全文获取类型
收费全文 | 630篇 |
免费 | 35篇 |
专业分类
化学 | 479篇 |
晶体学 | 4篇 |
力学 | 12篇 |
数学 | 59篇 |
物理学 | 111篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 28篇 |
2015年 | 28篇 |
2014年 | 20篇 |
2013年 | 41篇 |
2012年 | 43篇 |
2011年 | 58篇 |
2010年 | 37篇 |
2009年 | 21篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 42篇 |
2005年 | 34篇 |
2004年 | 22篇 |
2003年 | 22篇 |
2002年 | 22篇 |
2001年 | 21篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有665条查询结果,搜索用时 187 毫秒
661.
A novel approach to the synthesis of indoline derivatives is presented. The key cyclization step features the phenyliodine(III) bis(trifluoroacetate)- (PIFA-) mediated formation of a N-acylnitrenium ion and its succeeding intramolecular trapping by the olefin fragment. In addition, difunctionalization of the alkene moiety is achieved since the in situ generation of an additional hydroxy group at the terminal position of the original double bond accompanies the intramolecular C-N bond formation. 相似文献
662.
E. Onofre-Bustamante M. A. Domínguez-Crespo A. M. Torres-Huerta A. Olvera-Martínez J. Genescá-Llongueras F. J. Rodríguez-Gómez 《Journal of Solid State Electrochemistry》2009,13(11):1785-1799
The role of hydrogen peroxide in the formation of cerium conversion coatings by immersing AISI 1010 commercial carbon steel
substrates into solutions containing various concentrations of CeCl3 (0.1, 1, and 10 g L−1) has been investigated as an alternative method for their protection against corrosion. The deposits prepared from the solutions
with H2O2 consist of yellow thin and non-uniform coatings with agglomerates of small CeO2 and Ce2O3 crystallites whose sizes increased over the metallic surface as the cerium concentration was increased. Cerium pre-treatments
in the presence of H2O2 displayed layers that were rougher than those synthesized without H2O2. A comparison with the chromate conversion pre-treatment is also simultaneously carried out with the discussion of the possible
reactions involved in the different stages of process. The coating obtained from the solution containing 0.1 g in 1,000 mL
produced better corrosion resistance on the substrate than that observed for its counterparts due to the fact that the surface
was more uniformly covered by the conversion coating. The addition of H2O2 to the cerate baths improves visible roughness, corrosion resistance of the conversion coatings and bond strength because
hydrogen peroxide acts as an oxygen source during the formation of the coatings. 相似文献
663.
J. A. Murillo-Hernández S. López-Ramírez J. M. Domínguez C. Duran-Valencia I. García-Cruz J. A. González-Guevara 《Journal of Thermal Analysis and Calorimetry》2009,95(1):173-179
A survey on the effect of ionic liquids (ILs) over the thermal stability of a heavy Mexican oil was performed. ILs used were
based on [Cnim]+ and [Cnpyr]+ organic cations with FeCl4− metal anion. Mixtures of heavy crude oil (HCO) with ILs show three oxidation zones: low temperature oxidation (LTO), full
deposition (FD) and high temperature oxidation (HTO). Thermal stability and mass loss decrease in the LTO zone but increase
in the FD and HTO zones for every ILs used. The activation energy of the oxidation is influenced by the ILs in the HTO zone.
It decreases when increasing the size of the organic radical substitute in the cation of the ILs while it increases with the
presence of hydroxyl groups. The influence of electronic structure and reactivity indexes are rationalized to understand the
variations of activation energy obtained of the reaction systems. Among all cations used, cation-3 (IL-3) shows the greater
value of HOMO-LUMO gap as well as the lower activation energy. 相似文献
664.
Jehovani M. Lázaro-Rangel Analilia Sánchez Dr. Motomichi Inoue Dr. José Luis Olivares-Romero Dr. Rocío Meza-Gordillo Dr. Magali Salas-Reyes Dr. Claudia Virués Dr. Zaira Domínguez 《European journal of organic chemistry》2023,26(5):e202201326
A eutectic mixture of L-menthol and malonic acid, Me / MA (4 : 1), was characterized by calorimetry and other physical measurements. The new deep eutectic solvent (m.p. 6 °C) solvates 338 mg of ibuprofen per mL, and the solution is stable in a wide temperature range. Strategies of NMR titration used in supramolecular chemistry were employed to explore binding forces between the eutectic constituents as well as solute-solvent interaction in ibuprofen solution. Even in acetonitrile, Me 4 MA is formed through a hydrogen-bonding network, where the constituents act as hydrogen donors and acceptors at the same time. The estimated association constant is around 30 M−1; the binding forces are enough to build the eutectic mixture at high concentrations. The aggregate Me 4 MA forms a molecular complex with ibuprofen in acetonitrile as a result of the cooperative effect of the constituents. In addition, van der Waals interactions are operative between ibuprofen and menthol in the saturated IB - Me / MA (4 : 1) solution. 相似文献
665.
Prof. Dr. Antonio Doménech-Carbó Silvana López Bastián Chandía Gustavo Cáceres Prof. Dr. Eduardo Muñoz 《Chemphyschem》2023,24(9):e202200853
The cation-insertion solid state electrochemistry of a potassium copper(II) hexacyanoferrate in contact with LiClO4/DMSO, NaPF6/DMSO, and KPF6/DMSO electrolytes has been theoretically and experimentally studied using the voltammetry of immobilized particles methodology. Voltammetric data, combined with SEM/EDS analysis permit to determine a K0.876CuII1.328FeIII0.049[FeIII0.318FeII0.682(CN)6] stoichiometry for the synthesized solid. Separation of electronic and ionic contributions to Gibbs energy changes can be made based on cyclic voltammetric and open circuit potential measurements. These parameters can be combined to measure values of the Gibbs energy of cation-independent electron transfer of 7.2±0.4 (K+), 7.1±0.5 (Na+) kJ mol−1, in close agreement with the expected independence of this parameter on the electrolyte cation. The reduction Fe(III) centers bound to cyano groups exhibit a cation-dependent, essentially Nernstian character which can be described in terms of Na+ and K+ insertion/deinsertion while in the case of Li+ electrolytes there is significant co-cation diffusion. Chronoamperometric data provide estimates of the diffusion coefficients of Na+, and K+ ions through the solid around 10−9 cm2 s−1. 相似文献