全文获取类型
收费全文 | 355篇 |
免费 | 17篇 |
专业分类
化学 | 227篇 |
晶体学 | 1篇 |
数学 | 9篇 |
物理学 | 135篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 7篇 |
2020年 | 25篇 |
2019年 | 14篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 17篇 |
2012年 | 22篇 |
2011年 | 23篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 24篇 |
2007年 | 21篇 |
2006年 | 8篇 |
2005年 | 16篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 11篇 |
1999年 | 3篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1994年 | 11篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1990年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 7篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 4篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1936年 | 2篇 |
1931年 | 1篇 |
1888年 | 2篇 |
排序方式: 共有372条查询结果,搜索用时 15 毫秒
301.
Pablo Baudin Dmytro Bykov Dmitry Liakh Patrick Ettenhuber Kasper Kristensen 《Molecular physics》2017,115(17-18):2135-2144
ABSTRACTThe recently developed Local Framework for calculating Excitation energies (LoFEx) is extended to the coupled cluster singles and doubles (CCSD) model. In the new scheme, a standard CCSD excitation energy calculation is carried out within a reduced excitation orbital space (XOS), which is composed of localised molecular orbitals and natural transition orbitals determined from time-dependent Hartree–Fock theory. The presented algorithm uses a series of reduced second-order approximate coupled cluster singles and doubles (CC2) calculations to optimise the XOS in a black-box manner. This ensures that the requested CCSD excitation energies have been determined to a predefined accuracy compared to a conventional CCSD calculation. We present numerical LoFEx-CCSD results for a set of medium-sized organic molecules, which illustrate the black-box nature of the approach and the computational savings obtained for transitions that are local compared to the size of the molecule. In fact, for such local transitions, the LoFEx-CCSD scheme can be applied to molecular systems where a conventional CCSD implementation is intractable. 相似文献
302.
Thomas Bierkandt Patrick Hemberger Patrick Oßwald Dominik Krüger Markus Köhler Tina Kasper 《Proceedings of the Combustion Institute》2019,37(2):1579-1587
Two laminar, premixed, fuel-rich flames fueled by anisole-oxygen-argon mixtures with the same cold gas velocity and pressure were investigated by molecular-beam mass spectrometry at two synchrotron sources where tunable vacuum-ultraviolet radiation enables isomer-resolved photoionization. Decomposition of the very weak O–CH3 bond in anisole (C6H5OCH3) by unimolecular decomposition yields the resonantly-stabilized phenoxy radical (C6H5O). This key intermediate species opens reaction routes to five-membered ring species, such as cyclopentadiene (C5H6) and cyclopentadienyl radicals (C5H5). Anisole is often discussed as model compound for lignin to study the phenolic-carbon structure in this natural polymer. Measured temperature profiles and mole fractions of many combustion intermediates give detailed information on the flame structure. A very comprehensive reaction mechanism from the literature which includes a sub-scheme for anisole combustion is used for species modeling. Species with the highest measured mole fractions (on the order of 10?3–10?2) are CH3, CH4, C2H2, C2H4, C2H6, CH2O, C5H5 (cyclopentadienyl radical), C5H6 (cyclopentadiene), C6H6 (benzene), C6H5OH (phenol), and C6H5CHO (benzaldehyde). Some are formed in the first destruction steps of anisole, e.g., phenol and benzaldehyde, and their formation will be discussed and with regard to the modeling results. There are three major routes for the fuel destruction: (1) formation of benzaldehyde (C6H5CHO), (2) formation of phenol (C6H5OH), and (3) unimolecular decomposition of anisole to phenoxy (C6H5O) and CH3 radicals. In the experiment, the phenoxy radical could be measured directly. The phenoxy radical decomposes via a bicyclic structure into the soot precursor C5H5 and CO. Formation of larger oxygenated species was observed in both flames. One of them is guaiacol (2-methoxyphenol), which decomposes into fulvenone. The presented speciation data, which contain more than 60 species mole fraction profiles of each flame, give insights into the combustion kinetics of anisole. 相似文献
303.
304.
Kasper Tolborg Dr. Mads R. V. Jørgensen Dr. Mattia Sist Dr. Aref Mamakhel Dr. Jacob Overgaard Prof. Dr. Bo B. Iversen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6814-6822
The covalent nature of the low-barrier N−H−N hydrogen bonds in the negative thermal expansion material H3[Co(CN)6] has been established by using a combination of X-ray and neutron diffraction electron density analysis and theoretical calculations. This finding explains why negative thermal expansion can occur in a material not commonly considered to be built from rigid linkers. The pertinent hydrogen atom is located symmetrically between two nitrogen atoms in a double-well potential with hydrogen above the barrier for proton transfer, thus forming a low-barrier hydrogen bond. Hydrogen is covalently bonded to the two nitrogen atoms, which is the first experimentally confirmed covalent hydrogen bond in a network structure. Source function calculations established that the present N−H−N hydrogen bond follows the trends observed for negatively charge-assisted hydrogen bonds and low-barrier hydrogen bonds previously established for O−H−O hydrogen bonds. The bonding between the cobalt and cyanide ligands was found to be a typical donor–acceptor bond involving a high-field ligand and a transition metal in a low-spin configuration. 相似文献
305.
