全文获取类型
收费全文 | 242629篇 |
免费 | 2787篇 |
国内免费 | 872篇 |
专业分类
化学 | 130452篇 |
晶体学 | 3688篇 |
力学 | 9897篇 |
综合类 | 2篇 |
数学 | 27089篇 |
物理学 | 75160篇 |
出版年
2020年 | 1784篇 |
2019年 | 2046篇 |
2018年 | 2495篇 |
2017年 | 2412篇 |
2016年 | 3841篇 |
2015年 | 2612篇 |
2014年 | 3916篇 |
2013年 | 11189篇 |
2012年 | 8079篇 |
2011年 | 10018篇 |
2010年 | 6581篇 |
2009年 | 6477篇 |
2008年 | 8987篇 |
2007年 | 9133篇 |
2006年 | 8375篇 |
2005年 | 7833篇 |
2004年 | 6987篇 |
2003年 | 6205篇 |
2002年 | 6136篇 |
2001年 | 7196篇 |
2000年 | 5357篇 |
1999年 | 4218篇 |
1998年 | 3548篇 |
1997年 | 3577篇 |
1996年 | 3288篇 |
1995年 | 3128篇 |
1994年 | 2944篇 |
1993年 | 3000篇 |
1992年 | 3293篇 |
1991年 | 3327篇 |
1990年 | 3143篇 |
1989年 | 3098篇 |
1988年 | 3159篇 |
1987年 | 3029篇 |
1986年 | 2923篇 |
1985年 | 3985篇 |
1984年 | 4145篇 |
1983年 | 3399篇 |
1982年 | 3749篇 |
1981年 | 3645篇 |
1980年 | 3517篇 |
1979年 | 3551篇 |
1978年 | 3777篇 |
1977年 | 3606篇 |
1976年 | 3814篇 |
1975年 | 3387篇 |
1974年 | 3516篇 |
1973年 | 3819篇 |
1972年 | 2327篇 |
1971年 | 1786篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
A. Lashgari S. Ghammamy R. Ramirez-Tagle G. Salgado-Moran 《Journal of Structural Chemistry》2015,56(8):1505-1513
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data. 相似文献
32.
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
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
33.
34.
35.
36.
37.
38.
39.
40.