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101.
Nicolas Fedullo Michel Sclavons Christian Bailly Jean-Marc Lefebvre Jacques Devaux 《Macromolecular Symposia》2006,233(1):235-245
Polyamide 6 and pristine montmorillonite have been melt blended in an extruder and water was injected into the melt in order to produce nanocomposites. The pristine clay was found to be exfoliated and dispersed homogenously in the nanocomposites. A mechanism explaining the formation of such nanocomposites is presented. 相似文献
102.
Horst Schneider Gerd T. Puchta Franz A. R. Kaul Gabriele Raudaschl-Sieber Frdric Lefebvre Guillaume Saggio Dimitrios Mihalios Wolfgang A. Herrmann Jean Marie Basset 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):127-141
The modification of a mesoporous silica surface with Si(Ind)(CH3)2Cl and the immobilization of CpZr(NMe2)3 on this surface was studied via IR-spectroscopy. To reduce side reactions, the indenyl-modified silica was reacted with hexamethyldisilazane (HMDS) under IR-control before the CpZr(NMe2)3-immobilization. The role of the hydroxyl group protection with HMDS is discussed. The surface modifications have been repeated via Schlenk technique at the same conditions and the surface modifications were studied with 13C CP MAS–NMR, 1H MAS–NMR, elemental-, SEM- and BET-analysis. The surface species of the resulting catalysts are discussed. The precatalysts have been treated with methylaluminoxane (MAO) (Al:Zr (mol:mol)=500:1) and the resulting Zr contents (leaching-effect) are discussed. All catalysts have been tested in ethylene and propylene polymerization. 相似文献
103.
104.
Mathieu Joubert Christelle Delaite Elodie Bourgeat‐Lami Philippe Dumas 《Journal of polymer science. Part A, Polymer chemistry》2004,42(8):1976-1984
Coating of silica nanoparticles by biocompatible and biodegradable polymers of ε‐caprolactone and L ‐lactide was performed in situ by ring‐opening polymerization of the cyclic monomers with aluminum, yttrium, and tin alkoxides as catalysts. Hydroxyl groups were introduced on the silica surface by grafting of a prehydrolyzed 3‐glycidoxypropyl trimethoxysilane to initiate a catalytic polymerization in the presence of metal alkoxides. In this manner, free polymer chains were formed to grafted ones, and the graft density was controlled by the nature of the metal and the alcohol‐to‐metal ratio. The grafting reaction was extensively characterized by spectroscopic techniques and quantified. Nanocomposites containing up to 96% of polymer were obtained by this technique. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1976–1984, 2004 相似文献
105.
Alkylation of p-cresol with tert-butanol catalyzed by heteropoly acid supported on zirconia catalyst
Biju M. Devassy G. V. Shanbhag F. Lefebvre S. B. Halligudi 《Journal of molecular catalysis. A, Chemical》2004,210(1-2):125-130
Butylation of p-cresol by tert-butanol was catalyzed by 12-tungstophosphoric acid supported on zirconia (TPA/ZrO2) under flow conditions. Catalysts prepared with different TPA loading (5–30 wt.%) were calcined at 1023 K and acidity was estimated by temperature programmed desorption (TPD) of NH3. Fifteen percent TPA/ZrO2 showed the highest acidity and found to be the most active catalyst in butylation of p-cresol. The effects of temperature, space velocity (LHSV) and molar ratio of the reactants on the conversion of p-cresol and products selectivities were optimized and the optimum reaction conditions evaluated were 403 K, tert-butanol/p-cresol (Bu/Cr) molar ratio 3 and LHSV 4 h−1. Under the optimized conditions, conversion of p-cresol was found to be 61 mol% with product selectivity for 2-tert-butyl-p-cresol (TBC) 81.4%, 2,6-di-tert-butyl-p-cresol (DTBC) 18.1% and tert-butyl-p-tolyl ether (ether) 0.5%. Study of time on stream (TOS) performed as a function of time for 100 h showed that the loss in activity in terms of conversion of p-cresol was 6%. 相似文献
106.
Ab initio Hartree-Fock calculations on NO3 using a Gaussian basis give the lowest electronic states in the order 2A2, 2E and 2E, with a near degeneracy of 2A2 and 2E.
Groupe de Recherches du C.N.R.S. associé à la Faculté des Sciences d'Orsay.
Remerciements. Les auteurs remercient W. Fink pour avoir mis à leur disposition son programme et les avoir aider par ses suggestions. Ils remercient également J. Horsley pour les avoir initier à l'exploitation du programme. 相似文献
Groupe de Recherches du C.N.R.S. associé à la Faculté des Sciences d'Orsay.
Remerciements. Les auteurs remercient W. Fink pour avoir mis à leur disposition son programme et les avoir aider par ses suggestions. Ils remercient également J. Horsley pour les avoir initier à l'exploitation du programme. 相似文献
107.
