全文获取类型
收费全文 | 317篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 122篇 |
力学 | 4篇 |
数学 | 78篇 |
物理学 | 128篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 10篇 |
2012年 | 35篇 |
2011年 | 20篇 |
2010年 | 19篇 |
2009年 | 8篇 |
2008年 | 25篇 |
2007年 | 17篇 |
2006年 | 16篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 8篇 |
2000年 | 27篇 |
1999年 | 19篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有332条查询结果,搜索用时 33 毫秒
11.
Yuri A. de Oliveira Só Mônica de Abreu Silva Fernando M. Carvalho Alessandra S. Kiametis Ricardo Gargano 《International journal of quantum chemistry》2020,120(11):e26194
Oxidative stress is an imbalance between the production of free radicals and the antioxidant defenses of the organism. Heart diseases, anemia, inflammation, and neurodegenerative disorders have been associated with this biological condition. Trolox is a notable antioxidant drug similar to vitamin E, and it is used to decrease the oxidative stress or repair the damage caused by it. In this work, the virtual screening technique is applied to identify compounds with antioxidant activities similar to Trolox. The antioxidant activity of these compounds was assessments by the mechanisms of hydrogen atom transfer and single electron transfer. Properties such as bond dissociation enthalpy, adiabatic ionization potential, Gibbs free reaction energy, spin density, highest occupied molecular orbital (HOMO), and GAP (HOMO-LUMO) energies, obtained from the DFT approach, point out to the predominance of the HAT mechanism for the antioxidant action of these compounds. The obtained results contribute to a better understanding of the chemical and physical properties responsible for antioxidant activity and the design of new antioxidant agents. 相似文献
12.
Langone Marta A. P. De Abreu Melissa E. Rezende Michelle J. C. Sant’Anna Geraldo L. 《Applied biochemistry and biotechnology》2002,98(1-9):987-996
The synthesis of monocaprin, monolaurin, and monomyristin in a solvent-free system was conducted by mixing a commercial immobilized
lipase with the organic reactants (glycerol and fatty acids) in a 20-mL batch reactor with constant stirring. The effects
of temperature, fatty acid/glycerol molar ratio, and enzyme concentration on the reaction conversion were determined. The
addition of molecular sieves in the assays of monomyristin synthesis was also evaluated. The reactions were carried out for
5 to 6 h and the nonpolar phase was analyzed by gas chromatography. The best results in terms of selectivity and conversion
(defined as the percentage of fatty acid consumed) were achieved when the stoichiometric amount of reagents (molar ratio=1)
and 9% (w/w) commercial enzyme were used and the reaction was performed at 60°C. The addition of molecular sieves did not
improve the synthesis of monomyristin. Conversions as high as 80%, with monoglycerides being the major products, were attained.
After 5 h of reaction, the concentration of monoglyceride was about twice that of diglyceride, and only trace amounts of triglyceride
were found. The results illustrate the technical possibility of producing medium chain monoglycerides in a solvent-free medium
using a simple batch reactor. 相似文献
13.
G. Spavieri V. Guerra R. De Abreu G. T. Gillies 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):457-463
Propagation of Aharonov-Bohm matter waves and light waves in moving media is
characterized by the interaction electromagnetic momentum. Thus, recent
models of light propagation in moving rarefied media justify and call for an optical experiment of the Mascart-Jamin type,
capable of testing the
modern interpretations of ether drift experiments. 相似文献
14.
Properties associated with the infrared, Rayleigh, and Raman spectra of the CO(3) molecule are calculated by the Hartree-Fock and M?ller-Plesset perturbation theory methods. Vibrational frequencies and infrared activities are found to be in agreement with the experiment and previous calculations. The values obtained for the Raman spectrum show a very sensitive dependence to the treatment of electron correlation. The OCO wag normal mode, unobserved in the IR experiment, is predicted to have a very small Raman scattering activity. Copyright 2000 Academic Press. 相似文献
15.
Moldovan L Melinte S Bayot V Papadakis SJ De Poortere EP Shayegan M 《Physical review letters》2000,85(20):4369-4372
We report very low temperature ( T) thermopower and resistivity ( rho) measurements on variable-density, two-dimensional hole systems confined to GaAs quantum wells. As the hole density is lowered from 1.49x10(11) cm(-2) to 0.14x10(11) cm(-2), the system crosses from an insulating ( drho / dT less, similar0) to a metallic regime ( drho / dT>0) and finally displays insulating behavior ( drho / dT<0). Diffusion thermopower shows a striking sign reversal in a narrow range of density in the metallic regime, suggesting a qualitative change in the conduction or the scattering mechanism. 相似文献
16.
In a recent article [M. Consoli, E. Costanzo, Phys. Lett. A 333 (2004) 355], M. Consoli and E. Costanzo have investigated classical and modern aether drift experiments and explored the narrow window for detection of a preferred reference frame. This Letter proposes an easy to perform variant of Fizeau's experiment, which may confirm or deny Consoli–Costanzo's claims. 相似文献
17.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》1999,11(3):383-407
The data collected with the DELPHI detector at centre-of-mass energies between 130 and 172 GeV, during LEP operation in 1995
and 1996, have been used to determine the hadronic and leptonic cross-sections and leptonic forward–backward asymmetries.
In addition, the cross-section ratios and forward–backward asymmetries for flavour-tagged samples of light (uds), c and b
quarks have been measured. No significant deviations from the Standard Model expectations are found. The results are interpreted
by performing S-matrix fits to these data and to the data collected previously at the energies near the resonance peak (88-93 GeV). The results are also interpreted in terms of physics beyond the Standard Model: contact interactions,
R-parity violating SUSY particle exchange and of possible Z bosons.
Received: 9 February 1999 / Published online: 14 October 1999 相似文献
18.
19.
Rafael Y. O. Moreira Davi S. B. Brasil Cláudio N. Alves Giselle M. S. P. Guilhon Lourivaldo S. Santos Mara S. P. Arruda Adolfo H. Müller Patrícia S. Barbosa Alcicley S. Abreu Edilene O. Silva Victor M. Rumjanek Jaime Souza Jr. Albérico B. F. da Silva Regina H. de A. Santos 《International journal of quantum chemistry》2008,108(3):513-520
Julocrotine, N‐(2,6‐dioxo‐1‐phenethyl‐piperidin‐3‐yl)‐2‐methyl‐butyramide, is a potent antiproliferative agent against the promastigote and amastigote forms of Leishmania amazonensis (L.). In this work, the crystal structure of Julocrotine was solved by X‐ray diffraction, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. IR and NMR spectra also have been obtained and compared with theoretical calculations. IR absorptions calculated with the B3LYP level of theory employed together with the 6‐311G+(d,p) basis set, are close to those observed experimentally. Theoretical NMR calculations show little deviation from experimental results. The results show that the theory is in accordance with the experimental data. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
20.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》2001,19(2):201-212
A search for pair-production of neutralinos at a LEP centre-of-mass energy of 189 GeV gave no evidence for a signal. This
limits the neutralino production cross-section and excludes regions in the parameter space of the Minimal Supersymmetric Standard
Model (MSSM).
Received: 22 November 2000 / Revised version: 11 January 2001 / Published online: 15 March 2001 相似文献