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排序方式: 共有201条查询结果,搜索用时 15 毫秒
91.
92.
Avi Shalav Dinesh K. Venkatachalam Robert G. Elliman 《Applied Physics A: Materials Science & Processing》2012,107(3):749-754
Silica nanowires, grown via the active oxidation of a silicon substrate, have been coated with TiO2 using two coating methods: solution-based deposition of Ti-alkoxides and atomic layer deposition. Analysis of as-deposited and annealed films shows that it is possible to produce stable conformal coatings of either the anatase or rutile phases of TiO2 on nanowires with diameters greater than 100 nm when annealed between 500–600°C and 800–900°C, respectively, with annealing at higher temperatures (1050°C) producing coatings with a highly facetted rutile morphology. The efficacy of the process is shown to depend on nanowire diameter, with nanowires having diameters less than about 100 nm fusing together during solution-based coating and decomposing during TiO2 atomic layer deposition. The use of a suitable buffer layer is shown to be an effective means of minimizing nanowire decomposition. Finally, annealing coated nanowires under active oxidation conditions (1100°C) is shown to be an effective technique for depositing additional conformal SiO x coatings, thereby providing a means of fabricating multi-layered coaxial nanostructures. 相似文献
93.
The use of chemical warfare agents has become an issue of emerging concern. One of the challenges in analytical monitoring of the extremely toxic ‘V’‐type chemical weapons [O‐alkyl S‐(2‐dialkylamino)ethyl alkylphosphonothiolates] is to distinguish and identify compounds of similar structure. MS analysis of these compounds reveals mostly fragment/product ions representing the amine‐containing residue. Hence, isomers or derivatives with the same amine residue exhibit similar mass spectral patterns in both classical EI/MS and electrospray ionization‐MS, leading to unavoidable ambiguity in the identification of the phosphonate moiety. A set of five ‘V’‐type agents, including O‐ethyl S‐(2‐diisopropylamino)ethyl methylphosphonothiolate (VX), O‐isobutyl S‐(2‐diethylamino)ethyl methylphosphonothiolate (RVX) and O‐ethyl S‐(2‐diethylamino)ethyl methylphosphonothiolate (VM) were studied by liquid chromatography/electrospray ionization/MS, utilizing a QTRAP mass detector. MS/MS enhanced product ion scans and multistage MS3 experiments were carried out. Based on the results, possible fragmentation pathways were proposed, and a method for the differentiation and identification of structural isomers and derivatives of ‘V’‐type chemical warfare agents was obtained. MS/MS enhanced product ion scans at various collision energies provided information‐rich spectra, although many of the product ions obtained were at low abundance. Employing MS3 experiments enhanced the selectivity for those low abundance product ions and provided spectra indicative of the different phosphonate groups. Study of the fragmentation pathways, revealing some less expected structures, was carried out and allowed the formulation of mechanistic rules and the determination of sets of ions typical of specific groups, for example, methylphosphonothiolates versus ethylphosphonothiolates. The new group‐specific ions elucidated in this work are also useful for screening unknown ‘V’‐type agents and related compounds, utilizing precursor ion scan experiments. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
94.
Avi Lin 《国际流体数值方法杂志》1985,5(4):381-391
A new method for solving elliptic difference equations is derived based on the strongly implicit method. This parametrized strongly implicit method has three free parameters which may be functions of the field's nodal point. The method has some resemblance to the SOR techniques, but in the present method the off-diagonal entries are also over-relaxed. The main application of this method is for transport equations such as those governing the fluid flow and heat transfer fields. 相似文献
95.
We report a systematic empirical investigation of ESI(+)-MS-MS dissociation pathways of over 1000 spectra of small organic compounds, containing more than 30 chemical functional groups. The dissociation processes of the protonated molecular ions were explored and interpretated. We derived typical basic fragmentation channels for individual functional groups and established a unified set of fragmentation rules. Multiple bond cleavages of molecules containing single and multiple functional groups were explored as well and the corresponding fragmentation rules were derived. Applying these rules enabled to match between proposed chemical structures and an ESI(+)-MS-MS spectrum of an “unknown”. Comparison to EI fragmentation routes was also carried out. Despite the general dissimilarity between ESI(+)-MS-MS and EI-MS spectra, we exploit the minor similarities between the spectra, and utilizing NIST-EI database and search option, can be successfully reduced the number of proposed structures. The two step methodology developed here is demonstrated and evaluated in the identification of various “unknowns”. 相似文献
96.
Lavi A Cohen H Bendikov T Vilan A Cahen D 《Physical chemistry chemical physics : PCCP》2011,13(4):1293-1296
We show that electronic transport quality alkyl chain mono-layers can be prepared from dilute solution, rather than from neat alkanes, and on Si (100) instead of (111) surfaces. High monolayer quality was deduced from XPS and from comparing current-voltage curves of Hg/alkyl/Si junctions with those for junctions with monolayers made from neat alkanes. XPS shows that limited surface oxidation does not harm the integrity of the monolayer. Solution preparation significantly widens the range of molecules that can be used for transport studies. 相似文献
97.
