全文获取类型
收费全文 | 1296篇 |
免费 | 322篇 |
国内免费 | 281篇 |
专业分类
化学 | 1020篇 |
晶体学 | 86篇 |
力学 | 48篇 |
综合类 | 7篇 |
数学 | 11篇 |
物理学 | 727篇 |
出版年
2024年 | 5篇 |
2023年 | 26篇 |
2022年 | 65篇 |
2021年 | 64篇 |
2020年 | 118篇 |
2019年 | 80篇 |
2018年 | 62篇 |
2017年 | 76篇 |
2016年 | 108篇 |
2015年 | 80篇 |
2014年 | 67篇 |
2013年 | 135篇 |
2012年 | 82篇 |
2011年 | 84篇 |
2010年 | 93篇 |
2009年 | 80篇 |
2008年 | 67篇 |
2007年 | 77篇 |
2006年 | 83篇 |
2005年 | 52篇 |
2004年 | 58篇 |
2003年 | 56篇 |
2002年 | 25篇 |
2001年 | 39篇 |
2000年 | 26篇 |
1999年 | 22篇 |
1998年 | 18篇 |
1997年 | 24篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1899条查询结果,搜索用时 15 毫秒
101.
Rongrong Li Hongjie Peng Qingping Wu Xuejun Zhou Jiang He Hangjia Shen Minghui Yang Chilin Li 《Angewandte Chemie (International ed. in English)》2020,59(29):12129-12138
Herein, we propose the construction of a sandwich‐structured host filled with continuous 2D catalysis–conduction interfaces. This MoN‐C‐MoN trilayer architecture causes the strong conformal adsorption of S/Li2Sx and its high‐efficiency conversion on the two‐sided nitride polar surfaces, which are supplied with high‐flux electron transfer from the buried carbon interlayer. The 3D self‐assembly of these 2D sandwich structures further reinforces the interconnection of conductive and catalytic networks. The maximized exposure of adsorptive/catalytic planes endows the MoN‐C@S electrode with excellent cycling stability and high rate performance even under high S loading and low host surface area. The high conductivity of this trilayer texture does not compromise the capacity retention after the S content is increased. Such a job‐synergistic mode between catalytic and conductive functions guarantees the homogeneous deposition of S/Li2Sx, and avoids thick and devitalized accumulation (electrode passivation) even after high‐rate and long‐term cycling. 相似文献
102.
Juan M. Venegas Zisheng Zhang Theodore O. Agbi William P. McDermott Anastassia Alexandrova Ive Hermans 《Angewandte Chemie (International ed. in English)》2020,59(38):16527-16535
Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts. 相似文献
103.
Fang Yuanxing Zheng Yun Fang Tao Chen Yong Zhu Yaodong Liang Qing Sheng Hua Li Zhaosheng Chen Chuncheng Wang Xinchen 《中国科学:化学(英文版)》2020,63(2):149-181
Photocatalysis,which is the catalyzation of redox reactions via the use of energy obtained from light sources,is a topic that has garnered a lot of attention in recent years as a means of addressing the environmental and economic issues plaguing society today.Of particular interest are photosynthesis can potentially mimic a variety of vital reactions,many of which hold the key to develop sustainable energy economy.In light of this,many of the technological and procedural advancements that have recently occurred in the field are discussed in this review,namely those linked to:(1)photocatalysts made from metal oxides,nitride,and sulfides;(2)photocatalysis via polymeric carbon nitride(PCN);and(3)general advances and mechanistic insights related to TiO2-based catalysts.The challenges and opportunities that have arisen over the past few years are discussed in detail.Basic concepts and experimental procedures which could be useful for eventually overcoming the problems associated with photocatalysis are presented herein. 相似文献
104.
