全文获取类型
收费全文 | 16242篇 |
免费 | 754篇 |
国内免费 | 181篇 |
专业分类
化学 | 11787篇 |
晶体学 | 138篇 |
力学 | 727篇 |
综合类 | 5篇 |
数学 | 2056篇 |
物理学 | 2464篇 |
出版年
2024年 | 30篇 |
2023年 | 123篇 |
2022年 | 734篇 |
2021年 | 733篇 |
2020年 | 577篇 |
2019年 | 674篇 |
2018年 | 662篇 |
2017年 | 545篇 |
2016年 | 906篇 |
2015年 | 618篇 |
2014年 | 786篇 |
2013年 | 1610篇 |
2012年 | 1182篇 |
2011年 | 1168篇 |
2010年 | 802篇 |
2009年 | 660篇 |
2008年 | 771篇 |
2007年 | 719篇 |
2006年 | 531篇 |
2005年 | 519篇 |
2004年 | 363篇 |
2003年 | 347篇 |
2002年 | 302篇 |
2001年 | 136篇 |
2000年 | 118篇 |
1999年 | 106篇 |
1998年 | 73篇 |
1997年 | 98篇 |
1996年 | 91篇 |
1995年 | 66篇 |
1994年 | 79篇 |
1993年 | 54篇 |
1992年 | 69篇 |
1991年 | 66篇 |
1990年 | 72篇 |
1989年 | 64篇 |
1988年 | 56篇 |
1987年 | 64篇 |
1986年 | 57篇 |
1985年 | 73篇 |
1984年 | 52篇 |
1983年 | 38篇 |
1982年 | 50篇 |
1981年 | 38篇 |
1980年 | 40篇 |
1979年 | 37篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1976年 | 25篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Inas A. Abdallah Sherin F. Hammad Alaa Bedair Mohamed A. Abdelaziz Neil D. Danielson Ahmed H. Elshafeey Fotouh R. Mansour 《Biomedical chromatography : BMC》2022,36(6):e5365
Favipiravir is a potential antiviral medication that has been recently licensed for Covid-19 treatment. In this work, a gadolinium-based magnetic ionic liquid was prepared and used as an extractant in dispersive liquid–liquid microextraction (DLLME) of favipiravir in human plasma. The high enriching ability of DLLME allowed the determination of favipiravir in real samples using HPLC/UV with sufficient sensitivity. The effects of several variables on extraction efficiency were investigated, including type of extractant, amount of extractant, type of disperser and disperser volume. The maximum enrichment was attained using 50 mg of the Gd-magnetic ionic liquid (MIL) and 150 μl of tetrahydrofuran. The Gd-based MIL could form a supramolecular assembly in the presence of tetrahydrofuran, which enhanced the extraction efficiency of favipiravir. The developed method was validated according to US Food and Drug Administration bioanalytical method validation guidelines. The coefficient of determination was 0.9999, for a linear concentration range of 25 to 1.0 × 105 ng/ml. The percentage recovery (accuracy) varied from 99.83 to 104.2%, with RSD values (precision) ranging from 4.07 to 11.84%. The total extraction time was about 12 min and the HPLC analysis time was 5 min. The method was simple, selective and sensitive for the determination of favipiravir in real human plasma. 相似文献
2.
Elnaz Marzi Khosrowshahi Behnaz Limuie Khosrowshahi Mir Ali Farajzadeh Abolghasem Jouyban Mustafa Tuzen Mohammad Reza Afshar Mogaddam Mahboob Nemati 《Biomedical chromatography : BMC》2022,36(7):e5371
A dispersive solid-phase extraction method based on a new sorbent has been performed on plasma and wastewater samples to determine metoprolol by high-performance liquid chromatography–tandem mass spectrometry. In this study, the analyte was adsorbed from the samples onto microcrystalline cellulose as a green and efficient sorbent and then eluted for use in the determination step. In the mass spectrometer, the analyte was detected in the positive mode and selectivity of the analysis was increased by sequential mass analysis through multiple reaction monitoring. All of the effective parameters in the extraction of metoprolol from plasma and wastewater were optimized. Under optimal conditions the method was linear in the ranges of 1–1,000 and 0.1–1,000 ng/ml in plasma and wastewater samples, respectively. The detection limits of the method were 0.30 and 0.03 ng/ml in plasma and wastewater samples, respectively. The data showed that the method provides low detection limit, wide linear range, good precision and high extraction recovery. Finally several plasma and wastewater samples were successfully analyzed using the method. The use of a small amount of a green and inexpensive sorbent and a low volume of plasma without the need for further pretreatment steps are the main advantages of the method. 相似文献
3.
4.
Journal of Algebraic Combinatorics - The symbolic powers, in general, are not equal to the ordinary powers. Therefore, one interesting question here is for what classes of ideals ordinary and... 相似文献
5.
6.
Elasasy M. E. A. Elnaggar D. H. Hafez N. A. Abdel Azab M. E. Amr A. E. Omran M. M. Mohamed A. M. 《Russian Journal of General Chemistry》2021,91(5):915-925
Russian Journal of General Chemistry - Some new fluoro-heterocyclic compounds containing thiazole and pyridine moities have been synthesized and studied for their antiproliferative activity.... 相似文献
7.
A sensitive and efficient method for trace analysis of some phenolic compounds using simultaneous derivatization and air‐assisted liquid–liquid microextraction from human urine and plasma samples followed by gas chromatography–nitrogen phosphorous detection 下载免费PDF全文
Mir Ali Farajzadeh Mohammad Reza Afshar Mogaddam Ali Akbar Alizadeh Nabil 《Biomedical chromatography : BMC》2015,29(12):1921-1931
In present study, a simultaneous derivatization and air‐assisted liquid–liquid microextraction method combined with gas chromatography–nitrogen phosphorous detection has been developed for the determination of some phenolic compounds in biological samples. The analytes are derivatized and extracted simultaneously by a fast reaction with 1‐flouro‐2,4‐dinitrobenzene under mild conditions. Under optimal conditions low limits of detection in the range of 0.05–0.34 ng mL?1 are achievable. The obtained extraction recoveries are between 84 and 97% and the relative standard deviations are less than 7.2% for intraday (n = 6) and interday (n = 4) precisions. The proposed method was demonstrated to be a simple and efficient method for the analysis of phenols in biological samples. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
8.
Ahmed Waqar Chowdhury Z. Z. Kazi S. N. Johan MR. Akram Naveed Oon C. S. Abdelrazek Ali H. 《Journal of Thermal Analysis and Calorimetry》2021,144(4):1517-1534
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers... 相似文献
9.
Ramesh G. K. Manjunatha S. Roopa G. S. Chamkha Ali J. 《Journal of Thermal Analysis and Calorimetry》2021,146(3):1347-1357
Journal of Thermal Analysis and Calorimetry - Modeling and computations are performed to study the ND-Co3O4/EG hybrid nanoliquid mixed convective flow past a vertical porous cylinder. The flow... 相似文献
10.