全文获取类型
收费全文 | 7320篇 |
免费 | 1276篇 |
国内免费 | 840篇 |
专业分类
化学 | 2103篇 |
晶体学 | 61篇 |
力学 | 274篇 |
综合类 | 70篇 |
数学 | 607篇 |
物理学 | 2558篇 |
无线电 | 3763篇 |
出版年
2024年 | 32篇 |
2023年 | 131篇 |
2022年 | 234篇 |
2021年 | 279篇 |
2020年 | 312篇 |
2019年 | 216篇 |
2018年 | 211篇 |
2017年 | 327篇 |
2016年 | 366篇 |
2015年 | 301篇 |
2014年 | 511篇 |
2013年 | 520篇 |
2012年 | 518篇 |
2011年 | 516篇 |
2010年 | 379篇 |
2009年 | 395篇 |
2008年 | 448篇 |
2007年 | 455篇 |
2006年 | 428篇 |
2005年 | 402篇 |
2004年 | 314篇 |
2003年 | 341篇 |
2002年 | 282篇 |
2001年 | 299篇 |
2000年 | 258篇 |
1999年 | 179篇 |
1998年 | 139篇 |
1997年 | 108篇 |
1996年 | 91篇 |
1995年 | 84篇 |
1994年 | 74篇 |
1993年 | 49篇 |
1992年 | 45篇 |
1991年 | 35篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有9436条查询结果,搜索用时 781 毫秒
11.
12.
13.
介绍了单端正向变换器基本电路,重点叙述带三路调节DC电压的100KHZ180W离线电源。它采用具有低导电阻RDS和低栅极电荷Qg的新型场效应管(QFET)作为变换电路的主开关器件,降低了电源开关损耗并提高了效率3%-5%。 相似文献
14.
Murray Hodgson 《Applied Acoustics》2004,65(1):69-89
The acoustical characteristics of 14 university classrooms at the University of British Columbia were measured before and after renovation—seven of these are discussed in detail here. From these measurements, and theoretical considerations, values of quantities used to assess each classroom configuration were predicted, and used to evaluate renovation quality. Information on each renovation was determined with the help of the university campus-planning office and/or the project acoustical consultant. These were related to the evaluation results in order to determine the relationship between design and acoustical quality. The criteria focused on the quality of verbal communication in the classrooms. Room-average Speech Intelligibility (SI) and its physical correlate, Speech Transmission Index (STI), were used to quantify verbal-communication quality. A simplified STI-calculation procedure was applied. The results indicate that some renovations were beneficial, others were not. Verbal-communication quality varied from ‘poor’ to ‘good’. The effect of a renovation depends on a complex interplay between changes in the reverberation and changes in the signal-to-noise level difference, as affected by sound absorption and the source outputs. Renovations which reduce noise are beneficial unless signal-to-noise level differences remain optimal. Renovations often put too much emphasis on adding sound absorption to control reverberation, at the expense of lower speech levels, particularly at the backs of classrooms. The absorption and noise contributed by room occupants has apparently often been neglected. 相似文献
15.
We investigate the dynamics of the Λ system driven by two resonant laser fields in presence of dissipation for coupling strengths where the rotating‐wave approximation starts to break down. This regime is characterised by Rabi frequencies being approximately equal or smaller than the field frequencies. A systematic procedure to obtain an expansion for the solution of the Bloch evolution equations of the system is presented. The lowest contribution results to be the well‐known rotating‐wave approximation. The method is based on a semi‐classical treatment of the problem, and its predictions are interpreted fully quantum mechanically. The theory is illustrated by a detailed study of the disappearance of coherent population trapping as the intensities of the fields increase. 相似文献
16.
感应式电能表的智能化改进 总被引:2,自引:0,他引:2
介绍了利用AVR单片机AT90S8515的输入捕捉功能对感应式电能表进行智能化改进的方法,讨论了新型防盗电系统的结构原理,给出了用AT90S8515单片机设计带有防盗电功能的感应式电能袁的改进电路组成及工作过程。 相似文献
17.
软件无线电中采样率转换技术的实现及在3G中的应用 总被引:1,自引:0,他引:1
目前移动通信标准繁多,且新旧体制混杂,很难做到统一.为了实现互连互通,目前比较可行的方法是采用软件无线电.采样率转换技术是实现互连互通的关键.文中针对第三代移动通信系统(3G)中不同通信体制的带宽、速率要求,根据分级变换的思想,对3G中的CDMA2000和TDSCDMA的采样率转换方案进行了设计,并对3G中的5种制式的采样率转换方案进行了分析比较.实验表明,这一方案可以在采样率变换的高效网络结构基础上进一步降低滤波运算量和存储量. 相似文献
18.
Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles. 相似文献
19.
M型四能级原子与三模场相互作用系统的动力学特性 总被引:2,自引:2,他引:0
采用全量子理论,研究了M型四能级原子与三模场相互作用系统的动力学特性,通过数值计算,分析了光场失谐量、初始光子数和原子初始状态对原子布居概率和光子统计演化规律的影响. 相似文献
20.
Zhang Xinliang Huang Dexiu Sun Junqiang Liu Deming 《Optical and Quantum Electronics》2004,36(7):627-634
A simple scheme for single to multi-channel wavelength conversion based on cross-gain modulation of amplified spontaneous emission (ASE) spectrum in semiconductor optical amplifier (SOA) is described. Single to 16-channel wavelength conversion at 10 Gb/s is first demonstrated without any additional probe lights, the modulation information carried by input signal could be converted into arbitrary many channels if only the demultiplexer with enough channels is exploited. Output performance and pattern effects are investigated experimentally. 相似文献