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Jorma Hölsä Taneli Laamanen Mika Lastusaari Pavel Novák 《Journal of luminescence》2009,129(12):1606-1609
The present status of the persistent luminescence mechanisms is reviewed and the remaining unsolved details are discussed. These details include the identification and role of defects in the Eu2+-doped and R3+ co-doped alkaline earth aluminates (MAl2O4) and disilicates (M2MgSi2O7; M:Ca, Sr, Ba) which can be partly resolved by the thermoluminescence (TL) measurements. The use of the synchrotron radiation - presently only sparsely used in the studies of persistent luminescence - is introduced: the oxidation state of the presumed R2+/R3+/RIV species occurring in the persistent luminescence materials during the luminescence processes were examined with synchrotron radiation XANES (and EXAFS) methods. The band gap energies (Eg), the defect-related luminescence as well as the 4f7→4f65d1 transition energies were derived from the synchrotron radiation excitation spectra of the materials. Subsequently, the early steps of the density functional theory (DFT) calculations involving the solution of the persistent luminescence mechanisms (band gap energies, position of the Eu2+ levels) are discussed. Some remaining challenges are eventually highlighted. 相似文献
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Markus Albrecht Prof. Dr. Michael Müller Olga Mergel Kari Rissanen Prof. Dr. Arto Valkonen Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(17):5062-5069
Simple pentafluorobenzyl‐substituted ammonium and pyridinium salts with different anions can be easily obtained by treatment of the parent amine or pyridine with the respective pentafluorobenzyl halide. Hexafluorophosphate is introduced as the anion by salt metathesis. In the case of the ammonium salt 4 , water co‐crystallisation seems to suppress effective anion–π interactions of bromide with the electron‐deficient aromatic system, whereas with salts 5 and 6 such interactions are observed despite the presence of water. However, due to asymmetric hydrogen‐bonding interactions with ammonium side chains, the anion of 5 is located close to the rim of the pentafluorophenyl group (η1 interaction). In 6 the CH–anion hydrogen bonding is more symmetric and fixes the anion on top of the ring (η6). A similar structure‐controlling effect is observed in case of the 1,4‐diazabicyclo[2.2.2]octane derivatives 7 . Here the position of the anion (Cl, Br, I) is shifted according to the length of the weak CH–halide interaction. The hexafluorophosphate 7 d reveals that this “non‐coordinating” anion can be located on top of an aromatic π system. In the methyl‐substituted pyridinium salts 9 and 10 different locations of the bromide anions with respect to the π system are observed. This is due to different conformations of the mono‐ versus disubstituted pyridine, which leads to different directions of the weak, but structurally important, HMe? Br bonds. 相似文献
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Michele Bedin Alavi Karim Marcus Reitti Anna-Carin C. Carlsson Filip Topi? Mario Cetina Fangfang Pan Vaclav Havel Fatima Al-Ameri Vladimir Sindelar Kari Rissanen Jürgen Gr?fenstein Máté Erdélyi 《Chemical science》2015,6(7):3746-3756
A detailed investigation of the influence of counterions on the [N–I–N]+ halogen bond in solution, in the solid state and in silico is presented. Translational diffusion coefficients indicate close attachment of counterions to the cationic, three-center halogen bond in dichloromethane solution. Isotopic perturbation of equilibrium NMR studies performed on isotopologue mixtures of regioselectively deuterated and nondeuterated analogues of the model system showed that the counterion is incapable of altering the symmetry of the [N–I–N]+ halogen bond. This symmetry remains even in the presence of an unfavorable geometric restraint. A high preference for the symmetric geometry was found also in the solid state by single crystal X-ray crystallography. Molecular systems encompassing weakly coordinating counterions behave similarly to the corresponding silver(i) centered coordination complexes. In contrast, systems possessing moderately or strongly coordinating anions show a distinctly different behavior. Such silver(i) complexes are converted into multi-coordinate geometries with strong Ag–O bonds, whereas the iodine centered systems remain linear and lack direct charge transfer interaction with the counterion, as verified by 15N NMR and DFT computation. This suggests that the [N–I–N]+ halogen bond may not be satisfactorily described in terms of a pure coordination bond typical of transition metal complexes, but as a secondary bond with a substantial charge-transfer character. 相似文献
99.
Mäkinen M Holopainen S Rissanen K Vainiotalo P 《Rapid communications in mass spectrometry : RCM》2006,20(7):1082-1086
Five N-alkylated ammonium resorcarene derivatives, differing either in the nitrogen atom or in the lower rim alkyl chain, were studied using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The main purpose was to clarify the fragmentation and the relative stabilities of the protonated molecules by collision-induced dissociation (CID) experiments. The results indicate that fragmentation of the upper rim alkyl amino substituents at the 2-position occurs readily. Variation in the gas-phase stabilities of these molecules was also observed. In addition, the proposed fragmentation pathways are depicted. 相似文献
100.
[reaction: see text] A novel, biomimetic concept for the direct reductive amination of ketones is described that relies on selective imine activation by hydrogen bond formation. The mild, acid- and metal-free process requires only catalytic amounts of thiourea as hydrogen bond donor and utilizes the Hantzsch ester for transfer hydrogenation. The method allows the efficient synthesis of structurally diverse amines. 相似文献