全文获取类型
收费全文 | 713篇 |
免费 | 65篇 |
国内免费 | 256篇 |
专业分类
化学 | 636篇 |
晶体学 | 13篇 |
力学 | 38篇 |
综合类 | 1篇 |
数学 | 22篇 |
物理学 | 324篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 44篇 |
2019年 | 21篇 |
2018年 | 16篇 |
2017年 | 42篇 |
2016年 | 21篇 |
2015年 | 21篇 |
2014年 | 43篇 |
2013年 | 49篇 |
2012年 | 46篇 |
2011年 | 81篇 |
2010年 | 41篇 |
2009年 | 65篇 |
2008年 | 62篇 |
2007年 | 53篇 |
2006年 | 59篇 |
2005年 | 41篇 |
2004年 | 40篇 |
2003年 | 32篇 |
2002年 | 27篇 |
2001年 | 19篇 |
2000年 | 17篇 |
1999年 | 16篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1034条查询结果,搜索用时 390 毫秒
101.
MoS2 nanosheet arrays supported on hierarchical nitrogen-doped porous carbon(MoS2@C)have been synthesized by a facile hydrothermal approach combined with high-temperature calcination.The hierarchical nitrogen-doped porous carbon can serve as three-dimensional conductive frameworks to improve the electronic transport of semiconducting MoS2.When evaluated as anode material for lithium-ion batteries,the MoS2@C exhibit enhanced electrochemical performances compared with pure MoS2 nanosheets,including high capacity(1305.5 mA h g-1 at 100 mA g-1),excellent rate capability (438.4 mA h g-1 at 1000 mA g-1).The reasons for the improved electrochemical performances are explored in terms of the high electronic conductivity and the facilitation of lithium ion transport arising from the hierarchical structures of MoS2@C. 相似文献
102.
Nb2O5/C nanosheets are successfully prepared through a mixing process and followed by heating treatment.Such Nb2O5/C based electrode exhibits high rate performance and remarkable cycling ability, showing a high and stable specific capacity of ~380 mAh g-1 at the current density of 50 mA g-1(much higher than the theoretical capacity of Nb2O5).Further more,at a current density of 500 mA g-1,the nanocomposites electrode still exhibits a specific capacity of above 150 mAh g-1 after 100 cycles.These results suggest the Nb2O5/C nanocomposite is a high performance anode material for lithium-ion batteries. 相似文献
103.
将石墨涂覆于传统铜箔(CCC)与穿孔铜箔(PCC)集流体表面,通过内部短路的方式进行预嵌锂处理,再以商业化的活性炭及预锂化的石墨分别为正、负极材料组装成锂离子电容器(LIC)。以PCC为集流体的LIC在0.1和2.0 A?g~(-1)的电流密度下,能量密度分别为118.2和51.7 Wh?kg~(-1),并且在0.5 A?g~(-1)的电流密度下循环1000次后的能量密度保持率为90%;以CCC为集流体的LIC在0.1和2.0 A?g~(-1)的电流密度下的能量密度分别为125.5和43.3 Wh?kg~(-1),在同等电流密度下2.0-3.8 V之间循环1000次后的能量密度保持率仅为73.2%。进一步研究表明,石墨采用PCC在预嵌锂的过程中避免了金属锂沉积,生成了均一且稳定的固体电解质膜(SEI),有效防止充放电过程中SEI膨胀,活性物质与集流体间粘结力降低,活性物质脱落等现象发生。因此,LIC通过PCC完成预嵌锂后的自放电及内阻更小,具有更佳的倍率性能和循环性能。 相似文献
104.
SnS2 is considered as an attractive anode material to substitute commercial graphite anodes of lithium-ion batteries due to its high specific capacity of 645 mAh·g-1 as well as low cost. Nevertheless, it suffers poor large volume expansion during the lithiation/delithiation processes, leading to the loss of electrical contact and rapid capacity fading. Herein, by using a facile one-step solvothermal method, SnS2 nanoflower/graphene nanocomposites (SnS2 NF/GNs) were prepared, where flower-like SnS2 hierarchical nanostructures consisting of ultrathin nanoplates, are tightly enwrapped in graphene nanosheets. As anode materials for lithium-ion batteries, the SnS2 NF/GNs electrode exhibit superior electrochemical performance, with a reversible capacity of 523 mAh·g-1 after 200 charge-discharge cycles. The enhanced Li storage performance was attributed to the synergistic effect of SnS2 and graphene. The SnS2 NF can effectively accommodate the volume change and shorten Li+ diffusion distance, while graphene nanosheets can further alleviate the volume expansion of SnS2 and improve the electronic conductivity. 相似文献
105.
