全文获取类型
收费全文 | 428篇 |
免费 | 60篇 |
国内免费 | 40篇 |
专业分类
化学 | 141篇 |
晶体学 | 2篇 |
力学 | 20篇 |
综合类 | 3篇 |
数学 | 61篇 |
物理学 | 105篇 |
无线电 | 196篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 22篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 25篇 |
2018年 | 9篇 |
2017年 | 19篇 |
2016年 | 23篇 |
2015年 | 24篇 |
2014年 | 28篇 |
2013年 | 24篇 |
2012年 | 30篇 |
2011年 | 51篇 |
2010年 | 23篇 |
2009年 | 24篇 |
2008年 | 47篇 |
2007年 | 28篇 |
2006年 | 20篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 15篇 |
2002年 | 6篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有528条查询结果,搜索用时 15 毫秒
121.
基于小波变换的鲁棒型特征提取及说话人识别 总被引:4,自引:0,他引:4
说话人识别系统在实际应用中面临的主要困难之一是鲁棒性问题,干净语音环境下识别率很高的说话人识别系统,在有噪语音环境下识别性能显著降低。解决这一问题的方法之一是寻找具有鲁棒性的特征参数。本文结合具有多分辨率分析特点的小波变换技术,提出一种基于小波变换的鲁棒型特征提取算法,以提高说话人识别系统在噪声环境下的识别性能。对40个说话人的语音库SUDA2002-D2,在加性高斯白噪声环境下进行的识别实验结果表明,本文提出的特征提取算法可以有效地提高说话人识别系统在噪声环境下的识别性能。 相似文献
122.
在对蓝牙高级音频应用的协议模型进行深入研究的基础上,提出了一种基于蓝牙技术的音频流传输解决方案。方案利用CSR的BlueCore3MultiMedia芯片实现了音频信源端和音频信宿端硬件结构的设计,并在音视频分发传输协议层之上构建了控制音频流传输的高级音频分发框架软件实体,最终实现了点对点立体声音频传输的功能。 相似文献
123.
Ying Tao Zhong Ma Wenchao Wang Chi Zhang Lanlan Fu Qiong Zhu Yanliu Li Guisheng Li Dieqing Zhang 《Advanced functional materials》2023,33(9):2211169
The photoelectrocatalytic urea oxidation reaction (PEC-UOR) holds a great promise for the wastewater remediation and energy production. However, the low efficiency of semiconductor/cocatalysts type photoanodes for UOR restricts their applications in photoelectrocatalytic system. Herein, a new semiconductor/cocatalyst, Ni2P clusters sensitized TiO2 nanotube arrays photoanode (Ni2P/TiO2-NTAs) for PEC-UOR with high efficiency are developed. The 1D TiO2-NTAs structure accelerates urea molecules diffusion and promotes CO2 gas release at the electrode interface. Meanwhile, Ni2P is also beneficial to urea molecule absorption and CO2 desorption and enable to lower the energy barrier for amine (N H) dehydrogenation. Furthermore, the robust interfacial charge transfer pathway between Ni2P and TiO2 interface promotes the separation of photogenerated electrons and holes and the transfer of photogenerated electrons from Ni2P to TiO2. Therefore, this photoanode shows excellent PEC-UOR performance with the potential of 1.43 V versus reversible hydrogen electrode (RHE) when the current density reaches 10 mA cm−2, which is much lower than that of 2.24 V versus RHE and 1.58 V versus RHE for TiO2-NTAs and Ni(OH)2/TiO2-NTAs, respectively. 相似文献
124.
Gang Li Zimeng Li Lanlan Li Shan Liu Peng Wu Min Zhou Chenwen Li Xiaodong Li Gaoxing Luo Jianxiang Zhang 《Advanced functional materials》2023,33(2):2209466
Effective therapies capable of simultaneously inhibiting inflammation and promoting bone healing remain to be developed for inflammatory bone disease. Stem cell therapies hold great promise for a variety of diseases, but their translation is hampered by low cell survival, rapid clearance, and limited functional integration of transplanted stem cells in target tissues. Herein, a multifunctional hydrogel-based stem cell niche engineering strategy is reported for the treatment of inflammatory bone loss. By rationally integrating different functional modules, an injectable hydrogel-based stem niche is engineered, which possesses temperature-triggered gelling performance, inflammation/oxidative stress-resolving activity, stem-cell binding and survival-enhancing capacity, and osteogenesis-promoting capability. Using ectomesenchymal stem cells (EMSCs), effectiveness of this functionally advanced synthetic stem cell niche is demonstrated in rats with periodontitis, a representative inflammatory bone loss disease. Synergistic effects of the multifunctional hydrogel and EMSCs are also confirmed, with respect to normalizing the pathological microenvironment and improving alveolar bone regeneration in the periodontal tissue. Mechanistically, inflammation/oxidative stress-resolving and osteogenic differentiation promoting capacities of the synthetic stem cell niche are mainly achieved by an incorporated nanotherapy via the GDF15/Atf3/c-Fos axis of the MAPK signaling pathway. Besides periodontitis, the newly engineered hydrogel-stem cell therapies are promising for the treatment of other inflammatory bone defects. 相似文献
125.
