全文获取类型
收费全文 | 873篇 |
免费 | 130篇 |
国内免费 | 86篇 |
专业分类
化学 | 149篇 |
晶体学 | 17篇 |
力学 | 85篇 |
综合类 | 18篇 |
数学 | 471篇 |
物理学 | 349篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 21篇 |
2019年 | 25篇 |
2018年 | 14篇 |
2017年 | 30篇 |
2016年 | 30篇 |
2015年 | 18篇 |
2014年 | 46篇 |
2013年 | 88篇 |
2012年 | 40篇 |
2011年 | 56篇 |
2010年 | 45篇 |
2009年 | 50篇 |
2008年 | 61篇 |
2007年 | 65篇 |
2006年 | 58篇 |
2005年 | 50篇 |
2004年 | 56篇 |
2003年 | 31篇 |
2002年 | 51篇 |
2001年 | 37篇 |
2000年 | 28篇 |
1999年 | 22篇 |
1998年 | 33篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 22篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1089条查询结果,搜索用时 15 毫秒
91.
92.
93.
A technique for determining the criterion of transition from the laminar to the turbulent flow regime on a stabilized plasmatron channel section is proposed. The technique uses experimental data and the methods of numerical simulation of plasma flows. A criterial generalization of the experimental data which for the first time makes it possible to establish the boundary of transition from the laminar to the turbulent flow regime on a stabilized plasmatron channel section is proposed. The experimental results are in good agreement with the theoretical dependences derived in the study. A curve (analog of the neutral curve) separating the domains of existence of laminar and turbulent plasma flows in a cylindrical channel is constructed in the space of the plasmatron working parameters.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, 2004, pp. 49–61. Original Russian Text Copyright © 2004 by Sinkevich and Chikunov. 相似文献
94.
Effects of anodic oxidation on corrosion properties of Al coating by arc spraying in seawater 下载免费PDF全文
A layer of Al coatings was prepared on the S355 steel by arc spraying, which was conducted by anodic oxidation treatment; the morphologies, chemical element compositions and phases of Al coating, and anodic oxide layer were analyzed with field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and X‐ray diffraction (XRD), respectively. The corrosion protections of Al coating before and after anodic oxidation were discussed with a seawater immersion test; the corrosion resistance mechanisms of Al coating and anodic oxide layer in the seawater were also investigated. The results show that the thickness of Al coating is about 300 µm by arc spraying, the sample surfaces become loose after seawater immersion corrosion and Cl? and O2? penetrate into the substrate from the cracks, destroying the binding properties of coating–substrate, and the coating fails. After anodic oxidation, the oxide layer is formed in the surface of Al coating with the thickness of about 30 µm; the corrosion products are mainly composed of Al(OH)3, which barraged the holes caused by seawater corrosion. The corrosion cracks are formed during the corrosion, while the number and depth of cracks decrease obviously after anodic oxidation treatment. The corrosion of Al coating becomes the local corrosion after anodic oxidation treatment, and the grains are smaller, which are easily nucleated to form a new corrosion resistance layer. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
95.
Pavel Trojovský 《Journal of Difference Equations and Applications》2017,23(10):1737-1746
This paper is devoted to a generalization of some previous results, as we completely solve a linear homogeneous difference equation of the second order with an exponential coefficient. 相似文献
96.
An arc of a digraph is called universal if and are in a common cycle for any vertex of . In this paper we characterize local tournaments whose every arc is universal. 相似文献
97.
98.
采用金属蒸气真空弧离子源对1Cr18Ni9Ti不锈钢进行Co离子注入,考察了注入处理试样的摩擦磨损性能.结果表明:Co注入处理样品的表面硬度比未注入样品的高1.0~1.5倍,且硬度随离子束流密度的增大而增大;Co注入处理试样的摩擦系数显著降低至约0.20,磨损体积损失降低25%~45%;当束流密度为22μA/cm2、注入剂量为5×1017/cm2时,注入处理样品的摩擦系数为0.19,耐磨寿命最长;在所选定的试验参数范围以内,当临界束流密度处于22μA/cm2时,保留剂量最大,改性表面硬度最高,耐磨性能最佳. 相似文献
99.
在电磁轨道炮发射过程中,膛口外的高温气团以远高于声速的运动速度向内膛运动,这会使得膛口的电弧形态发生改变以及电弧位移。为了实现膛口电弧运动过程的数值计算,本文基于磁流体理论,引入了一种和电弧等离子体自身电导率密切相关的电位边界条件处理方法,建立了膛口位置电弧仿真模型。对回流效应下的电弧运动规律进行了分析,并且研究了运动过程中电弧对内膛流场的温度分布产生的影响。结果表明电弧的运动加剧了膛内温升。 相似文献
100.
冲击速度和磨粒粒度对FeCrAl/WC复合涂层冲蚀性能的影响 总被引:4,自引:2,他引:4
采用粉芯丝材作为原料,利用高速电弧喷涂技术制备了具有良好抗高温冲蚀磨损性能的FeCrAl/WC复合涂层;考察了650℃下冲击速度和磨粒粒度对复合涂层高温冲蚀磨损性能的影响.结果表明,复合涂层和20G锅炉钢的耐高温冲蚀磨损能力随着磨粒粒度的增加而有所提高;30°攻角下冲蚀率随磨粒粒度的变化速率比90°攻角下的小;同20G锅炉钢相比,复合涂层对速更加敏感,速度越低,FeCrAl/WC复合涂层的抗冲蚀磨损性能越好. 相似文献