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81.
The infrared and Raman spectra of perfluorocyclobutane isolated in argon matrices at 1:100 and 1:200 mole ratios have been measured between 200 and 2000 cm?1. Although the ring-puckering fundamental (ν16) was not observed directly, an assignment for the 2 ← 1 (30 cm?1) transition of ν16 has been deduced from sum and difference bands resolved in the infrared spectrum. Potential functions based upon valence force models are considered in detail and correlated with those of similar ring systems. By using the frequency of the 2 ← 1 transition for ν16 and a vibrational reduced mass of 1501 amu, an approximate model potential function calculation yields a slightly puckered equilibrium conformation with a barrier on the order of 124 cm?1. The vibrational assignment for perfluorocyclobutane is discussed in terms of the new matrix isolation spectra. 相似文献
82.
Lee AM Coe JD Ullrich S Ho ML Lee SJ Cheng BM Zgierski MZ Chen IC Martinez TJ Stolow A 《The journal of physical chemistry. A》2007,111(47):11948-11960
Femtosecond time-resolved photoelectron spectroscopy and high-level theoretical calculations were used to study the effects of methyl substitution on the electronic dynamics of the alpha,beta-enones acrolein (2-propenal), crotonaldehyde (2-butenal), methylvinylketone (3-buten-2-one), and methacrolein (2-methyl-2-propenal) following excitation to the S2(pipi*) state at 209 and 200 nm. We determine that following excitation the molecules move rapidly away from the Franck-Condon region, reaching a conical intersection promoting relaxation to the S1(npi*) state. Once on the S1 surface, the trajectories access another conical intersection, leading them to the ground state. Only small variations between molecules are seen in their S2 decay times. However, the position of methyl group substitution greatly affects the relaxation rate from the S1 surface and the branching ratios to the products. Ab initio calculations used to compare the geometries, energies, and topographies of the S1/S0 conical intersections of the molecules are not able to satisfactorily explain the variations in relaxation behavior. We propose that the S1 lifetime differences are caused by specific dynamical factors that affect the efficiency of passage through the S1/S0 conical intersection. 相似文献
83.
84.
Helen A. Clement Michele Boghi Rory M. McDonald Louise Bernier Jotham W. Coe William Farrell Christopher J. Helal Matthew R. Reese Neal W. Sach Jack C. Lee Dennis G. Hall 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18576-18580
Cyclobutane rings are important in medicinal chemistry, yet few enantioselective methods exist to access this scaffold. In particular, cyclobutylboronates are receiving increasing attention in the literature due to the synthetic versatility of alkylboronic esters and the increasing role of boronic acids in drug discovery. Herein, a conjugate borylation of α‐alkyl,β‐aryl/alkyl cyclobutenones is reported leading to the first synthesis of enantioenriched tertiary cyclobutylboronates. Cyclobutanones with two stereogenic centers are obtained in good to high yield, with high enantioselectivity and diastereoselectivity. Vital to this advance are the development of a novel approach to α,β unsymmetrically disubstituted cyclobutenone substrates and the use of a high‐throughput chiral ligand screening platform. The synthetic utility of both the boronic ester and ketone functionalities is displayed, with remarkable chemoselectivity for either group being possible in this small ring scaffold. 相似文献
85.
Renate M. Gleixner Kévin M. Joly Dr. MaryJane Tremayne Dr. Benson M. Kariuki Dr. Louise Male Dr. Diane M. Coe Dr. Liam R. Cox Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(19):5769-5777
1,1′‐Divinyl ferrocene ( 2 ) reacts with K3[Fe(CN)6] under basic biphasic conditions to give a [4]ferrocenophane ( 4 ) in good yield. Incorporating deuterium labels into the internal positions of the vinyl groups of 2 affects the chemoselectivity of the reaction; thus under identical reaction conditions, [D2]‐ 2 reacts to provide a diol‐functionalised [4]ferrocenophane, [D2]‐D /L ‐ 6 in addition to the expected keto‐alcohol, [D1]‐ 4 . Variants on this one‐electron oxidative cyclisation methodology can be used to give other [4]ferrocenophanes; thus, the reaction of 2 with CuCl2 in MeOH or iPrOH leads to dialkoxy [4]ferrocenophanes 19 and 20 , respectively, whereas the reaction of 2 with benzyl carbamate in the presence of tBuOCl gives a bis(carbamate)[4]ferrocenophane, 21 . Mechanisms to account for the formation of the products, the stereoselectivity, and the unusual isotope‐dependent chemoselectivity in the reaction of 2 and [D2]‐ 2 with K3[Fe(CN)6] are proposed. 相似文献
86.
