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311.
We report a study of the acid-base properties of Na-montmorillonite suspensions at temperatures from 25 degrees C to 80 degrees C, by continuous and batch potentiometric methods, combined with analysis of the dissolved and readsorbed species. The batch titration curves reveal that the dissolution processes of Na-montmorillonite and silica-rich secondary phases are increasingly predominant, respectively at acid and basic pH, and according to the temperature. The continuous titration curves are less affected by these side reactions. In the absence of a common intersection point, the thermodynamic analysis of the curves was based on the shift of the PZNPC with the ionic strength. This shift was not significantly altered by the temperature, by comparison with the dissociation product of water in the same conditions. Therefore we concluded that protonation-deprotonation of the dissociable sites at the edges of the clay platelets is not significantly temperature dependent. 相似文献
312.
Grgoire Herzog Brian McMahon Myriam Lefoix Nicholas D. Mullins Courtney J. Collins Humphrey A. Moynihan Damien W.M. Arrigan 《Journal of Electroanalytical Chemistry》2008,622(1):109-114
The homo-oxo-calix[3]arene-facilitated electrochemistry of dopamine at the polarised liquid|liquid interface is presented. Cyclic voltammetry indicated that the dopamine: homo-oxo-calix[3]arene complex formed at the interface between water and 1,2-dichloroethane had a 1:2 stoichiometry, which was confirmed by 1H NMR titration. The electrochemically-determined association constants for the homo-oxo-calix[3]arene complexes with dopamine (log β 8.3), Na+ (8.0) and K+ (7.5) showed that the ionophore was more selective for dopamine over the two alkali metal cations than the dibenzo-18-crown-6 ionophore. Square wave voltammetry was employed for assessment of low concentration measurements, with a limit of detection of 3.8 μM dopamine achieved. These results show that oxo-calixarene-based ionophores are useful reagents for the detection of dopamine at the interface between two immiscible electrolyte solutions. 相似文献
313.
Faouzi Achouri Serge Corbel Abdelhay Aboulaich Lavinia Balan Ahmed Ghrabi Myriam Ben Said Raphaël Schneider 《Journal of Physics and Chemistry of Solids》2014
We report a facile synthesis of ZnO/Fe2O3 heterostructures based on the hydrolysis of FeCl3 in the presence of ZnO nanoparticles. The material structure, composition, and its optical properties have been examined by means of transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and diffuse reflectance UV–visible spectroscopy. Results obtained show that 2.9 nm-sized Fe2O3 nanoparticles produced assemble with ZnO to form ZnO/Fe2O3 heterostructures. We have evaluated the photodegradation performances of ZnO/Fe2O3 materials using salicylic acid under UV-light. ZnO/Fe2O3 heterostructures exhibited enhanced photocatalytic capabilities than commercial ZnO due to the effective electron/hole separation at the interfaces of ZnO/Fe2O3 allowing the enhanced hydroxyl and superoxide radicals production from the heterostructure. 相似文献
314.
Burroughs L Clarke PA Forintos H Gilks JA Hayes CJ Vale ME Wade W Zbytniewski M 《Organic & biomolecular chemistry》2012,10(8):1565-1570
Esters of proteinogenic amino acids efficiently catalyse the formation of erythrose and threose under potentially prebiotic conditions in the highest yields and enantioselectivities yet reported. Remarkably while esters of (L)-proline yield (L)-tetroses, esters of (L)-leucine, (L)-alanine and (L)-valine generate (D)-tetroses, offering the potential to account for the link between natural (L)-amino acids and natural (D)-sugars. The effect of pH and NaCl on the yields and enantioselectivities was also investigated and was shown to be significant, with the optimal enantioselectivities occurring at pH 7. 相似文献
315.
Rupérez FJ Ramos-Mozo P Teul J Martinez-Pinna R Garcia A Malet-Martino M Camafeita E Lopez JA Pastor-Vargas C Egido J Balayssac S Gilard V Barbas C Martin-Ventura JL 《Analytical and bioanalytical chemistry》2012,403(6):1651-1660
Abdominal aortic aneurysm (AAA) is an important health problem, both because of AAA rupture and death and because of increased cardiovascular mortality. Identification of new biomarkers of AAA may suggest novel pathological mechanisms and targets for new medical treatments to slow AAA progression. Metabolic changes in AAA patients were mainly related to carbohydrate and lipid metabolism and many of these changes can be associated with a situation of insulin resistance (which can be related to metabolic syndrome) together with altered amino acid metabolism. For the first time, metabolites that can be associated with differential metabolism by the gut microflora of AAA patients have also been found. Moreover, aminomalonic acid in plasma has been shown to be the metabolite with the biggest difference between patients suffering from large aneurysm (>5 cm) and controls. 相似文献
316.
