作高成绩下降可能的原因

通过对操作反应时的研究,表明作高的过程中存在表象旋转现象．这提示我们,在钝角边偏离正位时,作高成绩下降可能是表象旋转所致．     

用核分析法评估环境污染Ⅰ.测定植物和土壤中氟含量

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金属间化合物的环境脆性

In this paper the effect of alloying elements on the environmental embrittlement of Ll₂ type intermetallics is summarized. The results show that the ductilizing effect of boron doping in Ni₃Al is mainly to suppress the moisture-induced environmental embrittlement. The mechanism of this suppression effect is proved to be related to its severely reducing the hydrogen diffusivity along the grain boundaries. However, the boron doping in Co₃Ti alloys does not have the same effect of suppressing the environmental embrittlement. The different behavior of boron doping in Ni₃Al and Co₃Ti may be attributed to its different segregation behavior on the grain boundaries. Boron in Co₃Ti does not segregate on the grain boundaries and can not effectively reduce the hydrogen diffusivity along the grain boundaries. The moisture-induced environmental embrittlement of Co₃Ti alloy can be completely suppressed by the addition of Fe. It is proved by Auger that this suppression effect is due to its obvious reduction of the kinetics of the surface reaction with water vapor. Supported by the National Natural Science Foundation of China (Grant No.59895157,59081415,59371002,59771007)     

对乙酰基偶氮羧与钯的显色反应及应用研究

研究了对乙酰基偶氮羧与钯的显色反应的最佳条件及其应用 .建立了一种在水相中直接测定微量钯的高选择性分光光度分析法 .其摩尔吸光系数ε=3.4× 1 0 4 L·mol- 1 ·cm- 1 ,钯含量在 0 .2～ 1 .4μg·mL- 1 范围内符合比尔定律 .     

英语情感动词的语义特点及句法逆向功能

英语情感动词是英语动词中的重要类别。它特点明显,功能突出,运用广泛,自成一体。把握好英语情感动词的语义特点及句法逆向功能对于学好英语是十分有益的。     

激励介质的非线性波型动力学(英文)

以刻划著名的Belousov Zhabotinsky化学反应的俄勒冈振子为数学模型,研究解决了激励介质中一些悬而未决的理论问题 (如波的存在性和稳定性等),进一步完善了激励介质的非线性波型动力学的理论体系.通过Painlev啨分析,B¨acklund变换和奇异摄动方法,分析地给出了一些常见的波型解 (如行波,螺旋波,靶型波,V 型波,涡卷波等).在波前的邻域内,通过引进新的运动坐标系,获得了波在直角坐标下的运动方程.特别是定量地给出了刻划小幅波的组织中心沿轴向和径向运动的规律,并由此可判定波的组织中心何时沿径向呈现膨胀或收缩,何时沿轴向有正向或反向漂移.这一结果很好地与实验和数值模拟结果相吻合.此外,研究了耦合的俄勒冈振子,解决了Tyson于 1 979年提出的一个猜想 (即对耦合的俄勒冈振子,稳定的回声波可以和稳定的正定态共存),提出了一套解决类似问题的一般方法.     

手反应时测量可靠性的研究

本研究采用实验及统计分析法 ,对 44名体院学生的手反应时分别用不同重复测量次数进行多次测量 ,用积差相关法、单因素方差分析等方法对测量数据的可靠性及相关系数用exce17.5软件进行统计分析。结果表明 :手反应时重复测量的最佳次数是 15次 ,取值的最好方法是剔除 5次最大值和 5次最小值计算平均值。可靠性系数可达到 0 95     

相转移催化反应及其运用

相转移催化是一项有机合成新技术 ,它在有机合成上已得到了广泛的应用和研究。可用于各种类型的取代反应、消化反应、加成反应、氧化反庆还原反应、Witig反应、Michel反应、Darzens反应     

基于正交设计葡萄废弃物基生物活化炭的制备及其吸附性能

以葡萄皮为原材料,用限氧热解法制备生物炭.通过设计3因素3水平的正交实验,选择出最佳的活化条件进行活化,得到活化生物炭用于吸附实验.考察反应物初始浓度、反应温度和接触时间对吸附的影响规律,并进行分析.由动力学拟合结果,可以得出葡萄皮基生物炭对甲基橙的吸附过程用准二级动力学方程较好拟合,说明生物炭对甲基橙的吸附不是单一的...     

A fast and versatile cross-linking strategy via o-phthalaldehyde condensation for mechanically strengthened and functional hydrogels

Fast and catalyst-free cross-linking strategy is of great significance for construction of covalently cross-linked hydrogels. Here, we report the condensation reaction between o-phthalaldehyde (OPA) and N-nucleophiles (primary amine, hydrazide and aminooxy) for hydrogel formation for the first time. When four-arm poly(ethylene glycol) (4aPEG) capped with OPA was mixed with various N-nucleophile-terminated 4aPEG as building blocks, hydrogels were formed with superfast gelation rate, higher mechanical strength and markedly lower critical gelation concentrations, compared to benzaldehyde-based counterparts. Small molecule model reactions indicate the key to these cross-links is the fast formation of heterocycle phthalimidine product or isoindole (bis)hemiaminal intermediates, depending on the N-nucleophiles. The second-order rate constant for the formation of phthalimidine linkage (4.3 M⁻¹ s⁻¹) is over 3000 times and 200 times higher than those for acylhydrazone and oxime formation from benzaldehyde, respectively, and comparable to many cycloaddition click reactions. Based on the versatile OPA chemistry, various hydrogels can be readily prepared from naturally derived polysaccharides, proteins or synthetic polymers without complicated chemical modification. Moreover, biofunctionality is facilely imparted to the hydrogels by introducing amine-bearing peptides via the reaction between OPA and amino group.