全文获取类型
收费全文 | 898篇 |
免费 | 8篇 |
国内免费 | 5篇 |
专业分类
化学 | 740篇 |
力学 | 16篇 |
数学 | 88篇 |
物理学 | 67篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 7篇 |
2016年 | 20篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 24篇 |
2012年 | 38篇 |
2011年 | 55篇 |
2010年 | 27篇 |
2009年 | 14篇 |
2008年 | 43篇 |
2007年 | 45篇 |
2006年 | 50篇 |
2005年 | 47篇 |
2004年 | 48篇 |
2003年 | 39篇 |
2002年 | 31篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 14篇 |
1971年 | 5篇 |
1967年 | 3篇 |
排序方式: 共有911条查询结果,搜索用时 15 毫秒
61.
62.
The most general coordinate system in which the Galilean symmetries of the ordinary and the Bell and Ruegg light-cone frames appear is found. With a modification of this general coordinate system it is possible to go from the Galilei group in two space dimensions to the Lorentz group, a process inverse to the contraction of the Lorentz group with respect to the subgroup of rotations. As an example of the applicability of this modified general light-cone frame, the two-dimensional Schrödinger-Pauli equation is obtained to all orders. 相似文献
63.
64.
65.
66.
Electrochemical properties of iron oxides, crystallographic data and examination of etching pits by scanning electron microscopy, suggest that ferric iron has electrochemical reactivity which differs according to its crystallographic position in the solid. 相似文献
67.
John J. Daly Peter Schnholzer Jean-Paul Behr Jean-Marie Lehn 《Helvetica chimica acta》1981,64(5):1444-1451
The crystal and molecular structure of the complex formed by the ionized bistartro-[18]-crown-6 receptor molecule 1 with the ethylenediammonium cation, is described. The macrocycle is roughly planar, the carboxy groups of each tartaric acid residue being in a diaxial relationship and extending above and below this plane. This conformation allows ‘lateral’ interactions with bound species to occur. The substrate is sandwiched between two macrocycles, with one of its NH heads anchored to the polyether core, and the other one in contact with the two carboxy groups of the neighboring molecule. 相似文献
68.
Frennet A Visart de Bocarmé T Bastin JM Kruse N 《The journal of physical chemistry. B》2005,109(6):2350-2359
The aim of this paper is to demonstrate the importance of providing time-resolved information in catalysis research. Two truly in situ methods will be presented and compared for their merits and drawbacks: chemical transient kinetics (CTK) and pulsed field desorption mass spectrometry (PFDMS). The presentation will be given by way of example choosing the syngas (CO/H2) reaction over cobalt-based catalysts as a catalytic process. Despite numerous efforts in the past, the mechanism of this reaction is still under debate. In CTK the reaction is studied on a metal-supported catalyst under flow conditions in a pressure range extending from atmospheric pressure down to 100 Pa. Sudden changes in the partial pressures of the reactants then allow following the relaxation to either steady-state conditions ("transients") or cleanoff ("back transients"). In PFDMS short field pulses of several volts per nanometer are applied to a model catalyst which resembles a single metal particle grain (a "tip"). These pulses intervene during the ongoing reaction under flow conditions at pressures ranging from 10(-1) to 10(-5) Pa and cause field desorption of adsorbed species. This method is particularly suited to detect reaction intermediates in a time-dependent manner since the repetition frequency of the pulses can be systematically varied. It is shown that both methods lead to complementary results. While CTK allows conclusions on the mechanism of CO hydrogenation by following the time-dependent formation of hydrocarbon species, PFDMS provides insight into the initial steps leading to adsorbed CxHy species. A quantitative assessment of the CTK data allows the demonstration that the catalyst under working conditions is in an oxidized rather than metallic state. The initial steps to oxidation are also traced by PFDMS. Most importantly, however, CTK results allow formulation of a reaction mechanism that is common for both hydrocarbon and oxygenate formation and is based on the occurrence of a formate-type species as the most abundant surface intermediate. 相似文献
69.
70.
Thieuleux C Quadrelli EA Basset JM Döbler J Sauer J 《Chemical communications (Cambridge, England)》2004,(15):1729-1731
The silica-supported Zr(iv) dihydride [(triple bond)SiO)2ZrH2] reacts quickly and completely with methane to yield [(triple bond)SiO)2ZrMe2] through the intermediate [(triple bond)SiO)2ZrHMe], while its monohydride analogue [(triple bond)SiO)3ZrH] yields the monomethylated product [(triple bond)SiO)3ZrMe] slowly and incompletely. 相似文献