全文获取类型
收费全文 | 2312篇 |
免费 | 74篇 |
国内免费 | 5篇 |
专业分类
化学 | 1478篇 |
晶体学 | 5篇 |
力学 | 65篇 |
数学 | 460篇 |
物理学 | 383篇 |
出版年
2024年 | 3篇 |
2023年 | 30篇 |
2022年 | 55篇 |
2021年 | 61篇 |
2020年 | 57篇 |
2019年 | 62篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 101篇 |
2015年 | 76篇 |
2014年 | 85篇 |
2013年 | 121篇 |
2012年 | 188篇 |
2011年 | 164篇 |
2010年 | 98篇 |
2009年 | 105篇 |
2008年 | 138篇 |
2007年 | 138篇 |
2006年 | 124篇 |
2005年 | 103篇 |
2004年 | 111篇 |
2003年 | 83篇 |
2002年 | 92篇 |
2001年 | 33篇 |
2000年 | 22篇 |
1999年 | 20篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 26篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1948年 | 2篇 |
1943年 | 3篇 |
排序方式: 共有2391条查询结果,搜索用时 15 毫秒
31.
Alfonsi M Arcadi A Aschi M Bianchi G Marinelli F 《The Journal of organic chemistry》2005,70(6):2265-2273
[reaction: see text] The gold-catalyzed reaction of 2-alkynyl-phenylamines with alpha,beta-enones represents a new general one-pot entry into C-3-alkyl-indoles by sequential reactions. Gold-catalyzed sequential cyclization/alkylation, N-alkylation/cyclization, or N-alkylation/cyclization/alkylation reactions leading to different indoles can be directed by changing the 2-alkynyl-phenylamine 1/alpha,beta-enone 3 ratio and the reaction temperature. Unusual gold-catalyzed rearrangement reaction of indoles are observed at 140 degrees C. New gold-catalyzed formation of propargyl-alkyl ether under mild conditions and the hydration reaction of N-acetyl-2-ethynyl-phenylamine are reported. 相似文献
32.
An enantioselective addition of titanium phenylacetylide to ketones, promoted by BINOL, is described; this new enantioselective protocol gives high enantiomeric excess (up to 90% ee) with aromatic ketones using a simple procedure without pyrophoric or expensive reagents. 相似文献
33.
[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide. 相似文献
34.
Thapper A Behrens A Fryxelius J Johansson MH Prestopino F Czaun M Rehder D Nordlander E 《Dalton transactions (Cambridge, England : 2003)》2005,(21):3566-3571
Reaction of the tetradentate ligand N-(2-hydroxybenzyl)-N,N-bis(2-pyridylmethyl)amine (L-OH) with MoO2Cl2 in methanol in the presence of NaOMe and PF6- results in the formation of [MoO2(L-O)]PF6. Similarly, the reaction of N-(2-mercaptobenzyl)-N,N-bis(2-pyridylmethyl)amine (L-SH) with MoO2(acac)2 leads to the formation of [MoO2(L-S)]+. The dioxo-molybdenum complex [MoO2(L-O)]+ reacts with phosphines in methanol to afford phosphine oxides and an air-sensitive molybdenum complex, tentatively identified as [Mo(IV)O(L-O)(OCH3)]. The latter complex is capable of reducing biological oxygen donors such as DMSO or nitrate, thereby mimicking the activity of DMSO reductase and nitrate reductase. Reaction of [MoO2(L-O)]PF6 with PPh3 in other solvents than methanol leads to the formation of the Mo(V) dimer [(L-O)OMo(micro-O)MoO(L-O)](PF6)2. The crystal structures of [MoO2(L-O)]PF6 and the micro-oxo bridged dimer are presented. 相似文献
35.
The synthesis of CF(3)OC(O)OOC(O)F is accomplished by the photolysis of a mixture of (CF(3)CO)(2)O, FC(O)C(O)F, CO, and O(2) at -15 degrees C using a low-pressure mercury lamp. The new peroxide is obtained in pure form in low yield after repeated trap-to-trap condensation and is characterized by NMR, IR, Raman, and UV spectroscopy. Geometrical parameters were studied by ab initio methods [B3LYP/6-311+G(d)]. At room temperature, CF(3)OC(O)OOC(O)F is stable for many days in the liquid or gaseous state. The melting point is -87 degrees C, and the boiling point is extrapolated to 45 degrees C from the vapor pressure curve log p = 8.384 - 1715/T (p/mbar, T/K). A possible mechanism for the formation of CF(3)OC(O)OOC(O)F is discussed, and its properties are compared with those of related compounds. 相似文献
36.
