全文获取类型
收费全文 | 138篇 |
免费 | 1篇 |
国内免费 | 34篇 |
专业分类
化学 | 169篇 |
综合类 | 2篇 |
物理学 | 2篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 12篇 |
2011年 | 11篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 16篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有173条查询结果,搜索用时 15 毫秒
81.
82.
Cyclic imides belong to a well-known class of organic compounds with various biological activities, promoting a great interest in compounds with this functional group. Due to the structural complexity of some molecules and their spectra, it is necessary to use several spectrometric methods associated with auxiliary tools, such as the theoretical calculation for the structural elucidation of complex structures. In this work, the synthesis of epoxy derivatives of 5-methylhexahydroisoindole-1,3-diones was carried out in five steps. Diels–Alder reaction of isoprene and maleic anhydride followed by reaction with m-anisidine afforded the amide (2). Esterification of amide (2) with methanol in the presence of sulfuric acid provided the ester (3) that cyclized in situ to give imides 4 and 4-ent. Epoxidation of 4 and 4-ent with meta-chloroperbenzoic acid (MCPBA) afforded 5a and 5b. The diastereomers were separated by silica gel flash column chromatography, and their structures were determined by analyses of the spectrometric methods. Their structures were confirmed by matching the calculated 1H and 13C NMR chemical shifts of (5a and 5b) with the experimental data of the diastereomers using MAE, CP3, and DP4 statistical analyses. Biological assays were carried out to evaluate the potential herbicide activity of the imides. Compounds 5a and 5b inhibited root growth of the weed Bidens pilosa by more than 70% at all the concentrations evaluated. 相似文献
83.
构建了高岭石铝氧八面体层表面模型Al13O48H57和硅氧四面体层表面模型Si13O37H22,采用B3LYP/6-31G(d,p)方法, 对其与2,4-二氯苯氧乙酸(2,4-D)、 2,4-二氯苯氧丙酸(2,4-DP)、 2,4-二氯苯氧丁酸(2,4-DB)、 2-甲基-4-氯苯氧乙酸(MCPA)、 2-甲基-4-氯苯氧丙酸(MCPP)和2-甲基-4-氯苯氧丁酸(MCPB)等苯氧羧酸类农药分子间的相互作用及吸附性质进行了研究, 包括优化的几何构型、 结构参数、 吸附能及自然键轨道(NBO)电荷. 八面体层表面的中心原子(OH2, OH3及OH11)与四面体层表面的中心原子(O2, O3及O11)并未表现出明显的吸附活性. 相较于侧链为乙酸基的分子, 含有丙酸基或丁酸基的分子因带有更多的吸附位点而具有较强的吸附性. 研究发现MCPP的吸附性高于MCPA. 结合2,4-D的吸附性高于MCPA的结论, 可以推断2,4-D与MCPA更倾向于吸附在高岭石的硅氧层表面. 因此在农药施用的过程中, 应充分考虑各分子的活性及其与高岭石表面的作用强弱, 确保淋洗对去除农药在土壤中残留的可行性. 相似文献
84.
二茂铁基1,3,4-三唑席夫碱衍生物合成及生物活性和电化学性质 总被引:2,自引:2,他引:0
首次合成了二茂铁基-1,3,4-三唑Schiff碱衍生物(5a~5e),利用IR、1H NMR和HRMS等手段对其进行了结构表征。 用黄瓜子叶生根法以及小麦芽鞘法,分别测试化合物的细胞分裂素活性和生长素活性。 结果表明,在10 mg/L浓度下,有4个化合物的子叶生根促进作用为46.9%~73.6%,比对参照物的细胞分裂活性更高,但生长素活性不明显,化合物5c仅提高25%;化合物的除草活性在68%~72%之间。 以石墨烯修饰的玻碳电极为工作电极,在Britton-Robison缓冲溶液中,研究了目标化合物电化学行为。 结果表明,在pH值为2或3的溶液中,合成目标化合物具有良好的氧化还原可逆性,氧化峰电流对数(lg Ipc)与扫描速度对数(lg v)、浓度对数(lg c)均呈现良好线性关系,目标化合物(5a~5d)的电子转移过程均受吸附-扩散混合控制,该类化合物的循环伏安法最低检出限为10-5 mol/L。 相似文献
85.
