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排序方式: 共有62条查询结果,搜索用时 15 毫秒
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H Morrison B Mauclair R M Deibel G Pandey W M Baird 《Photochemistry and photobiology》1985,41(3):251-257
Abstract— Urocanic acid (UA) has previously been shown to photochemically react with N, N-dimethylthymine and with phage G4 single-stranded DNA. In this study, E-[ring-2-14C]-U A and calf thymus DNA have been irradiated with UV light (Λ > 270 nm) in buffered, aqueous solutions. Rc-isolation of the DNA indicates covalent binding of UA at levels of up to 80 nmol UA/mg DNA. Binding is observed for both native and heat denatured DNA. Equilibrium dialysis studies give no evidence for complexation of UA to either form of DNA in the dark. Enzymatic cleavage of the UA bound DNA and analysis by HPLC shows peaks for l4C-labelled products with retention volumes identical to those of a marker mixture prepared by irradiating UA with [3H-methyl]thymidine. Photolysis of the DNA before irradiation with U A leads to the formation of a second product with a retention volume corresponding to that for a deoxyadenosine/UA marker. 相似文献
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EI Rodriguez Martinez CI Barriga-Paulino MI Zapata CC Chinchilla AM López-Jiménez CM Gómez 《BMC neuroscience》2012,13(1):104-23
ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages. 相似文献
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Redox‐Induced Spin‐State Switching and Mixed Valency in Quinonoid‐Bridged Dicobalt Complexes
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David Schweinfurth Yvonne Rechkemmer Stephan Hohloch Naina Deibel Irina Peremykin Jan Fiedler Raphael Marx Dr. Petr Neugebauer Prof. Dr. Joris van Slageren Prof. Dr. Biprajit Sarkar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(12):3475-3486
The complexes [{(tmpa)CoII}2(μ‐L1)2?]2+ ( 12+ ) and [{(tmpa)CoII}2(μ‐L2)2?]2+ ( 22+ ), with tmpa=tris(2‐pyridylmethyl)amine, H2L1=2,5‐di‐[2‐(methoxy)‐anilino]‐1,4‐benzoquinone, and H2L2=2,5‐di‐[2‐(trifluoromethyl)‐anilino]‐1,4‐benzoquinone, were synthesized and characterized. Structural analysis of 22+ revealed a distorted octahedral coordination around the cobalt centers, and cobalt–ligand bond lengths that match with high‐spin CoII centers. Superconducting quantum interference device (SQUID) magnetometric studies on 12+ and 22+ are consistent with the presence of two weakly exchange‐coupled high‐spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 12+ and ferromagnetic for 22+ . Both complexes exhibit several one‐electron redox steps, and these were investigated with cyclic voltammetry and UV/Vis/near‐IR spectroelectrochemistry. For 12+ , it was possible to chemically isolate the pure forms of both the one‐electron oxidized mixed‐valent 13+ and the two‐electron oxidized isovalent 14+ forms, and characterize them structurally as well as magnetically. This series thus provided an opportunity to investigate the effect of reversible electron transfers on the total spin‐state of the molecule. In contrast to 22+ , for 14+ the metal–ligand distances and the distances within the quinonoid ligand point to the existence of two low‐spin CoIII centers, thus showing the innocence of the quintessential non‐innocent ligands L. Magnetic data corroborate these observations by showing the decrease of the magnetic moment by roughly half (neglecting spin exchange effects) on oxidizing the molecules with one electron, and the disappearance of a paramagnetic response upon two‐electron oxidation, which confirms the change in spin state associated with the electron‐transfer steps. 相似文献
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An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations. 相似文献
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Alcorta M Rehm KE Back BB Bedoor S Bertone PF Deibel CM DiGiovine B Esbensen H Greene JP Hoffmann CR Jiang CL Lighthall JC Marley ST Pardo RC Paul M Rogers AM Ugalde C Wuosmaa AH 《Physical review letters》2011,106(17):172701
The structure of (15)C, with an s(1/2) neutron weakly bound to a closed-neutron shell nucleus (14)C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction (15)C+(232)Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring (14)C+(232)Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for (15)C, while the cross sections for (14)C match the trends measured for (12,13)C. 相似文献
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CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
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CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献