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41.
Re(eta(5)-C5H5)(CO)3]+ family of 17-electron compounds: monomer/dimer equilibria and other reactions
Chong D Laws DR Nafady A Costa PJ Rheingold AL Calhorda MJ Geiger WE 《Journal of the American Chemical Society》2008,130(8):2692-2703
The anodic electrochemical oxidations of ReCp(CO)3 (1, Cp = eta(5)-C5H5), Re(eta(5)-C5H4NH2)(CO)3 (2), and ReCp*(CO)3 (3, Cp* = eta(5)-C5Me5), have been studied in CH2Cl2 containing [NBu4][TFAB] (TFAB = [B(C6F5)4]-) as supporting electrolyte. One-electron oxidations were observed with E(1/2) = 1.16, 0.79, and 0.91 V vs ferrocene for 1-3, respectively. In each case, rapid dimerization of the radical cation gave the dimer dication, [Re2Cp(gamma)2(CO)6]2+ (where Cp(gamma) represents a generic cyclopentadienyl ligand), which may be itself reduced cathodically back to the original 18-electron neutral complex ReCp(gamma)(CO)3. DFT calculations show that the SOMO of 1+ is highly Re-based and hybridized to point away from the metal, thereby facilitating the dimerization process and other reactions of the Re(II) center. The dimers, isolated in all three cases, have long metal-metal bonds that are unsupported by bridging ligands, the bond lengths being calculated as 3.229 A for [Re2Cp2(CO)6]2+ (1(2)2+) and measured as 3.1097 A for [Re2(C5H4NH2)2(CO)6]2+ (2(2)2+) by X-ray crystallography on [Re2(C5H4NH2)2(CO)6][TFAB]2. The monomer/dimer equilibrium constants are between K(dim) = 10(5) M(-1) and 10(7) M(-1) for these systems, so that partial dissociation of the dimers gives a modest amount of the corresponding monomer that is free to undergo radical cation reactions. The radical 1+ slowly abstracts a chlorine atom from dichloromethane to give the 18-electron complex [ReCp(CO)3Cl]+ as a side product. The radical cation 1+ acts as a powerful one-electron oxidant capable of effectively driving outer-sphere electron-transfer reactions with reagents having potentials of up to 0.9 V vs ferrocene. 相似文献
42.
Tendai J. Mafireyi Madeleine Laws John W. Bassett Pamela B. Cassidy Dr. Jorge O. Escobedo Prof. Dr. Robert M. Strongin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15259-15263
We report the first diselenide-based probe for the selective detection of thioredoxin reductase (TrxR), an enzyme commonly overexpressed in melanomas. The probe design involves conjugation of a seminaphthorhodafluor dye with a diselenide moiety. TrxR reduces the diselenide bond, triggering a fluorescence turn-on response of the probe. Kinetic studies reveal favorable binding of the probe with TrxR with a Michaelis–Menten constant (Km) of 15.89 μm . Computational docking simulations predict a greater binding affinity to the TrxR active site in comparison to its disulfide analogue. In vitro imaging studies further confirmed the diselenide probe exhibited improved signaling of TrxR activity compared to the disulfide analogue. 相似文献
43.
DR Matravers 《Contemporary Physics》2013,54(3):251-254
The history of absolute measurements of gravity is mentioned and the reasons for making absolute measurements are indicated. The principles and main advantages and difficulties of the main method—reversible pendulum, free fall, symmetrical free motion—are discussed and examples of each method are described. Problems of comparison of different determinations and of estimating systematic errors are considered. 相似文献
44.
N. Laws 《Journal of Elasticity》1975,5(3-4):227-235
The paper contains a succinct analysis of interfacial discontinuities in anisotropic elastic solids. The results are combined with known results on the ellipsoidal inclusion problem to provide some general formulae for the determination of stress (and strain) concentration factors. Some explicit results are given for cavities in an infinite matrix under arbitrary uniform loading at infinity. 相似文献
45.
An in depth study into the development and decay of distorted turbulent pipe flows in incompressible flow has yielded a vast quantity of experimental data covering a wide range of initial conditions. Sufficient detail on the development of both mean flow and turbulence structure in these flows has been obtained to allow an implied radial static pressure distribution to be calculated. The static pressure distributions determined compare well both qualitatively and quantitatively with earlier experimental work. A strong correlation between static pressure coefficient Cp and axial turbulence intensity is demonstrated.List of symbols
C
p
static pressure coefficient = (pw-p)/1/2
-
D
pipe diameter
-
K
turbulent kinetic energy
- (r, , z)
cylindrical polar co-ordinates. / 0
-
R, y
pipe radius, distance measured from the pipe wall
-
U, V
axial and radial time mean velocity components
-
mean value of u
-
u,
u/
, /
-
u, , w
fluctuating velocity components
-
axial, radial turbulence intensity
-
turbulent shear stress
-
u
friction velocity, (u
2
= 0/p)
- 0
wall shear stress
- *
boundary layer thickness
A version of this paper was presented at the Ninth Symposium on Turbulence, University of Missouri-Rolla, October 1–3, 1984 相似文献
46.
