全文获取类型
收费全文 | 520篇 |
免费 | 47篇 |
国内免费 | 63篇 |
专业分类
化学 | 389篇 |
晶体学 | 14篇 |
力学 | 5篇 |
综合类 | 2篇 |
数学 | 1篇 |
物理学 | 219篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 15篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 44篇 |
2012年 | 47篇 |
2011年 | 24篇 |
2010年 | 22篇 |
2009年 | 42篇 |
2008年 | 32篇 |
2007年 | 25篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 16篇 |
2003年 | 23篇 |
2002年 | 26篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有630条查询结果,搜索用时 15 毫秒
51.
C. H. Patel A. B. Patel N. K. Bhatt P. N. Gajjar 《Physics and Chemistry of Liquids》2018,56(2):153-163
The calculations of electrical resistivity of Sn–Pb liquid metallic alloys/solutions are investigated by self-consistent approach. We employ modified empty-core pseudopotential to represent electron–ion interaction, while partial structure factors are calculated using Aschroft–Langreth scheme with hard sphere reference system. The potential parameters for elemental metals were optimised to structural data in our previous paper. Computed results for resistivity as a function of temperature and concentration are discussed with other such results. Overall good agreement confirms the applicability of the present model potential for computing the electrical properties, including thermal conductivity and thermoelectric power for liquid metallic alloys. 相似文献
52.
A carbon supported Pt–Sn electrocatalyst in the Pt/Sn atomic ratio 50:50 was prepared by the reduction of Pt and Sn precursors
with formic acid and thermally treated at 200 °C (i.e., in the presence of solid tin) and 500 °C (in the presence of molten
tin) in flowing hydrogen. In the absence of thermal treatment, X-ray diffraction (XRD) analysis showed a solid solution of
Sn in the face centered cubic (fcc) Pt and SnO2. After thermal treatment, the formation of a main phase of hexagonal PtSn (niggliite) and a secondary phase of cubic Pt3Sn was observed in the Pt50Sn50 catalyst. The relative amount of the PtSn phase increased with increasing thermal treatment
temperature. The presence of molten tin gave rise to the formation of some big particles during annealing at 500 °C. The activity
for the ethanol oxidation reaction (EOR) of the as-prepared catalyst was higher than that of both thermally treated catalysts
and Pt75Sn25/C and Pt50Ru50/C by E-TEK. The higher activity for the EOR of the as-prepared Pt–Sn catalysts was ascribed to
the presence of a large amount of SnO2.
Dedicated to Teresa Iwasita’s 65th birthday. 相似文献
53.
Using a slightly simplified version of the integrate and fire model of a neural network with delay, I study the stability
of the phase-locked state dependent on the coupling between the neurons and especially on a delay time. The coupling between
neurons may be arbitrary. It is shown that the phase-locked state becomes less stable with increasing delay and that relaxation
oscillations occur.
Received 28 December 1999 and Received in final form 13 June 2000 相似文献
54.
Organotincompoundsareextensivelystudiedfortheirbiologicalactivity'.Organogermaniumisanotherkindofelementthathasawiderangeofbiologicalactivity=.Tolinkbiologicalactivepropertiesoforganotinandorganogermaniumcompounds.wehavepreviouslyreportedthebiologicalactivityoftrialkyltingermylpropionates'andanticanceractivityofdibutyltindigermylpropionates'.ItiswellknownthatTorque(his[tri(2-methyl-2-phenylpropyl)tin]oxide)iswidelyusedinagricultureasanacaricide.Inthispaper,asthecontinuationofourpreviouswork"'… 相似文献
55.
56.
57.
Jens Beckmann Klaus Jurkschat Stephanie Rabe Markus Schürmann Dainis Dakternieks 《无机化学与普通化学杂志》2001,627(3):458-464
The syntheses of the asymmetrically substituted tetraorganodistannoxanes [t‐Bu2(X)SnOSn(Y)(CH2SiMe3)2]2 ( 1 , X = Y = OH; 2 , X = Cl, Y = OH; 3 , X = Y = Cl) are reported and their structures in solution and in the solid state are characterized by multinuclear NMR spectroscopy and single crystal X‐ray analyses. In toluene, the tetrahydroxy‐substituted derivative 1 is in equilibrium with the organotin oxides cyclo‐[t‐Bu2Sn{OSn(CH2SiMe3)2}2O] ( 4 ), cyclo[(Me3SiCH2)2Sn(OSnt‐Bu2)2O] ( 5 ), and cyclo‐(t‐Bu2SnO)3, and some additional, undefined species containing pentacoordinated tin atoms. In contrast, the dihydroxydichloro‐substituted derivative 2 is inert in solution. 相似文献
58.
(tBu2SnAsH)2 and (tBu2SnAsH)3: Two Novel Ring-Oligomeric Stannylarsines tBu2SnCl2 reacts with NaAsH2 in liquid ammonia to give the four-membered As–H-functional stannylarsine (tBu2SnAsH)2 ( 1 ). The oligomeric six-membered heterocycle (tBu2SnAsH)3 ( 2 ) is obtained by transamination of tBu2Sn(NHtBu)2 with AsH3. The novel compounds are characterized by NMR (1H, 119Sn) and mass spectroscopy and their molecule structures determined by X-ray crystallography. In the solid state both compounds contain molecules with planar tin-arsenic rings ( 1 : space group P21/n, Z = 2; 2 : space group P63/m, Z = 2). 相似文献
59.
Yasemin Caglar Seval Aksoy Saliha Ilican Mujdat Caglar 《Superlattices and Microstructures》2009,46(3):469-475
Undoped and tin (Sn) doped ZnO thin films have been prepared by spray pyrolysis method. Effect of Sn dopant on the crystalline structure and morphological properties of ZnO thin films has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) method. XRD patterns confirm that the films have polycrystalline nature. While undoped ZnO film has (101) as the preferred orientation, Sn doped ZnO thin films have (002) as the preferred orientation. Grain sizes, lattice parameters and texture coefficient values of the films were determined. Microstructure was analyzed by SEM and the influence of the doping concentration in the microstructure of the films is investigated. 相似文献
60.
The structure and surface composition of a Ni3Sn alloy at conditions relevant for the steam reforming reaction was investigated using density functional theory calculations. Both the flat Ni3Sn(0 0 0 1) surface and a surface with steps in the closed packed direction [1 0 0]were considered. The adsorption geometries and energies of the species CO, C, OH and H were calculated. Chemical potentials were used to map out which adsorbates are on the surface under varying conditions. It was found that adsorbates preferably bind to Ni as nearest neighbor with Sn as second-nearest neighbor. The binding energy is slightly stronger than on pure Ni. Adsorbate binding to Sn was found to be very unfavorable. Binding free energies indicate that at high temperature the alloy surface will be predominantly covered by CO and C, and at low temperatures one may find H and almost no OH. Even though the nominal composition of the investigated alloy is Ni3Sn, the surface composition may differ significantly depending on temperature and pressure of the gas phase. This effect was investigated by calculating segregation energies both in the absence and in the presence of adsorbates. For the flat surface, it was found that only the bulk termination is present under relevant conditions. In contrast, it was found that for steps preferential adsorption of CO and C on Ni sites may lead to adsorption-induced segregation at temperatures below 400 °C. When taking segregation into account, the most stable Ni3Sn surfaces will not bind CO or C at the same condition that Ni does. This is in excellent agreement with the previously proven ability of Ni-Sn alloys to inhibit graphite formation. 相似文献