全文获取类型
收费全文 | 528篇 |
免费 | 108篇 |
国内免费 | 88篇 |
专业分类
化学 | 453篇 |
晶体学 | 15篇 |
力学 | 3篇 |
数学 | 5篇 |
物理学 | 248篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 19篇 |
2014年 | 13篇 |
2013年 | 38篇 |
2012年 | 23篇 |
2011年 | 26篇 |
2010年 | 23篇 |
2009年 | 49篇 |
2008年 | 50篇 |
2007年 | 41篇 |
2006年 | 23篇 |
2005年 | 43篇 |
2004年 | 81篇 |
2003年 | 50篇 |
2002年 | 52篇 |
2001年 | 22篇 |
2000年 | 24篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有724条查询结果,搜索用时 15 毫秒
641.
傅里叶变换近红外光谱仪扫描条件对数学模型预测精度的影响 总被引:21,自引:5,他引:16
以小麦粉状样品为例 ,研究了傅里叶变换近红外光谱仪在不同分辨率 ,不同的激光频率下扫描样品对近红外光谱用于分析小麦样品蛋白质含量的影响。结果表明 :以 4 ,8,16cm- 1 的分辨率扫描样品或当激光频率改变幅度在 1cm- 1 以内时对小麦蛋白模型的影响不显著 ,样品粒度对模型影响较大 相似文献
642.
FT‐IR and FT‐Raman spectra of benzoic acid (BA) and 3,5‐dichloro salicylic acid (SA) have been recorded in the regions of 4000–400 and 4000–50 cm−1 respectively. The spectra were interpreted with the aid of normal coordinate analysis following the full structure optimizations and force field calculations based on density functional theory (DFT) using standard B3LYP6‐31G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well‐established set of scale factors that were found to be transferable to the title compounds. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
643.
The solid phase mid‐FTIR and FT‐Raman spectra of 1‐hydroxy naphthalene (HNP) were recorded in the regions 4000–400 and 4000–50 cm, respectively. The spectra were interpreted with the help of normal coordinate analysis following full structure optimization and force field calculations based on the density functional theory (DFT) using the standard B3LYP/6‐31G** method and basis set combination. The results of the calculations were applied to simulate infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
644.
V. Bena Jothy D. Sajan C. Ravikumar I. Nmec Chun‐Nian Xia V. K. Rastogi I. Hubert Joe 《Journal of Raman spectroscopy : JRS》2009,40(12):1822-1830
As part of the efforts for the design of new organic nonlinear optical(NLO) materials with high efficiency for present day technological requirements, a comprehensive investigation on the intramolecular charge transfer(CT) of an efficient π‐conjugated potential push–pull NLO chromophore, ethyl‐3‐(3,4‐dihydroxyphenyl)‐2‐propenoate(EDP) to a strong electron‐acceptor group through the π‐conjugated bridge has been carried out from their vibrational spectra. The first hyperpolarizabilities of caffeic derivatives are investigated by ab initio method. The NLO efficiency is experimentally measured by powder efficiency experiment. The strongest vibrational modes contributing to the electro‐optic effect from the simultaneous infrared(IR) and Raman activities of the ring CC stretching modes, in‐plane deformation modes, and the umbrella mode of the methyl groups have been identified and analyzed unambiguously. The influence of electronic effects, hyperconjugation and backdonation, on the C H stretching vibrations of both methyl and methylene groups causing the decrease of stretching wavenumbers and IR intensities has been extensively investigated. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
645.
V. Krishnakumar M. Sivasubramanian S. Muthunatesan 《Journal of Raman spectroscopy : JRS》2009,40(8):987-991
The Fourier transform infrared (FT‐IR) spectrum of N‐hydroxyphthalimide has been recorded in the range of 4000–400 cm−1, and the Fourier transform Raman (FT‐Raman) spectrum of N‐hydroxyphthalimide has been recorded in the range of 4000–50 cm−1. With the hope of providing more and effective information on the fundamental vibrations, the Density Functional Theory (DFT)‐Becke3‐Lee‐Yang‐Parr (B3LYP) level with 6‐31G* basis set has been employed in quantum chemical analysis, and normal coordinate analysis has been performed on N‐hydroxyphthalimide by assuming Cs symmetry. The computational wavenumbers are in good agreement with the observed results. The theoretical spectra obtained along with intensity data agree well with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
646.
I. Hubert Joe Irena Kostova C. Ravikumar M. Amalanathan Simona CîntÎ Pînzaru 《Journal of Raman spectroscopy : JRS》2009,40(8):1033-1038
The FT‐IR and FT‐Raman spectra of sodium salt of 4‐hydroxy‐3[1‐(4‐nitrophenyl)‐3‐oxobutyl]‐2H‐1‐benzopyran‐2‐one (acenocoumarol sodium salt) in solid phase have been recorded and analyzed. The optimization geometry, intramolecular hydrogen bonding, and harmonic vibrational wavenumbers of acenocoumarol sodium salt have been investigated with the help of B3LYP density functional theory (DFT) methods. The infrared and Raman spectra were predicted theoretically from the calculated intensities. Natural bond orbital (NBO) analysis indicates the presence of C H···O hydrogen bonding in the molecule. The first static hyperpolarizability of the molecule has been computed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
647.
Hema Tresa Varghese C. Yohannan Panicker V.S. Madhavan Samuel Mathew Jarmila Vinsova Christian Van Alsenoy 《Journal of Raman spectroscopy : JRS》2009,40(9):1211-1223
FT‐IR and FT‐Raman spectra of 4‐chloro‐2‐(4‐bromophenylcarbamoyl)phenyl acetate were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighbouring oxygen atom. The simultaneous IR and Raman activations of the CO stretching mode give the charge transfer interaction through a π‐conjugated path. Optimized geometrical parameters of the title compound are in agreement with similar reported structures. From the optimized structure, it is clear that the hydrogen bonding decreases the double bond character of CO bond and increases the double bond character of the C N bonds. The first hyperpolarizability, predicted infrared intensities and Raman activities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non‐linear optics. The assignments of the normal modes are done by potential energy distribution (PED) calculations. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
648.
649.
Gustavo M. do Nascimento Mrcia L. A. Temperini 《Journal of Raman spectroscopy : JRS》2008,39(7):772-778
The effects of near‐IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANI‐ES) and base (PANI‐EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm−1 in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm−1 were associated to νC N of polarons with different conjugation lengths and the bands from 1450 to 1500 cm−1 in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to νCN modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 nm causes the deprotonation of PANI‐ES and the formation of cross‐linking segments having phenazine and/or oxazine rings. For PANI‐EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
650.
Two strong bands centered at 446 and 607 cm−1 have been observed in the FT‐Raman spectrum of almandine [Fe3Al2(SiO4)3] excited with 1064 nm, which were completely absent in the corresponding dispersive Raman spectra obtained using 488, 514.5 and 532 nm excitation. Furthermore, the mentioned strong bands have not been registered in the anti‐Stokes side of the FT‐Raman spectrum, and were therefore assigned to laser‐induced fluorescence bands. Their appearance is related to the presence of rare‐earth element traces as impurities in the almandine sample. Additionally, the FT‐Raman (and dispersive Raman) spectrum of the isomorphous spessartine [Mn3Al2(SiO4)3] mineral has been introduced, which did not show the presence of these fluorescence emission bands. The purity of the minerals was confirmed by study of their powder X‐ray diffraction (PXRD) patterns. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献