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排序方式: 共有417条查询结果,搜索用时 15 毫秒
271.
以苯乙酸和酚类化合物为主要原料,在微波辅助下,以BF3-Et2O为催化剂,DMF-PCl5为关环试剂,用改进的"一锅煮"法,一步高产率地合成了7,4’-二羟基异黄酮,7-羟基异黄酮,4’,5,7-三羟基异黄酮和5,7-二羟基异黄酮.与传统转化方法相比,该方法简单、快速和经济. 相似文献
272.
A numerical program is written to simulate the process of vapor bubble growth with spherical symmetry from the thermodynamic critical radius in an initially uniformly superheated liquid. The program is validated by the experimental data of superheated water. The calculated results agree with those of experiments well. The program takes into account the variations of properties with temperature precisely to simulate the DME bubble growth under flash boiling conditions. Considering the influences of pressure, surface tension and viscous stress, the linear stability analysis method is adopted to deduce the dispersion equation to represent the disturbance development during the bubble growth, and a new criterion for bubble breakup is established. The results show the bubble becomes more unstable with the increase of bubble Weber number and void fraction, and that with the increase of bubble growth rate or the decrease of initial radius ration of droplet to bubble, the breakup time of bubble becomes shorter. 相似文献
273.
GAO Yanhong QIN Lipeng ZHANG Peng CHEN Lin YUAN Hongfeng BAI Cixian YAN Fang YUE Wen PEI Xuetao 《自然科学进展(英文版)》2004,14(11):966-970
A novel human gene, spindlin1, recently cloned in our laboratory, is highly expressed in the tissue of ovary cancer. To study its biological function, a vector expressing green fluorescent-spindlin1 fusion protein was constructed and transfected into COS-7 and NIH3T3 cells by lipofectamine methods. The results showed that the fusion protein pEGFP-N1-spindlin1 was localized in the nucleus of COS-7 and NIH3T3 cells. NIH3T3 cells which could stably express spindlin1 as a result of RT-PCR analysis compared with the parental NIH3T3 cells displayed a complete morphological change, improved the cell growth and increased the percentage of cells in G2/M phase (12.6% vs control cells at 3.4%). Furthermore, overexpressed spindlin1 cells formed colonies in soft agar, more motile in migration assay in vitro and formed tumors in nude mice. Our findings provide direct evidence that spindlin1 gene may be a prooncogene which is associated with tumorigenesis. 相似文献
274.
Effects of simulated on-fire processing conditions on the microstructure and mechanical performance of Q345R steel 下载免费PDF全文
A series of simulated on-fire processing experiments on Q345R steel plates was conducted, and the plates’ Brinell hardness, tensile strength, and impact energy were tested. Microstructure morphologies were systematically analyzed using a scanning electron microscope with the aim of investigating the effect of the steel’s microstructure on its performance. All examined performance parameters exhibited a substantial decrease in the cases of samples heat-treated at temperatures near 700℃. However, although the banded structure decreased with increasing treatment temperature and holding time, it had little effect on the performance decline in fact. Further analysis revealed that pearlite degeneration near 700℃, which was induced by the interaction of both subcritical annealing and conventional spherical annealing, was the primary reason for the degradation behavior. Consequently, some nonlinear mathematical models of different mechanical performances were established to facilitate processing adjustments. 相似文献
275.
XU GuanHua GE QuanSheng GONG Peng FANG XiuQi CHENG BangBo HE Bin LUO Yong XU Bing 《科学通报(英文版)》2013,58(25):3161-3168
It is now widely accepted that carbon emission from human activities is an important driving force in global warming, and global change has a deep impact on sustainable development of human society. To meet the challenges of global change, the international community has reached a consensus that developed countries take strict actions in emission reduction, whereas developing countries take spontaneous efforts in reducing emissions under the guiding principle of common but differentiated responsibilities, with an agreed goal to restrict global surface temperature increase due to human activities to within 2℃ of pre-industrial levels. However, there is no clear pathway to reach this goal. A number of related questions must be addressed on principles to be followed, research emphasis and policy measures. Here we argue that response policies to address global change issues must be based on balanced development at regional and international levels, and on advancements in science and technology. This requires consideration of harmony not only between humans and nature but also within human societies, to properly deal with the relationship between global change and sustainable development. We must make equal efforts toward carbon emission reduction and carbon sequestration, and toward mitigation and adaptation. There should be more research support to reduce uncertainties in our understanding of global change. Addressing the challenges of global change creates great opportunities for the development of human society. This will facilitate transformation of energy use structure, improve and restore ecological functioning of the earth environment, transform production modes and ways of living in human society, and promote harmonic and balanced development at regional and international levels. 相似文献
276.
Peng Han Zhipeng Liu Zhenjia Xie Hua Wang Yaohui Jin Xuelin Wang Chengjia Shang 《矿物冶金与材料学报》2023,(7):1329-1337
This study investigated the influence of band microstructure induced by centerline segregation on carbide precipitation behavior and toughness in an 80 mm-thick 1 GPa low-carbon low-alloy steel plate. The quarter-thickness(1/4t) and half-thickness(1/2t) regions of the plate exhibited similar ductility and toughness after quenching. After tempering, the 1/4t region exhibited~50%and~25%enhancements in both the total elongation and low-temperature toughness at-40°C, respectively, without a decrease... 相似文献
277.
Understanding the in situ stress state is crucial in many engineering problems and earth science research.The present article presents new insights into the interaction mechanism between the stress state and faults.In situ stresses can be influenced by various factors,one of the most important being the existence of faults.A fault could significantly affect the value and direction of the stress components.Reorientation and magnitude changes in stresses exist adjacent to faults and stress jumps/d... 相似文献
278.
279.
Wang Z Zang C Rosenfeld JA Schones DE Barski A Cuddapah S Cui K Roh TY Peng W Zhang MQ Zhao K 《Nature genetics》2008,40(7):897-903
280.
New developments in the studies of nanocomposites based on polymer matrixes and layered double hydroxides (LDHs) in recent years are reviewed combining our relative research work, among which the synthesis techniques, the physicochemical characterizations, and the improved material properties are especially discussed. The possible application of polymer/LDH nanocomposites is also proposed. 相似文献