全文获取类型
收费全文 | 151篇 |
免费 | 6篇 |
国内免费 | 11篇 |
专业分类
化学 | 65篇 |
晶体学 | 1篇 |
力学 | 4篇 |
综合类 | 1篇 |
数学 | 20篇 |
物理学 | 77篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 6篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 5篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1991年 | 1篇 |
排序方式: 共有168条查询结果,搜索用时 15 毫秒
121.
Determination of tetracyclines in food samples by molecularly imprinted monolithic column coupling with high performance liquid chromatography 总被引:4,自引:0,他引:4
A novel solid phase extraction (SPE) method for determination of tetracyclines (TCs) in milk and honey samples by molecularly imprinted monolithic column was developed. Using tetracycline (TC) as the template, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, methanol as the solvent, cyclohexanol and dodecanol as the mixed porogenic solvents, a TC imprinted monolithic column was prepared by in situ molecular imprinting technique for the first time, and the optimal synthesis conditions and the selectivity of TC imprinted monolithic column were investigated. The interfering substances in food samples and TCs can be separated successfully on imprinted column. Molecularly imprinted solid phase extraction (MISPE) coupling with C18 column was used to determinate the TCs in milk and honey. The recoveries of this method for six tetracyclines antibiotics such as tetracycline (TC), oxytetracycline (OTC), minocycline (MINO), chlortetracycline (CTC), metacycline (MTC) and doxycycline (DTC) were investigated, and high recoveries of 73.3-90.6% from milk samples and 62.6-82.3% from honey samples were obtained. A method for determination of TCs at low concentration level in milk and honey samples was successfully developed by using the monolithic column as the precolumn for solid phase extraction of six TCs compounds. 相似文献
122.
一个简易的2,6-二氨基-3,5-二硝基吡啶-1-氧化物的合成方法 总被引:3,自引:0,他引:3
研究了2,6-二氨基-3,5-二硝基吡啶-1-氧化物(DADNP-1-O)的一个简易合成方法. 该方法是以2,6-二氨基吡啶(DAP)为原料, 利用两步法得到高纯度高产率的2,6-二氨基-3,5-二硝基吡啶, 再在三氟乙酸和双氧水作用下进行N-氧化反应得到DADNP-1-O, 总收率在90%以上, 并对主要反应影响因素进行了讨论, 经傅立叶变换红外光谱(FT2IR), 氢核磁(1H NMR), 碳核磁(13C NMR), 高效液相色谱(HPLC), 元素分析, DSC等方法对中间体和DADNP-1-O结构进行了表征. 相似文献
123.
基于洞原子退激发的辐射-俄歇级联退激发模型(radiative-Auger cascade model简称RAC模型),本文详细研究了Ar2 (2s-2)、Ar2 (2s-12p-1)和Ar2 (2p-2)三种离子的退激发过程及其末电离态离子分布,讨论了末电离态离子分布随初态洞的深浅变化的规律.结果表明:随着初态洞分布的变浅,退激发过程变简单,退激发后产生的高离化度离子分布降低,低离化度离子分布增大. 相似文献
124.
In oxidative electrochemical organic synthesis, radical intermediates are often oxidized to cations on the way to final product formation. Herein, we describe an approach to transform electrochemically generated organic radical intermediates into neutral products by reaction with a metal catalyst. This approach combines electrochemical oxidation with Cu catalysis to effect formal aza‐Wacker cyclization of internal alkenes. The Cu catalyst is essential for transforming secondary and primary alkyl radical intermediates into alkenes. A wide range of 5‐membered N‐heterocycles including oxazolidinone, imidazolidinone, thiazolidinone, pyrrolidinone, and isoindolinone can be prepared under mild conditions. 相似文献
125.
126.
Imaging spectrometer has obtained wide development since rich feature information can be obtained by it; now, we focus on its high spectral resolution and miniaturization. In this paper, we design the Dyson imaging spectrometer system based on Fery prism. The average spectral resolution is 4.3 nm and the structure of the total length is 229 mm. It is a small, high-spectrometer imaging system. The front and rear surface of the traditional prism are plane, but the surfaces of the Fery prism are spherical, which can provide some optical power to realize imaging function and produce the dispersion effect. The Fery prism does not need to be placed in the parallel optical path, which simplifies the collimator lens and the imaging lens and are necessary in the prism spectrometer, making it possible to obtain a compact spectrometer. Full-spectrum transmittance of the prism is up to 94 %. Compared to the convex grating, the energy efficiency is greatly improved, and the free spectral range is wider, and its dispersion will not bring higher-order spectral aliasing problem. The small high spectrometer only includes two components. Its spectral range is from 400 to 1000 nm, covering the near-ultraviolet to near-infrared. The various aberrations of the typical spectrum are corrected. The spectrometer is excellent in performance. 相似文献
127.
Thanks to the strong electronic interaction and support-metal interaction between NiPt and spherical CeO2, the obtained Ni5Pt5-CeO2 catalyst exhibits superior catalytic performance for hydrogen generation from alkaline solution of hydrazine at room temperature. 相似文献
128.
Lipophilicity was evaluated using a novel RP-HPLC stationary phase (Discovery-RP-Amide-C16) with and without 1-octanol added to the mobile phase. A set of 46 drugs and flavonoids characterized by a broad structural diversity and a wide log Poct range (-0.69 to 5.70) was selected for this study. This set consists of neutral solutes and solutes with acidic or ampholytic functionalities which were maintained neutral at pH 2.5 or 4. In our conditions, the addition of 1-octanol in the mobile phase proved a key factor to derive a lipophilicity index log k(w) highly correlated with log Poct for all investigated solutes. 1-Octanol improved the correlation between log Poct and log k(w) mainly by influencing the retention behavior of the solutes with log Poct values below +3. This study brings additional evidence that under proper experimental conditions of stationary and mobile phases, RP-HPLC is a very useful method to obtain log Poct values. 相似文献
129.
Mathias EV Liu X Franco O Khan I Ba Y Kornfield JA 《Langmuir : the ACS journal of surfaces and colloids》2008,24(3):692-700
Rf-IPDU-PEGs belong to a class of fluoroalkyl-ended poly(ethylene glycol) polymers (Rf-PEGs), where the IPDU (isophorone diurethane) functions as a linker to connect each end of the PEG chain to a fluoroalkyl group. The Rf-IPDU-PEGs form hydrogels in water with favorable sol-gel coexistence properties. Thus, they are promising for use as drug delivery agents. In this study, we introduce an electron-spin induced 19F relaxation NMR technique to probe the location and drug-loading capacity for an electron-spin labeled hydrophobic drug, CT (chlorambucil-tempol adduct), enclosed in the Rf-IPDU-PEG micelle. With the assistance of molecular dynamics simulations, a clear idea regarding the structures of the Rf-IPDU-PEG micelle and its CT-loaded micelle was revealed. The significance of this research lies in the finding that the hydrophobic drug molecules were loaded within the intermediate IPDU shells of the Rf-IPDU-PEG micelles. The molecular structures of IPDU and that of CT are favorably comparable. Consequently, it appears that this study opens a window to modify the linker between the Rf group and the PEG chain for achieving customized structure-based drug-loading capabilities for these hydrogels, while the advantage of the strong affinity among the Rf groups to hold individual micelles together and to interconnect the micellar network is still retained in hopes of maintaining the sol-gel coexistence of the Rf-PEGs. 相似文献
130.