BaGa2O4 and Ba3Co2O6(CO3)0.6 compounds were studied as electrolyte and cathode materials for Proton Ceramic Fuel Cells (PCFC), respectively. Not only BaGa2O4 rapidly reacts with atmospheric H2O and CO2 and leads to a progressive material decomposition, but it does not present real hydration properties in normal conditions of pressure. On the other hand, the basic cobalt oxocarbonate Ba3Co2O6(CO3)0.6 exhibits an interesting tendency for weight uptake and formation of hydrogencarbonate groups in moist heating/cooling conditions. This material was therefore considered for complementary studies in order to confirm its potential use as mixed proton-electron conductor, taking into account the ordered intergrowth of carbonates and face sharing Co-octahedra columns forming a pseudo-one-dimensional structure. Some preliminary results concerning electrochemical properties of the barium cobalt oxocarbonate as a PCFC cathode are also described and show at the moment modest performance, possibly related to a hydrated/carbonated surface layer contribution and/or the lack of electron percolation within the electrode layer. 相似文献
106.
锂离子电池由于具有工作电压高、体积小、质量轻、比能量高、寿命长和自放电率小等优点,成为
替代传统镍氢、镍镉电池的第三代航天器用储能电源。寿命预测是锂离子电池健康管理的重要方面,是掌
握电源衰退的重要手段。锂离子电池剩余使用寿命预测问题已成为电子系统健康管理领域的研究热点和具
有挑战性的问题之一。本文基于NASA埃姆斯中心的锂离子电池地面试验采集数据,首先分析了3种类型
的锂离子电池预测方法,之后重点研究了几种有效的数据驱动的锂离子电池寿命预测方法,并对各种预测
方法的效果进行了评价。实验结果表明,本文提出的方法能够有效的用于基于数据驱动的锂离子电池寿命
预测中,具有较强的工程应用价值。 相似文献
107.
Single-component molecular conductors [M(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate; M = Ni, Au, Pt, Cu), exhibit a variety of electromagnetic properties, which originate from the differences of the metal’s d-orbitals role in the band structure formation. The [Au(tmdt)2] crystal undergoes an antiferromagnetic transition at 110 K, while maintaining a metallic state at lower temperatures. The Au analog has a high magnetic transition temperature as compared to traditional magnetic molecular conductors due to the strong three-dimensional (3-D) structure and the contribution of the metal d-orbitals. The single-component molecular conductor, [Cu(tmdt)2], with π- and d-like frontier orbitals is isostructural with other metallic [M(tmdt)2] systems (M = Ni, Pt, Au). The Cu(tmdt)2 molecule is planar, which strikingly contrasts the tetrahedral coordination of Cu(dmdt)2 (dmdt = dimethyltetrathiafulvalenedithiolate) with similarly extended TTF type ligands. Interestingly, unlike other [M(tmdt)2] with metallic behavior, [Cu(tmdt)2] shows semiconducting behavior at room temperature (σ(RT) = ∼7 S cm−1). The RT conductivity increased linearly with increased pressure to 110 S cm−1 at 15 kbar despite the compressed pellet sample. The magnetic susceptibility indicates one-dimensional (1-D) Heisenberg behavior with J = 117 cm−1 and shows antiferromagnetic ordering at 13 K. The [Cu(tmdt)2] is a new multi-frontier π-d system, which introduces a d(σ)-type frontier orbital around the Fermi level of the π-like metal bands. 相似文献
108.
Corey T. Love Wojtek Dmowski Karen E. Swider-Lyons 《Journal of solid state chemistry》2011,184(9):2412-2419
We use electrochemistry, high-energy X-ray diffraction (XRD) with pair-distribution function analysis (PDF), and density functional theory (DFT) to study the instabilities of Li2CuO2 at varying state of charge. Rietveld refinement of XRD patterns revealed phase evolution from pure Li2CuO2 body-centered orthorhombic (Immm) space group to multiphase compositions after cycling. The PDF showed CuO4 square chains with varying packing during electrochemical cycling. Peaks in the G(r) at the Cu-O distance for delithiated, LiCuO2, showed CuO4 square chains with reduced ionic radius for Cu in the 3+ state. At full depth of discharge to 1.5 V, CuO was observed in fractions greater than the initial impurity level which strongly affects the reversibility of the lithiation reactions contributing to capacity loss. DFT calculations showed electron removal from Cu and O during delithiation of Li2CuO2. 相似文献
109.
The solid solubilities of potential B-site dopants in LaNb1-xMxO4−δ, materials, M=Ga, Ge, Si, Al, B, P, Zr or Ti, have been investigated in the search for possible novel proton conductors. In general, the solubility levels of these cations were found to be very low (x≤0.03). At the maximum value x=0.03, only compositions containing Ti, Ge, Ga and Si appeared pure at the limit of resolution of XRD. The literature phase diagram, La2O3-Nb2O5-ZrO2, has been re-analysed for compositions of low Zr-content around the composition LaNbO4. The electrical properties of phase pure Ti-doped compositions have been studied. Higher bulk and total conductivities were observed in wet than dry conditions, suggesting a significant protonic contribution to total conductivity. In wet conditions, the activation energy for bulk conductivity of LaNb0.98Ti0.02O4-δ was found to be much higher than that of an A-site, Sr-doped material, Sr0.02La0.98NbO4-δ, of similar acceptor dopant concentration. The Sr-doped composition offered higher conductivities than the Ti-doped composition up to approximately 900°C. 相似文献
110.