全文获取类型
收费全文 | 915篇 |
免费 | 65篇 |
国内免费 | 1篇 |
专业分类
化学 | 713篇 |
晶体学 | 2篇 |
力学 | 30篇 |
数学 | 102篇 |
物理学 | 134篇 |
出版年
2023年 | 12篇 |
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 23篇 |
2019年 | 23篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 40篇 |
2015年 | 27篇 |
2014年 | 36篇 |
2013年 | 47篇 |
2012年 | 79篇 |
2011年 | 66篇 |
2010年 | 41篇 |
2009年 | 43篇 |
2008年 | 67篇 |
2007年 | 54篇 |
2006年 | 66篇 |
2005年 | 55篇 |
2004年 | 40篇 |
2003年 | 31篇 |
2002年 | 37篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1962年 | 3篇 |
1932年 | 2篇 |
1931年 | 2篇 |
1930年 | 2篇 |
1929年 | 2篇 |
排序方式: 共有981条查询结果,搜索用时 15 毫秒
971.
972.
Erik?Rosenbaum Magnus?Sellstedt Fredrik?Almqvist Lennart?B.-A.?Johansson 《Journal of fluorescence》2010,20(6):1249-1253
UV-VIS absorption and fluorescence spectroscopic properties of six related polyaromatic 2-pyridones have been studied. Excitation of the lowest and rather weak and structure-less transition [ε max (430 nm)?≈?3,000 mol?1dm3cm?1] gives rise to a broad fluorescence band in the visible region, for these compounds. These S 0 ? S 1 transitions are compatible with symmetrically forbidden transitions, promoted by intensity borrowing, as is revealed by fluorescence depolarisation data. With one exception, all compounds exhibit strong fluorescence, with quantum yields in glycerol varying between 40% and 70%. The corresponding fluorescence lifetimes range from 11 ns to 17 ns, while the radiative lifetimes are very similar (≈26 ns), for all compounds. Interestingly and rarely observed, the calculated radiative lifetimes for the weak absorption band are significantly longer, i.e. between 37 and 40 ns. 相似文献
973.
P.J. von Ranke N.A. de Oliveira V.S.R. de Sousa A. Magnus G. Carvalho 《Journal of magnetism and magnetic materials》2010,322(1):84-87
In this work we present a model to describe the magnetocaloric effect (MCE) in ferrimagnetic arrangements. Our model takes into account the magnetoelastic interactions in the two coupled magnetic sublattices, which can lead to the onset of the first order magnetic phase transition and the giant-MCE. Several profiles of the MCE, such as: the inverse- and giant-MCE were systematically studied. Application of the model to the ferromagnetic compounds GdAl2, Gd5(Ge1.72Si2.28), Gd5(Ge2Si2), and to the ferrimagnetic compound Y3Fe5O12 was performed, showing a good agreement with the experimental data. 相似文献
974.
Zheng-Jia Shen Dr. Chen Zhu Xiao Zhang Prof. Dr. Chao Yang Prof. Dr. Magnus Rueping Prof. Dr. Lin Guo Prof. Dr. Wujiong Xia 《Angewandte Chemie (International ed. in English)》2023,62(7):e202217244
(Deuterium-labeled) CF2H- and CFH2-moieties are of high interest in drug discovery. The high demand for the incorporation of these fluoroalkyl moieties into molecular structures has witnessed significant synthetic progress, particularly in the (deutero)hydrodefluorination of CF3-containing compounds. However, the controllable replacement of fluorine atoms while maintaining high chemoselectivity remains challenging. Herein, we describe the development of a selective (deutero)hydrodefluorination reaction via electrolysis. The reaction exhibits a remarkable chemoselectivity control, which is enabled by the addition of different organoboron sources. The procedure is operationally simple and scalable, and provides access in one step to high-value building blocks for application in medicinal chemistry. Furthermore, density functional theory (DFT) calculations have been carried out to investigate the reaction mechanism and to rationalize the chemoselectivity observed. 相似文献
975.
