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341.
Alvarez-Manzaneda E Chahboun R Alvarez E Fernández A Alvarez-Manzaneda R Haidour A Ramos JM Akhaouzan A 《Chemical communications (Cambridge, England)》2012,48(4):606-608
The first enantiospecific synthesis of akaol A, a marine sesquiterpene quinol, has been achieved. Key steps of the synthetic sequence are the oxidative degradation of (-)-sclareol to a dinorlabdane ketoester, mediated by the ozone-lead(IV) acetate system, the diastereoselective α-methylation of a ketoaldehyde, followed by an intramolecular aldol condensation and the further Diels-Alder cycloaddition of a dienol ether. 相似文献
342.
Lidia Kim Abdelwaheb Hamdi Ana Delia Stancu Rachid Souane Lucia Mutihac Jacques Vicens 《Journal of inclusion phenomena and macrocyclic chemistry》2010,66(1-2):55-59
The selective active transport through liquid membrane assisted by the pH gradient of amino acid methylesters by using a series of calix[4]arenes substituted by acid and amido functions, glycolic chains, and hydroxyl groups as carriers has been performed. All these receptors have been found to act as carriers for transport of aromatic amino acid methylesters from the aqueous source phase to the aqueous receiving phase aiming at their separation. The receptors bearing diacid and tetraamido functions have the better ability to transport of amino acids than the other receptors studied. The influence of calixarene and amino acid structures upon transport through liquid membrane is discussed. The obtained results are correlated with those acquired by solvent extraction. 相似文献
343.
Rachid El Moussaoui G rald Pourcelly Maurice Maeck Henry D. Hurwitz Claude Gavach 《Journal of membrane science》1994,90(3):283-292
The influence of co-ion leakage through a bipolar membrane on both I–V response and current efficiency of water dissociation was studied. The monofilm bipolar membrane was synthetized from a pretreated ETFE film functionalized by quaternized ammonium groups on one side and sulphonic groups on the other. The co-ion leakage of this bipolar membrane immersed in NaCl solutions was measured by means of radiotracers. The results showed that the greater the co-ion leakage, the lower was the current efficiency of water dissociation. A theoretical analysis of ion transfer through the bipolar membrane pointing out the effect of boundary layer on the limiting leakage current is presented. 相似文献
344.
An overview of the main simulation methods of fractional systems is presented. Based on Oustaloup’s recursive poles and zeros approximation of a fractional integrator in a frequency band, some improvements are proposed. They take into account boundary effects around outer frequency limits and simplify the synthesis of a rational approximation by eliminating arbitrarily chosen parameters. 相似文献
345.
Miao S Kocher M Rez P Fultz B Ozawa Y Yazami R Ahn CC 《The journal of physical chemistry. B》2005,109(49):23473-23479
Samples of Li(x)Ni0.5Mn0.5O2 and Li(x)Ni(1/3)Mn(1/3)Co(1/3)O2 were prepared as active materials in electrochemical half-cells and were cycled electrochemically to obtain different values of Li concentration, x. Absorption edges of Ni, Mn, Co, and O in these materials of differing x were measured by electron energy loss spectrometry (EELS) in a transmission electron microscope to determine the changes in local electronic structure caused by delithiation. The work was supported by electronic structure calculations with the VASP pseudopotential package, the full-potential linear augmented plane wave code WIEN2K, and atomic multiplet calculations that took account of the electronic effects from local octahedral symmetry. A valence change from Ni2+ to Ni4+ with delithiation would have caused a 3 eV shift in energy of the intense white line at the Ni L3 edge, but the measured shift was less than 1.2 eV. The intensities of the "white lines" at the Ni L-edges did not change enough to account for a substantial change of Ni valence. No changes were detectable at the Mn and Co L-edges after delithiation either. Both EELS and the computational efforts showed that most of the charge compensation for Li+ takes place at hybridized O 2p states, not at Ni atoms. 相似文献
346.
Guianvarc'h D Fourrey JL Tran Huu Dau ME Guérineau V Benhida R 《The Journal of organic chemistry》2002,67(11):3724-3732
We report herein a short stereocontrolled synthesis of heterocyclic C-nucleosides (indole, imidazole, benzimidazole, and 6-iodobenzimidazole). First, condensation of 2-lithiated heterocycles 2-5 with 5-(tert-butyldiphenylsilyl)-2,3-O-isopropylidene-D-gamma-ribonolactone (1) afforded the hemiacetals 6-9 in good yields. Then, borohydride reduction (NaBH(4)) of the protected hemiacetals proceeded stereoselectively to give predominantly the S diols 10-13, which upon Mitsunobu cyclization afforded the alpha-C-nucleosides 14-17. In contrast, the same PPh(3)/DEAD treatment of the 1:1 diastereomeric mixture of the free heterocyclic diols 10d and 11d gave exclusively the beta-anomers 14dbeta and 15dbeta, respectively, by a stereocontrolled process. The mechanisms of these stereocontrolled steps are discussed with the support of molecular modeling studies. 相似文献
347.
348.
Yoann Marsac Stéphanie Legoupy Muriel Pipelier Anne-Marie Aubertin Rachid Benhida 《Tetrahedron》2005,61(32):7607-7612
Enantiomerically enriched cyclobutene compounds 13 and 24 are good precursors of several cyclobutane nucleoside analogs. The synthetic ways involve, in the key step, either hydroboration or dihydroxylation. 相似文献
349.
Novel isoxazolines and isoxazoles of N-substituted saccharin derivatives are synthesized in good yields by 1,3-dipolar cycloaddition of N-allyl or propargyl N-substituted saccharin with arylnitrile oxide under solvent-free microwave irradiation. In this process, the yields were significantly improved over conventional heating, without alteration of the selectivity. The regioselectivity as well as the nonthermal specific microwave effect are discussed. 相似文献
350.
Stéphane Brémier Rachid Hasnaoui Stéphane Portier Olivier Bildstein Clive T. Walker 《Mikrochimica acta》2006,155(1-2):113-120
A CAMECA IMS 6F secondary ion mass spectrometer (SIMS) for the analysis of irradiated nuclear fuel has been installed in the
Microbeam Analysis Laboratory of the Institute for Transuranium Elements (ITU). This device is specially equipped with heavy
metal shielding to enable the safe examination of irradiated nuclear fuel samples with activities up to 75 GBq. At ITU the
shielded SIMS will be used in conjunction with EPMA taking advantage of the complementary nature of the two techniques and
will make important contributions to ongoing research programmes such as the safety of nuclear fuels, the partitioning and
transmutation programme and the characterisation of spent fuels. The paper describes the shielded SIMS installation and presents
a selection of results from the commissioning tests. 相似文献