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21.
We study degree spectra of structures with respect to the bi‐embeddability relation. The bi‐embeddability spectrum of a structure is the family of Turing degrees of its bi‐embeddable copies. To facilitate our study we introduce the notions of bi‐embeddable triviality and basis of a spectrum. Using bi‐embeddable triviality we show that several known families of degrees are bi‐embeddability spectra of structures. We then characterize the bi‐embeddability spectra of linear orderings and study bases of bi‐embeddability spectra of strongly locally finite graphs. 相似文献
22.
Classical parameters obtained from surface tension technique coupled to small angle X-ray scattering (SAXS) measurements gave support to investigate conformational changes in the bovine serum albumin (BSA)-sodium dodecyl sulfate (SDS) complexes, as well as the size of the micelle-like clusters distributed along the polypeptide chain. The studied systems were composed of 1 wt% of BSA in the absence and presence of increasing SDS molar concentration up to 80 mM, under experimental conditions of low ionic strength and pH 5.40. At SDS concentrations below the critical aggregation concentration (cac) of 2.2 mM, SAXS results indicate that the detergent does not modify the native protein conformation. However, the beginning of protein unfolding, evidenced by SAXS through an increase in the values of radius of gyration Rg and protein maximum dimension Dmax, is coincident with the onset of SDS cooperative binding to BSA identified by the first breakpoint in the surface tension-SDS profile. Further SDS addition leads to the formation of micelle-like aggregates randomly distributed along the unfolded polypeptide chain, consistent to a necklace and bead model. The SAXS data also demonstrate that the SDS micelles grow in size up to 50 mM detergent. At 50 mM surfactant, the micelles stop growing. This concentration is near the BSA saturation binding by SDS measured by dialyzes and indicated by the second breakpoint in surface tension-SDS profile. The SAXS and surface tension data are also consistent with the formation of free micelles in equilibrium with BSA-SDS complexes for surfactant amount above the saturation. 相似文献
23.
Dino Boccaletti Francesco Catoni Vincenzo Catoni 《Advances in Applied Clifford Algebras》2007,17(4):611-616
The use of hyperbolic numbers for studying space-time geometry and trigonometry is extended for demonstrating the Frenet’s
formulas in space-time.
By means of this introduction the twin paradox for non-uniformly accelerated motions is formalized in a straightforward way. 相似文献
24.
A general quantitative treatment for salt effects by means of an empirical relationship between the observed rates k and the concentrations of added electrolyte is presented. The proposed equation has been successfully tested for a variety of processes in the literature. 相似文献
25.
Geng Y Romsted LS Froehner S Zanette D Magid LJ Cuccovia IM Chaimovich H 《Langmuir : the ACS journal of surfaces and colloids》2005,21(2):562-568
Sphere-to-rod transitions of cetyltrimethylammonium (CTA+) micelles with dichlorobenzoate counterions are remarkably substituent dependent. Simultaneous estimates of the interfacial molarities of H2O, MeOH, and Cl- and 2,6- and 3,5-dichlorobenzoate (2,6OBz and 3,5OBz) counterions were obtained by the chemical trapping method in mixed micelles of CTACl/CTA3,5OBz and CTACl/CTA2,6OBz without added salt. Increasing the CTA3,5OBz mole fraction produces a marked concurrent increase in interfacial 3,5OBz- and a decrease in interfacial H2O concentrations through the sphere-to-rod transition. No abrupt concentration changes are observed with increasing CTA2,6OBz mole fraction. Counterion-specific changes in the interfacial water concentration may be a major contributor to the delicate balance of forces governing micellar morphology. 相似文献
26.
Cotton FA Donahue JP Lichtenberger DL Murillo CA Villagrán D 《Journal of the American Chemical Society》2005,127(31):10808-10809
A new synthetic path, far superior to either of those previously available, to the W2(hpp)4 molecule (Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) is reported. The reaction of W(CO)6 with Hhpp in o-dichlorobenzene at 200 degrees C produces W2(hpp)4Cl2 in a one-pot reaction in over 90% yield. This compound is stable and easily stored for further use, and it can be efficiently reduced in a one-step reaction to the title compound W2(hpp)4. 相似文献
27.
