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1INTRODUCTION Streptococcus pneumoniae is a key pathogen in many respiratory tract infections.In a Canada-wide surveillance study published in1999,it was reported that21.2%of pneumococcal tested were interme-diately susceptible or resistant to penicillin.As the newer respiratory fluoroquinolones are active aga-inst both penicillin-susceptible and penicillin-resis-tant isolates of S.pneumoniae,they will be increa-singly important in the future treatment of infections caused by this pathoge…  相似文献   
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利用主成分分析和分层聚类分析方法研究了具有抗肺炎克雷伯氏菌的氟诺喹酮类药物分子的结构活性关系.主成分分析方法表明变量ELUMO、ΔEHL、μ、Q3、Q5、QA、lgP、MP、MR能够有效地对抗肺炎克雷伯氏菌的氟诺喹酮类药物进行分类.分层聚类方法和主成分分析方法的结果一致.这表明两种方法都能够对新的具有抗肺炎克雷伯氏菌的氟诺喹酮类药物的分类提供一个可信的规律.利用主成分分析法和分层聚类分析法对其他4个氟诺喹酮类药物分子进行分析,结果都表明有三个药物分子具有较强的抗肺炎克雷伯氏菌活性,此结果和临床结果相吻合.  相似文献   
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利用密度泛函(DFT)三种交换/相关函数(B3LYP,B3PW91,B3P86)结合6—31G^**和 6-311G^**基组,计算了13个取代氯苯化合物的键离解能.结果表明B3PS6/6—311G^**方法是计算取代氯苯化合物键离解能的可信方法,研究发现C—Cl键的键离解能与所使用的基组和计算方法密切相关,取代基对C—Cl键的键离解能的影响不明显.研究了目标化合物的前线轨道能级差,并对取代氯苯化合物的热稳定性做了评估.  相似文献   
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李小红  张现周  张瑞州  杨向东 《中国物理》2007,16(10):2924-2929
Using the time-dependent multilevel approach, we have calculated the coherent population transfer between the quantum states of potassium atom by a single frequency-chirped laser pulse. The result shows that a pair of sequential 'broadband' frequency-chirped laser pulses can efficiently transfer population from the initial state of the ladder system to the target state. It is also found that the population can be efficiently transferred to a target state and trapped there by using an 'intuitive' or a 'counterintuitive' frequency sweep laser pulse in the case of 'narrowband' frequency-chirped laser pulse. Our research shows that the complete population transfer is related to the pulse duration, chirp rate, and amplitude of the laser pulse.  相似文献   
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利用"反直觉"频率啁啾激光脉冲分析了偶能级ladder系统的布局数迁移,其中在缀饰激光场作用下N-2个中间态进行耦合.作为偶能级ladder系统的代表,我们着重分析了四能级ladder系统.研究发现如果缀饰激光场足够强且发生共振,则在能级1和能级4之间发生完全布局数迁移必须要求有一个恰当的脉冲叠加面积,调谐pump激光和stokes激光,使其中一个缀饰中间态发生共振,则可以使这个四能级系统简化为三能级系统.  相似文献   
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利用密度泛函(DFT)三种交换/相关函数(B3LYP, B3PW91,B3P86)结合6-31G**和6-311G**基组,计算了13个取代氯苯化合物的键离解能. 结果表明B3P86/6-311G**方法是计算取代氯苯化合物键离解能的可信方法,研究发现C-Cl键的键离解能与所使用的基组和计算方法密切相关,取代基对C-Cl键的键离解能的影响不明显. 研究了目标化合物的前线轨道能级差,并对取代氯苯化合物的热稳定性做了评估.  相似文献   
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1 INTRODUCTION In recent years, with the development of mole- cular biology, biological chemistry, structural chemi- stry and computer chemistry, reasonable molecular design based on the structure of drug receptor has captured the interest of researchers. Molecular pro- perties of drugs are usually correlated with biolo- gical activities and this correlation study is known as quantitative structure-activity relationship (QSAR)[1~7]. QSAR studies have been extensively used to corre- la…  相似文献   
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使用DFT的B3LYP方法对几种咪唑二氧杂环化合物的分子结构、红外光谱、生成焓、爆轰性能和化学/热稳定性进行了研究.四种不同含能基团-NO2,-NH2,-N3和-ONO2对该化合物各项性能的影响进行了比较.结果表明-NO2和-ONO2基团有效地增加了化合物的密度,而-N3基团极大地增加了化合物的生成焓.其中-NO2取代物爆轰性能接近1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane,-ONO2取代物的爆轰性能低于hexahydro-1,3,5-trinitro-1,3,5-triazine.自然键轨道分析表明,这些化合物中相对较弱的键为取代基和咪唑环之间的键,以及二氧杂环中的C-O键.吸电子基团(-NO2, -N3和-ONO2)在分子中产生了明显的诱导效应,减弱了基团与咪唑环之间的链接,降低了对应键的键裂解能.研究表明基团的电负性与化合物的稳定性有关.考虑到化合物的爆轰性能和热稳定性,DNTNDI化合物满足高能量密度材料的要求.  相似文献   
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Bond dissociation energies for the removal of nitrogen dioxide group in some nit- roalkane energetic materials have been calculated by using the three hybrid density functional theory (DFT) methods B3LYP, B3PW91 and B3P86 with 6-31g** and 6-311g** basis sets. The computed BDEs have been compared with the available experimental results. It is found that the B3P86 method with 6-31g** and 6-311g** basis sets can obtain satisfactory bond dissociation energies (BDEs), which are in extraordinary agreement with the experimental data. Considering the smaller mean absolute deviation and maximum difference, the reliable B3P86/6-311g** method was recommended to compute the BDEs for the removal of nitrogen dioxide group in the nitroalkane energetic materials. Using the method, the BDEs of 8 other nitroalkane energetic materials have been calculated and the maximum difference from experimental value is 1.76 kcal·mol-1 (for the BDE of tC4H9–NO2), which further proves the reliability of B3P86/6-311g** method. In addition, it is noted that the BDEs of C–NO2 bond change slightly for main chain nitroalkane compounds with the maximum difference of only 3.43 kcal mol-1.  相似文献   
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