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排序方式: 共有209条查询结果,搜索用时 41 毫秒
1.
Thermal behaviour of a polyhedral oligomeric silsesquioxane with epoxy resin cured by diamines 总被引:1,自引:0,他引:1
Ramírez C. Abad M. J. Barral L. Cano J. Díez F. J. López J. Montes R. Polo J. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):421-429
A new material belongs to the family of polyhedral oligomeric silsesquioxanes, the 1-(3-glycidyl) propoxy-3,5,7,9,11,13,15-isobutylpentacyclo-[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxane
(glycidylisobutyl-POSS) is characterized by differential scanning calorimetry, thermogravimetric analysis and atomic force
microscopy. Epoxy systems based on diglycidyl ether of bisphenol A (DGEBA) cured with the diamines, 4,4'-diamine-diphenylmethane
(DDM) and 1,4-phenylenediamine (pPDA), were kinetically studied by differential scanning calorimetry in isothermal and dynamic
modes. The thermal behaviour of these systems as the glycidylisobutyl-POSS was added, is discussed later.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
García Fernández R Montes Bayón M García Alonso JI Sanz-Medel A 《Journal of mass spectrometry : JMS》2000,35(5):639-646
A novel interface design for coupling gas chromatography and inductively coupled plasma mass spectrometry (GC/ICP-MS) was used to perform mercury speciation in biological tissues. Three derivatization approaches were optimized and compared for this purpose: anhydrous butylation using a Grignard reagent, aqueous ethylation by means of NaEt(4)B and aqueous propylation with NaPr(4)B. The last reagent was synthesized in the laboratory as it is not commercially available. Detection limits obtained by GC/ICP-MS ranged between 100 and 200 fg (as absolute mass) for methylmercury and between 500 and 600 fg for inorganic mercury using a 1 microl injection. Quantification of methyl- and inorganic mercury was carried out by resorting to aqueous calibration, using ethylmercury as internal standard for both propylation and butylation derivatization techniques. For ethylation procedures, a methylpropylmercury solution was used as internal standard. The absence of transmethylation during sample preparation was checked using a 97% enriched (202)Hg inorganic standard. The accuracy of the three derivatization approaches was evaluated by the analysis of the certified reference material DOLT-2 (dogfish liver) from the National Research Council of Canada and certified for methylmercury, with satisfactory results. 相似文献
3.
Ponce De León CA Montes Bayón M Caruso JA 《Analytical and bioanalytical chemistry》2002,374(2):230-234
Vitamin E supplements are either isolated from plants sources or prepared synthetically. Isolation from plants includes eight different tocopherol structures. Vitamin E synthesis includes seven different stereoisomers, which involves the use of several catalysts that may lead to trace element contamination in the vitamin. The use of ICP-MS is an ideal technique for detecting these trace elements. However, the oily nature of the samples requires the development of a sample preparation methodology. This study was done upon the request of synthetic vitamin E manufacturers to test the trace metal purity of their samples. In this work, the comparison of an acid microwave digestion and emulsion preparation is discussed. Cromium, nickel, tin and lead were found in the synthetic vitamin E analyzed and 200, 60, 9 and 45 ppb were the concentrations found respectively for these elements.Digesting the samples gives slightly lower detection limits compared to the emulsion preparation. 相似文献
4.
L. Barral F.J. Díez S. García-Garabal J. López B. Montero R. Montes C. Ramírez M. Rico 《European Polymer Journal》2005,41(7):1662-1666
Lifetime of the epoxy system formed by diglycidyl ether of bisphenol A, DGEBA/4,4′-diaminediphenylmethane, DDM, modified with the silsesquioxane, glycidylisobutyl-POSS, was calculated from thermogravimetric analysis. The activation energy of the decomposition of this system was evaluated by the integral method developed by Flynn-Wall-Ozawa (E = 88.9 ± 2.1 kJ mol−1) and by Coats and Redfern method (E = 85.2 ± 1.5 kJ mol−1). The kinetic parameters have been used to estimate the lifetime of the system POSS/DGEBA/DDM. The obtained results by two different ways are similar. 相似文献
5.
