全文获取类型
收费全文 | 820篇 |
免费 | 246篇 |
国内免费 | 240篇 |
专业分类
化学 | 405篇 |
晶体学 | 16篇 |
力学 | 113篇 |
综合类 | 22篇 |
数学 | 240篇 |
物理学 | 510篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 30篇 |
2021年 | 27篇 |
2020年 | 20篇 |
2019年 | 37篇 |
2018年 | 46篇 |
2017年 | 26篇 |
2016年 | 41篇 |
2015年 | 25篇 |
2014年 | 58篇 |
2013年 | 52篇 |
2012年 | 51篇 |
2011年 | 50篇 |
2010年 | 58篇 |
2009年 | 56篇 |
2008年 | 64篇 |
2007年 | 56篇 |
2006年 | 48篇 |
2005年 | 43篇 |
2004年 | 42篇 |
2003年 | 46篇 |
2002年 | 23篇 |
2001年 | 32篇 |
2000年 | 37篇 |
1999年 | 40篇 |
1998年 | 26篇 |
1997年 | 35篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1966年 | 3篇 |
1964年 | 2篇 |
1963年 | 3篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1306条查询结果,搜索用时 0 毫秒
151.
We investigate the granular flow states in a channel with bottleneck by molecular dynamics simulations.Our study is restricted only on a selected key area rather than on the whole system to focus on the flow properties of a single granular state.A random force field is introduced to control the granular temperature.It is also pointed out that the flow rate in the granular flow can be correlated with the pressure,which leads us to carry out a comprehensive study similar to the classical study for general liquid-gas phase transition.Our results show that the dilute flow state and the dense flow state of the granules are similar to the gas state and the liquid state of general substances,respectively,and the properties of phase transition and critical phenomenon are also similar to those occurring in general substances. 相似文献
152.
在HL-2A 装置上优化和发展了偏滤器靶板上的红外测温系统,并利用该系统分析了高约束模放电期间边缘局域模的热沉积分布特性。在高约束模式放电期间,超声分子束注入使边缘局域模所引起的偏滤器靶板上瞬间热通量峰值下降了~60%,并伴随着边缘局域模爆发频率增加了2~3 倍,而等离子体储能仅下降了~8%。分析结果表明,大幅度的丝状结构在超声分子束注入之后得到了有效抑制,沉积到偏滤器靶板上的瞬间热通量峰值也随之下降。此外,在超声分子束注入之后偏滤器室内的热辐射损失大幅度增加,从而耗散了热输运所携带的部分能量,进一步分散了沉积到偏滤器靶板上的能量,有效地保护了偏滤器靶板。 相似文献
153.
We report a diode-pumped self-Q-switched 1064-nm Cr,Nd:YAG of 16-18 ns. The maximum average output power up to 7 W, 3370, is obtained in a simple and compact linear cavity by using transmittance of 1570. The laser operates at TEM00 mode with a laser with pulse duration in the range corresponding to a slope efficiency of a plane-concave output coupler with a pump power of 14.2 W. 相似文献
154.
Three-dimensional optical matters are created by combining the single beam optical trapping with the conventional Z-scan technique. Dynamic light diffraction is employed to evaluate the structure and quality of the optical matter formed at the optimum trapping power. The lattice constant of the optical matter is extracted based on the Bragg and Snell laws, showing that polystyrene spheres are nearly close-packed in the optical matter, confirmed by comparing the diffraction pattern of the optical matter with that of a colloidal photonic crystal fabricated by the self-assembled technique. The relatively broad diffraction peaks observed in the optical matter indicate that the density of disorders in it is higher than that in the photonic crystal. It is suggested that the optical matter possesses a random close-packed structure rather than a face centered cubic one.Three-dimensional optical matters are created by combining the single beam optical trapping with the conven- tional Z-scan technique. Dynamic light diffraction is employed to evaluate the structure and quality of the optical matter formed at the optimum trapping power. The lattice constant of the optical matter is extracted based on the Bragg and Snell laws, showing that polystyrene spheres are nearly close-packed in the optical matter, confirmed by comparing the diffraction pattern of the optical matter with that of a colloidal photonic crystal fabricated by the self-assembled technique. The relatively broad diffraction peaks observed in the optical matter indicate that the density of disorders in it is higher than that in the photonic crystal. It is suggested that the optical matter possesses a random close-packed structure rather than a face centered cubic one. 相似文献
155.
Modulated supersonic molecular beam (SMB) injection is introduced to study transport features of non-local transport phenomenon on HL-2A. Repetitive non-local effect induced by modulated SMBI allows Fourier trans-formation of the temperature perturbation, yielding detailed investigation of the pulse propagation. Fourier analysis provides evidence for existence of internal transport barriers. Meanwhile, experimental progress of nonlocal effect was made in the HL-2A Tokamak in 200Z The core electron temperature Te rise increases from 18% to more than 40% and the duration of the Te rise could be prolonged by changing the conditions of SMB injection. 相似文献
156.
PC/EAA共混体系在加工过程中的反应 总被引:3,自引:0,他引:3
采用差示扫描量热法(DSC)和核磁共振氢谱法(1H-NMR)研究了不同聚碳酸酯(PC)/乙烯-丙烯酸共聚物(EAA)共混体系在加工过程中的大分子反应,考察了有机金属催化剂二丁基锡DBTO)含量和反应时间对体系的影响.采用哈克(Haake)转矩流变仪的混合器作反应釜,索氏抽提器分离产物.结果表明,PC和EAA在加工中反应剧烈,在共混体系的界面原位形成接枝或交联的PC-EAA共聚物,随催化剂用量增大、反应时间延长易生成共交联的PC-EAA共聚物.但混合时间过长,体系的断链反应会加剧,生成产物不稳定. 相似文献
157.
THE OPPENHEIM-TYPE INEQUALITIES FOR THE HADAMARD PRODUCT OF M-MATRIX AND POSITIVE DEFINITE MATRIX 总被引:2,自引:0,他引:2
For the lower bound about the determinant of Hadamard product of A and B, where A is a n x n real positive definite matrix and B is a n x n M-matrix, Jianzhou Liu [SIAM J. Matrix Anal. Appl., 18(2)(1997).. 305-311] obtained the estimated inequality as follows 相似文献
158.
159.
160.
随着当前全球石化行业的快速发展,水资源的短缺和工业废水排放的增长已经极大地阻碍了社会和环境的可持续性发展。含油废水是其中占比最大也是比较难处理的一种废水,膜分离法是目前处理含油废水的有效方法之一。而目前市场上主流的油水分离膜部分或全部使用了不可再生和非降解性原料,会对环境造成二次污染。以生物质材料为主要原材料的生物质基油水分离膜以其绿色、可持续、高效、可降解等优势得到了极大地关注。本文从生物质基油水分离膜的生物质来源、种类、相应的制备及改性方法、应用研究现状及主要问题进行论述,对未来生物质基油水分离膜的前景进行展望。 相似文献