Dr. Haibo Wu Dr. Zhiyao Zheng Dr. Kaiheng Zhang Dr. Johan Kajanus Dr. Magnus J. Johansson Prof. Dr. Armando Córdova Prof. Dr. Jan-E. Bäckvall 《Angewandte Chemie (International ed. in English)》2023,62(50):e202314512
Classical Crabbé type SN2' substitutions of propargylic substrates has served as one of the standard methods for the synthesis of allenes. However, the stereospecific version of this transformation often requires either stoichiometric amounts of organocopper reagents or special functional groups on the substrates, and the chirality transfer efficiency is also capricious. Herein, we report a sustainable methodology for the synthesis of diverse 1,3-di and tri-substituted allenes by using a simple and cheap cellulose supported heterogeneous nanocopper catalyst (MCC-Amp-Cu(I/II)). This approach represents the first example of heterogeneous catalysis for the synthesis of chiral allenes. High yields and excellent enantiospecificity (up to 97 % yield, 99 % ee) were achieved for a wide range of di- and tri-substituted allenes bearing various functional groups. It is worth noting that the applied heterogeneous catalyst could be recycled at least 5 times without any reduced reactivity. To demonstrate the synthetic utility of the developed protocol, we have applied it to the total synthesis of several chiral allenic natural products. 相似文献
976.
Liubov V. Stepakova Mikhail Yu. Skripkin Lyudmila V. Chernykh Galina L. Starova Lszl Hajba Jnos Mink Magnus Sandstrm 《Journal of Raman spectroscopy : JRS》2008,39(1):16-31
Vibrational spectroscopic and force field studies have been performed of 15 related copper(II) chloride and copper(II) bromide compounds, including hydrated salts crystallizing in ternary aqueous systems with alkali and ammonium halides. For halocuprates with distorted octahedral coordination characteristic stretching Raman wavenumbers, corresponding to symmetric stretching CuII X modes in the equatorial plane, were found in the ranges 247–288 cm−1 for X = Cl, and 173–189 cm−1 for X = Br, while the low‐wavenumber stretching modes for the weaker axial Cu X interactions varied considerably. The tetrahedral coordination for Cs2CuCl4 and Cs2CuBr4 leads to somewhat lower Cu X symmetric stretching wavenumbers, 295 and 173 cm−1, respectively. The assignments of the copper–ligand stretching vibrations were performed with the aid of normal coordinate calculations. Correlations between force constants, averaged Cu X stretching wavenumbers and bond distances have been evaluated considering the following aspects: (1) Jahn–Teller tetragonal distortion (axial elongation) of the octahedral copper(II) coordination environment, (2) differences between terminal and bridging halide ligands (3) effects of coordinated water and the influence of outer‐sphere cations. Force constant ratios for terminal and bridging metal–halide bonds reveal characteristic differences between planar and tetrahedrally coordinated M2X6 species. In the hydrated copper(II) halide complexes, the halide ligands are more strongly bound than coordinated water molecules. The crystal structure of KCuBr3 (K2Cu2Br6), which was determined to provide structural information for the force field analyses, contains stacks of planar dimeric [Cu2Br6]2− complexes held together by weak axial Cu Br interactions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
977.
Dr. Seetharaman Manojveer Nitish K. Garg Zarif Gul Ayesha Kanwal Dr. Yogesh Goriya Dr. Magnus T. Johnson 《ChemistryOpen》2023,12(1):e202200245
A new class of palladium complexes bearing bidentate 2-hydroxypyridine based ligands have been prepared and fully characterized. The applications of these new complexes towards ketone alkylation reactions with alcohols through a metal-ligand cooperative borrowing-hydrogen (BH) process were demonstrated. 相似文献
978.
Farideh Jalilehvand Mikhail Maliarik Janos Mink Magnus Sandstroem Andrey Ilyukhin Julius Glaser 《ChemInform》2002,33(27):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
979.
980.
Dr. Haifeng Chen Dr. Chen Zhu Prof. Dr. Huifeng Yue Prof. Dr. Magnus Rueping 《Angewandte Chemie (International ed. in English)》2023,62(33):e202306498
The difunctionalization of unsaturated bonds plays a vital role in the enrichment of molecular complexity. While various catalytic methods for alkene and alkyne difunctionalization have been developed in recent years, hetero-functionalization the introduction of two different atoms has been less explored. This is mainly due to the challenges associated with achieving high chemo-, regio-, and stereoselectivity, especially when adding two similar atoms from the same group across unsaturated bonds. In this study, we describe a nickel-catalyzed, three-component reductive protocol for group 14 element hetero-difunctionalization of 1,3-enynes using electrochemistry. This new method is mild, selective, and general, allowing for the silyl-, germanyl-, and stannyl-alkylation of enynes. Various chlorosilanes as well as chlorogermans, and chlorostannanes can be successfully used in combination with aryl/alkyl-substituted 1,3-enynes and primary, secondary, and tertiary alkyl bromides in the electroreductive coupling. 相似文献