全文获取类型
收费全文 | 321篇 |
免费 | 23篇 |
国内免费 | 2篇 |
专业分类
化学 | 207篇 |
晶体学 | 4篇 |
力学 | 23篇 |
数学 | 88篇 |
物理学 | 24篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 24篇 |
2014年 | 21篇 |
2013年 | 23篇 |
2012年 | 20篇 |
2011年 | 26篇 |
2010年 | 17篇 |
2009年 | 14篇 |
2008年 | 19篇 |
2007年 | 30篇 |
2006年 | 23篇 |
2005年 | 10篇 |
2004年 | 17篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有346条查询结果,搜索用时 15 毫秒
101.
Reinhard Zell Erich Widmer Teodor Luk
Hans Georg Wilhelm Leuenberger Peter Schnholzer Emil A. Broger 《Helvetica chimica acta》1981,64(7):2447-2462
Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6-Oxo-isophorone. III. A New Concept for the Synthesis of the Enantiomeric Astaxanthins A new and efficient concept for the total synthesis of (3S, 3'S)- and (3R, 3'R)-astaxanthin ( 1a and 1c , resp.) in high overall yield and up to 99,2% enantiomeric purity is described. Key intermediates are the (S)- and (R)-acetals 10 and 17 , respectively (Scheme 2). These chiral building blocks were synthesized via three different routes: a) functionalization of the enantiomeric 3-hydroxy-6-oxo-isophorons4) 2 and 11 , respectively (Scheme 2); b) optical resolution of 3,4-dihydroxy-compound4) 19 (Scheme 3), and c) fermentative reductions of 6-oxo-isophorone derivatives (Schemes 4 and 5). - The absolute configurations of the two intermediates 12 and 13 (Scheme 2) have been confirmed by X-ray analysis. - The final steps leading to the enantiomeric astaxanthins are identical with those described for optically inactive astaxanthin [1]. 相似文献
102.
Ramon AlibésPedro de March Marta FigueredoJosep Font Marta RacamondeAlbert Rustullet Angel Alvarez-LarenaJuan F. Piniella Teodor Parella 《Tetrahedron letters》2003,44(1):69-71
A highly stereoselective and efficient synthetic approach to cyclobutane and cyclobutene derivatives has been developed consisting of a [2+2] photochemical cycloaddition of chiral 2(5H)-furanones to (Z)-1,2-dichloroethylene followed by dihydrodehalogenation or dihaloelimination. 相似文献
103.
104.
We find a combinatorial formula for the Haar measure of quantum permutation groups. This leads to a dynamic formula for laws of diagonal coefficients, explaining the Poisson/free Poisson convergence result for characters. 相似文献
105.
We analyze self-similar solutions to a nonlinear fractional diffusion equation and fractional Burgers/Korteweg–deVries equation in one spatial variable. By using Lie-group scaling transformation, we determined the similarity solutions. After the introduction of the similarity variables, both problems are reduced to ordinary nonlinear fractional differential equations. In two special cases exact solutions to the ordinary fractional differential equation, which is derived from the diffusion equation, are presented. In several other cases the ordinary fractional differential equations are solved numerically, for several values of governing parameters. In formulating the numerical procedure, we use special representation of a fractional derivative that is recently obtained. 相似文献
106.
Teodor M. Atanackovic Alvin M. Strauss 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1987,38(6):839-855
The stability of a column loaded with continuously distributed tangential load is analyzed. It is assumed that imperfections in the shape (initial deformation) and loading (a small concentrated force) are present. It is shown that the influence of the imperfections is modelled by a Whithney cusp. 相似文献
107.
Sens C Romero I Rodríguez M Llobet A Parella T Benet-Buchholz J 《Journal of the American Chemical Society》2004,126(25):7798-7799
We have prepared three new dinuclear ruthenium complexes having the formulas [Ru2II(bpp)(trpy)2(mu-L)]2+ (L = Cl, 1; L = AcO, 2) and [Ru2II(bpp)(trpy)2(H2O)2]3+ (3). The three complexes have been characterized through the usual spectroscopic and electrochemical techniques and, in the cases of 1 and 2, the X-ray crystal structures have been solved. In aqueous acidic solution, the acetato bridge of 2 is replaced by aqua ligands, generating the bis(aqua) complex 3 which, upon oxidation to its RuIVRuIV state, has been shown to catalytically oxidize water to molecular oxygen. The measured pseudo-first-order rate constant for the O2-evolving process is 1.4 x 10-2 s-1, more than 3 times larger than the higher one previously reported for Ru-O-Ru type catalysts. This new water-splitting catalyst also has improved stability with regard to any previously described, achieving a total of 18.6 metal cycles. 相似文献
108.
Dr. Karel Hernández Dr. Jesús Joglar Dr. Jordi Bujons Dr. Teodor Parella Prof. Dr. Pere Clapés 《Angewandte Chemie (International ed. in English)》2018,57(14):3583-3587
Pyruvate‐dependent aldolases exhibit a stringent selectivity for pyruvate, limiting application of their synthetic potential, which is a drawback shared with other existing aldolases. Structure‐guided rational protein engineering rendered a 2‐keto‐3‐deoxy‐l ‐rhamnonate aldolase variant, fused with a maltose‐binding protein (MBP‐YfaU W23V/L216A), capable of efficiently converting larger pyruvate analogues, for example, those with linear and branched aliphatic chains, in aldol addition reactions. Combination of these nucleophiles with N‐Cbz‐alaninal (Cbz=benzyloxycarbonyl) and N‐Cbz‐prolinal electrophiles gave access to chiral building blocks, for example, derivatives of (2S,3S,4R)‐4‐amino‐3‐hydroxy‐2‐methylpentanoic acid (68 %, d.r. 90:10) and the enantiomer of dolaproine (33 %, d.r. 94:6) as well as a collection of unprecedented α‐amino acid derivatives of the proline and pyrrolizidine type. Conversions varied between 6–93 % and diastereomeric ratios from 50:50 to 95:5 depending on the nucleophilic and electrophilic components. 相似文献
109.
Inside Cover: An Efficient Synthesis of Porphyrins with Different meso Substituents that Avoids Scrambling in Aqueous Media (Chem. Eur. J. 4/2015) 下载免费PDF全文
110.
Cover Picture: Nucleophile Promiscuity of Engineered Class II Pyruvate Aldolase YfaU from E. Coli (Angew. Chem. Int. Ed. 14/2018) 下载免费PDF全文