全文获取类型
收费全文 | 505篇 |
免费 | 27篇 |
专业分类
化学 | 437篇 |
晶体学 | 4篇 |
力学 | 6篇 |
数学 | 34篇 |
物理学 | 51篇 |
出版年
2023年 | 5篇 |
2022年 | 24篇 |
2021年 | 23篇 |
2020年 | 17篇 |
2019年 | 14篇 |
2018年 | 10篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 14篇 |
2014年 | 27篇 |
2013年 | 32篇 |
2012年 | 34篇 |
2011年 | 35篇 |
2010年 | 18篇 |
2009年 | 28篇 |
2008年 | 43篇 |
2007年 | 19篇 |
2006年 | 19篇 |
2005年 | 34篇 |
2004年 | 28篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
排序方式: 共有532条查询结果,搜索用时 15 毫秒
1.
For a dynamical system (X, B, T, μ) we investigate the connections between metric invariants, the rankr(T) and the covering numberF
*(T) and a spectral property for having a simple spectrum. Given a positive integerr≥2, a real numberb, 0<b<1 such thatr·b≥1, we construct examples of systems withr(T)=r, F
*(T)=b and having a simple spectrum. 相似文献
2.
R. M. Vlasova N. V. Drichko B. V. Petrov V. N. Semkin E. I. Zhilyaeva R. N. Lyubovskaya I. Olejniczak A. Kobayashi H. Kobayashi 《Physics of the Solid State》2004,46(11):1985-1993
Polarized reflectance and optical conductivity spectra of single crystals of two new isostructural organic conductors based
on the BEDT-TSeF molecule, namely, the κ-(BETS)4Hg2.84Br8 superconductor (T
c
=2 K) and the κ-(BETS)4Hg3Cl8 metal, which undergoes a smooth transition to the dielectric state near 35 K, have been obtained in the spectral region 700–6500
cm−1 at temperatures of 300–15 K. At 300 K, the spectra of both compounds are nearly identical and differ from the Drude spectrum
characteristic of metals. The nature of the observed difference is discussed, and the spectra are described in terms of a
cluster approach with inclusion of electron-electron correlations in the Hubbard approximation combined with the Drude model.
The parameters of the theory were determined, including the electron transfer integrals between molecules in a cluster. The
spectra in the conducting plane of the crystals were found to be essentially anisotropic, which should be assigned to specific
features of in-plane interaction between molecules. The spectra of the superconductor and the metal become increasingly different
as the temperature is lowered. The spectra of the metal obtained for T<150 K exhibit splitting of the broad electronic maximum in the mid-IR region into two bands, which is accompanied by a splitting
of a vibronic feature deriving from electron interaction with intramolecular BETS vibrations of ν3(A
g
) symmetry. No such splitting is observed in the superconductor spectra with decreasing temperature.
__________
Translated from Fizika Tverdogo Tela, Vol. 46, No. 11, 2004, pp. 1921–1929.
Original Russian Text Copyright ? 2004 by Vlasova, Drichko, Petrov, Semkin, Zhilyaeva, Lyubovskaya, Olejniczak, A. Kobayashi,
H. Kobayashi. 相似文献
3.
The title compound (C14H8N2O7,M
r
=306.2) crystallizes in the orthorhombic space group Pbca witha=6.962(1).b=24.688(1), andc=15.890(1)Å,V=2731.0 Å3,D
x
=1.489 g·cm–3 forZ=8,=0.98 mm–1,F(000)=1296,T=293 K. FinalR=0.053 for 1873 observed reflections. The structure was solved by direct methods. Approximately planar molecules lie perpendicular to the [100] direction and show partial stacking. The structure is the first example of a symmetric anhydride which does not retain the symmetry in the crystal state. The two independent nitro groups twist out of the ring planes by 10.5 and 14.8°, respectively. 相似文献
4.
The copper(II) complex [Cu(sat)], where Hsat is salicylidene-2-aminothiazole (bidentate Schiff - base), was studied in variety of solvents. In the solid state, the complex is black. It has been characterized by elemental analysis, solubility in common solvents, molar conductivity, and ultraviolet (UV) and visible (Vis) spectroscopy. The complex is easily soluble in common solvents such as chloroform, dimethylformamide, dimethyl sulfoxide, and 1,4-dioxane. The known crystal structure of similar compounds shows planar coordination geometry for the copper center. Combined multitechnique experiments have been applied to confirm the structure of the complex in solutions. The molar conductivities indicate their nonelectrolyte properties in all these solvents. The spectroscopic measurements were used to study the coordination properties of donoratoms and their bonding abilities. 相似文献
5.
