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   150篇
  免费   5篇
  国内免费   9篇
化学   124篇
力学   10篇
综合类   1篇
数学   4篇
物理学   25篇
  2023年   3篇
  2022年   6篇
  2021年   4篇
  2020年   2篇
  2019年   6篇
  2018年   7篇
  2017年   4篇
  2016年   5篇
  2015年   3篇
  2014年   6篇
  2013年   22篇
  2012年   10篇
  2011年   4篇
  2010年   3篇
  2009年   5篇
  2008年   11篇
  2007年   5篇
  2006年   5篇
  2005年   10篇
  2004年   3篇
  2003年   3篇
  2002年   4篇
  2001年   3篇
  2000年   3篇
  1999年   2篇
  1998年   1篇
  1997年   2篇
  1996年   3篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   1篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1986年   3篇
  1984年   2篇
  1982年   1篇
  1979年   2篇
排序方式: 共有164条查询结果,搜索用时 15 毫秒
61.
The effect of temperature of activation on bone charcoal, used as adsorbent for the removal of Patent Blue VF from water solutions was studied. The adsorbent was characterized by FTIR, XRD, SEM and EDS. The kinetic of adsorption of dye was carried out at 10 °C and 45 °C. Carbonization temperature (600–1000 °C) of the adsorbent has significant effect on the removal of dye from water solutions. The first order kinetic, Elovich, Bangham, parabolic diffusion and power function equations were found to fit the kinetic data. Activation energies of adsorption (Δ≠) have higher values for the charcoal activated at high temperatures and the other thermodynamic parameters like ΔH≠, ΔS≠ and ΔG≠ were also found.  相似文献   
62.
Perfluorinated surfactants of heptafluorobutylate and pentadecafluorooctanoate ions were adsorbed on an activated charcoal cartridge and decomposed with sodium biphenyl (SBP) reagent to form inorganic fluoride ion. The fluoride ion thus formed was determined by flow injection analysis (FIA) using quercetin-Zr complex as a fluorimetric reagent, where λex and λem were 422 and 491 nm, respectively. The limit of detection for fluoride ion by the FIA system was developed to 1.1 × 10−6 M (signal to noise ratio of three), when 50% (v/v) tetrahydrofuran (THF) was used as a dissolving solvent for quercetin. The perfluorinated surfactants in the sample solution were quantitatively adsorbed on the cartridge containing 100 mg of activated charcoal and were decomposed with 0.5 mL of sodium biphenyl reagent after drying thoroughly by flowing through dry nitrogen gas. The fluoride ion formed was recovered with 3 mL of purified water as an eluent, and it was determined by the fluorimetric flow injection system. The blank fluorescence signal accompanied during the adsorption/decomposition on the cartridge was reduced by washing the activated charcoal with acetone. The blank signal was also observed from dimethoxyethane, which was used in sodium biphenyl reagent. When 600 mL sample solution was used and 200 times enrichment was applied, the heptafluorobutylate and pentadecafluorooctanoate ions at the concentrations of 2.1 μg L−1 were quantitatively recovered as fluoride ion, and the limit of detections for the perfluorinated surfactants were 0.3 and 0.3 μg L−1 for the two perfluorinated surfactants, respectively (3 sigma of the blank signal).  相似文献   
63.
Summary Air sampling of ethylene oxide on active charcoal tubes followed by GC analysis is a frequently proposed method. This paper studies just to what extent it can be used, defining its limitations (concentration range, influence of ambient temperature and relative humidity), which are seldom taken seriously into account. This method proves inadequate to determine low pollution levels, i.e. around 2 mg m−3.  相似文献   
64.
The effects of polypyrrole coatings on the tensile and tribological properties of bamboo fiber reinforced polyamide 6 (PA6) composites were studied. Tribological tests were conducted using a block‐on‐ring arrangement. It was observed that the polypyrrole coatings played a main role in the tensile‐resistant and wear‐resistant properties of the PA6 composites. The tensile properties were ruled by the fiber‐matrix adhesion. And the excellent tribological performance of the fillers improved the tribological properties of PA6 composites. The optimum content of polypyrrole coating concentration is 7vol%.  相似文献   
65.
Passive methods for radon measurements, especially those based on radon adsorption, require observation of proper calibration methods.

