全文获取类型
收费全文 | 2384篇 |
免费 | 84篇 |
国内免费 | 23篇 |
专业分类
化学 | 1469篇 |
晶体学 | 7篇 |
力学 | 43篇 |
数学 | 400篇 |
物理学 | 572篇 |
出版年
2023年 | 9篇 |
2022年 | 27篇 |
2021年 | 28篇 |
2020年 | 38篇 |
2019年 | 29篇 |
2018年 | 30篇 |
2017年 | 36篇 |
2016年 | 61篇 |
2015年 | 59篇 |
2014年 | 61篇 |
2013年 | 121篇 |
2012年 | 187篇 |
2011年 | 176篇 |
2010年 | 123篇 |
2009年 | 111篇 |
2008年 | 159篇 |
2007年 | 166篇 |
2006年 | 167篇 |
2005年 | 203篇 |
2004年 | 139篇 |
2003年 | 125篇 |
2002年 | 115篇 |
2001年 | 21篇 |
2000年 | 24篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 34篇 |
1995年 | 19篇 |
1994年 | 20篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有2491条查询结果,搜索用时 15 毫秒
111.
112.
Bas B. Van Aken Martial Duchamp Chris B. Boothroyd Rafal E. Dunin-Borkowski Wim J. Soppe 《Journal of Non》2012,358(17):2179-2182
The p-type Si layer in a-Si and μc-Si solar cells on foil needs to fulfil several important requirements. The layer is necessary to create the electric field that separates the photo-generated charge carriers; the doping also increases the conductivity to conduct the photocurrent to the front contact; on the other hand, the p-layer should transmit the incident light efficiently to the intrinsic absorber layer. We show that it is possible to study TEM samples prepared, for analysis of possible layer defects, by focussed ion beam milling to detect boron and carbon concentrations as low as 1020 cm-3, using core-loss EELS combined with numerical analysis. We control the band gap and activation energy of p-a-SiC by varying the B2H6 and CH4 flow during deposition in the process chamber. We have found a linear relation between the activation energy of the dark conductivity Eact and the optical band gap E04. Modelling shows that the optimum efficiency in nip solar cells is obtained when the p-a-SiC band gap is slightly larger than the band gap of the absorber layer. We have assessed the potential of core-loss EELS for detecting B and C concentrations as low as 1020 cm-3 in a spatially resolved manner, and of low-loss EELS as a probe of the local variations in plasmon energy. 相似文献
113.
In this article, we investigate the artistic puzzle of designing mathematics experiences (MEs) to engage young children with ideas of group theory, using a combination of hands-on and computational thinking (CT) tools. We elaborate on: (1) group theory and why we chose it as a context for young mathematicians’ experiences with symmetry and transformations; (2) our ME design principles of agency, access, surprise and audience; (3) the affordances of CT that complement our design principles; and (4) three ME variations we tested in grades 3–6 classrooms. We then reflect on the ME variations based on our design principles and the affordances of CT, and consider how the MEs may be further adapted and improved. 相似文献
114.
115.
116.
We construct a family of finite 2-groups which have commuting graph of increasing diameter. 相似文献
117.
118.
Carbon K‐edge X‐ray spectroscopy has been applied to the study of a wide range of organic samples, from polymers and coals to interstellar dust particles. Identification of carbonaceous materials within these samples is accomplished by the pattern of resonances in the 280–320 eV energy region. Carbonate minerals are often encountered in the study of natural samples, and have been identified by a distinctive resonance at 290.3 eV. Here C K‐edge and Ca L‐edge spectra from a range of carbonate minerals are presented. Although all carbonates exhibit a sharp 290 eV resonance, both the precise position of this resonance and the positions of other resonances vary among minerals. The relative strengths of the different carbonate resonances also vary with crystal orientation to the linearly polarized X‐ray beam. Intriguingly, several carbonate minerals also exhibit a strong 288.6 eV resonance, consistent with the position of a carbonyl resonance rather than carbonate. Calcite and aragonite, although indistinguishable spectrally at the C K‐edge, exhibited significantly different spectra at the Ca L‐edge. The distinctive spectral fingerprints of carbonates provide an identification tool, allowing for the examination of such processes as carbon sequestration in minerals, Mn substitution in marine calcium carbonates (dolomitization) and serpentinization of basalts. 相似文献
119.
120.