全文获取类型
收费全文 | 11352篇 |
免费 | 1852篇 |
国内免费 | 1398篇 |
专业分类
化学 | 8434篇 |
晶体学 | 154篇 |
力学 | 642篇 |
综合类 | 96篇 |
数学 | 1492篇 |
物理学 | 3784篇 |
出版年
2024年 | 29篇 |
2023年 | 239篇 |
2022年 | 376篇 |
2021年 | 392篇 |
2020年 | 443篇 |
2019年 | 446篇 |
2018年 | 355篇 |
2017年 | 373篇 |
2016年 | 572篇 |
2015年 | 549篇 |
2014年 | 740篇 |
2013年 | 846篇 |
2012年 | 1031篇 |
2011年 | 1108篇 |
2010年 | 730篇 |
2009年 | 638篇 |
2008年 | 711篇 |
2007年 | 584篇 |
2006年 | 572篇 |
2005年 | 522篇 |
2004年 | 453篇 |
2003年 | 339篇 |
2002年 | 325篇 |
2001年 | 270篇 |
2000年 | 218篇 |
1999年 | 278篇 |
1998年 | 199篇 |
1997年 | 157篇 |
1996年 | 175篇 |
1995年 | 156篇 |
1994年 | 141篇 |
1993年 | 88篇 |
1992年 | 95篇 |
1991年 | 73篇 |
1990年 | 94篇 |
1989年 | 58篇 |
1988年 | 38篇 |
1987年 | 27篇 |
1986年 | 39篇 |
1985年 | 22篇 |
1984年 | 28篇 |
1983年 | 22篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
941.
942.
介绍了小波变换的基本概念和特性.通过对岩石超声波检测信号的小波分析和处理,表明该方法在奇异信号检测和局部化分析方面具有优异特性. 相似文献
943.
利用傅立叶转换红外光谱和Raman谱仪分析了0.98 GeV的Fe离子在电子能损Se为3.5 keV/nm时, 不同辐照剂量(5×1010 —8×1013 ions/cm2)下, 在C60薄膜中引起的辐照损伤效应。 分析表明, Fe离子辐照引起了C60分子的聚合与损伤。 在辐照剂量达到一中间值1×1012 ions/cm2, C60分子的损伤得到部分恢复, 归因于电子激发引起的退火效应。 通过对Raman数据的拟合分析, 演绎出Fe离子辐照在C60材料中形成的潜径迹截面或引起损伤的截面约为1.32×10-14 cm2。 相似文献
944.
Zhongzhi Zhang Shuigeng Zhou Lichao Chen Jihong Guan Lujun Fang Yichao Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):99-107
We propose a geometric growth model for weighted
scale-free networks, which is controlled by two tunable parameters.
We derive exactly the main characteristics of the networks, which
are partially determined by the parameters. Analytical results
indicate that the resulting networks have power-law distributions of
degree, strength, weight and betweenness, a scale-free behavior for
degree correlations, logarithmic small average path length and
diameter with network size. The obtained properties are in agreement
with empirical data observed in many real-life networks, which shows
that the presented model may provide valuable insight into the real
systems. 相似文献
945.
One of the main differences between a low-pressure plasma treatment and an atmospheric pressure plasma treatment is that in atmosphere, the substrate material may absorb significant amount of water which may potentially influence the plasma treatment effects. This paper investigates how the moisture absorbed by aramid fibers during the atmospheric pressure plasma treatment influences the aging behavior of the modified surfaces. Kevlar 49 fibers with different moisture regains (MR) (0.5, 3.5 and 5.5%, respectively) are treated with atmospheric pressure plasma jet (APPJ) with helium as the carrier gas and oxygen as the treatment gas. Surface wettability and chemical compositions, and interfacial shear strengths (IFSS) to epoxy for the aramid fibers in all groups are determined using water contact angle measurements, X-ray photoelectron spectroscopy (XPS), and micro-bond pull out tests, respectively. Immediately after the plasma treatment, the treated fibers have substantially lower water contact angles, higher surface oxygen and nitrogen contents, and larger IFSS to epoxy than those of the control group. At the end of 30 day aging period, the fibers treated with 5.5% moisture regain had a lower water contact angle and more polar groups on the fiber surface, leading to 75% improvement of IFSS over the control fibers, while those for the 0.5 and 3.5% moisture regain groups were only 30%. 相似文献
946.
