全文获取类型
收费全文 | 5206篇 |
免费 | 549篇 |
国内免费 | 385篇 |
专业分类
化学 | 2586篇 |
晶体学 | 27篇 |
力学 | 197篇 |
综合类 | 20篇 |
数学 | 489篇 |
物理学 | 1388篇 |
无线电 | 1433篇 |
出版年
2024年 | 16篇 |
2023年 | 79篇 |
2022年 | 133篇 |
2021年 | 138篇 |
2020年 | 157篇 |
2019年 | 131篇 |
2018年 | 123篇 |
2017年 | 113篇 |
2016年 | 160篇 |
2015年 | 171篇 |
2014年 | 223篇 |
2013年 | 283篇 |
2012年 | 390篇 |
2011年 | 351篇 |
2010年 | 257篇 |
2009年 | 263篇 |
2008年 | 336篇 |
2007年 | 263篇 |
2006年 | 240篇 |
2005年 | 223篇 |
2004年 | 178篇 |
2003年 | 156篇 |
2002年 | 137篇 |
2001年 | 132篇 |
2000年 | 136篇 |
1999年 | 109篇 |
1998年 | 97篇 |
1997年 | 103篇 |
1996年 | 110篇 |
1995年 | 76篇 |
1994年 | 86篇 |
1993年 | 68篇 |
1992年 | 76篇 |
1991年 | 64篇 |
1990年 | 46篇 |
1989年 | 54篇 |
1988年 | 48篇 |
1987年 | 37篇 |
1986年 | 45篇 |
1985年 | 34篇 |
1984年 | 46篇 |
1983年 | 30篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 28篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 22篇 |
1975年 | 17篇 |
排序方式: 共有6140条查询结果,搜索用时 15 毫秒
41.
Jau-Jiun Chen Soohwan Jang F. Ren Yuanjie Li Hyun-Sik Kim D. P. Norton S. J. Pearton A. Osinsky S. N. G. Chu J. F. Weaver 《Journal of Electronic Materials》2006,35(4):516-519
Wet etch rates at 25°C for Zn0.9Mg0.1O grown on sapphire substrates by pulsed laser deposition (PLD) were in the range 300–1100 nm · min−1 with HCl/H2O (5×10−3−2×10−2 M) and 120–300 nm · min−1 with H3PO4/H2O (5×10−3−2×10−2 M). Both of these dilute mixtures exhibited diffusion-limited etching, with thermal activation energies of 2–3 kCal · mol−1. By sharp contrast, the etch rates for ZnO also grown on sapphire by PLD were much slower in similar solutions, with rates
of 1.2–50 nm · min−1 in HCl/H2O (0.01–1.2 M) and 12–54 nm · min−1 in H3PO4/H2O (0.02–0.15 M). The etching was reaction limited over the temperature range 25–75°C, with activation energies close to 6
kCal · mol−1. The resulting selectivity of Zn0.9Mg0.1O over ZnO can be a high as ∼400 with HCl and ∼30 with H3PO4. 相似文献
42.
In this letter, we report on the electrical characteristic and the comparison of the metal-insulator-metal (MIM) capacitors with PECVD silicon nitride (SiN) and silicon oxynitride (SiON). Both capacitors are found to exhibit low leakage and high breakdown field strength, as well as absence of dispersive behavior, good linearity, and comparable quality factor behaviors. 相似文献
43.
Fabrication and characteristics of high-speed implant-confined index-guided lateral-current 850-nm vertical cavity surface-emitting lasers 总被引:2,自引:0,他引:2
Dang G.T. Mehandru R. Luo B. Ren F. Hobson W.S. Lopata J. Tayahi M. Chu S.N.G. Pearton S.J. Chang W. Shen H. 《Lightwave Technology, Journal of》2003,21(4):1020-1031
Process technology of high-speed implant-apertured index-guide lateral-current-injection top dielectric-mirror quantum-well 850-nm vertical cavity surface-emitting lasers (VCSELs) has been developed. Oxygen and helium implantation for aperture definition and extrinsic capacitance reduction, dielectric mirror formation, p- and n-ohmic contact formation, VCSEL resistance, and thermal analysis were investigated. Employing this technology, GaAs/AlGaAs-based 850-nm VCSELs with small signal modulation bandwidths up to 11.5 Gb/s and an eye diagram generated at 12 Gb/s by a pseudorandom bit sequence of 2/sup 31/-1 were achieved. The bit-error rates were below 10/sup -13/. The threshold current is as low as 0.8 mA for 7-/spl mu/m-diameter current apertures and typical slope efficiencies of 0.45-0.5 mA/mW were obtained. 相似文献
44.
45.
采用ππ偏振激光,通过两步激发和光电离方法,在0-154V/cm电场范围内,测定了Yb原子n-18附近m=0的斯塔克光谱,首次把包含斯塔克效应的能量矩阵对角化方法推广到Yb原子,所获得的理论斯塔克图与实验结果基本符合,观察到低场中斯塔克簇随电场增加呈现线性结构以及^1P1态与斯塔克簇在抗交叉过程中振子强度发生转移的现象,讨论了结构与量子亏损的关系。 相似文献
46.
本文以金属指示剂甲基百里(香)酚蓝作为鳌合剂制得具有相应鳌合基团的负载树脂.研究了该树脂的某些分析特性及其在富集天然水中微量铜、钻、镍、锌中的应用. 相似文献
47.
Very high-order microring resonator filters for WDM applications 总被引:6,自引:0,他引:6
B.E. Little S.T. Chu P.P. Absil J.V. Hryniewicz F.G. Johnson F. Seiferth D. Gill V. Van O. King M. Trakalo 《Photonics Technology Letters, IEEE》2004,16(10):2263-2265
High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications. 相似文献
48.
A classical Fermi accelerator model (FAM) is known to show chaotic behavior. The FAM is defined by a free particle bouncing elastically from two rigid walls, one fixed and the other oscillating periodically in time. The central aim of this paper is to connect the quantum and the classical solutions to the FAM in the semiclassical limit. This goal is accomplished using a finite inverted parametric oscillator (FIPO), confined to a box withfixed walls, as an alternative representation of the FAM. In the FIPO representation, an explicit correspondence between classical and quantum limits is accomplished using a Husimi representation of the quasienergy eigenfunctions. 相似文献
49.
50.