全文获取类型
收费全文 | 3888篇 |
免费 | 187篇 |
国内免费 | 505篇 |
专业分类
化学 | 3841篇 |
晶体学 | 28篇 |
力学 | 5篇 |
综合类 | 18篇 |
数学 | 150篇 |
物理学 | 538篇 |
出版年
2024年 | 10篇 |
2023年 | 103篇 |
2022年 | 117篇 |
2021年 | 136篇 |
2020年 | 161篇 |
2019年 | 114篇 |
2018年 | 131篇 |
2017年 | 175篇 |
2016年 | 171篇 |
2015年 | 119篇 |
2014年 | 207篇 |
2013年 | 619篇 |
2012年 | 309篇 |
2011年 | 235篇 |
2010年 | 185篇 |
2009年 | 190篇 |
2008年 | 208篇 |
2007年 | 239篇 |
2006年 | 216篇 |
2005年 | 191篇 |
2004年 | 171篇 |
2003年 | 112篇 |
2002年 | 79篇 |
2001年 | 33篇 |
2000年 | 35篇 |
1999年 | 44篇 |
1998年 | 35篇 |
1997年 | 35篇 |
1996年 | 26篇 |
1995年 | 28篇 |
1994年 | 29篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有4580条查询结果,搜索用时 0 毫秒
1.
Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles. 相似文献
2.
5-Perfluorophenyl 4,5-dihydro-1H-pyrazoles were synthesized from 1,3-dipolar cycloaddition reaction of perfluorobenyl 2,4,6-triisopropylbenzenesulfonylhydrazone and α,β-unsaturated carbonyl compounds or acrylonitrile in THF or water. It was worthy to note that better results were obtained when water was employed as the solvent, which was considered as an effective, economic and environmentally friendly method to synthesize these pyrazole derivatives. 相似文献
3.
An indium-induced reduction-rearrangement reaction of nitro-substituted β-lactams has been used for facile synthesis of oxazines in aqueous ethanol. 相似文献
4.
Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods. 相似文献
5.
Pavla Fialová Inmaculada Robina Petr Sedmera Lucie Petrásková-Hušáková 《Tetrahedron letters》2005,46(50):8715-8718
Glycosyl azides are new efficient donors for glycosidases. Their high water solubility facilitates transglycosylations with comparable or better yields than common O-glycosides. The azido group totally changes the β-GalNAc-ase/β-GlcNAc-ase ratio in β-N-acetylhexosaminidases (from the usual 0.3-1.0 to <0.01), contrary to all known aglycons. 相似文献
6.
M. E. Carlotti S. Sapino R. Cavalli M. Trotta F. Trotta K. Martina 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):445-450
This work deals with the formation of inclusion complexes between cinnamaldehyde and two synthetic alkylcarbonates of γ-cyclodextrin, namely ethylcarbonate-γ-CD and octylcarbonate-γ-CD. Complexation was monitored by phase-solubility studies, by FT-IR spectroscopy and by DSC and TG analysis.
The diffusion of cinnamaldehyde through a cellulose membrane was investigated in the absence and in the presence of each of
the two γ-CD alkylcarbonates. Studies on photostability and stability over time were carried out on different cosmetic formulations
containing pure cinnamaldehyde or an equivalent amount of cinnamaldehyde complexed with the two alkylcarbonates.
Phase-solubility diagrams, DSC, FTIR and TGA analysis suggested the formation of inclusion complexes. The diffusion of cinnamaldehyde
through the cellulose membrane decreased in the presence of the two alkylcarbonates confirming the interaction of this molecule
with the inclusion agents.
Moreover the stability of cinnamaldehyde to light and heat resulted increased by complexing this fragrance material with the
two alkylcarbonates. 相似文献
7.
Maryam Mirza-Aghayan Rabah Boukherroub Mahshid Rahimifard 《Journal of organometallic chemistry》2007,692(23):5113-5116
The palladium(II) chloride/triethylsilane system has been successfully applied for the selective hydrogenation of the carbon-carbon double bond of α,β-unsaturated ketones to yield the corresponding saturated carbonyl compounds. The reaction takes place under mild conditions and affords high yields. 相似文献
8.
9.
Dávid Szegvári Romána Zelkó Péter Horváth András Gergely 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):169-172
Enantioselective solubility of rac-norgestrel was found in the presence of γ-cyclodextrin or hydroxypropyl-γ-cyclodextrin.
In both cases the efficacious enantiomer was dissolved in greater extent. Calculating the molar absorptivity and molar ellipticity
spectra of the γ- and hydroxypropyl-γ-cyclodextrin aqueous complexes, a simple and rapid direct circular dichroism (CD) spectrometric
method was obtained for the determination of the enantiomer ratio in aqueous solutions. 相似文献
10.
简要地介绍了中子俘获瞬发γ射线数据及其衰变纲图的评价方法技术、主要程序及其功能、数据评价流程、强度平衡检验,以及对A=1-44的稳定核素和A>190的部分稳定核素的热中子俘获瞬发γ射线数据及其衰变纲图评价的具体应用.The method of prompt γ-ray data evaluation for neutron capture and how to calculate the prompt γ-ray intensities of neutron capture have been briefly presented. The prompt γ-ray data of thermal-neutron capture of some stable nuclei for A=1-44 and A>190 have been evaluated. The ENSDF format has been adopted. The checks of intensity balance and format have been made. The examples are given to illustrate its application. 相似文献