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71.
dl-[2-13C]Leucine was prepared by condensing the sodium salt of ethyl acetamido-[2-13C]cyanoacetate with isobutylbromide in hexamethylphosphoroustriamide followed by acid hydrolysis. N-Boc-dl-[2-13C]Leucine was prepared and incorporated into [8-dl-[2-13C]leucine]oxytocin by total synthesis. The 13C-labeled hormone derivative [8-[2-13C]leucine]oxytocin was separated from its 8-position diastereoisomer by partition chromatography. The specifically 13C-labeled peptide hormone diastereoisomeric analog [3-dl-[2-13C]leucine]oxytocin also was prepared by solid phase peptide synthesis. No suitable solvent system for partition chromatography separation of the latter diastereoisomeric peptide mixture could be found. However an excellent preparative separation of the diastereoisomers could be obtained by reverse phase high pressure liquid chromatography on a partisil 10 M9 ODS column using the solvent system 0.05 M ammonium acetate (pH 4.0), acetonitrile (81:19, ) to give pure [3-(2-13C]leucine]oxytocin and [3-D-(2-13C]leucine]oxytocin. An excellent separation of [8[2-13C]leucine]oxytocin and the corresponding 8-D-leucine diastereoisomer derivative could also be accomplished by high pressure liquid chromatography. 相似文献
72.
Soloshonok VA Cai C Hruby VJ Van Meervelt L Yamazaki T 《The Journal of organic chemistry》2000,65(20):6688-6696
Via the rational design of a single-preferred transition state, stabilized by electron donor-acceptor-type attractive interactions, structural and geometric requirements for the corresponding starting compounds have been determined. The Ni(II) complex of the Schiff base of glycine with o-[N-alpha-picolylamino]acetophenone, as a nucleophilic glycine equivalent, and N-(trans-enoyl)oxazolidin-2-ones, as derivatives of an alpha,beta-unsaturated carboxylic acid, were found to be the substrates of choice featuring geometric/conformational homogeneity and high reactivity. The corresponding Michael addition reactions were found to proceed at room temperature in the presence of catalytic amounts of DBU to afford quantitatively the addition products with virtually complete diastereoselectivity. Acidic decomposition of the products followed by treatment of the reaction mixture with NH4OH gave rise to the diastereomerically pure 3-substituted pyroglutamic acids. 相似文献
73.
The existence of surface guided electromagnetic waves has been theoretically predicted from Maxwell's equations and investigated during the first decades of the 20th century. However, it is only since the late 1960's that they have attracted the interest of surface physicists and earned the moniker of "surface plasmon". With the advent of commercially available instruments and well established theories, the technique has been used to study a wide variety of biochemical and biotechnological phenomena. Spectral response of the resonance condition serves as a sensitive indicator of the optical properties of thin films immobilized within a wavelength of the surface. This enhanced surface sensitivity has provided a boon to the surface sciences, and fosters collaboration between surface chemistry, physics and the ongoing biological and biotechnological revolution. Since then, techniques based on surface plasmons such as Surface Plasmon Resonance (SPR), SPR Imaging, Plasmon Waveguide Resonance (PWR) and others, have been increasingly used to determine the affinity and kinetics of a wide variety of real time molecular interactions such as protein-protein, lipid-protein and ligand-protein, without the need for a molecular tag or label. The physical-chemical methodologies used to immobilize membranes at the surface of these optical devices are reviewed, pointing out advantages and limitations of each method. The paper serves to summarize both historical and more recent developments of these technologies for investigating structure-function aspects of these molecular interactions, and regulation of specific events in signal transduction by G-protein coupled receptors (GPCRs). 相似文献
74.
A stereodivergent synthetic route has been developed to make the optically pure anti- and syn-beta-substituted cysteine and serine derivatives. In this approach, the key intermediates, > 94% enantiomerically pure cyclic sulfates 3 and aziridines 7, were prepared from alpha,beta-unsaturated esters 1, employing the Sharpless asymmetric dihydroxylation. The high regio- and stereoselective ring-opening reactions of cyclic sulfates and aziridines provided enantiomerically pure beta-substituted cysteine and serine derivatives. 相似文献
75.
[reaction: see text] The novel dipeptide beta-turn mimetic, 4,8-disubstituted azabicyclo[4.3.0]nonane amino acid ester (15), has been synthesized to serve as a peptide mimetic of the dipeptide Phe-Arg, which contains two important pharmacophore elements in melanotropin peptides. Introduction of side-chain functionality at C-8 was achieved by using beta-functionalized pyroglutamate (8) as a synthetic precursor. The side chain at C-4 was introduced by bromination of dehydroamino acid intermediate (10) followed by Suzuki cross-coupling. 相似文献
76.
77.
78.
Immobilized Metal Affinity Chromatography of Phosphorylated Proteins Using High Performance Sorbents
The interactions of two model phosphoproteins (porcine pepsin and ovalbumin) with two different immobilized metal affinity chromatography (IMAC) sorbents containing immobilized Fe3+, Ga3+, and UO2 2+ ions have been investigated under various conditions. Both proteins were adsorbed on immobilized uranyl ions under acidic conditions similar to those on immobilized Fe3+ and Ga3+ ions. The retained proteins could be released either by the presence of phosphate ions in the elution buffer (immobilized Ga3+ and Fe3+ ions) or by an increased pH (all tested immobilized ions). The IMAC sorbents employed could be used under the conditions of high-performance chromatography and are suitable for the separation and analysis of intact phosphoproteins. 相似文献
79.
A novel synthesis of optically active anti-beta-substituted gamma,delta-unsaturated amino acids via a thio-Claisen rearrangement has been achieved. A 2,5-diphenylpyrrolidine was used as a C2-symmetric chiral auxiliary to control the stereochemistry, giving good yields and excellent diastereoselectivities and enantioselectivities. 相似文献
80.
Isuru R. Kumarasinghe Victor J. Hruby Gary S. Nichol 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(4):o163-o166
The synthesis of 3‐[5‐(4‐chlorophenyl)‐1‐(4‐methoxyphenyl)‐1H‐pyrazol‐3‐yl]propionic acid, C19H17ClN2O3, (I), and its corresponding methyl ester, methyl 3‐[5‐(4‐chlorophenyl)‐1‐(4‐methoxyphenyl)‐1H‐pyrazol‐3‐yl]propionate, C20H19ClN2O3, (II), is regiospecific. However, correct identification of the regioisomer formed by spectroscopic techniques is not trivial and single‐crystal X‐ray analysis provided the only means of unambiguous structure determination. Compound (I) crystallizes with Z′ = 2. The propionic acid groups of the two crystallographically unique molecules form a hydrogen‐bonded dimer, as is typical of carboxylic acid groups in the solid state. Conformational differences between the methoxybenzene and pyrazole rings give rise to two unique molecules. The structure of (II) features just one molecule in the asymmetric unit and the crystal packing makes greater use than (I) of weak C—H...A interactions, despite the lack of any functional groups for classical hydrogen bonding. 相似文献