全文获取类型
收费全文 | 665篇 |
免费 | 10篇 |
国内免费 | 4篇 |
专业分类
化学 | 339篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 283篇 |
物理学 | 48篇 |
出版年
2023年 | 7篇 |
2022年 | 3篇 |
2021年 | 21篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 30篇 |
2015年 | 41篇 |
2014年 | 49篇 |
2013年 | 79篇 |
2012年 | 46篇 |
2011年 | 39篇 |
2010年 | 40篇 |
2009年 | 35篇 |
2008年 | 31篇 |
2007年 | 33篇 |
2006年 | 16篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 15篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有679条查询结果,搜索用时 46 毫秒
61.
Corneliu I. Oprea Fanica Cimpoesu Petre Panait Bogdan Frecuş Marilena Ferbinteanu Mihai A. Gîrţu 《Theoretical chemistry accounts》2011,129(6):847-857
We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compounds (TPP = meso-tetraphenylporphyrinato, TCNE = tetracyanoethylene), based on Density Functional Theory (DFT) methods, in order to interpret
the magnetic ordering in these prototypic systems. We compare and contrast the results of broken-symmetry DFT calculations
for extended systems, with periodic boundary conditions, and for finite systems, magnetic dimers modeling the actual molecular
magnets. By varying systematically the main angles, we are able to determine the geometry dependence of the exchange interaction.
Structure–properties correlations in these charge-transfer salts reveal the determinant role of the Mn-(N≡C)TCNE bond angle on the strength of the ferrimagnetic coupling between the S
1 = 2 spin located on the MnIII-porphyrin donor and the S
2 = 1/2 spin positioned on the cyanocarbon acceptor. When the Mn-(N≡C)TCNE angle is decreased, the intrachain magnetic coupling strengthens, correlated with the increase in the dz2 - p* d_{{z^{2} }} - \pi * orbital overlap. The exchange coupling constants resulting from DFT calculations of extended systems, with periodic boundary
conditions, were found to be consistent with those obtained for the dimers, but systematically smaller. The exchange constants
vary strongly with the functional used, hybrid functionals such as B3LYP leading to results that better correlate with the
experimental mean-field critical temperatures. The coupling constant varies significantly with the type of broken-symmetry
approach, depending on the overlap between magnetic orbitals, but weakly on the basis set once polarization effects are included.
The electronic structure calculations for the extended systems provide a density of states consistent with the energy spectrum
of the corresponding dimer, allowing for an intuitive explanation of the intrachain ferrimagnetic ordering. 相似文献
62.
Ioana Diaconu Hassan Y. Aboul-Enein Mohammed A. Al-Omar Gheorghe Nechifor Elena Ruse Andrei A. Bunaciu Eugenia Eftimie Totu 《Arabian Journal of Chemistry》2011,4(1):99-103
The paper presents experimental data obtained in the study of liquid–liquid partition equilibriums in biphasic system in order to optimize the process of transport through bulk liquid membranes (triphasic partition systems). The partition equilibriums of some nitrophenols using chloroform as extraction solvent and membranary solvent, respectively, were studied. The influence of the pH on the partition equilibriums was investigated. The repartition constants and the pKa values of the studied nitrophenols were calculated. Nitrophenols were transferred in triphasic system from a feed phase with pH 2, through a chloroform liquid membrane, into a receiving phase with pH 12, with efficiencies over 90%. 相似文献
63.
Inhibitive properties of the antibacterial sulfa drug sulfathiazole—IUPAC name being 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide—on the corrosion of carbon steel in 1.0 M HCl solution were investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Sulfathiazole is a good adsorption inhibitor, and the inhibition efficiency increases with increasing concentration. Adsorption is spontaneous and is best described by Temkin isotherm. XPS analysis showed, at this stage, that the main product of corrosion is a nonstoichiometric Fe3+ oxide/oxyhydroxide consisting of a mixture of Fe2O3, α, and γ-FeO(OH) and/or Fe(OH)3, where α, γ-FeO(OH) is the main phase. 相似文献
64.
Presented by R. S. Pierce. 相似文献
65.
A new Ag(+)-selective membrane electrode obtained by impregnating a graphite rod (attached to the end of a Teflon tube) with the silver(I) chelate of 1-(2',3',5'-tri-O-benzoyl-beta-D-ribofuranosyl)-4-thioxo-5-methylthio-6-azauracil dissolved in chloroform gives a stable and reproducible response to silver in the 10(-1)-10(-5)M range with a slope of 60 mV/decade. A new method for determination of some beta-chlorovinyl ketones is based on use of the electrode in potentiometric titration of the chloride displaced by tertiary amines from beta-chlorovinyl ketones in forming the corresponding quaternary ammonium salts. 相似文献
66.
The P-V-T relations of high pressure polyethylene free of additives have been studied in a modified universal testing machine. These polymers show a rapid compression at the melting point of the crystalline phase. 相似文献
67.
Ioana Cioranescu 《Mathematische Annalen》1974,211(1):37-46
Sans résumé 相似文献
68.
Vasilescu IM Bray DJ Clegg JK Lindoy LF Meehan GV Wei G 《Dalton transactions (Cambridge, England : 2003)》2006,(43):5115-5117
Four previously documented ligand design strategies for achieving Ag(I) discrimination have been applied to the design of a new N-benzylated N2S3-donor macrocycle; the latter shows high selectivity for Ag(I) over Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) in log K and bulk membrane transport studies. 相似文献
69.
Mohamed-Adel Slamani Andrzej Krol Jacques Beaumont Robert L Price Ioana L Coman Edward D Lipson 《Microscopy and microanalysis》2006,12(2):106-112
We have implemented and tested a new automatic method for the montage synthesis and three-dimensional (3D) reconstruction of large tissue volumes from confocal laser scanning microscopy data (CLSM). This method relies on maximization of the phase correlation between adjacent images. It was tested on a large specimen (a murine heart) that was cut into a number of individual sections with thickness appropriate for CLSM. The sections were scanned horizontally (in-plane) and vertically (perpendicular to the optical planes) to produce "tiles" of a 3D volume. Phase correlation maximization was applied to the montage synthesis of in-plane tiles and 3D alignment of optical slices within a given physical section. The performance of the new method is evaluated. 相似文献
70.
We present and study a lattice (Monte Carlo) model of a food web consisting of three levels. Agents on the lowest level produce food from dead agents (detritus) of the upper levels and are themselves eaten by the first level species, which in turn are prey for the top level species. Agents which do not find food in a given time, die with a given probability, while eating enables them to produce offspring in their neighborhood. This rule applies to species on all levels, including the lowest one. The dynamics is therefore nutrient limited. We are considering two pathways — grazers and detritus (using dead organic matter). We show that the emerging dynamics is more complex than the ordinary predator-prey systems in which bottom species are indestructible. We investigate the viability of our model and we construct appropriate (extinct-alive) phase diagrams. We demonstrate how the temporal fluctuations in the densities of the three populations are correlated. We show also that the density of the middle level agents plays the key role in the viability of the investigated food web. 相似文献