全文获取类型
收费全文 | 1238篇 |
免费 | 429篇 |
国内免费 | 438篇 |
专业分类
化学 | 887篇 |
晶体学 | 60篇 |
力学 | 85篇 |
综合类 | 51篇 |
数学 | 261篇 |
物理学 | 761篇 |
出版年
2024年 | 7篇 |
2023年 | 51篇 |
2022年 | 71篇 |
2021年 | 58篇 |
2020年 | 48篇 |
2019年 | 37篇 |
2018年 | 57篇 |
2017年 | 35篇 |
2016年 | 40篇 |
2015年 | 51篇 |
2014年 | 86篇 |
2013年 | 47篇 |
2012年 | 53篇 |
2011年 | 58篇 |
2010年 | 70篇 |
2009年 | 77篇 |
2008年 | 81篇 |
2007年 | 69篇 |
2006年 | 61篇 |
2005年 | 70篇 |
2004年 | 78篇 |
2003年 | 68篇 |
2002年 | 75篇 |
2001年 | 63篇 |
2000年 | 57篇 |
1999年 | 45篇 |
1998年 | 76篇 |
1997年 | 60篇 |
1996年 | 41篇 |
1995年 | 40篇 |
1994年 | 41篇 |
1993年 | 51篇 |
1992年 | 42篇 |
1991年 | 40篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1964年 | 3篇 |
1960年 | 4篇 |
1956年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有2105条查询结果,搜索用时 15 毫秒
71.
72.
Molecular dynamics simulations are performed to investigate the behaviour of helium atoms in titanium at a temperature of 30OK. The nucleation and growth of helium bubble has been simulated up to 50 helium atoms. The approach to simulate the bubble growth is to add helium atoms one by one to the bubble and let the system evolve. The titanium cohesion is based on the tight binding scheme derived from the embedded atom method, and the helium-titanium interaction is characterized by fitted potential in the form of a Lennard-Jones function. The pressure in small helium bubbles is approximately calculated. The simulation results show that the pressure will decrease with the increasing bubble size, while increase with the increasing helium atoms. An analytic function about the quantitative relationship of the pressure with the bubble size and number of helium atoms is also fitted. 相似文献
73.
Self-Injection and Acceleration of Monoenergetic Electron Beams from Laser Wakefield Accelerators in a Highly Relativistic Regime 下载免费PDF全文
H.Yoshitama ;T.Kameshima ;谷渝秋 ;郭仪 ;焦春晔 ;刘红杰 ;彭翰生 ;唐传铭 ;王小东 ;温贤伦 ;温天舒 ;吴玉迟 ;张保汉 ;朱启华 ;黄晓军 ;安维民 ;黄文会 ;唐传祥 ;林郁正 ;王小东 ;陈黎明 ;H.Kotaki ;M.Kando ;K.Nakajima 《中国物理快报》2008,25(8):2938-2941
Self-injection and acceleration of monoenergetic electron beams from laser wakefield accelerators are first investigated in the highly relativistic regime, using 100 TW class, 27 fs laser pulses. Quasi-monoenergetic multi- bunched beams with energies as high as multi-hundredMeV are observed with simultaneous measurements of side-scattering emissions that indicate the formation of self-channelfing and self-injection of electrons into a plasma wake, referred to as a 'bubble'. The three-dimensional particle-in-cell simulations confirmed multiple self-injection of electron bunches into the bubble and their beam acceleration with gradient of 1.5 GeV/cm. 相似文献
74.
We investigate the third-order optical nonlinearities in four novel porphyrin dimers (dimers A to D) and a monomeric porphyrin H2 CPTPP measured by using the single-beam z-scan technique with a pulsed Q-switched Nd:YAG nanosecond laser at 532nm. All the samples show strong excited state absorption (ESA) and high value of Х^(3) in the ns domain at this wavelength. We perform a comparison between dimer A and its monomer H2 CPTPP in their third-order optical nonlinearity, and discuss the relationships between the values of Х^(3) and the different bridging groups for all the dimers. 相似文献
75.
面粉、米粉中铅的悬浮进样石墨炉原子吸收法测定 总被引:3,自引:0,他引:3
在食品材料的微量元素分析中。已广泛采用石墨炉原子吸收法作为测试手段,固体进样技术的发展摆脱了繁琐的样品消解过程,从而在很大程度上克服了长期以来令人头痛的化学沾污问题。然而,由于直接固体进样技术称样量小,它要求样品具有高度的 相似文献
76.
本文指出在核子中存在玻色型荷电部份子(双夸克)的可能性。对核子中双夸克的分布函数作出一定假设选取适当参数后,将它们的贡献和原有的QCD计算结果合起来,能够使e-P深度非弹散射中预言的(?)值与实验数据较好的符合。 相似文献
77.
78.
该文建立了Henstock-Kurzweil 可积函数的 Laplace变换, 讨论了其基本性质及解析性质, 得到Henstock-Kurzweil可积意义下的反演公式, 并给出反例说明这一结果不能改进 相似文献
79.
Simulation study on terahertz vibrational absorption in liquid crystal compounds 总被引:1,自引:0,他引:1 下载免费PDF全文
The terahertz (THz) spectrum absorptions of nematic liquid crystal
(LC) material, i.e. N-(p-methoxybenzylidene)-p-butylaniline (MBBA),
and its relevant compounds are simulated in this paper by using the
density functional theory (DFT) method. A strong absorptive
frequency is located at 3.65 THz for the MBBA, which is in
agreement with experimental data found in the literature. The result
suggests that the DFT method is effective for dealing with the
anisotropic nematic LC compounds. 相似文献
80.
Ultrafast multiplex CARS investigation of vibrational characteristics in chloroform and PMMA 下载免费PDF全文
This paper demonstrates the femtosecond time-resolved coherent
anti-Stokes Raman scattering by using folded BOXCARS geometry where
an ultrashort broadband coherent white light continuum was used as
Stokes pulse, and carries out the non-contact detection at long
distance. The CARS signal is so easy to be detected that it can be
seen even by nude eye. The C--H bonds of chloroform or PMMA were
detected and the vibration modes belonging to the side chain and the
main chain in PMMA were also compared. Their vibrational
characteristics involved decay process and quantum beating were
discussed. This modified CARS experimental technique could make up
the deficiency of traditional CARS technique. 相似文献