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121.
Wrackmeyer B Klimkina EV Maisel HE Tok OL Herberhold M 《Magnetic resonance in chemistry : MRC》2008,46(Z1):S30-S35
Three series of ferrocenes, derived from aminoferrocene Fc-NH2 and 1,1'-diaminoferrocene fc(NH2)2, were studied by 57Fe NMR spectroscopy. A marked decrease in 57Fe magnetic nuclear shielding with respect to ferrocene is observed if the nitrogen atom becomes part of a pi-acceptor linked to one or both cyclopentadienyl rings. In contrast, pi-donor properties of the amino group(s) affect delta57Fe to a much smaller extent. In the case of the fairly rigid structures of 1,3-diaza-2-element-[3]ferrocenophanes, a significant increase of 57Fe nuclear magnetic shielding is observed, in contrast to the corresponding [n]ferrocenophanes with n > 3. Structures of numerous of the ferrocene derivatives have been optimized for the gas phase by calculations (B3LYP/6-311 + G(d,p) level of theory), and 57Fe nuclear magnetic shieldings were calculated using these geometries. There is reasonable agreement in the trends for experimental and calculated data. 相似文献
122.
Titanium-mediated cross-coupling of allenic alcohols with alkynes has been investigated. Divergent reaction pathways were discovered that provide either stereodefined 1,4-dienes or substituted cross-conjugated trienes. In short, allene substitution plays a critical role in the determination of reaction pathway. 相似文献
123.
Heidi L. Shimp 《Tetrahedron》2008,64(16):3437-3445
Titanium-mediated cross-coupling of allenic alcohols with alkynes has been investigated. Divergent reaction pathways were discovered that provide either stereodefined 1,4-dienes or substituted cross-conjugated trienes. In short, allene substitution plays a critical role in the determination of reaction pathway. 相似文献
124.
N. Gañán Gutiérrez F. Sánchez Rojas J. M. Cano Pavón 《Fresenius' Journal of Analytical Chemistry》1996,355(1):88-91
A room-temperature flow injection spectrofluorimetric method is presented for the determination of Zn(II), based on the use of salicylaldehyde thiocarbohydrazone in the presence of Triton X-100 and sodium acetate-acetic acid buffer. Various physical and chemical variables affecting the reaction in the flow system were evaluated. The proposed method is very selective. The calibration graph is linear over the range 10–1000 ng/ml, with a detection limit of 5 ng/ml and a relative standard deviation at the 50 ng/ml level of 1.8 %. The method was successfully applied to the determination of Zn(II) in drinking waters and biological samples. 相似文献
125.
Rafael Jimnez Elena Bueno Israel Cano Elizabeth Corbacho M. Eugenia Fernndez Lidia Gmez Jesús Graciani María Hernndez M. Teresa Matitos Jos Ortíz Pilar Lpez‐Cornejo Rafael Prado‐Gotor 《国际化学动力学杂志》2004,36(12):627-633
The kinetics of substitution of H2O by Ru(NH3)5pz2+ (pz = pyrazine) in Fe(CN)5H2O3? have been studied in micellar aqueous solutions of sodium dodecylsulfate (SDS). Experimental results are discussed by using an approach based on the transition‐state theory. This approach is better than others based on the pseudophase model, which can also be used, because it is able to give a clear meaning to the parameters of the model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants to the micelles (Ru(NH3)5pz2+ in the present work). This association is governed by an equilibrium constant that depends on the electrostatic potential at the surface of the micelles. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 627–633, 2004 相似文献
126.
127.
128.
A notion of stability of dynamics under distant perturbations is introduced. It is demonstrated, for quasi-local systems, that the stability of an equilibrium state under the same perturbations implies the state is factorial, i.e. strongly clustering in space. We also characterize the set of perturbations necessary to ensure the equivalence of stability and factorialness. 相似文献
129.
M. C. Apreda F. H. Cano C. Foces-Foces S. Garcia-Blanco 《Journal of chemical crystallography》1981,11(1-2):1-9
Crystals of C20H16N2O2 are orthorombic:P212121,a = 28.1364(21),b = 7.6474(2),c = 7.5376(2) Å,Z = 4, = 6.4 cm–1 (CuK radiation), andM = 316.36. The structure has been solved by direct methods and refined by two-block least-squares toR = R
w = 0.042. The conformation of ringB is a distorted envelope at N(10), and the phenyl rings have acis configuration with respect to the pyridazine ring. Thermal motion of the molecule has been analyzed in terms of the rigid-body TLS model.On leave from Departamento de Fisica, Facultad de Ciencias Exactas, U.N.L.P., calle 115 esq. 49, La Plata, Buenos Aires, Argentina. 相似文献
130.
The stereochemistry of N-bromosuccinimide electrophilic additions to the double bond at the terminal tetrahydropyridazine ring moiety of the 4a,12a-diazatetracyclic compounds 1-4 has been studied. These reactions appear as very regio- and stereoselective. Most the of the results obtained support the hypothesis that the N-bromoamide additions to cyclohexenes and heterocyclic analogous do not occur via the usual AdE2 mechanism, because the nucleophilic step is the rate-limiting one and the main product-determining factor. On the other hand, epoxidation of the double bond in 1-4 and further opening of the oxirane ring take place in accordance with the normal stereochemical rules. 相似文献