全文获取类型
收费全文 | 67335篇 |
免费 | 18980篇 |
国内免费 | 3428篇 |
专业分类
化学 | 70962篇 |
晶体学 | 541篇 |
力学 | 3253篇 |
综合类 | 297篇 |
数学 | 4939篇 |
物理学 | 9751篇 |
出版年
2024年 | 408篇 |
2023年 | 4284篇 |
2022年 | 1987篇 |
2021年 | 3133篇 |
2020年 | 5268篇 |
2019年 | 3173篇 |
2018年 | 2861篇 |
2017年 | 1304篇 |
2016年 | 6395篇 |
2015年 | 6433篇 |
2014年 | 6037篇 |
2013年 | 6657篇 |
2012年 | 5213篇 |
2011年 | 3061篇 |
2010年 | 4957篇 |
2009年 | 4894篇 |
2008年 | 2831篇 |
2007年 | 2271篇 |
2006年 | 1665篇 |
2005年 | 1491篇 |
2004年 | 1163篇 |
2003年 | 936篇 |
2002年 | 985篇 |
2001年 | 755篇 |
2000年 | 603篇 |
1999年 | 479篇 |
1998年 | 308篇 |
1997年 | 300篇 |
1996年 | 282篇 |
1995年 | 328篇 |
1994年 | 259篇 |
1993年 | 353篇 |
1992年 | 179篇 |
1991年 | 170篇 |
1988年 | 160篇 |
1982年 | 142篇 |
1981年 | 173篇 |
1980年 | 205篇 |
1979年 | 198篇 |
1978年 | 197篇 |
1977年 | 321篇 |
1976年 | 368篇 |
1975年 | 462篇 |
1974年 | 477篇 |
1973年 | 287篇 |
1972年 | 373篇 |
1971年 | 356篇 |
1970年 | 541篇 |
1969年 | 413篇 |
1968年 | 459篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Yong Huang Ke-Yong Zhu Jun Wang 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(14):2363-2371
The curved ray-tracing method is extended to radiative transfer in the graded index medium with diffuse gray boundary conditions instead of black boundary conditions and the pseudo-source adding method is extended to the case of the linear-anisotropic scattering medium with graded index from non-scattering medium. Furthermore, the equivalence of the two methods is verified by formulation derivation. As exact analytical solutions, both the methods have high accuracy and fast computational speed. The predicted temperature distributions and dimensionless radiative heat flux at radiative equilibrium are determined by the proposed methods, and the numerical results are compared with the data in references. The results show that the present methods have a good accuracy. Influences of various combinations of refractive index and boundary emissivities on the temperature distributions and dimensionless radiative heat flux are also investigated. 相似文献
993.
The formulae of photon angular distribution and polarization degree for radiative recombination are presented to include the contribution of multipoles and their correlations. A fully relativistic code is then developed to calculate the photon angular distribution and polarization. The calculated polarization degree and differential cross-sections agree well with that of Scofild's results within 10%. The effects of multipoles on polarization and angular distribution are investigated. The polarization and the angular distribution become asymmetric when the multipoles are accounted as the electron energy increases. 相似文献
994.
Hye Young Kwon Jun Taek Woo Dea Uk Lee Tae Whan Kim Young Ju Park 《Solid State Communications》2009,149(1-2):52-55
Strained potential profiles and electronic subband energies of InAs/GaAs coupled double quantum dots (DQDs) were calculated by using a three-dimensional finite-difference method (FDM) taking into account shape-based strain and nonparabolic effects. The interband transition energies from the ground electronic subband to the ground heavy-hole band (E1-HH1) in the InAs/GaAs DQDs, as determined from the FDM calculations taking into account strain and nonparabolic effects, were in reasonable agreement with the experimental peaks corresponding to the (E1-HH1) interband transition energies at several temperatures, as determined from the temperature-dependent photoluminescence spectra. 相似文献
995.
The structural and electronic properties of silicon nanoribbons on Ag(110): A first principles study
We have investigated the structures of silicon nanoribbons on Ag(110) using first principles calculations. The armchair silicon nanoribbons (ASiNRs) and zigzag silicon nanoribbons (ZSiNRs) with different widths are analyzed. The formation energy study shows that the ASiNRs with the width of 16 Å are the most stable structures. These ASiNRs have the structural parameters same as experimental ones. The simulated scanning tunneling microscope (STM) images of these ASiNRs also agree well with the experimental results. Thus, these ASiNRs are supposed to be the nanoribbons grown in experiment. The electronic structures shows that the ASiNRs are metallic, which is in agreement with the experiments. 相似文献
996.
We use inelastic neutron scattering to probe magnetic excitations of an optimally electron-doped superconductor Nd1.85Ce0.15CuO4-delta above and below its superconducting transition temperature Tc=25 K. In addition to gradually opening a spin pseudogap at the antiferromagnetic ordering wave vector Q=(1/2,1/2,0), the effect of superconductivity is to form a resonance centered also at Q=(1/2,1/2,0) but at energies above the spin pseudogap. The intensity of the resonance develops like a superconducting order parameter, similar to those for hole-doped superconductors and electron-doped Pr0.88LaCe0.12CuO4. The resonance is therefore a general phenomenon of cuprate superconductors, and must be fundamental to the mechanism of high-Tc superconductivity. 相似文献
997.
利用改进型衍射理论对直边衍射效应的解释 总被引:2,自引:0,他引:2
利用改进型衍射理论MTPO(Modified Theory of Physics Optics)对直边衍射现象做出了解释.用数值模拟方法得出了直边衍射场强随衍射角度的变化曲线,并与广泛采用的菲涅耳近似衍射方法结果进行比较,发现在很大的角度空间上,二者所得出的衍射场强与精确解吻合较好.但在入射波的几何传播方向上,即边缘上的衍射场强分布,MTPO方法则具有更高的准确度. 相似文献
998.
999.
Hydrogen Passivation Effect on Enhanced Luminescence from Nanocrystalline Si/SiO2 Multilayers 下载免费PDF全文
Nanocrystalline Si/SiO2 multilayers are prepared by thermally annealing amorphous Si/SiO2 stacked structures. The photoluminescence intensity is obviously enhanced after hydrogen passivation at various temperatures. It is suggested that the hydrogen trapping and detrapping processes at different temperatures strongly influence the passivation effect. Direct experimental evidence is given by electron spin resonance spectra that hydrogen effectively reduces the nonradiative defect states existing in the Si nanocrystas/SiO2 system which enhances the radiative recombination probability. The luminescence characteristic shows its stability after hydrogen passivation even after aging eight months. 相似文献
1000.
Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of thestationary laser intensity distribution Pst(Ⅰ) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationarylaser intensity distribution Pst(Ⅰ) by cross-correlation between noises and “color“ of noises (non-Markovian effect) whenthe laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(τ1 = τ2 = τ3 = τ). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect thatonly when λ≠ 0 can the noise-induced transition occur in the Pst(Ⅰ) curve, and only when τ≠ 0 and λ≠ 0, can the“reentrant noise-induced transition“ occur. The other case is that the three correlation times are not the same value,τ1 ≠τ2 ≠τ3. For this case, we find that the noise-induced transition occurring in the Pst (Ⅰ) curve is entirely differentwhen the values of τ1, τ2, and τ3 are changed respectively. In particular, when τ2 (self-correlation time of additivenoise) is changing, the ratio of the two maximums of the Pst(Ⅰ) curve R exhibits an interesting phenomenon, “reentrantnoise-induced transition“, which demonstrates the effect of noise “color“ (non-Markovian effect). 相似文献