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41.
Cross WB Daly CG Ackerman RL George IR Singh K 《Dalton transactions (Cambridge, England : 2003)》2011,40(2):495-505
With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used to prepare amine bis(imidazolium) salts (3a and 3b) and an amine mono(imidazolium) salt (6) as precursors to chelating amido-NHC ligands. Treating the pro-ligands 3 with 3 equivalents of the bulky base KHMDS and Pd(OAc)(2) or PtCl(2)(COD) gave the four amido bis(N-heterocyclic carbene) pincer complexes [CNC-R]M-I [M = Pd (7) or Pt (8); R = i-Pr (a) or n-Bu (b)], including the first examples of platinum complexes of a CNC ligand. The reaction of 7a with AgOTf in pyridine gave the cationic complex {[CNC-i-Pr]Pd-py}OTf (9a). Heating a mixture of amine mono(imidazolium) salt 6 with PdCl(2) or K(2)PtCl(4), K(2)CO(3) and KI in pyridine at 100 °C gave the complexes [C,NH]MI(2)py [M = Pd (10) or Pt (11)], in which the amine arm of the NHC ligand is not deprotonated and does not coordinate to the metal. For a solution of 10 in 1,4-dioxane, deprotonation of the amine occurred in a biphasic reaction with aqueous KOH at 40 °C, giving the dimeric amido complex {[C,N]Pd(μ-OH)}(2) (12). The more inert Pt analogue 11 was unreactive under the same conditions. Solid-state structures of the complexes 7a, 7b, 9a, 10, 11 and 12 have been determined by single crystal X-ray diffraction. 相似文献
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The Effect of Sterilization Methods on the Structural and Chemical Properties of Fibrin Microthread Scaffolds 下载免费PDF全文
Jonathan M. Grasman Megan P. O'Brien Kevin Ackerman Keith A. Gagnon Gregory M. Wong George D. Pins 《Macromolecular bioscience》2016,16(6):836-846
A challenge for the design of scaffolds in tissue engineering is to determine a terminal sterilization method that will retain the structural and biochemical properties of the materials. Since commonly used heat and ionizing energy‐based sterilization methods have been shown to alter the material properties of protein‐based scaffolds, the effects of ethanol and ethylene oxide (EtO) sterilization on the cellular compatibility and the structural, chemical, and mechanical properties of uncrosslinked, UV crosslinked, or 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDC) crosslinked fibrin microthreads in neutral (EDCn) or acidic (EDCa) buffers are evaluated. EtO sterilization significantly reduces the tensile strength of uncrosslinked microthreads. Surface chemistry analyses show that EtO sterilization induces alkylation of EDCa microthreads leading to a significant reduction in myoblast attachment. The material properties of EDCn microthreads do not appear to be affected by the sterilization method. These results significantly enhance the understanding of how sterilization or crosslinking techniques affect the material properties of protein scaffolds.
45.
Bilodeau RC Bozek JD Gibson ND Walter CW Ackerman GD Dumitriu I Berrah N 《Physical review letters》2005,95(8):083001
Threshold behavior in inner-shell photodetachment is studied for the first time, specifically with 2-, 3-, or 4-electron emission from He- and S-. The threshold shapes are surprisingly consistent with the Wigner threshold law in all cases, despite large PCI effects observed in He-. In S-, the s-wave law is observed to agree with the data over an unprecedented range, more than an order of magnitude greater than predictions, and allows for the observation of the d-wave component. The measurements also demonstrate a means for obtaining precise core-excitation energies of free atoms. 相似文献
46.
Jie Luo Xiang He D. Andre’ d’Avignon Joseph J.H. Ackerman Dmitriy A. Yablonskiy 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2010,202(1):102-108
Defining the biophysics underlying the remarkable MRI phase contrast reported in high field MRI studies of human brain would lead to more quantitative image analysis and more informed pulse sequence development. Toward this end, the dependence of water 1H resonance frequency on protein concentration was investigated using bovine serum albumin (BSA) as a model system. Two distinct mechanisms were found to underlie a water 1H resonance frequency shift: (i) a protein-concentration-induced change in bulk magnetic susceptibility, causing a shift to lower frequency, and (ii) exchange of water between chemical-shift distinct environments, i.e., free (bulk water) and protein-associated (“bound”) water, including freely exchangeable 1H sites on proteins, causing a shift to higher frequency. At 37 °C the amplitude of the exchange effect is roughly half that of the susceptibility effect. 相似文献
47.
Nathanael Leedom Ackerman 《Annals of Pure and Applied Logic》2010,161(10):1299-1312
In this paper we define a notion of relativization for higher order logic. We then show that there is a higher order theory of Grothendieck topoi such that all Grothendieck topoi relativizes to all models of set theory with choice. 相似文献
48.
Peiran Liu Malloree A. Tarnowski Brian W. O'Mara Wei Wu Haiying Zhang James K. Tamura Michael S. Ackerman Li Tao Michael J. Grace Reb J. Russell 《Rapid communications in mass spectrometry : RCM》2009,23(20):3343-3349
S‐thiolation is a reversible post‐translational modification in which thiol metabolites of low molecular masses are linked to protein sulfhydryl groups through disulfide bonds. This modification is commonly observed in recombinant proteins secreted from E. coli cells. Since it can alter protein functions and introduce molecular heterogeneity, S‐thiolation is undesirable for recombinant protein production. To date, few published studies have characterized thiol modifiers or investigated the mechanism of S‐thiolation in recombinant proteins. In this work, reversed‐phase liquid chromatography and mass spectrometry were used to characterize four of the most abundant thiol modifiers on recombinant proteins secreted from E. coli BL21 (DE3) strain. These thiol modifiers have been identified as glutathione, 4‐phosphopantetheine, gluconoylated glutathione, and dephosphorylated coenzyme A. S‐thiolation by these thiol modifiers increases protein mass by 305, 356, 483, and 685 Da, respectively. These specific mass increases can be used as markers for identifying S‐thiolation in recombinant proteins. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
49.
The degenerate crossing number ${\text{ cr}^{*}}(G)$ of a graph $G$ is the minimum number of crossing points of edges in any drawing of $G$ as a simple topological graph in the plane. This notion was introduced by Pach and Tóth who showed that for a graph $G$ with $n$ vertices and $e \ge 4n$ edges ${\text{ cr}^{*}}(G)=\Omega \big (e^4 / n^4\big )$ . In this paper we completely resolve the main open question about degenerate crossing numbers and show that ${\text{ cr}^{*}}(G)=\Omega \big (e^3 / n^2 \big )$ , provided that $e \ge 4n$ . This bound is best possible (apart for the multiplicative constant) as it matches the tight lower bound for the standard crossing number of a graph. 相似文献
50.
Anderson JR Ye Q Neil JJ Ackerman JJ Garbow JR 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,211(1):30-36
Diffusion of spins between physical or virtual, communicating compartments having different states of longitudinal magnetization leads to diffusion-driven longitudinal relaxation. Herein, in two model systems, the effects of diffusion-driven longitudinal relaxation are explored experimentally and analyzed quantitatively. In the first case, longitudinal relaxation in a single slice of a water phantom is monitored spectroscopically as a function of slice thickness. In the second case, mimicking vascular flow/diffusion effects, longitudinal relaxation is monitored in a two-compartment, semi-permeable fiber phantom. In both cases, apparent longitudinal relaxation, though clearly multi-exponential, is well-modeled as bi-exponential. 相似文献