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51.
The T1,2 ← S0 spectra of benzaldehydes have been studied as a function of the energy separation between the vibrationless levels. It is shown that the spectra are very complicated in the region of ΔE[T20(nπ*)-T10(ππ*)] = 250–400 cm−1, reflecting effective vibronic interferences between T20(0-0) and each of the ν36-ν33 out-of-plane vibrational levels of T10(ππ*). The simulated spectra correspond to the observed spectra. In the case of T10 = 3nπ* and T20 = 3ππ* the spectral change is not so drastic as in the reverse case loc. cit. because the optical intensity generally concentrates in the longest wavelength band, i.e., the origin band of the T1(nπ*) ← S0 transition. The simulation spectra are useful for interpretation of the absorption spectra in similar electronic structure systems of substituted benzaldehydes. 相似文献
52.
T1 ← S0 absorption and T1 → S0 phosphorescence spectra of neat cystalline hexachloroacetone have been analyzed at 4.2°K. From the lifetime and energy the upper state is assigned as 3nπ*. The spectra are sharp compared to other aliphatic ketones, with the 0-0 band at 26 248 ± 2 cm ?1. The phosphorescence shows two strong progressions; one involving the CO stretching mode at 1784 cm?1 (x), the other a long progression of at least 8 bands involving a mode at 143 cmt-1 (a). The 143 cm?1 progression forming mode can best be asigned to the CO out-of-plane wagging vibration. The absorption shows the same two strong progressions, reduced in frequency to 1270 cmt-1 and 123 cm?1, respectively, but with the progression in mode a broadened with increasing n. The broadening is interpreted as arising from inversion doublets; the close harmonicity up to n = 5 allowing the potential barrier to inversion to be estimated as > 700 cm?1. A feature of the spectra is the absence of low frequency torsional modes suggesting lack of pseudo Jahn-Teller distortion of the triplet state potential surface. For comparison, the phosphorescence of crystalline hexafluoroacetone was also studied at 4.2°K. The spectrum exhibits broad bandedness with a 00 band tentatively assigned at 26 870 ± 20 cm?1. 相似文献
53.
Reactions of atomic lanthanide cations (excluding Pm+) with D2O have been surveyed in the gas phase using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer to measure rate coefficients and product distributions in He at 0.35+/-0.01 Torr and 295+/-2 K. Primary reaction channels were observed corresponding to O-atom transfer, OD transfer and D2O addition. O-atom transfer is the predominant reaction channel and occurs exclusively with Ce+, Nd+, Sm+, Gd+, Tb+ and Lu+. OD transfer is observed exclusively with Yb+, and competes with O-atom transfer in the reactions with La+ and Pr+. Slow D2O addition is observed with early lanthanide cation Eu+ and the late lanthanide cations Dy+, Ho+, Er+ and Tm+. Higher-order sequential D2O addition of up to five D2O molecules is observed with LnO+ and LnOD+. A delay of more than 50 kcal mol(-1) is observed in the onset of efficient exothermic O-atom transfer, which suggests the presence of kinetic barriers of perhaps this magnitude in the exothermic O-atom transfer reactions of Dy+, Ho+, Er) and Tm+ with D2O. The reaction efficiency for O-atom transfer is seen to decrease as the energy required to promote an electron to make two non-f electrons available for bonding increases. The periodic trend in reaction efficiency along the lanthanide series matches the periodic trend in the electron-promotion energy required to achieve a d1s1 or d2 excited electronic configuration in the lanthanide cation, and also the periodic trends across the lanthanide row reported previously for several alcohols and phenol. An Arrhenius-like correlation is also observed for the dependence of D2O reactivity on promotion energy for early lanthanide cations, and exhibits a characteristic temperature of 2600 K. 相似文献
54.
Rhodopsins (rhodopsins and their related photopigments) are phylogenetically classified into at least seven subfamilies, which are also roughly discriminated by molecular function. The Gq-coupled rhodopsin subfamily, members of which activate the Gq type G protein upon light absorption, contains pigments which underlie both visual and nonvisual physiologic functions. Gq-coupled visual pigments have been found in the rhabdomeric photoreceptor cells of varied protostomes, and those of molluskans and arthropods have been extensively investigated. Recently, a novel photopigment, melanopsin, and its homologs have been identified in varied vertebrates. In mammals, melanopsin is localized in retinal ganglion cells and is involved in nonvisual systems, including circadian entrainment and pupillary light responses. More recently, we discovered a melanopsin homolog in amphioxus, the closest living invertebrate to vertebrates. Amphioxus melanopsin is localized in putative nonvisual photoreceptor cells with rhabdomeric morphology and exhibits molecular properties almost identical to those of invertebrate Gq-coupled visual pigments. The localization and properties of amphioxus melanopsin bridged the functional and evolutionary gap between invertebrate Gq-coupled visual pigments and vertebrate circadian photopigment melanopsins. Research into the Gq-coupled rhodopsin subfamily, especially invertebrate melanopsins, will provide an opportunity to investigate the evolution of various physiologic functions, based on orthologous genes, during animal evolution. 相似文献
55.
