全文获取类型
收费全文 | 78635篇 |
免费 | 7572篇 |
国内免费 | 6006篇 |
专业分类
化学 | 32720篇 |
晶体学 | 1184篇 |
力学 | 12930篇 |
综合类 | 1076篇 |
数学 | 22401篇 |
物理学 | 21902篇 |
出版年
2024年 | 163篇 |
2023年 | 804篇 |
2022年 | 1831篇 |
2021年 | 1942篇 |
2020年 | 2130篇 |
2019年 | 1953篇 |
2018年 | 1863篇 |
2017年 | 2499篇 |
2016年 | 3038篇 |
2015年 | 2368篇 |
2014年 | 3589篇 |
2013年 | 5563篇 |
2012年 | 4643篇 |
2011年 | 4793篇 |
2010年 | 4075篇 |
2009年 | 4819篇 |
2008年 | 4697篇 |
2007年 | 5019篇 |
2006年 | 4387篇 |
2005年 | 4021篇 |
2004年 | 3666篇 |
2003年 | 3177篇 |
2002年 | 2646篇 |
2001年 | 2189篇 |
2000年 | 2092篇 |
1999年 | 1888篇 |
1998年 | 1746篇 |
1997年 | 1540篇 |
1996年 | 1315篇 |
1995年 | 1183篇 |
1994年 | 1066篇 |
1993年 | 867篇 |
1992年 | 848篇 |
1991年 | 685篇 |
1990年 | 589篇 |
1989年 | 415篇 |
1988年 | 384篇 |
1987年 | 261篇 |
1986年 | 201篇 |
1985年 | 246篇 |
1984年 | 219篇 |
1983年 | 105篇 |
1982年 | 162篇 |
1981年 | 102篇 |
1980年 | 71篇 |
1979年 | 112篇 |
1978年 | 63篇 |
1977年 | 50篇 |
1976年 | 35篇 |
1957年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
K.V. Stepurska О.О. Soldatkin I.S. Kucherenko V.M. Arkhypova S.V. Dzyadevych A.P. Soldatkin 《Analytica chimica acta》2015
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed. 相似文献
4.
Erosion and sediments transport processes have a great impact on industrial structures and on water quality. Despite its limitations, the Saint‐Venant‐Exner system is still (and for sure for some years) widely used in industrial codes to model the bedload sediment transport. In practice, its numerical resolution is mostly handled by a splitting technique that allows a weak coupling between hydraulic and morphodynamic distinct softwares but may suffer from important stability issues. In recent works, many authors proposed alternative methods based on a strong coupling that cure this problem but are not so trivial to implement in an industrial context. In this work, we then pursue 2 objectives. First, we propose a very simple scheme based on an approximate Riemann solver, respecting the strong coupling framework, and we demonstrate its stability and accuracy through a number of numerical test cases. However, second, we reinterpret our scheme as a splitting technique and we extend the purpose to propose what should be the minimal coupling that ensures the stability of the global numerical process in industrial codes, at least, when dealing with collocated finite volume method. The resulting splitting method is, up to our knowledge, the only one for which stability properties are fully demonstrated. 相似文献
5.
Thalia Tsiaka Panagiotis Zoumpoulakis Vassilia J. Sinanoglou Constantinos Makris Georgios A. Heropoulos Antony C. Calokerinos 《Analytica chimica acta》2015
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE. 相似文献
6.
7.
《Journal of separation science》2018,41(10):2288-2295
New psychoactive substances represent serious social and health problem as tens of new compounds are detected in Europe annually. They often show structural proximity or even isomerism, which complicates their analysis. Two methods based on ultra high performance supercritical fluid chromatography and ultra high performance liquid chromatography with mass spectrometric detection were validated and compared. A simple dilute‐filter‐and‐shoot protocol utilizing propan‐2‐ol or methanol for supercritical fluid or liquid chromatography, respectively, was proposed to detect and quantify 15 cathinones and phenethylamines in human urine. Both methods offered fast separation (<3 min) and short total analysis time. Precision was well <15% with a few exceptions in liquid chromatography. Limits of detection in urine ranged from 0.01 to 2.3 ng/mL, except for cathinone (5 ng/mL) in supercritical fluid chromatography. Nevertheless, this technique distinguished all analytes including four pairs of isomers, while liquid chromatography was unable to resolve fluoromethcathinone regioisomers. Concerning matrix effects and recoveries, supercritical fluid chromatography produced more uniform results for different compounds and at different concentration levels. This work demonstrates the performance and reliability of supercritical fluid chromatography and corroborates its applicability as an alternative tool for analysis of new psychoactive substances in biological matrixes. 相似文献
8.
Riboflavin was covalently linked to mesoporous SBA-15 silica surface via grafting technique. Then fluorescence properties of the system obtained were analyzed in the presence of several metal and organic cations. Both quenching and strengthening of fluorescence as well as significant changes in the maximum fluorescence wavelength were observed. The results were compared with absorption and fluorescence data obtained for riboflavin water solutions. 相似文献
9.
Rong Yin Jihui Zhang Xudong Shang 《Mathematical Methods in the Applied Sciences》2020,43(15):8736-8752
This paper is dedicated to studying the following Schrödinger–Poisson system Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions. 相似文献
10.