全文获取类型
收费全文 | 102篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 91篇 |
数学 | 2篇 |
物理学 | 15篇 |
出版年
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 9篇 |
2013年 | 3篇 |
2012年 | 4篇 |
2011年 | 7篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 10篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1991年 | 2篇 |
1978年 | 1篇 |
1976年 | 6篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1941年 | 1篇 |
排序方式: 共有108条查询结果,搜索用时 562 毫秒
81.
Zhang L Abbenhuis HC Gerritsen G Bhriain NN Magusin PC Mezari B Han W van Santen RA Yang Q Li C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(4):1210-1221
A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single-site titanium active center, was immobilized successfully by in-situ copolymerization on a mesoporous SBA-15-supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (>380 m2 g-1) and pore volume (>or==0.46 cm3 g-1)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert-butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2 as the oxidant. In two-phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites. 相似文献
82.
Ojwang JG van Santen R Kramer GJ van Duin AC Goddard WA 《The Journal of chemical physics》2008,128(16):164714
We have parametrized a reactive force field for NaH, ReaxFF(NaH), against a training set of ab initio derived data. To ascertain that ReaxFF(NaH) is properly parametrized, a comparison between ab initio heats of formation of small representative NaH clusters with ReaxFF(NaH) was done. The results and trend of ReaxFF(NaH) are found to be consistent with ab initio values. Further validation includes comparing the equations of state of condensed phases of Na and NaH as calculated from ab initio and ReaxFF(NaH). There is a good match between the two results, showing that ReaxFF(NaH) is correctly parametrized by the ab initio training set. ReaxFF(NaH) has been used to study the dynamics of hydrogen desorption in NaH particles. We find that ReaxFF(NaH) properly describes the surface molecular hydrogen charge transfer during the abstraction process. Results on heat of desorption versus cluster size shows that there is a strong dependence on the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. To gain more insight into the structural transformations of NaH during thermal decomposition, we performed a heating run in a molecular dynamics simulation. These runs exhibit a series of drops in potential energy, associated with cluster fragmentation and desorption of molecular hydrogen. This is consistent with experimental evidence that NaH dissociates at its melting point into smaller fragments. 相似文献
83.
Winfred G. Beyersbergen van Henegouwen Rutger M. Fieseler Floris P. J. T. Rutjes Henk Hiemstra 《Angewandte Chemie (International ed. in English)》1999,38(15):2214-2217
A novel iodide-promoted, allene-terminated cyclization of an N-acyliminium ion, a stereoselective Heck spirocyclization, and a chemoselective demethylation at the nitrogen atom of an oxindole are the key transformations in the first total synthesis of the indole alkaloid (+)-gelsedine ( 1 ). This dextrorotatory form of natural gelsedine was formed as a single enantiomer in 21 steps from (S)-malic acid. 相似文献
84.
Simon Krijnen Hendrikus C. L. Abbenhuis Rob W. J. M. Hanssen Jan H. C. van Hooff Rutger A. van Santen 《Angewandte Chemie (International ed. in English)》1998,37(3):356-358
The heterogenization of a titanium(IV ) silsesquioxane complex in an MCM-41 molecular sieve , by tailoring the polarity of MCM-41, results in self-assembled materials (see the space-filling model on the right) that are active, truly heterogeneous, and recyclable catalysts for liquid-phase alkene epoxidation. 相似文献
85.
86.
Rmi Platel Ludovic Chaveriat Sarah Le Guenic Rutger Pipeleers Maryline Magnin-Robert Batrice Randoux Pauline Trapet Vincent Lequart Nicolas Joly Patrice Halama Patrick Martin Monica Hfte Philippe Reignault Ali Siah 《Molecules (Basel, Switzerland)》2021,26(1)
The hemibiotrophic fungus Zymoseptoria tritici, responsible for Septoria tritici blotch, is currently the most devastating foliar disease on wheat crops worldwide. Here, we explored, for the first time, the ability of rhamnolipids (RLs) to control this pathogen, using a total of 19 RLs, including a natural RL mixture produced by Pseudomonas aeruginosa and 18 bioinspired RLs synthesized using green chemistry, as well as two related compounds (lauric acid and dodecanol). These compounds were assessed for in vitro antifungal effect, in planta defence elicitation (peroxidase and catalase enzyme activities), and protection efficacy on the wheat-Z. tritici pathosystem. Interestingly, a structure-activity relationship analysis revealed that synthetic RLs with a 12 carbon fatty acid tail were the most effective for all examined biological activities. This highlights the importance of the C12 chain in the bioactivity of RLs, likely by acting on the plasma membranes of both wheat and Z. tritici cells. The efficacy of the most active compound Rh-Est-C12 was 20-fold lower in planta than in vitro; an optimization of the formulation is thus required to increase its effectiveness. No Z. tritici strain-dependent activity was scored for Rh-Est-C12 that exhibited similar antifungal activity levels towards strains differing in their resistance patterns to demethylation inhibitor fungicides, including multi-drug resistance strains. This study reports new insights into the use of bio-inspired RLs to control Z. tritici. 相似文献
87.
88.
89.
Mignon P Pidko EA Van Santen RA Geerlings P Schoonheydt RA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(17):5168-5177
The disproportionation of N(2)O(4) into NO(3)(-) and NO(+) on Y zeolites has been studied through periodic DFT calculations to unravel 1) the role of metal cations and the framework oxygen atoms and 2) the relationship between the NO(+) stretching frequency and the basicity of zeolites. We have considered three situations: adsorption on site II cations with and without a cation at site III and adsorption on a site III cation. We observed that cations at sites II and III cooperate to stabilize N(2)O(4) and that the presence of a cation at site III is necessary to allow the disproportionation reaction. The strength of the stabilization is due to the number of stabilizing interactions increasing with the size of the cation and to the Lewis acidity of the alkali cations, which increases as the size of the cations decreases. In the product, NO(3)(-) interacts mainly with the cations and NO(+) with the basic oxygen atoms of the tetrahedral aluminium through its nitrogen atom. As the cation size increases, the NO(3)(-)...cation interaction increases. As a result, the negative charge of the framework is less well screened by the larger cations and the interaction between NO(+) and the basic oxygen atoms becomes stronger. NO(+) appears to be a good probe of zeolite basicity, in agreement with experimental observations. 相似文献
90.
Wijdeven MA Wijtmans R van den Berg RJ Noorduin W Schoemaker HE Sonke T van Delft FL Blaauw RH Fitch RW Spande TF Daly JW Rutjes FP 《Organic letters》2008,10(18):4001-4003
A stereoselective synthesis of (+)-epiquinamide is presented in combination with determination of the absolute configuration of the natural product. Key steps in the sequence involved chemoenzymatic formation of an enantiomerically pure cyanohydrin, reductive cyclization to the corresponding cyclic N,N-acetal, and subsequent conversion into a suitable N-acyliminium ion precursor to enable construction of the second ring. 相似文献