Laura García-Cansino María ngeles García María Luisa Marina 《Molecules (Basel, Switzerland)》2021,26(17)
The different activity and toxicity that the enantiomers of agrochemicals may have requires the development of stereoselective analytical methodologies enabling the individual determination of each enantiomer. The aim of this work was to develop the first Electrokinetic Chromatography methodology enabling the simultaneous enantiomeric separation of carfentrazone-ethyl herbicide and its hydrolysis metabolite carfentrazone. The use of an anionic cyclodextrin as chiral selector (captisol at 2.5% (w/v)) in a 25 mM acetate buffer, at a temperature of 30 °C, and an applied voltage (reverse polarity) of −30 kV, allowed the simultaneous separation of the four enantiomers of the two compounds studied in 6.8 min with enantiomeric resolutions of 5.0 for carfentrazone-ethyl and 5.1 for carfentrazone. Analytical characteristics of the developed method were evaluated and found adequate to achieve the quantitation of carfentrazone-ethyl and carfentrazone. Analysis of a commercial herbicide formulation showed the potential of the method for the quality control of these agrochemical products. Degradation studies for carfentrazone-ethyl revealed that no significant degradation took place in cleaned sand samples while a significant but not stereoselective degradation took place in soils for the whole period of time considered (seven days). 相似文献
86.
Summary A silica gel-bound, imprinted polymer for selective recognition of the diquat herbicide: 5,6-dihydropyrazino [1,2,3,4-lmn]-1,10-phenanthrolinium
dichloride, is reported. It was used in the solid-phase extraction procedure, following liquid chromatography-differential
pulse, adsorptive-stripping voltammetric (LC-DPAdSV) technique. The operational conditions for 100% retention of the diquat
herbicide on a chromatographic column (13.0×1.4 cm, adsorbent bed 1.0g) were realized at pH 6.9 and a flow rate of 5.0 mL
min−1. The adsorbent used could be regenerated during elution with 5.0 mL MHCl within 20 min. The limit of detection was 0.65 nM
(0.18 ppb) with an enrichment factor as high as 99-fold. 相似文献
87.
Lei Gao Peng Wang Zhongxiang Chen Qirui Hao Shuyan Bai Ningning Du Chenhui Li Xiaoli Huang Dongli Qin 《Electrophoresis》2022,43(13-14):1455-1465
In this study, we developed a new method combining thin-layer ultrasonic extraction, efficient SPE purification, ultra-performance liquid chromatography separation, and high-resolution mass spectrometry characterization for seven amide herbicides in fishery products. In sample preparation, to rapidly increase the contact area between the fish meat and the extractant, the fish meat was smeared on a glass slide. This process resulted in quickly reaching the extraction equilibrium and relatively high extraction efficiency. In data analysis, a strategy for characterization and qualitative analysis was constructed by analyzing the fragmentation of amide herbicides using product ion scans. Isomeric pretilachlor and butachlor were separated chromatographically, while the coeluting isomers, alachlor and acetochlor, could be separated by differences in the fragmentation of their selected precursor ions. This method overcame the challenge of poor dispersion in the extractant caused by the high viscosity of fish meat, and the challenge of separation and characterization for isomers. Compared with other methods, the extraction efficiency was improved and the amide herbicides in aquatic products was characterized and quantified rapidly and accurately. Moreover, the qualitative information was much greater and provided an additional strategy for analytes identification. This rapid and accurate method will benefit workers involved in monitoring fishery. 相似文献
88.
89.
高效液相色谱法分析快杀稗 总被引:4,自引:0,他引:4
In this paper,determination of quinclorac by reversedphase high performance liquid chromatographicmethod,using a Shim-Pack CLC-CN column and methanol-water(containing 0.5%CH_3COOH)(30:70)asmobile phase has been described,The method proved to be accurate and good in linear correlation. 相似文献
90.