全文获取类型
收费全文 | 321篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
化学 | 214篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 81篇 |
物理学 | 34篇 |
出版年
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 21篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 6篇 |
2015年 | 10篇 |
2014年 | 23篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 21篇 |
2010年 | 20篇 |
2009年 | 13篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 3篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有332条查询结果,搜索用时 31 毫秒
1.
Ioana Dumitriu Alan Edelman 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2005,41(6):1083-1099
In this paper we examine the zero and first order eigenvalue fluctuations for the β-Hermite and β-Laguerre ensembles, using tridiagonal matrix models, in the limit as β→∞. We prove that the fluctuations are described by multivariate Gaussians of covariance O(1/β), centered at the roots of a corresponding Hermite (Laguerre) polynomial. The covariance matrix itself is expressed as combinations of Hermite or Laguerre polynomials respectively.We show that the approximations are of real value even for small β; we can use them to approximate the true functions even for the traditional β=1,2,4 values. 相似文献
2.
Marilena Vasilescu Titus Constantinescu Mariana Voicescu Helge Lemmetyinen Elina Vuorimaa 《Journal of fluorescence》2003,13(4):315-322
The spectrophotometric study of luminol (LH2) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH2 absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L2–) formation at 3 × 10–4 – 2.4 × 10–3
M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH2-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10–3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH2-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH+
3 cation formation. In LH2-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH2-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed. 相似文献
3.
V. Badescu M. Radu M. Zaharescu A. Vasilescu 《Journal of Sol-Gel Science and Technology》1994,2(1-3):43-49
Gas-chromatography coupled with mass spectrometry was used to investigate the hydrolysis and condensation of tetra-ethoxysilane (TEOS) in nonparental solvents (MeOH and nPrOH). In the presence of nonparental solvents, the reaction that advanced at highest rate is alkoxy group scrambling, that changes the precursor at the molecular level. Subsequent stages of hydrolysis-polycondensation process are essentially determined by the reactivity of the new molecular species formed. 相似文献
4.
The sulfur mustard, HD, a chemical warfare agent, has been studied by ab initio quantum molecular computations (HF /6-31G * and 6-31G ) on its various forms (neutral, ethylene sulfonium, and free carbonium ions). The geometries of these molecules have been completely optimized and the minimal energy conformations determined with their associated charge distributions. We discuss these results on electrostatic properties with respect to the mechanism of DNA alkylation by HD and compare them with our previous study of the nitrogen mustard mechlorethamine. 相似文献
5.
Conformational transformations of the tetraenic nystatin chromophore under the influence of solvents and UV irradiation have been studied by absorption, fluorescence and wide-line NMR spectroscopy. 相似文献
6.
Bercu C Oncescu T Lupan L Bandula R Vasilescu M Sandu T Mitran L 《Analytical and bioanalytical chemistry》1996,355(5-6):753-755
The influence of SDS upon the molecular properties of proflavine (3,6-diaminoacridine), acridine yellow (2,7-dimethyl-3,6-diaminoacridine) and methylene blue (3,7-bis-dimethylamino-phenothiazine) was studied comparatively to their properties in that of aqueous media. The absorption and emission spectra of the three dyes in SDS aqueous solution (1-100 mmol/l) were recorded. The spectroscopic data also allowed the evaluation of the critical micellization concentration (CMC), acidity constants in fundamental (pk(a)) and excited (pK(*)(a)) states, and lifetimes of excited singlet states. 相似文献
7.
A recently proposed perturbational approach to the electron correlation cusp problem 1 is tested in the context of three spherically symmetrical two‐electron systems: helium atom, hydride anion, and a solvable model system. The interelectronic interaction is partitioned into long‐ and short‐range components. The long‐range interaction, lacking the singularities responsible for the electron correlation cusp, is included in the reference Hamiltonian. Accelerated convergence of orbital‐based methods for this smooth reference Hamiltonian is shown by a detailed partial wave analysis. Contracted orbital basis sets constructed from atomic natural orbitals are shown to be significantly better for the new Hamiltonian than standard basis sets of the same size. The short‐range component becomes the perturbation. The low‐order perturbation equations are solved variationally using basis sets of correlated Gaussian geminals. Variational energies and low‐order perturbation wave functions for the model system are shown to be in excellent agreement with highly accurate numerical solutions for that system. Approximations of the reference wave functions, described by fewer basis functions, are tested for use in the perturbation equations and shown to provide significant computational advantages with tolerable loss of accuracy. Lower bounds for the radius of convergence of the resulting perturbation expansions are estimated. The proposed method is capable of achieving sub‐μHartree accuracy for all systems considered here. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
8.
Laura Pop Pierrik Lassalas László Csaba Bencze Monica Ioana Toşa Botond Nagy Florin Dan Irimie Christophe Hoarau 《Tetrahedron: Asymmetry》2012,23(6-7):474-481
Stereoselective preparative enzymatic acylation and hydrolysis/methanolysis of various C-substituted rac-thiazol-2-yl-methanols were achieved for the preparation of enantiopure or enantiomerically enriched, naturally occurring 2-hydroxymethylthiazoles. The absolute configurations of the resulting secondary alcohols were determined by a detailed 1H NMR study of Mosher’s derivatives. 相似文献
9.
10.