全文获取类型
收费全文 | 2872篇 |
免费 | 32篇 |
国内免费 | 195篇 |
专业分类
化学 | 2765篇 |
晶体学 | 9篇 |
综合类 | 78篇 |
物理学 | 247篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 23篇 |
2021年 | 26篇 |
2020年 | 15篇 |
2019年 | 25篇 |
2018年 | 24篇 |
2017年 | 37篇 |
2016年 | 34篇 |
2015年 | 40篇 |
2014年 | 47篇 |
2013年 | 128篇 |
2012年 | 299篇 |
2011年 | 85篇 |
2010年 | 71篇 |
2009年 | 71篇 |
2008年 | 99篇 |
2007年 | 126篇 |
2006年 | 126篇 |
2005年 | 142篇 |
2004年 | 159篇 |
2003年 | 124篇 |
2002年 | 131篇 |
2001年 | 125篇 |
2000年 | 128篇 |
1999年 | 140篇 |
1998年 | 133篇 |
1997年 | 107篇 |
1996年 | 122篇 |
1995年 | 95篇 |
1994年 | 77篇 |
1993年 | 68篇 |
1992年 | 75篇 |
1991年 | 42篇 |
1990年 | 42篇 |
1989年 | 42篇 |
1988年 | 21篇 |
1987年 | 7篇 |
1986年 | 17篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有3099条查询结果,搜索用时 7 毫秒
991.
S. A. Abbasi 《International journal of environmental analytical chemistry》2013,93(3):173-184
Abstract Zinc (II) was selectively extracted from aqueous solutions of pH 7.8–8.5 into chloroform with N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA). 1-(2-pyridylazo)-2-naphthol (PAN) or 2-[(5-nitro-2-pyridyl)azo]-1-naphthol (NPAN) were added to the extract to form intensely coloured ternary complexes measurable spectrophotometrically at 550 nm (? = 6.03 × 104 1 mol?1 cm?1) and 625 nm (? = 8.15 × 104 mol?1 cm?1) respectively. For atomic absorption spectrometric analysis, methyl isobutyl ketone (MIBK) was used as extracting solvent instead of chloroform and the zinc-MFHA-MIBK extract was aspirated directly into an air-acetylene flame. The absorbance was measured at the 213.9 nm resonance line with a detection limit of 0.05 ppb, which was significantly better than the limit of 1.0 ppb achieved for zinc previously with flame AAS. The method tolerated a large number of anions and cations normally occurring with zinc in environmental samples, and was applied to the trace analysis of zinc in alloys, coal, plant tissues, animal tissues and natural waters. The combinations of MFHA and PAN/NPAN were chosen from eleven hydroxamic acids and nine pyridylazo reagents as detailed in the paper. 相似文献
992.
《Analytical letters》2012,45(12):2341-2353
Abstract A simple method for direct determination of Zn2+ by spectrophotometry using dithizone in micellar solutions is possible. Surfactants are used to overcome the solubility problems of dithizone in aqueous medium. The proposed method saves time and chemicals and is of extremely high sensitivity. Zn2+ concentrations of about 2×10-7 M can be determined. The important analytical parameters and their effects on the reported system are investigated. 相似文献
993.
《Analytical letters》2012,45(5):814-822
UV-Vis spectrophotometry and multivariate calibration model, Principal Components Regression (PCR), were used for individual and simultaneous quantification of ternary mixtures of reactive dyes (Yellow Procion HE4R, Navy Blue Procion HER, and Blue Procion HEGN) in a sample of industrial effluent and effluents obtained in the laboratory. A Centroid-Simplex-type experimental design was used. The percentages of the dyes Yellow Procion HE4R, Navy Blue Procion HER, and Blue Procion HEGN not fixed to the fiber in the industrial dyeing process and laboratory scale were 47.40%, 10.99%, 24.72% and 4.20%, 46.06%, 32.04%, respectively. 相似文献
994.
