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排序方式: 共有127条查询结果,搜索用时 31 毫秒
1.
P. Forgacs J. Provost A. Touche D. Guenard C. Thal J. Guilhem 《Tetrahedron letters》1985,26(29):3457-3460
From the trunk bark of Odyendea gabonensis (Pierre) Engl. Simaroubaceae, two-new quassinoids have been isolated : Odyendane and Odyendene. Their structures were established from spectral data and X-Ray diffraction analysis. 相似文献
2.
C. Brenier-Maurel C. Delaurent G. Pages M. -C. Guilhem A. M. Siouffi 《Chromatographia》2002,56(5-6):277-282
Summary An optimization procedure for the separation of flavonoids from St John's Wort by reversed-phase high-performance liquid chromatography
on monolithic stationary phase is described. Three-component mobile phase systems are studied using experimental design methodology.
The starting experimental domain is a triangle, each vertex of which is a pure component. From preliminary isocratic experiments,
truncations in the domain are performed leading to a quadrilateral shape working domain with no symmetry. To cope with both
separation and analysis time, desirability functions are used. Optimal conditions are finally given by binary systems and
the four flavonoids are separated in less than seven minutes. 相似文献
3.
The new 10 μg l−1 arsenic standard in drinking water has been a spur to the search for reliable routine analytical methods with a limit of detection at the μg l−1 level. These methods also need to be easy to handle due to the routine analyses that are required in drinking water monitoring. Graphite furnace atomic absorption spectrometry (GFAAS) meets these requirements, but the limit of detection is generally too high except for methods using a pre-concentration or separation step. The use of a high-intensity boosted discharge hollow-cathode lamp decreases the baseline noise level and therefore allows a lower limit of detection. The temperature program, chemical matrix modifier and thermal stabilizer additives were optimized for total inorganic arsenic determination with GFAAS, without preliminary treatment. The optimal furnace program was validated with a proprietary software. The limit of detection was 0.26 μg As l−1 for a sample volume of 16 μl corresponding to 4.2 pg As. This attractive technique is rapid as 20 samples can be analysed per hour. This method was validated with arsenic reference solutions. Its applicability was verified with artificial and natural groundwaters. Recoveries from 91 to 105% with relative standard deviation <5% can be easily achieved. The effect of interfering anions and cations commonly found in groundwater was studied. Only phosphates and silicates (respectively at 4 and 20 mg l−1) lead to significant interferences in the determination of total inorganic arsenic at 4 μg l−1. 相似文献
4.
Bernard Dietrich Jean Guilhem Jean-Marie Lehn Claudine Pascard Etienne Sonveaux 《Helvetica chimica acta》1984,67(1):91-104
The crystal structures of four anion cryptates [X? ? BT -6H+] formed by the protonated macrobicyclic receptor BT -6H+ with F?, Cl?, Br? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F?-ion is tetracoordinated, while Cl? and Br? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H+ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H+ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP2?, ADP3?, ATP4?, P2O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F?, Cl?, Br?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H+ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered. 相似文献
5.
6.
Guilhem Godeau Christophe Brun Hélène Arnion Cathy Staedel Philippe Barthélémy 《Tetrahedron letters》2010,51(7):1012-1015
The synthesis of two novel glycosyl-nucleoside fluorinated amphiphiles (GNFs) derived from the 2H,2H,3H,3H-perfluoro-undecanoyl hydrophobic chain is described. The GNF amphiphiles, which feature either β-d-glucopyranosyl or β-d-lactopyranosyl moieties linked to a thymine base via a 1,2,3 triazole linker, were prepared using a ‘double click’ chemistry route. Surface tension measurements, gelation properties, and TEM studies show that GNFs spontaneously assemble into supramolecular structures. Similarly to their hydrocarbon analogues (GNLs), the GNFs have unique gelation properties in water. A minimum hydrogelation concentration of 0.1% (w/w), was determined in the case of the β-d-glucopyranosyl derivative. Cell viability studies indicate that fluorocarbon GNF 5 was not toxic for human cells (Huh7), whereas hydrocarbon analogue GNL is toxic above 100 μm. 相似文献
7.
8.
Shermin S. Goh Guilhem Chaubet Birgit Gockel Marie‐Caroline A. Cordonnier Hannah Baars Andrew W. Phillips Edward A. Anderson 《Angewandte Chemie (International ed. in English)》2015,54(43):12618-12621
Two enantioselective total syntheses of the nortriterpenoid natural product rubriflordilactone A are described, which use palladium‐ or cobalt‐catalyzed cyclizations to form the CDE rings, and converge on a late‐stage synthetic intermediate. These key processes are set up through the convergent coupling of a common diyne component with appropriate AB‐ring aldehydes, a strategy that sets the stage for the synthetic exploration of other members of this family of natural products. 相似文献
9.
Dale McMorrow Michon Irons Wyche Pi Tai Chou Michael Kasha 《Photochemistry and photobiology》2015,91(3):576-585
Trace quantities of hydrogen‐bonding impurities in otherwise highly purified and dried glassy hydrocarbon matrices at 77 K can modify the relative triplet state energy levels, and hence the photophysical properties of two aromatic ketones, xanthone and chromone, to the extent that the intrinsic spectroscopic properties are obscured. The intrinsic spectroscopic properties of each are revealed in multicrystalline n‐alkane Shpol'skii matrices, and also can be observed in rigorously purified and dried hydrocarbon glasses at 77 K. The extreme sensitivity to stoichiometric, and even substoichiometric quantities of hydrogen‐bonding impurities arises from the near‐degeneracy of the two lowest‐lying triplet states, and the sensitive nature of the n→π* blueshift phenomena to specific hydrogen‐bonding interactions. 相似文献
10.
Steven van Zutphen Vicente J. Margarit Guilhem Mora Pascal Le Floch 《Tetrahedron letters》2007,48(16):2857-2859
Nucleophilic substitution of a phospholide anion onto protected 3-iodoalanine leads to the formation of an amino acid with an appended phosphole in excellent yield. Manipulation of the protecting groups, leads to building blocks suitable for the synthesis of phosphole-containing polypeptides. 相似文献