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21.
A metal-insulator crossover appears in the experimental data for in-plane resistivity of underdoped cuprates and a range of
superconducting cuprates in the presence of a strong magnetic field suppressing superconductivity. We propose an explanation
for this phenomenon based on a gauge field theory approach to the t-J model. In this approach, based on a formal spin-charge
separation, the low energy effective action describes gapful spinons (with a theoretically derived doping dependence of the
gap m
s
2
∼ δ| ln δ|) and holons with finite Fermi surface (ɛF ∼ tδ) interacting via a gauge field whose basic effect on the spinons is to bind them into overdamped spin waves, shifting their
gap by a damping term linear in T, which causes the metal-insulator crossover. The presence of a magnetic field perpendicular to the plane acts by increasing
the damping, in turn producing a big positive transverse in-plane magnetoresistance at low T, as experimentally observed. 相似文献
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23.
Rodolfo Graziani Maurizio Vidali Umberto Casellato P. Alessandro Vigato 《Transition Metal Chemistry》1978,3(1):138-141
Summary The structure of the homobinuclear complex Cu2(aapen)H2O, where aapen is the tetraanionic ligand derived from the condensation of 1,2-diaminocthane witho-acetoacetylphenol, has been determined from diffractometer data and refined to R = 6.1%. The crystals are monoclinic,P21/c, witha = 12.991(5),b = 8.530(4),c = 18.546(6) Å, and = 104.10(4)°; Z = 4. The ligand employed has two different coordination sets of atoms, N2O2 and O2O2, two oxygen atoms being common to both donor sets. In the complex, one copper atom is retained in the plane of the inner N2O2 chamber whilst the other, which is incorporated in the outer O2O2 chamber, is five-coordinate, being axially bonded to a water molecule. 相似文献
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25.
Piero Zanello Sergio Tamburini Pietro Alessandro Vigato Gian Antonio Mazzocchin 《Transition Metal Chemistry》1984,9(5):176-180
Summary The electrochemical behaviour of a series of mononuclear and dinuclear complexes of dioxouranium(VI), nickel(II) and copper(II) ions with the Schiff base, H4fsalacen, derived from the condensation of 3-formylsalicylic acid and 1,2-diaminoethane, is reported.The potentially hexadentate compartmental ligand H4fsalacen has an outer O2O2 and an inner N2O2 coordination site. The redox properties of the metal ions in these two different and adjacent chambers have been investigated and compared with those of the analogous complexes with the ligand H4 aapen, obtained by reaction ofo-acetoacetylphenol and 1,2-diaminoethane.A preliminary report was presented at the 1st International Conference on the Chemistry and Technology of the Lanthanides and Actinides, Venice, 5 September, 1983, Italy. 相似文献
26.
27.
泥沙输运模拟综述——现状及其发展趋势 总被引:1,自引:0,他引:1
随着流体力学中数值方法的飞速发展,计算模型已经成为研究流体运动,泥沙输运和不同环境(诸如河流,湖泊及沿海地区)中相应污染物归趋过程等方面非常有吸引力的工具,在过去的30多年里,发展了许多计算水动力学/泥沙输运模型.文章追溯当前具有代表性的(一维、二维、三维)模型的发展历程,描述他们各自的特点,优势及局限,力图作为对模型方面感兴趣读者的第一指南,同时也为大家讨论模型的局限性,未来的发展趋势和研究需求方面搭建一个平台.给出了模型的表达,时空特性,水动力学和沉积物的耦合方式,处理非恒定流,推移质和悬移质,泥沙交换过程,泥沙类型(粘性或非粘性)及非均匀泥沙输运的能力.总结了不同模型的应用实例,读者可以运用这些例子作为研究模型设置,模型率定及模型验证的参考.给出了选择泥沙输运模型应遵循的原则,模型输入及率定方面存在的问题及改进的途径.探讨了现有水动力学/泥沙输运模型在处理复杂湍流,泥沙携带,流动与输沙耦合,非均匀泥沙,离散和扩散系数,河岸来沙处理等方面的局限性及改进的方向.最后,对基于多相流思想的泥沙输运模型及其它一些交叉性问题作了评述与展望. 相似文献
28.
Piero Zanello Pietro Alessandro Vigato Gian Antonio Mazzocchin 《Transition Metal Chemistry》1982,7(6):291-293
Summary The ethylenediamine Schiff base derivative ofo-acetoacetylphenol, H4aapen, is a ligand able to form both mononuclear and dinuclear complexes with copper(II) ion. Mononuclear positional isomers can be obtained, having the copper in the O2O2 site and in the N2O2 site. The electrochemistry of these copper(II) complexes in dimethylsulfoxide shows that the two positional isomers are reduced at different potentials through an e.c.e. mechanism, in which a chemical reaction is coupled between two one-electron transfers, the N2O2 isomer being the less reducible. They also undergo complicated oxidation processes at high potentials, less significant in distinguishing the two isomers. The electrochemical behaviour of the dinuclear copper(II) complex parallels that of the two mononuclear isomers. 相似文献
29.
30.
The behaviour of the acrylic-silicone mixture commonly known as Bologna Cocktail, composed of commercial acrylic polymer Paraloid B72 and the silicon-based product, Dri Film 104, extensively employed as stone preservative for monuments in the last thirty years, has been tested on specimens appropriately prepared and submitted to ageing simulating reliable outdoor environment. After chemical characterization, the acrylic-silicone mixture was applied as thin film on slides, as thick film on Petri dishes and on marble by brush or by absorption; the resulting samples were artificially aged by light and saline solution. The chemical modifications were evaluated by FT-IR, NMR and SEC determinations, while preservative properties were tested by removability tests, ultrasonic and colorimetric measurements. The mixture consists of two immiscible phases and the two components have distinctive chemical behaviours, leading - after ageing - to irreversible molecular modifications and loss of conservative properties. The deterioration processes identified through laboratory simulation have been also verified on treated marble surfaces of two Venetian case studies. 相似文献