47.
J. B. Alexander Ross William R. Laws John Clark Sutherland Angeliki Buku Panayotis G. Katsoyannis Irving L. Schwartz Herman R. Wyssbrod 《Photochemistry and photobiology》1986,44(3):365-370
A linked-function approach to fluorescence decay data analysis is presented that permits complex systems to be resolved from a single decay curve. The method involves linking fluorescence decay parameters based on a relationship established by independent physical measurements. As an example, by correlating the fluorescence data with 1 H-NMR results, the complex fluorescence decay kinetics of tyrosine analogs and single tyrosyl residues in simple polypeptides can be explained by ground-state rotameric populations of the phenol ring about the Cα-Cβ bond. 相似文献
48.
Havlin RH Laws DD Bitter HM Sanders LK Sun H Grimley JS Wemmer DE Pines A Oldfield E 《Journal of the American Chemical Society》2001,123(42):10362-10369
We have carried out a solid-state magic-angle sample-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic investigation of the (13)C(alpha) chemical shielding tensors of alanine, valine, and leucine residues in a series of crystalline peptides of known structure. For alanine and leucine, which are not branched at the beta-carbon, the experimental chemical shift anisotropy (CSA) spans (Omega) are large, about 30 ppm, independent of whether the residues adopt helical or sheet geometries, and are in generally good accord with Omega values calculated by using ab initio Hartree-Fock quantum chemical methods. The experimental Omegas for valine C(alpha) in two peptides (in sheet geometries) are also large and in good agreement with theoretical predictions. In contrast, the "CSAs" (Deltasigma) obtained from solution NMR data for alanine, valine, and leucine residues in proteins show major differences, with helical residues having Deltasigma values of approximately 6 ppm while sheet residues have Deltasigma approximately 27 ppm. The origins of these differences are shown to be due to the different definitions of the CSA. When defined in terms of the solution NMR CSA, the solid-state results also show small helical but large sheet CSA values. These results are of interest since they lead to the idea that only the beta-branched amino acids threonine, valine, and isoleucine can have small (static) tensor spans, Omega (in helical geometries), and that the small helical "CSAs" seen in solution NMR are overwhelmingly dominated by changes in tensor orientation, from sheet to helix. These results have important implications for solid-state NMR structural studies which utilize the CSA span, Omega, to differentiate between helical and sheet residues. Specifically, there will be only a small degree of spectral editing possible in solid proteins since the spans, Omega, for the dominant nonbranched amino acids are quite similar. Editing on the basis of Omega will, however, be very effective for many Thr, Val, and Ileu residues, which frequently have small ( approximately 15-20 ppm) helical CSA (Omega) spans. 相似文献
49.
The mechanism of the coupling step in polynucleotide synthesis using 5'-4,4'-dimethoxytritylthymidine-3'-beta-cyanoethyl-N,N-diisopropylphosphoramidite as the phosphitylating agent and catalysed by the salt of saccharin and N-methylimidazole in acetonitrile has been studied by (31)P NMR. Pre- and post-equilibria between the activator salt and released diisopropylamine have been examined by (1)H NMR and ITC, which show that the salt between saccharin and diisopropylamine will be present in acetonitrile. Activation of the phosphoramidite by the salt of saccharin and N-methylimidazole involves nucleophilic catalysis and the formation of a reactive saccharin adduct bonded through its carbonyl oxygen to phosphorus. The rate constants for the reaction of the 4-methoxyphenol with 5'-4,4'-dimethoxytritylthymidine-3'-beta-cyanoethyl-N,N-diisopropylphosphoramidite in the presence of saccharin-N-methylimidazole salt show a non-linear dependence on phenol concentration, becoming independent at high phenol concentrations, compatible with a change in rate limiting step from the alcoholysis step to the activation step. 相似文献
50.
A Copper(II) Phenanthroline Metallopeptide That Targets and Disrupts Mitochondrial Function in Breast Cancer Stem Cells 下载免费PDF全文
Kristine Laws Ganka Bineva‐Todd Arvin Eskandari Dr. Chunxin Lu Nicola O'Reilly Dr. Kogularamanan Suntharalingam 《Angewandte Chemie (International ed. in English)》2018,57(1):287-291
The breast cancer stem cell (CSC) and bulk breast cancer cell potency of a series of metallopeptides containing dichloro(1,10‐phenanthroline)copper(II) and various organelle‐targeting peptide sequences is reported. The mitochondria‐targeting metallopeptide 1 exploits the higher mitochondrial load in breast CSCs over the corresponding non‐CSCs and the vulnerability of breast CSCs to mitochondrial damage to potently and selectively kill breast CSCs. Strikingly, 1 reduces the formation and size of mammospheres to a greater extent than salinomycin, an established CSC‐potent agent. Mechanistic studies show that 1 enters CSC mitochondria, induces mitochondrial dysfunction, generates reactive oxygen species (ROS), activates JNK and p38 pathways, and prompts apoptosis. To the best of our knowledge, 1 is the first metallopeptide to selectivity kill breast CSCs in vitro. 相似文献