P. Carpentier P. Zieliński J. Lefebvre R. Jakubas 《Zeitschrift für Physik B Condensed Matter》1997,102(3):403-414
A phenomenological model is proposed to describe the sequence of phase transitions in Pentakis (methylammonium) Undecachlorodibismuthate (111), (CH3NH3)5Bi2Cl11 (PMACB) crystal on the basis of the recent structural data. The ferroelectric phase transition at 307 K is attributed to the ordering in a sublattice of the methylammonium cations CH3NH 3 + } placed in centrosymmetric sites in the paraelectric phase, whereas the isomorphous anomaly at about 180 K is related to a variation of the order in the sublattice of the remaining CH3NH 3 + } cations. The phenomenological thermodynamic potential is constructed for this system of two nonequivalent sublattices and the numerical values of its coefficients are then estimated from the dielectric, pyroelectric and calorimetric data. The sublattices are found to be weakly coupled near the ferroelectric phase transition. The anomaly at 180 K is interpreted as a continuous trace of a first order phase transition in a field created by the cations already ordered in the ferroelectric phase transition. This is analogous to a cusp A+3 in the catastrophes theory. The comparison of the Curie constants with the saturation values of the spontaneous polarization suggests that the sublattices cannot be treated as consisting of simple two-states pseudospins. 相似文献
108.
The synthesis and coordination chemistry of two chiral tetradentate pyridylimine Schiff base ligands are reported. The ligands were prepared by the nucleophilic displacement of both bromides of 1,3-bis(bromomethyl)benzene (2) or 3,5-bis(bromomethyl)toluene (3) by the anion of (S)-valinol, followed by capping of both amine groups with pyridine-2-carboxaldehyde. Both ligands react with CoCl(2) and NiCl(2) to give [M(2)L(2)Cl(2)](2+) complexes. Remarkably, neither fluoride nor bromide ions can act as bridging ligands. The formation of [Co(2)((S)-3)(2)Cl(2)](2+) is highly diastereoselective, and X-ray crystallography shows that both metal centers in the [Co(2)((S)-3)(2)Cl(2)](CoCl(4)) complex adopt the lambda configuration (crystal data: [Co(2)(C(31)H(40)N(4)O(2))(2)Cl(2)](CoCl(4)).(CH(3)CN)(3), monoclinic, P2(1), a = 11.595(2) A, b = 22.246(4) A, c = 15.350(2) A, V = 3705(1) A(3), beta = 110.643(3) degrees, Z = 2). Structurally, the dinuclear complex can be viewed as a helicate with the helical axis running perpendicular to the [Co(2)Cl(2)] plane. The reaction of racemic 2 with CoCl(2) was shown by (1)H NMR spectroscopy to yield a racemic mixture of Lambda,Lambda-[Co(2)((S)-2)(2)Cl(2)](2+) and delta,delta-[Co(2)((R)-2)(2)Cl(2)](2+) complexes; that is, a homochiral recognition process takes place. Spectrophotometric titrations were performed by titrating (S)-3 with Co(ClO(4))(2) followed by Bu(4)NCl, and the global stability constants of [Co((S)-3)](2+) (log beta(110) = 5.7), [Co((S)-3)(2)](2+) (log beta(120) = 11.6), and [Co(2)((S)-3)(2)Cl(2)](2+) (log beta(110) = 23.8) were calculated. The results revealed a strong positive cooperativity in the formation of [Co(2)((S)-3)(2)Cl(2)](2+). Variable-temperature magnetic susceptibility curves for [Co(2)((S)-2)(2)Cl(2)](BPh(4))(2) and [Co(2)((S)-3)(2)Cl(2)](BPh(4))(2) are very similar and indicate that there are no significant magnetic interactions between the cobalt(II) centers. 相似文献
109.
The harmonic oscillator interacting with a monochromatic electromagnetic field is one of the few soluble models in the application of Floquet theory. After recalling the form of the Floquet wave functions and eigenenergies we show how they can be derived as a limiting case of the solution for two oscillators with a bilinear coupling. We also derive a solution in the acceleration frame and examine the high-frequency regime. Finally, the model offers an opportunity to test the performances of a coupled-channel formulation of Floquet theory. 相似文献
110.
Balland V Banse F Anxolabéhère-Mallart E Ghiladi M Mattioli TA Philouze C Blondin G Girerd JJ 《Inorganic chemistry》2003,42(7):2470-2477
Two new iron complexes, [L(5)(3)Fe(II)Cl]PF(6) (1.PF(6)) and [(L(5)(3)H(+))Fe(III)Cl(3)]PF(6) (2.PF(6)), were synthesized (L(5)(3) = N-methyl-N,N',N'-tris(2-pyridylmethyl)propane-1,3-diamine), and their molecular structures were determined by X-ray crystallography. Their behavior in solution was studied by UV-vis spectroscopy and electrochemistry. Upon addition of a base to an acetonitrile solution of 2, the new unsymmetrical dinuclear complex [L(5)(3)Fe(III)OFe(III)Cl(3)](+) was detected. Treating 1 with hydrogen peroxide has allowed us to detect the low spin [L(5)(3)Fe(III)OOH](2+). Its spectroscopic properties (UV-vis, EPR and resonance Raman) are similar to those reported for related FeOOH complexes obtained with amine/pyridine ligands. Using stopped-flow absorption spectroscopy, the formation and degradation of [L(5)(3)Fe(III)OOH](2+) has been monitored, and a mechanism is proposed to reproduce the kinetic data. 相似文献