全文获取类型
收费全文 | 111篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 66篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 20篇 |
物理学 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 2篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1997年 | 1篇 |
1993年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有117条查询结果,搜索用时 78 毫秒
91.
Optical Review - Multimode fibers (MMF) are enjoying a renewed attention boosted by recent advances in multimode complex nonlinear optics. Reason behind nonlinearity is occurred either due to... 相似文献
92.
Faouzi Mahdhaoui Rania Zaier Nejeh Dhahri Sahbi Ayachi Taoufik Boubaker 《国际化学动力学杂志》2019,51(4):249-257
A kinetic study is reported for the reactions of 2-methoxy-3-nitropyridine 1a and 2-methoxy-5-nitropyridine 1b with three secondary amines 2a–c (morpholine, piperidine, and pyrrolidine) in aqueous solution at 20°C. The Brønsted-type plots are linear with βnuc = 0.52 and 0.55 for pyridines 1a and 1b , respectively, indicating that the reaction proceeds through a SNAr mechanism in which the first step is the rate-determining step. Additional theoretical calculations using the DFT/B3LYP method confirm that the C-2 carbon being the most electrophilic center for the both pyridines 1a and 1b . The second-order rate constants have been used to evaluate the electrophilicity parameters E of 1a and 1b according to the linear free energy relationship log k (20°C) = sN (N + E). The E parameters thus derived are compared with the electrophilic reactivities of a large variety of anisoles. The validity of these E values has been satisfactorily verified by comparison of calculated and experimental second-order rate constants for the reactions of pyridines 1a and 1b with anion of ethyl benzylacetate. 相似文献
93.
The (C7H12N2)2[SnCl6]Cl2·1.5H2O complex is a new member of the family of hybrid organic–inorganic perovskite compounds. It exhibits two order–disorder phase transitions with changes in the conformation of aromatic cations at the two transition temperatures 360 and 412 K. Differential scanning calorimetry, nuclear magnetic resonance (NMR), and Fourier-transform infrared (FT-IR) spectroscopy were used to investigate these phase transitions. These transition mechanisms were investigated in terms of the spin–lattice relaxation times T1 for 1H static NMR and the chemical shifts for 13C CP–MAS. The temperature dependence of T1(1H) and 13C chemical shifts are changed near TC1 and TC2. Furthermore, the splitting for 13C NMR signals in Phases (II) and (III) indicated a ferroelastic characteristic of the compound. In addition, FT-IR results indicate that the ordered conformational structure of aromatic cations undergoes a remarkable disorder with increasing temperature. The NMR and FT-IR studies suggest that the phase transition mechanisms are related to the reorientational motion of [C7H12N2]2+ cations as a whole. Phase transition was examined in light of the interesting optical properties of this material. 相似文献
94.
Nesrine Hafedh Faouzi Aloui Vincent Dorcet Houcine Barhoumi 《Comptes Rendus Chimie》2018,21(7):652-658
A short and efficient synthetic pathway leading to a new chiral π-conjugated system is reported. The X-ray structure of the target compound was determined and showed a helical conformation. Its resolution was successfully accomplished, leading to two enantiomers in high optical purity, and their chiroptical properties were examined experimentally. The photophysical properties of the organic material were also evaluated, showing an emission in the visible region, and HOMO and LUMO levels have been estimated experimentally, demonstrating an electrochemical band gap of 2.37 eV. 相似文献
95.
96.
Fatimah Mohammed Alzahrani Norah Salem Alsaiari Khadijah Mohammedsaleh Katubi Abdelfattah Amari Abubakr M. Elkhaleefa Faouzi Ben Rebah Mohamed A. Tahoon 《Molecules (Basel, Switzerland)》2021,26(16)
We report in the present study the in situ formation of magnetic nanoparticles (Fe3O4 or Fe) within porous N-doped carbon (Fe3O4/N@C) via simple impregnation, polymerization, and calcination sequentially. The synthesized nanocomposite structural properties were investigated using different techniques showing its good construction. The formed nanocomposite showed a saturation magnetization (Ms) of 23.0 emu g−1 due to the implanted magnetic nanoparticles and high surface area from the porous N-doped carbon. The nanocomposite was formed as graphite-type layers. The well-synthesized nanocomposite showed a high adsorption affinity toward Pb2+ toxic ions. The nanosorbent showed a maximum adsorption capacity of 250.0 mg/g toward the Pb2+ metallic ions at pH of 5.5, initial Pb2+ concentration of 180.0 mg/L, and room temperature. Due to its superparamagnetic characteristics, an external magnet was used for the fast separation of the nanocomposite. This enabled the study of the nanocomposite reusability toward Pb2+ ions, showing good chemical stability even after six cycles. Subsequently, Fe3O4/N@C nanocomposite was shown to have excellent efficiency for the removal of toxic Pb2+ ions from water. 相似文献
97.
In the present work, linear polystyrene (PS) was functionalized by a sulfonation reaction providing sulfonated polystyrene (PSS). Then, the PSS polymer chains were cross-linked with the 1,4-phenylene diisocyanate (PPDI) group in tetrahydrofuran (THF), which led to a PSS-PPDI polymer. The PSS-PPDI was grafted by diethylenetriamine (DETA) in a solution of THF to obtain polymer PSS-PPDI-DETA. Their structures were characterized by infrared spectroscopy (ATR-FTIR), elemental analysis (EA), differential scanning calorimetry (DSC), thermogravemetric (TGA), thermodynamic (DTA) and differential thermogravimetric (DTG) analysis. Subsequently, the obtained polymers were tested for their ability to remove some metal ions from aqueous media such as Zn2+, Cd2+ and Co2+. 相似文献
98.
Alassane Sidibe Frédérique Gadot Benoit Belier Guillaume Bordier Davide Cammilleri Adnan Ghribi Andrea Tartari Michel Piat Joseph Martino François Pajot Faouzi Boussaha 《Applied Physics A: Materials Science & Processing》2014,117(2):523-526
Designed for astrophysical applications, this coupler must be as small as possible to be integrated in a low temperature superconducting detection chain. By using metamaterials, dimensions can be reduced and performances enhanced compared with a conventional coupler. The novelty of the work presented in this paper is a coupler that operates at millimeter waves (W band) and cryogenic temperatures (4 K) for astrophysics applications and more precisely for the detection of the cosmological microwave background radiation. 相似文献
99.
100.
Mourad Ben Braiek Faouzi Aloui Souad Moussa Moncef Tounsi Jérome Marrot Béchir Ben Hassine 《Tetrahedron letters》2013
A new helically chiral pentacyclic system containing one pyrrole ring was prepared in a good yield and purity via a three-step sequence involving Heck coupling and classical oxidative photocyclization. X-ray crystal structure analysis indicated that the conformation resembled that of unsubstituted pentahelicene, the idealized symmetry of which is C2. The optical properties of the pentacyclic helicene were investigated and show interesting behaviour. 相似文献