全文获取类型
收费全文 | 941篇 |
免费 | 61篇 |
国内免费 | 63篇 |
专业分类
化学 | 784篇 |
晶体学 | 1篇 |
力学 | 16篇 |
综合类 | 2篇 |
物理学 | 17篇 |
综合类 | 245篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 14篇 |
2021年 | 26篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 30篇 |
2016年 | 32篇 |
2015年 | 40篇 |
2014年 | 33篇 |
2013年 | 38篇 |
2012年 | 108篇 |
2011年 | 49篇 |
2010年 | 35篇 |
2009年 | 61篇 |
2008年 | 51篇 |
2007年 | 82篇 |
2006年 | 51篇 |
2005年 | 74篇 |
2004年 | 38篇 |
2003年 | 43篇 |
2002年 | 23篇 |
2001年 | 19篇 |
2000年 | 25篇 |
1999年 | 20篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1065条查询结果,搜索用时 15 毫秒
991.
992.
A carbon paste electrode was used for the electrochemical determination of linuron concentrations in water and vegetable extracts. Optimal conditions were established with respect to electrode activation (electrochemical pretreatment), time accumulation, potential accumulation, scan rate, and pH. The limit of detection achieved with a pre-concentration step was 23.0 μg L−1. Recovery measurements in vegetable extract and natural water samples were in the range of 98-103%, indicating that the proposed electrochemical method can be employed to analyze linuron in these matrices. The determination results were in good agreement with HPLC results. 相似文献
993.
超高效液相色谱-串联质谱法快速检测番茄酱中吡虫啉等6种农药残留 总被引:4,自引:0,他引:4
建立了番茄酱中吡虫啉、多菌灵、甲基硫菌灵、霜霉威、灭多威和烯酰吗啉等农药残留的超高效液相色谱-串联质谱(UPLC-MS/MS)检测方法。样品用含0.1%(体积分数)乙酸的甲醇-水(1:1, v/v)混合溶液提取,采用Waters Acquity UPLC BEH C18色谱柱,以甲醇和10 mmol/L乙酸铵溶液为流动相进行梯度洗脱分离,经电喷雾正离子(ESI+)电离及多反应监测(MRM)模式来测定目标化合物,采用基质标准溶液曲线法进行定量。结果表明: 6种农药在0.005~0.2 mg/L的范围内线性关系良好(r>0.995);当标准添加水平为0.02、0.05和0.2 mg/kg时,回收率为66.8%~102.9%;相对标准偏差均小于15%; 6种农药的定量限(以信噪比(S/N)>10计)均为0.02 mg/kg。该方法简便、快速、灵敏和准确,非常适合番茄酱中这6种农药残留的快速检测及定量分析。 相似文献
994.
本文制备了离子液体-Ni微/纳米粒子修饰碳糊电极.研究了离子液体对Ni微/纳米粒子氧化还原的促进作用,用循环伏安法在0.1 mol/L B-R缓冲溶液(pH=4.5)中研究了维生素B2(VB2)在该修饰电极上的电化学行为,优化了各种实验条件.实验结果表明,本文制备的修饰电极能很好地催化氧化VB2,VB2在该修饰电极上的... 相似文献
995.
N‐(3,4‐dihydroxyphenethyl)‐3,5‐dinitrobenzamide modified multiwall carbon nanotubes paste electrode was used as a voltammetric sensor for oxidation of penicillamine (PA), uric acid (UA) and tryptophan (TP). In a mixture of PA, UA and TP, those voltammograms were well separated from each other with potential differences of 300, 610, and 310 mV, respectively. The peak currents were linearly dependent on PA, UA and TP concentrations in the range of 0.05–300, 5–420, and 1.0–400 µmol L?1, with detection limits of 0.021, 2.0, and 0.82 µmol L?1, respectively. The modified electrode was used for the determination of those compounds in real samples. 相似文献
996.
Mohammad Bagher Gholivand Behrooz Geravandi Mohammad Hadi Parvin 《Electroanalysis》2011,23(6):1345-1351
A differential pulse anodic stripping voltammetric procedure was developed for the determination of trace amounts of iron(II) in the presence of iron(III) at a carbon paste electrode (CPE) modified with dithiodianiline and gold nanoparticle. At the pH working of 3.0, a wide concentration range from 0.1 nM to 100 nM was observed with the detection limit of 0.05 nM. The relative standard deviation for a solution containing 50 nM of iron(II) was found to be 3.11 % (n=9). Possible interferences from the coexisting ions were also investigated. The validity of the method and applicability of the sensor were successfully tested by determining of iron(II) in lentil, wheat seed and barley seed samples. 相似文献
997.
