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61.
Effects of substituents on synthetic analogs of chlorophylls. Part 2: Redox properties, optical spectra and electronic structure 总被引:1,自引:0,他引:1
Kee HL Kirmaier C Tang Q Diers JR Muthiah C Taniguchi M Laha JK Ptaszek M Lindsey JS Bocian DF Holten D 《Photochemistry and photobiology》2007,83(5):1125-1143
The optical absorption spectra and redox properties are presented for 24 synthetic zinc chlorins and 18 free base analogs bearing a variety of 3,13 (beta) and 5,10,15 (meso) substituents. Results are also given for a zinc and free base oxophorbine, which contain the keto-bearing isocyclic ring present in the natural photosynthetic pigments such as chlorophyll a. Density functional theory calculations were carried out to probe the effects of the types and positions of substituents on the characteristics (energies, electron distributions) of the frontier molecular orbitals. A general finding is that the 3,13 positions are more sensitive to the effects of auxochromes than the 5,10,15 positions. The auxochromes investigated (acetyl>ethynyl>vinyl>aryl) cause a significant redshift and intensification of the Qy band upon placement at the 3,13 positions, whereas groups at the 5,10,15 positions result in much smaller redshifts that are accompanied by a decrease in relative Qy intensity. In addition, the substituent-induced shifts in first oxidation and reduction potentials faithfully track the energies of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The calculations show that the LUMO is shifted more by substituents than the HOMO, which derives from the differences in the electron densities of the two orbitals at the substituent sites. The trends in the substituent-induced effects on the wavelengths and relative intensities of the major features (By, Bx, Qx, Qy) in the near-UV to near-IR absorption bands are well accounted for using Gouterman's four-orbital model, which incorporates the effects of the substituents on the HOMO-1 and LUMO+1 in addition to the HOMO and LUMO. Collectively, the results and analysis presented herein and in the companion paper provide insights into the effects of substituents on the optical absorption, redox and other photophysical properties of the chlorins. These insights form a framework that underpins the rational design of chlorins for applications encompassing photomedicine and solar-energy conversion. 相似文献
62.
Orchestrated Triple CH Activation Reactions Using Two Directing Groups: Rapid Assembly of Complex Pyrazoles 下载免费PDF全文
Dr. Weibo Yang Dr. Shengqing Ye Dewey Fanning Timothy Coon Yvonne Schmidt Paul Krenitsky Dean Stamos Prof. Dr. Jin‐Quan Yu 《Angewandte Chemie (International ed. in English)》2015,54(8):2501-2504
A sequential triple C? H activation reaction directed by a pyrazole and an amide group leads to the well‐controlled construction of sterically congested dihydrobenzo[e]indazole derivatives. This cascade reaction demonstrates that the often problematic competing C? H activation pathways in the presence of multiple directing groups can be harvested by design to improve step economy in synthesis. Pyrazole as a relatively weak coordinating group is shown to direct C? H activation for the first time. 相似文献
63.
Springer JW Faries KM Diers JR Muthiah C Mass O Kee HL Kirmaier C Lindsey JS Bocian DF Holten D 《Photochemistry and photobiology》2012,88(3):651-674
Assessing the effects of substituents on the spectra of chlorophylls is essential for gaining a deep understanding of photosynthetic processes. Chlorophyll a and b differ solely in the nature of the 7-substituent (methyl versus formyl), whereas chlorophyll a and d differ solely in the 3-substituent (vinyl versus formyl), yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13(1)-oxophorbines that contain ethynyl, acetyl, formyl and other groups at the 3-, 7- and/or 13-positions. Substituent effects on the absorption spectra are well accounted for using Gouterman's four-orbital model. Key findings are that (1) the dramatic difference in auxochromic effects of a given substituent at the 7- versus 3- or 13-positions primarily derives from relative effects on the LUMO+1 and LUMO; (2) formyl at the 7- or 8-position effectively "porphyrinizes" the chlorin and (3) the substituent effect increases in the order of vinyl < ethynyl < acetyl < formyl. Thus, the spectral properties are governed by an intricate interplay of electronic effects of substituents at particular sites on the four frontier MOs of the chlorin macrocycle. 相似文献
64.
