全文获取类型
收费全文 | 64篇 |
免费 | 0篇 |
专业分类
化学 | 45篇 |
力学 | 4篇 |
数学 | 5篇 |
物理学 | 10篇 |
出版年
2024年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 5篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2010年 | 1篇 |
2009年 | 4篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有64条查询结果,搜索用时 15 毫秒
1.
Ehsan A. H. Gomaa H. Schut A. Van Veen M. Mohsen U. Fromm P. Morshuis 《Journal of Radioanalytical and Nuclear Chemistry》1996,211(1):77-83
Using the positron annihilation lifetime technique, the annihilation parameters have been measured for epoxy and high density polyethylene (HDPE) as a function of AC electric field strength and the exposure time. The lifetime spectra have been resolved into three components, the longest component (I33) is attributed to the pick-off annihilation of o-Ps in the amorphous regions. The intermediate one (I22) is due to the annihilation of free positrons, while the shorter component (I11) stems from self annihilation of p-Ps. In HDPE, the o-Ps parameters 3 andI
3 are measured as a function of electric field strengths in the range from 10 to 100 kV/cm exposed for 24 hours. A decrease inI
3 of 8% is observed from zero to 50 kV/cm followed by an increase of the same order from 50 to 100 kV/cm. By investigating the effect of the exposure time from 2 to 24 hours at 16 and 50 kV/cm, the effect is confirmed and is attributed to the inhibition of o-Ps formation at lower field strength. In epoxy, the effect or exposure time onI
3 at 166 and 133 kV/cm shows a similar behavior as in HDPE. At 133 kV/cmI
3 decreases by only 2.5%. On the other hand, the changes in 3 occur at short exposure times. Again at large times the saturation is obtained. These effects are attributed to the expansion of free volume (increase of 3) competing at longer exposure times with other phenomena, such as liberation of free radicals, which reduce the o-Ps intensityI
3 through the conversion to p-Ps. The reactions between o-Ps and free radicals might also lead to free positrons, which could explain the increase ofI
2 and the decrease of 3 at longer exposure times. 相似文献
2.
E. A. Gomaa M. A. Ghandour R. A. Abo-Doma 《Monatshefte für Chemie / Chemical Monthly》1985,116(1):33-42
The polarographic behaviour of uranyl ion in maleic acid solution shows two reduction waves. The half wave potential of the first wave is shifted to more negative values in contrast to that of the second wave, which is shifted to less negative potentials on increase of thepH of the solution. The first wave represents the reduction of the 1:1 uranyl-maleate complex, while the second wave represents the reduction of the 1:2 complex. The presence of 1:1 and 1:2 complexes is supported by spectrophotometric and conductometric methods. The stability constants were also determined and the reduction mechanism is discussed.
Das polarographische Verhalten von Uranyl-Ionen in Maleinsäure- und Maleat-Puffer-Lösungen
Zusammenfassung Die polarographische Kurve von Uranyl-Ionen in Maleinsäurelösung zeigt zwei Reduktionswellen. Das Halbwellenpotential der ersten Welle verschiebt sich bei ansteigendempH der Lösung zu negativeren Werten, im Gegensatz zur zweiten Welle, die eine positive Verschiebung zeigt. Die erste Welle repräsentiert die Reduktion des 1:1-Uranyl-Maleat-Komplexes, die zweite Welle hingegen die Reduktion des 1:2-Komplexes. Die Präsenz von 1:1- und 1:2-Komplexen wird auch durch spektrophotometrische und konduktometrische Messungen erhärtet. Die Stabilitätskonstanten wurden bestimmt, der Mechanismus der Reduktion wird diskutiert.相似文献
3.
A synthesis of 5,11b-dihydro-1H-dibenzo[d,f][1,3]diazepin-1-ones was found in the reaction of nitro-substituted N1,N2-diarylamidines with 3,4,5,6-tetrachloro-1,2-benzoquinone. In contrast, 6,7,8,9-tetrachlorodibenzodioxins were obtained from reaction of N1,N2-diphenylpropionamidine and N1,N2-di-(4-tert-butylphenyl)acetamidine with 3,4,5,6-tetrachloro-1,2-benzoquinone. 相似文献
4.
Basma H. Amin Mohamed I. Abou-Dobara Mostafa A. Diab Essam A. Gomaa Mohammed A. El-Mogazy Adel Z. El-Sonbati Mohamed S. EL-Ghareib Mostafa A. Hussien Hanaa M. Salama 《应用有机金属化学》2020,34(8):e5689
A novel series of mixed-ligand complexes of 5,5′-{(1E,1E′)-1,4-phenelynebis(diazene-2,1-diyl)}bis(quinolin-8-ol) (H2L1) as a primary ligand and 4-aminoantipyrine(L2) as a secondary ligand with Mn(II) ion were prepared using two general formulae: [Mn2(H2L1)2(L2)2X4].4Cl (X = OH2( 1 ), ONO2−( 2 ), Cl=nil; OAc( 3 ), Cl = nil) and [Mn2(H2L1)(L2)2(O2SO2)2]( 4 ). Free ligands and their complexes were characterized. Electronic absorption spectra of the mixed-ligand complexes indicate a distorted octahedral geometry around the central metal ion, and the anions X− are in the axial positions for all compounds. The ligands behave in a neutral bidentate manner, through nitrogen atoms and oxygen atoms of the carbonyl group (L2), whereas H2L1 coordinated through nitrogen and OH groups as a neutral bidentate ligand. All complexes do not contain coordinated water molecules, but complex ( 1 ) contains four water molecules. The water molecules are removed in a single step. The complexes exhibited magnetic susceptibility corresponding to five unpaired electrons. The antimicrobial activity of the Mn(II) mixed-ligand complexes ( 1–4 ) against two gram-positive bacteria, three local gram-negative bacteria, and three fungi species was tested. Mn(II) mixed-ligand complex ( 2 ) exhibited significant antibacterial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas sp. Mixed-ligand complex ( 2 ) exhibited a high potential cytotoxicity against the growth of human lung cancer cells. 相似文献
5.
