全文获取类型
收费全文 | 108篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 81篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 9篇 |
物理学 | 25篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 7篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 2篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 13篇 |
2007年 | 10篇 |
2006年 | 2篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 1篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有117条查询结果,搜索用时 203 毫秒
91.
Trindade JR Visak ZP Blesic M Marrucho IM Coutinho JA Lopes JN Rebelo LP 《The journal of physical chemistry. B》2007,111(18):4737-4741
The effects of the addition of three inorganic salts, namely, NaCl, Na(2)SO(4), and Na(3)PO(4), on the liquid-liquid (L-L) phase diagram of aqueous solutions containing the model ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF(4)], were investigated. All three inorganic salts trigger salting-out effects, leading to significant upward shifts of the L-L demixing temperatures of the systems. The magnitude of the shifts depends on both the water-structuring nature of the salt and its concentration; that is, the effects are correlated with the ionic strength of the solution and the Gibbs free energy of hydration of the inorganic salt. The pH effect and the occurrence of salt precipitation in concentrated solutions are also discussed. 相似文献
92.
Trindade AF Gois PM Veiros LF André V Duarte MT Afonso CA Caddick S Cloke FG 《The Journal of organic chemistry》2008,73(11):4076-4086
An efficient new methodology for the arylation of aldehydes is disclosed which uses dirhodium(II) catalysts and N-heterocyclic carbene (NHC) ligands. Complexes of Rh 2(OAc) 4 with one and two NHCs attached on the axial positions were successfully isolated, fully characterized, and used as catalysts in the reaction. The saturated monocomplex ((NHC 5)Rh 2(OAc) 4) 31 was shown to be the most active catalyst and was particularly efficient in the arylation of alkyl aldehydes. DFT calculations support participation of complexes with one axial NHC in the reaction as the catalysts active species and indicate that hydrogen bonds involving dirhodium unit, reactants, and solvent (alcohol) play an important role on the reaction mechanism. 相似文献
93.
Dennys Reis Ana C. Trindade Maria Helena Godinho Laura C. Silva Maria do Carmo Gonçalves Antônio M. Figueiredo Neto 《Brazilian Journal of Physics》2017,47(1):19-25
The nanostructure of urethane/urea elastomeric membranes was investigated by small-angle X-ray scattering (SAXS) in order to establish relationships between their structure and mechanical properties. The networks were made up of polypropylene oxide (PPO) and polybutadiene (PB) segments. The structural differences were investigated in two types of membranes with the same composition but with different thermal treatment after casting. Type I was cured at 70–80 °C and type II at 20 °C. Both membranes showed similar phase separation by TEM, with nanodomains rich in PB or PPO and 25 nm dimensions. The main difference between type I and type II membranes was found by SAXS. The type I membrane spectra showed, besides a broad band at a 27-nm q value (modulus of the scattering vector), an extra band at 6 nm, which was not observed in the type II membrane. The SAXS spectra were interpreted in terms of PPO, PB soft segments, and urethane/urea links, as well as hard moiety segregation in the reaction medium. This additional segregation (q = 7 nm), although subtle, results in diverse mechanical behavior of in both membranes. 相似文献
94.
J. Zukerman‐Schpector Antonio Carlos Trindade P. O. Dunstan 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):763-765
In both title compounds, (acetylacetonato‐O,O′)bis(3‐cyanopyridine‐N)nickel(II), (I), and (acetylacetonato‐O,O′)bis(4‐cyanopyridine‐N)nickel(II), (II), both [Ni(C5H7O2)2(C6H4N2)2], the NiII atom, which is situated on a centre of symmetry, is octahedrally coordinated. Distances and angles for (I) and (II), respectively, are: Ni—O 2.009 (2)/2.016 (2) and 2.0110 (16)/2.0238 (18) Å, Ni—N 2.116 (3) and 2.179 (2) Å, O—Ni—O 91.86 (10) and 90.19 (7)°, and O—Ni—N 91.27 (11)/90.19 (11) and 89.65 (8)/90.79 (7)°. 相似文献
95.
de Souza Poliana Santos Clain Almir Faria Filho Octávio Luiz Trindade de Oliveira Estela Maria Delgado Jose Ubiratan Lopes Ricardo Tadeu 《Journal of Radioanalytical and Nuclear Chemistry》2019,321(3):851-856
Journal of Radioanalytical and Nuclear Chemistry - The production of environmental reference materials such as soil, sediment, water and vegetation containing radionuclides for interlaboratory... 相似文献
96.
Ana C. Trindade Joo P. Canejo Paulo I. C. Teixeira Pedro Patrício Maria H. Godinho 《Macromolecular rapid communications》2013,34(20):1618-1622
The excellent properties of elastomers are exploited to trigger wrinkling instabilities in curved shells. Micro‐ and nano‐fibres are produced by electrospinning and UV irradiated: each fibre consists of a soft core and a stiff outer half‐shell. Upon solvent de‐swelling, the fibres curl because the shell and the core have different natural lengths. Wrinkling only starts after the fibre has attained a well‐defined helical shape. A simple analytical model is proposed to find the curling curvature and wrinkle wavelength, as well as the transition between the “curling” and “wrinkling” regimes. This new instability resembles that found in the tendrils of climbing plants as they dry and lignify.
97.
