全文获取类型
收费全文 | 718篇 |
免费 | 132篇 |
国内免费 | 46篇 |
专业分类
化学 | 180篇 |
晶体学 | 8篇 |
力学 | 48篇 |
综合类 | 1篇 |
数学 | 23篇 |
物理学 | 636篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 27篇 |
2020年 | 20篇 |
2019年 | 25篇 |
2018年 | 17篇 |
2017年 | 24篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 23篇 |
2013年 | 44篇 |
2012年 | 29篇 |
2011年 | 59篇 |
2010年 | 40篇 |
2009年 | 53篇 |
2008年 | 41篇 |
2007年 | 48篇 |
2006年 | 42篇 |
2005年 | 38篇 |
2004年 | 30篇 |
2003年 | 43篇 |
2002年 | 23篇 |
2001年 | 29篇 |
2000年 | 32篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 16篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 1篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有896条查询结果,搜索用时 234 毫秒
151.
对ITER包层屏蔽块进行了热工水力学设计及分析,并给出了两套合理的加热方案。分析结果表明,可以通过分阶段改变入口气体温度的方法实现在高效加热屏蔽块的同时满足工程及部件热应力的技术要求,并通过热应力计算验证了加热过程不会对屏蔽块产生不可预期的结构破坏。 相似文献
152.
The use of molten salts based on fluorides/chlorides/nitrates/sulfates or carbonates is now an accepted practice in energy conversion technologies and many other industrial processes. However, compatibility of molten salts with the structural alloys and materials corrosion has been of real concern at such temperatures (600–900°C). Hence, the material development and corrosion studies turn out to be an essential part of research. The results of recent studies are reviewed to understand the developments that have occurred in the latter part of the last decade. The corrosion kinetics of modern materials in variety of molten salts with focus on reaction mechanisms and corrosion products is investigated by scientists around the globe. Emphasis has also been given on the composition of the oxide films/corrosion products on alloys of interest in wide a range of melts. By and large, molten salt corrosion has been predominantly studied by gravimetric, electrochemical techniques and, morphology and chemical analysis of corrosion products by means of XRD, SEM/EDX, ICP/AAS, etc. This article gives in-depth insight into the composition of materials, the molten salt mixtures, and various aggressive environments mainly high temperatures and long exposures. 相似文献
153.
为了能从交通事故现场的微量物证中检测出道路标线涂料,并进一步区分其厂牌,选取国内三个不同厂牌的热熔型反光道路标线涂料及其配方原料,利用一维红外光谱(FTIR)、二阶导数光谱(SD-IR)、二维相关光谱(2D-IR)进行三级鉴定研究。实验结果表明,三个厂牌的涂料在一维谱图上峰形相似度很高,只是吸收峰波数有一定的差异,在1 435 cm-1附近都有宽强吸收峰,879,2 955,2 919,2 870 cm-1附近也有较强吸收峰,经过分区域局部放大并与每种配方原料图谱比对分析,可将三个厂牌涂料加以区分,700~970和1 370~1 660 cm-1区域内主要反映出三厂牌涂料的重质碳酸钙相对含量不同,2 800~2 960 cm-1区域内主要反映出聚乙烯蜡(PE蜡)、乙烯醋酸乙烯树脂(EVA)、邻苯二甲酸二辛酯(DOP)的相对含量不同。二阶导数谱图不仅验证了一维光谱分析的结果,而且进一步扩大微观差异,并在512~799 cm-1区域内反映出石英砂相对含量的不同。在1 351~1 525 cm-1范围内的二维红外相关光谱中,自动峰出现的位置和个数有着更为显著的差异。因此,红外光谱三级鉴定是一种快速有效识别、区分热熔型反光道路标线漆的方法,并且表观分辨率逐级提高。 相似文献
154.
The fretting corrosion behaviour of hot dipped tin coating is investigated at low fretting cycles at ±25 μm displacement amplitude, 0.5N normal load, 3 Hz frequency, 45-50% relative humidity, and 25 ± 1 °C temperature. The typical characteristics of the change in contact resistance with fretting cycles are explained. The fretted surface is examined using laser scanning microscope, scanning electron microscope and energy dispersive X-ray analysis to assess the surface profile, extent of fretting damage, extent of oxidation and elemental distribution across the contact zone. The interdependence of extent of wear and oxidation increases the complexity of the fretting corrosion behaviour of tin coating. The variation of contact resistance clearly revealed the fretting of tin coating from 50 to 1200 cycles and the fretting of the substrate above 1200 cycles. The observed low and stable contact resistance region and the fluctuating resistance region at various fretting cycles are explained and substantiated with Scanning electron microscopy (SEM), laser scanning microscope (LSM) and energy dispersive analysis of X-rays (EDAX) analysis results of the fretted surface. 相似文献
155.
