全文获取类型
收费全文 | 130篇 |
免费 | 6篇 |
专业分类
化学 | 97篇 |
力学 | 1篇 |
数学 | 19篇 |
物理学 | 19篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 7篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 9篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1937年 | 2篇 |
1931年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 31 毫秒
121.
122.
Maria Alexsandra de Sousa Rios Selma Elaine Mazzetto 《Journal of Thermal Analysis and Calorimetry》2013,111(1):553-559
This study shows the synthesis, characterization, and evaluation of the effect of organophosphate antioxidant on the thermo-oxidative degradation of a mineral oil. The organophosphate was synthesized by nucleophilic substitution (SN2) of hydrogenated cardanol. For this study, were employed thermogravimetry, derivative thermogravimetry, differential scanning calorimetry, and differential thermal analysis techniques. The results showed that organophosphate contributed for thermo-oxidative stability of mineral oil (initial decomposition temperature (IDT) mineral oil: 91.28 °C < IDT mineral oil + organophosphate (1%): 156.42 °C). The organophosphate obtained shows significant thermal stability when compared with other compound of the same class (diphenyl phosphate). 相似文献
123.
Agnaldo de Souza Gonçalves Sergio Antonio Marques de Lima Marian Rosaly Davolos Selma Gutierrez Antônio Carlos de Oliveira Paiva-Santos 《Journal of solid state chemistry》2006,179(5):1330-1334
Gallium-doped zinc oxide (ZnO:Ga 1, 2, 3, 4 and 5 at%) samples were prepared in powder form by modifying the Pechini method. The formation of zinc gallate (ZnGa2O4) with the spinel crystal structure was observed even in ZnO:Ga 1 at% by X-ray diffraction. The presence of ZnGa2O4 in ZnO:Ga samples was also evidenced by luminescence spectroscopy through its blue emission at 430 nm, assigned to charge transfer between Ga3+ at regular octahedral symmetry and its surrounding O2− ions. The amount of ZnGa2O4 increases as the dopant concentration increases, as observed by the quantitative phase analysis by the Rietveld method. 相似文献
124.
Jos E.B. Freitas Diego Lomonaco Giuseppe Mele Selma E. Mazzetto 《Journal of luminescence》2009,129(11):1260-1265
The luminescence quenching of excited Tris(2,2-bipyridine)ruthenium(II) ions by trans-[RuCl2{P(OR)3}4] complexes with different alkyl chain ligands (R=C2H5, C2H5Cl, nC4H9, iC3H7 o-tolyl and tC4H9) was investigated. None of the acceptor Ru(II) phosphite complexes were luminescent, and the rate constants of the bimolecular system were determined within the range of 1.15 and 0.28×108 M−1 s−1 for R=C2H5 and tC4H9, respectively. The results indicate a direct effect of the alkyl chains in the rate constants, showing a decrease of kq as a function of increased of the alkyl chains (R) in the ruthenium(II) tetraphosphite complexes. The greater the R group content in the phosphite ligand, the more difficult the electron transfer is. 相似文献
125.
The previously reported triphosphino/trithiolato-ruthenium anion, [tris-(2-diphenylphosphinothia-phenolato)ruthenium(II)](-), [Ru(DPPBT)(3)](-), has been isolated as the PPN salt (PPN = bis(triphenylphosphoranylidene) ammonium), 1, from chlorobenzene/ether as light-orange crystalline plates, and the X-ray crystal structure has been determined. In dichloromethane, the cis positioned thiolates are alkylated by solvent yielding the methylene-bridged triphosphino/dithioether/thiolato complex [(bis-(2-diphenylphosphinothiaphenolato)methane)(2-diphenyl-phosphinothiaphenolato)ruthenium(II)]chloride, [Ru((DPPBT)(2)CH(2))(DPPBT)]Cl (2). Dichloromethane solutions of 1 layered with hexanes yield 2 as orange cubes. The ruthenium-sulfur bond distances in the alkylated, thioether product are slightly shorter than in the thiolate precursor. Within 2, the iron-thioether bond distances are comparable to the iron-thiolate distances. 相似文献
126.
Selma Kurra 《Applied Acoustics》1980,13(5):331-355
This paper describes a computer technique involving a procedure for finding the performance values within the shadow zone of a barrier-building of rectangular cross-section used as a point source. Reflections from the ground are also taken into account and a control operation is designed for different source and receiver locations related to the building. Consideration is given to the combined effects of wide barriers and finite size screens. The results are confirmed by several experimental measurements carried out in an anechoic room. Some examples of the application of the technique are given. 相似文献
127.
128.
The energy positions and the wavefunctions of 2S autoionizing states of the neutral lithium atom have been calculated using the derivative method with a Hylleraas-type basis set. Computed energies are in good agreement with experiment and with other theoretical results. 相似文献
129.
Naphthenic acids (general formula C(n)H(2n+Z)O(2)) are water-soluble, toxic compounds found in petroleum and bitumen. Some of the current methods for detecting these acids in waters depend on measuring the presence of the carboxylic acid functional group, and therefore many of these methods also detect naturally occurring carboxylic acids that are not naphthenic acids. We report a procedure that includes liquid-liquid extraction, cleanup, and derivatization to form t-butyldimethylsilyl esters prior to gas chromatography-mass spectrometry (GC-MS) analysis. Using low- and high-resolution MS to detect the ion C(15)H(27)O(2)Si(+) (nominal m/z=267) is an excellent indicator of the presence of naphthenic acids at concentrations > or =10microgL(-1). 相似文献
130.
Raid A. Ismail Selma M. H. Al-Jawad Naba Hussein 《Applied Physics A: Materials Science & Processing》2014,117(4):1977-1984
In this study, n-ZnO/p-Si solar cells were fabricated by spraying ZnO nanoparticles (NPs) film synthesised by dissolving of high purity zinc in hydrogen peroxide H2O2 followed by thermal oxidation in air on p-type silicon substrates. The oxidation was carried out at different temperatures (200–500) °C. The crystalline structure of the ZnO NPs films was investigated by X-ray diffraction which indicated wurtzite structure films along (100) plane. The morphology of the NPs was studied by atomic force microscopy and scanning electron microscopy. The result showed an average grain size of ZnO NPs in the range of (72.7–95.8) nm and the surface roughness increasing with oxidation temperature. Three peaks located at ultraviolet, violet and green emission regions were noticed in the photoluminescence spectra of ZnO NPs. From optical studies, it was shown that the direct optical band gap is found to be in the range of (3.85–3.96) eV depended on the oxidation temperature. The synthesised ZnO films have n-type conductivity, and the mobility was in the range of (7–24) cm2 V?1 s?1. Current–voltage I–V and capacitance–voltage C–V of ZnO NPs/Si heterojunction solar cell were investigated as function of oxidation temperature. The spectral response of n-ZnO NPs/p-Si solar cell showed two peaks of response and its maximum value approaching 0.62 mA W?1 at λ = 800 nm. Solar cell oxidized at 500 °C gave open circuit voltage V OC of 375 mV, short circuit current density J SC of 25 mA cm?2, a fill factor FF of 0.72, and conversion efficiency η of 6.79 % under illumination of 100 mW cm?2. 相似文献