Effects of engine placement on flutter characteristics of a very flexible high-aspect-ratio wing are investigated using the code NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft). Gravity for this class of wings plays an important role in flutter characteristics. In the absence of aerodynamic and gravitational forces and without an engine, the kinetic energy of the first two modes are calculated. Maximum and minimum flutter speed locations coincide with the area of minimum and maximum kinetic energy of the second bending and torsion modes. Time-dependent dynamic behavior of a turboshaft engine (JetCat SP5) is simulated with a transient engine model and the nonlinear aeroelastic response of the wing to the engine’s time-dependent thrust and dynamic excitation is presented. Below the flutter speed, at the wing tip and behind the elastic axis, the impulse engine excitation leads to a stable limit cycle oscillation; and for the ramp kind of excitation, beyond the flutter speed, at 75 % span, behind the elastic axis, it produces chaotic oscillation in the wing. Both the excitations above the flutter speed are stabilized, inboard of the wing. 相似文献
65.
Dewey H. Barich Mark T. Zell Douglas R. Powell Eric J. Munson 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(4):o261-o262
The title compounds (both C9H10O4) have nearly planar structures, and the methyl and/or carboxylic acid groups lie out of the molecular plane, as dictated by steric interactions. 2,5‐Dimethoxybenzoic acid (2,5‐DMBA) forms an unusual intramolecular hydrogen bond between the carboxylic acid group and the O atom of the methoxy group in the 2‐position [O⋯O = 2.547 (2) Å and O—H⋯O = 154 (3)°]. 2,4‐DMBA forms a typical hydrogen‐bond dimer with a neighboring molecule. 相似文献
66.
Xi Chen Zihui Li Xiaoxi Zhang Fengxian Hu Dewey D. Y. Ryu Jie Bao 《Applied biochemistry and biotechnology》2009,159(3):591-604
High cost of triacylglycerol lipid feedstock is the major barrier for commercial production of biodiesel. The fermentation
of oleaginous yeasts for lipid production using lignocellulose biomass provides a practical option with high economic competitiveness.
In this paper, the typical oleaginous yeast strains were screened under the pressure of lignocellulose degradation compounds
for selection of the optimal strains tolerant to lignocellulose. The inhibitory effect of lignocellulose degradation products
on the oleaginous yeast fermentation was carefully investigated. Preliminary screening was carried out in the minimum nutritious
medium without adding any expensive complex ingredients then was carried out in the lignocellulosic hydrolysate pretreated
by dilute sulfuric acid. Seven typical lignocellulose degradation products formed in various pretreatment and hydrolysis processing
were selected as the model inhibitors, including three organic acids, two furan compounds, and two phenol derivatives. The
inhibition of the degradation compounds on the cell growth and lipid productivity of the selected oleaginous yeasts were examined.
Acetic acid, formic acid, furfural, and vanillin were found to be the strong inhibitors for the fermentation of oleaginous
yeasts, while levulinic acid, 5-hydroxymethylfurfural, and hydroxybenzaldehyde were relatively weak inhibitors. Trichosporon cutaneum 2.1374 was found to be the most adopted strain to the lignocellulose degradation compounds. 相似文献
67.
68.
Ron Selensky Dewey Holten Maurice W. Windsor John B. Paine David Dolphin Martin Gouterman John C. Thomas 《Chemical physics》1981,60(1):33-46
We have studied the absorption spectra, emission spectra, and fluorescence excitation polarization spectra of a series of free base and diprotonated etioporphyrin-I dimers covalently linked through (CH2)n bridges, n = 0–8. The absorption spectra of the n = 0 and n = 1 dimer show red shifts, which are largest (≈15 mm) for the Soret band of the n = 0 dimer. The Soret bands of the diprotonated dimers n = 0–3 show splitting (≈500–1000 cm?1) which can be interpreted by an exciton model assuming a reasonable geometry. The fluorescence spectra and quantum yields are similar to that of the monomer, except for the same red shift seen in absorption; however, the n = 0 diprotonated dimer shows an anomalo vibronic structure. The fluorescence excitation polarization spectra for the n = 0 and the n = 1 dimers differ substantially from the monomer; dimers n ? 3 have fluorescence excitation polarization spectra that suggest that some of the excitation stays localized in one moiety while the r hops to the dimer partner. 相似文献
69.
J. M. Dewey 《Shock Waves》1994,4(2):113-115
This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
70.
Excitation with 35 ps flashes of uncomplexed Ni(II) porphyrins in a complexing (basic) solvent results in the binding of ligands in the excited state. 相似文献