全文获取类型
收费全文 | 4221篇 |
免费 | 161篇 |
国内免费 | 327篇 |
专业分类
化学 | 3614篇 |
晶体学 | 26篇 |
力学 | 17篇 |
综合类 | 10篇 |
数学 | 4篇 |
物理学 | 1038篇 |
出版年
2024年 | 10篇 |
2023年 | 83篇 |
2022年 | 50篇 |
2021年 | 66篇 |
2020年 | 81篇 |
2019年 | 83篇 |
2018年 | 59篇 |
2017年 | 65篇 |
2016年 | 117篇 |
2015年 | 93篇 |
2014年 | 107篇 |
2013年 | 297篇 |
2012年 | 324篇 |
2011年 | 280篇 |
2010年 | 195篇 |
2009年 | 245篇 |
2008年 | 248篇 |
2007年 | 258篇 |
2006年 | 278篇 |
2005年 | 232篇 |
2004年 | 201篇 |
2003年 | 214篇 |
2002年 | 126篇 |
2001年 | 103篇 |
2000年 | 90篇 |
1999年 | 79篇 |
1998年 | 100篇 |
1997年 | 75篇 |
1996年 | 68篇 |
1995年 | 68篇 |
1994年 | 60篇 |
1993年 | 60篇 |
1992年 | 35篇 |
1991年 | 51篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 4篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 5篇 |
排序方式: 共有4709条查询结果,搜索用时 31 毫秒
991.
The effects of foreign impurity ions in the conduction plane on the β″-Al2O3 lattice have been analyzed by molecular dynamics. As impurity ions, K and Ca ions were chosen and Na sites in the conduction plane were replaced with these ions. Results are summarized as follows: (1) The β″-Al2O3 lattice expands perpendicular to the conduction plane when K ions are doped; (2) Ca ions do not contribute to expansions of the β″-Al2O3 lattice; (3) both K and Ca ions reduce the mean square displacement of Na ions, which can be attributed to decreased Na ion diffusion. 相似文献
992.
Insulating lines and channels prepared by focused ion beam implantation on SIMOX wafers have been investigated by thermally modulated optical reflectance microscopy using optical and electrical excitation. Continuous hot lines and hot spots can be visualized by modulated electrical heating, whereas insulating lines forming channels can be imaged only with simultaneous optical and electrical excitation. Three different schemes have been investigated for the combined excitation: (i) optical modulation with additional DC voltage, (ii) optical and electrical pumps modulated at the same frequency with the detection effected at higher harmonics and (iii) two different modulation frequencies used for optical and electrical excitation with the detection effected at sum and difference frequencies. When detecting at higher frequencies, best contrast for the observation of the insulating lines adjacent to a channel is achieved by recording the modulated reflectance signal at the fourth harmonic 4f where f is the modulation frequency of the optical and electrical pump. The observed contrast enhancement of the double excited thermoreflectance signal is found to be mainly of a thermal origin. 相似文献
993.
本文叙述在HL-1M装置上用弯晶谱仪获取Fe的类He离子谱,用谱线的多谱勒加宽测量等离子体的离子温度,得到的等离子体HL-1M装置离子温度为500—800eV。 相似文献
994.
镍基溅射钨注碳电极的催化性能张季爽,吕瑶姣,李青莲(湖南大学化学化工系环境工程系,长沙410082)沈报恩(杭州大学化学系,杭州310028)析氢反应研究涉及到氢能、燃料电池、氯碱工业等的能源开发及节能技术,并具有重要的理论意义 ̄[1~5].本工作研... 相似文献
995.
996.
In principle, the depth distribution of the different chemical elements near the surface of solids can be determined quantitatively and absolutely with subnanometric depth resolution using medium energy ion scattering (MEIS), which is a refined version of Rutherford backscattering spectrometry (RBS). The energy resolution of current MEIS analyzers reveals spectral features that cannot be resolved using conventional RBS detectors. Thus, the usual data analysis framework based on a standard Gaussian approximation for the ion energy distribution in the target is applicable to regular RBS, but not generally to MEIS, in particular if one aims at subnanometric depth resolution. The observed asymmetry in the ion energy loss distributions is a direct consequence of the asymmetric character of inelastic energy transfers during individual atomic collisions and of the stochastic character of the resulting energy losses. We propose a model that accounts for the proper statistics of the small energy loss events and for an approximate electronic energy loss distribution during the backscattering event. The validity of this model is discussed and applied to the determination of HfO2 and TiO2 film thicknesses as well as to detect Al2O3 and HfO2 intermixing. This final application case also illustrates the potentialities as well as some inherent limitations of MEIS. The model developed here has been made available to the public in the form of a software for MEIS data analysis. 相似文献
997.
Contact angle hysteresis on nano-structured surfaces 总被引:1,自引:0,他引:1
We present results from an experimental study on the phenomenon of contact angle hysteresis on solid surfaces decorated by a random array of nanometric hollows. For weak values of the areal density of defects φd, the hysteresis H increases linearly with φd. This evolution is described by a pinning–depinning process of the contact line by individual defects. At higher values of φd, a collective pinning effect appears and H decreases with increasing φd. In the linear regime, our experimental results are compared to theoretical predictions for contact angle hysteresis induced by a single isolated defect on the solid surface. We suggest that the crossover from the individual to the collective pinning effects could be interpreted in terms of an overlapping of wetting cross sections. Finally, we analyse the influence of both the size and the morphology (hollows/hillocks) of defects on the anchorage of the contact line. 相似文献
998.
We present a study of the growth of silver nanoparticles or clusters on a TiO2(1 1 0) substrate in ultra-high vacuum. The growth is monitored in situ by ion and neutral scattering spectroscopy using He+ scattering and Auger spectroscopy. The scattering measurements show that only part of the surface is covered by Ag suggesting formation of clusters. Additionally an ex-situ study was performed by scanning electron microscopy and atomic force microscopy to determine the size distribution of these clusters. The average size distributions were found to range from about 5 to about 20 nm as a function of the evaporation flux. At the higher evaporation flux we observe formation of the smaller sized clusters. 相似文献
999.
1000.
《Electroanalysis》2004,16(9):779-782
Digital simulation of the cyclic voltammogram for the ion transfer through a liquid membrane of thickness from 1 mm to 10 nm was performed. The magnitude of current and the shape of the voltammogram simulated for extremely thin membrane (10 nm thick) were similar to those observed experimentally with a bilayer lipid membrane, BLM, of about 10 nm in thick, when the diffusion coefficient of an ion in the BLM was assumed to be extraordinary small (10?13 to 10?14 cm2 s?1). 相似文献