全文获取类型
收费全文 | 3895篇 |
免费 | 687篇 |
国内免费 | 332篇 |
专业分类
化学 | 2582篇 |
晶体学 | 54篇 |
力学 | 287篇 |
综合类 | 17篇 |
数学 | 398篇 |
物理学 | 1576篇 |
出版年
2024年 | 9篇 |
2023年 | 107篇 |
2022年 | 117篇 |
2021年 | 161篇 |
2020年 | 159篇 |
2019年 | 155篇 |
2018年 | 149篇 |
2017年 | 118篇 |
2016年 | 210篇 |
2015年 | 187篇 |
2014年 | 217篇 |
2013年 | 293篇 |
2012年 | 371篇 |
2011年 | 368篇 |
2010年 | 248篇 |
2009年 | 215篇 |
2008年 | 239篇 |
2007年 | 224篇 |
2006年 | 214篇 |
2005年 | 177篇 |
2004年 | 129篇 |
2003年 | 104篇 |
2002年 | 82篇 |
2001年 | 72篇 |
2000年 | 82篇 |
1999年 | 69篇 |
1998年 | 65篇 |
1997年 | 52篇 |
1996年 | 55篇 |
1995年 | 52篇 |
1994年 | 28篇 |
1993年 | 40篇 |
1992年 | 39篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 1篇 |
1983年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4914条查询结果,搜索用时 5 毫秒
11.
1689-nm diode lasers used in medical apparatus have been fabricated and characterized. The lasers had pnpn InP current confinement structure, and the active region consisted of 5 pairs of InGaAs quantum wells and InGaAsP barriers. 相似文献
12.
13.
14.
Novel oxyfluoride glasses are developed with the composition of 30SiO2-15Al2O3-28PbF2-22CdF2-0.1TmF3 - xYbF3 - (4.9 - x) AlF3(x=0, 0.5, 1.0, 1.5, 2.0) in tool fraction, Furthermore, the upconversion luminescence characteristics under a 970nm excitation are investigated. Intense blue, red and near infrared luminescences peaked at 453nm, 476nm, 647nm and 789nm, which correspond to the transitions of Tm^3+: ^1D2 →^3F4, ^1G4 →^3H6, ^1G4 →^3F4, and ^3H4 →^3H6, respectively, are observed. Due to the sensitization of Yb^3+ ions, all the upconversion luminescence intensities are enhanced considerably with Yb^3+ concentration increasing. The upconversion mechanisms are discussed based on the energy matching rule and quadratic dependence on excitation power. The results indicate that the dominant mechanism is the excited state absorption for those upconversion emissions. 相似文献
15.
Xie Ruixiang Wang Min Duan Changchun Yan Yihua R. A. Sych A. T. Altyntsev 《中国科学A辑(英文版)》2002,45(1):97-105
A complex solar radio moving type IV burst was observed on 23 September 1998 with the broadband (1.0–2.0 GHz and 2.6–3.8 GHz) spectrometers with high temporal and spectral resolutions at National Astronomical Observatories of China (NAOC). Comparing to the high spatial resolution data of Siberian Solar Radio Telescope (SSRT), we find that this burst is a rare type of moving type IV burst which is caused by the expanding arches, and the spatial structure oscillations of the radio sources are related with the time structure pulsations of the radio emission. Furthermore, the burst is associated with the multiple quasi-periodic long-term pulsations, and this suggests the existence of multi-scale magnetic structures in a large expanding coronal arch. We think the moving type IV burst is due to the synchrotron emission of the energetic electrons trapped in the expanding arch, and the multiple quasi-periodic pulsations are due to the second harmonic plasma emission. 相似文献
16.
本文研究并揭示了L_(2~a)(2~(2~a-1))型正交表行(列)间的递推规律,提出了一种泛函梯度数值计算的新方法——正交试验法,该方法在计算速度和精度上优于直接梯度法;在通用性及节省内存方面优于伴随算子法。 相似文献
17.
18.
The theoretical proton-40Ca optical potential is constructed based on theα-particle model of the nucleus. With this potential, the differential cross section, analysing power and the spin rotation function for 200 MeV proton-40Ca elastic scattering are calculated. The results are in good agreement with the experimental data. 相似文献
19.
Starting from the vectorial Rayleigh diffraction integral formula and without using the far-field approximation, a solution of the wave equation beyond the paraxial approximation is found, which represents vectorial non-paraxial elliptical Gaussian beams in free space. The far-field expressions for non-paraxial Gaussian beams and elliptical Gaussian beams can be regarded as special cases treated in this paper. Some basic propagation properties of vectorial non-paraxial elliptical Gaussian beams, including the irradiance distribution, phase term, beam widths and divergence angles are studied. Numerical results are given and illustrated. 相似文献
20.
Ziqing Duan Xiaofeng Wang Danfeng Yang Xiaoming Pan Pingchu Wang 《Solid State Communications》2005,134(8):559-563
0.65Pb(In1/2Nb1/2)O3-0.35PbTiO3 (PINT65/35) (starting composition) single crystals were grown successfully through the solution Bridgman technique using PbO flux and PMNT67/33 seed crystals. Because of the composition variation, the final composition of achievable crystals is in a range of 0.32-0.34 with the corresponding Tc range of 265-269 °C. The (001) plates of as-grown PINT66/34 single crystals show high Curie temperature (Tc=269 °C) and rhombohedral-tetragonal phase transition temperature (Trt=134 °C). Besides, good electrical properties with high dielectric constant (ε>3000), low dielectric loss (tan δ∼1.2%), high piezoelectric constant (d33∼2000 pC/N) and large electromechanical coupling factor (kt≈59%) at room temperature have been obtained on the (001) plates. The sound velocity, acoustic impedance and other piezoelectric parameters were also measured on the (001) plates in this study, which provide us more detailed information about PINT66/34 single crystals. 相似文献