Coe BJ Harries JL Helliwell M Jones LA Asselberghs I Clays K Brunschwig BS Harris JA Garín J Orduna J 《Journal of the American Chemical Society》2006,128(37):12192-12204
In this article, we describe a series of complex salts in which electron-rich {Fe(II)(CN)(5)}(3)(-) centers are coordinated to pyridyl ligands with electron-accepting N-methyl/aryl-pyridinium substituents. These compounds have been characterized by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses have been determined by using hyper-Rayleigh scattering (HRS) at 1064 nm, and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d --> pi* metal-to-ligand charge-transfer (MLCT) bands. The relatively large static first hyperpolarizabilities, beta(0), increase markedly on moving from aqueous to methanol solutions, accompanied by large red-shifts in the MLCT transitions. Acidification of aqueous solutions allows reversible switching of the linear and NLO properties, as shown via both HRS and Stark experiments. Time-dependent density functional theory and finite field calculations using a polarizable continuum model yield relatively good agreement with the experimental results and confirm the large decrease in beta(0) on protonation. The Stark-derived beta(0) values are generally larger for related {Ru(II)(NH(3))(5)}(2+) complexes than for their {Fe(II)(CN)(5)}(3)(-) analogues, consistent with the HRS data in water. However, the HRS data in methanol show that the stronger solvatochromism of the Fe(II) complexes causes their NLO responses to surpass those of their Ru(II) counterparts upon changing the solvent medium. 相似文献
87.
Coe BJ Harries JL Harris JA Brunschwig BS Horton PN Hursthouse MB 《Inorganic chemistry》2006,45(26):11019-11029
Four new complex salts trans[RuIICl(pdma)2LA][PF6]n [pdma = 1,2-phenylenebis(dimethylarsine); LA = 1,4-bis[E-2-(4-pyridyl)ethenyl]benzene (bpvb), n = 1, 1; LA = N-methyl-1,4-bis(E-2-(4-pyridyl)ethenyl)benzene (Mebpvb+), n = 2, 2; LA = N-phenyl-1,4-bis(E-2-(4-pyridyl)ethenyl)benzene (Phbpvb+), n = 2, 3; LA = N-(2-pyrimidyl)-1,4-bis(E-2-(4-pyridyl)ethenyl)benzene (Pymbpvb+), n = 2, 4] have been prepared. The electronic absorption spectra of 1-4 display intense, visible metal-to-ligand charge-transfer (MLCT) bands, with lambda(max) values in the range 432-474 nm in acetonitrile. Intense intraligand charge-transfer (ILCT) bands due to LA are also observed, with lambda(max) values in the range 350-416 nm. Cyclic voltammetric studies in acetonitrile reveal reversible RuIII/II waves with E(1/2) values of ca. 1.05 V vs Ag/AgCl, together with LA-based reduction processes that are irreversible with the exception of 1. Salts 1-4 have been investigated by using Stark (electroabsorption) spectroscopy in butyronitrile glasses at 77 K. These studies have afforded dipole moment changes, Deltamu12, for the MLCT and ILCT transitions which have been used to calculate molecular static first hyperpolarizabilities, Beta0, according to the two-state equation Beta0 = 3Deltamu12(mu12)2/(Emax)2 (mu12 = transition dipole moment, Emax = MLCT/ILCT energy). In contrast with related RuII ammine complexes, replacement of a central E-ethylene bond with a 1,4-phenylene unit does not appear to be an especially effective strategy for combating the NLO transparency-efficiency tradeoff in these pdma complexes. Single-crystal X-ray studies with the complex salts 2 and 3 and also with the pro-ligand salt [Phbpvb+] PF6.0.5HPF6 show that these materials all adopt centrosymmetric packing structures. 相似文献
88.
Malone MA Prakash S Heer JM Corwin LD Cilwa KE Coe JV 《The Journal of chemical physics》2010,133(18):185101
The scattering effects in the infrared (IR) spectra of single, isolated bread yeast cells (Saccharomyces cerevisiae) on a ZnSe substrate and in metal microchannels have been probed by Fourier transform infrared imaging microspectroscopy. Absolute extinction [(3.4±0.6)×10(-7) cm(2) at 3178 cm(-1)], scattering, and absorption cross sections for a single yeast cell and a vibrational absorption spectrum have been determined by comparing it to the scattering properties of single, isolated, latex microspheres (polystyrene, 5.0 μm in diameter) on ZnSe, which are well modeled by the Mie scattering theory. Single yeast cells were then placed into the holes of the IR plasmonic mesh, i.e., metal films with arrays of subwavelength holes, yielding "scatter-free" IR absorption spectra, which have undistorted vibrational lineshapes and a rising generic IR absorption baseline. Absolute extinction, scattering, and absorption spectral profiles were determined for a single, ellipsoidal yeast cell to characterize the interplay of these effects. 相似文献
89.
John M. Zielinski Charles G. Coe Randy J. Nickel Anthony M. Romeo Alan C. Cooper Guido P. Pez 《Adsorption》2007,13(1):1-7
A differential pressure adsorption unit (DPAU) has been constructed which is capable of accurately measuring isotherm data
up to 2000 psia with as little as 100 mg of sample. This non-traditional adsorption/desorption method has been benchmarked
by comparing hydrogen and methane isotherms measured with standard volumetric and gravimetric instruments on a NaA (4A) zeolite
and an activated carbon at near ambient temperatures. The results from stability tests and well as the details of the mathematical
analysis for this differential pressure method are also provided. 相似文献
90.
Benjamin J. Coe James A. Harris Simon J. Coles Michael B. Hursthouse 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(7):857-858
In the title compound, C15H18N3+·C7H7O3S?, the phenylene and pyridyl rings are somewhat twisted with respect to each other, forming a dihedral angle of 23.49 (6)°. The compound contains a dipolar chromophoric cation, but crystallizes in the centrosymmetric space group P21/n and is thus not expected to display quadratic non‐linear optical effects. 相似文献