全文获取类型
收费全文 | 998篇 |
免费 | 12篇 |
国内免费 | 56篇 |
专业分类
化学 | 859篇 |
力学 | 1篇 |
综合类 | 3篇 |
数学 | 8篇 |
物理学 | 195篇 |
出版年
2023年 | 6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 | 59篇 |
2008年 | 53篇 |
2007年 | 70篇 |
2006年 | 64篇 |
2005年 | 68篇 |
2004年 | 43篇 |
2003年 | 37篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 20篇 |
1999年 | 31篇 |
1998年 | 43篇 |
1997年 | 19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1066条查询结果,搜索用时 31 毫秒
1.
Tomáš Hložek Martin Štícha Miroslava Bursová Ivan Jelínek Petr Tůma Radomír Čabala 《Electrophoresis》2020,41(18-19):1564-1567
Riociguat is novel antihypertensive drug for treatment of pulmonary hypertension. As such, it is still being tested in many clinical and pharmacokinetic trials. Existing methods that determine serum riociguat and desmethylriociguat (DMR) are based solely on liquid chromatography with mass spectrometry. Therefore, we present a novel capillary electrophoresis with mass spectrometry method (CE-MS) for their determination in human serum as alternative method for ongoing trials. Complete resolution of both analytes was achieved by means of pH optimization of ammonium formate background electrolytes that are fully compatible with ESI/MS detection. Simple liquid-liquid extraction was used as sample pretreatment. The calibration dependence of the method was linear (in the range of 10–1000 ng/mL), with adequate accuracy (90.1–114.9%) and precision (13.4%). LOD and LOQ were arbitrarily set at 10 ng/mL for both analytes. Clinical applicability was validated using serum samples from patients treated with riociguat in pharmacokinetic study and the results corresponded with reference HPLC-MS/MS values. Capillary electrophoresis proved to be sensitive and selective tool for the analysis of riociguat and DMR. 相似文献
2.
The solubility of tricin in water and ethanol mixtures was measured over the temperature range of (288.15 to 328.15) K. The concentrations of tricin in the aqueous mixtures were assayed by the ultraviolet spectrophotometric method. The experimental solubility data indicated that the solubility of tricin increases with an increase in temperature and an enrichment in ethanol content. The two models, including the modified Apelblat equation and λh equation were used to correlate the experimental solubility data. The calculated solubility of tricin shows good agreement with the experimental results. Additionally, the estimation of thermodynamic properties including the activity coefficients, dissolution enthalpy, and entropy were obtained from the experimental data. Within the studied temperature range the dissolution process of tricin is endothermic, and the driving force is the entropy. 相似文献
3.
《Analytical letters》2012,45(10):1281-1287
Abstract Nitrite is determined by its reaction with a measured but excessive amount of pyridine-4-carboxylic acid hydrazide in acid medium (when the two substances react in a 1:1 molar ratio) and evaluation of the surplus hydrazide by titration with chloramine-T in the presence of acidified potassium bromide, the end-point being shown by the decolorization of the methyl red indicator. Nitrate, copper(II), mercury(II), etc. are found not to interfere, and the determination of nitrite in the presence of diazotized aromatic amines is demonstrated. 相似文献
4.
Zucheng Wu Ying Sing Fung 《International journal of environmental analytical chemistry》2013,93(7):431-442
The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water. 相似文献
5.
Mohammed A. Al-Nuri Nidal A. Za'tar Maher A. Abu-Eid Mohammad A. Hannoun Waheed J. Al-Jondi Ahmad I. Hussein 《光谱学快报》2013,46(8):1539-1543
A new method for isolation and specrophotometric determination of emodin is presented. Emodin was isolated by thin layer chromatography (tlc) and column chromatography (cc) techniques, as an orange long crystalline substance. Emodin exhibits two absorption maxima, at 420 and 520 nm. Stability of the color and the effect of pH were studied. Beer's law is obeyed in the range 2–30 ppm. The method is applied to the determination of emodin in roots, stems, and leaves of Rumex cyprius plant. 相似文献
6.
《Analytical letters》2012,45(14):2939-2950
ABSTRACT The solid surface fluorimetry (SSF) for the determination of 6-thioguanine (6-TG) has been presented. Several experimental conditions such as the type of solid substrate, pH of the medium, rigidity state of substrate, drying condition etc. were optimized. The new and highly sensitive procedure has a linear range of 3.3~668.6ng/spot with the correlation coefficient 0.999, the relative standard deviation (RSD) 3.16% and the limit of detection 0.47 ng/spot corresponding to three times the standard deviation of the blank (n=11). The recovery of standard 6-TG added to urine was over the range of 97.4-107.4%. The method is simple, rapid and sensitive and can be applied to analysis of urine without interference. 相似文献
7.
《Analytical letters》2012,45(18):2892-2904
A spectrofluorimetric method has been developed for trace amount of aluminum(III) by using a novel Schiff base, N,N′-bis(salicylidene)-1,4-diaminobuthane (BUTAS), and 4-methyl-2-aminophenol (OAP). Since the aluminum complexes are generally fluorescent, aluminum(III) increases the fluorescence intensity of BUTAS-OAP by formation of Al-BUTAS-OAP complex. The fluorescence of the complex is measured at an excitation wavelength of 410 nm with an emission at 526 nm. Aluminum(III) can be detected within a concentration limit of 0.11–1.62 ppb and the lowest detection limit being 0.07 ppb. The proposed method was applied to diluted hemodialysis solution and spectrofluorimetric data was compared with data of standard pharmacopoeia method. 相似文献
8.
9.
10.
《Arabian Journal of Chemistry》2020,13(9):7147-7159
In this study, silica@chitosan-glutaraldehyde (Si@Cs-G) was synthesized as a novel adsorbent for extraction of Penicillin G (PG) from the synthetic and real samples followed by HPLC determination. The synthesized adsorbents were characterized by the scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM) and nitrogen adsorption–desorption techniques. The factors influencing the extraction efficiency including pH, sorbent dose, extraction time, extraction solvent type and its volume were investigated and optimized.Under the optimal conditions (sorbent dosage: 25 mg, desorption solvent (acetonitrile) with volume of 0.75 mL; pH: 6 and extraction time: 50 min), the Si@Cs-G demonstrated high efficiency and linearity (R2 > 0.999) with the concentration of penicillin G ranging from 1 to 300 μg L−1. Extraction recovery in synthetic samples was 98.977%, with LOD = 0.493 μg L−1, LOQ = 1.638 μg L−1 and RSD < 1.953%. The method was successfully applied for determination of PG in real water samples (tap, river, lake and well water) and wastewater samples (SH and SHB hospital effluent). The obtained relative recoveries were in the range of 91.31% -123.27% with RSD less than 6.34% for all the real samples. The dominant mechanism in the PG adsorption process was involved in the π-π interaction, hydrogen bonding, and electrostatic interaction. 相似文献