全文获取类型
收费全文 | 129篇 |
免费 | 3篇 |
专业分类
化学 | 95篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 12篇 |
物理学 | 21篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 4篇 |
2012年 | 6篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 15篇 |
2007年 | 12篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 7篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有132条查询结果,搜索用时 15 毫秒
101.
Chaves S Gil M Canário S Jelic R Romão MJ Trincão J Herdtweck E Sousa J Diniz C Fresco P Santos MA 《Dalton transactions (Cambridge, England : 2003)》2008,(13):1773-1782
Two O,S-donor ligands, hydroxythiopyrone and hydroxythiopyridinone derivatives, were developed and studied, as well as the corresponding O,O-derivatives, with a view to their potential pharmacological applications as xanthine oxidase (XO) inhibitors. The biological assays revealed that the O,S-ligands present high inhibitory activity towards XO (nanomolar order, close to that of the pharmaceutical drug allopurinol), in contrast to the corresponding O,O-analogues. Due to the biomedical relevance of this molybdenum-containing enzyme, the corresponding Mo(VI) complexes were studied both in solution and in the solid state, aimed at identifying the source of the biological properties. The solution studies showed that, in comparison with the O,O-analogues, the Mo(VI) complexes with the O,S-ligands present some stabilization, which is even more pronounced for the reduced Mo(IV) species. The crystal structures of the Mo(VI) complexes with the hydroxythiopyrone revealed good flexibility of the coordination modes, with two structural isomers and two polymorphic forms for a mononuclear and a binuclear species, respectively. These results give some support to mechanistic proposals for the XO inhibition involving the interaction of the thione group with the molybdenum cofactor, thus indicating a role of the sulfur atom in the XO inhibition. 相似文献
102.
A Novel Sensor Based on Manganese azo‐Macrocycle/Carbon Nanotubes to Perform the Oxidation and Reduction Processes of Two Diphenol Isomers 下载免费PDF全文
Saimon Moraes Silva Fernando Mota de Oliveira Danielle Diniz Justino Lauro Tatsuo Kubota Auro Atsushi Tanaka Flavio Santos Damos Rita de Cássia Silva Luz 《Electroanalysis》2014,26(3):602-611
The present work describes the development of a selective and sensitive voltammetric sensor for simultaneous determination of catechol (CC) and hydroquinone (HQ), based on a glassy carbon (GC) electrode modified with manganese phthalocyanine azo‐macrocycle (MnPc) adsorbed on multiwalled carbon nanotubes (MWCNT). Scanning electron microscopy and scanning electrochemical microscopy were used to characterize the composite material (MnPc/MWCNT) on the glassy carbon electrode surface. The modified electrode showed excellent electrochemical activity towards the simultaneous oxidation and reduction of CC and HQ. On the MnPc/MWCNT/GC electrode, both CC and HQ can generate a pair of quasi‐reversible and well‐defined redox peaks. Under optimized experimental and operational conditions, the cathodic peak currents were linear over the range 1–600 µmol L?1 for both CC and HQ, with limits of detection of 0.095 and 0.041 µmol L?1, respectively. The anodic peak currents were also linear over the range 1–600 µmol L?1 for both CC and HQ, with limits of detection of 0.096 and 0.048 µmol L?1, respectively. The proposed method was effectively applied for the simultaneous detection of hydroquinone and catechol in water samples and the results were in agreement with those obtained by a comparative method described in the literature. 相似文献
103.
Daniella M. de Faria Maria Irene Yoshida Carlos B. Pinheiro Kassílio José Guedes Klaus Krambrock Renata Diniz Luiz Fernando C. de Oliveira Flávia C. Machado 《Polyhedron》2007
The preparation, crystal structures and spectroscopic characterization of four oxalate copper(II) complexes containing the 4,4′-dimethyl-2,2′-bipyridine (Mebpy) or di(2-pyridyl)sulfide (DPS) nitrogen ligands namely [μ-(ox){Cu(Mebpy)(NO3)(H2O)}2] (1), [μ-(ox){Cu(Mebpy)(ClO4)(H2O)}2] (2), [μ-(ox){Cu(DPS)(H2O)}2](ClO4)2 (3) and [Cu(DPS)(ox)(H2O)] · 2H2O (4) are described. X-ray diffraction measurements have shown that complexes 1–3 are binuclear, in which the oxalate anion bridges two Cu(II) centers, while the complex (4) is mononuclear and the oxalate anion adopts the terminal bidentate chelating coordination mode. In 1 and 2 the Cu(II) sites display a distorted octahedral geometry (4+2 environment) and in compounds 3 and 4 the Cu(II) centers exhibit a slightly distorted square pyramidal geometry. In addition, complexes 1 and 2 present a 2D supramolecular arrangement through hydrogen bonds between coordination water molecules and nitrate or perchlorate anions and π-stacking interaction between the pyridyl rings of Mebpy nitrogen ligands. 相似文献
104.
