全文获取类型
收费全文 | 238篇 |
免费 | 10篇 |
国内免费 | 7篇 |
专业分类
化学 | 163篇 |
晶体学 | 1篇 |
力学 | 13篇 |
数学 | 41篇 |
物理学 | 37篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 24篇 |
2012年 | 32篇 |
2011年 | 23篇 |
2010年 | 12篇 |
2009年 | 11篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1972年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有255条查询结果,搜索用时 328 毫秒
31.
32.
Julián I. Peña Rosselló Horacio S. Wio Roberto R. Deza Peter Hänggi 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(2):34
The performance of a ring of linearly coupled, monostable nonlinear oscillators is optimized towards its goal of acting as energy harvester – through piezoelectric transduction – of mesoscopic fluctuations, which are modeled as Ornstein-Uhlenbeck noises. For a single oscillator, the maximum output voltage and overall efficiency are attained for a soft piecewise-linear potential (providing a weak attractive constant force) but they are still fairly large for a harmonic potential. When several harmonic springs are linearly and bidirectionally coupled to form a ring, it is found that counter-phase coupling can largely improve the performance while in-phase coupling worsens it. Moreover, it turns out that few (two or three) coupled units perform better than more. 相似文献
33.
Mayra Cortés‐Hernández Susana Rojas‐Lima Marcos Hernández‐Rodríguez Julián Cruz‐Borbolla Heraclio López‐Ruiz 《Helvetica chimica acta》2016,99(6):416-424
An efficient, simple protocol for the synthesis of a new family of chiral ureas 1 – 4 is described. The binding properties of 1 – 4 toward different anion (acetate, benzoate, fluoride, and chloride) have been studied by 1H‐NMR titration and have been observed in the case of 4 is a selective receptor for acetate. The theoretical calculation M06/6‐311+G(d,p) helped us explain the binding properties observed. The most interesting observation is that this calculated structure is consistent with expected, based on the concept of allylic 1,3‐strain (A1,3 strain). When chiral caboxylates were studied, urea 1 was the best in discriminating between enantiomers. 相似文献
34.
Dr. Martin Wolffs Juliën L. J. van Velthoven Dr. Xianwen Lou Ralf A. A. Bovee Maarten Pouderoijen Joost L. J. van Dongen Dr. Albertus P. H. J. Schenning Prof. Dr. E. W. Meijer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(47):15057-15064
The self‐assembly of two enantiomerically pure hexa(oligo (p‐phenylene vinylene))‐substituted benzenes having 24 stereocenters was studied in pure methylcyclohexane (MCH) and in a mixture of MCH/toluene (4:1). Irrespective of the solvent a cooperative supramolecular polymerization mechanism was determined for these star‐shaped molecules by using temperature‐dependent CD and UV/Vis spectroscopy. Quite remarkably, a transition from one helical supramolecular state (A) to a second more thermodynamically stable supramolecular helical assembly (B) was observed. The rate of the A→B transition was strongly dependent on the nature of the solvent; being faster in the solvent mixture than in pure MCH. By using size exclusion chromatography we could relate the increased rate to a decreased stability of the supramolecular A state in the solvent mixture. Next, we mixed the two enantiomerically pure hexa‐substituted benzene derivatives in a so‐called majority‐rules experiment, which lead to the anitcipated chiral amplification in the A state. More importantly it appeared that the A→B transition was significantly hampered in these mixed systems. Furthermore, the absence of chiral amplification in the B state revealed the formation of separated enantiomerically pure assemblies. Therefore, by using a wide variety of spectroscopic and chromatographic techniques we determined the influence of solvent and enantiomeric purity on the transition between different supramolecular states. 相似文献
35.
Mesa JA Velázquez-Palenzuela A Brillas E Coll J Torres JL Juliá L 《The Journal of organic chemistry》2012,77(2):1081-1086
The condensation reaction of D-maltose to free radicals of the series of tris(2,4,6-trichlorophenyl)methyl (TTM) and tris(perchlorophenyl)methyl (PTM) has been described for the first time. The new persistent radicals 1 and 2 are very stable and have been characterized by EPR. Their cyclic voltammograms show a quasi-reversible process in the cathode, being reduced to the corresponding anions, with redox potentials a little lower than those of TTM and PTM, respectively. Their oxidant activity is in close relation with their reduction potentials. Therefore, while 2 is reduced by ascorbic acid, 1 remains unaltered. 相似文献
36.
Hadad C García-Martínez JC Rodríguez-López J 《The Journal of organic chemistry》2012,77(14):6223-6230
A series of new hybrid, layer-block π-conjugated dendrons and dendrimers with alternating thienylenevinylene and phenylenevinylene units has been prepared by means of an orthogonal and convergent-growth methodology that made use of the Horner-Wadsworth-Emmons (HWE) reaction. The placement of the thiophene and benzene rings can be accurately controlled to afford a large variety of dendritic structures, although access to compounds of high generation proved difficult. The optical properties of the synthesized dendrimers were determined by UV/vis and fluorescence spectroscopy, and the influence of the generation and nature of the core on the behavior of these materials was evaluated. 相似文献
37.
38.
Reinaldo Rodríguez-Ramos Raúl Guinovart-Díaz Juan C. López-Realpozo Julián Bravo-Castillero Federico J. Sabina 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(4):377-388
A fiber-reinforced periodic piezoelectric composite, where the constituents exhibit transverse isotropic properties, is considered. The fiber cross-section is circular and the periodicity is the same in two orthogonal directions. Imperfect mechanic contact conditions at the interphase between the matrix and fibers are represented in parametric form. In order to analyze the influence of the imperfect interface effect over the behavior of the composite, the effective axial piezoelectric moduli are obtained by means of the Asymptotic Homogenization Method. Some numerical examples are given. 相似文献
39.
Yuan Chen Baobao Sun Haohui Feng Ranran Wang Ming Cheng Dr. Peng Wang Zhiping Zhou Prof. Juli Jiang Prof. Leyong Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(48):12305-12309
Chirality at different levels is widely observed in nature, but the clue to connect it all together, and the way chirality transfers among different levels are still obscure. Herein, a l -/d -lysine-based self-assembly system was constructed, in which two-step chirality transfer among three different levels was observed in aqueous solution. The chirality originated from the point chirality of amino acid derivatives l -/d -PyLys hydrochloride, and was transferred to the planar conformational chirality of water-soluble pillar[5]arene pR-/pS-WP5. Then, with the aid of pR-/pS-WP5, nanoparticles were formed that exhibited L-/R-handed circularly polarized luminescence with a dissymmetry factor of up to ±0.001, arising from pyrene chiral excimers. This multilevel chirality transfer not only provides a perspective to trace potential clues, and to pursue certain ways by which the chirality transfers, but also offers a strategy to create controllable CPL emission in aqueous media. 相似文献
40.
Thesyntheticmethodsinliteratureforpreparingcycloalkanedionecompoundsusedasvaluableperfumeusuallyarespecial,thesynthesesofsomecycloalkanedionecompoundsareextremelydifficult.1,6CyclododecanedionewaspreparedpreviouslybyFonkenetal.[1]viamicrobiologicalhydrox… 相似文献