全文获取类型
收费全文 | 130篇 |
免费 | 9篇 |
国内免费 | 4篇 |
专业分类
化学 | 76篇 |
数学 | 15篇 |
物理学 | 52篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 1篇 |
2012年 | 10篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有143条查询结果,搜索用时 15 毫秒
21.
Nilson C. Bernardes Jr. 《Proceedings of the American Mathematical Society》2005,133(12):3473-3483
Given a metrizable compact topological -manifold with boundary and a metric compatible with the topology of , we prove that ``most' continuous functions are non-sensitive at ``most' points of but are sensitive at every point of an infinite set which is dense in the set of all periodic points of . We also establish some results concerning sets of periodic points and non-wandering points.
22.
Santos RC Bernardes CE Diogo HP Piedade MF Canongia Lopes JN Minas da Piedade ME 《The journal of physical chemistry. A》2006,110(6):2299-2307
The energetics of the thermal dimerization of acenaphthylene to give Z- or E-heptacyclene was investigated. The standard molar enthalpy of the formation of monoclinic Z- and E-heptacyclene isomers at 298.15 K was determined as Delta(f)H(m)o (E-C24H16, cr) = 269.3 +/- 5.6 kJ x mol(-1) and Delta(f)H(m)o (Z-C24H16, cr) = 317.7 +/- 5.6 kJ x mol(-1), respectively, by microcombustion calorimetry. The corresponding enthalpies of sublimation, Delta(sub)H(m)o (E-C24H16) = (149.0 +/- 3.1) kJ x mol(-1) and Delta(sub)H(m)o (Z-C24H16) = (128.5 +/- 2.3) kJ x mol(-1) were also obtained by Knudsen effusion and Calvet-drop microcalorimetry methods, leading to Delta(f)H(m)o (E-C24H16, g) = (418.3 +/- 6.4) kJ x mol(-1) and Delta(f)H(m)o (Z-C24H16, g) = (446.2 +/- 6.1) kJ x mol(-1), respectively. These results, in conjunction with the reported enthalpies of formation of solid and gaseous acenaphthylene, and the entropies of acenaphthylene and both hepatcyclene isomers obtained by the B3LYP/6-31G(d,p) method led to the conclusion that at 298.15 K the thermal dimerization of acenaphthylene is considerably exothermic and exergonic in the solid and gaseous states (although more favorable when the E isomer is the product), suggesting that the nonobservation of the reaction under these conditions is of kinetic nature. A full determination of the molecular and crystal structure of the E dimer by X-ray diffraction is reported for the first time. Finally, molecular dynamics computer simulations on acenaphthylene and the heptacyclene solids were carried out and the results discussed in light of the corresponding structural and Delta(sub)H(m)o data experimentally obtained. 相似文献
23.
The leading asymptotic term for the function that counts theeigenvalues of the Stokes operator is determined for fairlygeneral underlying bounded domains. Moreover, the remainderis estimated in terms of the fractality of the boundary of thedomain. The results obtained resemble corresponding ones forthe Dirichlet Laplacian. 1991 Mathematics Subject Classification:35P20. 相似文献
24.
Amado FD Rodrigues MA Morisso FD Bernardes AM Ferreira JZ Ferreira CA 《Journal of colloid and interface science》2008,320(1):52-61
In this study different membranes were produced, aiming to evaluate their use in electrodialysis. These membranes were produced using conventional polymer (high-impact polystyrene) and polyaniline. The membrane characterization was done by FTIR spectroscopy, scanning electron microscopy (SEM), and thermogravimetry (TGA). The studies of the zinc and proton extraction ionic transport through the membranes were evaluated using a three-compartment cell. The results obtained using the produced membranes were compared to the results obtained with the commercial membrane Nafion 450. It was found that a synthesized membrane can be used to recover zinc in acid media. In addition, a preliminary computational essay about the structures of PAni and CSA is presented. 相似文献
25.
