全文获取类型
收费全文 | 8185篇 |
免费 | 1187篇 |
国内免费 | 3360篇 |
专业分类
化学 | 6238篇 |
晶体学 | 395篇 |
力学 | 1069篇 |
综合类 | 118篇 |
数学 | 2425篇 |
物理学 | 2487篇 |
出版年
2024年 | 32篇 |
2023年 | 92篇 |
2022年 | 223篇 |
2021年 | 261篇 |
2020年 | 292篇 |
2019年 | 279篇 |
2018年 | 263篇 |
2017年 | 429篇 |
2016年 | 558篇 |
2015年 | 380篇 |
2014年 | 549篇 |
2013年 | 962篇 |
2012年 | 843篇 |
2011年 | 808篇 |
2010年 | 673篇 |
2009年 | 659篇 |
2008年 | 661篇 |
2007年 | 654篇 |
2006年 | 543篇 |
2005年 | 479篇 |
2004年 | 402篇 |
2003年 | 345篇 |
2002年 | 348篇 |
2001年 | 293篇 |
2000年 | 245篇 |
1999年 | 243篇 |
1998年 | 200篇 |
1997年 | 170篇 |
1996年 | 157篇 |
1995年 | 138篇 |
1994年 | 121篇 |
1993年 | 88篇 |
1992年 | 71篇 |
1991年 | 47篇 |
1990年 | 55篇 |
1989年 | 27篇 |
1988年 | 31篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1971年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
151.
用固相反应法制备(1-x)La0.6Dy0.1Sr0.3MnO3/x/2(Sb2O3)(x=0.00,0.02,0.15)样品,通过X射线衍射(XRD)图谱,扫描电子显微镜(SEM)照片及SEM能谱(EDS),ρ~T曲线研究样品的结构及电输运性质.结果表明:Sb离子没有进入Mn位,Sb2O3包覆在La0.6Dy0.1Sr0.3MnO3颗粒表面,Sb2O3起助熔剂作用,使得复合样品的颗粒变大且大小相对均匀;复合样品的绝缘体-金属转变温度TP较纯的La0.6Dy0.1Sr0.3MnO3的TP提高20K左右,对x=0.15的样品电阻高峰值比纯的La0.6Dy0.1Sr0.3MnO3的峰值电阻率增大两个数量级,用自旋极化隧穿理论予以解释. 相似文献
152.
Electrical property is an important problem in the field of natural science and physics, which usually involves potential, current and resistance in the electric circuit. We investigate the electrical properties of an arbitrary hammock network, which has not been resolved before, and propose the exact potential formula of an arbitrary m × n hammock network by means of the Recursion-Transform method with current parameters(RT-I) pioneered by one of us [Z. Z. Tan, Phys. Rev. E 91(2015) 052122], and the branch currents and equivalent resistance of the network are derived naturally. Our key technique is to setting up matrix equations and making matrix transformation, the potential formula derived is a meaningful discovery, which deduces many novel applications. The discovery of potential formula of the hammock network provides new theoretical tools and techniques for related scientific research. 相似文献
153.
Adopting both conducting polyaniline (PANI) and organic titanium dioxide (TiO2), which possesses a high dielectric constant, we synthesized PANI/TiO2 hybrids via in situ oxidative polymerization to prepare an electrorheological (ER) materials. These were then characterized via thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The ER responses and dielectric properties of the synthesized hybrids dispersed in silicone oil were measured as a function of different particle fractions of TiO2 under an applied electric field. Series of analyses revealed that composite composition (the ratio of TiO2 to PANI) plays a crucial role in affecting the ER performance, which exhibited interesting behaviors when the ratio of TiO2 to PANI approaches a critical value. Interestingly, we found that our proposed constitutive equation fit the shear stress in the low shear rate region better than the Bingham fluid model. The dielectric spectra of the ER fluid, along with polarizability, were found to explain the flow behaviors of the PANI/TiO2 under applied electric fields. 相似文献
154.
Ortho phthalic anhydride was modified with long chain alcohol (1-docosanol) to its corresponding monodocosyl phthalate (22-Phth). Subsequently, three novel lanthanide (Eu3+, Tb3+, and Dy3+) complexes with the long chain monodocosyl phthalate were synthesized and characterized by elemental analysis and Infrared spectra. The photophysical properties of these complexes were studied in detail with ultraviolet-visible absorption spectra, low temperature phosphorescence spectra and fluorescent spectra. The triplet state energy of 22-Phth was determined to be around 25,000 cm−1 from the maximum phosphorescent peak at 400 nm, suggesting 22-Phth is suitable for the sensitization of the luminescence of Eu3+, Tb3+, and Dy3+. The fluorescence excitation and emission spectra for these lanthanide complexes of the three ligands take agreement with the above predict from energy match principle. 相似文献
155.
Current state and historical progress in experimental and theoretical studies of surface relief appertaining to persistent slip bands (PSBs) and leading to fatigue crack initiation in cyclically deformed metals is presented as a thorough critical overview. A comprehensive inventory of microscopic techniques used for this study is tabulated chronologically with emphasis to their applicability to polycrystals. The most relevant experimental characteristics concerning surface relief evolution, namely the form of extrusions and intrusions in single- and polycrystalline materials, are surveyed. Theoretical models and computational simulations of extrusion and intrusion formation and fatigue crack initiation are critically reviewed. 相似文献
156.
157.
Kerr效应对非简并双光子J—C模型中光场相位的影响 总被引:3,自引:1,他引:3
应用Pegg-Barnett相位理论研究了高Q Kerr介质腔中的二能级原子与双模光场相互作用系统中光场相位的演化特性,通过计算光场的相位几率分布函数,频率漂移量以相位涨落,分析讨论了Kerr效应对光场相位性质的影响。 相似文献
158.
通过理论推导,构建了抗蚀剂的感光特性、光源的光效与曝光量之间的数学模型,为液晶光阀代替穿孔带提供了理论依据.结合液晶光阀的工作原理和光刻快门的控制原理,对液晶光阀组的控制进行了研究并给出了其控制电路图.通过实际光刻试验,自控液晶光阀组光刻快门机构可以完成编码图案的控制,通光控制达到了预计要求,刻出的图案清晰,线条陡直.证明液晶光阀组替代穿孔带用作光刻快门是完全可行的. 相似文献
159.
This paper reports that DLC (diamond like carbon)/Ti and DLC films were prepared by
using pulsed laser arc deposition. R-ray diffraction, Auger electron spectroscopy,
Raman spectroscopy, atomic force microscopy, nanoindenter, spectroscopic
ellipsometer, surface profiler and micro-tribometer were employed to study the
structure and tribological properties of DLC/Ti and DLC films. The results show that
DLC/Ti film, with $I(D)/I(G)$ 0.28 and corresponding to 76{\%} sp$^{3}$ content
calculated by Raman spectroscopy, uniform chemical composition along depth
direction, 98 at{\%} content of carbon, hardness 8.2 GPa and Young's modulus 110.5
GPa, compressive stress 6.579 GPa, thickness 46~nm, coefficient of friction 0.08,
and critical load 95mN, exhibits excellent mechanical and tribological properties. 相似文献
160.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献