全文获取类型
| 收费全文 | 416篇 |
| 免费 | 58篇 |
| 国内免费 | 23篇 |
专业分类
| 化学 | 235篇 |
| 晶体学 | 4篇 |
| 力学 | 23篇 |
| 综合类 | 6篇 |
| 数学 | 21篇 |
| 物理学 | 71篇 |
| 无线电 | 137篇 |
出版年
| 2025年 | 3篇 |
| 2024年 | 37篇 |
| 2023年 | 29篇 |
| 2022年 | 32篇 |
| 2021年 | 64篇 |
| 2020年 | 50篇 |
| 2019年 | 54篇 |
| 2018年 | 19篇 |
| 2017年 | 24篇 |
| 2016年 | 39篇 |
| 2015年 | 27篇 |
| 2014年 | 29篇 |
| 2013年 | 21篇 |
| 2012年 | 23篇 |
| 2011年 | 9篇 |
| 2010年 | 9篇 |
| 2009年 | 7篇 |
| 2008年 | 2篇 |
| 2007年 | 4篇 |
| 2006年 | 4篇 |
| 2005年 | 1篇 |
| 2004年 | 2篇 |
| 2001年 | 2篇 |
| 1999年 | 1篇 |
| 1994年 | 1篇 |
| 1990年 | 2篇 |
| 1979年 | 1篇 |
| 1959年 | 1篇 |
排序方式： 共有497条查询结果，搜索用时 0 毫秒
31.
一种基于等距线的碰撞检测算法 总被引：1，自引：0，他引：1
碰撞检测是虚拟现实场景模拟中的关键技术之一.文中试图在投影包围盒交集内通过判断等距线与投影线交点个数及位置的方法来构建一种高效优化的碰撞检测算法.该算法在适应虚拟环境的实时性要求的同时,减少了误判的产生. 相似文献
32.
对在非线性模拟电路中采用基于灵敏度序列的故障诊断方法进行了研究.针对非线性参数特性,首先采用分段线性叠代方法构建元件的线性模型,在被测电路中采用戴维南和诺顿定理等效替换;而后分段进行测前仿真,构造故障字典.采用分段线性叠代的方法,巧妙地构建了非线性元件的分析模型,避免了求解繁复的非线性代数方程或非线性微分方程.通过对两种等效替代模型进行分析和比较,指出各自的适用范围.在分段线性化后,引入工作域分析策略,简化了含多个非线性元件电路的测前分析.理论分析和相关实验为研究非线性电路的测试与故障诊断提供了新的方法. 相似文献
33.
34.
Xiaobo Zhu Tongen Lin Eric Manning Yuancheng Zhang Mengmeng Yu Bin Zuo Lianzhou Wang 《Journal of nanoparticle research》2018,20(6):160
The ever-growing market of electrochemical energy storage impels the advances on cost-effective and environmentally friendly battery chemistries. Lithium-ion batteries (LIBs) are currently the most critical energy storage devices for a variety of applications, while sodium-ion batteries (SIBs) are expected to complement LIBs in large-scale applications. In respect to their constituent components, the cathode part is the most significant sector regarding weight fraction and cost. Therefore, the development of cathode materials based on Earth’s abundant elements (Fe and Mn) largely determines the prospects of the batteries. Herein, we offer a comprehensive review of the up-to-date advances on Fe- and Mn-based cathode materials for LIBs and SIBs, highlighting some promising candidates, such as Li- and Mn-rich layered oxides, LiNi0.5Mn1.5O4, LiFe1-xMnxPO4, NaxFeyMn1-yO2, Na4MnFe2(PO4)(P2O7), and Prussian blue analogs. Also, challenges and prospects are discussed to direct the possible development of cost-effective and high-performance cathode materials for future rechargeable batteries. 相似文献
35.
模式匹配在网络安全领域有着重要的应用,随着网络环境的日益复杂,模式集合也随之增加.如何高效处理千万模式集下的字符串匹配成为网络安全的瓶颈之一.本文针对多模式匹配算法AC算法和WM算法进行了研究,采用了新型基于层次扫描和子节点数目搜索的双数组AC算法;从hash函数的选取和模式串的Tree树存储对WM算法进行了优化.能有效减少系统的内存占用,提高匹配效率. 相似文献
36.
研究一类具有分数阶线性微分算子的非线性微分方程积分边值问题解的存在性与唯一性.利用Schauder不动点定理及压缩映射原理,建立并证明了边值问题解的存在性定理和唯一性定理,并给出两个例子以说明所得结论. 相似文献
37.
