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241.
Timo Hatanpää Mikko Ritala Markku Leskelä 《Journal of organometallic chemistry》2007,692(23):5256-5262
Sterically hindered Lewis base free bis(1,2,4-tri-tert-butylcyclopentadienyl)strontium (1) and bis(1,2,4-tri-tert-butylcyclopentadienyl)barium (2) were synthesized using the common metathesis route and characterized with NMR, MS, TGA/SDTA and XRD. Compound 1 crystallized as a monomer with typical bent structure. Asymmetric unit contains two independent slightly different Sr(t-Bu3C5H2)2 molecules with Cp(centroid)-Sr-Cp(centroid) angles of 165.1° and 169.4°. Depending on the way of crystallization two polymorphs (2a and 2b) were observed for Ba(t-Bu3C5H2)2. On sublimation Ba(t-Bu3C5H2)2 crystallizes as chains in which one methyl group of each Ba(t-Bu3C5H2)2 unit interacts with neighboring Ba(t-Bu3C5H2)2 unit’s barium atom. Slow crystallization of waxy evaporation residue of toluene solution results in monoclinic crystals (2b) whose asymmetric unit contains four slightly different individual Ba(t-Bu3C5H2)2 molecules with Cp(centroid)-Ba-Cp(centroid) angles of 161.3-164.9°. Both compounds prepared are volatile, thermally stable and reactive and thus suitable precursors for atomic layer deposition of thin films. 相似文献
242.
243.
Lauri Järvinen Jarkko Leiro Markku Heinonen 《Surface and interface analysis : SIA》2014,46(6):399-406
Conventional X‐ray photoelectron spectroscopy (XPS) and synchrotron‐based X‐ray photoelectron spectroscopy (HRXPS) have been used to study Iceland spar calcite (CaCO3) and dolomite (CaMg(CO3)2). The obtained full widths at half maximum (FWHMs) are mostly narrower than in the previous results, which together with the symmetry of the fitted peaks indicate effective neutralisation of surface charging. Some previously unidentified features observed in the Ca 2p, C 1s and O 1s spectra of calcite have been suggested to be bulk plasmons. Also, surface core level shifts in Ca 2p (in calcite) and Mg 2p (in dolomite) spectra have been obtained and found to be consistent between XPS and HRXPS measurements. A peak attributed to carbide (CaC2) has been suggested to indicate beam‐assisted interaction with hydrocarbons found on the surface. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
244.
The synthesis and structural characterization of new tantalum(V) compounds containing a single hydrazido(I) ligand are reported. Hydrazinolysis of TaCl(NMe2)4 using trimethylsilyl(dimethyl)hydrazine affords the compound TaCl(NMe2)3[N(TMS)NMe2] in essentially quantitative yield. Metathetical replacement of the chloride ligand in TaCl(NMe2)3[N(TMS)NMe2] by LiNMe2 gives the all-nitrogen coordinated compound Ta(NMe2)4[N(TMS)NMe2]. VT 1H NMR studies support the existence of low-energy pathways involving rotation about the Ta–N bonds of the ancillary amido and hydrazido ligands in both hydrazido-substituted compounds. X-ray crystallographic analyses confirm the octahedral disposition about the tantalum metal in TaCl(NMe2)3[N(TMS)NMe2] and Ta(NMe2)4[N(TMS)NMe2] and the presence of an η2-hydrazido(I) ligand. Preliminary data using Ta(NMe2)4[N(TMS)NMe2] as an ALD precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented. 相似文献
245.
Hongxue Zhang Hannu Moilanen Antti Uusimäki Seppo Leppävuori Risto Rautioaho 《Journal of Electronic Materials》1993,22(4):419-422
Transformation behavior of piezoelectric lead zirconate titanate (PZT) thin films prepared by laser ablation on unheated Al2O3 substrates was investigated within a broad temperature region. As-deposited films were mainly amorphous containing some microcrystalline
perovskite and pyrochlore phases. The rhombohedral perovskite was the main phase in the films annealed between 500 and 800°C.