We study the properties of a one-dimensional (1D) granular gas consisting of N hard rods on a line of length L (with periodic boundary conditions). The particles collide inelastically and are fluidized by a heat bath at temperature Tb and viscosity gamma. The analysis is supported by molecular dynamics simulations. The average properties of the system are first discussed, focusing on the relations between granular temperature Tg=mv2, kinetic pressure, and density rho=N/L. Thereafter, we consider the fluctuations around the average behavior obtaining a slightly non-Gaussian behavior of the velocity distributions and a spatially correlated velocity field; the density field displays clustering: this is reflected in the structure factor which has a peak in the k approximately 0 region suggesting an analogy between inelastic hard core interactions and an effective attractive potential. Finally, we study the transport properties, showing the typical subdiffusive behavior of 1D stochastically driven systems, i.e., approximately Dt(1/2), where D for the inelastic fluid is larger than the elastic case. This is directly related to the peak of the structure factor at small wave vectors. 相似文献
37.
6-Trifluoromethyl-12-acylindolo[1,2-c]quinazolines are prepared in high yield through the palladium-catalyzed reaction of bis(o-trifluoroacetamidophenyl)acetylene with aryl or vinyl halides and triflates. The reaction, which tolerates a variety of important functional groups, probably involves the formation of a 3-acyl-2-(o-trifluoroacetamidophenyl)indole intermediate, followed by its cyclization to the indoloquinazoline product. [reaction: see text] 相似文献
38.
Andrs Zelcer Zulema D. Chaia Fabio D. Cukiernik Oscar E. Piro Eduardo E. Castellano 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m144-m146
The title compound, catena‐poly[[tetrakis(μ‐decanoato‐κ2O:O′)diruthenium(II,III)(Ru—Ru)]‐μ‐octanesulfonato‐κ2O:O′], [Ru2(C10H19O2)4(C8H17O3S)], is an octanesulfonate derivative of the mixed‐valence complex diruthenium tetradecanoate. The equatorial carboxylate ligands are bidentate, bridging two Ru atoms to form a dinuclear structure. Each of the two independent dinuclear metal complexes in the asymmetric unit is located at an inversion centre. The octanesulfonate anion bridges the two dinuclear units through axial coordination. The alkyl chains of the carboxylate and sulfonate ligands are arranged in a parallel manner. The global structure can be seen as infinite chains of polar moieties separated by a double layer of non‐polar alkyl groups, without interdigitation of the alkyl chains. 相似文献
39.
Marcia Araque-Marin Fabio Bellot Noronha Mickel Capron Franck Dumeignil Michle Friend Egon Heuson Ivaldo Itabaiana Jr. Louise Jalowiecki-Duhamel Benjamin Katryniok Axel Lfberg Sbastien Paul Robert Wojcieszak 《Molecules (Basel, Switzerland)》2022,27(12)
The development of the future French and European bioeconomies will involve developing new green chemical processes in which catalytic transformations are key. The VAALBIO team (valorization of alkanes and biomass) of the UCCS laboratory (Unité de Catalyse et Chimie du Solide) are working on various catalytic processes, either developing new catalysts and/or designing the whole catalytic processes. Our research is focused on both the fundamental and applied aspects of the processes. Through this review paper, we demonstrate the main topics developed by our team focusing mostly on oxygen- and hydrogen-related processes as well as on green hydrogen production and hybrid catalysis. The social impacts of the bioeconomy are also discussed applying the concept of the institutional compass. 相似文献
40.
D. Cozzi A. A. Kolessnik W. D. McFarlane A. J. Sutherland K. Halaka P. Meunier Ch. Mentzer L. S. Lanke C. Gatti und A. Kñalinsky 《Fresenius' Journal of Analytical Chemistry》1943,126(4):153-155
Ohne Zusammenfassung 相似文献