全文获取类型
收费全文 | 237篇 |
免费 | 13篇 |
国内免费 | 39篇 |
专业分类
化学 | 252篇 |
晶体学 | 7篇 |
综合类 | 3篇 |
物理学 | 27篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 17篇 |
2012年 | 15篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
排序方式: 共有289条查询结果,搜索用时 31 毫秒
41.
Yuliang Li Nan Zhang Shuai Xu Qi Zhu Jing Hu 《Journal of Dispersion Science and Technology》2019,40(6):874-883
In this article, the equilibrium behavior of solutions of 1-ethyl-3-methylimidazolium dimethyl phosphate ([Emim]DMP) and ethyl acetate or acetone in aqueous two-phase system (ATPS) was discussed to understand the liquid–liquid equilibrium (LLE) behavior of these organic solvents. Thus, we determined phase diagrams and LLE data at 303.15, 308.15, 313.15, and 323.15 K for the investigated biphasic systems. Four empirical equations were used to study the tie lines. The results showed that for the [Emim]DMP?+?acetone?+?water biphasic systems within the investigated temperature range, temperature influences the phase behavior, but for the [Emim]DMP?+?ethyl acetate?+?water biphasic systems within the investigated temperature range, there are no notable changes on the phase behavior with rising temperature. The results may have important applications for the separation of antibiotics and for the recovery of ionic liquids (ILs). 相似文献
42.
Dr. David Tejedor Samuel Delgado-Hernández Lucía Colella Dr. Fernando García-Tellado 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(66):15046-15049
A universal, practical and scalable organocatalytic hydrocyanation manifold to provide β-substituted acrylonitriles bearing an electron-withdrawing functionality has been implemented. The catalytic manifold operates under the reactivity generation principle “a good nucleophile generates a strong base”, and it uses 1,4-diazabicyclo[2.2.2]octane (DABCO) as the catalyst, activated terminal alkynes as substrates and acetone cyanohydrin as the cyanide source. The acrylonitriles obtained as E,Z mixtures are straightforwardly resolved by simple flash chromatography delivering the pure isomers in preparative amounts. 相似文献
43.
ABSTRACT The asymmetric cross-aldol reaction of simple ketones (acetone, cyclohexanone) with isatin derivatives in the presence of crude extract from earthworms as green and effective biocatalyst proceeds easily in MeCN/H2O (1:1) as solvent to afford 3-hydroxy-2-oxindoles derivatives. Ten compounds were synthesized in high yields (62–88%) and moderate ee (29–42%). Structure of the synthesized compounds has been characterized on the basis of NMR spectra and CHN analysis. The ee of the obtained compounds was determined by chiral phase HPLC analysis. 相似文献
44.
Parameshwara Chary Jilloju 《合成通讯》2018,48(14):1739-1746
A facile, one-pot three-component protocol for the synthesis of substituted 4-(benzylideneamino)-5-(3,5-dimethyl-1H-pyrazol-1-yl)-4H-1,2,4-triazole-3-thiols have been reported by the reaction of 4-amino-5-hydrazinyl-4H-1,2,4-triazole-3-thiol with acetyl acetone and various substituted benzaldehydes via multi component reaction. The newly synthesized derivatives were characterized by their elemental analysis and spectral data. The current strategy provides heterocyclic compounds in good yields with broad substrate scope. 相似文献
45.
The molecular structure of malagashanine (C23H30N2O4), a new alkaloid occurring in MadagascanStrychnos species and showing chloroquine-potentiating action, has been determined by single crystal X-ray diffraction. The crystals, in the form of a 11 acetone solvate, are monoclinic, space group P21, witha=10.328(2),b=10.554(6),c=11.490(5)Å, =96.67(2)0,Z=2. Refinement based on 3650 reflections measured at 294K yieldedR=0.045. The X-ray analysis shows that the ring system in malagashanine differs from that in alkaloids of the strychnobrasiline type in containing only five-and six-membered rings. Thermal analysis of the solvate indicates that the acetone molecules are firmly held in the crystal and the X-ray analysis reveals that they are trapped in crystal voids. Only van der Waals forces and C–H...O hydrogen bonds stabilize the crystal structure. 相似文献
46.
T.E. Vittal Prasad M. Vasavi M. Jyotsna V. Jhansi G. Smitha D.H.L. Prasad 《The Journal of chemical thermodynamics》2008,40(9):1418-1421
Bubble point temperatures (at 95.35 kPa) over the entire composition range were measured for the binary mixtures formed by ethyl benzene with: acetyl acetone, o-, and p-cresols, 1-hexanol, and tetraethoxysilane, employing a Swietoslawski type ebulliometer. Wilson equation was used to represent the measured liquid phase composition versus bubble point temperature data, and the computed values of the vapor phase mole fractions, activity coefficients, and excess Gibbs free energy were tabulated and briefly discussed. 相似文献
47.
48.
Naader Alizadeh Mahsa Amiri Fariba Mohammadpour Parviz Norouzi 《Electroanalysis》2023,35(10):e202300114
This research represents a novel detection method of acetone level in the exhaled breath samples (RH=88 %) based on polypyrrole/tungsten oxide (PPy/WO3) nanocomposite sensor. The PPy/WO3 sensor was fabricated by the deposition of nanocomposite on/between interdigitated electrodes (IDEs) through electrospray coating and was then characterized by FE-SEM imaging. In this detection method, the coulometric signal of the sensor was calculated using Fast Fourier Continuous Cyclic Voltammetry (FFTCCV), where cyclic voltammetry (CV) was applied to the sensor in the defined potential rang and then charge changes of the sensor was obtained by integration of the current in all scanned potential ranges. FFTCCV method enhances the sensitivity of the sensor when exposed to the gas mixtures containing acetone. In addition to its fast coulometric response time (≤5 s) in the two linear ranges of 0.7–2.8 ppm and 2.8–28.2 ppm (R2=0.99), FFTCCV method provides the low detection limit of 70 ppb, and high sensitivity toward acetone at the optimum values of the parameters. The fabricated sensor showed great selectivity toward acetone when exposed to humid air and some exhaled gas like carbon dioxide, ammonia, methanol, ethanol and alkyl amines. The results were very satisfying as the sensor was capable to detect different acetone levels in human exhaled breath as non-invasive diagnosis of diabetes with a good correlation (R2≃0.9) to the routine blood sugar test taken by different commercial glucometers results. 相似文献
49.
50.