全文获取类型
收费全文 | 5099篇 |
免费 | 517篇 |
国内免费 | 258篇 |
专业分类
化学 | 693篇 |
晶体学 | 110篇 |
力学 | 227篇 |
综合类 | 36篇 |
数学 | 3356篇 |
物理学 | 1452篇 |
出版年
2024年 | 7篇 |
2023年 | 46篇 |
2022年 | 81篇 |
2021年 | 87篇 |
2020年 | 101篇 |
2019年 | 135篇 |
2018年 | 121篇 |
2017年 | 138篇 |
2016年 | 132篇 |
2015年 | 127篇 |
2014年 | 265篇 |
2013年 | 582篇 |
2012年 | 280篇 |
2011年 | 378篇 |
2010年 | 286篇 |
2009年 | 429篇 |
2008年 | 409篇 |
2007年 | 353篇 |
2006年 | 272篇 |
2005年 | 206篇 |
2004年 | 190篇 |
2003年 | 207篇 |
2002年 | 145篇 |
2001年 | 112篇 |
2000年 | 108篇 |
1999年 | 94篇 |
1998年 | 86篇 |
1997年 | 89篇 |
1996年 | 78篇 |
1995年 | 56篇 |
1994年 | 67篇 |
1993年 | 29篇 |
1992年 | 32篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 23篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有5874条查询结果,搜索用时 15 毫秒
61.
Xuegui SongJulian Cheng 《Optics Communications》2012,285(24):4727-4732
The generalized method of moments (GMM) is introduced in the framework of estimating the lognormal-Rician parameters. This GMM approach provides a systematic procedure for finding the moment-based parameter estimators. The GMM estimator can estimate the two shaping parameters of the lognormal-Rician PDF jointly. The asymptotic performance of the GMM estimator is compared with Monte Carlo simulation results. The results show that the GMM approach can lead to estimators with satisfactory performance over a wide range of channel conditions. The proposed method can be easily applied to both noiseless and noisy environments. 相似文献
62.
Effect of void formation during MEVVA tungsten ion implantation on the microstructure and surface properties of H13 die steel 下载免费PDF全文
H13 die steel was implanted with tungsten using a metal vapour vacuum arc (MEVVA) ion source. When the pulsed beam current density of tungsten ions increased to 6mA?cm-2, some voids appeared in the high voltage electron microscope (HVEM) micrograph, which would disappear at an annealing temperature of 600℃. HVEM and x-ray diffraction were used for observing the phase structure of the annealed and un-annealed H13 steel after the steel was implanted. Results of wear and hardness tests indicated that whether the voids appear significantly influences the hardness and wear of H13 steel. Reasons for the formation of voids and the relation between the surface mechanical property and voids are discussed in terms of collision theory. 相似文献
63.
为阐明磁性离子在不同替代位置对YBCO体系超导电性的影响机制,利用正电子湮没及相关实验手段结合数值模拟,系统研究了Fe和Ni掺杂的YBa2Cu3O7-δ体系. 结果表明,Fe和Ni离子在替代过程中均以离子团簇的形式进入晶格. 当离子进入CuO2面时,由于团簇改变了周围的电子结构,造成电子的局域化,并直接影响了电子对的配对和输运,因而强烈抑制了体系的超导电性.而当掺杂离子进入Cu-O链区时,它们同样通过团簇的形式改变周围
关键词:
YBCO超导体
磁性离子替代
正电子湮没
数值模拟 相似文献
64.
65.
利用能量为2.0GeV的136Xe和2.7GeV的238U离子对C60薄膜进行了辐照,并用傅立叶变换红外光谱、X射线衍射谱和拉曼散射技术分析了辐照过的C60样品,在傅立叶变换红外光谱上,首次观察到一个位于670cm-1处的,表征未知结构的新峰,研究了其强度随电子能损和辐照剂量的变化规律.分析结果表明,电子能量转移主导了C60薄膜的损伤过程;而损伤的部分恢复是由强电子激发的退火效应引起的;另外,离子的速度在损伤的建立过程中也起了一定的作用 相似文献
66.
Carleson measure characterization of Bloch functions 总被引:1,自引:0,他引:1
Lou Zengjian 《数学学报(英文版)》1996,12(2):175-184
We give several equivalences of Bloch functions and little Bloch functions. Using these results we obtain the generalized Carleson measure characterization of Bloch functions and the generalized vanishing Carleson measure characterization of little Bloch functions, that is,f B if and only if |D
f(z)|
p
(1-|z|2)p-1
dm(z) is a generalized Carleson measure;f B
0 if and only if |D
f(z)|
p
(1-|z|2)p-1
dm(z) is a generalized vanishing Carleson measure, whereD
f( > 0) is the fractional derivative of analytic functionf of order, m denotes the normalised Lebesgue measure.Supported partly by the Young Teacher Natural Science Foundation of Shandong Province. 相似文献
67.
Applying simulated annealing to location-planning models 总被引:9,自引:0,他引:9
Simulated annealing is a computational approach that simulates an annealing schedule used in producing glass and metals. Originally developed by Metropolis et al. in 1953, it has since been applied to a number of integer programming problems, including the p-median location-allocation problem. However, previously reported results by Golden and Skiscim in 1986 were less than encouraging. This article addresses the design of a simulated-annealing approach for the p-median and maximal covering location problems. This design has produced very good solutions in modest amounts of computer time. Comparisons with an interchange heuristic demonstrate that simulated annealing has potential as a solution technique for solving location-planning problems and further research should be encouraged. 相似文献
68.
69.
《Current Applied Physics》2015,15(2):59-63
We have synthesized an efficient Cu2ZnSn(SxSe1−x)4 (CZTSSe) absorbers by using single-step rapid thermal sulfo-selenization process of sputtered stack metallic precursor (Zn/Sn/Cu) films. The structural and morphological studies confirm that the suitability of the rapid thermal sulfo-selenization process for the synthesis of a CZTSSe absorber without any secondary phases with large grains. The annealing atmosphere with a mixed-chalcogen source enhances the grain growth of the CZTSSe absorber as compared with pure Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) absorbers. The CZTSSe thin film solar cell shows the best conversion efficiency of ∼7%. 相似文献
70.
Cao Li-Ping 《Frontiers of Physics》2015,10(4):107801
The optical absorption properties of femtosecond-laser-made “black silicon” as a function of the annealing conditions were investigated. We found that the annealing process changes the surface morphology and absorption spectroscopy of the “black silicon” samples, and obtained a maximum sub-band-gap absorptance value of approximately 30% by annealing at 1000 °C for 30 min. The thermal relaxation and atomic structural transformation mechanisms are used to describe the lattice recovery and the increase and decrease of the substitutional dopant atom concentration in the microstructured surface during the annealing. Our results confirm that: i) owing to the thermal relaxation, the lattice defects decrease with the increase of the annealing temperature; ii) the quasi-substitutional and interstitial configurations of the doped atoms transform into substitutional arrangements when the annealing temperature increases; iii) the quasi-substitutional and interstitial configurations with higher energies of the doped atoms transform into interstitial configurations with the lowest energy after high-temperature annealing for a long period of time, causing the deactivation or reactivation of the sub-band-gap absorptance by diffusion. The results demonstrate that the annealing can improve the properties of “black silicon”, including defects repairing, carrier lifetime lengthening, and retention of a high absorptive performance. 相似文献