全文获取类型
收费全文 | 559篇 |
免费 | 31篇 |
国内免费 | 15篇 |
专业分类
化学 | 422篇 |
晶体学 | 3篇 |
力学 | 18篇 |
数学 | 69篇 |
物理学 | 93篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 21篇 |
2020年 | 37篇 |
2019年 | 18篇 |
2018年 | 40篇 |
2017年 | 20篇 |
2016年 | 43篇 |
2015年 | 24篇 |
2014年 | 40篇 |
2013年 | 67篇 |
2012年 | 58篇 |
2011年 | 56篇 |
2010年 | 41篇 |
2009年 | 39篇 |
2008年 | 28篇 |
2007年 | 26篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有605条查询结果,搜索用时 15 毫秒
11.
12.
13.
Zahra Taji Ali A. Ensafi Elahe Heydari-Soureshjani Behzad Rezaei 《Electroanalysis》2021,33(2):304-313
In this work, a modified 3D-rGO/MWCNT with nickel and copper oxide nanoparticles were synthesized. The structural properties of this nanocomposite were investigated by several techniques. The fabricated sensor at optimum condition potential of +0.60 V (vs. Ag/AgCl) and a rotational rate of 1800 rpm gave a detection limit of 0.04 μmol L−1 with two dynamic ranges of 0.10–300 and 300–900 μmol L−1 glucose with high stability. The good accuracy of the fabricated sensor was proved in the determination of glucose in a blood sample (with recoveries between 95 % to 105 % and RSDs of 1.2 to 2.5 %). 相似文献
14.
15.
Preparation,characterization and heterogeneous catalytic applications of GO/Fe3O4/HPW nanocomposite in chemoselective and green oxidation of alcohols with aqueous H2O2
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Graphene oxide ‐ Fe3O4 ‐ NH3+H2PW12O40 ‐ magnetic nanocomposite (GO/Fe3O4/HPW) was prepared by linking amino ‐ functionalized Fe3O4 nanoparticles (Fe3O4 ‐ NH2) on the graphene oxide (GO), and then grafting 12 ‐ tungstophosphoric acid (H3PW12O40) on the graphene oxide ‐ magnetite hybrid (GO ‐ Fe3O4 ‐ NH2). The obtained GO/Fe3O4/HPW nanocomposite was well characterized with different techniques such as FT ‐ IR, TEM, SEM, XRD, EDX, TGA ‐ DTA, AGFM, ICP and BET measurements. The used techniques showed that the graphene oxide layers were well prepared and the various stages of preparation of the GO/Fe3O4/HPW nanocomposites successfully completed. This new nanocomposite displayed excellent performance as a heterogeneous catalyst in the oxidation of alcohols with H2O2. The as ‐ prepared GO/Fe3O4/HPW catalyst was more stable and recyclable at least five times without significantly reducing its catalytic activity. 相似文献
16.
17.
Nanostructured γ-Al2O3 with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N2adsorption-desorption,TPR, TPO, TPH, NH3-TPD and SEM techniques. The BET analysis showed a high surface area of 204 m2 g-1and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and O2 to dry reforming feed increased the methane conversion and led to carbon free operation in combined processes. 相似文献
18.
Tungstate ions were successfully loaded onto triazine‐based ionic liquid‐functionalized magnetic nanoparticles through an anion exchange process. The use of triazine core for creating ionic liquid led to the immobilization of high amounts of WO42?. The resulting catalyst showed high activity and selectivity in the oxidation of sulfides to sulfoxides with H2O2 as a green oxidant at room temperature. In addition, due to the presence of ammonium groups in the catalyst structure, water dispersibility of the catalyst was increased. More important, the catalyst was magnetically recovered and reused for up to six runs without any marked decrease of activity and selectivity. Finally, easy gram‐scale oxidation of methylphenyl sulfide as well as fast separation of catalyst and product makes the protocol economical and industrially applicable. 相似文献
19.
A heterogeneous magnetic copper catalyst was prepared via anchoring of copper sulfate onto multi‐layered poly(2‐dimethylaminoethyl acrylamide)‐coated magnetic nanoparticles and was characterized using various techniques. The catalyst was found to be active, effective and selective for one‐pot three‐component reaction of alkyl halide, sodium azide and alkyne, known as copper‐catalyzed click synthesis of 1,2,3‐triazoles. As little as 0.3 mol% of catalyst was found to be effective under the optimum conditions. The catalyst could also be recycled and reused up to seven times without significant loss of activity. Thermal stability, high loading level of copper on catalyst, broad diversity of alkyl/benzyl/allyl bromide/chloride and alkyl/aryl terminal alkynes without isolation of azide intermediate, and good to excellent yields of products make this procedure highly economical. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
20.
Qamrul Hasan Ansari Mahboubeh Rezaei 《Journal of Optimization Theory and Applications》2012,153(3):587-601
In this paper, we introduce the notion of invariant pseudolinearity for nondifferentiable and nonconvex functions by means
of Dini directional derivatives. We present some characterizations of invariant pseudolinear functions. Some characterizations
of the solution set of a nonconvex and nondifferentiable, but invariant, pseudolinear program are obtained. The results of
this paper extend various results for pseudolinear functions, pseudoinvex functions, and η-pseudolinear functions, and also for pseudoinvex programs, pseudolinear programs, and η-pseudolinear programs. 相似文献