全文获取类型
收费全文 | 994篇 |
免费 | 10篇 |
国内免费 | 56篇 |
专业分类
化学 | 854篇 |
力学 | 1篇 |
综合类 | 3篇 |
数学 | 8篇 |
物理学 | 194篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 17篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 41篇 |
2012年 | 132篇 |
2011年 | 41篇 |
2010年 | 32篇 |
2009年 | 58篇 |
2008年 | 52篇 |
2007年 | 69篇 |
2006年 | 64篇 |
2005年 | 68篇 |
2004年 | 43篇 |
2003年 | 37篇 |
2002年 | 32篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 30篇 |
1998年 | 44篇 |
1997年 | 18篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 28篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1060条查询结果,搜索用时 21 毫秒
141.
基于棉涤线进样通道、过滤区、检测区和"开关元件",研制了一种新型3D纸基微流控分析器件,并应用于食盐中IO-3的测定。实验探讨并优化了该器件的制备和测定条件。在优化的测定条件下,显色测定灰度值与IO-3浓度在5~250μmol/L范围内呈线性关系,检出限为2.3μmol/L。该方法可应用于实际样品中IO-3的测定。 相似文献
142.
Rapid and Sensitive Determination of Dinotefuran Residue Based on Electrochemical Enhancement of β‐cyclodextrin‐Graphene Composite 下载免费PDF全文
A rapid method for sensitive voltammetric determination of dinotefuran residue was reported. The proposed method was based on the electrocatalytic reduction of dinotefuran on β‐cyclodextrin‐graphene composite modified glassy carbon electrode (β‐CD‐rGO/GCE), giving rise to a higher reduction signal to dinotefuran relative to the bare (GCE) and graphene modified electrode (rGO/GCE). Moreover, a further signal enhancement was observed when the modified electrode incubated in solution at low temperature (0 °C) for a short time. The reduction mechanism and binding affinity were also discussed. The external standard calibration curve was obtained from linear sweep voltammetry in the range of 0.5 to 16.0 μM with a detection limit of 0.10 μM. In addition to optimization of pretreatment, this electrochemical method has been applied to the dinotefuran residue determination in millet samples with the detection limit of 0.01 mg kg?1 and compared with an high performance liquid chromatography method. The proposed electrode and analysis methods were proven to be sensitive, accurate and rapid under the used conditions. 相似文献
143.
Flow injection (FI) methodology, using diffuse reflectance in the visible region of the spectrum, for the analysis of nickel, precipitated in the form of dimethylglyoximate, is presented. A reflectance cell, constructed in polytetrafluoroethylene, using a LED (light emitting diode) as light source and a LDR (light dependent resistor) as detector, is described. The analytical signal (S) correlates with nickel concentration (C) between 1.6 × 10−4 and 6.6 × 10−4 mol L−1. This correlation is described by the equation S = −1.108 + 3.314 × 104C − 2.081 × 107C2 (r = 0.9996). The experimentally observed limit of detection is about 1.3 × 10−4 mol L−1, as in lower concentrations the formation of precipitate is not observed. The experimental quantitation limit is about 1.6 × 10−4 mol L−1. The mean R.S.D. (relative standard deviation) is about 2.7%. Samples containing nickel were analyzed and the results obtained in this method were compared with those of other methods using the statistical Student's t-test. 相似文献
144.
Determination of drugs of abuse in blood is of great importance in clinical and forensic toxicology. This review describes
procedures for detection of the following drugs of abuse and their metabolites in whole blood, plasma or serum: Δ9-tetrahydrocannabinol,
11-hydroxy-Δ9-tetrahydrocannabinol, 11-nor-9-carboxy-Δ9-tetrahydrocannabinol, 11-nor-9-carboxy-Δ9-tetrahydrocannabinol glucuronide,
heroin, 6-monoacetylmorphine, morphine, morphine-6-glucuronide, morphine-3-glucuronide, codeine, amphetamine, methamphetamine,
3,4-methylenedioxymethamphetamine, N-ethyl-3,4-methylenedioxyamphetamine, 3,4-methylenedioxyamphetamine, cocaine, benzoylecgonine, ecgonine methyl ester, cocaethylene,
other cocaine metabolites or pyrolysis products (norcocaine, norcocaethylene, norbenzoylecgonine, m-hydroxycocaine, p-hydroxycocaine, m-hydroxybenzoylecgonine, p-hydroxybenzoylecgonine, ethyl ecgonine, ecgonine, anhydroecgonine methyl ester, anhydroecgonine ethyl ester, anhydroecgonine,
noranhydroecgonine, N-hydroxynorcocaine, cocaine N-oxide, anhydroecgonine methyl ester N-oxide). Metabolites and degradation products which are recommended to be monitored for assessment in clinical or forensic
toxicology are mentioned. Papers written in English between 2002 and the beginning of 2007 are reviewed. Analytical methods
are assessed for their suitability in forensic toxicology, where special requirements have to be met. For many of the analytes
sensitive immunological methods for screening are available. Screening and confirmation is mostly done by gas chromatography
(GC)–mass spectrometry (MS) or liquid chromatography (LC)–MS(/MS) procedures. Basic information about the biosample assayed,
internal standard, workup, GC or LC column and mobile phase, detection mode, and validation data for each procedure is summarized
in two tables to facilitate the selection of a method suitable for a specific analytic problem. 相似文献
145.
