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81.
Sañudo EC Smith AA Mason PV Helliwell M Aromí G Winpenny RE 《Dalton transactions (Cambridge, England : 2003)》2006,(16):1981-1987
Solid-state decomposition of [V3O(O2CPh)6(H2O)3]Cl at 300 degrees C followed by alcoholysis of the product gives the new vanadium complexes [V6O6(PhCO2)6(CH3O)6(CH3OH)3] (1), [V6O6(PhCO2)6(C2H5O)6(C2H5OH)3] (2), [V6O6(PhCO2)6(C3H7O)6(C3H7OH)3] (3), [V6O6(PhCO2)6(C4H9O)6(C4H9OH)3] (4) and [V4O4(OCH3)6(O2CPh)2(HOCH3)2] (5). Complexes 2, 3 and 5 have been crystallographically characterised. DC magnetic susceptibility studies on complex shows antiferromagnetic coupling leading to a S = 0 spin ground state. 相似文献
82.
In this paper we study integral operators of the form $$T\,f\left( x \right) = \int {k_1 \left( {x - a_1 y} \right)k_2 \left( {x - a_2 y} \right)...k_m \left( {x - a_m y} \right)f\left( y \right)dy} ,$$ $$k_i \left( y \right) = \sum\limits_{j \in Z} {2^{\frac{{jn}}{{q_i }}} } \varphi _{i,j} \left( {2^j y} \right),\,1 \leqq q_i < \infty ,\frac{1}{{q_1 }} + \frac{1}{{q_2 }} + ... + \frac{1}{{q_m }} = 1 - r,$$ $0 \leqq r < 1$ , and $\varphi _{i,j}$ satisfying suitable regularity conditions. We obtain the boundedness of $T:L^p \left( {R^n } \right) \to T:L^q \left( {R^n } \right)$ for $1 < p < \frac{1}{r}$ and $\frac{1}{q} = \frac{1}{p} - r$ . 相似文献
83.
Aromí G Batsanov AS Christian P Helliwell M Parkin A Parsons S Smith AA Timco GA Winpenny RE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(20):5142-5161
The synthesis and characterisation of a range of cobalt pivalate cage complexes are reported. The cages include: a dinuclear Co(II) complex; an oxo-centred Co(III) triangle; tetranuclear Co(II) heterocubanes and butterflies; tetranuclear heterovalent cobalt butterflies and hexanuclear edge-sharing bitetrahedra; heterovalent penta-, hexa- and hepta-nuclear cages based on [M(4)O(4)] heterocubane cores; and a tetradecanuclear cage based on heterocubanes sharing edges and vertices. Spectroscopic studies suggest that some of these cores are retained in solution, but that only in the Co(III) triangle is the structure including ligands retained. A scheme is proposed to account for the many structures observed, which may be applicable to other polymetallic cage complexes. 相似文献
84.
Let
be realhomogeneous functions in
ofdegree
and let bethe Borel measure on
given by
where dx denotes theLebesgue measure on
and > 0. Let T
be the convolution operator
and let
Assume that, for x 0, the followingtwo conditions hold:
vanishes only at h = 0 and
. In this paper we show that if
then E
is the empty set and if
then E
is the closed segment withendpoints
and
. Also, we give some examples. 相似文献
85.
Pere M. Deyà Antonio Frontera Guillem A. Suñer David Quiñonero Carolina Garau Antoni Costa Pau Ballester 《Theoretical chemistry accounts》2002,108(3):157-167
The structural and energetic changes associated with C–N bond rotation in a squaric acid derivative as well as in formamide,
3-aminoacrolein and vinylamine have been studied theoretically using ab initio molecular orbital methods. Geometry optimizations
at the MP2(full)/6-31+G* level confirmed an increase in the C–N bond length and a smaller decrease in the C=O length on going
from the equilibrium geometry to the twisted transition state. Other geometrical changes are also discussed. Energies calculated
at the QCISD(T)/6-311+G** level, including zero-point-energy correction, show barrier heights decreasing in the order formamide,
squaric acid derivative, 3-aminoacrolein and vinylamine. The origin of the barriers were examined using the atoms-in-molecules
approach of Bader and the natural bond orbital population analysis. The calculations agree with Pauling's resonance model,
and the main contributing factor of the barrier is assigned to the loss of conjugation on rotating the C–N bond. Finally,
molecular interaction potential calculations were used to study the changes in the nucleophilicity of N and O (carbonyl) atoms
upon C–N rotation, and to obtain a picture of the abilities of the molecules to act in nonbonded interactions, in particular
hydrogen bonds. The molecular interaction potential results confirm the suitability of squaramide units for acting as binding
units in host–guest chemistry.
