全文获取类型
收费全文 | 947篇 |
免费 | 48篇 |
国内免费 | 23篇 |
专业分类
化学 | 848篇 |
晶体学 | 4篇 |
力学 | 21篇 |
数学 | 64篇 |
物理学 | 81篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 38篇 |
2020年 | 64篇 |
2019年 | 56篇 |
2018年 | 80篇 |
2017年 | 41篇 |
2016年 | 75篇 |
2015年 | 54篇 |
2014年 | 73篇 |
2013年 | 131篇 |
2012年 | 69篇 |
2011年 | 75篇 |
2010年 | 54篇 |
2009年 | 47篇 |
2008年 | 43篇 |
2007年 | 29篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 3篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有1018条查询结果,搜索用时 31 毫秒
811.
812.
Sobhan Rezayati Fatemeh Sheikholeslami-Farahani Faramarz Rostami-Charati Saeid Afshari Sharif Abad 《Research on Chemical Intermediates》2016,42(5):4097-4107
Pechmann condensation reaction of 3-hydroxyphenol and ethyl acetoacetate in the presence of 1,1′‐butylenebispyridinium hydrogen sulfate as an efficient, green, and recyclable catalyst produces 7-hydroxy-4-methylcoumarin in good yield under solvent-free conditions at room temperature. This catalyst has advantages such as the following: good to excellent yields, short reaction times, simplicity in operation, and easy workup procedure. 相似文献
813.
814.
Journal of Solution Chemistry - An attempt to understand the interactions between metformin, a drug, and a water-soluble polymer, polyethylene glycol (PEG 4000) in aqueous solutions through... 相似文献
815.
Kazem Karami Ali Reza Allafchian Razieh Amiri Fatemeh Shirani Parvaneh Bayat Behzad Rezaei 《应用有机金属化学》2019,33(6)
The Glucose amount of human blood is very vital because in higher levels than allowed value the corporal biological system was hampered. Therefore, in this study, the Cu2O was deposited on the reduced Graphene oxide (RGO) by polydopamin (PDA) as linker. The new RGO‐PDA‐Cu2O nanocomposite was deposited on the glassy carbon electrode (GCE) surface after its characterization by UV–Visible, fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), Energy‐dispersive X‐ray (EDX), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) techniques. The electroanalysis of the new electrode was investigated by the cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) methods. The obtained detection limit of glucose (Glu) showed that the deposited GCE by RGO‐PDA‐Cu2O nanocomposite has a high potential for its diagnosis. In addition, this electrode was applied to the Glu detection as biosensor in real samples in order to utilize in commercial applications. 相似文献
816.
In this study, 2‐aminopyridine functionalized magnetite nanoparticles were chemically synthesized and used for removing Cd2+ ions from aqueous solutions. The synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis of X‐rays (EDX), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). The SEM results showed the synthesized magnetite nanoparticles have particle size around 26 nm. The effects of several variables including solution pH and volume, adsorbent mass, ionic strength and contact time on the Cd2+ adsorption were studied in batch experiments and finally the optimum conditions for adsorption were obtained. The kinetic data were investigated by pseudo‐ first‐order, pseudo‐ second‐order, intraparticle diffusion and Elovich kinetic models and data were described reasonably by pseudo‐ second‐order model (R2 = 0.9996) with qe = 2.31 mg g?1. Adsorption data were analyzed using Langmuir, Freundlich and Temkin isotherm models. The results indicated that the data were well fitted to the Freundlich isotherm model (R2 = 0.9907). After study the possible interference effect of foreign ions on Cd2+ removal, the applicability of the proposed nanoparticles for adsorption from real samples confirmed the successfully removal of Cd2+ ions with removal efficiency higher than 92%. The obtained results showed that the synthesized nanoparticles as a reusable adsorbent can act as a good choice for Cd2+ removal with an easy procedure. 相似文献
817.
Hydrothermal carbonization of salep as a domestic biosource was carried out to afford a biochar, BC, with exceptional catalytic activity. BC can be further magnetized by incorporation of magnetic nanoparticles to furnish a magnetic catalyst, BC‐Fe, with improved recovery and recyclability for the hydrogenation of nitroarenes in the absence of any precious metal. BC‐Fe was also applied as a catalyst support for the immobilization of Pd nanoparticles and development of an efficient, biocompatible and cost‐effective catalyst, Pd@BC‐Fe, with utility for the oxidation of benzyl alcohols under mild reaction condition in a selective manner to afford corresponding acids in high yields. The study of the recyclability of the catalyst confirmed high recyclability of Pd@BC‐Fe. 相似文献
818.
Fatemeh Alemi Tameh Javad Safaei-Ghomi 《Journal of the Iranian Chemical Society》2018,15(7):1633-1637
Magnetic nanoparticles (MNPs) Fe3O4-immobilized guanidine (Fe3O4 MNPs-guanidine) have been used as an efficient catalyst for the preparation of spiro[pyrazoloquinoline-oxindoles] and spiro[chromenopyrazolo-oxindoles] by four-component reactions of phenylhydrazine or hydrazine hydrate, isatins, ketoesters and naphthylamine or 2-naphthol under reflux condition in ethanol. This method provides several advantages including mild reaction conditions, the applicability to a wide range of substrates, the reusability of the catalyst and low catalyst loading. 相似文献
819.
A phenoxybutane‐based Schiff base complex of cis‐dioxo‐Mo(VI) was supported on paramagnetic nanoparticles and characterized using powder X‐ray diffraction, infrared, diffuse reflectance and atomic absorption spectroscopies, scanning and transmission electron microscopies and vibrating sample magnetometry. The separable nanocatalyst was tested for the selective epoxidation of cyclohexene, cyclooctene, styrene, indene, α‐pinene, 1‐octene, 1‐heptene, 1‐dodecene and trans‐stilbene using tert‐butyl hydroperoxide (80% in di‐tert‐butyl peroxide–water, 3:2) as oxidant in chloroform. The catalyst was efficient for oxidation of cyclooctene with 100% selectivity for epoxidation with 98% conversion in 10 min. We were able to separate magnetically the nanocatalyst using an external magnetic field and used the catalyst at least six successive times without significant decrease in conversion. The turnover frequency of the catalyst was remarkable (2556 h?1 for cyclooctene). The proposed nanomagnetic catalyst has advantages in terms of catalytic activity, selectivity, catalytic reaction time and reusability by easy separation. 相似文献
820.
Preparation of novel palladium nanoparticles supported on magnetic iron oxide and their catalytic application in the synthesis of 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols
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)
Novel Pd nanoparticles were prepared in five successive stages: 1) preparation of the Fe3O4 magnetic nanoparticles (Fe3O4 MNPs), 2) coating of Fe3O4 MNPs with SiO2 (Fe3O4@SiO2), 3) functionalization of Fe3O4@SiO2 with 3‐chloropropyltrimethoxy‐ silane (CPTMS) ligand (Fe3O4@SiO2@CPTMS), 4) further functionalization with 3,5‐diamino‐1,2,4‐triazole (DAT) ligand (Fe3O4@SiO2@CPTMS @DAT), and 5) the complexation of Fe3O4@SiO2@CPTMS@DAT with PdCl2 (Fe3O4@SiO2@CPTMS@ DAT@Pd). Then, the obtained Pd nano‐catalyst characterized by different methods such as the elemental analysis (CHN), FT‐IR, XRD, EDX, SEM, TEM, TG‐DTA and VSM. Finally, the Pd catalyst was applied for the synthesis of various 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols. 相似文献