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The target donor-acceptor compound forms an acridinium-like, locally excited (LE) singlet state on illumination with blue or near-UV light. This LE state undergoes rapid charge transfer from the acridinium ion to the orthogonally sited mesityl group in polar solution. The resultant charge-transfer (CT) state fluoresces in modest yield and decays on the nanosecond time scale. The LE and CT states reside in thermal equilibrium at ambient temperature; decay of both states is weakly activated in fluid solution, but decay of the CT state is activationless in a glassy matrix. Analysis of the fluorescence spectrum allows precise location of the relevant energy levels. Intersystem crossing competes with radiative and nonradiative decay of the CT state such that an acridinium-like, locally excited triplet state is formed in both fluid solution and a glassy matrix. Phosphorescence spectra position the triplet energy well below that of the CT state. The triplet decays via first-order kinetics with a lifetime of ca. 30 micros at room temperature in the absence of oxygen but survives for ca. 5 ms in an ethanol glass at 77 K. The quantum yield for formation of the LE triplet state is 0.38 but increases by a factor of 2.3-fold in the presence of iodomethane. The triplet reacts with molecular oxygen to produce singlet molecular oxygen in high quantum yield. In sharp contradiction to a recent literature report, there is no spectroscopic evidence to indicate the presence of an unusually long-lived CT state.  相似文献   
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Summary Transition metal(II) tetrafluoroborates react with 1-alkyltetrazoles to give complexes with six ligands per metal ion,viz.; ML6(BF4)2 with M2+ = Mn2+, Co2+, Ni2+, Cu2+ or Zn2+ and L =1-methyltetrazole (MTz), 1-ethyltetrazole (ETz) and 1-propyltetrazole (PTz). The complexes were identified and characterized by chemical analyses, i.r. and ligand field spectra. They are apparently mononuclear, containing monodentate ligands for which the Dq values are exceptionally high.  相似文献   
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Energy distributions of electrons were measured under an observation angle of 42.3° by bombarding thin carbon foils with protons of 0.5 to 2.5 MeV and with Neon of 10 MeV energies. Comparison of the experimental results with binary-encounter-approximation calculations, taking into account the electron energy loss in the solid, show that the spectra from proton bombardment can be described by this model.  相似文献   
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Using a chemical cross-linking procedure, surface-grafted polyglutamate films with a permanently perpendicular helix orientation were prepared. A surface-grafted alpha-helical polyglutamate film containing polymerizable side groups was synthesized by ring-opening terpolymerization of 50 molar% gamma-methyl-L-glutamate N-carboxyanhydride (NCA), 30% gamma-stearyl-L-glutamate NCA and 20% gamma-4-vinylbenzyl-L-glutamate NCA initiated from a silicon substrate functionalized with primary amino groups. The average tilt angle of the end-grafted helices in this film is approximately 66 degrees , indicating a nearly parallel helix orientation with respect to the substrate surface. After swelling of the grafted terpolyglutamate film in stearyl methacrylate and subsequent radical cross-linking, the average helix tilt angle decreases to about 11 degrees, indicating an almost perpendicular helix orientation. The film thickness increases accordingly from 151 A before to approximately 390 A after cross-linking. Extensive solvent treatment of the cross-linked film shows that the perpendicular helix orientation is permanent.  相似文献   
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Zusammenfassung Die Anwendung der photometrischen Indizierung bei reduktometrischen Bestimmungen mit Cr(II) wird beschrieben.Durch, die Ausführung in schwach alkalischer Lösung in Anwesenheit von ÄDTA als Komplexbildner für Cr(II) steht ein stark reduzierendes Reaktionsmilieu zur Verfügung. Die Anwendbarkeit dieser Methode zur Bestimmung kleiner Mengen anorganischer Anionen bzw. organischer Stoffe mit reduzierbaren Gruppen, wird anhand von Beispielen gezeigt. Eine Fehlerdiskussion wird gegeben.
Summary A report is given on the application of photometric end-point indication for reductometric determinations with Cr(II).Performance in weakly alkaline solution in the presence of EDTA makes use of the strong reduction properties of the Cr(II)-EDTA complex. Examples are given for the determination of mg-quantities of inorganic anions and organic compounds with reducible groups. An error calculation is also presented.


Wir danken Herrn J. C. Kraak für die genaue Durchführung zahlreicher Analysen.  相似文献   
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Fascination with and the need for evermore increasing efficiency, power, or strength have been the cornerstones for developing new materials and methods for their creation. Higher solar cell conversion efficiencies, increased battery storage power, and lightweight strong materials are some that have been at the forefront of attention for these efforts. Materials created for most applications start as simple chemical compounds. A study of how these chemicals have been used in the past can be used to create new materials and new methods of production. Herein, a class of materials that are valuable in a multitude of applications, metal sulfide nanoparticles, are examined, along with how they are being produced and how new methods can be established that will help to standardize and increase production capabilities. Precursor–solvent combinations that can be used to create metal sulfide nanoparticles in the gas phase are also explored.  相似文献   
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Photoinduced electron transfer is a widely applied method to convert photon energy into a useful (electro)chemical potential, both in nature and in artificial devices. There is a continuing effort to develop molecular systems in which the charge-transfer state, populated by photoinduced electron transfer, survives sufficiently long to tap the energy stored in it. In general this has been found to require the construction of rather complex molecular systems, but more recently a few approaches have been reported that allow the use of much more simple and relatively small electron donor-acceptor dyads for this purpose. The most successful examples of such systems seem to be those that apply "electron spin control" to slow down the spontaneous decay of the charge-transfer state, and these are reviewed in this minireview, with a discussion of the underlying principles and a critical evaluation of some of the claims made with regard to using a pronounced "inverted-region effect" as an alternative method to prolong the lifetime of charge-transfer states.  相似文献   
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