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1.
From the study of the CuCuBrCu2?εSC solid cell in the range of cubic digenite and “high temperature” hexagonal chalcocite we have deduced the laws of variation of the deviation from stoichiometry and the holes concentration with the equilibrium partial pressure of sulfur (δ and p are found to be proportional to ). The electronic model corresponding to the formation of associations (V×CuV′Cu) in the presence of neutral vacancies V×Cu allows one to explain these laws. In the low temperature range (range of “low temperature” hexagonal chalcocite and orthorhombic chalcocite) the study of thermal variations of Hall coefficient permits us to propose the following models: (a) the deviation from stoichiometry of the “low temperature” hexagonal chalcocite is due to the simple ionized vacancies V′Cu; (b) the deviation from stoichiometry of the orthorhombic chalcocite is due to the vacancies V′Cu and to the associations (V×CuV×Cu). 相似文献
2.
Kai WuQing-Yun Chen 《Journal of fluorine chemistry》2002,113(1):79-83
Treatment of 2,2,2-trifluoroethyl chloride (HCFC-133a) with alcohols (phenols) and aqueous KOH in autoclave at 240-280 °C gives the corresponding 2,2,2-trifluoroethyl (2-chloro-1,1-difluoroethyl) ethers in good yields. 相似文献
3.
Titanates de cuivre substitués à structure bixbyite: Les composés Cu1−xTi1−xFe2xO3 (0.15 ≤ x ≤ 0.33)
A new bixbyite family, Cu1?xTi1?xFe2xO3 (0.15 ≤ x ≤ 0.33) has been synthesized and characterized. The unit cell is cubic: a ~ 9.40Å. The X-ray powder diffraction study shows up an isotypism with the (Fe, Mn)2O3 compounds. There is a disordered distribution of CuII, TiIV, and FeIII over the two cyrstallographic sites: PI and PII. PII is highly distorted (two long MO distances) by the Jahn-Teller effect of CuII. The bixbyite structure is described in terms of polyhedra arrangement, as a particular case of the CM2O3 family. The cation packing is discussed in relation with the existence of the bixbyite structure for the Cu1?xTi1?xFe2xO3 compounds. The electrical properties (σ ~ 10?5(Ω cm)?1 for x = 0.286 at room temperature) show an electron conduction with probably a hopping mechanism. 相似文献
4.
Moktar Ferid Mahmoud Dogguy Néjia Kbir-Ariguib Melika Trabelsi 《Journal of solid state chemistry》1984,53(2):149-154
The MIPO3Sm(PO3)3(MI = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO3)4, NaSm(PO3)4, and AgSm(PO3)4 were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO3)4, NaLn(PO3)4, AgLn(PO3)4 (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO3)4 unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group and Z = 4. NaSm(PO3)4 and AgSm(PO3)4 are isotypic; they cristallize in the space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), , b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates. 相似文献
5.
A series of di- and trisilanes of general structure Ph3SiSiMe2R and (Ph3Si)2SiR′R″ were synthesized, and the 29Si and 13C chemical shifts and one-bond siliconsilicon coupling constants (1JSiSi) were measured. The coupling constants of the disilanes were found to be primarily dependent upon the inductive effect of the alkyl group, R, as measured by the Taft o★ constant. In both series of compounds, increasing alkyl substitution at silicon led to a decrease in 1JSiSi. 相似文献
6.
In a route towards enantiomerically enriched 1-(β-hydroxypropyl)indoles, which are potentially useful building blocks for high value-added chemicals synthesis, a kinetic resolution approach by means of lipase-catalyzed enantioselective acylation as well as hydrolysis/methanolysis has been elaborated for the first time. The enzymatic resolution of chiral N-substituted indole-based sec-alcohols was successfully accomplished, yielding both enantiomeric forms of the employed derivatives with up to >99% enantiomeric purity via an enantioselective transesterification under mild reaction conditions. The most selective resolutions were obtained using fungal (CAL-B and TLL) and bacterial (PFL and BCL) lipases and vinyl acetate as the acyl?group donor. The synthetic protocol described herein is very simple, user-friendly and efficient, thus paving the way for future access towards more complex compounds of this type. The absolute configurations of novel enantiomeric derivatives, and thus stereoselectivity of the described enzymatic reactions were confirmed by application of CDA-based NMR methodology and single-crystal X-ray diffraction analysis. 相似文献
7.
采用沉淀法和浸渍法制备了2种铬基(Cr2O3和CrO3/Cr2O3)催化剂,用于气相氟化2-氯-1,1,1-三氟乙烷合成1,1,1,2-四氟乙烷。研究发现含有低价铬(Cr3+)物种的Cr2O3催化剂上2-氯-1,1,1-三氟乙烷的稳态转化率为18.5%,而含有高价铬(Cr6+)物种和低价铬(Cr3+)物种的CrO3/Cr2O3催化剂初始转化率达到30.6%,然而存在明显的失活。含有Cr6+物种的CrO3/Cr2O3催化剂的2-氯-1,1,1-三氟乙烷氟化反应初始TOF值为1.71×10-4 molHCFC-133a·molCr(Ⅵ)-1·s-1,高于含有Cr3+物种的Cr2O3催化剂(4.16×10-5 molHCFC-133a·molCr(Ⅲ)-1·s-1)。Cr2O3催化剂在氟化反应前后催化剂的物相结构保持不变;而含有高价铬物种的CrO3/Cr2O3催化剂经HF反应后生成了CrOxFy活性物种。然而,CrOxFy物种在反应中挥发或转化成稳定但无活性的CrF3,从而导致催化剂失活。 相似文献
8.
9.
A solid-state rotational-echo double resonance (REDOR) NMR method was introduced to identify the ?- and ψ-torsion angle from a 1H–15N or 1H–13C′ spin system of alanine-like residues in a selectively, uniformly, or extensively 15N-/13C-labeled peptide. When a Cα(i) or a 15N peak is site-specifically obtainable in the NMR spectrum of a uniformly 15N/13C-labeled sample system, the ψ- or ?-torsion angle specified by the conformational structure of peptide geometry involving 15N(i)–1Hαi–15N(i + 1) or 13C′(i − 1)–1HNi–13C′(i) spin system can be identified based on 13Cα- or 15N-detected 1Hα–15N or 1HN–13C REDOR experiment. This method will conveniently be utilized to identify major secondary motifs, such as α-helix, β-sheet, and β-turn, from a uniformly 15N-/13C-labled peptide sample system. When tested on a 13C-/15N-labeled model system of a three amino acid peptide Gly–[U–13C, 15N]Ala–[U–13C, 15N]Leu, the ψ-angle of alanine obtained experimentally, ψ = −40 ± 30°, agreed reasonably well with the X-ray determined angle, ψ = −39°. 相似文献
10.
Abderrahmane Baïri 《Comptes Rendus Mecanique》2003,331(8):557-562
The heat transfer at the interface of two solids in sliding/rolling contact depends on the constriction phenomenon which occurs at the vicinity of asperities. In order to study this problem, the micro-contacts are represented by multiple moving circular heat sources on the surface of a body. The studied body is constituted of a substrate and a surface coating. The thermal constriction resistance due to those contacts is determined analytically in this paper. The solution is developed by using the integral Fourier transforms, and it is valid regardless of the velocity and the relative contact size values. To cite this article: A. Baïri, C. R. Mecanique 331 (2003). 相似文献