Peter J. Brockwell Richard A. Davis A. Alexandre Trindade 《Journal of multivariate analysis》2004,90(2):1934-347
We establish consistency and derive asymptotic distributions for estimators of the coefficients of a subset vector autoregressive (SVAR) process. Using a martingale central limit theorem, we first derive the asymptotic distribution of the subset least squares (LS) estimators. Exploiting the similarity of closed form expressions for the LS and Yule–Walker (YW) estimators, we extend the asymptotics to the latter. Using the fact that the subset Yule–Walker and recently proposed Burg estimators satisfy closely related recursive algorithms, we then extend the asymptotic results to the Burg estimators. All estimators are shown to have the same limiting distribution. 相似文献
98.
Fa-Nian Shi Luís Cunha-Silva Jacek Klinowski Vítor S. Amaral Tito Trindade 《Journal of solid state chemistry》2008,181(6):1330-1336
A synthetic analogue of leucophosphite, an iron phosphate, was synthesized hydrothermally at 180 °C and its chemical composition determined to be {K[(FeV)(PO4)2(OH)(H2O)]·H2O}. The compound crystallizes in the monoclinic P21/c space group, with a=9.7210(19) Å, b=9.6500(19) Å, c=12.198(4) Å and β=128.569(18)°. While the original all-iron compound is reported to be antiferromagnetic, the inclusion of substitutional vanadium(III) ions renders the structure ferrimagnetic. Diffraction studies and magnetic characterization show that iron and vanadium are disordered throughout the crystallographic sites. The magnetic behaviour of this system was interpreted in terms of a classic ferrimagnetic mean field model, consisting of two antiferromagnetically coupled non-crystallographic “sublattices”. 相似文献
99.
Fernanda Ely José ES Nunes Evelyn K Schroeder Jeverson Frazzon Mário S Palma Diógenes S Santos Luiz A Basso 《BMC biochemistry》2008,9(1):13
Background
The emergence of multi- and extensively-drug resistant Mycobacterium tuberculosis strains has created an urgent need for new agents to treat tuberculosis (TB). The enzymes of shikimate pathway are attractive targets to the development of antitubercular agents because it is essential for M. tuberculosis and is absent from humans. Chorismate synthase (CS) is the seventh enzyme of this route and catalyzes the NADH- and FMN-dependent synthesis of chorismate, a precursor of aromatic amino acids, naphthoquinones, menaquinones, and mycobactins. Although the M. tuberculosis Rv2540c (aroF) sequence has been annotated to encode a chorismate synthase, there has been no report on its correct assignment and functional characterization of its protein product.Results
In the present work, we describe DNA amplification of aroF-encoded CS from M. tuberculosis (Mt CS), molecular cloning, protein expression, and purification to homogeneity. N-terminal amino acid sequencing, mass spectrometry and gel filtration chromatography were employed to determine identity, subunit molecular weight and oligomeric state in solution of homogeneous recombinant Mt CS. The bifunctionality of Mt CS was determined by measurements of both chorismate synthase and NADH:FMN oxidoreductase activities. The flavin reductase activity was characterized, showing the existence of a complex between FMNox and Mt CS. FMNox and NADH equilibrium binding was measured. Primary deuterium, solvent and multiple kinetic isotope effects are described and suggest distinct steps for hydride and proton transfers, with the former being more rate-limiting.Conclusion
This is the first report showing that a bacterial CS is bifunctional. Primary deuterium kinetic isotope effects show that C4-proS hydrogen is being transferred during the reduction of FMNox by NADH and that hydride transfer contributes significantly to the rate-limiting step of FMN reduction reaction. Solvent kinetic isotope effects and proton inventory results indicate that proton transfer from solvent partially limits the rate of FMN reduction and that a single proton transfer gives rise to the observed solvent isotope effect. Multiple isotope effects suggest a stepwise mechanism for the reduction of FMNox. The results on enzyme kinetics described here provide evidence for the mode of action of Mt CS and should thus pave the way for the rational design of antitubercular agents.100.
Lidija Matjacic Martin P. Seah Gustavo F. Trindade Alexander Pirkl Rasmus Havelund Jean-Luc Vorng Ewald Niehuis Ian S. Gilmore 《Surface and interface analysis : SIA》2022,54(4):331-340
In 2017, we introduced the OrbiSIMS instrument that features a dual analyser configuration with a time-of-flight (ToF) mass spectrometer (MS) and an Orbitrap MS, which confer advantages of speed and high-performance mass spectrometry, respectively. The ability to combine the MS performance usually found in a state-of-the-art proteomics and metabolomics MS with 3D imaging at the microscale and from nanolayers of <10 nm of material has proved popular in a broad field of application from organic electronics to drug discovery. There are now several instruments in operation around the world, and metrology is needed to help ensure repeatability and reproducibility of the intensity scale. We conduct a systematic study of two key parameters, the target potential, VT, and the collision cell pressure, P, in the transfer optics on the transmitted secondary ion intensities. We measure VT–P maps of the ions across the mass range for Ag as a representative of inorganic materials and two different organic materials, Irganox 1010 and NPB (N,N′-Di[1-naphthyl]-N,N′-diphenyl-4,4′-biphenyldiamine). The manufacturer's defaults for these values ensure very good transmission for a broad range of analyte classes. However, the maps reveal a sometimes complex behaviour and indicate the possibility for additional separation of ions based on their shape, labile nature and kinetics of formation. Guidance is provided on how to optimise these parameters for sensitivity for different material classes and also the need for optimisation to improve spectral repeatability and reproducibility. 相似文献