全文获取类型
收费全文 | 375篇 |
免费 | 20篇 |
国内免费 | 73篇 |
专业分类
化学 | 431篇 |
晶体学 | 7篇 |
综合类 | 2篇 |
物理学 | 28篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 6篇 |
2014年 | 13篇 |
2013年 | 47篇 |
2012年 | 30篇 |
2011年 | 19篇 |
2010年 | 14篇 |
2009年 | 23篇 |
2008年 | 20篇 |
2007年 | 24篇 |
2006年 | 18篇 |
2005年 | 19篇 |
2004年 | 21篇 |
2003年 | 21篇 |
2002年 | 9篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有468条查询结果,搜索用时 328 毫秒
1.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献
2.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献
3.
Marilena Vasilescu Titus Constantinescu Mariana Voicescu Helge Lemmetyinen Elina Vuorimaa 《Journal of fluorescence》2003,13(4):315-322
The spectrophotometric study of luminol (LH2) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH2 absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L2–) formation at 3 × 10–4 – 2.4 × 10–3
M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH2-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10–3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH2-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH+
3 cation formation. In LH2-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH2-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed. 相似文献
4.
合成了重稀土高氯酸盐甲基苯甲酰甲基亚砜配合物RE(ClO4)3·L5·C2H5OH(RE=Gd,Tb,Dy,Tm,Yb;L=C6H5COCH2SOCH3).经元素分析、稀土络合滴定、摩尔电导及热重分析确定了配合物的组成,测定了配体及配合物的IR谱、1H NMR及铽配合物的磷光光谱、荧光激发和发射光谱,根据荧光发射光谱数据计算了铽配合物的各能级值. 相似文献
5.
Shiraz A. Markarian Liana S. Gabrielyan Karine R. Grigoryan 《Journal of solution chemistry》2004,33(8):1005-1015
FT IR ATR spectra of urea/dimethyl sulfoxide and urea/diethyl sulfoxide mixtures in the S=O and N—H stretching vibration regions at different molar ratios have been measured. On the basis of the band deconvolution data, various types of intermolecular associated forms, including dimers and hydrogen-bonded urea–sulfoxide complexes, have been revealed. The latter has been confirmed also by ab initio calculations. 相似文献
6.
不对称亚砜与1,10—双(1‘苯基—3’—甲基—5‘氧化吡唑—4’—基)癸二酮—[1,10]对… 总被引:1,自引:0,他引:1
7.
S. F. Malysheva N. K. Gusarova N. A. Belogorlova A. V. Afonin S. N. Arbuzova B. A. Trofimov 《Russian Chemical Bulletin》1997,46(10):1799-1801
Diorganylvinylphosphine oxides were synthesized in 31–38% yields on heating (50°C) diorganylphosphine oxides with vinyl sulfoxides
or divinyl sulfone in the presence of KOH.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1895–1896, October, 1997. 相似文献
8.
9.
Push-pull 2-alkylidene-4-oxothiazolidine vinyl bromides undergo efficient C(5) functionalization through DMSO-assisted carbon-bromine cleavage, followed by a bromine transfer-substitution (or elimination) sequence. A mechanism for this novel transformation is proposed. 相似文献
10.
Sadagopan Raghavan A. RajenderM.Abdul Rasheed S.Ramakrishna Reddy 《Tetrahedron letters》2003,44(45):8253-8256
A novel, unprecedented transformation of δ-hydroxysulfoxides into substituted tetrahydrofurans by a silicon promoted Pummerer type reaction is disclosed. The transformation is shown to be general and is brought about under very mild reaction conditions. The products with the sulfide group at the anomeric carbon provide a suitable handle to carry out further transformations. 相似文献