全文获取类型
收费全文 | 1088篇 |
免费 | 417篇 |
国内免费 | 103篇 |
专业分类
化学 | 495篇 |
晶体学 | 178篇 |
力学 | 49篇 |
综合类 | 8篇 |
数学 | 59篇 |
物理学 | 819篇 |
出版年
2024年 | 5篇 |
2023年 | 8篇 |
2022年 | 57篇 |
2021年 | 42篇 |
2020年 | 43篇 |
2019年 | 34篇 |
2018年 | 32篇 |
2017年 | 55篇 |
2016年 | 73篇 |
2015年 | 60篇 |
2014年 | 46篇 |
2013年 | 148篇 |
2012年 | 80篇 |
2011年 | 81篇 |
2010年 | 72篇 |
2009年 | 94篇 |
2008年 | 71篇 |
2007年 | 82篇 |
2006年 | 71篇 |
2005年 | 55篇 |
2004年 | 62篇 |
2003年 | 62篇 |
2002年 | 23篇 |
2001年 | 35篇 |
2000年 | 35篇 |
1999年 | 30篇 |
1998年 | 24篇 |
1997年 | 29篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有1608条查询结果,搜索用时 125 毫秒
871.
872.
在密度函数理论的基础上,采用中性原子叠加模型和有限差分方法(SNA-FD)计算了石墨,金刚石和C60这三种碳的同素异形体中的正电子分布和湮没情况. 计算表明,在片层结构的石墨晶体中,正电子主要在石墨层间的空隙中湮没,计算出的石墨中的正电子寿命为208ps,与文献中的实验结果210ps符合很好. 在金刚石单晶中,正电子主要在碳原子之间的空隙中存在并发生湮没,计算出的金刚石中的正电子寿命为1159ps,与文献中的实验结果110ps相符合;在面心立方结构的C60晶体中,正电子主要在C60分子球壳内外侧及分子之
关键词:
石墨
金刚石
C60
正电子寿命 相似文献
873.
874.
875.
实现金刚石薄膜的异质外延是目前CVD金刚石薄膜制研究的主要奋斗目标,而直流负偏压增强金刚石成核法被认为是达到这一目标的有效途径。文章简要评述了微波等离子体CVD制备金刚石薄膜中的直流负偏压增强成核法,以及由此而发展的直流正偏压增强成核法和叠加交流成分的直流负偏压增强成核法,介绍了它们在异质外延金刚石薄膜中的应用。 相似文献
876.
本文讨论六角系统中将宽度与直径结合起来的几个极值问题,并给出相应的极图构造。最后,指出并补正[4]中一个计数结果的不足。 相似文献
877.
Potential energy calculations have been made for hexane aggregates in the hexagonal arrangement as models of paraffin-like solids. As a part of the general energy hypersurface the feasibility of translation and rotation of extended chains in aggregate has been examined for various degrees of packing. The pure translation is favoured over the pure rotation at all interchain separations. The energy map of coupled rotation-translation motion has been developed for the intermediate degree of packing. The energy minima on the map correspond to the parallel orientation of chain backbones and are presumed to represent the prevailing short-range structure of the rotator phase in n-alkane crystals. The calculated barriers are used for the rationalization of chain dynamics in the rotator phase, and in the disorded phases with the similar alkyl chain packing as found in crystals, monolayers and bilayers of amphiphiles. Probability of formations of the translational, rotational and conformational defects in the above systems is discussed. 相似文献
878.
Terblanche CJ Reynhardt EC Rakitianski SA Van Wyk JA 《Solid state nuclear magnetic resonance》2001,19(3-4):107-129
13C Spin–lattice relaxation (SLR) times in the laboratory frame have been measured at room temperature as a function of field in the range of 500 to 5000 G on two natural type Ib and Ia diamonds after dynamic nuclear polarization. Each of the diamonds contains two types of fixed paramagnetic centers with overlapping inhomogeneous electron paramagnetic resonance (EPR) lines. EPR techniques have been employed to identify these defects and to determine their concentrations and relaxation times at X-band. Three different nuclear SLR paths, namely that due to electron SLR and two types of three spin processes, are discussed. The one three-spin process (TSP) (type 1) involves a simultaneous transition of two electron spins belonging to the same hyperfine EPR line and a 13C spin while the other process (type 2) involves two electron spins belonging to different hyperfine EPR lines and a 13C spin. It is shown that the thermal contact between the 13C nuclear Zeeman and electron dipole–dipole interaction reservoirs decreases with an increase in field intensity, thus forming a bottleneck in the 13C relaxation path due to the type 1 TSP. The contribution of TSP of type 1 dominates that due to electron SLR and the type 2 TSP in relaxing the 13C nuclei in type Ib diamond from about 1200 to 5000 G, while for type Ia diamond it dominates from 500 up to about 2200 G. In type Ia diamond over the range 2200 to 5000 G it seems that the type 2 TSP, which involves electrons of neighboring P2 hyperfine lines, dominates that of electron spin–lattice and the type 1 TSP. Over the range 500 to about 1200 G, a field-dependent electron SLR mechanism associated with N3 centers appears to dominate the 13C SLR. 相似文献
879.
880.
G. A. Gusakov N. M. Lapchuk A. V. Mudryi G. G. Fedoruk 《Journal of Applied Spectroscopy》2003,70(3):440-444
Optical and paramagnetic properties of synthetic diamond single crystals grown by the temperature gradient method in the Fe-Co-C and Fe-Co-Al-C systems using split-sphere high-pressure apparatus have been investigated. For crystals with a high (>5·1017 cm–3) nitrogen concentration a good agreement of the concentrations of single substitution nitrogen atoms obtained from EPR, IR, and UV measurements was observed. For crystals with a low ((0.5–5.0)·1017 cm–3) nitrogen concentration, there was no correlation between the results of substituting nitrogen concentrations obtained by the methods mentioned. It is shown that this behavior is attributable to the transition of the substituting nitrogen atoms from the paramagnetic neutral to nonparamagnetic positive charge state due to compensation by the boron impurity. 相似文献