全文获取类型
收费全文 | 968篇 |
免费 | 35篇 |
国内免费 | 31篇 |
专业分类
化学 | 1018篇 |
综合类 | 4篇 |
物理学 | 12篇 |
出版年
2023年 | 12篇 |
2022年 | 29篇 |
2021年 | 26篇 |
2020年 | 24篇 |
2019年 | 22篇 |
2018年 | 28篇 |
2017年 | 28篇 |
2016年 | 32篇 |
2015年 | 26篇 |
2014年 | 33篇 |
2013年 | 56篇 |
2012年 | 71篇 |
2011年 | 62篇 |
2010年 | 43篇 |
2009年 | 66篇 |
2008年 | 48篇 |
2007年 | 53篇 |
2006年 | 50篇 |
2005年 | 44篇 |
2004年 | 31篇 |
2003年 | 24篇 |
2002年 | 19篇 |
2001年 | 24篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 24篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 3篇 |
排序方式: 共有1034条查询结果,搜索用时 15 毫秒
961.
一种新的衍生试剂9,10 蒽醌 2 磺酰氯(ASC)首次用于酚类衍生。几种不同极性的酚被用于评价该试剂。为便于考察ASC对酚衍生的机理及优化衍生条件,制备了不同酚的标准衍生物并对它们进行了结构确证。衍生过程涉及去质子酚与特丁基铵阴离子形成离子对后被有机溶剂提取。衍生反应可以在室温下3min内在两相界面上定量完成。衍生产物很稳定,可以分别被正相和反相分离(相应地在320nm或256nm波长处检测),其浓度和响应在0 2μmol/L~200μmol/L内存在很好的线性关系。 相似文献
962.
研究用衍生化气相色谱-质谱法 测定硝苯催化法生产的对氨基酚及其中杂质苯胺,4、4'-二氨基二苯醚等。探讨了对氨基酚的萃取条件及色谱行为,选择了最佳衍生化方法。 相似文献
963.
Valerie A. Frerichs Jennifer K. Herrmann Alfredo Aguirre Luis A. Coln 《Microchemical Journal》2004,78(2):135-142
An analytical method was developed to determine the undecapetide substance P (SP) based on capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. SP was derivatized with the fluorogenic reagent 2,3-naphthalenedicarboxaldehyde (NDA) prior to injection into the CE-LIF system. The pre-column derivatization scheme combined with injection enhancement techniques extends the detectability of SP to the subnanomolar level. Limit of detection (LOD) of 100 pM was achieved without pre-concentrating the sample prior to injection. The reproducibility for six different preparations of a standard sample containing 5 nM of SP was 6.8% RSD and that of the CE migration time was 0.08% RSD. The method was used to determine SP in a saliva sample. 相似文献
964.
K. Haider M. Spiteller K. Reichert M. Fild 《International journal of environmental analytical chemistry》2013,93(1-3):201-211
Abstract Bound residues of pesticides and their metabolites are defined as being nonextractable with organic solvents, but partly extractable together with the humic matrix by NaOH or other solvents suitable to extract humic compounds. Recently, an improvement in humus extraction from soils was achieved upon derivatization of the organic matter with silylating reagents at room temperature. By this method 70–90% of the organic carbon or nitrogen either from soil or from humin became soluble in organic solvents. The extracts were analyzed by means of 13C NMR-spectroscopy. The spectra were well resolved with signal-separation of less than 1 ppm. The extracted humic compounds were of rather low molecular weight, ranging from 300 to 4000 to 6000 d or more. 14C-labeled residues of pesticides or other xenobiotics found to be nonextractable after exhaustive organic solvent extraction became readily dissolved along with most of the humic matrix using this derivatization procedure. Between 60–80% of 14C anilazine residues or of 14C-labeled chlorinated phenols or anilines originating from both previously solvent extracted soil samples or from humin became solubilized in organic solvents. 相似文献
965.
