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81.
82.
Members of a series of carbon-poor sulfur-nitrogen heterocycles and polycycles are shown by direct ab initio ipsocentric calculation to support diatropic ring currents and hence to be aromatic on the basis of magnetic criteria. They include 7-cycles S(3)N(2)(CH)(2), S(3)N(3)(CH), and S(3)N(4) and 8-cycles S(2)N(4)(CH)(2) and S(2)N(2)(CH)(4), all with 10 pi electrons. The unknown trithiatetrazepine S(3)N(4) is predicted to be at least as aromatic as its known diaza and triaza homologues. Angular-momentum arguments show that the pi-electron-rich nature of (4n + 2) SN heterocycles is the key to their diatropic current. The Woodward dithiatetrazocine parent framework S(2)N(4)(CH)(2) supports a diatropic ring current, as does its analogue in which N and CH groups are formally exchanged. Formal expansion of (4n + 2)-pi carbocyclic systems by insertion of NSN motifs in every CC bond is predicted to lead to structures that support diatropic ring currents: explicit ab initio calculation of magnetic response predicts the 24-center, 30-pi-electron heterocycle S(6)N(12)(CH)(6), formally derived from benzene, to be aromatic on the basis of this criterion. 相似文献
83.
Ogurtsov VA Rakitin OA Rees CW Smolentsev AA Belyakov PA Golovanov DG Lyssenko KA 《Organic letters》2005,7(5):791-794
On heating with alkynes, the readily prepared 1,3-dithioles 3 undergo a new cycloaddition reaction and an unprecedented molecular rearrangement with loss of chlorine to give the first 7H-thieno[2,3-c]thiopyran-7-thiones 4 and 4H-thieno[3,2-c]thiopyran-4-thiones 5 whose structures were confirmed by X-ray diffraction. Unexpectedly, the different alkynes used to form 3 and to convert it into 4 and 5 were incorporated regiospecifically into the thiophene and thiopyran rings, respectively. [reaction: see text] 相似文献
84.
We consider decompositionsK
n
H, whereH is eitherP
3 (the path with 3 edges) or the complete bipartite graphK
1, 3, with the property that upon taking the complement of each graph in the decomposition one obtains a new decompositionK
n
H
c
.Research supported in part by an NSERC postgraduate Scholarship. 相似文献
85.
When 3-bromo-5-phenyl-1,2,4-oxadiazole (1b) is heated with sodium azide in anhydrous dimethylformamide at 130°, 3-dimethylamino-() and 3-dimethylaminomethyleneamino-5-phenyl-1,2,4-oxadiazole () are formed, the latter by a new deoxygenative coupling of the azide (), or the nitrene derived from it, with the solvent. 相似文献
86.
A novel optimisation algorithm is presented for full spectrum calibration models in near-infrared (NIR) spectroscopy. The algorithm is used to investigate the affect of removing continuous spectral regions on parameters critical to the validity of the model (e.g. explained variance, bias etc.) and ultimately identify and remove problem areas of the spectrum. As an example of its application, this paper shows how to optimise partial least squares regression (PLSR) calibration models for predicting moisture content within an intact pharmaceutical product and how problems due to changes in the nature of samples since setting up the original model may be eliminated. On application of two validated calibration models to a new set of samples unacceptable results were obtained for bias (-0.26 and -0.21% m/m moisture content) between the NIR predicted values and the true values (Karl Fischer analysis). The optimisation algorithm identified small regions of the spectrum, which if included in development of the models contributed significant bias to the final prediction. On removal of these problem regions the calibration models were found to be equally accurate and precise, but with the added advantage of robustness to a variable region of the sample spectrum (bias reduced to -0.05 and -0.09% m/m). 相似文献
87.
