全文获取类型
收费全文 | 301篇 |
免费 | 20篇 |
国内免费 | 16篇 |
专业分类
化学 | 222篇 |
晶体学 | 2篇 |
力学 | 7篇 |
综合类 | 4篇 |
数学 | 42篇 |
物理学 | 60篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 13篇 |
2021年 | 10篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 28篇 |
2012年 | 28篇 |
2011年 | 25篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 13篇 |
2007年 | 20篇 |
2006年 | 7篇 |
2005年 | 10篇 |
2004年 | 10篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 8篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1981年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有337条查询结果,搜索用时 15 毫秒
71.
72.
酚藏花红与DNA作用的共振光散射特征及微量DNA的光散射测定 总被引:17,自引:0,他引:17
研究了酚藏花红与脱氧核糖核酸在近中性条件下作用中的共振光散射特征,并以此建立起纳克级核酸的分析方法。考察了影响因素和最佳反映条件,建立了用RLS光谱测定纳克级DNA的新方法。 相似文献
73.
介绍自我设计的一种实验仪器和偏振光实验仪结合使用,根据光的折射定律和光的全反射规律来测定透明液体的折射率。又用此实验方法实际测量蒸馏水的折射率,进行实验数据处理和分析。 相似文献
74.
基于介质阻挡放电(DBD)原理和结构,建立了适用于原子荧光光谱仪(AFS)的低温等离子体小型原子化器(Atomizer),并研究了氢化物发生-低温等离子体原子化器-原子荧光光谱(HG-DBDAtomizer-AFS)测定环境样品中痕量碲(Te)的分析方法。DBD等离子体原子化器具有小型、低温等优点。对DBD放电结构和放电功率、载气气体流速,氢化物发生过程中的酸度、KBH4浓度,以及观测高度等实验条件进行了详细的考察并优化。本系统测定Te的检出限(3σ)为0.08μg/L;线性范围为0.5~80μg/L;测定精密度为2.1%(n=7);加标回收率为90%~103%。对国家级标准样品(GBW07404,GBW07405,GBW07406)进行测定,测定结果与标准值一致,证明本方法准确可行。 相似文献
75.
Three new diterpenoids with jatrophane‐type skeleton, sororianolides A–C ( 1 – 3 , resp.), were isolated from Euphorbia sororia. The identification and structure elucidation of these compounds were based on 1D‐ and 2D‐NMR‐spectral data analysis. It was the first time to isolate diterpenoids in this species. 相似文献
76.
Cycloaddition of 3-carbomethoxy-2H-pyran-2-one to a vinylated sugar followed by the loss of bridging CO(2) from the cycloadduct affords a cyclohexadiene which can be manipulated to a carbasugar-sugar pseudodisaccharide. 相似文献
77.
Guan-Ping Yu Wen-Zhao Bi Guo-Dong Si Ya-Xun Yang Haji Akber Aisa Liang-Zhong Xu 《Structural chemistry》2009,20(4):569-576
A series of 1-[(1,3,4-thiadiazol-2-yl)methyl]-1H-1,2,4-triazole derivatives were prepared and evaluated for their antifungal
activities. The chemical structures of these compounds were determined by means of elemental analyses, 1H NMR, and X-ray crystallography. Quantitative structure–activity relationship (QSAR) studies were performed on these compounds
using physicochemical parameters as independent parameters and antifungal activity as a dependent parameter, where antifungal
activity correlated best (r > 0.9) with hydrophobic parameters (π) and indicator (H). Moreover, the results are interpreted on the basis of a multiple regression model. The model has been internally and externally
validated. Furthermore, the domain of applicability which indicates the area of reliable predictions is defined. 相似文献
78.
Mahsa Fatehi Mahmood Haji Shaabani Derek Thompson 《Complex Analysis and Operator Theory》2018,12(7):1767-1778
In this paper, we study quasinormal and hyponormal composition operators \(W_{\psi ,\varphi }\) with linear fractional compositional symbol \(\varphi \) on the Hardy and weighted Bergman spaces. We characterize the quasinormal composition operators induced on \(H^{2}\) and \(A_{\alpha }^{2}\) by these maps and many such weighted composition operators, showing that they are necessarily normal in all known cases. We eliminate several possibilities for hyponormal weighted composition operators but also give new examples of hyponormal weighted composition operators on \(H^2\) which are not quasinormal. 相似文献
79.
冷原子荧光光谱法测定海产品中痕量镉 总被引:2,自引:0,他引:2
建立了氢化物发生-冷原子荧光光谱法测定海产品中镉(Cd)的分析方法,研究了硫脲-抗坏血酸-Co(Ⅱ)体系经KBH4还原产生Cd挥发性组分。对实验条件如载气流速、屏蔽气流速、原子化器高度、硫脲-抗坏血酸浓度、KBH4浓度及HCl浓度等进行了优化。在最优条件下,对海藻、紫菜等海产品中痕量Cd的含量进行测定。本方法中Cd的检出限为0.005μg/L,线性范围为0.02~20.0μg/L,实际样品加标回收率为94%~101%。对海藻和紫菜等国家一级标准物质进行测定,结果与标准值相符。 相似文献
80.
Yang Y Zhao Y Gu D Ayupbek A Huang Y Dou J Ito Y Zhang T Aisa HA 《液相色谱法及相关技术杂志》2010,33(16):1502-1515
An effective high-speed countercurrent chromatography (HSCCC) method was established for further separation and purification of four minor flavonols in addition to five major flavonols which were reported by our previous study from extracts of Flos Gossypii. HSCCC was performed with three two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water (7.5:15:6:7, v/v), (2.5:15:2:7, v/v) and (0:1:0:1, v/v). The separation was repeated 3 times, and 3.8 mg of 8-methoxyl-kaempferol-7-O-β-D-rhamnoside (HPLC purity 98.27%), 6.7 mg of astragalin (HPLC purity 94.18%), 3.3 mg of 4'-methoxyl-quercetin-7-O-β-D-glucoside (HPLC purity 94.30%) and 8.2 mg of hyperoside (HPLC purity 93.48%) were separated from 150 mg of the crude sample. The chemical structures of the flavonols were confirmed by MS, (1)H NMR and (13)C NMR. Meanwhile, the results indicated that the target compound with smaller K value (<0.5) can be separated by increasing column length of HSCCC. And four separation rules of flavonols according to the present study and references were summarized, which can be used as a useful guide for separation of flavonols by HSCCC. 相似文献