Na Yan Lei Zhou Zaifang Zhu Huige Zhang Ximin Zhou Xingguo Chen 《Journal of chromatography. A》2009,1216(20):4517-4523
In this work, a novel method combining constant pressure-assisted head-column field-amplified sample injection (PA-HC-FASI) with in-capillary derivatization was developed for enhancing the sensitivity of capillary electrophoresis. PA-HC-FASI uses an appropriate positive pressure to counterbalance the electroosmotic flow in the capillary column during electrokinetic injection, while taking advantage of the field amplification in the sample matrix and the water of the “head column”. Accordingly, the analytes were stacked at the stationary boundary between water and background electrolyte. After 600 s PA-HC-FASI, 4-fluoro-7-nitro-2,1,3-benzoxadiazole as derivatization reagent was injected, followed by an electrokinetic step (5 kV, 45 s) to enhance the mixing efficiency of analytes and reagent plugs. Standing a specified time of 10 min for derivatization reaction under 35 °C, then the capillary temperature was cooled to 25 °C and the derivatives were immediately separated and determined under 25 °C. By investigating the variables of the presented approach in detail, on-line preconcentration, derivatization and separation could be automatically operated in one run and required no modification of current CE commercial instrument. Moreover, the sensitivity enhancement factor of 520 and 800 together with the detection limits of 16.32 and 6.34 pg/mL was achieved for model compounds: glufosinate and aminomethylphosphonic acid, demonstrating the high detection sensitivity of the presented method. 相似文献
966.
Maria N. Bakola‐Christianopoulou 《应用有机金属化学》2001,15(11):889-900
The silylation of quinones and their substituted derivatives for the protection of the reactive quinonic moiety and/or reactive substituents (in particular hydroxyl groups) is discussed in view of the wide applicability of the reaction for synthetic, biological and analytical purposes. Furthermore, the most common and efficient methods for the subsequent desilylation of the silylated quinones and their derivatives to the parent quinones or to the corresponding hydroquinones are discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
967.
采用一种新型紫外、荧光衍生试剂咔唑-9-乙基氯甲酸酯对9种氨基酸(丝氨酸、苏氨酸、甘氨酸、谷氨酸、天冬氨酸、缬氨酸、异亮氨酸、亮氨酸、苯丙氨酸)进行柱前衍生,采用胶束电动色谱模式在14 min内完成分离。分离条件:以pH 9.0的 20 mmol/L硼酸盐-30 mmol/L十二烷基硫酸钠(SDS)溶液(含3%(体积分数)乙腈)为缓冲溶液,柱温25 ℃,分离电压18 kV,紫外检测波长214 nm。该方法的线性范围为0.025~0.25 mmol/L,检出限为2.15~2.46 μmol/L。 相似文献
968.
969.
970.
M. Freney H. Irth H. Lindberg U. Alkner L. Greiff C. G. A. Persson M. Andersson G. Marko-Varga 《Chromatographia》2001,54(7-8):439-445
Summary Fucose (6-deoxygalactose) is a constituent of airway mucous glycoproteins. In this paper we describe a high-throughput method
for screening nasal lavage fluid samples and induced sputum samples for fucose. Fucose was released by hydrolysis with 0.5m sulfuric acid at 100°C for 4 h. After pH adjustment remaining proteins were removed by on-line dialysis. Chromatography was
performed with two 300 mm×7.8 mm i.d. Bio-Rad Aminex HPX-87H columns arranged in a box-car configuration. Post-column derivatization
was performed with benzamidine under alkaline conditions. Fluorescence was monitored at an excitation wavelength of 360 nm,
using an optical cut-off filter of 420 nm. The limit of quantitation for fucose was 40 μm (S/N=3) in 300μL nasal lavage medium, with use of a 20-μL injection loop. Relative standard deviation (RSD) values for intra and inter assay data were below 15% and 20%, respectively, at spike levels of 635 μm l-fucose. The method was used to monitor the fucose content of human airway secretions.
Presented at: 23rd International Symposium on Chromatography, London, UK, October 1–5, 2000 相似文献