Czechowski F Golonka I Jezierski A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(6):1387-1394
The lignins separated from angiosperm and gymnosperm trees, peat and xylitic brown coal were investigated by quantitative EPR. Observed free radicals in lignins are sensitive to alkaline environment. Gaseous ammonia interacting with solid lignins in resonance cavity shifts quinone-hydroquinone equilibria towards formation of semiquinone anions. Complexation of copper(II) by lignins causes drastic decrease of the semiquinones in the matrices. Formation of lignin-Pb(II) complexes yielded radicals characterised by unusually low g-value (1.9999-2.0003). Monomeric structural units of the investigated lignins were recognised by pyrolysis with in situ methylation by tetramethylammonium hydroxide. Although for the natural lignins the mixture of normal semiquinone signals at g about 2.0034 and signals at g 1.9999 were observed, some monomeric components of lignins (e.g., caffeic acid, pyrogallol) gave pure lines at g = 1.9999. The bacterial oxidative biodegradation of lignin monomeric components and their Pb(II) complexes resulted in increase of the radical signals. 相似文献
6.
Lewiński J Marciniak W Lipkowski J Justyniak I 《Journal of the American Chemical Society》2003,125(42):12698-12699
Studies on the reaction of zinc alkyls with O2 are reported which demonstrate that the selective oxygenation of organozinc compound is viable. The reaction of [EtZn(azol)]n (azol = deprotonated 1-aziridineethanol) with an excess of dry O2 in toluene affords the zinc ethylperoxide [EtOOZn(azol)]2[EtZn(azol)]2, while the analogous reaction between Me2Zn and O2 results in the isolation of the Me6Zn7(OMe)8 cluster in high yield. 相似文献
7.
Pt(II) and Pd(II) dichloride complexes with 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) have been synthesized and characterized by infrared and 1H, 13C NMR, 13C CPMAS spectroscopy. The structures of the cis-PtCl2(dbtp)2 · EtOH (1) and cis-PdCl2(dbtp)(dmso) (2) has been determined by signal-crystal X-ray diffraction. In both complexes the X-ray crystal structures shows that heterocycle ligand (dbtp) binds the central atom monodentate via nitrogen atom N(3). In addition, compound (2) is interesting for its structural features, because it is the first report of mixed dichloride Pd(II) complexes with N-donor (triazolopyrimidine) and S-donor (dimethylsulfoxide) ligands. In this structure the Pd–Cl distances are: 2.302(1) and 2.281(1) Å, Pd–N 2.041(3) Å and Pd–S 2.245(1) Å. The 1H, 13C NMR studies show clearly that these structures are retained in solution. 相似文献
8.
Alumina-silica possessing various Al2O3/SiO2 ratios was used as a carrier of surface titanium complexes. The systems obtained were examined as models for the investigation of the macroligand (inorganic gel) influence on the physicochemical properties of supported transition metal complexes. The titanium complexes were prepared first by the reaction of CpTiCl3, with the hydroxyl groups of the gel and then reduced by an excess of BuLi. The influence was established of the basic gel properties on: (a) the amount of titanium(IV) and titanium(III) complexes on the alumina-silica gel surfaces; (b) the symmetry of the surface TiIII surface complexes; (c) the electron density around the surface-TiIII ions, ionic or covalent bonds character in a complex; and (d) the catalytic activity in olefin hydrogenation. 相似文献
9.
A brief treatment of 2-thiopyrimidine nucleosides (s2U∗) with trans-2-phenylsulfonyl-3-phenyloxaziridine (PSO) results in efficient substrate desulfurization leading to the corresponding 4-pyrimidinone analogues (H2U∗). The key transformation proceeds through oxidation of the 2-thiocarbonyl group to a sulfur oxyacid derivative and subsequent elimination of sulfur dioxide. 4-Pyrimidinone 1-β-d-riboside (H2U) has been transformed into the respective phosphoramidite, a ready-to-use monomer for the introduction of a modified nucleoside into an oligonucleotide chain. Moreover, the effective desulfurization of the 2-thiouridine nucleotide could be achieved directly at the oligonucleotide level, by treatment of the TdA(s2U)dGdC oligonucleotide with PSO, as verified by MALDI-TOF mass spectrometry. 相似文献
10.
Andrzej Czerwiński Iwona Kiersztyn Michał Grdeń 《Journal of Solid State Electrochemistry》2003,7(6):321-326
The effect of temperature on hydrogen and deuterium electrosorption into a palladium LVE (limited-volume electrode) has been
investigated. A decrease in hydrogen capacity (H/Pd ratio) with increasing temperature has been observed. Temperature strongly
influences the plots of measured H(D)/Pd values vs. potential scan rate. In addition, hydrogen absorption was found to be
dependent on the composition of the surrounding electrolyte solution. These results have confirmed the hypothesis that two
different mechanisms of hydrogen desorption from the palladium electrode take place, namely electrochemical oxidation and
non-electrochemical recombination. Further, the ratio between the rate constants for these two processes has been found to
change with temperature.
Electronic Publication 相似文献