Received: 13 March 2002 / Accepted: 23 June 2002 / Published online: 21 August 2002 相似文献
86.
Chemical elemental compositions of some silicate, magnetic and glass spherules were investigated with INAA. The elements determined include Os, Ir, Ni, Co, Fe, Cr, Au, La, Ce, Sm, Eu, Yb, Lu and Sc etc. The elemental correlation, as well as their enrichment (or depletion) factors relative to Cl chondrite were examined. The high concentrations of the refractory siderophile elements contained in these spherules support the proposal that they originate from extraterrestrial substances. Some useful chemical criteria for identifying the sources of silicate, magnetic and glass spherules are put forward. 相似文献
87.
Sargentelli V. Mauro A. E. de Godoy Netto A. V. Mattioli M. P. D. Nogueira V. M. De Lucca Neto V. A. 《Journal of Thermal Analysis and Calorimetry》2002,69(2):455-464
Pseudohalide complexes of copper(II) with aliphatic bidentate amines, [Cu(N3)2(N,N-diEten)]2 1, [Cu(NCO)2(N,N-diEten)]2 2, [Cu(NCO)2(N,N-diMeen)]2 3, [Cu(N3)(NCS)(N,N'-diMeen)]2 4 and [Cu(N3)(NCO)(N,N-diMeen)]2 5 (N,N-diEten=N,N-diethylethylenediamine; N,N-diMeen=N,N- dimethyl-ethylenediamine and N,N'-diMeen = N,N'-dimethylethylenediamine), were prepared, characterized and their thermal behavior was investigated by TG curves. According to thermal analysis and X-ray diffraction patterns all compounds decomposed giving copper(II) oxide as final product. The mechanisms of decomposition were proposed and an order of thermal stability was established.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
88.
David Quiñonero Antonio Frontera Salvador Tomàs Guillem A. Suñer Jeroni Morey Antoni Costa Pau Ballester Pere M. Deyà 《Theoretical chemistry accounts》2000,104(1):50-66
A computational study of the mechanism of host–guest complexation between quaternary ammonium compounds and squaramido-based
tripodal receptors has been carried out. Semiempirical molecular orbital calculations, which are in qualitative agreement
with experimental results have been performed using the PM3 Hamiltonian. Molecular interaction potential (MIP) maps were used
to analyze the suitability of both host and guest binding units for a high-affinity recognition process. MIP calculations
were computed from PM3 wavefunctions of the corresponding ammonium cations and dimethyl squaramide as a model compound for
the hydrogen-bond-acceptor unit of the receptors. MIP analyses are helpful for understanding the host–guest process from the
point of view of the double-complementarity principle.
Received: 23 June 1999 / Accepted: 22 September 1999 / Published online: 17 January 2000 相似文献
89.
Aromí G Bell A Teat SJ Whittaker AG Winpenny RE 《Chemical communications (Cambridge, England)》2002,(17):1896-1897
A novel Mn14 cluster is reported; this is a new nuclearity for manganese cages and highly unusual in that the ligands are not exclusively oxygen donors. 相似文献
90.
Saelzer R Godoy G Vega M de Diego M Godoy R Ríos G 《Journal of AOAC International》2001,84(4):1287-1295
Diazepam, chlordiazepoxide, and midazolam are determined by high-perfromance, thin-layer chromatography (HPTLC). Results are compared with those obtained by liquid chromatography (LC) and gas chromatography (GC). Analytical conditions for all the methods are also described. Validation parameters for linearity, precision, detection, and quantitative limits are informed. Correlation study of HPTLC with LC and GC gave a correlation factor between 0.98 and 0.99. The obtained results showed that HPTLC, LC, and GC techniques are comparable for determination of such benzodiazepins in the requested working range to be analyzed in raw materials. 相似文献