全文获取类型
收费全文 | 1278篇 |
免费 | 240篇 |
国内免费 | 154篇 |
专业分类
化学 | 184篇 |
力学 | 301篇 |
综合类 | 95篇 |
数学 | 95篇 |
物理学 | 997篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 42篇 |
2021年 | 44篇 |
2020年 | 47篇 |
2019年 | 31篇 |
2018年 | 36篇 |
2017年 | 62篇 |
2016年 | 50篇 |
2015年 | 50篇 |
2014年 | 77篇 |
2013年 | 95篇 |
2012年 | 68篇 |
2011年 | 72篇 |
2010年 | 63篇 |
2009年 | 66篇 |
2008年 | 73篇 |
2007年 | 100篇 |
2006年 | 81篇 |
2005年 | 87篇 |
2004年 | 79篇 |
2003年 | 78篇 |
2002年 | 74篇 |
2001年 | 41篇 |
2000年 | 31篇 |
1999年 | 23篇 |
1998年 | 27篇 |
1997年 | 31篇 |
1996年 | 21篇 |
1995年 | 28篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1672条查询结果,搜索用时 31 毫秒
91.
A new method to protect the copyright of digital museum based on digital holography is proposed. The Fresnel hologram of watermark image is embedded in the object to be protected through discrete wavelet transform (DWT). After the watermark detection, the copyright information appears in the reconstructed hologram. With the higher redundancy feature in the hologram, the proposed technique can actually survive several kinds of image processing. Experimental results prove that the presented method has good robustness in image protection. 相似文献
92.
In the cases of soft magnetic materials or complex domain configurations, investigations of the domain structure by the conventional Bitter pattern technique are generally difficult. It is demonstrated in this paper, referring to the examples of domain images of thin permalloy films and the basal surface of bulk cobalt single crystals, that this problem can be overcome by the application of digital image processing (DIP) system. In particular, the visibility limit in domain observation was expanded by an order of magnitude and high quality domain images could be obtained. Improvements over earlier results were achieved. 相似文献
93.
94.
95.
Forrer J Schmutz H Tschaggelar R Schweiger A 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,166(2):220-251
Direct detection of free induction decays and electron spin echoes, and the recording of echo-detected EPR spectra and electron spin echo envelope modulation patterns at a microwave frequency of 2.5 GHz is demonstrated. This corresponds to the measurement of the transverse magnetization in the laboratory frame, rather than in the rotating frame as usually done by down-converting the signal (homodyne detection). An oscilloscope with a 6-GHz analog bandwidth, a sampling rate of 20 GigaSamples per second, and a trigger frequency of 5 GHz for the edge trigger and 750 MHz for the advanced trigger, is used in these experiments. For signal averaging a 3-GHz microwave clock divider has been developed to synchronize the oscilloscope with the frequency of the EPR signal. Moreover, direct detection of continuous wave EPR signals at 2.5 GHz is described. 相似文献
96.
高频地波雷达频谱监测系统的前端电路设计 总被引:1,自引:0,他引:1
利用超外差式接收和直接数字合成(DDS)技术设计了高频地波雷达频谱监测系统的前端电路.该电路能够根据雷达探测距离的远近选择相对应的噪声信号接收频段,为后续的数据采集与处理提供噪声电平数据.实验证明:本系统的跳频本振信号信噪比(SNR)优于60dB;对输入信号具有60dB左右的增益和1μV的灵敏度,满足了武汉大学研制的下一代高频地波海态监测雷达对频谱监测的需要. 相似文献
97.
Let q 2 be an integer. Then –q gives rise to a number system in
, i.e., each number n
has a unique representation of the form n = c
0 + c
1 (–q) + ... + c
h
(–q)
h
, with c
i
{0,..., q – 1}(0 i h). The aim of this paper is to investigate the sum of digits function –q
(n) of these number systems. In particular, we derive an asymptotic expansion for
and obtain a Gaussian asymptotic distribution result for –q
(n) – –q
(–n). Furthermore, we prove non-differentiability of certain continuous functions occurring in this context. We use automata and analytic methods to derive our results. 相似文献
98.
99.
100.