These films also contained some pyrochIore, PbTiO3, PbO, and ZrO2. The PbO and ZrO2 disappeared in the optimal annealing temperature interval of 700 to 800°C. Decomposition reactions took place above 800°C
due to evaporation of lead and diffusion reactions occurred between substrate and film so that the films annealed at 1100°C
consisted of ZrO2, TiO2, and PbO. 相似文献
246.
Mikko Ritala Timo Asikainen Markku Leskel Janne Jokinen Reijo Lappalainen Mikko Utriainen Lauri Niinist Eero Ristolainen 《Applied Surface Science》1997,120(3-4):199-212
The reasons for the improvements gained by using intermediate zinc pulses in atomic layer epitaxy growth of TiN and NbN films were examined by a comprehensive characterization and comparison of films prepared from TiCl4 or NbCl5 and NH3 with and without zinc. The characterization techniques used comprise time-of-flight elastic recoil detection analysis, secondary ion mass spectrometry, Rutherford backscattering spectrometry, nuclear resonance broadening, proton backscattering spectrometry, deuteron induced reactions, proton induced X-ray emission, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and Hall effect and reflectance measurements. The effect of zinc was found to be manifold: both compositional and structural changes were observed. In the case of TiN the major improvement gained by using zinc was significantly decreased oxygen contamination whereas a marked increase of grain size was the dominant effect observed with NbN. A clear correlation between the compositional and structural changes and the improvements of the electrical properties was established. 相似文献
247.
Toni Andersson Miika Sumela Leonid Khriachtchev Markku Räsänen Vladimir Aseyev Heikki Tenhu 《Journal of Polymer Science.Polymer Physics》2008,46(6):547-557
Cationic poly(methacryl oxyethyl trimethylammonium chloride), PMOTAC, and its poly(oxyethylene), POE, grafted analog have been synthesised. The molar mass of the POE grafts was Mw = 200 g/mol, and the grafting degrees of the synthesised copolymers were 2, 5, and 15 mol %. The effect of the POE grafts on the solution properties and the conformation of the polycation has been investigated in aqueous NaNO3 by means of dynamic and static light scattering, viscometry, and Raman spectroscopy. It was found that the polyelectrolyte properties are more pronounced for the homopolymer than for the POE‐grafted copolymers. The increase of the POE‐grafting degree dramatically decreases the hydrodynamic radius of individual macromolecules and causes intermolecular association. It also suppresses the conformational response of the copolymers upon changing the ionic strength with respect to that of the homopolymer. DFT calculations have been used to estimate a possible mechanism of interaction between the POE grafts and the MOTAC repeating units. It has been revealed that the POE grafts are capable of forming intramolecular hydrogen bonds with the MOTAC groups. The latter was confirmed experimentally; addition of free POE chains to a solution of PMOTAC results in formation of intermolecular PMOTAC/POE complexes. Increasing the POE concentration decreases the solution viscosity. At the same time, the bimodal distributions of the hydrodynamic radius, which are typical for polyelectrolytes in salt‐free solutions, become monomodal representing the PMOTAC/POE complexes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 547–557, 2008 相似文献
248.
249.
A class of methods is presented for solving standard linear programming problems. Like the simplex method, these methods move from one feasible solution to another at each iteration, improving the objective function as they go. Each such feasible solution is also associated with a basis. However, this feasible solution need not be an extreme point and the basic solution corresponding to the associated basis need not be feasible. Nevertheless, an optimal solution, if one exists, is found in a finite number of iterations (under nondegeneracy). An important example of a method in the class is the reduced gradient method with a slight modification regarding selection of the entering variable. 相似文献
250.
In [3] Zinoviev presented a new method to get lower bounds for constant weight codes. In this note we show that a simple modification of the Zinoviev method gives further improvements. 相似文献