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排序方式: 共有455条查询结果,搜索用时 15 毫秒
1.
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Vijaya Gracias Alan F. Gasiecki Joel D. Moore Irini Akritopoulou-Zanze Stevan W. Djuric 《Tetrahedron letters》2006,47(50):8977-8980
A general method for the preparation of diaza-spirocycles is reported. This method used an olefin metathesis in order to construct the desired spirocyclic framework. Beginning with commercially available protected amino ketones, this strategy ultimately produced pharmacologically relevant diaza-scaffolds in an efficient and high-yielding process. 相似文献
3.
4.
K. Gowri Navada 《Proceedings Mathematical Sciences》1995,105(3):281-285
We give an estimate for the number of elements in the intersection of topological Sidon sets inR
n with compact convex subsets and deduce a necessary and sufficient conditions for an orbit of a linear transformation ofR
n to be a topological Sidon set. 相似文献
5.
R. Nagarajan S. Ayyappan C. N. R. Rao 《Physica C: Superconductivity and its Applications》1994,220(3-4):373-376
While YSr2Cu3O7 cannot be prepared under ambient conditions, partial substitution of the phosphate group for copper, as in YSr2Cu2.8(PO4)0.2Oy, stabilizes this phase in the orthorhombic structure, but the material is not superconducting. Superconductivity in YSr2Cu2.8(PO4)0.2Oy is obtained by increasing the hole concentration through partial substitution of Y by Ca, as in Y0.7Ca0.3Sr2Cu2.8(PO4)0.2Oy (Tc≈40 K). By incorporating the phosphate group in orthorhombic YBaSrCu3O 7, a stable tetragonal derivative of the formula YBaSrCu2.8(PO4)0.2Oy (Tc≈ 47 K) has been prepared; the Tc increases to 70 K by partial substitution of Y by Ca as in Y0.7Ca0.3BaSrCu2.8(PO4)0.2Oy. 相似文献
6.
7.
A Jayanth Kumar N M Gowri R Venkateswara Raju G Nirmala B S Bellubbi T Radha Krishna 《Pramana》2006,67(2):383-387
Over the last two decades, the fiber optic technology has passed through many analytical stages. Some commercially available
fiber optic sensors, though in a small way, are being used for automation in mechanical and industrial environments. They
are also used for instrumentation and controls.
In the present work, an intensity-modulated intrinsic fiber optic sugar sensor is presented. This type of sensor, with slight
modification, can be used for on-line determination of the concentration of sugar content in sugarcane juice in sugar industry.
In the present set-up, a plastic fiber made of polymethylmethacrylate is used. A portion of the cladding (1 cm, 2 cm, 3 cm)
at the mid-point along the length of the fiber is removed. This portion is immersed in sugar solution of known concentration
and refractive index. At one end of the fiber an 850 nm source is used and at the other end a power meter is connected. By
varying the concentration of sugar solution, the output power is noted. These studies are made due to the change in refractive
index of the fluid. The device was found to be very sensitive which is free from EMI and shock hazards, stable and repeatable
and they can be remotely interfaced with a computer to give on-line measurements and thus become useful for application in
sugar industries. 相似文献
8.
Synthesis of fused imidazo-pyridine and -azepine derivatives by sequential van Leusen/Heck reactions
Fused imidazo-pyridine and -azepine derivatives were synthesized using a sequential van Leusen/intramolecular Heck protocol. The combination of a multicomponent reaction followed by an intramolecular carbon-carbon bond forming reaction generates heterocycles of significant molecular complexity from readily available starting materials in just two steps. 相似文献
9.
Interactive effects of ultraviolet-B radiation and temperature on cotton physiology, growth, development and hyperspectral reflectance 总被引:1,自引:0,他引:1
Current conditions of 2-11 kJ m(-2) day(-1) of UV-B radiation and temperatures of >30 degrees C during flowering in cotton cultivated regions are projected to increase in the future. A controlled environment study was conducted in sunlit growth chambers to determine the effects of UV-B radiation and temperature on physiology, growth, development and leaf hyperspectral reflectance of cotton. Plants were grown in the growth chambers at three day/night temperatures (24/16 degrees C, 30/22 degrees C and 36/28 degrees C) and three levels of UV-B radiation (0, 7 and 14 kJ m(-2) day(-1)) at each temperature from emergence to 79 days under optimum nutrient and water conditions. Increases in main stem node number and the node of first fruiting branch and decrease in duration to first flower bud (square) and flower were recorded with increase in temperature. Main effects of temperature and UV-B radiation were significant for net photosynthetic rates, stomatal conductance, total chlorophyll and carotenoid concentrations of uppermost, fully expanded leaves during squaring and flowering. A significant interaction between temperature and UV-B radiation was detected for total biomass and its components. The UV-B radiation of 7 kJ m(-2) day(-1) reduced boll yield by 68% and 97% at 30/22 degrees C and 36/28 degrees C, respectively, compared with yield at 0 kJ m(-2) day(-1) and 30/22 degrees C. No bolls were produced in the three temperature treatments under 14 kJ m(-2) day(-1) UV-B radiation. The first-order interactions between temperature, UV-B radiation and leaf age were significant for leaf reflectance. This study suggests a growth- and process-related temperature dependence of sensitivity to UV-B radiation. 相似文献
10.
Irini Akritopoulou-Zanze Vijaya Gracias Joel D Moore Stevan W Djuric 《Tetrahedron letters》2004,45(17):3421-3423
We report the synthesis of novel fused isoxazoles and isoxazolines by employing an unprecedented Ugi/INOC synthetic sequence. The coupling of the Ugi multicomponent reaction with the intramolecular N-oxide cyclization provides access to unique heterocyclic ring systems in two steps from easily available starting materials in moderate to good overall yields. 相似文献