全文获取类型
收费全文 | 525篇 |
免费 | 17篇 |
国内免费 | 3篇 |
专业分类
化学 | 289篇 |
晶体学 | 1篇 |
力学 | 23篇 |
数学 | 87篇 |
物理学 | 145篇 |
出版年
2021年 | 7篇 |
2019年 | 8篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 17篇 |
2012年 | 19篇 |
2011年 | 27篇 |
2010年 | 11篇 |
2009年 | 10篇 |
2008年 | 21篇 |
2007年 | 18篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 12篇 |
1973年 | 13篇 |
1972年 | 4篇 |
1969年 | 7篇 |
1968年 | 6篇 |
1960年 | 6篇 |
排序方式: 共有545条查询结果,搜索用时 15 毫秒
51.
Kittiya Somphol Mardi Santoso Mohan Bhadbhade Christopher Gardner Naresh Kumar David StC. Black 《Tetrahedron》2012,68(7):1862-1868
Cyclotriveratrylenes containing one benzene ring and two indole rings linked through N1 and C2 can be prepared by acid-catalysed reactions of formaldehyde and aryl aldehydes with 1,2-di-(1-indolylmethyl)benzene compounds. 相似文献
52.
Asiya R. Mustafina Svetlana V. Fedorenko Nelya A. Makarova Ella KH. Kazakova Zul'fiya G. Bazhanova Vladimir E. Kataev Alexander I. Konovalov 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(1-2):73-76
The inclusion behaviour of a new water-soluble sulfonated calix[4]resorcinarene towards alkylammonium and N-methylpyridinium cations has been investigated on the basis of 1H NMR spectroscopy and pH-potentiometry data. The inclusion of the N-methylpyridinium cation has been found to be dependent on pH with the preferable inclusion of the methyl substituent in alkaline and the aromatic ring in neutral aqueous media. 相似文献
53.
54.
In the presence of low molecular weight organic acids (formic, acetic, propionic and malonic), inorganic selenium(IV) is converted by UV irradiation to volatile selenium carbonyl, dimethylselenide and diethylselenide, depending on the acid used. Gas chromatography–mass spectrometry analysis of the volatile products shows that, in 0.7 M formic acid solution, approximately 60–70% (v/v) SeH2 and 30–40% (v/v) SeCO are formed. The presence of nitrate ion appears to increase threefold the formation of SeCO while completely suppressing formation of SeH2. Copyright © 2003 Crown in the right of Canada. Published by John Wiley & Sons, Ltd. 相似文献
55.
Hole-doped rare-earth manganite La0.7Ca0.3MnO3 and the electron-doped manganite La0.7Ce0.3MnO3 both show a metal-insulator transition around 250 K associated with a ferromagnetic transition and colossal magnetoresistance.
In an earlier publication we have reported the rectifying characteristic of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction at room temperature, showing that it is possible to fabricate a diode out of the polaronic insulator regime
of doped manganites. Here we report the magneto-transport properties of such a tunnel junction above and below the metal-insulator
transition. We show, from the large positive magnetoresistance of the tunnel junction at low temperature, that La0.7Ce0.3MnO3 could be a minority spin carrier ferromagnet. The implication of this observation is discussed. 相似文献
56.
57.
Upstream porthole injection in a 2-D scramjet model 总被引:1,自引:0,他引:1
Injection from portholes upstream of the combustion chamber was investigated as a method of delivering fuel into a scramjet.
This method reduces the viscous drag on a model by allowing a reduction in the length of the combustion chamber. At experimental
enthalpies of 3.0 MJ/kg in the T4 shock tunnel, there was no evidence of combustion in the intake, either by shadowgraph or
pressure measurements. Combustion was observed in the combustion chamber. A theoretical extension of these results is made
to a hot wall scenario.
Received 2 January 2001 / Accepted 3 August 2001 相似文献
58.
Dr. Benedict M. Gardner Dr. Gábor Balázs Prof. Dr. Manfred Scheer Dr. Ashley J. Wooles Dr. Floriana Tuna Prof. Eric J. L. McInnes Dr. Jonathan McMaster Dr. William Lewis Prof. Dr. Alexander J. Blake Prof. Dr. Stephen T. Liddle 《Angewandte Chemie (International ed. in English)》2015,54(50):15250-15254
The HAsAsH molecule has hitherto only been proposed tentatively as a short‐lived species generated in electrochemical or microwave‐plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(TrenTIPS)}2(μ‐η2:η2‐As2H2)] ( 3 , TrenTIPS=N(CH2CH2NSiPri3)3; Pri=CH(CH3)2). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back‐bonding‐type interactions from uranium to the HAsAsH π*‐orbital. This experimentally confirms the theoretically predicted excellent π‐acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane‐1,2‐diide form. 相似文献
59.
Deniz Aydemir Alper Kiziltas Douglas J. Gardner Yousoo Han Gokhan Gunduz 《International Journal of Polymer Analysis and Characterization》2015,20(3):231-239
The aim of this study was to measure the thermal properties of foamed nano/macro filler–reinforced styrene maleic anhydride (SMA) composites. SMA (66%) as a polymer matrix (10% maleic anhydride content) and various fillers including wood flour, starch, α-cellulose, microcrystalline cellulose and cellulose nanofibrils as reinforcing agents (30%) and lubricant (4%) were used to manufacture the composites in a twin-screw extruder. According to the thermogravimetric analysis (TGA) results, thermal degradation of all the foamed composites was found to be lower than that of SMA composites. The storage modulus values were negatively affected with a second time foaming (reprocessing [recycling] the initially processed composites a second time), as were loss modulus and Tg. As a result, second-time-foamed composite modulus values were lower than those of the foamed composites. According to the melt flow index (MFI) results, viscosity of the SMA was found to increase with the addition of fillers. 相似文献
60.