全文获取类型
收费全文 | 8103篇 |
免费 | 1158篇 |
国内免费 | 673篇 |
专业分类
化学 | 4161篇 |
晶体学 | 1167篇 |
力学 | 485篇 |
综合类 | 114篇 |
数学 | 1576篇 |
物理学 | 2431篇 |
出版年
2024年 | 8篇 |
2023年 | 77篇 |
2022年 | 206篇 |
2021年 | 259篇 |
2020年 | 310篇 |
2019年 | 232篇 |
2018年 | 161篇 |
2017年 | 232篇 |
2016年 | 378篇 |
2015年 | 312篇 |
2014年 | 484篇 |
2013年 | 608篇 |
2012年 | 461篇 |
2011年 | 591篇 |
2010年 | 534篇 |
2009年 | 517篇 |
2008年 | 543篇 |
2007年 | 557篇 |
2006年 | 523篇 |
2005年 | 430篇 |
2004年 | 399篇 |
2003年 | 324篇 |
2002年 | 250篇 |
2001年 | 188篇 |
2000年 | 219篇 |
1999年 | 165篇 |
1998年 | 157篇 |
1997年 | 151篇 |
1996年 | 104篇 |
1995年 | 76篇 |
1994年 | 89篇 |
1993年 | 62篇 |
1992年 | 52篇 |
1991年 | 55篇 |
1990年 | 37篇 |
1989年 | 33篇 |
1988年 | 33篇 |
1987年 | 27篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1959年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有9934条查询结果,搜索用时 10 毫秒
101.
A.A. Shiryaev M. Wiedenbeck V.B. Polyakov A.A. Lebedev 《Journal of Physics and Chemistry of Solids》2008,69(10):2492-2498
The distribution of both carbon and silicon isotopes in synthetic sublimation growth SiC wafers and in natural SiC grains was studied using secondary ion mass-spectrometry (SIMS). Significant variations in both isotopic ratios were observed which were broadly correlated with the crystalline perfection as documented by Raman microspectroscopy. Domains consisting of 15R (or with its admixture) are, on average, enriched in 12C isotope relative to 6H domains, and they also show larger scatter in their observed silicon isotope ratios. We ascribe such heterogeneity to fluctuations of Si/C ratio in the growth medium and it is possible to model the spatial extent of such fluctuations. For the natural SiC grains the isotopic data suggest that they grew under relatively stable conditions, although some of them show significant isotopic zoning. 相似文献
102.
金刚石中氦、氢含量的变化及在金刚石生长中的意义 总被引:1,自引:0,他引:1
天然金刚石自中心至边缘的显微傅里叶变换红外光谱研究表明:氮和氢在金刚石中的分布是不均匀的,这说明金刚石在整个生长过程中的物质环境是有差异的;中心至边缘的含氮总量、C-H键含量的总体降低趋势表明金刚石的生长过程是一个氮、氢的消耗过程,而中部的升高变化说明金刚石生长环境中存在氮、氢的补充,但氮补充得比氢更早一些.据此,可以将金刚石的生长过程划分为早期成核与长大、中期长大及末期长大三个阶段,其中早期和末期是氮和氢的消耗阶段,中期需要进行氮和氢的补充,且氮应该更早补充.氢对金刚石的生长是有利的,氢和氮不是以氮氢化合物的形式存在于金刚石生长的物质环境中,这暗示着在高温高压合成金刚石中欲引入氢,应当避免氮氢化合物的形成. 相似文献
103.
研究了Si3N4层在ZrN/Si3N4纳米多层膜中的晶化现象及其对多层膜微结构与力学性能的影响. 一系列不同Si3N4层厚度的ZrN/Si3N4纳米多层膜通过反应磁控溅射法制备. 利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明,由于受到ZrN调制层晶体结构的模板作用,溅射条件下以非晶态存在的Si3N4层在其厚度小于0.9 nm时被强制晶化为NaCl结构的赝晶体,ZrN/Si3N4纳米多层膜形成共格外延生长的柱状晶,并相应地产生硬度升高的超硬效应. Si3N4随层厚的进一步增加又转变为非晶态,多层膜的共格生长结构因而受到破坏,其硬度也随之降低. 相似文献
104.