TiO2-coated activated carbon (TiO2/AC) composites and pure TiO2 powders were prepared by a sol-gel method using tetrabutylorthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), X-ray photoelectron spectrum (XPS) and nitrogen absorption. The photoactivity of samples was evaluated by methylene blue (MB) degradation. The analysis results show that compared with pure TiO2 powders, the spherical-shaped TiO2 particles are well-dispersed in the AC matrix and the size of the resulting TiO2 crystallites decreases to below 40 nm with increasing phase transformation temperature. The AC matrix creates anti-calcination effects and shows interfacial energy effects that control the growth of the TiO2 particles, baffle the anatase to rutile phase transition, and cumber the TiO2 particles to agglomerate. Compared with the surface areas of TiO2 powders, the combination of TiO2 and AC forms composites with high surface areas which are slightly affected by calcination temperature. By AC support, the photoactivity of TiO2 is increased in MB photocatalytic course, possible because active carbon increases photocatalytic activity of TiO2 particles by producing high concentration of organic compound near TiO2, and small-size TiO2 particles are well-dispersed on the surface of AC. 相似文献
947.
948.
The bandgap properties of 2D 8-fold symmetric photonic quasicrystals (PQCs) composed of a set of rods are numerically investigated for various fill factors, dielectric constants and propagation angles using the finite difference time domain (FDTD) method. Some interesting properties are found besides the known results: (i) the central frequency of the bandgap shifts to low frequency as r/a increases; (ii) an optimum fill factor to obtain the largest gap width exists, which decreases with increasing dielectric constant; (iii) compared with the behavior for a given fill factor, the variation of bandgap width for the optimum fill factor increases much more significantly with the dielectric constant. Selection guidelines for 8-fold symmetric PQC designs are provided for optimum fill factors and variation of the relative bandgap width at different dielectric constants. 相似文献
949.
Z.M. Tian J.H. He Y.Q. Wang P. Li H.Y. Xie L. Liu S.Y. Yin 《Solid State Communications》2007,142(9):545-549
Magnetic properties have been investigated on Mn doped TiO2(Ti0.98Mn0.02O2) bulk samples prepared by solid state reaction, which were sintered at different temperature ranging from 450 °C to 900 °C in air and argon atmosphere, respectively. The results show that the magnetic properties were strongly dependent on the sintering temperature and atmosphere. For samples sintered in air, the magnetization initially increase with the increase of sintering temperature up to 600 °C and thereafter it decrease. While the magnetization of samples sintered in argon atmosphere decreases monotonically with the increase of sintering temperature. Furthermore, for samples sintered at 600 °C in air, the magnetic susceptibility exhibits a dominant Curie-Weiss behaviour and no magnetic transition is observed over the temperature range from 10 to 300 K. In contrast, for samples sintered in argon atmosphere, besides the magnetic transition near 45 K perhaps caused by Mn3O4, another magnetic transition appears near room temperature. 相似文献
950.
Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce^4+ charge transfer transition
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ce^4+-doped Ca2SnO4 with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce^4+ ions doped in Ca2SnO4 occupy the Sn^4+ sites. The excitation and emission spectra of Ca2Sn1-xCexO4 appear to have broad bands with peaks at - 268nm and -442nm, respectively. A long excited-state lifetime (-83μs) for the emission from Ca2Sn1-xCexO4 suggests that the luminescence originates from a ligand-to-metal Ce^4+ charge transfer (CT). The luminescent properties of Ca2Snl_xCexO4 have been compared with those of Sr2CeO4, which is the only material reported so far to show Ce^4+ CT luminescence. More interestingly, it is observed that the emission intensity of Ca2Sn1-xCexO4 with a small doping concentration (x - 0.03) is comparable to that of Sr2CeO4 in which the concentration of active centre is 100%. 相似文献