全文获取类型
收费全文 | 3038篇 |
免费 | 536篇 |
国内免费 | 588篇 |
专业分类
化学 | 1803篇 |
晶体学 | 106篇 |
力学 | 340篇 |
综合类 | 19篇 |
数学 | 102篇 |
物理学 | 1792篇 |
出版年
2024年 | 12篇 |
2023年 | 38篇 |
2022年 | 81篇 |
2021年 | 91篇 |
2020年 | 107篇 |
2019年 | 81篇 |
2018年 | 81篇 |
2017年 | 126篇 |
2016年 | 151篇 |
2015年 | 121篇 |
2014年 | 173篇 |
2013年 | 217篇 |
2012年 | 216篇 |
2011年 | 272篇 |
2010年 | 185篇 |
2009年 | 214篇 |
2008年 | 208篇 |
2007年 | 222篇 |
2006年 | 197篇 |
2005年 | 173篇 |
2004年 | 171篇 |
2003年 | 159篇 |
2002年 | 118篇 |
2001年 | 113篇 |
2000年 | 107篇 |
1999年 | 75篇 |
1998年 | 82篇 |
1997年 | 65篇 |
1996年 | 46篇 |
1995年 | 37篇 |
1994年 | 43篇 |
1993年 | 30篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 22篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1973年 | 1篇 |
排序方式: 共有4162条查询结果,搜索用时 15 毫秒
91.
92.
TiO2 electrodes are coated with NiO by DC magnetron sputtering, and their structural, optical and electrochemical performance has been investigated. X-ray diffractometry (XRD), UV-vis spectrophotometry, scanning electron microscopy (SEM), AC impedance, and linear sweep voltammetry (LSV) are used to characterize the TiO2/NiO electrodes. Their performance is evaluated with a computer controlled electrochemical workstation in combination with three conventional electrodes. The experimental results indicate that the surface modification of TiO2 electrodes with sputtered NiO reduces trap sites on TiO2 and improves the electrochemical performance of dye-sensitized solar cells (DSSCs). Sputtering NiO for 7 min, which is about 21 nm thick, on 6.5 μm thick TiO2 greatly improves the DSSC parameters, and the conversion efficiency increases from 3.21 to 4.16%. Mechanisms of the influence of the NiO coating on electrochemical performance are discussed. 相似文献
93.
Thermal barrier coatings (TBCs) are frequently used as insulation system for hot components in gas-turbine, combustors and power plant industries. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Glazing the top coat by laser beam is advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. Plasma-sprayed yttria-stabilized zirconia (YSZ) coating was glazed with Nd-YAG laser at different operating conditions. The surface morphologies, before and after laser treatment, were investigated by scanning electron microscopy. Laser beam assisted the densification of the surface by remelting a thin layer of the exposed surface. The laser glazing converted the rough surface of TBCs into smooth micron-size grains with size of 2-9 μm and narrow grain boundaries. The glazed surfaces showed higher Vickers hardness compared to as-sprayed coatings. The results revealed that the hardness increases as the grain size decreases. 相似文献
94.
95.
96.
This work discusses the influence of changes to ultrasound (US) parameters over the nickel cobalt (Ni-Co) metal thin film properties produced by supercritical CO2 (SC-CO2) electroplating. Additionally, Ni-Co films were produced by conventional electroplating and silent SC-CO2 and compared against each other.The discussion on metal thin film properties revolves around variations to the bath type ultrasonic power (15 W and 20 W) and frequency (42 k Hz and 72 kHz) during experiments. The properties provided by the three electroplating processes and analyzed include: grain sizes, film elemental content analyses, surface microstructures, film hardness, corrosion resistance, surface roughness, crystalline structure and preferential growth, etc. From the results it was clear that quality of films produced by US-SC-CO2 was improved compared to that of films produced by silent SC-CO2, which itself was better than those produced by conventional electroplating. However, when US power was varied we observed a decline in the mechanical properties of the produced films.The combination of ultrasonic agitation with SC-CO2 allows for improved mechanical properties such as: lower surface roughness, finer grain size and surface morphologies, increased corrosion resistance and film hardness. The ultrasound agitation applied to SC-CO2 electroplating enhanced the formation of alloyed metal as ultrasonic agitation increased the electrolyte flowability during electroplating process resulting in increased mass transfer while at the same time achieving a surface cleaning effect which removed metal ions with poor adhesion and other unwanted particles. Moreover, application of ultrasonic agitation avoids the use of surfactants so only changes to the physical phenomena and no changes to the chemical composition of the deposited thin films were observed, meaning less pollution to the electrolyte and higher purity of the deposited films.The US-SC-CO2 electroplating method described in this work effectively enhanced the mechanical properties of the deposited thin films compared to those produced by both silent SC-CO2 and conventional electroplating processes. 相似文献
97.
