全文获取类型
收费全文 | 19357篇 |
免费 | 3179篇 |
国内免费 | 2422篇 |
专业分类
化学 | 14599篇 |
晶体学 | 270篇 |
力学 | 1034篇 |
综合类 | 132篇 |
数学 | 2100篇 |
物理学 | 6823篇 |
出版年
2024年 | 45篇 |
2023年 | 345篇 |
2022年 | 474篇 |
2021年 | 607篇 |
2020年 | 755篇 |
2019年 | 771篇 |
2018年 | 701篇 |
2017年 | 612篇 |
2016年 | 917篇 |
2015年 | 960篇 |
2014年 | 1184篇 |
2013年 | 1467篇 |
2012年 | 1687篇 |
2011年 | 1822篇 |
2010年 | 1337篇 |
2009年 | 1170篇 |
2008年 | 1407篇 |
2007年 | 1252篇 |
2006年 | 1115篇 |
2005年 | 959篇 |
2004年 | 759篇 |
2003年 | 665篇 |
2002年 | 675篇 |
2001年 | 516篇 |
2000年 | 423篇 |
1999年 | 348篇 |
1998年 | 278篇 |
1997年 | 225篇 |
1996年 | 206篇 |
1995年 | 168篇 |
1994年 | 202篇 |
1993年 | 147篇 |
1992年 | 134篇 |
1991年 | 103篇 |
1990年 | 93篇 |
1989年 | 88篇 |
1988年 | 54篇 |
1987年 | 40篇 |
1986年 | 40篇 |
1985年 | 38篇 |
1984年 | 28篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 23篇 |
1979年 | 6篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
31.
32.
Y. KAGAWAT. FUJITANI Y. FUJITAL. CHAI N. WAKATSUKIT. TSUCHIYA 《Journal of sound and vibration》2002,255(2):323-335
The application of the discrete Huygens' modelling has been discussed for acoustic wave propagation problems, in which the scalar wave field problems have been focused. The present paper extends the application of the modelling to the elastic wave propagation in a homogeneous elastic medium in which two types of waves, the longitudinal wave and the shear wave, are independent except at the boundary. Each wave can be treated like a scalar wave until the two waves reach the boundary where they couple so as to satisfy the displacement or stress boundary condition. We propose the approach confining ourselves to the two-dimensional field. Some examples are demonstrated, whose solutions are compared with the vectorial wave modelling and finite difference modelling solutions whenever they are available. 相似文献
33.
34.
强流脉冲电子束在材料中的能量沉积剖面、能量沉积系数和束流传输系数受其入射角的影响很大,理论计算了0.5~2.0MeV的电子束以不同的入射角在Al材料中的能量沉积剖面和能量沉积系数,并且还计算了0.4~1.4MeV电子束以不同入射角穿透不同厚度C靶的束流传输系数。计算结果表明,随着入射角的增大,靶材表面层单位质量中沉积的能量增大,电子在靶材料中穿透深度减小,能量沉积系数减小,相应的束流传输系数也减小;能量为0.5~2.0MeV的电子束当入射角在60°~70°时在材料表面层单位质量中沉积的能量较大。 相似文献
35.
C.-G. Duan L.-H. Song L.-J. Huo G.-L. Li 《The European Physical Journal C - Particles and Fields》2003,29(4):557-561
The energy loss effect in nuclear matter, which is a nuclear effect apart from the nuclear effect on the parton distribution as in deep-inelastic scattering process, can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of the nuclear parton distribution studied only with lepton deep-inelastic scattering experimental data, the measured Drell-Yan production cross sections for 800 GeV proton incident on a variety of nuclear targets are analyzed within the Glauber framework which takes into account the energy loss of the beam proton. It is shown that the theoretical results with considering the energy loss effect are in good agreement with the FNAL E866 data.Arrival of the final proofs: 24 June 2003 相似文献
36.
37.
A Promising MoO_x-based Catalyst for n-Heptane Isomerization 总被引:1,自引:0,他引:1
Song Hai CHAI Xin Ping WANG* Ying Jun WANG Tian Xi CAI State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 《中国化学快报》2003,14(7)
The increasing demand for higher-octane gasoline and the regulations limiting the amount of aromatics in the fuel motivate the interest in catalytic isomerization of n-alkanes. In the last ten years, transition metal oxides or oxycarbides based on molybdenum or tungstate have attracted much attention due to their high activity and isomerization selectivity compared to the conventional bifunctional supported platinum catalyst and high resistance to sulphur and nitrogen catalyst poisons1-5. Ma… 相似文献
38.
Song LI Guo Mao WANG Zhi Song LIU 《数学学报(英文版)》2005,21(6):1475-1486
The purpose of this paper is to investigate the mean size formula of wavelet packets in Lp for 0 〈 p ≤ ∞. We generalize a mean size formula of wavelet packets given in terms of the p-norm joint spectral radius and we also give some asymptotic formulas for the Lp-norm or quasi-norm on the subdivision trees. All results will be given in the general setting, 相似文献
39.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
40.
陈海珍 《宁波大学学报(理工版)》2004,17(4):444-448
选用了钛酸丁酯、硬脂酸和乙二醇作为表面活性剂,采用表面化学修饰和表面物理修饰2种方法修饰纳米氧化钛,然后分散在乙二醇溶剂中形成溶胶溶液.并通过红外光谱仪、紫外分光计、原子力显微镜,分析了表面化学修饰后的纳米氧化钛表面化学结构的变化,观测了纳米氧化钛溶胶在乙二醇溶剂中稳定性.试验结果表明表面活性剂与纳米氧化钛的表面的不饱和键之间形成了新的化学结构,粒子表面可能接枝上有机长链,提高了纳米粒子在溶剂中的相容性.表面化学修饰后的纳米氧化钛与乙二醇溶剂形成了较稳定的溶胶体系,而且纳米溶胶粒径较小.表面活性剂添加量与纳米粒子添加量控制在(1~1.2):1时,可以获得纳米溶胶粒径较小,同时溶胶稳定性较好的纳米氧化钛-乙二醇溶胶体系. 相似文献