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951.
Ivan V. Skovpin Vladimir V. Zhivonitko Igor V. Koptyug 《Applied magnetic resonance》2011,41(2-4):393-410
The use of heterogeneous catalysts for parahydrogen-induced polarization (PHIP) of nuclear spins opens new horizons for production of hyperpolarized substances. Immobilization of homogeneous hydrogenation catalysts is a promising approach for designing the efficient heterogeneous catalytic systems capable of PHIP generation. Herein, we study the formation of PHIP in the gas-phase and in the liquid-phase hydrogenations of propyne and propylene catalyzed by silica-immobilized Rh complexes synthesized by the ligand-exchange anchoring of the Wilkinson’s complex RhCl(PPh3)3, the binuclear complex Rh2Cl2(C8H12)2 and the cationic complex [Rh(C8H12)2]+[BF4]? to the phosphine-modified silica gel. We consider the stability and the mechanistic aspects of the hydrogenation over the immobilized Wilkinson’s catalyst in terms of PHIP observation. Using a PASADENA (parahydrogen and synthesis allow dramatically enhanced nuclear alignment) effect, it is found, in particular, that liquid-phase propyne hydrogenation over the immobilized Wilkinsons’s catalyst at 70°C proceeds in a stable regime with a stereoselective cis addition of a hydrogen molecule, while in the gas phase at the same temperature the hydrogenation stereoselectivity is observed only for a short time after the reaction is started, and then the catalyst rapidly loses its activity. The reasons of the catalyst deactivation are discussed based on the literature data, the results of infrared spectroscopy study, and the comparison to the behavior of the immobilized binuclear and cationic Rh complexes. In addition, it is shown that the immobilized Wilkinson’s catalyst is reduced as temperature increases in the range of 90–130°C, as confirmed by X-ray photoelectron spectroscopy. 相似文献
952.
G. V. Vaganov V. E. Yudin V. Yu. Elokhovskii E. M. Ivan’kova A. Ya. Volkov T. E. Sukhanova N. Z. Evtyukov L. N. Mashlyakovskii 《Russian Journal of Applied Chemistry》2011,84(8):1408-1413
Procedures for preparing nanomodified powder epoxy compounds with various concentrations of montmorillonite were examined.
The dispersion of particles in the epoxy oligomers was studied by X-ray diffraction analysis and electron microscopy. The
influence of the content of the modifiers on the physicomechanical properties of cured block specimens was analyzed. 相似文献
953.
954.
Vidoslav Dekić Niko Radulović Rastko Vukićević Biljana Dekić Danielle Skropeta Radosav Palić 《Magnetic resonance in chemistry : MRC》2010,48(11):896-902
Herein, we describe the synthesis and complete assignment of the 1H and 13C NMR chemical shifts of a series of antimicrobial 4‐arylamino‐3‐nitrocoumarin derivatives based on a combination of 1H and 13C NMR, 1H‐1H‐COSY, NOESY, HSQC and HMBC experiments. Conformational effects upon the chemical shifts of the coumarin moiety arising from the anisotropy of the aryl side group are briefly discussed. This study provides the first complete and fully assigned NMR data for this important group of antimicrobial compounds and bridges the gap existing in the literature with regard to NMR structural data for 4‐arylamino‐3‐nitrocoumarins. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
955.
956.
Ivan Poto?ňák Michal Dunaj-Jur?o Du?an Miklo? Lothar J?ger 《Monatshefte für Chemie / Chemical Monthly》2001,22(6):315-327
The structure of the new compound [Cu(bpy)2N(CN)2]C(CN)3 (6) is compared with thestructures of six copper(II) coordination compounds with phenanthroline or bipyridine ligands and N-donor pseudohalide anions: [Cu(phen)2NCS]C(CN)3 (1), [Cu(bpy)2NCS]C(CN)3 (2), [Cu(phen)2NCS]ONC(CN)2 (3), [Cu(phen)2N(CN)2]C(CN)3 (4), [Cu(bpy)2C(CN)3]C(CN)3 (5), and [Cu(bpy)2NCO]C(CN)3 (7). The Cu(II) atoms in all above compounds are five-coordinated with an N-donor atom of the pseudohalide anion located in the equatorial plane of a deformed trigonal bipyramid. The shape of the coordination polyhedra and the degree of trigonal bipyramidal distortion towards a tetragonal pyramid are discussed and described using one electronic and several structural criteria which are discussed and compared. 相似文献
957.
958.
We briefly review the active areas of current research in magnetic superlattices, emphasizing later years. With recent widening use of advanced technologies, more emphasis has been made on quantitative atomic level chemical and structural characterization. Examples where the multilayer structure has been controlled, characterized and correlated with the physical properties are discussed. The physical properties are categorized according to the complexity of a structure needed to observe a particular effect. We outline a number of general important unsolved problems, which could considerably benefit from theoretical and experimental input. An extensive list of magnetic multilayer materials is provided, with references to recent publications. 相似文献
959.
M. Stanković M. Blagojević S. Petrović 《Journal of Thermal Analysis and Calorimetry》1999,56(3):1375-1382
Hexogen can be used pressed only if its crystals are covered by some polymeric material [1], either natural or artificial.
Montan waxes, as natural polymeric materials, were used for the phlegmatization. The melting process of seven types of waxes
was analyzed by differential scanning calorimetry. The thermal decomposition processes of hexogens and phlegmatized hexogens
were investigated by dynamic differential scanning calorimetry and dynamic thermogravimetric analyses. Kinetic parameters
of the decomposition processes of hexogens were evaluated by using data obtained from differential scanning calorimetric curves.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
960.
A theory of nuclear reactions with three composite fragments in a final channel, based on a variational principle of Kohn type and the generatorcoordinate (GC) representation of the trial function, is proposed and tested numerically. The Hamiltonian operator is microscopic, and the GC basis enables the inclusion of any rearrangement channels. The trial function is totally antisymmetrized and exactly projected on the eigenstates of the angular momentum and parity operators. It consists of a correlation term and channel terms which have to be specified only in the regions not covered by the correlation term, in which a pair of fragments is not close together. The channel relative-motion wave functions, from which the GC representation of the channel terms is obtained, are calculated from an asymptotic series. The three-fragment part of the trial function is expanded in hyperspherical harmonics. In this paper we study primarily the convergence of the reaction parameters with respect to the GC basis applying the formalism to the reaction3He(3He,pp)4He without inclusion of the Coulomb interaction. The part of the rearrangement differential corss section corresponding to well-separated final fragments is compared to experimental data. 相似文献