全文获取类型
收费全文 | 166篇 |
免费 | 10篇 |
国内免费 | 4篇 |
专业分类
化学 | 50篇 |
晶体学 | 10篇 |
力学 | 13篇 |
数学 | 3篇 |
物理学 | 72篇 |
综合类 | 32篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 8篇 |
2019年 | 3篇 |
2018年 | 13篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 8篇 |
2013年 | 43篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有180条查询结果,搜索用时 296 毫秒
11.
Ng Seik Weng 《结构化学》2009,28(12):1657-1660
The procedure for collecting diffraction data at –173 °C on a twinned specimen of methyl 2-aminopyrazine-3-carboxylate by using the APEX-II software followed by de-twinning the non-merohedrally-twinned reflection data with PLATON is described. De-twinning significantly lowers the R index from 0.141 to 0.038 owing to 49% twinning. Crystal data: C6H7N3O2,monoclinic,P21/c (a = 6.3149(1),b = 16.5274(2),c = 6.4544(1) A,β = 95.759(1)°,V = 670.24(2) A^3). 相似文献
12.
13.
Inversion twinning in a second polymorph of the hydrochloride salt of the recreational drug ethylone
T. Stanley Cameron J. Stuart Grossert Chad R. Maheux Idralyn Q. Alarcon Catherine R. Copeland Anthony Linden 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(4):266-270
A second polymorph of the hydrochloride salt of the recreational drug ethylone, C12H16NO3+·Cl−, is reported [systematic name: (±)‐2‐ethylammonio‐1‐(3,4‐methylenedioxyphenyl)propane‐1‐one chloride]. This polymorph, denoted form (A), appears in crystallizations performed above 308 K. The originally reported form (B) [Wood et al. (2015). Acta Cryst. C 71 , 32–38] crystallizes preferentially at room temperature. The conformations of the cations in the two forms differ by a 180° rotation about the C—C bond linking the side chain to the aromatic ring. Hydrogen bonding links the cations and anions in both forms into similar extended chains in which any one chain contains only a single enantiomer of the chiral cation, but the packing of the ions is different. In form (A), the aromatic rings of adjacent chains interleave, but pack equally well if neighbouring chains contain the same or opposite enantiomorph of the cation. The consequence of this is then near perfect inversion twinning in the structure. In form (B), neighbouring chains are always inverted, leading to a centrosymmetric space group. The question as to why the polymorphs crystallize at slightly different temperatures has been examined by density functional theory (DFT) and lattice energy calculations and a consideration of packing compactness. The free energy (ΔG) of the crystal lattice for polymorph (A) lies some 52 kJ mol−1 above that of polymorph (B). 相似文献
14.
使用分子动力学方法,模拟研究了单晶Cu(001)薄膜在双向等轴拉伸应变下的塑性变形行为.当应变超过一定值时,样品通过产生位错、层错及孪晶而发生塑性变形.当应变相对较低时,不全位错首先在薄膜表面形核并在密排面上滑移,留下堆积层错;当应变增加时,位错在表面与内部同时成核生长,层错数量也随之增加.分析了相邻滑移面上的位错之间相互作用形成孪晶的微观过程.材料内部形成大量堆积层错及孪晶后,较大孪晶的密排面上的原子也会发生滑移,形成孪晶内部的层错结构以释放残余应力. 相似文献
15.
The evolution of texture during the tensile deformation of Mg–3.1%Al–1.05%Zn was studied by microtexture and macrotexture techniques. The deformation texture is shown to be the direct consequence of the variant selection that occurs during primary (contraction) and secondary (extension) twinning. During subsequent annealing, the secondary twins have a higher rate of nucleation than the primary twins and expanded within the latter rather than in the matrix grains. As a result, the primary twins did not contribute significantly to the annealing texture. 相似文献
16.
Especially with respect to high Mn and other austenitic TRansformation and/or TWinning Induced Plasticity (TRIP/TWIP) steels, it is a current trend to model the stacking fault energy of a stacking fault that is formed by plastic deformation with an equilibrium thermodynamic formalism as proposed by Olson and Cohen in 1976. In the present paper, this formalism is critically discussed and its ambiguity is stressed. Suggestions are made, how the stacking fault energy and its relation to the formation of hexagonal ?-martensite might be treated appropriately. It is further emphasized that a thermodynamic treatment of deformation-induced stacking fault phenomena always faces some ambiguity. However, an alternative thermodynamic approach to stacking faults, twinning and the formation of ?-martensite in austenitic steels might rationalize the specific stacking fault arrangements encountered during deformation of TRIP/TWIP alloys. 相似文献
17.
18.
19.
The (one-way) shape memory effect is a phenomenon that when a martensitic alloy is deformed in a martensitic state it recovers its original shape upon heating to the parent phase. This is a universal effect for certain martensitic alloys. We will assess the mechanism of the effect critically and select the essential factors which govern the effect. We try to understand it from a unified view, invoking the group–subgroup symmetry relation between the parent and martensite phase, along with analysis of reversible twinning modes in martensite. By such an assessment, we will show why typical shape memory alloys, such as Ti–Ni, Cu–Al–Ni etc., exhibit good shape memory characteristics, while others, such as ferrous alloys, do not. Thus, we will show that most of the shape memory characteristics of various martensitic alloys can be understood consistently from such an approach. 相似文献
20.
Andreas Leineweber 《哲学杂志》2013,93(14):1844-1864
The broadening of diffraction lines of layer faulted and, in particular, of microtwinned microstructures is analysed in detail. Thereby, stacked layer models turn out to be valuable to simulate the diffracted intensity if the metrics of the layers pertaining to the two types of domains are described by an average metrics plus domain-specific deviations from that metrics. Characteristic changes occur for the line-broadening effects if the fault probability and the extent of deviations from the average layer metrics vary. Emphasis is put, in particular, on a regime of line broadening characterised by merging of otherwise split peaks to yield single ones for sufficiently high twin probability. These merged peaks show unusual quadratic/parabolic increase of the integral breadths with the reflection order (parabolic microstrain broadening). This type of broadening has been predicted previously for special types of microstrain broadening, and indeed the (metrical) distortions of the domains with respect to the average structure allow perceiving even the twin-faulted microstructures as, in some sense, microstrained ones. Moreover, the special situation of superstructures is analysed, where the above mentioned merging is only observed for the fundamental but not for the superstructure reflections. Inconsistent (with respect to lattice metrics) peak positions can be observed for fundamental and superstructure reflections, which can affect lattice parameters determined from diffraction patterns. 相似文献