全文获取类型
收费全文 | 7116篇 |
免费 | 1631篇 |
国内免费 | 797篇 |
专业分类
化学 | 2747篇 |
晶体学 | 102篇 |
力学 | 55篇 |
综合类 | 35篇 |
数学 | 94篇 |
物理学 | 2921篇 |
无线电 | 3590篇 |
出版年
2024年 | 38篇 |
2023年 | 138篇 |
2022年 | 195篇 |
2021年 | 246篇 |
2020年 | 335篇 |
2019年 | 236篇 |
2018年 | 178篇 |
2017年 | 281篇 |
2016年 | 398篇 |
2015年 | 344篇 |
2014年 | 453篇 |
2013年 | 745篇 |
2012年 | 610篇 |
2011年 | 495篇 |
2010年 | 381篇 |
2009年 | 492篇 |
2008年 | 444篇 |
2007年 | 480篇 |
2006年 | 531篇 |
2005年 | 456篇 |
2004年 | 363篇 |
2003年 | 276篇 |
2002年 | 239篇 |
2001年 | 242篇 |
2000年 | 211篇 |
1999年 | 131篇 |
1998年 | 105篇 |
1997年 | 84篇 |
1996年 | 62篇 |
1995年 | 53篇 |
1994年 | 56篇 |
1993年 | 41篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 15篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 6篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有9544条查询结果,搜索用时 765 毫秒
51.
52.
Experiments employing photoreflectance spectroscopy have uncovered band bending due to electrically active defects at the Si(1 1 1)–SiO2 interface after sub-keV Ar+ ion bombardment. The band bending of about 0.5 eV resembles that for Si(1 0 0)–SiO2, and both interfaces exhibit two kinetic regimes for the evolution of band bending upon annealing due to defects healing. The healing takes place about an order of magnitude more quickly at the (1 1 1) interface, however, probably because of less fully saturated bonding and higher compressive stress. 相似文献
53.
地域通信网的干扰技术研究 总被引:1,自引:0,他引:1
本文在分析地域通信网结构及组成的基础上,研究了对地域通信网实施的节点破坏、末端信息封锁、局部阻塞瘫痪等对抗方法,并使用干扰地域通信网的程度、节点干扰率、末端节点封锁率和传递信息误差率等指标对干扰效果进行评估。 相似文献
54.
本文对远距离支援干扰飞机、随队支援干扰飞机、机载自卫电子对抗系统以及最近国外正在大力发展的分布式电子干扰系统等几种航空有源电子干扰装备的作战对象、战术应用、功能、使用局限性等特点进行了比较 ,探讨了综合发展和运用这几型装备的重要意义 相似文献
55.
虚拟仪器在教学中的应用 总被引:1,自引:0,他引:1
主要介绍了Multisim2001中虚拟仪器库中函数发生器、示波器的使用方法及功能;并在Multisim2001环境中仿真单管放大电路、桥式整流滤波电路。由调试结果,分析了其在教学中应用的可行性。 相似文献
56.
Michelle J. S. Spencer Andrew Hung Ian K. Snook Irene Yarovsky 《Surface science》2003,540(2-3):420-430
The adsorption of atomic S on the Fe(1 1 0) surface is examined using density functional theory (DFT). Three different adsorption sites are considered, including the atop, hollow and bridge sites and the S is adsorbed at a quarter monolayer coverage in a p(2 × 2) arrangement. The hollow site is found to be the most stable, followed by the bridge and atop sites. At all three sites, S adsorption results in relatively minor surface reconstruction, with the most significant being that for the hollow site, with lateral displacements of 0.09 Å. Comparisons between S-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the S. At the hollow site, the presence of S causes an increase in the surface Fe d-orbital density of states between 4 and 5 eV. However, S adsorption has no significant effect on the structure and magnetic properties of the lower substrate layers. 相似文献
57.
In this paper, we study the electronic band structure and the ferromagnetic properties of the organic radicalp-NPNN by employing density-functional theory with generalized gradient approximation (GGA) and local-spin densityapproximation (LSDA). The density of states, the total energy, and the spin magnetic moment are calculated. Thecalculations reveal that the δ-phase of p-NPNN has a stable ferromagnetic ground state. It is found that an unpairedelectron in this compound is localized in a single occupied molecular orbital (SOMO) constituted primarily of π* (NO)orbitals, and the main contribution of the spin magnetic moment comes from the π* (NO) orbitals. By comparison, wefind that the GGA is more suitable to describe free radical systems than LSDA. 相似文献
58.
59.
Stereoselectivity in the intermolecular Pauson-Khand reaction of electron-deficient terminal alkynes
A family of terminal alkyne dicobalthexacarbonyl complexes bearing groups with a range of electron-withdrawing abilities has been synthesized. After submitting these complexes to the intermolecular Pauson-Khand reaction with norbornadiene, electron-deficient substrates afforded up to 26% of the unexpected endo-cyclopentenone. 相似文献
60.
Image potential resonances on the Sn/Ge(1 1 1) α-phase are investigated by two closely related methods: specular electron reflection and so-called selective electron scattering. Electrons from image resonances are detected on this surface at 120 and 300 K, i.e. below and above the phase transition at about 200 K. The dispersion of the image resonances reveals at these two temperatures equivalent effective electron masses, which are characteristic for this type of electronic surface states. The results of the two methods are consistent according to the similarity of the scattering processes. Changes in the loss peak intensity with the annealing temperature are assigned to the surface quality and are reflected by characteristic photoemission intensities. 相似文献