6.
Coke formation on physically mixed catalysts containing hydrogen-mordenite and 0.6 wt. % platinum-alumina is found to be directly related to the hydrocracking activity of the catalyst for n-hexane, n-octane and n-decane. No clear relationship is found between coke formation and hydroisomerization activity.
, - 0,6% . % -, - -. .相似文献
7.
Liliana Castro Patricio Reyes Consuelo Montes de Correa 《Journal of Sol-Gel Science and Technology》2002,25(2):159-168
Fe-ZrO2 and Cu-ZrO2 xerogels were prepared by a sol-gel method. The effect of the hydrolysis catalyst during the gelation step, namely H2SO4 or NH4OH, on the properties of the resulting materials was investigated by XRD, BET, TGA/DTA, TPD of ammonia, FTIR, and TPR. Fe-ZrO2 and Cu-ZrO2 xerogels, with sulfuric acid introduced as the hydrolysis catalyst, mainly crystallyzed in the tetragonal phase and exhibited larger surface area and acid amount than those obtained with NH4OH. Ammonia TPD shows that copper promoted sulfated zirconia is the most acidic material. TGA and FTIR reveal that under oxidizing conditions sulfated zirconia promoted with iron and copper retains more sulfate species than unpromoted sulfated zirconia. Regardless of the hydrolysis catalyst employed, copper promoted catalysts calcined at 600°C, contain a large fraction of copper oxide specieseasily reduced at low temperatures. These copper oxide species are believed to have different environment and interactions with the surface oxygen vacancies of the zirconia support. A FeO-like phase appears to be the most probable one after reduction of Fe-ZrO2 catalysts prepared with NH4OH as the hydrolysis catalyst. The formation of Fe° species may be hindered by the high dispersion and interaction of Fe2+ ions with the zirconia support. On the other hand, the reduction peaks of iron oxide and sulfate species exhibit a considerable overlap in the TPR profiles of sulfated Fe-ZrO2 samples. Hence, the nature of the supported phase in the latter samples is rather uncertain. 相似文献
8.
Amanda B. Lima Eric O. Faria Rodrigo H. O. Montes Rafael R. Cunha Eduardo M. Richter Rodrigo A. A. Munoz Wallans T. P. dos Santos 《Electroanalysis》2013,25(7):1585-1588
The electrochemical oxidation of ibuprofen at a boron‐doped diamond electrode (BDDE) and its voltammetric determination is reported for the first time. A well‐defined oxidation peak was observed at around 1.6 V in 0.1 mol L?1 H2SO4 solution with 10 % (v/v) ethanol at the BDDE surface activated by either cathodic or anodic pretreatments. A differential‐pulse voltammetric method for the determination of ibuprofen in pharmaceutical formulations was optimized with a detection limit of 5 µmol L?1 and compared with the British Pharmacopeia method. 相似文献
9.
Villa de P AL Alarcón E Montes de Correa C 《Chemical communications (Cambridge, England)》2002,(22):2654-2655
MCM-41 was found to be an active heterogeneous catalyst for the synthesis of nopol by the Prins condensation of beta-pinene and paraformaldehyde, but Sn-MCM-41 in which Sn has been grafted on MCM-41 by chemical vapor deposition is far more active and combines high efficiency and recyclability. 相似文献
10.
S. Pietri P. H. Rega Zs. Podolyák A. Jungclaus M. Pfützner D. Rudolph A. B. Garnsworthy S. J. Steer R. Hoischen M. Górska J. Gerl H. J. Wollersheim I. Kojouharov H. Schaffner J. Grębosz F. Becker P. Bednarczyk L. Caceres P. Doornenbal H. Geissel A. Kelic N. Kurz F. Montes W. Prokopowicz T. Saito S. Tashenov E. Werner-Malento W. Gelletly 《The European physical journal. Special topics》2007,150(1):319-320
The RISING (Rare ISotope INvestigations at GSI) project constitutes a major
pan-european initiative to study nuclear structure in exotic nuclei.
A brief outline of the technical details specific to studies of isomeric decays
following relativistic projectile fragmentation reactions is presented. 相似文献