Dr. Marek Daszkiewicz Mariusz K. Marchewka Iryna Typilo Lubomir D. Gulay Dariya Semenyshyn 《无机化学与普通化学杂志》2011,637(10):1409-1413
The crystal structure of distrontium octacyanotungstate decahydrate, Sr2[W(CN)8] · 10H2O, was solved using X‐ray single crystal diffraction. The tungsten atom lies on a two fold axis. Eight cyanide anions create tetragonal antiprismatic coordination sphere of tungsten atom. The two edge‐sharing tetragonal antiprisms of [Sr(NC)3(OH2)5], create a dimer, [Sr2(CN)6(H2O)6(μ‐H2O)2], which lies on the inversion center. One symmetry independent water molecule is located in a void of 40 Å3. Vibrational (FT‐IR and FT‐Raman spectroscopic) behavior of main structural units is discussed. It was spectroscopically confirmed that the geometry of [W(CN)8]4– anion is slightly distorted from that corresponding to “free” anion. The number of observed bands is significantly lower than that expected for C2 point group. 相似文献
98.
It has been shown that the orbits of motion for a wide class of non-relativistic Hamiltonian systems can be described as geodesic
flows on a manifold and an associated dual by means of a conformal map. This method can be applied to a four dimensional manifold
of orbits in spacetime associated with a relativistic system. We show that a relativistic Hamiltonian which generates Einstein
geodesics, with the addition of a world scalar field, can be put into correspondence in this way with another Hamiltonian
with conformally modified metric. Such a construction could account for part of the requirements of Bekenstein for achieving
the MOND theory of Milgrom in the post-Newtonian limit. The constraints on the MOND theory imposed by the galactic rotation
curves, through this correspondence, would then imply constraints on the structure of the world scalar field. We then use
the fact that a Hamiltonian with vector gauge fields results, through such a conformal map, in a Kaluza-Klein type theory,
and indicate how the TeVeS structure of Bekenstein and Saunders can be put into this framework. We exhibit a class of infinitesimal gauge transformations
on the gauge fields Um(x){\mathcal{U}}_{\mu}(x) which preserve the Bekenstein-Sanders condition UmUm=-1{\mathcal{U}}_{\mu}{\mathcal{U}}^{\mu}=-1. The underlying quantum structure giving rise to these gauge fields is a Hilbert bundle, and the gauge transformations induce
a non-commutative behavior to the fields, i.e. they become of Yang-Mills type. Working in the infinitesimal gauge neighborhood
of the initial Abelian theory we show that in the Abelian limit the Yang-Mills field equations provide residual nonlinear
terms which may avoid the caustic singularity found by Contaldi et al. 相似文献
99.
Aamodt K Abelev B Abrahantes Quintana A Adamová D Adare AM Aggarwal MM Aglieri Rinella G Agocs AG Agostinelli A Aguilar Salazar S Ahammed Z Ahmad N Ahmad Masoodi A Ahn SU Akindinov A Aleksandrov D Alessandro B Alfaro Molina R Alici A Alkin A Almaráz Aviña E Alt T Altini V Altsybeev I Andrei C Andronic A Anguelov V Anson C Antičić T Antinori F Antonioli P Aphecetche L Appelshäuser H Arbor N Arcelli S Arend A Armesto N Arnaldi R Aronsson T Arsene IC Arslandok M Asryan A Augustinus A Averbeck R 《Physical review letters》2011,107(3):032301
We report on the first measurement of the triangular v3, quadrangular v4, and pentagonal v5 charged particle flow in Pb-Pb collisions at sqrt(s(NN)) = 2.76 TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show that the triangular flow can be described in terms of the initial spatial anisotropy and its fluctuations, which provides strong constraints on its origin. In the most central events, where the elliptic flow v2 and v3 have similar magnitude, a double peaked structure in the two-particle azimuthal correlations is observed, which is often interpreted as a Mach cone response to fast partons. We show that this structure can be naturally explained from the measured anisotropic flow Fourier coefficients. 相似文献
100.
Aamodt K;ALICE Collaboration Abrahantes Quintana A Adamová D Adare AM Aggarwal MM Aglieri Rinella G Agocs AG Aguilar Salazar S Ahammed Z Ahmad N Ahmad Masoodi A Ahn SU Akindinov A Aleksandrov D Alessandro B Alfaro Molina R Alici A Alkin A Almaráz Aviña E Alt T Altini V Altinpinar S Altsybeev I Andrei C Andronic A Anguelov V Anson C Antičić T Antinori F Antonioli P Aphecetche L Appelshäuser H Arbor N Arcelli S Arend A Armesto N Arnaldi R Aronsson T Arsene IC Asryan A Augustinus A Averbeck R 《Physical review letters》2011,106(3):032301
The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%-80%) to central (0%-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions. 相似文献