全文获取类型
收费全文 | 140篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 83篇 |
晶体学 | 4篇 |
力学 | 11篇 |
数学 | 22篇 |
物理学 | 26篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 10篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 9篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1989年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有146条查询结果,搜索用时 15 毫秒
91.
Hassen Khazri Ibtissem Ghorbel‐Abid Sihem Ben Hassine Sylvie Chevolleau Laurent Debrauwer Rafik Kalfat Malika Trabelsi‐Ayadi 《Journal of separation science》2019,42(9):1710-1716
In this work, clay‐Na particles are used as the adsorbent for the solid‐phase extraction of acidic compounds. The novel sorbent under study is based on high‐specific surface area, cation‐exchange capacity designed specifically to offer ion‐exchange properties with the goal being to selectively extract a group of acidic compounds. The effects of the extraction parameters including extraction elution solvent, sample volume and pH. In optimum conditions, the repeatability for one fiber (n = 3), expressed as % relative standard deviation, was between 0.3 and 4.3% for the acid compounds. The detection limits for the studied acidic compounds were between 0.1–0.6 μg/L. The developed method offers the advantages of being simple to use and having a low cost of equipment. 相似文献
92.
93.
Hassen Aydi 《Journal de Mathématiques Pures et Appliquées》2008,89(1):49-69
For disc domains and for periodic models, we construct solutions of the Ginzburg–Landau equations which verify in the limit of a large Ginzburg–Landau parameter specified qualitative properties: the limit density of the vortices concentrates on lines. 相似文献
94.
B. Ilahi L. Sfaxi F. Hassen H. Maaref B. Salem G. Guillot A. Jbeli X. Marie 《Applied Physics A: Materials Science & Processing》2005,81(4):813-816
Room temperature 1.3 μm emitting InAs quantum dots (QDs) covered by an In0.4Ga0.6As/GaAs strain reducing layer (SRL) have been fabricated by solid source molecular beam epitaxy (SSMBE) using the Stranski–Krastanov growth mode. The sample used has been investigated by temperature and excitation power dependent photoluminescence (PL), photoluminescence excitation (PLE), and time resolved photoluminescence (TRPL) experiments. Three emission peaks are apparent in the low temperature PL spectrum. We have found, through PLE measurement, a single quantum dot ground state and the corresponding first excited state with relatively large energy spacing. This attribute has been confirmed by TRPL measurements which allow comparison of the dynamics of the ground state with that of the excited states. Optical transitions related to the InGaAs quantum well have been also identified. Over the whole temperature range, the PL intensity is found to exhibit an anomalous increase with increasing temperatures up to 100 K and then followed by a drop by three orders of magnitude. Carrier’s activation energy out of the quantum dots is found to be close to the energy difference between each two subsequent transition energies. PACS 68.65.Ac; 68.65.Hb; 78.67.Hc 相似文献
95.
DSC, TGA and dielectric properties of carboxymethyl cellulose/polyvinyl alcohol blends 总被引:1,自引:0,他引:1
Films with different compositions of polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) blends have been prepared using the casting method. Differential scanning calorimetery (DSC), thermogravimetric analysis (TGA) and dielectric spectroscopy of all compositions have been investigated. It was found that PVA and CMC are compatible in the studied range of composition. With increasing CMC content, the thermal stability of PVA increases. Based on DSC and TGA data, the activation energies of all the investigated samples were calculated. The absorption edge (Ea) was also determined from Ultraviolet-visible (UV-vis) spectra.Dielectric permittivity, loss tangent and ac conductivity of all samples were studied as functions of temperature and frequency. The results show that the dielectric dispersion consists of both dipolar and interfacial polarization. The frequency dependence of the ac conductivity indicates that the correlated barrier hopping (CBH) is the most suitable mechanism for conduction. The polaron binding energy (UM) was determined. Results of the present system are compared with those of similar materials. 相似文献
96.
Afef Ghouili Michal Dusek Vaclav Petricek Taïcir Ben Ayed Rached Ben Hassen 《Journal of Physics and Chemistry of Solids》2014
A new coumarin chalcone 3-((2E)-3-(2-hydroxyphenyl) prop-2-enoyl)-4-hydroxy-2(H)-chromen-2-one was synthesized using the Claisen Schmidt reaction by the condensation of 3-acetyl-4-hydroxycoumarin and 2-hydroxybenzaldehyde using a mild organic base. This novel compound was characterized by 1H NMR, FT-IR and UV–vis spectroscopy. Single crystal X-ray diffraction investigation at low temperature (T=120 K) shows that this compound exhibits an intramolecular O3–H…O hydrogen bond, the coumarin ring and the phenyl group are nearly coplanar and the crystal packing is stabilized by intermolecular O3–H…O contacts and π–π stacking interactions. This ortho-hydroxyphenyl-4-hydroxycoumarin chalcone exhibits a strong blue-green emission under visible light excitation at 470 nm. The fluorescence behaviors of this compound doped in poly(methyl methacrylate) (PMMA) were investigated. 相似文献
97.
98.
The synthesis of gamma-functionalized cyclopentenones was carried out in a few steps, starting firstly with the preparation of nitroketonic intermediates 2, which were readily transformed into 1,4-diketones using the Nef conversion. The intramolecular cyclization of the gamma-diketones 3 in a basic medium, led to the functionalized cyclopentenones 4. 相似文献
99.
100.
Hassen Bel Abed Nils Weißing Jens Schoene Jannik Paulus Norbert Sewald Marc Nazaré 《Tetrahedron letters》2018,59(19):1813-1815
A simple and novel methodology for the synthesis of 3-perfluoroalkylated-2H-indazole derivatives has been elaborated. The perfluoroalkylation of readily available 2-nitrobenzaldimines bearing electron donating groups was performed using the Ruppert-Prakash reagent and its analogues to afford α-difluoromethylated, α-trifluoromethylated and α-pentafluoroethylated benzylamines. A final reductive cyclization mediated by SnCl2·2H2O led to 2H-indazoles containing perfluoroalkyl groups via the generation of a new NN bond in moderate to good yields. 相似文献