Dino Coppini 《Mikrochimica acta》1956,44(12):1818-1828
Zusammenfassung Es wird über Methoden für den Nachweis und die Bestimmung kleiner Mengen verschiedener Abbauprodukte des Tryptophans — auch in biologischen Flüssigkeiten —, die von zahlreichen Autoren ausgearbeitet wurden, berichtet. Hierbei handelt es sich um Kynurenin, 3-Hydroxykynurenin, Anthranilsäure und 3-Hydroxyanthranilsäure, Kynuren- und Xanthurensäure. Um das Interesse an jenen Forschungen verständlich zu machen, wird kurz hervorgehoben, daß sich die Anwendung dieser analytischen Methoden nicht auf die biologische Forschung beschränkt, sondern sich auf die Physiopathologie des Menschen ausdehnen läßt.
Vorgetragen im Rahmen des Symposiums für angewandte Mikrochemie in Graz, 8. bis 11. April 1956. 相似文献
Summary A report is given of methods for detecting and determining slight amounts of various degradation products of tryptophan — even in biological fluids, which were developed by various workers. Kynurenin, 3-hydroxykynurenin, anthranilic acid and 3-hydroxyanthranilic acid, kynurenic- and xanthurenic acid are included. To clarify the interest in such studies, it is briefly stressed that the application of these analytical methods is not restricted to biological studies but they can be extended to human physio-pathology.
Résumé Communication sur les méthodes d'identification et de dosage de faibles quantités de différents produits de dégradation du tryptophane, qui ont été les objets des travaux de nombreux auteurs. Il s'agit de la kynurénine, de la 3-hydroxykynurénine, de l'acide anthranilique et de l'acide 3-hydroxyanthranilique, des acides kynurénique et xanthurénique. L'auteur indique brièvement l'intérêt de ces méthodes analytiques dont l'emploi n'est pas limité aux recherches biologiques mais peut être étendu aux recherches sur la physiopathologie de l'homme.
Vorgetragen im Rahmen des Symposiums für angewandte Mikrochemie in Graz, 8. bis 11. April 1956. 相似文献
28.
[reaction: see text] A palladium-catalyzed/norbornene-mediated sequential coupling reaction involving an aromatic sp(2) C-H functionalization as the key step is described, in which an alkyl-aryl bond and an aryl-heteroaryl bond are formed in one pot. A variety of highly substituted six- and seven-membered annulated pyrroles and pyrazoles were synthesized in a one-step process in good yields from readily accessible N-bromoalkyl pyrroles or pyrazoles and aryl iodides. 相似文献
29.
Raúl G. Enríquez Juan M. Fernández-G Dino Gnecco Alain Pénicaud William F. Reynolds 《Journal of chemical crystallography》1998,28(7):529-537
The crystal structures of isoperezone (1), aminoperezone (2), and isoaminoperezone (3) have been determined by single-crystal X-ray diffraction. Compound (1) yields orange crystals, orthorhombic space group P212121 with unit cell dimensions a = 6.271(6), b = 30.373(7), c = 7.257(1) Å, and Z = 4; compound (2) yields purple crystals, orthorhombic space group P212121 with unit cell dimensions a = 6.498(3), b = 7.500(1) c = 29.200(6) Å, and Z = 4; compound (3) yields purple crystals, monoclinic space group P21 with unit cell dimensions a = 7.354(1), b = 7.511(1), c = 13.283(1) Å, = 102,07(1)°, and Z = 2. The side chains in (1)–(3) are oriented out of the plane of the quinone ring at an angle of 124, 144, and 97°, respectively. The molecules in the crystal are held together by hydrogen-bonding networks and van der Waals interactions. 相似文献
30.
Lifchits O Alberico D Zakharian I Charette AB 《The Journal of organic chemistry》2008,73(17):6838-6840
Nucleophilic ring opening of methyl 1-nitrocyclopropanecarboxylates by phenol derivatives in the presence of Cs2CO3 is described. The reaction tolerates a variety of substituents on both the aromatic alcohol and the cyclopropane and affords the products in good yields (53-84%) and with complete preservation of the enantiomeric excess at C-4. The methodology was applied in an enantioselective synthesis of the norepinephrine reuptake inhibitor atomoxetine (Strattera). 相似文献