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81.
Density functional theory calculations were carried out on the structurally characterized [(Cl(4)-cat)Mo(py)Fe(3)S(3) (CO)(4)(P(n)Pr(3))(3)], A, and (Cl(4)-cat)Mo(py)Fe(3)S(3)(CO)(6)(PEt(3))(2), B, and also on A(2)(-) and B(2+) clusters. The Fe-Fe distances in these molecules depend on the total number of valence electrons (60 e(-) in A and B(2)(+) and 62 e(-) in A(2)(-) and B) and undergo great structural changes upon addition or removal of electrons. The changes are consistent with known electron-counting rules in organometallic chemistry. The weak nature of the Fe-Fe bonding interactions in these clusters is apparent in the very similar energies of states with widely different Fe-Fe distances. 相似文献
82.
Hildeberto Nava Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》1986,24(5):965-990
A novel and convenient synthetic method for the preparation of α,ω-bis(2,6-dimethylphenol)–poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-2OH) is presented. It is based on the oxidative copolymerization of 2,6-dimethylphenol (DMP) with 2,2′-di(4-hydroxy-3,5-dimethylphenyl propane) (TMBPA) in a mixture of water–methanol or chlorobenzene–methanol. By using a 4/1 mole ratio of DMP to TMBPA and different solvent mixtures, it was possible to obtain bifunctional PPO-2OHs with number average molecular weights between 1000 and 5000. A phase-transfer-catalyzed etherification of PPO-2OH chain ends with a mixture of m- and p-chloromethylstyrene was used to synthesize α,ω-bis(vinylbenzyl)-poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO-2VBs). The thermal polymerization of the PPO-2VBs was studied by differential scanning calorimetry, and has demonstrated a very high thermal reactivity for this new class of reactive oligomers. 相似文献
83.
Daniela Kunkel Muenchen Janine Martinazzo Alexandra Nava Brezolin Alana Marie de Cezaro Aline Andressa Rigo Mateus Nava Mezarroba Alexandra Manzoli Fábio de Lima Leite Juliana Steffens Clarice Steffens 《Applied biochemistry and biotechnology》2018,184(4):1061-1072
A highly efficient process for reducing the fatty acid (FA) content of high-acid rice bran oil (RBO) was developed by immobilized partial glycerides-selective lipase SMG1-F278N-catalyzed esterification/transesterification using methanol as a novel acyl acceptor. Molecular docking simulation indicated that methanol was much closer to the catalytic serine (Ser-171) compared with ethanol and glycerol, which might be one of the reasons for its high efficiency in the deacidification of high-acid RBO. Additionally, the reaction parameters were optimized to minimize the FA content of high-acid RBO. Under the optimal conditions (substrate molar ratio of methanol to FAs of 1.8:1, enzyme loading of 40 U/g, and at 30 °C), FA content decreased from 25.14 to 0.03% after 6 h of reaction. Immobilized SMG1-F278N exhibited excellent methanol tolerance and retained almost 100% of its initial activity after being used for ten batches. After purification by molecular distillation, the final product contained 97.86% triacylglycerol, 2.10% diacylglycerol, and 0.04% FA. The acid value of the final product was 0.09 mg KOH/g, which reached the grade one standard of edible oil. Overall, methanol was a superior acyl acceptor for the deacidification of high-acid RBO and the high reusability of immobilized SMG1-F278N indicates an economically attractive process. 相似文献
84.
Melina Pérez Urquiza Yoshito Mitani Hector O. Nava Jaimes 《Accreditation and quality assurance》2009,14(5):269-271
The first proficiency testing round 630-IL-1002, was carried out with a Reference Material DMR-180a with reference values
obtained by using gas chromatography isotope dilution mass spectrometry methods, in which glucose, cholesterol and creatinine
were measured. The serum pool was obtained from blood donors and all the analytes were at the normal concentration in Mexican
population. The laboratories participants used different field methods to measure the analytes. The Mexican compulsory standard
NOM-064-SSA1-1993 “specifications for equipments in vitro diagnostic (IVD)” requests 5% precision and 5% maximum bias of the
IVD equipments in the measurements of analytes like glucose and cholesterol. The results obtained by field laboratories in
the proficiency testing round are compared to the reference value and uncertainty provided by the National Metrology Institute
(CENAM). The quality of measurements is dependent not only on the laboratory competence but also on the methods used by those
commercially available IVD kits. It is concluded that quality assessment of measurements in clinical laboratories should be
critically evaluated by using stable and certified reference materials.
Presented at MEFNM 2008, September 2008, Budapest, Hungary. 相似文献
85.
86.
Tin oxide was supported on alumina, titania, magnesia and silica, treated with hydrogen at different temperatures and characterized by Mössbauer spectroscopy and X-ray diffraction. For the samples calcined at 773 K, tin is present as SnO2 on alumina, magnesia and silica, but it occupies Ti sites on titania. After hydrogen treatment at high temperatures, tin is reduced from Sn(IV) to Sn(II) on alumina and titania, from Sn(IV) to Sn(0) on silica, but practically not reduced on magnesia. These results show the different degree of interaction between tin and the supporting material. 相似文献
87.
G. A. Domrachev A. I. Lazarev B. S. Kaverin A. N. Egorochkin A. M. Ob”edkov E. G. Domracheva L. G. Domracheva G. V. Markin E. Huipe Nava A. A. Sorokin O. N. Suvorova V. L. Karnatsevich A. I. Kirillov A. A. Zakurazhnov 《Physics of the Solid State》2004,46(10):1969-1983
The problem of self-assembly in a metal-carbon system under dynamic conditions (equilibrium and nonequilibrium) is considered using the iron-carbon system as an example. It is proved theoretically and experimentally that the ratio of the components of the system affects the possibility of carbon self-assembly with the formation of fractal iron structures and of metal self-assembly with the participation of polyhapto derivatives of iron and the formation of fullerene-like carbon structures. 相似文献
88.
89.
Pt-Sn was supported on titania and silica, and the resulting interactions between the components in prepared samples and the resulting interactions between the components before and after treatment with hydrogen were characterized by Mössbauer spectroscopy, X-ray diffraction, Rietveld refinement, high-resolution transmission electron microscopy (HRTEM) and catalytic tests data. Results show the presence of Pt and SnO2 after calcinations, and Pt3Sn, PtSn and PtSn3 after reduction. Rietveld analysis shows that some Ti4+ are replaced by Sn4+ atoms in the titania structure. Finally, HRTEM and the practically absence of activity observed confirms that metallic platinum is encapsulated. 相似文献
90.
Virgil Percec Hildeberto Nava 《Journal of polymer science. Part A, Polymer chemistry》1988,26(3):783-805
A novel synthetic method for the preparation of high molecular weight aromatic polyethers is presented. It consists in the Scholl reaction of di(1-naphthyl) ethers of aromatic derivatives exhibiting lower nucleophilicity and higher oxidation potential than the 1-naphthoxy groups. The examples described in this paper refer to the synthesis of aromatic polyether sulfones and aromatic polyether ketones by the polymerization of 4,4′-di(1-naphthoxy)diphenyl sulfone and respectively 4,4′-di(1-naphthoxy)benzophenone. Both polymerization reactions are performed at room temperature in nitrobenzene, using anhydrous FeCl3 as catalyst, and apparently follow a “reactive intermediate polycondensation” polymerization mechanism. 相似文献