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51.
We have investigated the infrared (IR) vibrational spectra of acetaminophen (N(4-hydroxyphenyl) acetamide or paracetamol) complexes formed with ethanol and acetone in relation to the nature of the specific intermolecular interactions involved in the stabilization of the complexes. The structures and binding energies of the complexes have been determined using Hartree-Fock (HF) and DFT-B3PW91 procedures and different Pople's basis sets as well. The main results are presented and discussed by considering the hydroxyl (OH), amino (NH), and carbonyl (CO) chemical groups of acetaminophen interacting with the acetone or ethanol molecules either separately or in conjunction in the complex formation. The frequency shifts and IR intensity variations associated with the internal modes of acetaminophen (namely nu(OH), nu(NH), and nu(CO)) as well as the most pertinent vibrational probes of ethanol (nu(OH)) and acetone (symmetric nu(CO) and nu(CCC) stretching modes) interacting with acetaminophen have been analyzed. The predicted spectral changes have been critically discussed in comparison with IR absorption measurements of acetaminophen dissolved as a solute in ethanol or acetone CO2 expanded solutions. It is argued that the exchange-correlation contribution taken into account in DFT calculations is likely significant in determining the main IR spectral features of acetaminophen complexes formed with acetone or involving hydrogen-bonded as with ethanol. 相似文献
52.
Nonracemic ethano-bridged Tr?ger bases are prepared using CuTC-catalyzed decompositions of diazo compounds. Excellent levels of diastereo- and enantio-control (dr and ee up to 12:1 and 95% respectively) are now obtained with aryl diazoketone precursors. 相似文献
53.
Cabaço MI Besnard M Danten Y Coutinho JA 《The journal of physical chemistry. A》2012,116(6):1605-1620
The unusual solubility of carbon dioxide in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been studied by Raman spectroscopy and DFT calculations. It is shown that the solubility results from the existence of two distinct solvation regimes. In the first one (CO(2) mole fraction ≤ 0.35), the usual Fermi dyad is not observed, a fact never reported before for binary mixtures with organic liquids or ionic liquids (IL). Strong experimental evidence complemented by effective DFT modeling shows that this regime is dominated by a chemical reaction leading to the carboxylation of the imidazolium ring accompanied by acetic acid formation. The reactive scheme proposed involves two concerted mechanisms, which are a proton exchange process between the imidazolium cation and the acetate anion and the carboxylation process itself initiated from the formation of "transient" CO(2)-1-butyl-3-methylimidazole 2-ylidene carbene species. In that sense, CO(2) triggers the carboxylation reaction. Moreover, this dynamic picture circumvents consideration of a long-lived carbene formation in dense phase. The second regime is characterized by the detection of the CO(2) Fermi dyad showing that the carboxylation reaction has been strongly moderated. This finding has been interpreted as due to the interaction of the acetic acid molecules with the COO group of acetate anions involved in monodentate forms with the cation. The observation of the Fermi doublet allows us to infer that CO(2) essentially preserves its linear geometry and that the nature and strength of the interactions with its environment should be comparable to those existing in organic liquids and other IL as well. These results have been supported by DFT calculations showing that the CO(2) molecule interacts with energetically equivalent coexisting structures and that its geometry departs only slightly from the linearity. Finally, we find that the CO(2) solvation in Bmim Ac and 1-butyl-3-methylimidazolium trifluoroacetate (Bmim TFA) cannot be straightforwardly compared neither in the first regime due to the existence of a chemical reaction nor in the second regime because CO(2) interacts with a variety of environments not only consisting of ions pairs like in Bmim TFA but also with carboxylate and acetic acid molecule. 相似文献
54.
Alan M. Downward Matteo Granelli Celine Besnard Laure Guénée Alan F. Williams 《Helvetica chimica acta》2023,106(11):e202300120
We report structural studies of a chiral tridentate ligand which forms helical cubanes with cobalt(II) and manganese(II). A quadruple helicate with (P)-chirality is obtained using a (S)-ligand with cobalt(II) but the ligand binds manganese(II) in one of two possible orientations and either (P)- or (M)-quadruple helicates may be observed for a given ligand enantiomer. The helicates may be linked into extended structures by p-nitrobenzoate capping ligands which show stacking interactions with neighbouring complexes. With cobalt(II) we find an extended helical structure with (M)-chirality linking helicates which themselves have (P)-chirality. With manganese(II) we observe a remarkable structure with extended (M)-helices coexisting with extended (P)-helices. 相似文献
55.
56.
Optical injection consists in the unidirectional coupling between a “slave” laser (SL) and a “Master” laser (ML). The injected
SL may exhibit different behaviors, showing frequency locking, wave mixing, relaxation regimes, period doubling, and chaos.
The different regimes may be mapped on a chart where the injected power and the detuning between the slave and the master
frequencies are varied. In this paper, a detailed overview of the regimes are given when the SL is submitted to both optical
injection and filtered optical feedback. This last coupling is realized thanks to an extended cavity, which includes a frequency
filter. When the SL is operating far from threshold (4 Ith), typical regimes mentioned for feedback-free laser are observed for all the external-cavity modes. On the contrary, when
the SL operates close to threshold (1.5 Ith), it is shown that the dynamics is wealthier. New regimes, as one for which simultaneously chaos and locking occur, can be
identified, in comparison to the case of a single-frequency SL. 相似文献
57.
F. Robert P. Besnard M. -L. Charès G. M. Stéphan 《Optical and Quantum Electronics》1995,27(9):805-811
We show that the light of a commercial vertical cavity surface-emitting laser with polarized optical feedback can be switched between two linear polarization eigenstates. The flip occurs when the feedback phase is scanned by either the external cavity length or the injection current. 相似文献
58.
Fabien Besnard 《Foundations of Physics》2012,42(9):1115-1134
Malament (No?s 11:293–300, 1977) proved a certain uniqueness theorem about standard synchrony, also known as Poincaré-Einstein simultaneity, which has generated many commentaries over the years, some of them contradictory. We think that the situation called for some clarification. After reviewing and discussing some of the literature involved, we prove two results which, hopefully, will help clarifying this debate by filling the gap between the uniquess of Malament’s theorem, which allows the observer to use very few tools, and the complete arbitrariness of a time coordinate in full-fledged Relativity theory. In the spirit of Malament’s theorem, and in opposition to most of its commentators, we emphasize explicit definability of simultaneity relations, and give only constructive proofs. We also explore what happens when we reduce to “purely local” data with respect to an observer. 相似文献
59.
60.
A new methodology is proposed to estimate displacement fields from pairs of images (reference and strained) that evaluates
continuous displacement fields. This approach is specialized to a finite-element decomposition, therefore providing a natural
interface with a numerical modeling of the mechanical behavior used for identification purposes. The method is illustrated
with the analysis of Portevin–Le Chatelier bands in an aluminum alloy sample subjected to a tensile test. A significant progress
with respect to classical digital image correlation techniques is observed in terms of spatial resolution and uncertainty. 相似文献