首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   45篇
  免费   3篇
  国内免费   9篇
化学   28篇
力学   3篇
数学   15篇
物理学   11篇
  2022年   1篇
  2017年   1篇
  2015年   1篇
  2014年   4篇
  2013年   2篇
  2012年   2篇
  2011年   4篇
  2010年   5篇
  2009年   2篇
  2008年   2篇
  2007年   2篇
  2006年   3篇
  2005年   1篇
  2004年   1篇
  2003年   2篇
  2002年   4篇
  2001年   3篇
  2000年   6篇
  1999年   3篇
  1992年   1篇
  1990年   1篇
  1985年   1篇
  1984年   2篇
  1982年   1篇
  1975年   1篇
  1970年   1篇
排序方式: 共有57条查询结果,搜索用时 15 毫秒
41.
IntroductionThe homoleptic sandwich~type porphyrinato and phthalocyaninato metal complexesRE (P) z and RE2 (P) 3 (RE =rare earth 1 P = Por or Pc) have been intensively studied over sev-eral decades due to their potential application in non-linear optical (NLO) materials, molecu-lar electronic and magnetic ..te.i.l.L1--l6j.The double-deckers have also aroused a growing interest as structural and spectroscopicsynthetic models for the dimmer of bacteriochlorophyl1 molecules in bacterial pho…  相似文献   
42.
43.
The effect of aromatic and non-aromatic solvents on the proton chemical shifts of 23 polar compounds has been determined. The protons which are activated by electron-withdrawing groups show large highfield shifts in benzene (relative to the isotropic solvents). Based on evidence provided by infrared data, the highfield shifts of the acidic protons in benzene solution are interpreted in terms of a model involving C? Hπ hydrogen bonding. This model successfully interprets the data reported previously for steroidal ketones. The same model can be extended to benzene solutions of other polar compounds containing strongly electron-deficient sites to which alkyl groups are attached. It is observed that the use of CCl4 as a reference solvent in studies of benzene induced shifts may have greater significance, since these two solvents have similar dielectric constants.  相似文献   
44.
In this study, the vibration and acoustic resonance, and dominant frequency range of simple concrete box and viaduct are examined from the measurement results. A narrow band analysis—fast Fourier transform (FFT) method is used to analyze the measurement results and finite element method (FEM) is used to validate resonance frequencies for noise and vibration. The experiment of the concrete box structure is a preliminary study of analyzing resonance frequency radiated from the vibrating concrete structure since railway viaduct is a concrete box structure too. According to their noise and vibration spectra, it shows that the vibration resonance is more significant than the acoustics resonance.Based on the measurement results of the rail viaduct structure-borne noise and vibration, the relationship in terms of transfer function and coherence between noise and vibration are evaluated. They show that the dominant frequency range for noise and vibration of concrete viaduct is between 20 and 157 Hz, the resonance frequencies are 43 and 54 Hz and have significant tonal noise characteristics. The experimental results are in good agreement with the theoretical relationship between sound and vibration.  相似文献   
45.
A software package has been developed to process perfusion, relaxation times and diffusion MRI dat a acquired in cancer research. This software package was written on MATLAB platf orm (Version 6.0). Parameter maps, such as permeability, apparent diffusion coef ficient and T1 were generated from original MRI data. The features of para metric analysis include ROI analysis, contrast adjust, statistical information generat ion, false color image and zoom in display. Since it was written in Matlab fun ct ions, this package can be used on almost all operation systems (Microsoft window s, Unix, Mac OS & Linux) and it is easy to expand the features.  相似文献   
46.
This note explains the relationship (as well as the absence of a relationship) between chiral space groups and chiral molecules (which have absolute configurations).For a chiral molecule,which must crystallize in a chiral space group,the outcome of the absolute configuration determination must be linked to some other properties of the chiral crystal such as its optical activity for the observation to the relevant.  相似文献   
47.
The KLn dielectronic recombination processes of trapped highly charged B-like through He-like Cu ions are studied theoretically, and the theoretical results are used to analyse our previous experimental data at Heidelberg electron beam ion trap (EBIT). The theoretical resonant positions agree with the experimental resonant positions to a precision of 0.4%, in comparison with the resonant positions of those highest peaks between theory and experiment. The experimental spectra are then fitted using a formula with the theoretical resonant energies and strengths, the result shows good overall agreement between theory and experiment over a wide electron energy range. The distribution of highly charged states is obtained from the fitting parameters.  相似文献   
48.
The title coordination polymer, [Co(bib)(L)].0.5H2O 1 (bib = 1,1'-(1,4-butanediyl)bis(imidazole) and L = 4,4'-oxy(bisbenzoate) has been hydrothermally synthesized and characterized by IR and single-crystal X-ray diffraction. It crystallizes in monoclinic, space group Cc with a = 8.8568(5), b = 19.936(1), c = 26.209(2) γ, y = 97.510(1)°, V= 4587.8(5) A3, Z = 8, CoC24H23N4O5.5, Mr = 514.39, Dc = 1.489 g/cm3, F(000) = 2128, μ(MoKa) = 0.795 mm^-1, R = 0.0419 and wR = 0.1002. Compound 1 exhibits a rare two-fold interpenetrating CdSO4 type topology. The O-H...O hydrogen bonds stabilize the structure of 1.  相似文献   
49.
One novel 3D 3d-4f coordination polymer, [LaZn(glc)(ox)2(H2O)2]n (1, glc = glycinate, ox = oxalate), was obtained by the in situ synthesis of glycinate from the reaction of tetrazole-1-acetic acid, sodium oxalate, zinc nitrate and lanthanide oxide in the presence of a trace quantity of nitric acid under hydrothermal conditions. Compound 1 is of monoclinic, space group P21/n with a = 0.99601(9), b = 1.14592(10), c = 1.19107(10) nm and β = 108.7150(10)°. 1 exhibits an unusual 3D heterometallic coordination framework constructed by heterometallic dinuclear LaZn subunits and mixed ox and glc linkers with a uninodal 6-connected vme {33 .43 .58 .6} net.  相似文献   
50.
Titanium dioxide was deposited from aqueous suspension onto cellulosic surfaces.Titania was sourced from Degussa (P25TM,70:30 anatase:rutile).Dry uptake of particles was shown to be rapid and dominant with one-third of the deposition occurring in less than 30 s and over one-half in the first minute.Isotherms were recorded to compare the rate of titanium deposition on dry and pre-wetted cotton.In the dry case uptake reached a maximum in 30 min whereas in the pre-wetted case the uptake was seen to continue beyond 180 min.A broad trend of higher deposition occurring at lower pH was seen,corresponding to the region where surface charges were opposite and thus attractive.Dry pickup was less significant at high pH.The response to varying ionic strength was complex and was attributed to the combined effect of charge screening,particle aggregation and consequent particle entrapment or occlusion.Titania deposition into the interstices of woven cotton sheets resulted in the formation of inorganic,nanoparticulate skeletons which could be isolated by controlled combustion of the cellulose and thus cotton was suggested to have potential for the templated synthesis of high surface area semiconductor materials.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号