V. Tsurkan J. Groza D. Samusi V. Zestrea R. Szymczak M. Mücksch R. Tidecks 《Journal of Physics and Chemistry of Solids》2005,66(11):2040-2043
The influence of cation substitution on the magnetic properties of single and polycrystals of FeCr2S4 spinel has been studied. The tetrahedral A-site substitution of the Fe by Cu in Fe1−xCuxCr2S4 was found to increase significantly the value of temperature Tm of the spin-glass like magnetization anomaly, whereas the octahedral B-site substitution of the Cr by In decreases Tm. This effect is suggested to result from a structural transformation influenced by variation of internal (chemical) pressure due to lattice contraction (Cu) or expansion (In). The observed reduced values of the Curie temperature for Cu-substituted single crystals compared to that of the polycrystalline samples are attributed to presence of Cl ions in samples detected by electron-probe microanalysis. The observed reduced value of saturation magnetization in the polycrystals compared to the single crystals is ascribed to the effect of surface anisotropy. Based on the experimental data the superexchange is concluded to be the dominant exchange interaction for 0≤x≤0.5 in Fe1−xCuxCr2S4, whereas the indirect exchange through the charge carriers is considered of minor importance. 相似文献
105.
J. D. Gunton 《Journal of statistical physics》1984,34(5-6):1019-1037
A review is given of recent developments involving the dynamics of random interfaces formed in the evolution of metastable and unstable systems. Topics which are discussed include interface growth and nonequilibrium dynamical scaling. The possibility of there being dynamical universality classes in first-order phase transitions is also discussed. There are a large number of systems of experimental interest which include binary alloys, binary fluids, and polymer mixtures. Other systems studied by computer simulation include the kinetic Ising, Potts, andZ
N
models.Work supported by NSF grant No. DMR-8013700. 相似文献
106.
Multiparticle fractal aggregation 总被引:1,自引:0,他引:1
Richard F. Voss 《Journal of statistical physics》1984,36(5-6):861-872
Kinetic fractal aggregation in a particle bath where a fractionf of the sites are initially occupied is studied withd=2 computer simulations. Independent particles diffusing to a fixed cluster produce an aggregate with fractal dimensionD 1.7 up to a correlation length(f). At larger lengthsD2.(f) asf 0. When the particles remain fixed but the cluster undergoes a rigid random walkD appears constant at larger scales but varies withf. D 1.95 at largef andD 1.7 asf 0. In both cases, the aggregate sizeN(t) grows with timet
(f)
. Aggregation on a surface by independently diffusing particles produces shapes reminiscent of electrochemical dendritic growth. The dependence of growth rate and geometry is studied as a function of particle concentration and sticking probability. 相似文献
107.
CUI YuanQing & YANG Wei School of Aerospace Engineering Applied Mechanics Tongji University Shanghai China University Office Zhejiang University Hangzhou 《中国科学:物理学 力学 天文学(英文版)》2011,(5)
Experimental results indicate three regimes for cracking in a ferroelectric double cantilever beam (DCB) under combined electromechanical loading. In the loading, the maximum amplitude of the applied electric field reaches almost twice the coercive field of ferroelectrics. Thus, the model of small scale domain switching is not applicable any more, which is dictated only by the singular term of the crack tip field. In the DCB test, a large or global scale domain switching takes place instead, which is driven... 相似文献
108.
Aijun Gao 《Journal of Physics and Chemistry of Solids》2011,72(10):1159-1164
Polyacrylonitrile (PAN)-based carbon fibers were heat treated at various temperatures for varying durations to simulate the graphitization process in the manufacture of C/C composites. Densification of the resulting fibers was confirmed by density measurement. The composition and structure of the fibers were investigated by means of elemental analysis, X-ray diffraction and Raman spectroscopy. For specified isothermal heat treatment time, the structural parameters depended strongly on heat treatment temperature. The nitrogen content decreased with increased heat treatment temperature and extended time at constant temperature. Nitrogen loss was complete at temperatures above 1900 °C. The graphite crystallite size increased rapidly with increasing heat treatment temperature, and slowly with extended isothermal heat treatment time. At 2100 °C a more ordered graphitic structure appeared. Denitrogenation induced “puffing”, which made the fibers expand. Decrease in density in the heat treatment temperature range 1500-1900 °C originated from the abrupt evolution of nitrogen, and above 1900 °C the graphitization transition induced steadily increasing density. Densification of the carbon fibers was determined both by the rate of denitrogenation and the rearrangement of carbon atoms. 相似文献
109.
Yang Wei 《Acta Mechanica Sinica》1987,3(4):344-353
Strain hardening, crack growth resistance and nonuniform load distribution have significant effects on the ductile tearing
process. A defect assessment procedure incorporating with the above features is proposed in the present paper, with the final
appearance of “design curves” to facilitate engineering applications. 相似文献
110.