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371.
372.
Küster A Tea I Sweeten S Rozé JC Robins RJ Darmaun D 《Analytical and bioanalytical chemistry》2008,390(5):1403-1412
A method is described whereby the concentrations and 2H isotope enrichment of glutathione (GSH) and cysteine can be simultaneously determined in a single gas chromatography–mass
spectrometry run following derivatization as their N,S-ethoxycarbonyl methyl esters. Improvements of the derivatization protocol and the use of a short gas chromatography column
combined with single-ion monitoring allow for rapid quantification of these parameters with acceptable precision and reproducibility
(coefficient of variation less than 5%). The method makes possible their quantitative measurement in very small volumes (50 μL)
of human umbilical cord blood, and is thus suitable for determining the cysteine and GSH concentrations and 2H isotope enrichments in blood samples from neonates or in other conditions in which sample size is restricted. It is shown
that the fractional synthesis rate of human umbilical erythrocyte lysates in vitro is several-fold greater than that measured
in vivo. 相似文献
373.
This paper discusses the biochemical and physiological factors underlying the site-specific, non-random distribution of 13C/12C isotope ratios within plant metabolites, which can be determined by isotopic 13C NMR spectrometry. It focuses on the key metabolite glucose and on enzyme activities and physiological processes that are responsible for the carbon isotope patterns in glucose from different biological origins. It further considers how intramolecular 13C/12C isotope ratios in glucose can be exploited to understand fundamental aspects of plant biological chemistry, how these are related to environmental parameters and how these influence metabolites beyond central sugar metabolism. It does not purport to be an extensive overview of intramolecular isotopic patterns. Rather, the aim is to show how a full understanding of 13C/12C fractionations occurring during plant metabolism can only be possible once the factors that define intramolecular isotope values are better delineated. 相似文献
374.
Baillif V Robins RJ Billault I Lesot P 《Journal of the American Chemical Society》2006,128(34):11180-11187
Previous experimental natural abundance deuterium (NAD) NMR results have shown an odd/even-related alternation in the ((2)H/(1)H) ratio of the methylene groups of fatty acids (ChemBioChem 2001, 2, 425) and, by NAD NMR in CLC, a marked difference between enantiotopic deuterons for each methylenic site (Anal. Chem. 2004, 76, 2827). However, to date, the assignment of the absolute configuration for each deuterium has not been possible. To investigate further the origin of these effects, the assignment of NAD quadrupolar doublets observed in chiral oriented solvent is required. Here we describe the assignment of R- and S-isomers resulting from the isotopic substitution in positions 4 and 5 in the aliphatic chain of 1,1'-bis(thiophenyl)hexane 1 (BTPH) derived from natural linoleic acid of plant origin. This was achieved using an optimized synthetic strategy to obtain separately four regio- and stereoselectively deuterated enantiomers of BTPH. By reference to the deuterium spectra of these isotopically labeled reference compounds, we demonstrate that, on both 4 and 5 positions of BTPH, the isotopic enantiomers of S configuration are depleted relative to those of R configuration. This finding effectively explains the observed low ((2)H/(1)H) ratio in NAD of some ethylenic sites of unsaturated fatty acids. 相似文献
375.
Synthetic routes to 4'-(2,2-difluorospirocyclopropane) analogues of adenosine, cytidine, and uridine are described. Treatment of 2',3'-O-isopropylidene-4',5'-unsaturated compounds derived from adenosine and uridine with difluorocarbene (generated from PhHgCF3 and NaI) gave diastereomeric mixtures of the 2,2-difluorospirocyclopropane adducts. Stereoselectivity resulting from hindrance by the isopropylidene group favored addition at the beta face. Removal of base and sugar protecting groups gave new difluorospirocyclopropane nucleoside analogues. The protected uridine analogue was converted into its cytidine counterpart via a 4-(1,2,4-triazol-1-yl) intermediate. Stannyl radical-mediated deoxygenation of the 3'-O-TBS-2'-thionocarbamate derivatives gave the 2'-deoxy products of direct hydrogen transfer. In contrast, identical treatment of the 2'-O-TBS-3'-thionocarbamate isomers resulted in opening of the vicinal difluorocyclopropane ring upon generation of a C3' radical followed by homoallylic hydrogen transfer to give 4'-(1,1-difluoroethyl)-3',4'-unsaturated nucleoside derivatives. Structural aspects and biological effect considerations are discussed. 相似文献
376.
C. E. Hadden P. B. Bowman W. H. Duholke J. E. Guido B. D. Kaluzny R. H. Robins D. J. Russell S. M. Sims T. J. Thamann G. E. Martin 《Journal of heterocyclic chemistry》2000,37(6):1623-1627
The structures of the major thermal degradation products of linezolid (Zyvox®, PNU‐100766) are reported. Following hydrolytic decarboxylation, the remaining oxazolidinone‐derived skeleton of the antibiotic underwent a variety of acetyl migrations prior to deacetylation. Three of the degradation products are structural isomers. Structural characterization of the degradants was accomplished via the concerted analysis of 2D NMR, mass spectrometric, and infrared data. Direct and long‐range 1H‐15N heteronuclear shift correlation experiments at natural abundance were performed on linezolid as well as each of the isolated products of the degradation cascade. 15N chemical shifts for linezolid and each of the degradants, as well as the observed long‐range 1H‐15N coupling pathways are reported. 相似文献
377.
Mark A. Hempenius Neil S. Robins Rob G. H. Lammertink G. Julius Vancso 《Macromolecular rapid communications》2001,22(1):30-33
The water soluble poly(ferrocenylsilane) polycation, poly(ferrocenyl(3‐ammoniumpropyl)methylsilane), was synthesized by transition metal‐catalyzed ring‐opening polymerization of the novel [1]ferrocenophane Fe(η‐C5H4)2SiCH3(CH2)3Cl and by subsequent side group modification. Amination of the chloropropyl moieties using potassium 1,1,3,3‐tetramethyldisilazide followed by acidic hydrolysis produced the polycation. The polycation was employed together with poly(sodium vinylsulfonate) in the electrostatic layer‐by‐layer self‐assembly process to form organometallic multilayers on quartz. The multilayer fabrication process was monitored using UV/Vis absorption spectroscopy and XPS. 相似文献