全文获取类型
收费全文 | 2291篇 |
免费 | 151篇 |
国内免费 | 232篇 |
专业分类
化学 | 266篇 |
力学 | 297篇 |
综合类 | 41篇 |
数学 | 1619篇 |
物理学 | 451篇 |
出版年
2023年 | 12篇 |
2022年 | 24篇 |
2021年 | 30篇 |
2020年 | 31篇 |
2019年 | 39篇 |
2018年 | 43篇 |
2017年 | 75篇 |
2016年 | 57篇 |
2015年 | 33篇 |
2014年 | 86篇 |
2013年 | 145篇 |
2012年 | 66篇 |
2011年 | 95篇 |
2010年 | 105篇 |
2009年 | 93篇 |
2008年 | 152篇 |
2007年 | 149篇 |
2006年 | 123篇 |
2005年 | 137篇 |
2004年 | 114篇 |
2003年 | 109篇 |
2002年 | 117篇 |
2001年 | 108篇 |
2000年 | 100篇 |
1999年 | 89篇 |
1998年 | 95篇 |
1997年 | 78篇 |
1996年 | 66篇 |
1995年 | 33篇 |
1994年 | 35篇 |
1993年 | 13篇 |
1992年 | 29篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 18篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 19篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1973年 | 3篇 |
1936年 | 3篇 |
排序方式: 共有2674条查询结果,搜索用时 125 毫秒
81.
82.
83.
Nejal M. Bhatt Vijay D. Chavada Mallika Sanyal Pranav S. Shrivastav 《Biomedical chromatography : BMC》2019,33(10)
The present work describes novel methods using densitometry and indirect or off‐line high performance thin‐layer chromatography–mass spectrometry (HPTLC–MS) for the simultaneous detection and quantification of asenapine, propranolol and telmisartan and their phase II glucuronide metabolites. After chromatographic separation of the drugs and their metabolites the analytes were scraped, extracted in methanol and concentrated prior to mass spectrometric analysis. Different combinations of toluene and methanol–ethanol–n‐butanol–iso‐propanol were tested for analyte separation and the best results were obtained using toluene–methanol–ammonia (6.9:3.0:0.1, v/v/v) as the elution solvent. All of the drug–metabolite pairs were separated with a homologous retardation factor difference of ≥22. The conventional densitometric approach was also studied and the method performances were compared. Both of the approaches were validated following the International Conference on Harmonization guidelines, and applied to spiked human plasma samples. The major advantage of the TLC–MS approach is that it can provide much lower limits of detection (1.98–5.83 pg/band) and limit of quantitation (5.97–17.63 pg/band) with good precision (?3.0% coefficient of variation) compared with TLC–densitometry. The proposed indirect HPTLC–MS method is simple yet effective and has tremendous potential in the separation and quantitation of drugs and their metabolites from biological samples, especially for clinical studies. 相似文献
84.
In this paper, we study the normality of the family of meromorphic functions from the viewpoint of hyperbolic metric. Then, a new sufficient and necessary condition is obtained, which can determine a given family of meromorphic functions is normal or not. 相似文献
85.
In this paper we give a short geometric proof of a generalization of a well-known result about reduction of codimension for submanifolds of Riemannian symmetric spaces. 相似文献
86.
《化学:亚洲杂志》2017,12(3):324-331
This work illustrates several theoretical fundamentals for the application of THz vibrational spectroscopy to molecular characterization in the solid state using two different types of saccharide systems as examples. Four subjects have been specifically addressed: (1) the qualitative differences in the molecular vibrational signatures monitored by THz and mid‐IR vibrational spectroscopy; (2) the selection rules for THz vibrational spectroscopy as applied to crystalline and amorphous systems; (3) a normal mode simulation, using α‐l ‐xylose as an example; and (4) a rigorous mode analysis to quantify the percentage contributions of the intermolecular and intramolecular vibrations to the normal mode of interest. 相似文献
87.
88.
89.
90.
Yuanzhong Yang Reinhard I. Boysen Chadin Kulsing Maria T. Matyska Joseph J. Pesek Milton T. W. Hearn 《Journal of separation science》2013,36(18):3019-3025
The retention behavior of a set of polar peptides separated on a silica hydride stationary phase was examined with a capillary HPLC system coupled to ESI‐MS detection. The mobile phases consisted of formic acid or acetic acid/acetonitrile/water mixtures with the acetonitrile content ranging from 5 to 80% v/v. The effects on peptide retention of these two acidic buffer additives and their concentrations in the mobile phase were systematically investigated. Strong retention of the peptides on the silica hydride phase was observed with relatively high‐organic low‐aqueous mobile phases (i.e. under aqueous normal‐phase conditions). However, when low concentrations of acetic acid were employed as the buffer additive, strong retention of the peptides was also observed even when high aqueous content mobile phases were employed. This unique feature of the stationary phase therefore provides an opportunity for chromatographic analysis of polar peptides with water‐rich eluents, a feature usually not feasible with traditional RP sorbents, and thus under conditions more compatible with analytical green chemistry criteria. In addition, both isocratic and gradient elution procedures can be employed to optimize peptide separations with excellent reproducibility and resolution under these high aqueous mobile phase conditions with this silica hydride stationary phase. 相似文献