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41.
The nature of the ground state and the lowest triplet excited state of the [Rh(2)(1,3-diisocyanopropane)(4)](2+) ion have been investigated by the density functional theory. Two locally stable geometrical conformations are found on the potential energy surfaces of both the ground and excited states, corresponding to the eclipsed and twisted conformations, the eclipsed conformation being more stable and having the shorter Rh-Rh bond length. While the Rh-Rh distances of the two conformations differ by approximately 0.4 A, they shorten to the same value upon excitation ( approximately 3.1 A). The excited state originates from the d(z)()()2 (metal antibonding) to p(z)() (ligand-metal bonding) electronic transition. The Mayer Rh-Rh bond order increases from approximately 0.2 to more than 0.8 upon excitation, while the Rh-C(N) bond order shows a slight decrease. A topological bond path between the Rh atoms is found in both the ground and excited states, while the electron localization function (ELF) indicates weak Rh-Rh covalent bonding for the excited state only. 相似文献
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Rados?aw Kamiński Timothy Graber Jason B. Benedict Robert Henning Yu‐Sheng Chen Stephan Scheins Marc Messerschmidt Philip Coppens 《Journal of synchrotron radiation》2010,17(4):479-485
The accuracy that can be achieved in single‐pulse pump‐probe Laue experiments is discussed. It is shown that with careful tuning of the experimental conditions a reproducibility of the intensity ratios of equivalent intensities obtained in different measurements of 3–4% can be achieved. The single‐pulse experiments maximize the time resolution that can be achieved and, unlike stroboscopic techniques in which the pump‐probe cycle is rapidly repeated, minimize the temperature increase due to the laser exposure of the sample. 相似文献
46.
Zheng SL Nygren CL Messerschmidt M Coppens P 《Chemical communications (Cambridge, England)》2006,(35):3711-3713
A new series of solids with ligand-unsupported Au(I) chains with short Au...Au contacts were synthesized; as Ag compounds with the same structure are known, the new phases now allow unbiased comparison of Ag...Ag and Au...Au metallophilic bonds not supported by bridging ligands, which shows the latter to be consistently shorter by 0.03-0.04 A. 相似文献
47.
Novozhilova IV Coppens P Lee J Richter-Addo GB Bagley KA 《Journal of the American Chemical Society》2006,128(6):2093-2104
A critical component of the biological activity of NO and nitrite involves their coordination to the iron center in heme proteins. Irradiation (330 < lambda < 500 nm) of the nitrosyl-nitro compound (TPP)Fe(NO)(NO(2)) (TPP = tetraphenylporphyrinato dianion) at 11 K results in changes in the IR spectrum associated with both nitro-to-nitrito and nitrosyl-to-isonitrosyl linkage isomerism. Only the nitro-to-nitrito linkage isomer is obtained at 200 K, indicating that the isonitrosyl linkage isomer is less stable than the nitrito linkage isomer. DFT calculations reveal two ground-state conformations of (porphine)Fe(NO)(NO(2)) that differ in the relative axial ligand orientations (i.e., GS parallel and GS perpendicular). In both conformations, the FeNO group is bent (156.4 degrees for GS parallel, 159.8 degrees for GS perpendicular) for this formally {FeNO}(6) compound. Three conformations of the nitrosyl-nitrito isomer (porphine)Fe(NO)(ONO) (MSa parallel, MSa perpendicular, and MSa(L)) and two conformations of the isonitrosyl-nitro isomer (porphine)Fe(ON)(NO(2)) (MSb parallel and MSb perpendicular) are identified, as are three conformations of the double-linkage isomer (porphine)Fe(ON)(ONO) (MSc parallel, MSc perpendicular, MSc(L)). Only 2 of the 10 optimized geometries contain near-linear FeNO (MSa(L)) and FeON (MSc(L)) bonds. The energies of the ground-state and isomeric structures increase in the order GS < MSa < MSb < MSc. Vibrational frequencies for all of the linkage isomers have been calculated, and the theoretical gas-phase absorption spectrum of (porphine)Fe(NO)(NO(2)) has been analyzed to obtain information on the electronic transitions responsible for the linkage isomerization. Comparison of the experimental and theoretical IR spectra does not provide evidence for the existence of a double linkage isomer of (TPP)Fe(NO)(NO(2)). 相似文献
48.
Coppens P 《Chemical communications (Cambridge, England)》2003,(12):1317-1320
The author describes his work for which he coined the word 'photocrystallography', a technique which consists of using a laser to pump, or excite, a molecular crystal while the X-ray diffractometer probes its structure at the atomic level. The technique is being used to study highly reactive excited molecules that exist for just millionths or even billionths of a second using very intense light sources at the National Synchrotron Light Source at Brookhaven National Laboratory and the Advanced Photon Source at Argonne National Laboratory. 相似文献
49.
A new solid based on C-methylcalix[4]resorcinarene and the linker molecule bis(4-pyridylmethylidyne)hydrazine (bpmh) has been prepared, in which brick-wall sheets are linked in the third dimension to give networks with three intersecting perpendicular channels; the networks interpenetrate three-fold, but nevertheless leave cavities capable of including sizable guest molecules. 相似文献
50.
Coppens P Gerlits O Vorontsov II Kovalevsky AY Chen YS Graber T Gembicky M Novozhilova IV 《Chemical communications (Cambridge, England)》2004,(19):2144-2145
A very large Rh-Rh contraction of approximately 0.85 A occurs on excitation of the [Rh(2)(1,8-diisocyano-p-menthane)(4)](2+) ion to its triplet state. 相似文献