Jingjing Yu Daxiang Liu Zhenyu Ding Yanan Yuan Jiayuan Zhou Fangfang Pei Haolin Pan Tianping Ma Feng Jin Lingfei Wang Wenguang Zhu Shouguo Wang Yizheng Wu Xue Liu Dazhi Hou Yang Gao Ziqiang Qiu Mengmeng Yang Qian Li 《Advanced functional materials》2024,34(2):2307259
The advent of van der Waals (vdW) ferromagnetic (FM) and antiferromagnetic (AFM) materials offers unprecedented opportunities for spintronics and magneto-optic devices. Combining magnetic Kerr microscopy and density functional theory calculations, the AFM-FM transition is investigated and a surprising abnormal magneto-optic anisotropy in vdW CrSBr associated with different magnetic phases (FM, AFM, or paramagnetic state) is discovered. This unique magneto-optic property leads to different anisotropic optical reflectivity from different magnetic states, permitting direct imaging of the AFM Néel vector orientation and the dynamic process of the AFM-FM transition within a magnetic field. Using Kerr microscopy, not only the domain nucleation and propagation process is imaged but also the intermediate spin-flop state in the AFM-FM transition is identified. The unique magneto-optic property and clear identification of the dynamics process of the AFM-FM phase transition in CrSBr demonstrate the promise of vdW magnetic materials for future spintronic technology. 相似文献
38.
Mengmeng Liu Xiaohang Zhu Yujie Song Guanlin Huang Jiamin Wei Xiaokai Song Qi Xiao Tao Zhao Wan Jiang Xiaopeng Li Wei Luo 《Advanced functional materials》2023,33(11):2213395
Oxygen reduction reaction (ORR) and sulfur reduction reaction (SRR) play key roles in advanced batteries. However, they both suffer from sluggish reaction kinetics. Here, an interesting nitrogen doped porous carbon material that can simultaneously activate oxygen and sulfur is reported. The carbon precursor is a nitrogen containing covalent organic framework (COF), constituting periodically stacked 2D sheets. The COF structure is well preserved upon pyrolysis, resulting in the formation of edge-rich porous carbon with structure resembling stacked holey graphene. The nitrogen containing groups in the COF are decomposed into graphitic and pyridinic nitrogen during pyrolysis. These edge sites and uniform nitrogen doping endow the carbon product with high intrinsic catalytic activities toward ORR and SRR. The COF derived carbon delivers outstanding performances when assembling as cathodes in the Li-S and Li-O2 batteries. Simultaneous activation of oxygen and sulfur also enables a new battery chemistry. A proof-of-concept Li-S/O2 hybrid battery is assembled, delivering a large specific capacity of 2,013 mAh g−1. This study may inspire novel battery designs based on oxygen and sulfur chemistry. 相似文献
39.
Qiuyun Zhang;Mengmeng Hu;Fan Chen;Jiao Lei;Jingsong Cheng;Juan Ma;Yongting Zhao;Yutao Zhang; 《应用有机金属化学》2024,38(6):e7504
Development of an energy-efficient and economical route is necessary for society to synthesize green biofuels. Herein, cobalt-doped tungstophosphoric acid (Co-HPW) is in-situ impregnated in the Zr-based metal–organic framework (MOF-801) forming composite of Co-HPW/MOF-801. The chemical composition, morphology, and acidic sites of the Co-HPW/MOF-801 composite were analyzed through x-ray diffractometer (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDS), thermogravimetric analysis (TG), N2 physisorption, ammonia temperature-programmed desorption (NH3-TPD), pyridine-adsorbed infrared spectra (Py-FTIR), and x-ray photoelectron spectroscopy (XPS). The catalytic performance of the as-synthesized catalyst was explored to catalyze esterification of lauric acid (LA) with methanol. The outcomes revealed that the Co-HPW/MOF-801 nanocatalyst achieved a high conversion of 86.3% under the optimized reaction condition (catalyst amount of 0.15 g, temperature of 100°C, time of 4 h, and methanol/LA molar ratio of 20:1). The excellent catalytical performance is mainly due to the large BET surface area, exposure of more active centers from available pore structure, and simultaneous possession of high Lewis and Brønsted acidity. Furthermore, the kinetic study revealed that the reaction process was kinetically controlled and the activation energy was found to be 42.1 kJ/mol. The results suggest that the synthesized Co-HPW/MOF-801 nanocatalyst is an environmental greenness, low cost, and suitable for easy scale-up for the production of biofuels. 相似文献
40.
Mengmeng Lao Kun Rui Guoqiang Zhao Peixin Cui Xusheng Zheng Shi Xue Dou Wenping Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(16):5486-5491
Heterostructured nanomaterials, generally have physicochemical properties that differ from those of the individual components, and thus have potential in a wide range of applications. New platinum (Pt)/nickel bicarbonate (Ni(HCO3)2) heterostructures are designed for an efficient alkaline hydrogen evolution reaction (HER). Notably, the specific and mass activity of Pt in Pt/Ni(HCO3)2 are substantially improved compared to the bare Pt nanoparticles (NPs). The Ni(HCO3)2 provides abundant water adsorption/dissociation sites and modulate the electronic structure of Pt, which determine the elementary reaction kinetics of alkaline HER. The Ni(HCO3)2 nanoplates offer a platform for the uniform dispersion of Pt NPs, ensuring the maximum exposure of active sites. The results demonstrate that, Ni(HCO3)2 is an effective catalyst promoter for alkaline HER. 相似文献