In this paper the minimum principle proposed for atomic systems by Hall, Hyslop and Rees [1] is generalized to molecules. It is shown that this generalization retains the advantage of admitting the use of a larger class of trial wave functions, for example those with discontinuities, than is possible in the usual minimum energy principle. The further advantage that the upper bounds obtained by this treatment are always at least as good as those of the Rayleigh-Ritz method is also preserved. The theory is applied to the H ion, potential energy curves are obtained for various “cut-off” wave functions, and the equilibrium internuclear distance is calculated. The optimization of the “cut-off” region so that the upper bound is minimized is also discussed. 相似文献
88.
Clegg AD Rees NV Klymenko OV Coles BA Compton RG 《Journal of the American Chemical Society》2004,126(19):6185-6192
The validity of Marcus theory for outer-sphere heterogeneous electron transfer for the electro-oxidation of a range of anthracene derivatives in alkyl cyanide solvents is investigated. The precision measurement of these fast electron transfers (k(0) >or= 1 cm s(-1)) is achieved by use of the high-speed channel electrode and, where necessary, fast-scan cyclic voltammetry. First, the solvent effect on the rate of electron transfer is studied by considering the first oxidation wave of 9,10-diphenylanthracene in the alkyl cyanide solvents: acetonitrile, propionitrile, butyronitrile, and valeronitrile. Second, the variation of k(0) for a series of substituted anthracenes is investigated by analyzing the voltammetric response of the one-electron oxidations of 9-phenylanthracene, 9,10-dichloroanthracene, 9-chloroanthracene, 9,10-dicyanoanthracene, 9-cyanoanthracene, 9-nitroanthracene, 9,10-diphenylanthracene, and anthracene in acetonitrile. It is shown that the rate of electron transfer of a single compound in different alkyl cyanides is determined by the longitudinal dielectric relaxation properties of the solvent, while differences in rate between the substituted anthracenes in acetonitrile can be quantitatively rationalized by considering their relative hydrodynamic radii. This makes possible the accurate prediction of electron-transfer rates for a molecule by interpolation of rate constants known for related molecules. 相似文献
89.
The thermoanalytical techniques e.g. DSC, TG/DTG and Hot Stage Microscopy have been used to examine the system of NaClO4, S and charcoal mixtures. The results show that there is no reaction between NaClO4 and S alone, but the presence of charcoal activates their reaction. Charcoal is oxidised by NaClO4 prior to the melting of NaClO4, showing a solid phase reaction. The presence of S activates the whole of the reaction to such a level that the mixture burns around 300C.
We wish to express our thanks to the Procurement Executive of the Ministry of Defence, UK for providing financial support for the research. 相似文献
Zusammenfassung Mittels DSC, TG/DTG und HSM wurde das System von Gemischen aus NaClO4, S und Holzkohle untersucht. Die Ergebnisse zeigen, da\ sich zwischen NaClO4 und S allein keine Reaktion abspielt, da\ diese Reaktion aber durch Gegenwart von Holzkohle aktiviert wird. Noch vor dem Schmelzen von NaClO4 wird Holzkohle in einer Feststoffreaktion von NaClO4 oxydiert. Die Gegenwart von S aktiviert die gesamte Reaktion in dem Ma\e, da\ das Gemisch bei 300C verbrennt.
We wish to express our thanks to the Procurement Executive of the Ministry of Defence, UK for providing financial support for the research. 相似文献
90.
This article introduces a set of localized orthonormal functions to serve as basis functions for quantum calculations. They are defined to be eigenfunctions of the position operator in a function space. Their properties, including their variances, for a one-dimensional system are developed. The application to simple harmonic motion is considered as an example and, in particular, the time evolution of an initially localized function is calculated and shown to be periodic. The theory can be interpreted as producing a discrete quantization of space with Hamiltonian interactions that are predominantly between nearest neighbors. These functions can also be used in approximate calculations. To illustrate their accuracy, the example of a Morse oscillator treated as a perturbation of a harmonic oscillator is reconsidered. It is shown that the localized functions in a variational calculation lead to a result that is a good approximation for the lowest states. Furthermore, the use of a wave function that is defined only at discrete points can be justified as the first approximation to this, so that its accuracy can also be discussed. © 1995 John Wiley & Sons, Inc. 相似文献