Chekmenev EY Jones SM Nikolayeva YN Vollmar BS Wagner TJ Gor'kov PL Brey WW Manion MN Daugherty KC Cotten M 《Journal of the American Chemical Society》2006,128(16):5308-5309
High magnetic field solid-state NMR was performed on amphipathic cationic antimicrobial peptides from fish to characterize their secondary structure and orientation in hydrated phospholipid bilayers. High-resolution distance and orientational restraints on 13C- and 15N-labeled amidated piscidins 1 and 3 provided site-specific information establishing alpha-helicity and an orientation parallel to the membrane surface. Few membrane-bound natural peptides with this topology have been structurally studied at high resolution in the presence of hydrated lipid bilayers. This orientation was foreseen since the partitioning of amphipathic cationic antimicrobial peptides at the water-bilayer interface allows for favorable peptide-lipid interactions, and it may be related to the mechanism of action. The enhanced resolution obtained at 900 MHz evidences a determinant advantage of ultra-high-field NMR for the structural determination of multiple-labeled peptides and proteins. 相似文献
317.
Moreira RF Salvadori MC Azevedo CP Oliveira-Silva D Borges DC Moreno RA Sverdloff CE Borges NC 《Biomedical chromatography : BMC》2010,24(11):1220-1227
The validation of a high throughput and specific method using a high‐performance liquid chromatography coupled to electrospray (ES+) ionization tandem triple quadrupole mass spectrometric (LC‐ESI‐MS/MS) method for ondansetron quantification in human plasma is described. Human plasma samples were extracted by liquid–liquid extraction (LLE) using methyl tert‐butyl ether and analyzed by LC‐ESI‐MS/MS. The limit of quantification was 0.2 ng/mL and the method was linear in the range 0.2–60 ng/mL. The intra‐assay precisions ranged from 1.6 to 7.7%, while inter‐assay precisions ranged from 2.1 to 5.1%. The intra‐assay accuracies ranged from 97.5 to 108.2%, and the inter‐assay accuracies ranged from 97.3 to 107.0%. The analytical method was applied to evaluate the relative bioavailability of two pharmaceutical formulations containing 8 mg of ondansetron each in 25 healthy volunteers using a randomized, two‐period crossover design. The geometric mean and respective 90% confidence interval (CI) of ondansetron test/reference percent ratios were 90.15% (81.74–99.44%) for Cmax and 93.11% (83.01–104.43%) for AUC0–t. Based on the 90% confidence interval of the individual ratios (test formulation/reference formulation) for Cmax and AUC0‐inf, it was concluded that the test formulation is bioequivalent to the reference one with respect to the rate and extent of absorption of ondansetron. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
318.
A path graph is the intersection graph of subpaths of a tree. In 1970, Renz asked for a characterization of path graphs by forbidden induced subgraphs. We answer this question by determining the complete list of graphs that are not path graphs and are minimal with this property. © 2009 Wiley Periodicals, Inc. J Graph Theory 62: 369–384, 2009 相似文献
319.
Jos Luis Alessandrini Jorge Alberto Vila Myriam Edith Villegas 《Macromolecular Symposia》2001,166(1):261-268
The influence of the polarisation of the solvent on the mean dimensions of model polyelectrolytes is incorporated by solving numerically the Poisson equation for each conformation of the chain embedded in a continuous dielectric media. The mean squared end to end distance reveals the screening effect introduced by the charges induced within the dielectric. The highest departure from continuous dielectric models occurs at intermediate values of the Coulomb coupling strength. 相似文献
320.
Oliver P. Williams Alyah F. Chmiel Myriam Mikhael Desiree M. Bates Charles S. Yeung Zachary K. Wickens 《Angewandte Chemie (International ed. in English)》2023,62(18):e202300178
Herein, we describe a practical protocol for the removal of alcohol functional groups through reductive cleavage of their benzoate ester analogs. This transformation requires a strong single electron transfer (SET) reductant and a means to accelerate slow fragmentation following substrate reduction. To accomplish this, we developed a photocatalytic system that generates a potent reductant from formate salts alongside Brønsted or Lewis acids that promote fragmentation of the reduced intermediate. This deoxygenation procedure is effective across structurally and electronically diverse alcohols and enables a variety of difficult net transformations. This protocol requires no precautions to exclude air or moisture and remains efficient on multigram scale. Finally, the system can be adapted to a one-pot benzoylation-deoxygenation sequence to enable direct alcohol deletion. Mechanistic studies validate that the role of acidic additives is to promote the key C(sp3)−O bond fragmentation step. 相似文献