全文获取类型
收费全文 | 58310篇 |
免费 | 6941篇 |
国内免费 | 3976篇 |
专业分类
化学 | 21495篇 |
晶体学 | 574篇 |
力学 | 4231篇 |
综合类 | 545篇 |
数学 | 10549篇 |
物理学 | 31833篇 |
出版年
2024年 | 44篇 |
2023年 | 453篇 |
2022年 | 857篇 |
2021年 | 1209篇 |
2020年 | 1270篇 |
2019年 | 1248篇 |
2018年 | 1159篇 |
2017年 | 1456篇 |
2016年 | 1640篇 |
2015年 | 1321篇 |
2014年 | 2209篇 |
2013年 | 3688篇 |
2012年 | 2620篇 |
2011年 | 3064篇 |
2010年 | 2314篇 |
2009年 | 3473篇 |
2008年 | 3862篇 |
2007年 | 4318篇 |
2006年 | 3662篇 |
2005年 | 2889篇 |
2004年 | 2542篇 |
2003年 | 2707篇 |
2002年 | 3121篇 |
2001年 | 2391篇 |
2000年 | 2333篇 |
1999年 | 1998篇 |
1998年 | 1864篇 |
1997年 | 1150篇 |
1996年 | 1023篇 |
1995年 | 928篇 |
1994年 | 949篇 |
1993年 | 719篇 |
1992年 | 795篇 |
1991年 | 545篇 |
1990年 | 497篇 |
1989年 | 370篇 |
1988年 | 318篇 |
1987年 | 327篇 |
1986年 | 270篇 |
1985年 | 229篇 |
1984年 | 248篇 |
1983年 | 137篇 |
1982年 | 187篇 |
1981年 | 186篇 |
1980年 | 115篇 |
1979年 | 138篇 |
1978年 | 103篇 |
1977年 | 86篇 |
1976年 | 43篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
91.
92.
93.
The influence of pulse duration on the stress levels in ablation of ceramics: A finite element study
A. Vila Verde 《Applied Surface Science》2006,252(13):4511-4515
We present a finite element model to investigate the dynamic thermal and mechanical response of ceramic materials to pulsed infrared radiation. The model was applied to the specific problem of determining the influence of the pulse duration on the stress levels reached in human dental enamel irradiated by a CO2 laser at 10.6 μm with pulse durations between 0.1 and 100 μs and sub-ablative fluence. Our results indicate that short pulses with durations much larger than the characteristic acoustic relaxation time of the material can still cause high stress transients at the irradiated site, and indicate that pulse durations of the order of 10 μs may be more adequate both for enamel surface modification and for ablation than pulse durations up to 1 μs. The model presented here can easily be modified to investigate the dynamic response of ceramic materials to mid-infrared radiation and help determine optimal pulse durations for specific procedures. 相似文献
94.
Spectral and temporal characteristics of metallic nanoparticles produced by femtosecond laser pulses
We study the time of flight optical emission from titanium and tungsten nanosized particles, generated through femtosecond laser-matter interaction in vacuum, in the wavelength spectral range from 300 to 900 nm. Typical spectra consist of broadband structureless signals similar to black body emission from a macroscopic object. Nanoparticles temperature, deduced from their emission spectra, decreases drastically as a function of their time of arrival at a given distance from the target. This behaviour is seen to be independent of individual particle velocities. 相似文献
95.
We show that when polystyrene is exposed (for 15–60 sec) to a UV laser light beam (λ = 248 nm), its absorption and luminescent
properties change significantly. In the irradiated polymer, optical centers are formed with absorption bands in the 280–460
nm region and fluorescence bands in the 330–520 nm region. We have established the chemical structure of the optical centers
for fluorescence of polystyrene.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 54–58, January–February, 2006. 相似文献
96.
97.
The spin-1 Ising model, which is equivalent to the three-component lattice gas model, is used to study wetting transitions in three-component surfactant systems consisting of an oil, water, and a nonionic surfactant. Phase equilibria, interfacial profiles, and interfacial tensions for three-phase equilibrium are determined in mean field approximation, for a wide range of temperature and interaction parameters. Surfactant interaction parameters are found to strongly influence interfacial tensions, reducing them in some cases to ultralow values. Interfacial tensions are used to determine whether the middle phase, rich in surfactant, wets or does not wet the interface between the oil-rich and water-rich phases. By varying temperature and interaction parameters, a wetting transition is located and found to be of the first order. Comparison is made with recent experimental results on wetting transitions in ternary surfactant systems.This paper is dedicated to J. K. Percus in honor of his 65th birthday. 相似文献
98.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
99.
在不同激光脉宽下的高次谐波 总被引:3,自引:2,他引:1
用数值计算方法计算了不同强激光脉冲宽度下高次谐波的产生.我们发现对于激光场强度不高,不能有效电离初态的激光场,长脉冲宽度可以更有效产生高次谐波;而对于高场强的激光场,由于它能够在几个光学周期之内把原子的初态全部电离,所以短脉冲的激光场能够更有效产生高次谐波. 相似文献
100.
系统研究了Nd0.5Ca0.5Mn1-xAlxO3(x=0,0.03)单相多晶样品在低温下的电磁性质和超声特性.电阻和磁化率测量表明,Nd0.5Ca0.5O3体系在TCO-257 K处发生了电荷有序相变.超声声速从室温开始随着温度的降低逐渐减小,并在TCO附近达到最小,之后,随着温度的进一步降低,声速急刷增加,同时伴随着一个尖锐的超声衰减峰出现.TCO附近的超声异常表明体系中存在着强烈的电-声子相互作用,该电-声子耦合来源于Mn3 的Jahn-Teller效应.在低温下,出现了另一个超声衰减峰,它的出现归结为反铁磁相与顺磁相之间的相分离现象.随着Al在Mn位的掺入,超声声速的最低点和衰减峰向低温移动,表明体系中的电荷有序态和反铁磁相均被部分抑制, 相似文献