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排序方式: 共有353条查询结果,搜索用时 62 毫秒
71.
电阻式核磁共振(RDNMR)测量是1988年由德国马普所的von Klitzing研究小组针对GaAs二维电子气中少量核自旋的探测而提出的一种具有超高灵敏度的实验技术. 目前, RDNMR已经成为研究单层或双层GaAs二维电子气核自旋和电子自旋特性的重要手段. 由于为实现电阻式核磁共振测量所建立的动态核极化方法强烈依赖于GaAs特有的材料属性, 至今这一技术一直没有扩展应用到其他半导体低维系统中. 最近,本研究小组发展了一种动态核极化新方法,成功实现了对典型窄带半导体锑化铟(InSb) 二维电子气的电阻式核磁共振测量.本文在介绍电阻式核磁共振测量工作原理及已建立的典型动态核极化方法的基础上,着重讨论所提出的动态核极化新方法的机理、 实验结果以及对今后研究的展望. 相似文献
72.
Usuki T Yamada H Hayashi T Yanuma H Koseki Y Suzuki N Masuyama Y Lin YY 《Chemical communications (Cambridge, England)》2012,48(26):3233-3235
Desmosine, a crosslinking amino acid of elastin, is an attractive biomarker for diagnosis of chronic obstructive pulmonary disease (COPD). In this study, the first total synthesis of (+)-desmosine was achieved in 11% overall yield in 13 steps utilizing stepwise and regioselective Sonogashira cross-coupling reactions. 相似文献
73.
Noriyuki Suzuki Kosuke Nishimura Nozomu Ohara Masayoshi Nishiura Yoshiro Masuyama 《Journal of organometallic chemistry》2012,696(26):4321-4326
The stereoisomerization of 2,5-disubstituted 1-zirconacyclopent-3-yne compounds, stable five-membered cycloalkynes, has been studied with regard to the mechanism. The bimetallic complex of 1,4-bis(trimethylsilyl)butatriene was synthesized and structurally characterized, although it seems unimportant for the stereoisomerization reactions. The isomerization of trans-1,1-bis(η5-cyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne 2a into the cis-form in benzene-d6 solution were observed using 1H NMR spectroscopy at 50 °C in various concentrations. The reaction was first order with respect to trans-2a. This ruled out the possibility that a bimetallic complex was responsible for the isomerization. A kinetic isotope effect was observed (kH/kD = 1.8), suggesting that C–H activation is involved in the rate-determining step. A mechanism via hydrogen elimination from the complex of η4-π,π-coordination mode is proposed. 相似文献
74.
Md. Badruz Zaman Masaaki Tomura Yoshiro Yamashita 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(5):621-624
The title compounds, 4,4′‐(ethyne‐1,2‐diyl)dipyridinium bis(squarate), C12H10N22+·2C4HO4?, and 4,4′‐(ethene‐1,2‐diyl)dipyridinium bis(squarate), C12H12N22+·2C4HO4?, are isomorphous and crystallize in space group P. The cocrystals contain linear hydrogen‐bonded molecular tape structures along the [120] direction. The squarate monoanions form a ten‐membered dimer linked by two intermolecular O—H?O hydrogen bonds. Each component molecule forms a segregated stack along the c axis. The bond lengths of the squarate monoanion indicate delocalization of the enolate anion. 相似文献
75.
Masaaki Tomura Yoshiro Yamashita 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(5):619-620
The title compound, 6‐(1,3‐benzodithiol‐2‐ylidene)‐5,7‐dimethyl‐1,2‐diphenylpentacyclo[5.4.0.02,5.03,11.04,8]undecane, C32H28S2, with a C1‐homobasketane framework, crystallizes in the P space group with one molecule in the asymmetric unit. The two cyclobutane rings in the cage are in a puckered conformation. Due to the enhanced through‐bond interaction of the phenyl π systems involving a strained σ bond, the (Ph—)C—C(—Ph) bond length is significantly extended, to 1.610 (3) Å. 相似文献
76.
Md. Akhtaruzzaman Masaaki Tomura Yoshiro Yamashita 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):751-753
The title compound, C20H10N4S, and its dipyridinium salt, 4,4′‐(2,1,3‐benzodiazol‐4,7‐diyldiethynyl)dipyridinium diperchlorate, C20H12N4S2+·2ClO4?, display bond alternation in the 2,1,3‐benzothiadiazole rings, which suggests their quinonoid character. The dipyridinium dication molecules stack along the a axis and form a dimer with short S?N interheteroatom contacts [3.146 (4) Å] between the two 1,2,5‐thiadiazole rings. The dimer is surrounded by the perchlorate anions with which it forms a large number of intermolecular N—H?O and C—H?O hydrogen bonds. 相似文献
77.
Targets at various positions in a noise image were detected by the optical matched filtering technique. In this case the thermoplastic optical recorder was used as a matched filter recorder. High accuracy of position detection was obtained, i.e. the position error was 2% or less. 相似文献
78.
Takeo Taguchi Tomoyuki Takigawa Yumiko Tawara Tsutomu Morikawa Yoshiro Kobayashi 《Tetrahedron letters》1984,25(49):5689-5692
β-Fluoroallyl alcohols () were obtained with high stereoselectivity by the LiA1H4 reduction of 1-acetoxy-3-alkyl-2,2-difluorocyclopropanes (). 相似文献
79.
80.
Yoshiro Kakehashi 《Journal of magnetism and magnetic materials》1984,43(1):79-88
The magnetic properties of NiMn alloys at finite temperatures are investigated on the basis of an improved theory of the local environment effect (LEE). Magnetization vs. concentration curves, magnetization-temperature curves, phase diagram, high-field susceptibility and atomic short-range order dependence of the magnetization vs. temperature curves are calculated. The asymmetric behaviour of the high-field susceptibility around the critical concentration of ferromagnetism is explained by the LEE, as well as the itinerant character of the amplitude of the Ni local moment, for the first time. Two self-consistent solutions, corresponding to the high magnetization state and the low magnetization state, are found for a certain intermediate region of atomic order in Ni3Mn. Therefore, the existence of metamagnetism is suggested in that region. The anomalous double-stage magnetization-temperature curves in Ni3Mn alloys are explained by the transition from the high magnetization state to the low magnetization state. 相似文献