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91.
H.V. Keer D.L. Dickerson H. Kuwamoto H.L.C. Barros J.M. Honig 《Journal of solid state chemistry》1976,19(1):95-102
Heat capacities have been measured for single crystals of V2O3, either pure or doped with 1 and 1.4 mole% Cr2O3 and Al2O3 over the temperature range 100–700°K. V2O3 undergoes a fairly sharp transition at low temperatures (~170°K) but fails to exhibit any thermal anomaly above 300°K. The thermal behavior of (MxV1?x)2O3, M = Cr, Al, is manifested by two transitions: one at low temperatures, 170–180°K for x = 0.01 and 180–190°K for x = 0.014, and the other at high temperatures. For x = 0.01, the high-temperature (HT) anomaly extended over the range 325–345°K (Cr-doped V2O3) and 345–365°K (Al-doped V2O3), respectively. The corresponding ranges for x = 0.014 were found to be 260–280°K and 270–290°K, respectively. Further, the HT anomaly was characterized by a large hysteresis (~50°K). The values of lattice heat capacity of pure and doped V2O3 were, however, found to be almost the same and could be empirically represented by the Debye (D)?Einstein (E) function with θ values 430°K (T = 100–230°K) and 465°K (T > 230°K), respectively. Further, the enthalpy change ΔH associated with the HT anomaly in doped V2O3 (80 ≤ ΔH ≤ 510 J/mole) was 5–10 times smaller than the ΔH corresponding to the lower-temperature transition. The results cited here appear incompatible with the Mott transition model that has been invoked to explain the HT anomaly. 相似文献
92.
On the structure and chemistry of complex oxide nanofeatures in nanostructured ferritic alloy U14YWT
D. Bhattacharyya P. Dickerson G.R. Odette S.A. Maloy A. Misra M.A. Nastasi 《哲学杂志》2013,93(16):2089-2107
The remarkable radiation damage resistance of nanostructured ferritic alloys (NFAs) is attributed to the large numbers of matrix nanofeatures (NFs) of various types, which can enhance the recombination of displacement defects and trap transmutant helium in fine scale bubbles. Characterizing the chemistry, crystallographic structure and orientation relationships of the NFs is critical to understanding how they enhance the radiation damage resistance of NFAs. Conventional and high-resolution transmission electron microscopy and energy-dispersive spectroscopy were used to characterize the various types of NF and larger oxide phases in a model 14Cr–3?W–0.4Ti–0.25Y2O3 NFA (14YWT) hot isostatic pressed (HIP-ed) at 1150°C. Large CrTiO3 precipitates (50–300?nm) and small diffracting NFs (<5?nm) were found in this alloy. One major new result is the observation of an additional type of nanofeature (10–50?nm), orthorhombic in structure, with a square center cross-section, which constitutes a new kind of Y–Ti-oxide phase with lattice parameters different from those of known Y and Ti complex oxides. The interfaces of these particles seem to be semicoherent, while manifesting a possible orientation relationship with the BCC matrix. The ratio of Y to Ti varies between <1 and 2 for these larger NFs. 相似文献
93.
Background
It is well known that both semantic and syntactic information play a role in pronoun resolution in sentences. However, it is unclear what the relative contribution of these sources of information is for the establishment of a coreferential relationship between the pronoun and the antecedent in combination with a local structural case constraint on the pronoun (i.e. case assignment of a pronoun under preposition governing). In a prepositional phrase in German and Dutch, it is the preposition that assigns case to the pronoun. Furthermore, in these languages different overtly case-marked pronouns are used to refer to male and female persons. Thus, one can manipulate biological/syntactic gender features separately from case marking features. 相似文献94.
Gill Barequet Prosenjit Bose Matthew T. Dickerson Michael T. Goodrich 《Journal of Discrete Algorithms》2005,3(1):1-26
In this paper we give solutions to several constrained polygon annulus placement problems for offset and scaled polygons, providing new efficient primitive operations for computational metrology and dimensional tolerancing. Given a convex polygon P and a planar point set S, the goal is to find the thinnest annulus region of P containing S. Depending on the application, there are several ways this problem can be constrained. In the variants that we address the size of the polygon defining the inner (respectively, outer) boundary of the annulus is fixed, and the annulus is minimized by minimizing (respectively, maximizing) the outer (respectively, inner) boundary. We also provide solutions to a related known problem: finding the smallest homothetic copy of a polygon containing a set of points. For all of these problems, we solve for the cases where smallest and largest are defined by either the offsetting or scaling of a polygon. We also provide some experimental results from implementations of several competing approaches to a primitive operation important to all the above variants: finding the intersection of n copies of a convex polygon. 相似文献
95.