In the nanosecond laser ablation regime, absorption of laser energy by the plasma during its early stage expansion critically influences the properties of the plasma and thus its interaction with ambient air. These influences can significantly alter spectral emission of the plasma. For organic samples especially, recombination of the plasma with the ambient air leads to interfering emissions with respect to emissions due to native species evaporated from the sample. Distinguishing interfering emissions due to ambient air represents a critical issue for the application of laser-induced breakdown spectroscopy (LIBS) to the analysis of organic materials. In this paper, we report observations of early stage expansion and interaction with ambient air of the plasma induced on a typical organic sample (nylon) using time-resolved shadowgraph. We compare, in the nanosecond ablation regime, plasmas induced by infrared (IR) laser pulses (1064 nm) and ultraviolet (UV) laser pulses (266 nm). Nanosecond ablation is compared with femtosecond ablation where the post-ablation interaction is absent. Subsequent to the early stage expansion, we observe for each studied ablation regime, spectral emission from CN, a typical radical for organic and biological samples. Time-resolved LIBS allows identifying emissions from native molecular species and those due to recombination with ambient air through their different time evolution behaviors. 相似文献
156.
在固态阴极射线发光中,过热电子碰撞激发有机材料而发光,因此加速层对电子的加速能力是影响器件发光亮度的关键因素之一.分别以SiO2和ZnO作为加速层.制备出两种固态阴极射线发光器件A:ITO/MEH-PPV/SiO2/Al和B:ITO/MEH-PPV/ZnO/Al.通过理论计算比较了电子从电极注入到加速层的隧穿电流密度以及SiO2层与ZnO层的电场强度,计算结果表明:在相同驱动电压下,SiO2作为电子加速层时隧穿电流的密度要大于ZnO层的隧穿电流的密度,并且SiO2层的电场强度比ZnO层的电场强度大.实验结果表明:SiO2作为加速层的器件的发光强度高于以ZnO为电子加速层器件的发光强度. 相似文献
157.
在薄膜电致发光中采用有机聚合物MEH-PPV和无机半导体SiO_2复合制成异质结发光器件,利用SiO_2的加速、倍增和离化的二次特性,实现了固态阴极射线发光.结构为ITO/SiO_2/MEH-PPV/SiO_2/Al的发光器件,其电致发光光谱的显著特征是有两个发光谱带.光谱中除了波长较长(峰值为583 nm)的MEH-PPV的激子发光谱外,还观察到了波长较短(峰值为403 nm)的蓝色发光谱,并且长短波的发光强度随着电压的不同而变化.电压较低时,只有长波光发射.当电压较高时,只有短波光存在.这种有两个谱带的发光是固态阴极射线发光的独特标志,它是一种全新的激发方式,引发出发光学中一些新而重要的问题.固态阴极射线发光理论的重要方面之一就足SiO_2的二次特性.文章研究了固态阴极射线发光动力学问题,高电场下SO_2二次特性及厚度对二次特性的影响. 相似文献
158.
159.
R. Plasil I. Korolov T. Kotrik P. Dohnal G. Bano Z. Donko J. Glosik 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):391-398
Experimental studies of the electron energy distribution function “EEDF” under well defined conditions in flowing afterglow
plasma, using a Langmuir probe are reported. The EEDF is measured in He2
+ and Ar+ dominated plasmas and in XeH+ and XeD+ dominated recombining plasmas. He is used as a buffer gas at medium pressures in all experiments (1600 Pa, 250 K). The deviation
of the measured EEDF from Maxwellian distribution is shown to depend on plasma composition and on the processes governing
the plasma decay. The influence of energetic electrons produced during the plasma decay on the body and tail of the EEDF is
observed. The mechanism of energy balance in afterglow plasma is discussed. 相似文献
160.
A. Laricchiuta D. Bruno M. Capitelli C. Catalfamo R. Celiberto G. Colonna P. Diomede D. Giordano C. Gorse S. Longo D. Pagano F. Pirani 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(3):607-612
In the perspective of higher approximations of the Chapman-Enskog theory for transport property calculations, existing transport
cross sections databases for interactions involving Earth atmosphere species have been updated and extended to Mars atmosphere
components, proposing a phenomenological approach for the derivation of the relevant elastic collision integrals in neutral-neutral
and neutral-ion interactions. Inelastic collision integrals terms, due to resonant charge exchange channels, have been considered
and the asymptotic approach extended to the estimation of charge transfer cross section of multiple resonant processes.
Electronic supplementary material Supplementary Online Material 相似文献