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1.
高等数学课程是高校所有专业的基础课程之一,对实现高校的人才培养目标起着十分重要的作用.本文遵循因材施教的原则,科学设计了分层次教学模式,对于开展分层次教学的意义和理论依据作了阐述,提出了分层次教学模式的组织与实施,并就教学内容、教学方法、考核模式的改革给出相应的实施方案.  相似文献   
2.
    
Some mono- and disaccharides were studied using the far infrared (FIR) spectroscopic method. Results show that every saccharide has a characteristic spectrum pattern. It is useful to distinguish between different saccharides based on the sequence of their relative intensities. Therefore, an encoding method was suggested to label each substance. In this investigation, the FIR spectra of the saccharides were demonstrated using the encoding method and prove the feasibility of the method.  相似文献   
3.
    
The vibrational spectra of 4-(dimethylamino)benzaldehyde (DABA) and its zinc complex are presented and vibrational assignments are proposed. Significant differences between the spectra of the parent molecule and the complex are observed. Examination of the form of the normal modes facilitates explanation of proposed frequency shifts of ring modes upon complexation. The spectra of the complex are interpreted by employing a quinonoid-type structure for the DABA ligand.  相似文献   
4.
    
Molecular structures of mercaptoacetaldehyde and mercaptoacetone in the crystalline state and in solutions have been studied by 1H-NMR, Raman and infrared spectroscopy. Both compounds exist as centrosymmetric dimers having six-membered 1,4-dithian ring skeletons in the crystalline state and in freshly-prepared dimethylsulfoxide and pyridine solutions. In equilibrium solutions, non-centrosymmetric dimers having 1,4-dithian ring skeletons and the monomer also exist. No evidence that suggests the existence of five-membered ring dimer in solutions has been obtained for both compounds. The most stable species in solution is the non-centrosymmetric dimer in the case of mercaptoacetaldehyde and the monomer in the case of mercaptoacetone.  相似文献   
5.
    
The near u.v. spectra of 2,4-diamino-6-piperidinopyrimidine (desoxyminoxidil) and 2,4-diamino-6-piperidinopyrimidine-3-oxide (minoxidil) can be viewed as perturbed pyrimidine spectra. The u.v. properties of pyrimidine and a series of aminopyrimidines, specifically 2,4,6-triaminopyrimidine, are examined to obtain u.v. spectral assignments for desoxyminoxidil and minoxidil. Minoxidil and its desoxy counterpart have Cs symmetry, and all π → π* absorptions are allowed 1A′ ← 1A′ transitions. The two lowest energy π →- π* absorptions observed in minoxidil (262 nm, 292 nm) are tentatively assigned as very mild oxygen → pyrimidine ring charge-transfer transitions. Intensity decreases in protic solvents, and the results of simple Hückel molecular orbital calculations indicate that the 292 nm transition has more charge-transfer character than the 262 nm absorption. The protonated species of desoxyminoxidil and minoxidil have very similar u.v. spectra. This is due to the lack of oxygen-related charge transfer in protonated minoxidil, and the high probability that the positive charge resides in similar environments in the minoxidil and desoxyminoxidil molecular frameworks.  相似文献   
6.
The structure of the new compound [Mo(η5-C5H5)2(2-NHNC5H4)][PF6] (1) has been determined. The crystals are orthorhombic, space group Pca21 with a 20.807(1), b 8.0030(8), c 10.056(3) Å, V 1674.5 Å3, Z = 4. The structure of [Mo(η5-C5H5)2(2-ONC5H4)][PF6] (2) has also been determined. The crystals are orthorhombic, space group Pnma with a 12.727(3), b 10.174(2), c 12.918(1) Å, V 1672.8 Å3, Z = 4. The structures were solved by Patterson and difference electron density syntheses and refined by least-squares to R of 0.028 for 1287 reflections for 1 and 0.059 for 1178 reflections for 2.Although not isostructural the two cationic complexes have equivalent geometries with the normal bent bismetallocene structure. For 1 the MoN bond lengths are 2.160(8) and 2.142(9) Å, with a NMoN bond angle of 59.8(3)°, whereas for 2 MoO is 2.142(10), MoN is 2.138(11) Å, the NMoO angle is 61.2(4)°. These parameters are discussed and compared with the corresponding data for similar biscyclopentadienyl complexes of molybdenum(IV). Extended Hückel molecular orbital calculations have been carried out to throw light on the nature of the bonding between the metal and the bidentate ligand.  相似文献   
7.
    
The characterization of dielectric materials in space environment requires to understand and predict their electric behaviour, taking into account ionisation, and ageing effect (through electron or UV radiation, thermal cycling, …)For this purpose, new methods have been developed for the characterisation and qualification of space materials and satellite structure. These studies led initially to the development of dedicated facilities for the simulation of representative irradiation conditions. This work is focused on a new non-disturbing technique for the measurement of charge distribution within space irradiated polymers. This technique named PEA (Pulsed Electro-Acoustic) has been implemented in the irradiation facility for in-situ and real time measurement during irradiation and relaxation of polymer materials. Implementation and validation of this technique are presented and discussed in this paper.  相似文献   
8.
    
Hydrodefluorination (HDF) is a very important fundamental transformation for conversion of the C−F bond into the C−H bond in organic synthesis. In the past decade, much progress has been achieved with HDF through the utility of low-valent metals, transition-metal complexes and main-group Lewis acids. Recently, novel methods have been introduced for this purpose through photo- and electrochemical pathways, which are of great significance, due to their considerable environmental and economical advantages. This Review highlights the HDF of fluorinated organic compounds (FOCs) through photo- and electrochemical strategies, along with mechanistic insights.  相似文献   
9.
15波长输出的布里渊掺铒光纤激光器   总被引:5,自引:3,他引:5  
多波长布里渊掺铒光纤激光器是一种新型的多波长光纤激光器,其原理是利用受激布里渊增益和掺铒光纤的线性增益,可以在常温下得到波长间隔约为0.08nm(~10GHz)的多波长输出。报道的布里渊掺铒光纤激光器,在布里渊抽运功率为1.7mW、980nm抽运功率为300mW的情况下得到稳定的15个波长(间隔~10GHz)的输出,这种激光器用作光传感器、光谱分析仪以及密集波分复用系统的光源。实验发现,输出波长的个数随着980nm抽运功率的增大而增加。另外,布里渊掺铒光纤激光器的信号功率主要来自于掺铒光纤的增益,而布里渊增益对它的影响不大。  相似文献   
10.
??We study the linear quadratic optimal stochastic control problem which is jointly driven by Brownian motion and L'{e}vy processes. We prove that the new affine stochastic differential adjoint equation exists an inverse process by applying the profound section theorem. Applying for the Bellman's principle of quasilinearization and a monotone iterative convergence method, we prove the existence and uniqueness of the solution of the backward Riccati differential equation. Finally, we prove that the optimal feedback control exists, and the value function is composed of the initial value of the solution of the related backward Riccati differential equation and the related adjoint equation.  相似文献   
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