有较好的工业应用前景。  相似文献   
115.
Introduction Many examples of complexes containing the eight-membered ring M(-dppm)M' are known with a variety of metals, oxidation states and stereochemis-tries.1-4 In general, they contain trans-bound, bridging dppm ligands to give a planar M2P4 core structure with the two metal atoms held in close proximity to each other (regardless of whether a metal-metal bond is pre-sent or not). This feature is presumably one of the chief reasons for the unusual bonding, reactivity and catalytic prope…  相似文献   
116.
Xanthenedione derivatives have held considerable interests in recent years, since theyconstitute a structural unit in a number of natural products1 and have been used asversatile synthons because of the inherent reactivity of the inbuilt pyran ring2. Usually,poly-hydrogenated xanthenediones (3, Scheme 1) can be obtained through the acid orbase catalyzed condensation of appropriate active methylene carbonyl compounds withaldehydes. But this method is not very satisfactory because of the prolong…  相似文献   
117.
Previous studies have reported a lateral migration in particle electrophoresis through a straight rectangular microchannel. This phenomenon arises from the inherent wall‐induced electrical lift that can be exploited to focus and separate particles for microfluidic applications. Such a dielectrophoretic‐like force has been recently found to vary with the buffer concentration. We demonstrate in this work that the particle zeta potential also has a significant effect on the wall‐induced electrical lift. We perform an experimental study of the lateral migration of equal‐sized polystyrene particles with varying surface charges under identical electrokinetic flow conditions. Surprisingly, an enhanced focusing is observed for particles with a faster electrokinetic motion, which indicates a substantially larger electrical lift for particles with a smaller zeta potential. We speculate this phenomenon may be correlated with the particle surface conduction that is a strong function of particle and fluid properties.  相似文献   
118.
An efficient synthesis of 2, 3-disubstituted indole derivatives through low-valent titanium induced reductive cyclization of acylamido carbonyl compounds is described.  相似文献   
119.
Shen Y  Han C  Jiang Y  Zhou X  Zhu Z  Lei X 《Talanta》2011,84(4):S106-1031
A new method based on pressurised liquid extraction (PLE) followed by liquid chromatography-triple quadrupole linear ion trap mass spectrometry (LC-QTrap-MS) analysis has been developed for the identification and quantification of four major alkaloids in extracts of Corydalis decumbens (Thunb.) Pers. PLE extractions were performed using 90% ethanol; temperature was set at 100 °C and pressure at 1500 psi. HPLC analysis was performed on a Waters XBridge™ C18 column (150 mm × 2.1 mm i.d., 3.5 μm) eluted by a mobile phase of acetonitrile and 0.2% acetic acid. Data acquisition was carried out in multiple reaction monitoring transitions (MRMs) mode, monitoring two MRM transitions to ensure an accurate identification of target compounds in the samples. Additional identification and confirmation of target compounds were performed using the enhanced product ion modus (EPI) of the linear ion trap. The novel LC-QTrap-MS platform offers the best sensitivity and specificity for characterization and quantitative determination of the four alkaloids in C. decumbens (Thunb.) Pers. and fulfils the quality criteria for routine laboratory application.  相似文献   
120.
A CrO3 catalyzed oxidation of homopropargyl alcohols with tert-butyl hydroperoxide under microwave irradiation was found to be an efficient and rapid alternative for the preparation of 1,2-allenic ketones.The advantages of this procedure include short reaction time,less adverse impact on the environment and reasonably high efficiency.  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