YU LIU RUI CAO YING-WEI YANG 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):183-191
Complex stability constants (K
S), standard molar enthalpy changes (ΔH°) and entropy changes (TΔS°) for the inclusion complexation of native β-cyclodextrin (β-CD) (1) and some modified β-CDs, i.e., mono(6-ethylenediamino-6-deoxy)-β-CD (3), mono[6-diethylenetriamino-6-deoxy]-β-CD (4) and their corresponding copper complexes 5 and 6, with four representative bile acid guests, i.e., cholate (CA), deoxycholate (DCA), glycocholate (GCA) and taurocholate (TCA), were determined at 25 °C in aqueous phosphate buffer solution (pH 7.20) by means of isothermal titration microcalorimetry (ITC). The stoichiometry of resulting inclusion complexes between CDs and bile acids was demonstrated by UV and conductivity as well as ITC experiments, showing 1:1 binding model upon all inclusion complexation except for metal-mediated dimer 5. The complex stability constants for modified β-CD 2–4 are dramatically magnified with the extended length of amino tether. As compared with 3 and 4, copper(II) complexes 5 and 6 significantly enhance not only binding ability but also molecular selectivity toward bile guest molecule CA through multipoint recognition, but decreased complexes stability toward TCA could be attributed to the decreased hydrophobic microenvironment of CDs cavity due to the introduction of copper(II) coordination center. Thermodynamically, the resulting complexes between hosts and bile guests are driven absolutely by enthalpy, accompanied by entropy gain or loss. Using the present data and those previously reported for mono(6-amino-6-deoxy)-β-CD (2), thermodynamic behavior and enhanced molecular selectivity could be discussed from the viewpoint of hydrophobic interactions, electrostatic cooperation and van der Waals between the hosts and guests. 相似文献
126.
127.
128.
129.
采用分步浸渍法制备了P改性的Cu/Al2O3催化剂,利用N2吸附-脱附、X射线衍射、红外光谱、紫外-可见光谱、H2程序升温还原、NH3程序升温脱附和N2O解离吸附等方法对催化剂进行了表征,考察了P含量及浸渍次序对催化剂结构及其催化甘油氢解反应性能的影响.结果表明,先浸渍P再浸渍Cu时,所制Cu/Al2O3催化剂酸性较高,同时还促进了Cu的分散.随P含量的增加,催化剂的酸量及Cu分散度提高,并且Cu与P物种的相互作用增强;然而,P含量较高时会覆盖Cu,使暴露的Cu表面降低.先浸渍Cu后浸渍P时,尽管也提高了相应催化剂的酸性,但对Cu分散的影响不大,并且还会覆盖Cu使暴露的Cu表面明显降低.先浸渍P明显提高了Cu/Al2O3上甘油氢解反应性能.在220oC,3MPa,质量空速2h?1以及H2/甘油摩尔比20的条件下,当P含量由0增加至6%时,甘油转化率从17.1%升至95.0%,1,2-丙二醇选择性从83.7%升至97.2%.这可归因于催化剂酸性的提高及Cu与P间的相互作用. 相似文献
130.
电感耦合等离子体原子发射光谱法测定不锈钢食具容器中12种重金属元素的迁移量 总被引:1,自引:0,他引:1
经清洗的不锈钢食具容器中加入乙酸(4+96)溶液至规定体积,煮沸30min,冷却,补充乙酸溶液至原体积,在室温浸泡24h,所得溶液用于原子发射光谱法测定其中的12种元素的含量。选择强度相对较高且干扰较少的谱线作为所测定元素的分析线,对3项仪器工作参数进行了优化,结果表明:发生器射频功率1 250W;载气流量0.6L·min-1;观测高度16mm。12种元素的质量浓度均在0.05~1.0mg·L-1范围内与其谱线强度之间呈线性关系,其检出限(3s)在0.001~0.013mg·L-1之间。对方法的回收率进行了试验,测得回收率在98.2%~104%之间,对浸出液平行测定10次,测定值的相对标准偏差均小于3.0%。 相似文献