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951.
Manfred Weidenbruch Hartmut Kilian Martin Stürmann Siegfried Pohl Wolfgang Saak Heinrich Marsmann Dirk Steiner Armin Berndt 《Journal of organometallic chemistry》1997,530(1-2):255-257
Addition of the diarylstannylene R″2Sn (R″ = 2−tBu−4,5,6-Me3C6H) to the cryptodiborylcarbene (Me3Si)2C(BtBu)2C furnishes the stannaethene (Me3Si)2C(BtBu)2C=SnR″2 (10). The X-ray structure analysis of 10 reveals a strictly planar environment of the tricoordinated tin and carbon atoms and a slight twisting of the Sn=C double bond. 相似文献
952.
We demonstrate that the Plancherel transform for Type-I groups provides
one with a natural, unified perspective for the generalized continuous wavelet
transform, on the one hand, and for a class of Wigner functions, on the other. We
first prove that a Plancherel inversion formula, well known for Bruhat functions on
the group, holds for a much larger class of functions. This result allows us to view
the wavelet transform as essentially the inverse Plancherel transform. The wavelet
transform of a signal is an L2-function on an appropriately chosen group while
the Wigner function is defined on a coadjoint orbit of the group and serves as an
alternative characterization of the signal, which is often used in practical applications.
The Plancherel transform maps L2-functions on a group unitarily to fields
of Hilbert-Schmidt operators, indexed by unitary irreducible representations of the
group. The wavelet transform can essentially be looked upon as a restricted inverse
Plancherel transform, while Wigner functions are modified Fourier transforms of
inverse Plancherel transforms, usually restricted to a subset of the unitary dual of
the group. Some known results on both Wigner functions and wavelet transforms,
appearing in the literature from very different perspectives, are naturally unified
within our approach. Explicit computations on a number of groups illustrate the
theory.
Communicated by Gian Michele Graf
submitted 05/06/01, accepted: 19/09/02 相似文献
953.
954.
The photocatalytic heterocyclotrimerisation of ethyne and nitrile initiated by cobalt(I) complexes was studied. General mechanistic features as proposed for the ‘dark’ reaction were found to apply as well under photolytic conditions albeit with modifications. The results suggest that the irradiated light accelerates that stage of reaction, leading to the organometallic species which is believed to be the common intermediate for the formation of pyridine and benzene. The rate of pyridine production is linear dependent from nitrile concentration. Benzene formation may be minimised by keeping the ethyne concentration low. An alternative mechanism, based on the initial coordination of nitrile at cobalt is not confirmed. A novel gas buret system was used, which allowed automatic feed of ethyne under isobaric conditions and to monitor all reactants simultaneously on-line. 相似文献
955.
956.
Smoothness of subdivision surfaces at extraordinary points 总被引:2,自引:0,他引:2
Hartmut Prautzsch 《Advances in Computational Mathematics》1998,9(3-4):377-389
A stationary subdivision scheme such as Catmull and Clark's is described by a matrix iteration around an extraordinary point.
We show how higher order smoothness of a limiting surface obtained by a stationary subdivision algorithm for tri- or quadrilateral
nets depends on the spectral properties of the matrix and give necessary and sufficient conditions. The results are also useful
to construct subdivision algorithms for surfaces of any smoothness order at extraordinary points.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
957.
958.
959.
Hartmut Backe 《Hyperfine Interactions》2006,171(1-3):93-107
Unique spectroscopic possibilities open up if a laser beam interacts with relativistic lithium-like ions stored in the heavy
ion ring accelerator SIS300 at the future Facility for Antiproton and Ion Research FAIR in Darmstadt, Germany. At a relativistic
factor γ = 36 the 2P1/2 level can be excited from the 2S1/2 ground state for any element with frequency doubled dye-lasers in collinear geometry. Precise transition energy measurements
can be performed if the fluorescence photons, boosted in forward direction into the X-ray region, are energetically analyzed
with a single crystal monochromator. The hyperfine structure can be investigated at the 2P1/2−2S1/2 transition for all elements and at the 2P3/2−2S1/2 transition for elements with Z≤50. Isotope shifts and nuclear moments can be measured with unprecedented precision, in principle even for only a few stored
radioactive species with known nuclear spin. A superior relative line width in the order of 5·10−7 may be feasible after laser cooling, and even polarized external beams may be prepared by optical pumping. 相似文献
960.
Anindita Ghosh Shyambo Chatterjee Susanta Banerjee Hartmut Komber Brigitte Voit 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):509-517
A new trifluoromethyl-activated AB monomer has been successfully synthesized by Pd-initiated coupling of 4-bromo anisole with 4-fluoro-3-trifluoromethylphenylboronic acid followed by demethylation. The monomer leads to a semifluorinated poly(arylene ether) by nucleophilic displacement polymerization reaction. The AB monomer has been further copolymerized with a corresponding AB 2 monomer to form the corresponding semifluorinated hyperbranched (hb) poly(arylene ether). The resulting linear and hb poly(arylene ether)s exhibited weight average molecular weight of 75700 and 144100 g/mol, respectively. The hb copolymer exhibited better solubility in different organic solvents compared to the linear poly(arylene ether). The polymers showed excellent thermal stability up to 522°C at 10% wt loss in air and glass transition temperatures as high as 187°C. The mechanical properties of the linear poly(arylene ether) film 1a exhibited tensile strength at break of 89 MPa, elongation at break of up to 3% and a Young’s modulus value of 2.66 GPa. The films of the polymers were hydrophobic in nature and showed water contact angle as high as 93.6°. 相似文献