《Analytical letters》2012,45(12):2143-2152
Abstract A simple and reproducible spectrophotometric method for the assay of ceftazidime with neocuproin-copper(II) reagent has been developed. The procedure is based on the drug in an acidic medium, subsequent formation of yellow ternary complex in citrate buffer solution (pH 4.2), and measurement at 454 nm. Beer's law is obeyed in the range 15.0–40.0 µg mL?1 with correlation coefficient r 2 = 0.9995. The procedure holds good accuracy and precision when applied to the analysis of ceftazidime in powder for injection with good recovery percent ranging from 100.17±1.0 without interference from additives. 相似文献
995.
《Analytical letters》2012,45(7-8):837-843
Abstract In this paper we devise a numerical method for the evaluation of acidity constants of single equilibria suitable for use when the limit absorbance of the pure species are unavailable since these species cannot be obtained pure in solutions. The method has been applied to the evaluation of the first acidity constant of methylglyoxal bis (4-pheny1-3-thiosemicarbazone) (MGBPT). 相似文献
996.
A. Hermann 《Isotopes in environmental and health studies》2013,49(3):89-98
Recent achievements of the most important methods of spent nuclear fuel analysis (mass spectrometry, gamma spectrometry, alpha spectrometry, spectrophotometry, X-ray fluorescence) are briefly reviewed. Especial emphasis is given to burnup determination and to the valuable output of spent fuel composition studies for the calibration of burnup calculation models and for nuclear safeguards (isotope correlation techniques). 相似文献
997.
《Analytical letters》2012,45(14):2975-2982
ABSTRACT Two methods for the simultaneous determination of Sunset Yellow and Ponceau 4R in gelatin powders by first derivative spectrophotometry and by partial least-squares multivariate spectrophotometric calibration are described. These procedures do not require any separation step. These methods were applied to determine both colorants in commercial gelatin powders and the results obtained were compared. A good statistical agreement was obtained between the results. 相似文献
998.
《Analytical letters》2012,45(7):1275-1288
Abstract A new method for determining the binary mixtures of procaine penicillin G and benzathine penicillin G using “zero-crossing” second derivative spectrophotometry is described. Calibration graphs were linear up to 8.80 10?5 M for procaine penicillin G and 4.40 10?5 M for benzathine penicillin G. The method was realized in ethanol/water medium (30 % v/v). A complete and exhaustive statistical analysis of the experimental data was realized to demonstrate the validity of method. The method was applied for determining procaine penicillin G and benzathine penicillin G synthetic mixtures with good results. The procedure does not require any separation step. 相似文献
999.
室温下,硒(IV)与邻苯二胺配位生成黄色配合物,用环己烷萃取后,在最大吸收波长330nm处测定其吸光度。实验结果表明:硒含量在4~20 μg/mL内线性关系良好,线性方程Y=0.1999C-0.0011(R=0.9995)。最优化条件下测定硒盐中硒的含量取得满意结果。该法操作简单,设备和药品价格低廉,准确度高,稳定性好,适宜于基层实验室对食品中微量元素硒的检验。 相似文献
1000.
建立了以紫尿酸为显色剂测定盐酸氯丙嗪的光度法。在弱酸性条件下,Fe(Ⅲ)被盐酸氯丙嗪定量还原成Fe(Ⅱ),Fe(Ⅱ)在碱性条件下与紫尿酸反应形成不稳定的蓝色配阴离子,该配阴离子与盐酸氯丙嗪形成稳定的蓝色离子缔合物,该离子缔合物的最大吸收波长位于635 nm,其表观摩尔吸光系数ε=2.62×104 L/(mol·cm),盐酸氯丙嗪质量浓度在0.5~10.0 mg/L范围内与体系的吸光度呈良好的线性关系,线性相关系数为0.999 2。测定结果的相对标准偏差为1.02%~2.65%(n=5),加标回收率为91.0%~95.0%。该法灵敏度较高、选择性及重现性良好,可用于片剂中盐酸氯丙嗪含量的测定。 相似文献