全文获取类型
收费全文 | 46篇 |
免费 | 0篇 |
专业分类
化学 | 23篇 |
力学 | 2篇 |
数学 | 9篇 |
物理学 | 12篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 3篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 1篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有46条查询结果,搜索用时 15 毫秒
1.
Ionel I Mangalagiu Geanina C MangalagiuCalin Deleanu Gabi DrochioiuMagda Ghe Petrovanu 《Tetrahedron》2003,59(1):111-114
The ability of 4-methylpyrimidinium ylides (as 1,3-dipoles) to react with activated non-symmetrical substituted dipolarophiles (alkenes and alkynes) is presented. 4-Methylpyrimidinium ylides did not react with alkenes. With alkynes the reactions are regiospecific, a single regioisomer being obtained. A possible mechanism for the reaction pathway is proposed. For the first time in the pyrimidinium ylides series both isomers resulting from bonding to the 2-and 6-positions of the heterocycle ring were obtained. The appropriate conditions in order to increase the selectivity of one of the isomers were determined. 相似文献
2.
Ireland T Tappe K Grossheimann G Knochel P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(4):843-852
A new family of ferrocenylphosphane ligands has been prepared. Their flexible synthesis allows many structural modifications. The asymmetric induction of these ligands was examined in the hydrogenation of functionalized C=C, C=O, and C=N bonds. The enantioselectivity of the reaction was strongly dependent on the substituent R at the position alpha to the ferrocene moiety. In many cases, both enantiomeric beta-hydroxyesters of the reduction product can be obtained by simply replacing a dimethylamino group in the ligand with a methyl group. 相似文献
3.
Shock waves in saturated thermoelastic porous media 总被引:1,自引:0,他引:1
The objective of this paper is to develop and present the macroscopic motion equations for the fluid and the solid matrix, in the case of a saturated porous medium, in the form of coupled, nonlinear wave equations for the fluid and solid velocities. The nonlinearity in the equations enables the generation of shock waves. The complete set of equations required for determining phase velocities in the case of a thermoelastic solid matrix, includes also the energy balance equation for the porous medium as a whole, as well as mass balance equations for the two phase. In the special case of a rigid solid matrix, the wave after an abrupt change in pressure propagates only through the fluid. 相似文献
4.
A series of tridentate P, N, P ligands comprising a central pyridine unit and two pendent diarylphosphane moieties (2, 6‐bis(CH2PAr2)pyridine; Ar = phenyl ( 1 ), 2‐methylphenyl ( 2 ), 2, 4, 6‐trimethylphenyl ( 3 )) as well as the corresponding iron ( 1‐FeCl2 , 2‐FeCl2 , 3‐FeCl2 ) and cobalt ( 1‐CoCl2 , 2‐CoCl2 , 3‐CoCl2 ) complexes were synthesized and characterized. An X‐ray structure analysis of 2‐CoCl2 and 3‐CoCl2 exhibited a trigonal‐bipyramidal coordination geometry at the metal center, the two chlorine atoms and the nitrogen occupying the equatorial and the phosphane units the apical positions. IR analysis indicated, that in all complexes the pyridine unit is coordinated to the metal center. The cobalt compounds were applied as catalyst precursors for the polymerization of ethene after activation with MAO. 相似文献
5.
6.
Gabi Drochioiu Ionel Mangalagiu Ecaterina Avram Karin Popa Alin Constantin Dirtu Ioan Druta 《Analytical sciences》2004,20(10):1443-1447
A new sensitive spectrophotometric method has recently been developed for the trace determination of cyanide with ninhydrin. Cyanide ion was supposed to act as a specific base catalyst. Nevertheless, this paper demonstrates that the reported assay is based on a novel reaction of cyanide with 2,2-dihydroxy-1,3-indanedione, which affords purple or blue colored salts of 2-cyano-1,2,3-trihydroxy-2H indene. Hydrindantin is merely an intermediary of the reaction. The formation of a stable and isolable ninhydrin-cyanide compound has been confirmed by its preparation in crystalline form. Also, it is thoroughly characterized by elemental as well as MS, IR, UV/VIS and 1H NMR analyses. The Ruhemann's sequence of reactions of cyanide with ninhydrin has been reconsidered and an adequate mechanism of the reaction is proposed. As a consequence, the interference of oxidizers as well as copper, silver and mercury ions with the cyanide determination has been elucidated. 相似文献
7.
8.
Prof. Dr. Gerhard Bringmann Guoliang Zhang Tobias Büttner Gabi Bauckmann Dr. Thomas Kupfer Prof. Dr. Holger Braunschweig Prof. Dr. Reto Brun Prof. Dr. Virima Mudogo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):916-923
A new dimeric naphthylisoquinoline alkaloid, jozimine A2 ( 2 ), was isolated from the root bark of an Ancistrocladus species from the Democratic Republic of Congo. Its absolute stereostructure was determined by chemical, spectroscopic, and chiroptical methods, and confirmed by X‐ray crystallography. Jozimine A2 ( 2 ) is one of the as yet very rare naphthylisoquinoline dimers whose central biaryl axis is rotationally hindered. Moreover, it is the first natural dimer of a Dioncophyllaceae‐type alkaloid, that is, lacking oxygen functions at C6, and bearing R configurations at C3 in its two isoquinoline portions. Despite this decreased steric hindrance, the outer biaryl axes are chiral, too, so that jozimine A2 ( 2 ) has three consecutive stereogenic axes and, together with the four stereogenic centers, seven elements of chirality and is C2‐symmetric. The new dimer exhibits excellent, and specific, antiplasmodial activity. To further confirm its stereostructure and for likewise testing the bioactivities of its (unnatural) atropo‐diastereomer, compound 2 was prepared by semi‐synthesis from the co‐occurring (and likewise synthetically available) dioncophylline A ( 5 ), along with its atropo‐diastereomer, 3′‐epi‐ 2 . 相似文献
9.
10.