氘化物真空弧放电在许多领域均有应用,如无损检测、石油探井、中子活化分析等。和金属阴极不同,氘化物阴极放电时会释放大量的气体分子,表现出许多不同性质。采用放大镜头和ICCD相机观察了氘化物阴极真空弧放电光斑分布。测量系统的空间分辨率约为5 μm,时间分辨率最小2 ns。放电脉冲半高全宽(FWHM)0.9 μs,弧流波形为半周期正弦波。实验结果表明,氘化物真空弧放电时,所有阴极斑聚集为一个群落,表现为一个大光斑;在液滴作用下,阴极斑群落偶尔也会分裂为两个或多个群落;光斑形状不受弧流影响,但面积和亮度会随弧流增加而增大。氘化物阴极放电斑点聚集有利于产生高密度等离子体,提高放电效率。 相似文献
98.
真空断路器的开断容量限制其在高压大电流开断领域的应用,获取燃弧过程中的等离子体参数对于提高真空断路器的开断容量至关重要。利用发射光谱法对真空电弧内的等离子体参数进行了诊断,研究了在不同电流幅值条件下真空电弧内电子温度、电子密度、谱线强度的轴向分布规律,结合真空电弧高速图片对真空电弧内不同粒子的扩散过程与弧柱直径之间的关系进行了分析。得到的电子温度在8000~10 000 K量级,电子密度在1019~1020 m−3量级,电子温度与电子密度从阴极向阳极逐渐下降,同时铜原子谱线强度主要集中在两极而一价铜离子谱线强度由阴极向阳极逐渐升高。铜原子谱线强度的径向分布呈现类平顶波分布、一价铜离子谱线强度的径向分布呈现类高斯分布的特点,且铜原子的谱线范围略大于弧柱直径,一价铜离子的谱线范围略小于弧柱直径,两种粒子的扩散速度存在差异。 相似文献
99.
本文采用溶胶-凝胶法制备了SiO2增透膜,然后对其进行等离子体结合六甲基二硅胺烷(HMDS)表面改性处理。研究了后处理改性对增透膜表面形貌、微观结构、光学性能及激光损伤性能的影响规律,获得了抗真空有机污染的二氧化硅增透膜。结果表明,增透膜在采用等离子体结合HMDS表面改性处理后,膜层收缩、粗糙度下降、极性羟基等有机基团含量减少;两步后处理改善了增透膜膜层结构和光学性能,显著提高了膜层疏水能力和真空条件下的抗污染性能,并且对溶胶-凝胶二氧化硅增透膜的高损伤阈值属性不产生影响。 相似文献
100.
真空弧放电等离子体含有多种离子成分,并且各离子在空间上具有不同的分布规律.本文针对金属氘化物电极真空弧离子源,搭建了一台紧凑型磁分析装置,用来研究放电等离子体中氘离子与金属离子的空间分布.当离子源弧流为100 A左右时,该装置能有效地传输引出束流,并且具有较好的二次电子抑制效果,可准确获得各离子流强.利用该装置测量并获得了氘化钛含氘电极真空弧放电等离子体内氘离子和钛离子空间分布规律,结果表明:径向上,氘离子和钛离子都呈高斯分布,但氘离子分布均匀,而钛离子相对集中在轴线附近,导致轴线附近氘离子比例最低;轴向上,所有离子数量都以自然指数函数减少,而且相对幅度接近,所以氘离子比例几乎不变.本文研究结果不仅有助于理解真空弧放电等离子体膨胀过程,还可以指导金属氘化物电极真空弧离子源及其引出设计. 相似文献