Microwave heating of ceramic composites 总被引:1,自引:0,他引:1
The microwave heating of a ceramic composite is modelled andanalysed. The composite consists of many small ceramic particlesembedded in a ceramic cement. The composite is assumed to bewell insulated, and each particle is assumed to be in imperfectthermal contact with the surrounding cement. Based on thesetwo assumptions an asymptotic theory exploiting the small Biotnumber and small non-dimensional contact conductance is developed.Our asymptotic theory yields a set of nonlinear partial differentialequations which govern the temperature in the composite. Theseare reduced to a set of coupled nonlinear ordinary differentialequations in which the surface area of each particle entersas a parameter. Recent experiments with such composites haveshown that the steady-state temperature of the composite isstrongly dependent upon the radii of the embedded particles.Our model captures this effect. In fact, our analysis showsthat the assumption of imperfect thermal contact between theparticles and the ceramic cement is essential for this trendto be established. 相似文献
96.
Nicki L. Davis Gretchen S. Mandel Neil S. Mandel Richard E. Dickerson 《Journal of chemical crystallography》1985,15(5):513-521
Ca2P2O7·4H2O, monoclinicP21/c, a=6.008(1),b=25.034(4),c=6.837(1) Å,=109.7 (1)°,Z=4,D
0=2.20,D
c
=2.24 g cm–3. The structure was solved by direct methods and refined by block-diagonal matrix least squares to a finalR value of 0.038. Both calcium atoms are seven coordinate. The
distance is 1.510(6) Å, whereas the
distance is 1.619(1) Å and the P-OB-P angle is 125.9(1)°. 相似文献
97.
ICP-AES法测定色漆可溶性金属含量 总被引:1,自引:0,他引:1
用ICP-AES法测定了色漆中的“可溶性”金属铬、镉、铅元素,考察了不同酸度对分析结果的影响,优化了测试条件。进行了回收率和精密度试验。并用原子吸收光谱国标方法进行对照,结果一致。 相似文献
98.
Dickerson TJ Reed NN LaClair JJ Janda KD 《Journal of the American Chemical Society》2004,126(50):16582-16586
The detection of toxic metals including mercury and lead has become a vital analytical tool for environmental remediation and regulation of food stocks. A prevalent obstacle with the current assessment of metal ion contamination originates from the lack of adequate assay throughput. In this context, a critical concern with current analyses stems from the fact that the majority of these assays are solution-based, and thus the response is highly dependent upon the assay environment. Herein, we describe a fluorescent dye-doped crystalline assay that offers convincing metal selection and provides detection comparable to conventional solution-based ligands used for the spectrofluorometric analysis of thiophilic heavy metal ions. While comparable in analytical performance to known methodologies, the formation of crystalline analytes provides for signal amplification and, consequently, a powerful platform whose analysis is directly amenable to high-throughput video capture systems. This procedure has been tested in a variety of scenarios and shows good performance using readily available equipment, including a commercially available Universal Serial Bus (USB) CCD camera. Furthermore, when developed in a microcapillary format, this assay is capable of screening thousands of samples per day for the presence of subnanomolar concentrations of Hg2+ using a conventional fluorescence microscope. 相似文献
99.
R. E. Lutz W. M. Hankins M. G. Hankins W. J. Welstead C. L. Dickerson 《Journal of heterocyclic chemistry》1970,7(3):569-573
2,5-Diphenyl-3-morpholinofuran ( 1 ) reacts with bromine and trifluoroacetic acid, giving respectively 2-bromo and 2-hydro furylium salts ( 2,3 ). The 2-hydroxy furylium bromide ( 4 ) was obtained by reaction of cis-morpholino-1,2-dibenzoylethylene ( 5 ) with hydrogen bromide. The nmr spectra of these salts show differences between the two morpholino dimethylene moieties of each caused by restricted rotation at the 3-immonium group. Chemical relationships studied include reductions to the morpholinofuran, conversions to 3-furanones, and the slow reaction of morpholinodibenzoylethylene with phenylmagnesium bromide to give cis-dibenzoylstyrene (13). 相似文献
100.