全文获取类型
收费全文 | 3686篇 |
免费 | 713篇 |
国内免费 | 482篇 |
专业分类
化学 | 2079篇 |
晶体学 | 92篇 |
力学 | 92篇 |
综合类 | 6篇 |
数学 | 161篇 |
物理学 | 2451篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 27篇 |
2020年 | 29篇 |
2019年 | 25篇 |
2018年 | 22篇 |
2017年 | 39篇 |
2016年 | 48篇 |
2015年 | 75篇 |
2014年 | 120篇 |
2013年 | 168篇 |
2012年 | 308篇 |
2011年 | 356篇 |
2010年 | 334篇 |
2009年 | 436篇 |
2008年 | 410篇 |
2007年 | 494篇 |
2006年 | 484篇 |
2005年 | 344篇 |
2004年 | 201篇 |
2003年 | 144篇 |
2002年 | 119篇 |
2001年 | 103篇 |
2000年 | 85篇 |
1999年 | 82篇 |
1998年 | 67篇 |
1997年 | 64篇 |
1996年 | 41篇 |
1995年 | 38篇 |
1994年 | 32篇 |
1993年 | 41篇 |
1992年 | 46篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4881条查询结果,搜索用时 15 毫秒
991.
Shijie Liu Zicai Shen Weijing Kong Jian Shen Zhenxia Deng Yuanan Zhao Zhengxiu Fan 《Optics Communications》2006,267(1):50-57
Multi-layer dielectric (MLD) gratings for pulse compressors in high-energy laser systems should provide high diffraction efficiency as well as high laser induced damage thresholds (LIDT). Nonuniform optical near-field distribution is one of the important factors to limit their damage resistant capabilities. Electric field distributions in the gratings and multi-layer film region are analyzed by using Fourier modal method. Optimization of peak electric field in the gratings ridge is performed with a merit function, including both diffraction efficiency and electric field enhancement when the top layer material is HfO2 and SiO2, respectively. A set of optimized gratings parameters is obtained for each structure, which reduce the peak electric field within the gratings ridge to being respective 1.39 and 1.84 times the value of incident light respectively. Finally, we also discuss the effects of gratings refractive index, gratings sidewall angle and incident angle on peak electric field in the gratings ridge. 相似文献
992.
Liping Liang Yao Xu Xianglin Hou Yuhan Sun Zhonghua Wu 《Journal of solid state chemistry》2006,179(4):959-967
Zirconia nanoparticles have been synthesized from zirconium hydroxide precipitates followed by a supercritical CO2 extraction. The microstructure evolution of these zirconia nanoparticles during the calcination at the moderate temperature has been investigated. Assisted by the analyses of TEM and XRD, small-angle X-ray scattering (SAXS) study offers possibilities to a comprehensive and quantitative characterization of the structural evolution on the nanometer scales. The as-synthesized zirconia sample exhibits a mass fractal structure constructed by the surface fractal particles. Such a structure can be preserved up to 300 °C. After calcination at 400 °C, considerable structural rearrangement occurs. In the interior of nanoparticles zirconia nanocrystallites emerge. It is the scattering from such zirconia nanoparticles that give rise to the broadened crossover in the ln[J(q)] vs. ln q plot and the scattering peak in the ln[q3J(q)] vs. q2 plot. With a further increase in the calcination temperature, the power-law region at large-q in ln J(q) vs. ln q plot expands, and the peak in ln[q3J(q)] vs. q2 plot shifts towards lower q values, indicating size increases in both the nanocrystallites and nanoparticles. Besides, the mass fractal structure constructed by zirconia nanoparticles can be largely preserved during the moderate temperature calcination. 相似文献
993.
Jungang Zhang Changtai Xia Qun Deng Hongsheng Shi Jun Xu 《Journal of Physics and Chemistry of Solids》2006,67(8):1656-1659
Tin oxide doped β-Ga2O3 single crystals are recognized as transparent conductive oxides (TCOs) materials. They have a larger band gap (4.8 eV) than any other TCOs, thus can be transparent in UV region. This property shows that they have the potential to make the optoelectronic device used in even shorter wavelength than usual TCOs. β-Ga2O3 single crystals doped with different Sn4+ concentrations were grown by the floating zone technique. Their optical properties and electrical conductivities were systematically studied. It has been found that their conductivities and optical properties were influenced by the Sn4+ concentrations and annealing. 相似文献
994.
Linear Thomson scattering by a relativistic electron of a short pulse laser has been investigated by computer simulation. Under a laser field with a pulse of 33.3-fs full-width at half-maximum, and the initial energy of an electron of γ0=10, the motion of the electron is relativistic and generates an ultrashort radiation of 76-as with a photon wave length of 2.5-nm in the backward scattering. The radiation under a high relativistic energy electron has better characteristic than under a low relativistic energy electron in terms of the pulse width and the angular distribution. 相似文献
995.
Many astrophysics data show that our universe has a critical energy density, and 73% of it is dark energy, which drives the
accelerating expansion of the universe. We consider the holographic dark energy in induced gravity by taking the Hubble scale,
particle horizon and event horizon as the infrared cutoff. We find that only the event horizon can give accelerating expansion
of our universe. 相似文献
996.
997.
We examined the symmetry aspect of the semi-inclusive one-pion production in the deep inelastic scattering of a lepton beam off an unpolarized nucleon target, with an emphasis on the positivity restrictions on the corresponding structure functions. In combination with the Callan-Gross-type relation between two twist-two structure functions W 1 and W 2, we derived an upper bound on the Levelt-Mulders asymmetry, which occurs when the lepton beam is longitudinally polarized. 相似文献
998.
《Physics letters. [Part B]》1997,400(3-4):395-400
The photon structure function F2γ has been measured at an average Q2 value of 6.8 GeV2 using data collected by the AMY detector at the TRISTAN e+e− collider. The measured F2γ is compared with several QCD-based parton density models. 相似文献
999.
Zaiguo Gan Junsheng Guo Hongye Liu Lijun Shi Weifan Yang Wantong Mou Tianrui Guo Keming Fang Shuifa Shen Shuanggui Yuan Xueqian Zhang Zhi Qin Ruichang Ma Jiquan Zhong Yixiao Luo Shuhong Wang Dengming Kong Jimin Qiao 《中国科学A辑(英文版)》1997,40(3):323-327
A new transuranium neutron-deficient isotope235Am was produced by 35 MeV proton to bombard the rare radioactive238Pu target. The products were transported and collected by the He-jet system. The Am isotopes were separated and purified by
radiochemistry method and the y-ray, X-ray and y-X(y) coincidence of the samples was measured. The synthesis of235Am was definitely identified. Its measured half-life is (15±5) min.
Project supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences. 相似文献
1000.
Multicore-fiber as gain medium for fiber laser is introduced. The cores are coupled via evanescent waves. Analysis of the coupling waves is agree with the numerical simulations and experimental results. 相似文献