Nabil Abdul‐kader Saleh Hussein El‐abd Saltani Fadhil Abbas Al‐Issa Al‐Sadek Gomaa Melad 《中国化学会会志》2013,60(10):1234-1240
The antimicrobial activity of thirteen newly synthesized 4‐thiazolidinones (TZONs) and four dithiolane derivatives was assessed against susceptible and resistant bacteria, including MRSA, as well as Candida albicans. The structure‐activity relationships revealed that 4‐Thiazolidinone derivatives harboring p‐chlorophenyl and dicarboxyethyl at the 2‐ethenyl and 5‐arylidine positions of the thiazolidinone ring display considerable antibacterial properties. No antifungal activity was recorded by all tested compounds against Candida albicans. The possible potentiative (synergistic) effect of the most active compounds to a few commercial antibiotics was also investigated. 相似文献
6.
Nabil Abdul‐Kader Saleh Hussein El‐Abd Saltani Fadhil Abbas Al‐Issa Ahmad Abul‐kasem Errabie Al‐Sadek Gomaa Melad 《中国化学会会志》2013,60(11):1353-1358
The antifungal and antioxidant activities of thirty newly synthesized 4‐thiazolidinone (TZON) derivatives were assessed against some fungal species including Candida albicans and Aspergillus niger. The introduction of different arylidene moieties at 5‐positions of the thiazolidinone ring successfully enhanced its biological activity. The structure–activity relationships revealed that 4‐thiazolidinone derivatives harboring dicarboxyethyl (at the 2‐ethenyl) and p‐nitrophenylhydrazyl arm (at the 5‐arylidine positions of the thiazolidinone ring) display considerable antifungal and antioxidant properties. 相似文献
7.
Alshymaa Abdel-Rahman Gomaa Usama Ramadan Abdelmohsen Markus Krischke Martin J. Mueller Amira Samir Wanas 《Natural product research》2020,34(18):2612-2615
AbstractThe present study evaluates the chemical composition of Zinnia elegans and Gazania rigens based on their metabolomic profiles using liquid chromatography coupled with high-resolution mass spectrometry (LC‐HR-MS), alongside with the anti-infective activities of their ethanol extracts, as well as, different fractions. A significant difference was observed between the LC-MS profiles of the two plants such as, coumarins, sesquiterpene lactones and phenylethanoids which were characteristic for Z. elegans, while amides and phenolic acid derivatives were characteristic for G. rigens. These results highlight the chemical potential of Z. elegans and G. rigens. Furthermore, the ethyl acetate fraction of Z. elegans showed a significant antimalarial activity with IC50 values of 21.03 and 13.72?µg/mL against Plasmodium falciparum D6 and P. falciparum W2, respectively. 相似文献
8.
Novel 4-(4-trifluoromethyl)phenoxy N-phenyl-maleimide (FPMI) was synthesized. The free radical-initiated polymerization of FPMI was carried out in 1,4-dioxane solution using azobisisobutyronitrile as initiator. The monomer was investigated by FTIR, 1H NMR, 13C NMR and elemental analysis, while the polymer was investigated by FTIR, 1H NMR and 13C NMR. The effect of the monomer concentration, initiator concentration and temperature on the rate of polymerization (Rp) was studied. The activation energy of the polymerization was calculated (ΔE = 48.94 kJ/mol). The molecular weight of PFPMI and polydispersity index of the polymer were determined by gel permeation chromatography and were equal to 73,500, 16,700 and 2.27, respectively. The properties of PFPMI, including thermal behavior, thermal stability, the glass transition temperature (Tg = 236 °C), photo-stability, solubility and solution viscosity were studied. 相似文献
9.
The temperature dependence of the mean size of nanoscale free‐volume holes, 〈Vh〉, in polymer blend system consisting of polar and nonpolar polymers has been investigated. The positron lifetime spectra were measured for a series of polymer blends between polyethylene (PE) and nitrile butadiene rubber (NBR) as a function of temperature from 100 to 300 K. The glass transition temperatures (Tg) for blends were determined from the ortho‐positronium (o‐Ps) lifetime τ3 and the mean size of free‐volume holes 〈Vh〉 versus temperature as a function of wt % of NBR. The Tgs estimated from the PALS data agree very well with those estimated from DSC in view of different time scales involved in the two measurements. Both DSC and PALS results for the blends showed two clear Tgs of a two‐phase system. Furthermore, from the variation of thermal expansivity of the nanoscale free‐volume holes, the thermal expansion coefficients of glass and amorphous phases were estimated. Variations of the o‐Ps formation probability I3 versus temperature for pure PE and blends with low wt % of NBR were interpreted on the basis of the spur reaction model of Ps formation with reference to the effects of localized electrons and trapping centers produced by positron irradiation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 227–238, 2009 相似文献
10.