The in-plane dispersion of the hole subband (HSB) in a Si quantum well is obtained for the first time by applying angle-resolved photoemission spectroscopy and surface science techniques. The entire shape of the HSB over a wide ranged wave vector, including admixing of heavy and light hole subbands around the crossing point and the camelback structure inducing negative effective mass, is visualized directly. Energy separations between the subbands are quantitatively explained. 相似文献
56.
Radiation relay using the radiation scaler acts at the time when the output of the scaler comes to a set value. By this action, the stop valve in infusing line (or exhausting line) is closed and the increment (or decrement) of liquid level of tank is stopped. Same as radiation relay using CR rate meter, switching time of the relay of this system varies statistically due to the statistical property of radioactivity. In this paper, the probability density function of the switching time is calculated on the assumption that the pulse train is the Poisson process. Then, the relation between the switching time and the uncertainty in the stop level is examined under a constant incremental (or decremental) velocity of liquid level. Using these results, the minimum intensity of radiation which is necessary to obtain a given accuracy is calculated and the optimum scaling time is given to minimize the uncertainty corresponding to various velocity of liquid level. 相似文献
57.
58.
B. S. Evans C. Charmetant Shiro Koyanagi N. J. Ugnjatschew A. Necke H. Müller W. Messerschmidt G. Tartler S. Wehrli A. J. Lindsey und H. J. S. Sand 《Fresenius' Journal of Analytical Chemistry》1936,105(3-4):121-128
Ohne Zusammenfassung 相似文献
59.
Shuji Hasegawa Xiao Tong Sakura Takeda Norio Sato Tadaaki Nagao 《Progress in Surface Science》1999,60(5-8):89-257
By utilizing a variety of surface superstructures formed on silicon surfaces and atomic layers grown on them, close correlations between the atomic-scale structures and electrical conduction phenomena at the surfaces have been revealed. State-of-art techniques for analyzing and controlling atomic/electronic structures of surfaces are leading to an understanding of the novel electronic transport properties at surfaces. For example, the electrical conduction through surface-state bands, which are inherent in the surface superstructure, has been confirmed in in-situ measurements. An important phenomenon has also been found, where adatoms donate carriers into the surface-state band, resulting in a remarkable enhancement in electrical conductance. The nucleation of the adatoms diminishes such a doping effect. Furthermore, electrical conduction through atomic layers grown on the surfaces, whose growth structures are sensitive to the substrate surface structures, will be also discussed. In this review, we emphasize that the surface electronic transport properties are closely related to the atomic structures and atomistic dynamics on surfaces. The ultimate two-dimensional electron systems, consisting of the surface-state bands and grown atomic layers, are expected to provide a new stage in surface physics, as well as a precursory stage leading to atomic-scale electronics devices. 相似文献
60.
Kobayashi J Ohki K Okimura K Hashimoto T Sakura N 《Chemical & pharmaceutical bulletin》2006,54(6):827-831
Application of aqueous methanesulfonic acid (MSA) for selective chemical removal of pyroglutamic acid (pGlu) residue from five biologically active pyroglutamyl-peptides (pGlu-X-peptides, X=amino acid residue at position 2) was examined. Gonadotropin releasing hormone (Gn-RH), dog neuromedin U-8 (d-NMU-8), physalaemin (PH), a bradykinin potentiating peptide (BPP-5a) and neurotensin (NT) as pGlu-X-peptides were incubated in either 70% or 90% aqueous MSA at 25 degrees C. HPLC analysis of the incubation solutions showed that the main decomposition product was H-X-peptide derived from each pGlu-X-peptide by the removal of pGlu. The results revealed that the pGlu-X peptide bond had higher susceptibility than various internal amide bonds in the five peptides examined, including the Trp-Ser bond in Gn-RH, the C-terminal Asn-NH(2) in d-NMU-8, and the Asp-Pro bond in PH, whose acid susceptibility is well known. Thus, mild hydrolysis with high concentrations of aqueous MSA may be applicable to chemically selective removal of pGlu from pGlu-X-peptides for structural examinations. 相似文献