Charlane C. Corrêa Renata Diniz Luciano H. Chagas Bernardo L. Rodrigues Maria I. Yoshida Wagner M. Teles Flávia C. Machado Luiz Fernando C. de Oliveira 《Polyhedron》2007
Synthesis, crystal structure and the vibrational spectra of coordination polymers with 1,3-bis(4-pyridyl)propane (BPP) and squarate ion ligands and transition metal ions (M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) are described. All compounds are isostructural, and the BPP is not coordinated to metal site since it is in cationic form due to protonation of N atoms from pyridyl rings. The metal is coordinated to two squarate ions and two water molecules in an octahedral distorted geometry. The two water molecules are involved in medium hydrogen bonds with squarate ligands and the average of O?O distance is 2.679(3) Å. Squarate ions adopt the 1,3-bis(monodentate) coordination mode bridging two metal centers giving rise to a 2D arrangement with (4,4) topology. The four-member ring is slightly distorted and the M–M distances are respectively 8.024 and 8.111 Å. The cationic form of BPP molecules are located inside of four-member ring cavity, presenting two different orientations, in which one molecule is inverted comparing to another. Vibrational spectra of all compounds are very similar, in agreement to crystal data. In all infrared spectra of the compounds a medium band at 1640 cm−1 is observed, assigned to the in plane deformation mode of NH bond, indicative of the formation of cationic BPP. In the Raman spectra of the investigated compounds is observed a weak band around 1800 cm−1, assigned to the stretching mode of free CO bond, whereas the medium band observed around 1600 cm−1 is tentatively assigned to coordinated CO stretching mode. At last, a very important achievement of this investigation refers to the coordination geometries of all the investigated compounds, which are governed only by the ligands, independently of the different electronic properties of the metal ions. 相似文献
105.
R.C. Teixeira I. Doi J.A. Diniz J.W. Swart M.B.P. Zakia 《Applied Surface Science》2007,254(1):207-212
This paper investigates the structure and surface characteristics, and electrical properties of the polycrystalline silicon-germanium (poly-Si1−xGex) alloy thin films, deposited by vertical reduced pressure CVD (RPCVD) in the temperature range between 500 and 750 °C and a total pressure of 5 or 10 Torr. The samples exhibited a very uniform good quality films formation, with smooth surface with rms roughness as low as 7 nm for all temperature range, Ge mole fraction up to 32% (at 600 °C), textures of 〈2 2 0〉 preferred orientation at lower temperatures and strong 〈1 1 1〉 at 750 °C, for both 5 and 10 Torr deposition pressures. The 31P+ and 11B+ doped poly-Si1−xGex films exhibited always lower electrical resistivity values in comparison to similar poly-Si films, regardless of the employed anneal temperature or implantat dose. The results indicated also that poly-Si1−xGex films require much lower temperature and ion implant dose than poly-Si to achieve the same film resistivity. These characteristics indicate a high quality of obtained poly-Si1−xGex films, suitable as a gate electrode material for submicron CMOS devices. 相似文献
106.
Elvira M. Gaspar José C. Santana João F. Lopes Marcos B. Diniz 《Analytical and bioanalytical chemistry》2010,397(1):369-380
Volatile organic compounds emitted from historical books made from cotton/linen rag and wood pulp paper have been studied.
Different profiles were obtained using different solid-phase microextraction (SPME) fibres to access the compounds involved
in the decomposition reactions occurring in cotton/linen rag and wood pulp paper upon natural ageing and precocious/accelerated
degradation. Contact headspace solid-phase extraction coupled with gas chromatography/time-of-flight mass spectrometry (GC-TOF-MS)
was improved as a non-destructive methodology for the analysis of historical books. Potential markers of cellulose degradation—linear
hydrocarbons, linear aldehydes, and 2-furfural—together with potential markers of cotton/linen rag paper (isopropylic esters)
were identified. Chiral analysis (SPME-c-GC-TOF-MS) showed that only the enantiomer (S)-2-ethyl-1-hexanol is present as an emanation compound in both types of paper. Validation studies for a larger number of
books are being done. 相似文献
107.
A. L.A. Penna J. B. Diniz F. A. Oliveira 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(1):27-31
We have examined the presence of a charge symmetry breaking in a screened system. Using a Thomas-Fermi-type potential and
a simple mathematical model, we show that screening on the nuclear charge α induces a charge parametrization α→(α,β) in which
appears a new dual charge β in the system. Considering this method,
the binding energy of electron becomes invariant under parity symmetry for an order parameter ρ=β-α. We find nontrivial solutions
for ρ at the minimum of energy which leads to the broken parity symmetry. The equations obtained for this new screening approach
is very similar to the Landau theory of phase transition. 相似文献
108.
