全文获取类型
收费全文 | 339篇 |
免费 | 17篇 |
专业分类
化学 | 269篇 |
力学 | 3篇 |
数学 | 5篇 |
物理学 | 79篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 20篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 23篇 |
2007年 | 26篇 |
2006年 | 27篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 7篇 |
2001年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1966年 | 2篇 |
1953年 | 1篇 |
排序方式: 共有356条查询结果,搜索用时 31 毫秒
351.
Swadhin Garain Shagufi Naz Ansari Anju Ajayan Kongasseri Bidhan Chandra Garain Swapan K. Pati Subi J. George 《Chemical science》2022,13(34):10011
Engineering the electronic excited state manifolds of organic molecules can give rise to various functional outcomes, including ambient triplet harvesting, that has received prodigious attention in the recent past. Herein, we introduce a modular, non-covalent approach to bias the entire excited state landscape of an organic molecule using tunable ‘through-space charge-transfer’ interactions with appropriate donors. Although charge-transfer (CT) donor–acceptor complexes have been extensively explored as functional and supramolecular motifs in the realm of soft organic materials, they could not imprint their potentiality in the field of luminescent materials, and it still remains as a challenge. Thus, in the present study, we investigate the modulation of the excited state emission characteristics of a simple pyromellitic diimide derivative on complexation with appropriate donor molecules of varying electronic characteristics to demonstrate the selective harvesting of emission from its locally excited (LE) and CT singlet and triplet states. Remarkably, co-crystallization of the pyromellitic diimide with heavy-atom substituted and electron-rich aromatic donors leads to an unprecedented ambient CT phosphorescence with impressive efficiency and notable lifetime. Further, gradual minimizing of the electron-donating strength of the donors from 1,4-diiodo-2,3,5,6-tetramethylbenzene (or 1,2-diiodo-3,4,5,6-tetramethylbenzene) to 1,2-diiodo-4,5-dimethylbenzene and 1-bromo-4-iodobenzene modulates the source of ambient phosphorescence emission from the 3CT excited state to 3LE excited state. Through comprehensive spectroscopic, theoretical studies, and single-crystal analyses, we elucidate the unparalleled role of intermolecular donor–acceptor interactions to toggle between the emissive excited states and stabilize the triplet excitons. We envisage that the present study will be able to provide new and innovative dimensions to the existing molecular designs employed for triplet harvesting.A modular, non-covalent donor–acceptor strategy is proposed to bias the excited-state manifold of organic systems and to realize unprecedented charge-transfer phosphorescence. 相似文献
352.
Swapan K. Ghosh Prajna P. De Dipak Khastgir Sadhan K. De 《Macromolecular rapid communications》1999,20(9):505-509
A new ionomer, containing both carboxylated and sufonated groups, was obtained by sulfonating a maleated styrene-ethylene/butylene-styrene (m-SEBS) block copolymer, followed by its neutralization with zinc acetate. Dielectric thermal analyses show that the incorporation of ionic groups in m-SEBS is responsible for the occurrence of the high temperature ionic relaxation in addition to the relaxations of the base polymer. Formation of the ionomer causes a significant improvement in stress-strain properties compared to the corresponding base polymer. 相似文献
353.
The development of cheap, eco-friendly electrocatalysts for urea synthesis which avoids the traditional nitrogen reduction to form ammonia, is very important to meet our growing demand for urea. Herein, based on density functional theory, we propose a novel electrocatalyst (dual Si doped C9N4 nanosheet) composed of totally environmentally benign non-metal earth abundant elements, which is able to adsorb N2 and CO2 together. Reduction of CO2 to CO happens, which is then inserted into activated N−N bond, and it produces *N(CO)N intermediate, which is the crucial step for urea formation. Eventually following several proton coupled electron transfer processes, urea is formed under ambient conditions. The limiting potential value for urea formation is found to be lower than that of NH3 formation and HER (hydrogen evolution reaction). Moreover, the faradaic efficiency of our proposed catalyst system is 100 % for urea formation, which suggests greater selectivity of urea formation over other competitive reactions. 相似文献
354.
Surajit Mondal Supriti Dutta Santanu Mal Swapan K. Pati Sayan Bhattacharyya 《Angewandte Chemie (International ed. in English)》2023,62(18):e202301269
The immiscibility of crystallographic facets in multi-metallic catalysts plays a key role in driving the green H2 production by water electrolysis. The lattice mismatch between tetragonal In and face-centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close-packed (hcp) Ni is 49.8 %. Hence, in a series of Ni−In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18–20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni0 state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h−1 H2 is evolved at −385 mV with mass activity of 57.5 A g−1 at—400 mV, 200 h stability at −0.18 V versus reversible hydrogen electrode (RHE), and Pt-like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH− ions and the prevention of catalyst poisoning. 相似文献
355.
Photochemical activation by triplet photosensitizers is highly expedient for a green focus society. In this work, we have theoretically probed excited state characteristics of thioxanthone and its derivatives for their triplet harvesting efficiency using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Absorption and triplet energies corroborate well with the available experimental data. Our results predict that both the S1 and T1 states are π-π* in nature, which renders a high oscillator strength for S0 to S1 transition. Major triplet exciton conversion occurs through intersystem crossing (ISC) channel between the S1 (1π-π*) and high energy 3n- π* state. Apart from that, there is both radiative and non-radiative channel from S1 to S0, which competes with the ISC channel and reduces the triplet harvesting efficiency. For thioxanthones with −OMe (Me=Methyl) or −F substitution at 2 or 2’ positions, the ISC channel is not energetically feasible, causing sluggish intersystem crossing quantum yield (ΦISC). For unsubstituted thioxanthone and for isopropyl substitution at 2’ position, the S1-T1 gap is slightly positive ( ), rendering a lower triplet harvesting efficiency. For systems with −OMe or −F substitution at 3 or 3’ position of thioxanthone, because of buried π state and high energy π* state, the S1-3nπ* gap becomes negative. This leads to a high ΦISC (>0.9), which is key to being an effective photocatalyst. 相似文献
356.