全文获取类型
收费全文 | 4736篇 |
免费 | 1275篇 |
国内免费 | 381篇 |
专业分类
化学 | 966篇 |
晶体学 | 45篇 |
力学 | 70篇 |
综合类 | 21篇 |
数学 | 74篇 |
物理学 | 2786篇 |
无线电 | 2430篇 |
出版年
2024年 | 23篇 |
2023年 | 88篇 |
2022年 | 130篇 |
2021年 | 137篇 |
2020年 | 144篇 |
2019年 | 123篇 |
2018年 | 132篇 |
2017年 | 166篇 |
2016年 | 201篇 |
2015年 | 237篇 |
2014年 | 369篇 |
2013年 | 337篇 |
2012年 | 382篇 |
2011年 | 336篇 |
2010年 | 271篇 |
2009年 | 301篇 |
2008年 | 367篇 |
2007年 | 344篇 |
2006年 | 339篇 |
2005年 | 275篇 |
2004年 | 248篇 |
2003年 | 238篇 |
2002年 | 186篇 |
2001年 | 161篇 |
2000年 | 145篇 |
1999年 | 103篇 |
1998年 | 109篇 |
1997年 | 88篇 |
1996年 | 75篇 |
1995年 | 56篇 |
1994年 | 48篇 |
1993年 | 42篇 |
1992年 | 51篇 |
1991年 | 28篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有6392条查询结果,搜索用时 125 毫秒
31.
32.
33.
基于极化不变量的飞机目标识别 总被引:5,自引:2,他引:3
基于宽带毫米波极化雷达体制背影,通过极化不变量之一的去极化系数,研究了飞机目标的极化散射特性,并提取了极化特征,设计了飞机目标的分类或识别器结构,它能对五种飞机目标进行有效的分类或识别。 相似文献
34.
35.
M. Ferro-Luzzi Z.-L. Zhou J.F.J. van den Brand H.J. Bulten J. Lang H.R. Poolman 《Hyperfine Interactions》1997,110(3-4):239-257
We present data showing hyperfine transitions in an atomic deuterium beam induced by the (476 MHz) radio-frequency field of
a 704 MeV electron beam in a storage ring. A polarized deuterium beam, produced in an atomic beam source, was crossed with
a stored electron beam and analyzed with a Breit--Rabi polarimeter. Electron-beam induced transitions were singled out by
injecting different combinations of hyperfine states. Transition probabilities as high as 70% were measured at large currents
(~ 100 mA). All possible deuterium transitions for a radio-frequency of 476 MHz were observed. In addition, a 1--6 transition
resulting from the first harmonic (952 MHz) was observed.
The effects of these transitions are of general importance for the polarized internal target technique applied in nuclear
and particle physics experiments. The data are reasonably described by numerical estimates. The observed mechanism can be
exploited to create nuclear polarized atoms when injecting electron polarized atoms with no net nuclear polarization into
a storage cell. However, when nuclear polarized atoms are injected, care should be taken to avoid this mechanism, since it
would result in depolarization of the atoms. The studies enabled us to choose the magnetic guide field during our spin-dependent
electron--deuteron scattering experiments, such that electron-beam induced depolarizing effects were avoided.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
36.
37.
The effect of radiation gain saturation in quantum-well heretostructures was investigated in the system GaAs—AlGaAs with regard
to the spectral line broadening and the type of radiation polarization.
Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 6, pp. 797–800, November–December, 1997. 相似文献
38.
Applied Biochemistry and Biotechnology - 相似文献
39.
40.
Vanessa de Freitas Cunha Lins Geraldo Francisco de Andrade Reis Carlos Roberto de Araujo 《Applied Surface Science》2006,253(5):2875-2884
In this work, electrochemical impedance spectroscopy and linear polarization are used in determining porosity of zinc phosphates, and of nickel and manganese modified zinc phosphates on electrogalvanized steel. The porosity of the phosphate layers ranges from 0.1% for the manganese-modified hopeite to 8% for hopeite, using the linear polarization and the electrochemical impedance spectroscopy techniques. The porosity values measured using the two techniques were in agreement. All impedance spectra of coated samples showed two steps, with two capacitive arcs and an inductive looping. 相似文献