全文获取类型
收费全文 | 29798篇 |
免费 | 6345篇 |
国内免费 | 2506篇 |
专业分类
化学 | 8168篇 |
晶体学 | 221篇 |
力学 | 1836篇 |
综合类 | 203篇 |
数学 | 1026篇 |
物理学 | 10278篇 |
无线电 | 16917篇 |
出版年
2024年 | 156篇 |
2023年 | 390篇 |
2022年 | 730篇 |
2021年 | 909篇 |
2020年 | 1083篇 |
2019年 | 1001篇 |
2018年 | 1016篇 |
2017年 | 1257篇 |
2016年 | 1470篇 |
2015年 | 1534篇 |
2014年 | 2157篇 |
2013年 | 2457篇 |
2012年 | 2333篇 |
2011年 | 2320篇 |
2010年 | 1867篇 |
2009年 | 1661篇 |
2008年 | 1840篇 |
2007年 | 1967篇 |
2006年 | 1888篇 |
2005年 | 1491篇 |
2004年 | 1298篇 |
2003年 | 1165篇 |
2002年 | 985篇 |
2001年 | 919篇 |
2000年 | 788篇 |
1999年 | 634篇 |
1998年 | 530篇 |
1997年 | 475篇 |
1996年 | 450篇 |
1995年 | 360篇 |
1994年 | 318篇 |
1993年 | 220篇 |
1992年 | 211篇 |
1991年 | 165篇 |
1990年 | 94篇 |
1989年 | 100篇 |
1988年 | 96篇 |
1987年 | 55篇 |
1986年 | 49篇 |
1985年 | 33篇 |
1984年 | 41篇 |
1983年 | 11篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Modification of the visual appearance when a rough surface is covered by a varnish is mostly attributed to the levelling of the substrate surface, which depends on the molecular weight of the varnish. The topography of varnished surfaces, however, has never been measured directly. Surfaces of varnishes applied over glass substrates of varying roughness were studied, therefore, using mechanical profilometry. Two different varnishes made with a low and a high molecular weight resin were studied. Both varnishes lower the r.m.s. roughness of the substrates and filter the high spatial frequencies. These results are amplified for the varnish containing the low molecular weight resin. The light reflected by the varnished samples is modelled from these topographical data. Its angular distribution, calculated from the probability density of slopes is presented, taking into account separately the air/varnish and the varnish/substrate interfaces. These analyses are presented in a back-scattering configuration. They show that varnishing significantly reduces the angular width of the reflected light and that this effect is magnified for the low molecular weight resin. Modelling furthermore shows that the influence of the roughness of the varnish/substrate interface is negligible in the total reflected light. 相似文献
52.
All-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity
Fei Wang 《Optics Communications》2006,257(2):334-339
A novel scheme for all-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity is proposed and investigated numerically. The results show, for a 2.5 GHz driving pulse train, it can be generated 5-25 GHz repetition rate pulse trains with low clock amplitude jitter, polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence signal can be realized based on the proposed scheme. 相似文献
53.
54.
详细分析了3G中TDD以及TDD与FDD之间的各种干扰,建立了一些可用于3G系统性能研究的干扰模型,并提出了一些有效的建议来避免或减少系统中的干扰。 相似文献
55.
本文设计了用于千兆以太网基带铜缆接收器均衡的甚高频自适应连续时间Gm-C二阶带通滤波器。基于最陡梯度下降算法,带通滤波器的零点在57-340MHz的频率范围内可以自适应地调节,中心频率为1.278GHz。通过外接电阻伺服环路,滤波器中跨导转换器的跨导值不受工艺偏差和温度变化的影响,采用CSMC-HJ0.6μm CMOS工艺器件模型,用Cadence Spectres仿真器仿真了设计的自适应滤波器电路,仿真结果验证了设计原理和设计的电路。系统的最长学习时间为880个参考时钟周期。 相似文献
56.
57.
D. Yafaev 《Proceedings Mathematical Sciences》2002,112(1):245-255
We find an explicit function approximating at high energies the kernel of the scattering matrix with arbitrary accuracy. Moreover,
the same function gives all diagonal singularities of the kernel of the scattering matrix in the angular variables.
This paper is dedicated to Jean-Michel Combes on the occasion of his sixtieth birthday. 相似文献
58.
DDS+PLL系统的频谱分析 总被引:4,自引:0,他引:4
简要介绍了 DDS+PLL频率合成的原理,分析了在 DDS没有相位截断误差时,DDS+PLL输出信号的杂散抑制度,并讨论了杂散抑制度与环路参数的关系。 相似文献
59.
基于同步辐射加速器的康普顿背散射γ射线源(Ⅰ)产生MeV量级γ光子的数值计算 总被引:1,自引:0,他引:1
提出在筹建的上海同步辐射装置上建造一条MeV量级γ射线束及应用站,采用μm波长的红外(或远红外)激光与储存环中3.5GeV电子束进行康普顿背散射,从而获得能区为1—25MeV的康普顿背散射γ光子束,该光子束具有高强度、高极化度(线和圆极化)、准单色、方向性好的优点,可以广泛地应用于核物理和核天体物理基础研究及相关的应用研究领域.介绍了康普顿背散射的基本原理,并结合储存环参数给出了光子束性能的数值计算结果. 相似文献
60.
Noboru Nakatani 《Optical Review》2003,10(4):206-210
This paper describes a compulsorily phase locked differential interferometer using an orthogonally polarized light source of a modulated LD with high extinction ratio to reduce non-linearity of the interferometer caused by polarization cross-talk. The current modulated LD is used as a light source to make the interferometer compact and for the scanning phase of the interferometer. The interferometer is operated compulsorily at the maximum inclination point of the fringe intensity curve by fringe scanning and an electric system. A Wollaston prism of high extinction ratio (50 dB) is used to combine the polarizing beams and to make the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis; in the other they have a small crossing angle (2.5 mrad ∼ 10 mrad) to completely exclude non-linearity of the interferometer causded by polarization cross-talk. Using jets of a gas mixture of nitrogen and ethylene, this interferometer was demonstrated to be useful in detecting the photothermal effect of a photothermal velocimeter under phase fluctuation in a turbulent flow. 相似文献