全文获取类型
收费全文 | 19683篇 |
免费 | 874篇 |
国内免费 | 98篇 |
专业分类
化学 | 13423篇 |
晶体学 | 126篇 |
力学 | 425篇 |
数学 | 2942篇 |
物理学 | 3739篇 |
出版年
2023年 | 120篇 |
2022年 | 175篇 |
2021年 | 276篇 |
2020年 | 381篇 |
2019年 | 402篇 |
2018年 | 236篇 |
2017年 | 238篇 |
2016年 | 611篇 |
2015年 | 566篇 |
2014年 | 650篇 |
2013年 | 1061篇 |
2012年 | 1140篇 |
2011年 | 1285篇 |
2010年 | 752篇 |
2009年 | 667篇 |
2008年 | 1056篇 |
2007年 | 1044篇 |
2006年 | 968篇 |
2005年 | 915篇 |
2004年 | 802篇 |
2003年 | 672篇 |
2002年 | 621篇 |
2001年 | 327篇 |
2000年 | 309篇 |
1999年 | 288篇 |
1998年 | 252篇 |
1997年 | 237篇 |
1996年 | 274篇 |
1995年 | 261篇 |
1994年 | 229篇 |
1993年 | 233篇 |
1992年 | 212篇 |
1991年 | 183篇 |
1990年 | 185篇 |
1989年 | 181篇 |
1988年 | 156篇 |
1987年 | 131篇 |
1986年 | 124篇 |
1985年 | 185篇 |
1984年 | 167篇 |
1983年 | 141篇 |
1982年 | 168篇 |
1981年 | 163篇 |
1980年 | 137篇 |
1979年 | 143篇 |
1978年 | 166篇 |
1977年 | 124篇 |
1976年 | 109篇 |
1975年 | 127篇 |
1974年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
922.
923.
924.
Christopher Jainski Martin Rißmann Suad Jakirlic Benjamin Böhm Andreas Dreizler 《Flow, Turbulence and Combustion》2018,100(1):177-196
The presence of a turbulent premixed flame strongly influences the properties of the adjacent velocity boundary layer. This influence is studied here using a generic configuration where at atmospheric pressure turbulent premixed methane/air flames interact with a temperature stabilized wall. The experiment is optimized for well-defined boundary conditions and optical accessibility in the zone where the flame impinges at the wall. Laser based diagnostic methods are used to measure two components of the velocity field by particle image velocimetry simultaneously with the flame front position using laser induced fluorescence of the OH molecule. Two measurement planes are selected that are aligned perpendicularly to the surface of the wall. Based on this data, the flow field near the wall is analyzed by different methodologies using laboratory-fixed and flame-conditioned statistics, a quadrant splitting analysis of the Reynolds stresses and an evaluation of the production term of the turbulent kinetic energy. The results of chemically reactive cases are compared to their corresponding non-reactive flows for otherwise identical inflow conditions. In the zone of flame-wall interactions the boundary layer structure and its turbulence are dominated by the turbulent flame. Important features are that the flame compresses the boundary layer already upstream the location where the flame is finally quenched and that ejection and sweeps are no longer the dominant mechanisms as in non-reactive boundary layers. This experimental data may serve additionally as a database for model development for near wall reactive flows. 相似文献
925.
926.
927.
Liping Liao Bing Wu Dr. Evgeniya Kovalska Dr. Vlastimil Mazánek Dr. Martin Veselý Ivo Marek Lucie Spejchalová Prof. Dr. Zdeněk Sofer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(52):13235-13241
The intercalation of cations into layered-structure electrode materials has long been studied in depth for energy storage applications. In particular, Li+-, Na+-, and K+-based cation transport in energy storage devices such as batteries and electrochemical capacitors is closely related to the capacitance behavior. We have exploited different sizes of cations from aqueous salt electrolytes intercalating into a layered Nb2CTx electrode in a supercapacitor for the first time. As a result, we have demonstrated that capacitive performance was dependent on cation intercalation behavior. The interlayer spacing expansion of the electrode material can be observed in Li2SO4, Na2SO4, and K2SO4 electrolytes with d-spacing. Additionally, our results showed that the Nb2CTx electrode exhibited higher electrochemical performance in the presence of Li2SO4 than in that of Na2SO4 and K2SO4. This is partly because the smaller-sized Li+ transports quickly and intercalates between the layers of Nb2CTx easily. Poor ion transport in the Na2SO4 electrolyte limited the electrode capacitance and presented the lowest electrochemical performance, although the cation radius follows Li+>Na+>K+. Our experimental studies provide direct evidence for the intercalation mechanism of Li+, Na+, and K+ on the 2D layered Nb2CTx electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes. 相似文献
928.
Maíra Fasciotti Gustavo B. Sanvido Vanessa G. Santos Priscila M. Lalli Michael McCullagh Gilberto F. de Sá Romeu J. Daroda Martin G. Peter Marcos N. Eberlin 《Journal of mass spectrometry : JMS》2012,47(12):1643-1647
The use of CO2 as a massive and polarizable drift gas is shown to greatly improve peak‐to‐peak resolution (Rp‐p), as compared with N2, for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline Rp‐p was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (Rp‐p = 0.76), maltose and sucrose (Rp‐p = 1.04), and maltose and lactose (Rp‐p = 0.74). Ion mobility mass spectrometry using CO2 as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
929.
930.
Although nuclear magnetic resonance in low fields around or below the Earth's magnetic field is almost as old as nuclear magnetic resonance itself, the recent years have experienced a revival of this technique that is opposed to the common trend towards higher and higher fields. The background of this development is the expectation that the low-field domain may open a new window for the study of molecular structure and dynamics. Here, we will give an overview on the specific features in the low-field domain, both from the technical and from the physical point of view. In addition, we present a short passage on the option of magnetic resonance imaging in fields of the micro-Tesla range. 相似文献