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73.
高超音速进气道粘性流场的分块计算 总被引:1,自引:0,他引:1
本文采用一种隐式迎风型TVD格式求解二维Navier—Stokes方程,使用分块技术数值模拟了某超音速进气道在飞行马赫数2.291和2.557两种状态下的流动,给出了该进气道的内外流场结构、捕获面积比、表面压力分布、总压恢复系数等等。 相似文献
74.
锐钛矿型纳米TiO2粉体的精细结构及其光催化降解苯酚的活性 总被引:4,自引:0,他引:4
摘要:以Ti(SO4)2·4H2O和尿素为原料,以聚乙二醇-1000为空间构
造剂,制备了不同粒径的具有高热稳定性的锐钛矿型纳米TiO2粉体,并
用XRD,BET和EXAFS技术对其晶相、粒径大小、比表面积及中心Ti原子
的K-边精细结构进行了表征,对其光催化降解苯酚反应的活性进行了
考察.结果表明,未经任何热处理的TiO2粉体即为锐钛矿型晶相,控制
焙烧温度可以达到控制其粒径及比表面积的目的.经850℃焙烧5h的样
品仍保持锐钛矿型晶相,未出现向金红石型晶相转变的迹象.随着纳米
TiO2晶粒的增大,Ti原子局域结构的有序度增强,边前结构A1,A2和A
3三个特征峰的强度增强,各壳层的配位数均呈增大的趋势.粒径处于
15~20nm的锐钛矿型TiO2粉体对光催化降解苯酚表现出较高的活性. 相似文献
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76.
Xuxia Zhuang Zuoyin Yang Jingchang Zhang Weiliang Cao 《Journal of Molecular Structure》2006,760(1-3):45-52
The selectivity of attacking sites and the reaction mechanisms of the bis-addition of methyl azide with its corresponding azafulleroid (C60NCH3) have been investigated using AM1 semi-empirical and density functional methods. The whole reaction processes can be divided into two stages. The first stage is the 1,3-dipolar cycloaddition (1,3-DC) reaction of methyl azide with C60NCH3 giving rise to a triazoline intermediate and the second is the N2 elimination. Based on the charge distributions, four patterns of the addition sites have been discussed. In view of the energy barriers, two kinds of 6–6 double bonds, which are in the most and the second vicinities of the –NCH3 addend group of the C60NCH3, are the two most possible attack sites in the reaction of 1,3-DC. The analyses of the π-orbital axis vector (POAV) and the deformation and interaction energies indicate that it is the favorable interaction energy rather than the strain release that dominates the two preferential attacking patterns. The subsequent thermal elimination of N2 takes place via two steps in which the breaking of N–N single bond precedes the cleavage of the C–N bonds of the unsubstituted N atom. The N2 elimination occurs simultaneously with the formation of the new C–N bonds (corresponding to the substituted N atom), giving rise to two isomers of the bisadducts. One is a double azafulleroid with two N atoms bonding to two consecutive 5-6 junctions of the same pentagon, and the other with two N atoms bonding to two alternate 5-6 junctions of the same pentagon. The analysis of the energy results shows that although the former reaction is preferred to some extent, both of the two reactions can take place and both of the two bisadducts are in principle obtainable. 相似文献
77.
Zhang Jingchang Wang Hongbin Liu Hongtao Cao Weiliang 《Journal of molecular catalysis. A, Chemical》2006,260(1-2):95-99
Hydroformylation of propylene has been carried out in supercritical CO2 + H2O and in supercritical propylene + H2O mixtures using Rh(acac)(CO)2 and triphenylphosphine trisulfonate trisodium salt (TPPTS), P(m-C6H4SO3Na)3, as catalyst. Visual observation of the reaction mixtures indicates that in both systems a single phase is present at supercritical temperatures and pressures so that the reaction occurs under homogeneous conditions. After reaction is complete, a biphasic system is formed when the pressure and temperature are reduced to ambient. This facilitates separation of the products in the organic phase and the rhodium catalyst in the aqueous phase. The rhodium concentration in the organic phase was found to be negligible (1.0 × 10−6 mg/ml). Furthermore, compared with traditional hydroformylation technology, the supercritical reactions also show better activity and selectivity. 相似文献
78.
Xiuli Wang Zuoyin Yang Ju Wang Jingchang Zhang Weiliang Cao 《Journal of Molecular Structure》2007,820(1-3):80-84
The potential energy surface (PES) of CN2H rotation of the encapsulated 1-bicyclo[2.2.1]heptyldiazirine (BHD) inside a molecular container: Cram’s hemicarcerand (CH) was explored using two different DFT involved ONIOM methods: B3LYP/6-31G**//ONIOM(B3LYP/6-31G*: AM1) and B971/6-31G**//ONIOM(B971/6-31G*: AM1). The free-state PES of CN2H rotation was also calculated, respectively by B3LYP/6-31G**//B3LYP/6-31G* and B971/6-31G**//B971/6-31G* methods for comparison. The findings in this study have shown that the PES profiles differ from each other notably in the two states. In the encapsulated state the rotation barrier corresponding to the free-state conversion with the largest rotation barrier increases by about 2 kcal/mol, which has exceeded the largest rotation barrier in the free-state. The conformational preference behavior towards certain BHD isomers, which might be in better conformational compatibility with the container, has been demonstrated. 相似文献
79.
超临界二氧化碳和水复合溶剂中铑膦配合物催化丙烯氢甲酰化反应 总被引:1,自引:0,他引:1
以乙酰丙酮羰基铑为催化剂母体,以水溶性三苯基膦三间磺酸钠(TPPTS)为配体,在超临界CO2和水复合溶剂中成功地实现了超临界条件下的均相丙烯氢甲酰化反应. 最佳反应条件为: 温度55 ℃,铑的浓度15 μg/ml, P/Rh摩尔比18. 在压力为12.0~14.0 MPa下反应6 h后,产物正丁醛/异丁醛摩尔比可达4.3~4.5,丁醛的时空收率达190.1~205.3 g/(g·h). 反应过程中体系处于超临界状态,反应结束后分为水、油两相,铑催化剂溶于水相,产物处于油相,油相中铑的含量仅为1.0 ng/ml,基本上消除了铑的流失,实现了催化剂与产物的有效分离,便于催化剂的回收和循环使用. 与相同反应条件下的水-有机两相氢甲酰化反应相比,超临界CO2和水复合溶剂中的丙烯氢甲酰化反应具有更高的反应速率和产物正异比. 相似文献
80.
垂直腔面发射激光器的结构生长及特性研究 总被引:1,自引:1,他引:0
在偏〈111〉A 2°的GaAs (100) 衬底上生长了Al0.9Ga0.1As /Al0.2Ga0.8As周期结构的垂直腔面发射激光器(VCSEL)外延片P 型DBR的周期数为24.5对,N型DBR的周期数为34.5对.用光荧光 (PL) 谱、扫描电子显微镜 (SEM)和X射线双晶衍射 (XRD) 方法对VCSEL的光学特性和结构特性进行了分析室温量子阱材料的PL谱峰值波长为837.0 nm,半高宽达到28.9 nm在X射线双晶衍射回摆曲线中,除了“0”级衍射峰外,还观察到一级和二级卫星峰.“0”级双晶衍射峰的半高宽为12.56弧秒(″),衬底GaAs的衍射峰半高宽为11.79″.“0”级衍射峰半高宽与衬底GaAs的衍射峰半高宽比较接近,表明晶格具有很高的完整性.实验结果表明腔模波长为837.2 nm,腔模波长与PL谱峰值波长相匹配. 相似文献