This work reports on phase diagrams for mixtures of a complex salt formed by a cationic surfactant and an oppositely charged polyelectrolyte, hexadecyltrimethylammonium polymethacrylate, in binary mixtures with water and in ternary mixtures containing water and organic solvents of different polarity ('oils'): decanol, octanol, p-xylene and cyclohexane. The liquid crystalline structures formed were identified by small angle X-ray scattering measurements, which also provided information about changes in the size of the aggregates as a function of the system composition. These results are analysed in comparison with others previously reported [Bernardes et al., J. Phys. Chem. B 110 (2006) 10332-10340] for the analog complex formed with polyacrylate and, in general, reveal that the presence of an extra methylene group in the polymer chain does not produce significant changes in the complex phase diagrams nor in the structure of the liquid crystalline phases formed. Additionally, the obtained results confirm once more the approach used to analyze these kinds of systems formed by polymer and oppositely charged surfactant. 相似文献
26.
Dr. Yanira Méndez Dr. Aldrin V. Vasco Galway Ivey Ana Laura Dias Dr. Peter Gierth Bárbara B. Sousa Dr. Claudio D. Navo Angel Torres-Mozas Dr. Tiago Rodrigues Dr. Gonzalo Jiménez-Osés Prof. Gonçalo J. L. Bernardes 《Angewandte Chemie (International ed. in English)》2023,62(44):e202311186
Multicomponent reactions are of utmost importance at generating a unique, wide, and complex chemical space. Herein we describe a novel multicomponent approach based on the combination of the isonitrile-tetrazine (4+1) cycloaddition and the Ugi four-component reaction to generate pyrazole amide derivatives. The scope of the reaction as well as mechanistic insights governing the 4H-pyrazol-4-imine tautomerization are provided. This multicomponent process provides access to a new chemical space of pyrazole amide derivatives and offers a tool for peptide modification and stapling. 相似文献
27.
KM Varier AM Vinodkumar NVSV Prasad PV Madhusudhana Rao DL Sastry Lagy T Baby MC Radhakrishna NG Puttaswamy JJ Das P Sugathan N Madhavan AK Sinha DO Kataria 《Pramana》1999,53(3):529-533
Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies.
Coupled channel calculations incorporating couplings to 2+ and 3− states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements
had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer
were carried out for 46,48Ti+61Ni systems. The present paper gives the results of these studies. 相似文献
28.
Netto-Ferreira JC Lhiaubet-Vallet V de Oliveira Bernardes B Ferreira AB Miranda MA 《Photochemistry and photobiology》2009,85(1):153-159
The photochemical reactivity of β-lapachone ( 1 ), nor -β-lapachone ( 2 ) and 1,2-naphthoquinone ( 3 ) towards amino acids and nucleobases or nucleosides has been examined employing the nanosecond laser flash photolysis technique. Excitation (λ = 355 nm) of degassed solutions of 1 – 3 , in acetonitrile, resulted in the formation of their corresponding triplet excited states. These transients were efficiently quenched by l -tryptophan, l -tryptophan methyl ester, l -tyrosine, l -tyrosine methyl ester and l -cysteine ( k q ≈ 109 L mol−1 s−1 ). For l -tryptophan, l -tyrosine and their methyl esters new transients were formed in the quenching process, which were assigned to the corresponding radical pair resulting from an initial electron transfer from the amino acids or their esters to the excited quinone, followed by a fast proton transfer. No measurable quenching rate constants could be observed in the presence of thymine and thymidine. On the other hand, efficient rate constants were obtained when 1 – 3 were quenched by 2'-deoxyguanosine ( k q ≈ 109 L mol−1 s−1 ). The quantum efficiency of singlet oxygen (1 O2 ) formation from 1 to 3 was determined employing time-resolved near-IR emission studies upon laser excitation and showed considerably high values in all cases (ΦΔ = 0.6), which are fully in accord with the ππ* character of these triplets in acetonitrile. 相似文献
29.
30.