The calibration method for diffusion-barrier charcoal detectors in a small (211 dm3) radon chamber has been proposed. The theoretical dependence of radon concentration vs. time inside the chamber during the exposure of charcoal detectors has been obtained and verified experimentally. For this purpose, the chamber volume as well as diffusion and adsorption parameters of the detector were taken into consideration.

For two types of detectors the conformity of calibration factors obtained in two ways: calculated from theoretical points (550 or 683 Bqm−3/cps depending on detector type) and from experimental points (553 or 691 Bqm−3/cps), was achieved.

The proposed method makes it possible to calibrate different kinds of radon-adsorbing detectors (not only charcoal canisters) in small chambers without the necessity of using any reference, active device.  相似文献   

66.
Substituted ethynyl heterocycles and heteroarylbutenynes are synthesized efficiently in good yields via a copper-free, cross-coupling reaction.  相似文献   
67.
《Analytical letters》2012,45(5):903-911
Abstract

In this report, we describe the finding that bamboo‐structured carbon nanotubes (CNT) showed superior electrocatalytic activity toward hydrogen peroxide. The slope of the calibration curve for hydrogen peroxide obtained with the bamboo‐structured CNT paste electrode was more than 20 times as large as the slopes obtained with hollow‐structured CNT paste and glassy carbon electrodes at an operating potential of ?0.1 V, with no interfering reactions. Incorporation of glucose oxidase within the bamboo‐structured CNT paste electrode allows the selective detection of glucose in the presence of common interferents without using any permselective membranes. This excellent ability of the bamboo‐structured CNT paste electrode toward hydrogen peroxide is applicable to the development of other enzymatic biosensors.  相似文献   
68.
In this work, bamboo charcoal (BC) was used as a sorbent for on-line solid phase extraction (SPE) coupling with flame atomic absorption spectrometry (AAS) for trace copper and zinc determination in environmental and biological samples. Under the optimum pH of 5.5 (for Zn) and 7.0 (for Cu), trace copper and zinc were effectively adsorbed on the microcolumn and the retained cations were efficiently eluted with HCl or HNO3 with an appropriate concentration and flow rate for on-line AAS determination. With a sample loading time of 60 s at a sample flow rate of 7.6 mL min?1, the enhancement factors of 39 (for Cu) and 30 (for Zn) and detection limits (3σ) of 0.60 µg L?1 (for Cu) and 0.36 µg L?1 (for Zn), respectively, were achieved. The sample throughput was 45 h?1. At the level of 20 µg L?1of Cu(II) and Zn(II), the precision (RSD, n?=?11) were found to be 0.26% and 1.6%, respectively. The proposed method has been successfully applied to the determination of copper and zinc in environmental and biological samples.  相似文献   
69.
In this Letter, an efficient and chemoselective deprotection of aryl- and styrenyldithioketals (acetals) is described. After being carefully examined, 10% Pd/C and Amberlite 120 in refluxing methanol was found to be an excellent condition for the chemoselective deprotection of aryl- and styrenyldithioketals (acetals) in good yields. Under this condition, no deprotection and no reduction of alkyldithioketals (acetals) was observed.  相似文献   
70.
采用原子吸收分光光度法测定了福建笋干中Mn、Fe、Cu、Zn、Mg、Ca等6种微量元素含量,发现其中Mg、Fe、Zn等含量均较高,远远高于25种蔬菜中的含量。结果表明,福建笋干中含有丰富的人体所需微量元素,提示福建笋干作为天然营养补充物质,具有较高的营养价值。  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