A.G. Cairns J.S.J. Hargreaves D. Mckay K. Wilson 《Journal of solid state chemistry》2010,183(3):613-61
The addition of 1 wt% Pd, Au, Ni and Cu dopants has been demonstrated to strongly alter the morphology of beta-phase molybdenum nitride prepared by treatment of MoO3 with a 3/1 H2/N2 mixture at 750 °C. Furthermore, the addition of Pd significantly enhances the surface area and the formation of the nitride phase. It is proposed that the facile formation of molybdenum bronzes in this system is important in this respect. The dopants have also been observed to modify the denitridation characteristics of the beta-phase, with an overall reduction of the proportion of NH3 formed upon using a 3/1 H2/Ar mixture with respect to the undoped sample. 相似文献
105.
Xinjiao Bai 《Applied Surface Science》2010,256(8):2327-1104
Hollow carbon nitride microspheres have been synthesized using a novel liquid phase electrodeposition technique. The microspheres are composed of numerous nanoparticles with size of about 5-30 nm. The diameters of the spheres range from 800 nm to 1.1 μm, and shell thickness is about 80-250 nm. This is the first attempt to synthesize carbon nitride with specific nanostructure by the electrodeposition method, which is proved to be facile and effective, and can be performed in an atmospheric environment and at a rather low temperature. The hollow carbon nitride may have potential applications as lubrication, catalysis, biomolecule adsorption, drug delivery, electronic materials, etc. in the future. 相似文献
106.
Béchir Rezgui Abel Sibai Tetyana Nychyporuk Mustapha Lemiti Georges Brémond 《Journal of luminescence》2009,129(12):1744-582
Silicon nitride (SiNx) films were prepared with a gas mixture of SiH4 and NH3 on Si wafers using the plasma-enhanced chemical vapor deposition (PECVD) method. High-resolution transmission electron microscopy and infrared absorption have been used to reveal the existence of the Si quantum dots (Si QDs) and to determine the chemical composition of the silicon nitride layers. The optical properties of these structures were studied by photoluminescence (PL) spectroscopy and indicate that emission mechanisms are dominated by confined excitons within Si QDs. The peak position of PL could be controlled in the wavelength range from 1.5 to 2.2 eV by adjusting the flow rates of ammonia and silane gases. Absorbance spectra obtained in the transmission mode reveal optical absorption from Si QDs, which is in good correlation with PL properties. These results have implications for future nanomaterial deposition controlling and device applications. 相似文献
107.
Structures and electronic properties of SimN8-m(0 〈 m 〈 8) clusters: a density functional theory study 下载免费PDF全文
The geometries, electronic structures and related properties of SimN8-m(0 〈 m 〈 8) clusters are studied using density functional theory (DFT) with hybrid functional B3LYP. The calculated results reveal several trends. For any stoichiometric clusters, the lowest energy isomers with an alteration of N and Si atoms are favourable in energy if the numbers of Si and N atoms are large enough to form ... Si N-Si-N... alternative chains. The bond lengths of single Si-N bonds are very close to the corresponding values of the bulk and other SiN clusters. The geometries for N-rich and Si4N4 clusters are planar structures, but three-dimensional structures are favourable in energy for Si-rich clusters. With the increase of m, the isotropic polarizability and average polarizability increase, the total binding energies generally decrease, the HOMO-LUMO gap and vertical ionization potential oscillate with increasing number of valence electrons, and their values with even valence electrons are larger than those with odd valence electrons. The atomic charges, IR and Raman properties are also reported. 相似文献
108.
109.
110.
立方氮化硅是高温高压研究近期合成得到的一种新物相,与已经在工业上普遍使用的氮化硅的两种六方物相(α相和β相)相比,新物相的密度增加了26%,预期是一种新型功能材料。简要综述了立方氮化硅的研究进展和存在的问题,讨论了立方氮化硅的人工合成和相关物性研究、Ⅳ(A)族氮化物(Ge3N4、Sn3N4、C3N4)的高密度物相研究,以及后尖晶石相氮化物的实验和理论探索等问题。介绍了作者最近利用炸药爆轰加载技术开展的冲击波合成实验结果,以α相氮化硅为冲击压缩前驱体,实现了在单次冲击波压缩实验中合成出了克量级立方氮化硅粉体,为进一步开展立方氮化硅的性能研究奠定了基础。 相似文献