全文获取类型
收费全文 | 454篇 |
免费 | 14篇 |
国内免费 | 130篇 |
专业分类
化学 | 400篇 |
晶体学 | 4篇 |
综合类 | 2篇 |
物理学 | 192篇 |
出版年
2023年 | 1篇 |
2022年 | 19篇 |
2021年 | 16篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 14篇 |
2017年 | 17篇 |
2016年 | 20篇 |
2015年 | 14篇 |
2014年 | 19篇 |
2013年 | 33篇 |
2012年 | 50篇 |
2011年 | 36篇 |
2010年 | 14篇 |
2009年 | 32篇 |
2008年 | 34篇 |
2007年 | 48篇 |
2006年 | 33篇 |
2005年 | 31篇 |
2004年 | 41篇 |
2003年 | 29篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有598条查询结果,搜索用时 15 毫秒
111.
研究了2-(4-二甲氨基苯基)-5-氟-6-吗啉-1-氢-苯并咪唑(1)在不同pH条件下的紫外-可见吸收光谱,采用非线性最小二乘法得出分子1的三级加质子常数lgβ1, lgβ2, lgβ3分别为4.96±0.03, 5.72±0.07和7.95±0.10。当pH 3.40时,分子1主要以一价离子状态存在,紫外-可见吸收光谱及荧光光谱表明该条件下分子与小牛胸腺DNA存在明显的相互作用,并得出分子1与DNA的结合常数Kb为(2.30±0.10)×104 mol-1·L。当分子浓度为10-8~1.2×10-6 mol·L-1时,荧光强度随DNA含量的增加而线性增强,分子1是一种潜在的测定DNA的定量试剂。 相似文献
112.
在AM1方法优化构型的基础上,用ZINDO/CI方法计算了系列芳香杂环聚合物的紫外-可见光谱,探索分子结构与其光学性质之间的关系.理论计算结果表明,模型化合物ABPBO,PBO,PBOV和PBODV的紫外-可见光谱最大吸收波长(λmax)依次增加,且相应吸收强度与分子链共轭长度相关.根据线性递变规律推导的理论λmax值与其实验值(薄膜干态紫外吸收)符合得较好.由于质子化效应等环境因素,溶液中测量值较理论值和薄膜紫外吸收偏大. 相似文献
113.
115.
Surface-enhanced Raman Scattering from Molecules Adsorbed on Mixed Silver/Gold Nanoparticle Surfaces
Introduction Since the first discovery of Surface-Enhanced Raman Scattering(SERS) from pyridine molecules adsorbed at roughened silver electrodes in 1974 by Fleischmann et al.[1],the research of SERS has made tremendous progress in applications of it to various fields of science and technology[2-8]. 相似文献
116.
117.
Vishnu Chauhan T. Gupta Paramjit Singh P.D. Sahare N. Koratkar Rajesh Kumar 《Physics letters. A》2019,383(9):898-907
The calibrated and controlled swift heavy ions (SHI) beam irradiation generate defects which can cause modifications in various properties of the materials such as structural, optical, magnetic, morphological, and chemical etc. The passage of ion through the target material causes the nuclear energy losses () and electronic energy losses (). The dominates over in SHI irradiation. In the present study, ZrO2 thin films were grown on silicon and glass substrate by using RF sputtering deposition technique. For the purpose of modifications induced by swift heavy ions, these films were irradiated by a 120 MeV S9+ ion beam of 1 pnA current, with varying ion fluences from 5E12 to 1E13 ions/cm2, using the tandem accelerator at the Inter University Accelerator Center (IUAC), New Delhi, India. The X-ray diffraction (XRD) patterns confirmed the formation of monoclinic and tetragonal phases and it was observed that XRD peaks intensity increased up to the fluence of 5E12 ions/cm2 followed by opposite behavior at higher fluences. Atomic force microscope (AFM) study revealed the increased surface roughness after SHI irradiation. In addition to it, the formation of electronic transition states in optical band gap region and enhancement of absorption edge was observed from UV-visible spectroscopy (UV-Vis) results due to which direct band gap energy value decreased from those of un-irradiated samples. Photoluminescence (PL) broad emission spectra were determined using the excitation wavelength at 290 nm with the prominent peak at 415 nm which can be ascribed to Zr vacancies due to band edge emission as a result of free-exciton recombination. Rutherford backscattering spectrometry (RBS) technique was used for depth profiling and elemental composition in zirconia thin films. The expected role of electronic energy loss during ion irradiation is to modify the properties of the material has been discussed. 相似文献
118.
Systematic studies on eight isomers of C70O were performed by means of INDO methods. It has been indicated that the O atom is mainly added to the C1-C2 or C3-C3 bond and an epoxide feature with Cs symmetry is formed. Based on the optimized geometries, the UV-Vis spectra were calculated. It has been found that the main
peaks of C70O resemble those of C70 and the characteristic absorptions beyond 460 nm are produced, which is in agreement with the experimental results. Theoretical
assignments about the absorptions were canied out and the reason for the red-shift of the absorptions was discussed. C70O is probably composed of four isomers according to the calculated results.
Project supported by the National Natural Science Foundation of China. 相似文献
119.
以钛酸四丁酯(Ti(OBu)4)、乙醇胺(MEA)、聚乙二醇(PEG)和无水乙醇为反应体系,采用溶胶-凝胶法制备了TiO2溶胶并通过浸渍提拉法制得了TiO2多孔膜,用UV-Vis,XRD和AFM对制得的多孔膜进行了表征,讨论了薄膜的紫外-可见透过光谱随着薄膜层数的变化规律以及其与膜厚的关系,结果表明在本实验条件下薄膜转移得很均匀,每层膜厚度约为60nm。多孔膜的光催化测试结果表明,随着薄膜层数的增加,光催化活性也逐渐增强,10层多孔膜的光催化活性最高。 相似文献
120.
阴阳离子菁染料在溴碘化银乳剂颗粒上J-聚体反射光谱 总被引:1,自引:1,他引:0
本文对两种阴阳离子菁染料在碘溴化银立方体颗粒表面的聚集行为进行了研究。用紫外-可见分光光度计测定了菁染料J-聚集的反射光谱曲线。与对应的阴离子、阳离子菁染料各自在碘溴化银立方体颗粒表面的聚集进行了实验对比。结果表明:阴阳离子菁染料吸附在碘溴化银立方体颗料表面形成的J-聚集态的反射光谱具有单个阴离子、阳离子菁染料形成J-聚体反射光谱的峰值波长。表明阴阳离子菁染料具有两个感色区域,既有阴离子菁染料的感色区又有阳离子菁染料的感色区。 相似文献