A novel strategy for preparing highly sensitive and easily renewable molecularly imprinted polymer (MIP) sensors was proposed. Using melamine (MA) as the template molecule, MIP particles were synthesized and embedded in a solid paraffin carbon paste to prepare the MIP sensor. MA was indirectly determined from the competition between the reactions of MA and horseradish peroxidase-labeled MA (MA-HRP) with the vacant cavities. The detection signals were amplified because of enzymatic reaction to the H2O2 catalytic oxidation. Sensitivity was markedly improved. Sensor renewal was achieved by a simple mechanical polishing of the sensitive film. The linear range for MA detection was 0.005–1 μmol L−1 and the detection limit was 0.7 nmol L−1. The molecularly imprinted solid paraffin carbon paste sensor was used for MA detection in milk samples. 相似文献
998.
膏体流变学的研究是矿业浆体流变学的热点和难点。膏体技术包括脱水、搅拌、输送、堆存(充填)4个阶段,均涉及到非牛顿流体流变特性。在脱水阶段,全尾砂的压缩屈服应力影响了尾砂浆的脱水浓度,浓度是剪切屈服应力的宏观表现,继而影响了混合搅拌和管道输送过程中浆体的剪切屈服应力。所以,压缩屈服应力和剪切屈服应力之间的关系成为了膏体充填技术领域中的关键问题。在压滤理论指导下,开展相关实验,提出了全浓度范围内床层脱水阻力和浆体输送性能表征方法,以表征全尾砂浆的可浓密性能。对全尾砂高压力作用下的可浓密性能进行测试,得到高压力下全尾砂浆体的压缩屈服应力;使用控制剪切速率法(CSR)操作桨式流变仪检测剪切屈服应力;继而得到两者之间的关系为:浆体屈服应力为剪切应力,压缩屈服应力为压缩应力;浆体的压缩屈服应力、剪切屈服应力与浓度指数均呈指数关系。并且压缩屈服应力远大于剪切屈服应力,因此剪切作用更易破坏絮团,是脱水的主要外部动力,从而解释了搅拌脱水的力学机理。 相似文献
999.
Sayed Mehdi Ghoreishi Mohsen Behpour Mahshid Golestaneh 《International journal of environmental analytical chemistry》2013,93(12):1403-1416
In this paper, a simple, convenient and sensitive electrochemical method has been developed for the determination of C.I. Direct Red 80. A gold nanoparticle modified carbon paste electrode was fabricated and used for study and sensitive determination of Direct Red 80 by cyclic voltammetry and differential pulse voltammetry. The overall analysis involved a two-step procedure: an accumulation step under open-circuit conditions, followed by voltammetric measurements of Direct Red 80 in a 0.1?M phosphate buffer solution at pH?=?3.0. The experimental conditions, such as the medium, pH and accumulation time, were optimised. The oxidation peak current was proportional to the concentration of Direct Red 80 from 5.0?×?10?8 to 5.0?×?10?7?M and 5.0?×?10?7 to 3.0?×?10?6?M, and the detection limit was 1.15?×?10?8?M (S/N?=?3). The proposed method was used to detect Direct Red 80 in natural water and sewage with good accuracy. 相似文献
1000.
Ali A. Ensafi Hassan Karimi-Maleh M. Keyvanfard 《International journal of environmental analytical chemistry》2013,93(6):650-660
The electrochemical response of a modified-carbon nanotubes paste electrode with p-aminophenol was investigated as an electrochemical sensor for sulfite determination. The electrochemical behaviour of sulfite was studied at the surface of the modified electrode in aqueous media using cyclic voltammetry and square wave voltammetry. It has been found that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurs at a potential about 680?mV less positive than that of an unmodified-carbon nanotubes paste electrode. Under the optimized conditions, the electrocatalytic peak current showed linear relationship with sulfite concentration in the range of 2.0?×?10?7–2.8?×?10?4?mol?L?1 with a detection limit of 9.0?×?10?8?mol?L?1 sulfite. The relative standard deviations for ten successive assays of 1.0 and 50.0?µmol?L?1 sulfite were 2.5% and 2.1%, respectively. Finally, the modified electrode was examined as a selective, simple and precise new electrochemical sensor for the determination of sulfite in water and wastewater samples. 相似文献