Pejić N Blagojević S Anić S Kolar-Anić L 《Analytical and bioanalytical chemistry》2007,389(6):2009-2017
A simple and reliable method for the determination of ascorbic acid (AA) is proposed and validated. It is based on potentiometric
monitoring of the concentration perturbations of an oscillatory reaction system in a stable nonequilibrium stationary state
close to the bifurcation point. The response of the Bray–Liebhafsky (BL) oscillatory reaction as a matrix, to the perturbation
by different concentrations of AA, is followed by a Pt electrode. The linear relationship between maximal potential shift
and the logarithm of the amount of AA is obtained between 0.01 and 1.0 μmol. The sensitivity of the proposed method (as the
limit of detection) is 0.009 μmol and the method has excellent sample throughput (30 samples per hour). The procedure was
used for AA determination in pharmaceutical formulations and urine. The results are in agreement with those obtained using
the official method. Some aspects of the possible mechanism of AA action on the BL oscillating chemical system are discussed. 相似文献
146.
A sensitive fluorimetric method for determination of phytic acid in human urine samples was described. The method was based on a fluorimetric replacement reaction, in which the added phytic acid replaced the Cu2+ ion from Cu2+-gelatin complex, liberating the fluorescent gelatin molecule. The fluorescence of the solution was accordingly recovered proportionally to the amount of the foreign phytic acid. The excitation wavelength was 273.5 nm and the characteristic emission wavelength was 305.0 nm, respectively. The calibration graph was obtained by plotting the recovered fluorescent intensity at maximum 305.0 nm against the added standard phytic acid, and was divided into two sections. One section was linear over the range of 0.40-2.40 mg L−1 with a linear regression equation of If = −0.895 + 15.146c (R2 > 0.9993), and the other over the range of 2.40-9.20 mg L−1 with a linear regression equation of If = −29.526 + 26.113c (R2 > 0.9996), respectively. The relative standard deviation (R.S.D.) at 95% confidence degree for a 2.0 mg L−1 of standard phytic acid within 1 month was less than 1.26% (n = 5), indicating the procedure is reproducible. The detection and the quantification limits of phytic acid were estimated to be 0.23 and 0.40 mg L−1, respectively. The proposed method was applied to the determination of phytic acid in urine samples and the found concentrations of phytic acid in urine were in the range of 0.49-0.75 mg L−1 with recoveries of 96.2-108.8%. Comparison of the obtained results with the reported HPLC was performed, indicating the proposed method was reliable. 相似文献
147.
探讨了HELP法在水中酚类色谱重叠峰的分辨与定性定量分析中的应用.实验结果表明,各组分浓度比为1:50的范围内分辨光谱与真实光谱十分吻合.在10-4~10-6g/mL的浓度范围内分辨色谱的定量结果线性关系良好.分辨下限3.0×10-7g/mL,相对标准偏差为5.0%. 相似文献
148.
对甲基二溴偶氮胂的合成及其与稀土显色反应的研究 总被引:9,自引:1,他引:8
本文报道了对甲基二溴偶氮胂的合成,该显色剂在酸性介质中与稀土元素产生高灵敏度显色反应,大多数常见元素不干扰,所拟分析方法已成功地应用于小麦和铝合金中稀土总量的测定 相似文献
149.
Introduction Flavonoids usually exist in the form of glycoside in nature. Different kinds of sugar and aglycone moieties will lead to different physiological activities.The natural flavonoid Dglycosides are usually β-anomers. 相似文献
150.
氟离子选择性电极测磷化液中氟化钠 总被引:1,自引:0,他引:1
利用F^-选择性电极,建立了测定磷化液中F^-含量的有效方法,线性范围为0.5 ̄5×10^-6mol·L^-1,回收率在87% ̄111%之间。方法简便,快速,准确,可用于磷化槽中磷化液的快速调整。 相似文献