全文获取类型
收费全文 | 1640篇 |
免费 | 245篇 |
国内免费 | 1366篇 |
专业分类
化学 | 2395篇 |
晶体学 | 54篇 |
力学 | 205篇 |
综合类 | 37篇 |
数学 | 31篇 |
物理学 | 529篇 |
出版年
2024年 | 18篇 |
2023年 | 55篇 |
2022年 | 59篇 |
2021年 | 88篇 |
2020年 | 93篇 |
2019年 | 84篇 |
2018年 | 76篇 |
2017年 | 88篇 |
2016年 | 87篇 |
2015年 | 126篇 |
2014年 | 167篇 |
2013年 | 184篇 |
2012年 | 180篇 |
2011年 | 166篇 |
2010年 | 170篇 |
2009年 | 171篇 |
2008年 | 142篇 |
2007年 | 140篇 |
2006年 | 151篇 |
2005年 | 115篇 |
2004年 | 129篇 |
2003年 | 103篇 |
2002年 | 98篇 |
2001年 | 94篇 |
2000年 | 67篇 |
1999年 | 49篇 |
1998年 | 39篇 |
1997年 | 49篇 |
1996年 | 38篇 |
1995年 | 42篇 |
1994年 | 40篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 30篇 |
1989年 | 34篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有3251条查询结果,搜索用时 171 毫秒
981.
982.
983.
Experimental improvements on determining the specific surface area of solid samples have been made by preparing adsorbent materials (MCM-41), measuring N2 adsorption-desorption isotherm and Origin software calculating the specific surface area through BET equation. These improvements enhance the students' understanding about the material synthesis, structure-property relationship, instrument operation and software data processing. 相似文献
984.
985.
986.
在负载型金属催化剂中,载体不仅可以提高金属分散度,同时还创造了独特的金属-载体界面.在特定的反应中,这些界面位点被认为是主要活性位点.对于这些体系,其催化性能的关键在于能否构建丰富且稳定的界面活性位点.本研究中,以乙二醇-钛前驱体水解得到的超高比表面积介孔TiO2作为载体(m-TiO2,490 m2/g),通过紫外光照沉积得到m-TiO2负载的高度分散的Pt纳米颗粒(1.9 wt% Pt,2.7 nm).相较而言,在商业P25 TiO2上负载量仅有0.2 wt%,而Pt的尺寸却达6.7 nm.通过简单的沉积沉淀法可以在Pt/m-TiO2和Pt/P25进一步构筑超高活性和稳定性的Pt-OH-Fe(Ⅲ)界面,所得到的Fe(OH)x-Pt/m-TiO2在催化低温CO氧化反应中表现出超高活性和稳定性,而Fe(OH)x-Pt/P25却会在测试过程中发生不可逆的失活.研究发现,相较于P25表面密度较小且对湿气不敏感的羟基物种,m-TiO2的高比表面积、介孔结构以及表面具有丰富(且对湿气敏感)的羟基(10.6 mmol/g,12.5 nm-2),可以确保Pt-OH-Fe(Ⅲ)界面在CO氧化的放热反应中不会因为脱水发生不可逆的失活. 相似文献
987.
988.
A superconducting squeezed type half-wave resonator (HWR) of β=0.09 has been developed at the Institute of Modern Physics, Lanzhou. In this paper, a basic design is presented for the stiffening structure for the detuning effect caused by helium pressure and Lorentz force. The mechanical modal analysis has been investigated the with finite element method (FEM). Based on these considerations, a new stiffening structure is proposed for the HWR cavity. The computation results concerning the frequency shift show that the low beta HWR cavity with new stiffening structure has low frequency sensitivity coefficient df/dp and Lorentz force detuning coefficient KL, and stable mechanical properties. 相似文献
989.
晶体硅纳米线及纳米孔阵列结构不仅有着优异的增吸收特性,而且与传统的硅膜电池相比能大幅降低原料成本,因而在光伏市场中有着巨大发展前景。本文采用严格耦合波分析(RCWA)研究了晶体硅正方形纳米线和纳米孔阵列结构的辐射特性,证明了两种结构的应用潜力。在AM1.5太阳能光谱辐射强度下,纳米线和纳米孔阵列结构最终效率都大于24%,高出同等厚度晶体硅薄膜70%P以上。两种纳米结构在周期600 nm附近达到最高,其中纳米线阵列结构有着更低的最优填充率。不同角度混合极化入射下,两种结构的最终效率能够维持在大的角度范围内(0~60°),表现了良好的角度特性。 相似文献
990.
Mesoporous SBA-15 with mesopore diameter up to 10.1 nm was prepared by a hydrothermal method, and was further functionalized to obtain different surface properties. Thus-prepared SBA-15 was employed as a template to synthesize rhombohedrally crystallized mesoporous La0.8Sr0.2CoO3 perovskite via a nanocasting method. The surface properties of the SBA-15 were adjusted by treatment with concentrated hydrochloric acid, trimethylchlorosilane (TMCS), and 3-aminopropyltriethoxysilane (APTES). A series of characterization techniques verified that all the synthesized templates possessed ordered two-dimensional hexagonal mesoporous structure, and the surface was successfully modified with methyl and amino groups. The mesoporous perovskite structure was formed in the samples and the surface properties of SBA-15 significantly influenced the structure and properties of La0.8Sr0.2CoO3 perovskite oxides. Wide-angle X-ray diffraction patterns suggested that the modified silica templates were conducive to the formation of pure perovskite frameworks with good crystallinity. The catalysts also possessed mesoporous structure, as confirmed by small-angle XRD patterns, high-resolution transmission electron microscopy images, and nitrogen adsorption analysis. Moreover, the La0.8Sr0.2CoO3 materials synthesized using surface-functionalized templates exhibited relatively higher catalytic activity and stability in CO oxidation. Complete CO conversion could be achieved at 140℃ using the thus-prepared La0.8Sr0.2CoO3 materials, and no significant loss in catalytic activity was observed after 100 h of on-stream reaction experiments. X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and O2 temperature-programmed desorption experiments revealed that the existence of Co4+, Sr enrichment in the perovskite structure, and high content of adsorbed oxygen species play a critical role in the enhanced catalytic activity of the catalysts. We also proposed the possible reasons for the effect of surface properties of the silica templates on the structure and properties of the La0.8Sr0.2CoO3 nanomaterials. 相似文献