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排序方式: 共有253条查询结果,搜索用时 15 毫秒
41.
Brito e Abreu S Skinner W 《Langmuir : the ACS journal of surfaces and colloids》2012,28(19):7360-7367
Methylated quartz surfaces are extensively used in colloid science for wettability studies and the control and impact of hydrophobicity in key physicochemical processes. In this study, time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to correlate the surface chemistry of trimethylchlorosilane-methylated quartz surfaces with the contact angle. Models have been developed for the calculation of both advancing and receding contact angles based on measurements of the ToF-SIMS signals for SiC(3)H(9)(+) (TMCS) and Si(+) (quartz). These models enable the contact angle across surfaces and, more importantly, that of individual particles to be determined on a micrometer scale. Distributions of contact angles in large ensembles of particles, therefore, can now be determined. In addition, from the ToF-SIMS analysis, the surface coverage of the methylated species can be quantitatively determined, in line with the Cassie equation. Moreover, advancing and receding contact angle maps can be calculated from ToF-SIMS images, and hence the variation in microscopic hydrophobicity (e.g., at the particle level) can be extracted directly from the images. 相似文献
42.
Christopher N. MunningsRuth Sayers Paul A. StuartStephen J. Skinner 《Solid State Sciences》2012,14(1):48-53
The oxidation of the n = 1 Ruddlesden-Popper phase, Sr2MnO3.5+x, where 0 ≤ x ≤ 0.5 has been investigated using a combination of in-situ diffraction techniques. In agreement with previous reports the room temperature structure of Sr2MnO3.5+x was determined to be monoclinic crystallising in space group P21/c. On heating in air the material undergoes rapid oxidation at a relatively modest temperature, ∼275 °C. The oxidation process is coincident with a significant change in the structure, with the material now adopting a tetragonal I4/mmm structure. In the oxygen deficient phase where x > 0 the Mn coordination is square pyramidal, with a sixth partially occupied oxygen position giving rise to octahedral coordination. Oxidation of Sr2MnO3.5+x results in the filling of the partially occupied O4 positions and a resulting increase in symmetry, with the Mn coordination now adopting solely a distorted octahedral environment. 相似文献
43.
When a time harmonic electromagnetic wave impinges on a slaba certain portion of the wave creates heat within the slab throughdipolar and ohmic heating. The electrical and thermal propertiesof the material dictate the dynamical nature of the heatingprocess, as well as the steady-state temperature profile. Thematerial considered here is a slab of fluid. We consider thecase where the fluid is bounded by thin rigid layers of transparentmaterial. The steady-state heating profile governs the typesof convective motions that can occur and also affects the stabilitycharacteristics of temperature, pressure and velocity perturbationsintroduced in the slab. The main objective here is to examinesuch stability characteristics, initially in the linear regime.Both rigid-rigid and rigid-free configurations are considered. 相似文献
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Georges S Skinner SJ Lacorre P Steil MC 《Dalton transactions (Cambridge, England : 2003)》2004,(19):3101-3105
A series of optimised materials in the family with parent compound La(2)Mo(2)O(9) have been studied using the isotope exchange depth profile technique and SIMS analysis. The data collected indicate that the oxide ion diffusion coefficients in both the parent compound and optimised materials are significantly higher than those reported for any of the fluorite structured electrolyte materials, with a peak value for the La(1.7)Gd(0.3)Mo(2)O(9) composition of 1.41 x 10(-6) cm(2) s(-1) at 800 degrees C. Further, it was found that the substitution of isotopic oxygen into the ceramic was limited in dry atmospheres but significantly enhanced in a H(2)(18)O/(16)O atmosphere, in common with recent reports on the diffusion/exchange behaviour of the BIMEVOX class of oxide ion conductors. 相似文献
49.
Merritt J. Winchester Lawrence J. Zappone Charles G. Skinner 《Journal of heterocyclic chemistry》1981,18(3):455-457
The ability of 2-amino-4-hydroxy-7H-pyrimido[4,5-b][1,4]oxazine derivatives to inhibit dihydrofolate reductase led to a search for means of synthesizing new side chain substituted analogs of this marginally stable pyrimidooxazine system. A study of the synthesis and use of 6-functionalized pyrimido[4,5-b][1,4]oxazines for coupling side chains was begun and has now revealed methods for coupling p-aminobenzoic acid with 2-amino-4-hydroxy-6-carboxy-7H-pyrimido[4,5-b][1,4]oxazine and hydrolyzed 2-amino-4-hydroxy-6-carbe-thoxymethylene-6,7-dihdyro-5H-pyrimido[4,5-b][1,4]oxazine. The products are of interest for evaluation as potential antifolates. 相似文献
50.
Leeuwenburgh MA Litjens RE Codee JD Overkleeft HS van der Marel GA van Boom JH 《Organic letters》2000,2(9):1275-1277
[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran. 相似文献