全文获取类型
收费全文 | 211637篇 |
免费 | 40787篇 |
国内免费 | 42334篇 |
专业分类
化学 | 70332篇 |
晶体学 | 2794篇 |
力学 | 7364篇 |
综合类 | 1673篇 |
数学 | 15358篇 |
物理学 | 69630篇 |
综合类 | 127607篇 |
出版年
2024年 | 867篇 |
2023年 | 1673篇 |
2022年 | 3439篇 |
2021年 | 3685篇 |
2020年 | 4218篇 |
2019年 | 6526篇 |
2018年 | 6638篇 |
2017年 | 8179篇 |
2016年 | 8108篇 |
2015年 | 9818篇 |
2014年 | 11320篇 |
2013年 | 13445篇 |
2012年 | 14042篇 |
2011年 | 16210篇 |
2010年 | 19925篇 |
2009年 | 20178篇 |
2008年 | 14433篇 |
2007年 | 13951篇 |
2006年 | 12637篇 |
2005年 | 11643篇 |
2004年 | 11073篇 |
2003年 | 8120篇 |
2002年 | 8236篇 |
2001年 | 7894篇 |
2000年 | 6875篇 |
1999年 | 4834篇 |
1998年 | 3015篇 |
1997年 | 2688篇 |
1996年 | 2876篇 |
1995年 | 3313篇 |
1994年 | 3363篇 |
1993年 | 3509篇 |
1992年 | 3055篇 |
1991年 | 2696篇 |
1990年 | 2216篇 |
1989年 | 2272篇 |
1988年 | 2291篇 |
1987年 | 1434篇 |
1986年 | 1435篇 |
1985年 | 1000篇 |
1984年 | 1100篇 |
1983年 | 465篇 |
1982年 | 962篇 |
1981年 | 786篇 |
1980年 | 815篇 |
1979年 | 574篇 |
1978年 | 549篇 |
1977年 | 637篇 |
1976年 | 1047篇 |
1972年 | 533篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Proton conductivity of phosphoric acid derivative of fullerene 总被引:1,自引:0,他引:1
The proton conductive property of methano [60] fullerene diphosphoric acid has been investigated under various humidity conditions at the temperature range between 15 and 45 °C. It shows proton conductivity as high as 10−2 S cm−1 at 25 °C under relative humidity of 95%. Thermal analyses including TG–DTA and thermal desorption mass spectroscopy (TDS) confirm that the compound is thermally stable up to 200 °C. Proton conduction of the compound depends very much on humidity or water content. The logarithmic conductivity at 25 °C is increased linearly with increasing relative humidity. The activation energy (Ea) estimated from the slope of log(σT) vs. 1/T is decreased from 1.08 to 0.52 eV, as the relative humidity is increased from 40% to 75%. The humidity dependence of conductivity is discussed in the light of the observed hydration isotherm. 相似文献
102.
A comprehensive study of the long pulse Nd:YAG laser drilling of multi-layer carbon fibre composites 总被引:2,自引:0,他引:2
W. S. O. Rodden S. S. Kudesia D. P. Hand J. D. C. Jones 《Optics Communications》2002,210(3-6):319-328
The results of an extensive experimental study of the free running Nd:YAG laser drilling of a multi-layer carbon fibre composite, where adjacent layers have differently orientated fibres, are reported. For holes drilled with the laser operating in fixed-Q mode at 1064 nm, parallel sections of blind holes illustrating discontinuities in the hole size along a given section direction will be shown to occur at the interface between adjacent layers. An explanation for this effect is proposed. Detailed single pulse drilling characteristics will be presented illustrating the exit hole diameter as a function of pulse energy and material thickness. These characteristics illustrate a ‘stable' drilling regime in which the exit hole diameters are least sensitive to changes in pulse energy or material thickness and a less ‘stable' regime in which they are more strongly dependent on these parameters. Drilling characteristics will be given for two different beam qualities, illustrating the greater drilling depth and reduced hole size achievable with an improved beam quality. Finally holes drilled through a 2 mm thick sample of material with multiple pulses are considered. Size distribution curves for entrance and exit holes will be presented. The total energy required (number of pulses × pulse energy) to drill through 2 mm thick material will be reported as a function of pulse energy in stationary air and argon atmospheres and in a partial vacuum, illustrating a threshold energy which is dependent upon the drilling atmosphere. The threshold energies will be discussed with reference to plasma formation and the reactivity of the drilling atmosphere. 相似文献
103.
陈泽乾 《数学物理学报(B辑英文版)》2002,22(3)
A new framework of Gaussian white noise calculus is established, in line with generalized expansion in [3, 4, 7]. A suitable frame of Fock expansion is presented on Gaussian generalized expansion functionals being introduced here, which provides the integral kernel operator decomposition of the second quantization of Koopman operators for chaotic dynamical systems, in terms of annihilation operators dt and its dual, creation operators t*. 相似文献
104.
A three-dimensional quasiclassical trajectory study of the dynamics of the light atom transfer reaction O(3P) + HCl(ν=0)→ OH + Cl was carried out employing two LEPS potential energy surfaces (I and II). Attention was focused mainly on three-dynamical properties; the oscillatory behavior of partial cross sections as a function of collision energy; the rotational excitation of the products; and the influence of reagent rotation on reactivity. Distinct differences were found between surfaces I and II with respect to these properties. The examination of individual trajectories indicated that there is a significant difference in the nature of these surfaces. While surface I is governed by weak repulsive forces, surface II is governed by strong attractive forces which tend to direct the reactants toward a collinear geometry. The present results confirm conclusions reached from an earlier study of the reaction Cl+HCl→ClH+Cl concerning correlations between dynamical properties and features of potential energy surfaces. For surfaces of the type that we termed HREP, since they are of repulsive nature and they lead to highly rotationally excited products, no significant oscillations of partial cross sections are obtained and reagent rotation promotes the reaction. On the other hand, for surfaces of the type that we termed COLD (collinearly directing), since they tend to direct the reactants toward a collinear geometry and form rotationally “cold” products, significant oscillations of partial cross sections are obtained and reagent rotation causes a decline in reactivity. 相似文献
105.
106.
复合体系方法测量液体力学谱 总被引:2,自引:0,他引:2
本文介绍了采用复合体系,测量得到凝聚态物质从固态到液态连续变化力学谱的一种新的实验方法。以簧振动为例,给出了解析的计算公式,以及应用条件。通过进一步综合分析,得到具有更广应用范围的近似公式,可以近似应用于其他不同的振动模式,如低频扭摆。应用新的测量方法,给出了典型小分子玻璃材料甘油和碳酸丙稀从玻璃态到液态的力学谱,观察到甘油和碳酸丙稀玻璃化转变、碳酸丙稀的再结晶、熔化和挥发的过程;测量得到挥发过程中水的质量随时间精确变化的曲线。最后,本文给出了新方法的一些应用展望。 相似文献
107.
108.
109.
果胶的提取率和质量与水解的环境关系密切 .本文重点在蚕沙中提取果胶从产率和颜色方面对水解的环境进行一些定性和定量的研究 ,获知各水解介质采用 0 3 %的稀硫酸液、温度 70— 80℃ ,时间 1h、pH1 5 ,提取的果胶从质量和产率上较理想 相似文献
110.
通过对我国环保产业的市场绩效、整体实力及立法现状进行分析,并针对入世对我国环保产业在机遇与挑战两方面的影响进行深入探讨,提出了完善市场竞争体制以提高市场绩效、调整环保产业结构以增强整体实力、建构环保产业法律体系以维护市场运行等相应的对策。 相似文献