Martens Dana L. Motuzas Julius Smart Simon Diniz da Costa João C. 《Journal of Sol-Gel Science and Technology》2021,98(3):470-477
Journal of Sol-Gel Science and Technology - This work reports the hydrothermal treatment effect on cobalt silica-seeded xerogels under harsh conditions at 550?°C for 100?h in a... 相似文献
109.
Celeste de Jesus Pereira Franco Oberdan Oliveira Ferreira Jorddy Neves Cruz Everton Luiz Pompeu Varela ngelo Antnio Barbosa de Moraes Lidiane Diniz do Nascimento Mrcia Moraes Cascaes Antnio Pedro da Silva Souza Filho Rafael Rodrigues Lima Sandro Percrio Mozaniel Santana de Oliveira Eloisa Helena de Aguiar Andrade 《Molecules (Basel, Switzerland)》2022,27(15)
The essential oil (EO) of Calycolpus goetheanus (Myrtaceae) specimens (A, B, and C) were obtained through hydrodistillation. The analysis of the chemical composition of the EOs was by gas chromatography coupled with mass spectrometry CG-MS, and gas chromatography coupled with a flame ionization detector CG-FID. The phytotoxic activity of those EOs was evaluated against two weed species from common pasture areas in the Amazon region: Mimosa pudica L. and Senna obtusifolia (L.) The antioxidant capacity of the EOs was determined by (DPPH•) and (ABTS•+). Using molecular docking, we evaluated the interaction mode of the major EO compounds with the molecular binding protein 4-hydroxyphenylpyruvate dioxygenase (HPPD). The EO of specimen A was characterized by β-eudesmol (22.83%), (E)-caryophyllene (14.61%), and γ-eudesmol (13.87%), while compounds 1,8-cineole (8.64%), (E)-caryophyllene (5.86%), δ-cadinene (5.78%), and palustrol (4.97%) characterize the chemical profile of specimen B’s EOs, and specimen C had α-cadinol (9.03%), δ-cadinene (8.01%), and (E)-caryophyllene (6.74%) as the majority. The phytotoxic potential of the EOs was observed in the receptor species M. pudica with percentages of inhibition of 30%, and 33.33% for specimens B and C, respectively. The EOs’ antioxidant in DPPH• was 0.79 ± 0.08 and 0.83 ± 0.02 mM for specimens A and B, respectively. In the TEAC, was 0.07 ± 0.02 mM for specimen A and 0.12 ± 0.06 mM for specimen B. In the results of the in silico study, we observed that the van der Waals and hydrophobic interactions of the alkyl and pi-alkyl types were the main interactions responsible for the formation of the receptor–ligand complex. 相似文献
110.
Diniz R De Abreu HA De Almeida WB Fernandes NG Sansiviero MT 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(8):1747-1757
Five salts of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), [C6H2(COO)4H4], have been synthesized and investigated by infrared and Raman spectroscopy and by single crystal X-ray diffraction methods: sodium salt [Na2(H2O)2][C6H2(COO)4H2], potassium salt [K(H2O)3][C6H2(COO)4H3] and transition metal salts [M(H2O)6][C6H2(COO)4H2], which M = Mn, Ni and Zn. Crystal structures of all five compounds show short intramolecular asymmetric hydrogen bonds (SHB) between adjacent carboxyl groups with O...O distance average of 2.40 A. The Raman and infrared spectra reported indicate the presence of short hydrogen bonds in all salts, in agreement with the X-ray data. The O-H stretching mode [nu(OH)] had been observed at about 2500 cm(-1). Deuterated analogues were synthesized and their Raman spectra show that nu(OH)/nu(OD) ratio average is about unit. The symmetric [nu(sym)(O..H..O)] and asymmetric [nu(asym)(O..H..O)] stretching modes have been attributed about 300 and 870 cm(-1), respectively, in all salts, and for deuterated analogues, the ratio nu(OH)/nu(OD) to nu(sym)(O..H..O, O..D..O) is close to unit like it occurs in nu(OH). The vibrational modes, mainly SHB modes, are tentatively assigned by molecular orbital ab initio calculations of pyromellitic acid and anions [C6H2(COO)4H3]- and [C6H2(COO)4H2]2-. Geometry optimizations showed a good agreement with experimental data. Frequency calculation confirms the assignment of specific vibrational modes. Ab initio calculations show that nu(C=O) and nu(sym)(COO) are strongly coupled with in plane OH bending [delta(OH)]. In Raman spectra of deuterated analogues is observed a frequency shift of these bands. 相似文献