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121.
Richard Brugidou Jean Pierre Bazureau Jack Hamelin Zohra Dahmani Mustapha Rahmouni 《Heteroatom Chemistry》1999,10(6):446-454
A range of various amines 2(a–i) was tested in transamination reactions using ethyl 2‐(1H‐benzimidazol‐2‐yl)‐3‐dimethylamino‐acrylate 1a. The (E)‐s‐cis/trans conformation of some representative products 4 was analyzed by 1H and 13C NMR spectra. The C‐2/C‐3 bond of the compounds 3(a–i) is strongly polarized by a push‐pull effect. In the same manner, reactions of ethyl 2‐(benzoxazol‐2‐yl)‐3‐dimethylamino‐acrylate 1c with 1,4‐diaminobenzene 2i, ethylenediamine 2i, and 1,5‐diaminomaphthalene 2k have been investigated and gave directly the corresponding symmetric bis‐acrylates 4(a–c) in good yields. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 446–454, 1999 相似文献
122.
We present new results on the behaviour of single chains in homo-and copolymer blends which are beyond the rendom phase approximation (RPA). The radius of gyration of a chain in the blend was found to depend strongly on the interactions as well as the effective diffusion constant of a single chain in the blend or copolymer melt. Note that these results cannot be obtained in the original formulation of the RPA. They are based on the effective Hamiltonian of the chain in the medium. In the equation found for the self diffusion constant of a single chain, Ds, the second term is directly the value of the effective potential at zero wave vector. Thus the measurement of Ds would detect the screened potential at q = 0. Experimental verification of these results is in progress. 相似文献
123.
124.
Mustapha Benmouna Thomas A. Vilgis Henri Benoit 《Macromolecular theory and simulations》1992,1(6):333-358
Theoretical models describing the dynamics of multicomponent polymer mixtures are reviewed. Some detailed derivations are shown to make the basic assumptions clear and to ease the comparison between these models. The effects of random noise and memory functions on the time evolution of dynamical correlation functions are examined. The long-range hydrodynamic interactions or mode-coupling effects are also included. A possible extension of these models to the kinetics of spinodal decomposition in solutions of polymer mixtures is briefly discussed. 相似文献
125.
126.
Muhammad Umair Saqib Jabbar Mustapha M. Nasiru Zhaoxin Lu Jianhao Zhang Muhammad Abid Mian Anjum Murtaza Marek Kieliszek Liqing Zhao 《Molecules (Basel, Switzerland)》2021,26(22)
Ultrasound-assisted extraction (UAE) was used to extract carotenoids from the carrot pomace. To investigate the effect of independent variables on the UAE, the response surface methodology (RSM) with central-composite design (CCD) was employed. The study was conducted with three independent variables including extraction time (min), temperature (°C), and ethanol concentration (%). The results showed that the optimal conditions for UAE were achieved with an extraction time of 17 min, temperature of 32 °C, and ethanol concentration of 51% of total carotenoids (31.82 ± 0.55); extraction time of 16 min, temperature of 29 °C, and ethanol concentration of 59% for a combination of β-carotene (14.89 ± 0.40), lutein (5.77 ± 0.19), and lycopene (2.65 ± 0.12). The non-significant (p > 0.05) correlation under optimal extraction conditions between predicted and experimental values suggested that UAE is the more productive process than conventional techniques for the extraction of carotenoids from the carrot pomace. 相似文献
127.
This work deals with spectral mapping theorems for neutron transport semigroups
in unbounded geometries and L1 setting. The mathematical analysis relies on harmonic analysis of certain measure valued mappings related to
Dyson-Phillips expansions and on some functional analytic results on the
critical spectrum. 相似文献
128.
Mustapha Mokhtar-Kharroubi 《Positivity》2006,10(2):231-249
We deal with a general streaming semigroup arising in transport theory. We show that in general such a semigroup has a direct
decomposition into three simpler semigroups one of which extends to a group. A general spectral theory of them is given and
is partly derived from that of a class of positive semigroups on Banach lattices. 相似文献
129.
Mustapha Mokhtar-Kharroubi 《Journal of Functional Analysis》2009,256(6):1998-2025
This paper deals with two related subjects. In the first part, we give generation theorems, relying on (weak) compactness arguments, for perturbed positive semigroups in general ordered Banach spaces with additive norm on the positive cone. The second part provides new functional analytic developments on semigroup theory for Schrödinger operators in Lp spaces with (L1) Δ-bounded potentials without restriction on the (L1) Δ-bound. In particular, our formalism enlarges a priori the classical Kato class and its subsequent refinements. The connection with form-perturbation theory is also dealt with. 相似文献
130.
Intermolecular radical addition to C=N bonds with acyclic stereocontrol offers excellent potential as a mild, nonbasic carbon-carbon bond construction approach to chiral amines. Here, complete details of the first radical additions to chiral N-acylhydrazones as an approach to asymmetric amine synthesis are disclosed. Novel N-acylhydrazones were designed as chiral C=N radical acceptors with Lewis acid activation, restriction of conformational mobility, and commercial availability of precursors. Amination of 4-alkyl-2-oxazolidinones with O-(mesitylenesulfonyl)hydroxylamine or O-(p-nitrobenzoyl)hydroxylamine afforded N-aminooxazolidinones which were condensed with aldehydes to afford N-acylhydrazones 3-8. Three synthetic methods were developed, implementing these N-acylhydrazones in Lewis acid-promoted intermolecular radical additions to C=N bonds. First, additions of various secondary and tertiary alkyl iodides to propionaldehyde and benzaldehyde hydrazones (3 and 7) under tin hydride radical chain conditions in the presence of ZnCl2 gave N-acylhydrazine adducts with diastereomeric ratios ranging from 93:7 to 99:1. Radical additions to a series of N-acylhydrazones with different substituents on the oxazolidinone revealed that benzyl and diphenylmethyl were more effective stereocontrol elements than those with the aromatic ring directly attached to the oxazolidinone. Second, a tin-free method, exploiting dual functions of triethylborane for both initiation and chain propagation, enabled improved yields in addition of secondary alkyl iodides. Third, under photolytic conditions with hexamethylditin, primary radical addition could be achieved with ethyl iodide in the presence of diethyl ether as cosolvent; the 1-ethoxyethyl adduct was observed as a minor product. Chloromethyl addition was achieved under both the tin-free and photolytic conditions; in this case, the adduct bears alkyl chloride functionality with potential for further elaboration. 相似文献