Maria Quant Andreas Erbs Hillers-Bendtsen Shima Ghasemi Mate Erdelyi Zhihang Wang Lidiya M. Muhammad Nina Kann Kurt V. Mikkelsen Kasper Moth-Poulsen 《Chemical science》2022,13(3):834
Molecular solar-thermal energy storage (MOST) systems are based on photoswitches that reversibly convert solar energy into chemical energy. In this context, bicyclooctadienes (BODs) undergo a photoinduced transformation to the corresponding higher energy tetracyclooctanes (TCOs), but the photoswitch system has not until now been evaluated for MOST application, due to the short half-life of the TCO form and limited available synthetic methods. The BOD system degrades at higher temperature via a retro-Diels–Alder reaction, which complicates the synthesis of the compounds. We here report a cross-coupling reaction strategy that enables an efficient synthesis of a series of 4 new BOD compounds. We show that the BODs were able to switch to the corresponding tetracyclooctanes (TCOs) in a reversible way and can be cycled 645 times with only 0.01% degradation. Half-lives of the TCOs were measured, and we illustrate how the half-life could be engineered from seconds to minutes by molecular structure design. A density functional theory (DFT) based modelling framework was developed to access absorption spectra, thermal half-lives, and storage energies which were calculated to be 143–153 kJ mol−1 (0.47–0.51 MJ kg−1), up to 76% higher than for the corresponding norbornadiene. The combined computational and experimental findings provide a reliable way of designing future BOD/TCO systems with tailored properties.Molecular solar-thermal energy storage (MOST) systems are based on photoswitches that reversibly convert solar energy into chemical energy. 相似文献
306.
Controlling the reciprocity between chemical reactivity and supramolecular structure is a topic of great interest in the emergence of molecular complexity. In this work, we investigate the effect of a covalent reaction as a trigger to depolymerize a supramolecular assembly. We focus on the impact of an in situ thiol–ene reaction on the (co)polymerization of three derivatives of benzene-1,3,5-tricarboxamide (BTA) monomers functionalized with cysteine, hexylcysteine, and alkyl side chains: Cys-BTA, HexCys-BTA, and a-BTA. Long supramolecular polymers of Cys-BTA can be depolymerized into short dimeric aggregates of HexCys-BTAvia the in situ thiol–ene reaction. Analysis of the system by time-resolved spectroscopy and light scattering unravels the fast dynamicity of the structures and the mechanism of depolymerization. Moreover, by intercalating the reactive Cys-BTA monomer into an unreactive inert polymer, the in situ thiol–ene reaction transforms the intercalator into a sequestrator and induces the depolymerization of the unreactive polymer. This work shows that the implementation of reactivity into supramolecular assemblies enables temporal control of depolymerization processes, which can bring us one step closer to understanding the interplay between non-covalent and covalent chemistry.We report on the controlled depolymerization of supramolecular 1D polymers into well-defined dimers triggered by a covalent reaction on the side chains of the monomer. 相似文献
307.
308.
Inside Back Cover: A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3‐triazol‐5‐ylidene) Ligands: Taming the MLCT Excited State of Iron(II) (Chem. Eur. J. 9/2015) 下载免费PDF全文
Dr. Yizhu Liu Dr. Kasper S. Kjær Dr. Lisa A. Fredin Dr. Pavel Chábera Tobias Harlang Dr. Sophie E. Canton Prof. Sven Lidin Dr. Jianxin Zhang Prof. Reiner Lomoth Dr. Karl‐Erik Bergquist Prof. Petter Persson Prof. Kenneth Wärnmark Prof. Villy Sundström 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3831-3831
309.
Dr. Sergio Sanz Helen M. O'Connor Eufemio Moreno Pineda Dr. Kasper S. Pedersen Dr. Gary S. Nichol Dr. Ole Mønsted Dr. Høgni Weihe Dr. Stergios Piligkos Prof. Eric J. L. McInnes Dr. Paul J. Lusby Prof. Euan K. Brechin 《Angewandte Chemie (International ed. in English)》2015,54(23):6761-6764
[CrIII8MII6]12+ (MII=Cu, Co) coordination cubes were constructed from a simple [CrIIIL3] metalloligand and a “naked” MII salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Computational techniques (known in theoretical nuclear physics as statistical spectroscopy) in tandem with EPR spectroscopy are used to interpret the magnetic behavior. 相似文献
310.
D. Kaczmarek S. Shaqiri B. Atakan T. Kasper 《Proceedings of the Combustion Institute》2021,38(1):233-241
Methane based polygeneration processes in piston engines offer the possibility of a controllable and flexible conversion of energy, to up-convert low value chemicals and to store energy. These processes preferably take place under fuel-rich conditions and at high pressures. Under fuel-rich conditions, there was one experimental report that a distinctive negative temperature coefficient (NTC) behavior occurs in methane oxidation (Petersen et al., 1999). To design a polygeneration process, reliable kinetic models are required to capture the impact of pressure and equivalence ratio variations on reactivity of the gas mixtures. Here, the experimental basis for methane oxidation is expanded to high pressures and very fuel-rich conditions and compared to literature models, both with special emphasis on the NTC behavior. The oxidation of methane/oxygen mixtures at 2 ≤ Φ≤ 20 and pressures ranging from 1 to 20 bar is investigated. The literature reaction mechanisms are assessed with respect to their ability to predict this phenomenon and used to identify reaction pathways. It is found that NTC behavior occurs in a temperature range between 700 and 1000 K and at pressures higher than 5 bar. The lower temperature limit is slightly shifted towards higher temperatures with decreasing equivalence ratio. In addition, the higher the equivalence ratio, the broader the pressure range, in which the NTC behavior is observed. In general, predictions of some models are in good agreement with the experimental data. Reaction path analyses reveal that the competition between oxidation and recombination pathways are responsible for the NTC region in methane oxidation. 相似文献