全文获取类型
收费全文 | 22650篇 |
免费 | 1277篇 |
国内免费 | 1122篇 |
专业分类
系统科学 | 2007篇 |
丛书文集 | 563篇 |
教育与普及 | 337篇 |
理论与方法论 | 336篇 |
现状及发展 | 975篇 |
研究方法 | 48篇 |
综合类 | 20781篇 |
自然研究 | 2篇 |
出版年
2024年 | 106篇 |
2023年 | 232篇 |
2022年 | 408篇 |
2021年 | 462篇 |
2020年 | 368篇 |
2019年 | 213篇 |
2018年 | 953篇 |
2017年 | 1017篇 |
2016年 | 778篇 |
2015年 | 622篇 |
2014年 | 872篇 |
2013年 | 853篇 |
2012年 | 1156篇 |
2011年 | 1909篇 |
2010年 | 1750篇 |
2009年 | 1350篇 |
2008年 | 1595篇 |
2007年 | 1745篇 |
2006年 | 886篇 |
2005年 | 810篇 |
2004年 | 719篇 |
2003年 | 705篇 |
2002年 | 793篇 |
2001年 | 714篇 |
2000年 | 526篇 |
1999年 | 609篇 |
1998年 | 407篇 |
1997年 | 396篇 |
1996年 | 315篇 |
1995年 | 320篇 |
1994年 | 317篇 |
1993年 | 202篇 |
1992年 | 195篇 |
1991年 | 193篇 |
1990年 | 161篇 |
1989年 | 130篇 |
1988年 | 115篇 |
1987年 | 77篇 |
1986年 | 41篇 |
1985年 | 14篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1958年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
The exponential Radon transform, a generalization of the Radon transform, is defined and studied as a mapping of function
spaces. It is represented in terms of Fourier transform of its domain and range, and this leads to the harmonic decomposition
reconstruction. The results are similar results of Tretiak and Metz.
Foundation item: Supported by the National Natural Science Foundation of China (No. 19971064), Key Project of Science and
Technology of Hubei Province Education Committee.
Biography: Wang Jin-ping (1963-), male, Ph.D. candidate, research direction: numberical solution of singular integral equation
and integral transformation etc. 相似文献
23.
24.
25.
YU Jianqiao LIAO Jianwei 《武汉大学学报:自然科学英文版》2007,12(5):887-892
We propose a multiple-tree overlay structure for resource discovery in unstructured P2P systems. Peers that have similar interests or hold similar type of resources will be grouped into a tree-like cluster. We exploit the heterogeneity of peers in each cluster by connecting peers with more capacities closer to the root of the tree. The capacity of a peer can be defined in different ways (e.g. higher network bandwidth, larger disk space, more data items of a certain type etc.) according to different needs of users or applications. 相似文献
26.
In October 1924, The Physical Review, a relatively minor journal at the time, published a remarkable two-part paper by John H. Van Vleck, working in virtual isolation
at the University of Minnesota. Using Bohr’s correspondence principle and Einstein’s quantum theory of radiation along with
advanced techniques from classical mechanics, Van Vleck showed that quantum formulae for emission, absorption, and dispersion
of radiation merge with their classical counterparts in the limit of high quantum numbers. For modern readers Van Vleck’s
paper is much easier to follow than the famous paper by Kramers and Heisenberg on dispersion theory, which covers similar
terrain and is widely credited to have led directly to Heisenberg’s Umdeutung paper. This makes Van Vleck’s paper extremely valuable for the reconstruction of the genesis of matrix mechanics. It also
makes it tempting to ask why Van Vleck did not take the next step and develop matrix mechanics himself.
This paper was written as part of a joint project in the history of quantum physics of the Max Planck Institut für Wissenschaftsgeschichte and the Fritz-Haber-Institut in Berlin. 相似文献
27.
DING Mingtao WEI Fangqiang ZHANG Jinghong WANG Hongjuan 《武汉大学学报:自然科学英文版》2007,12(4):599-604
By analyzing the observation data from Dongchuan Debris Flow Observation and Research Station and historical data from year 1965 to 1990 gotten from National Astronomical Ob-servatories/Yunnan Observatory,the responding of debris flow in Jiangjia Ravine to Solar Proton Flare is studied. The following conclusion can be drawn. Solar Proton Flare,as one of most im-portant astronomical factors,affects the activity of debris flow in Yunnan. Generally,from 1965 to1990,the more active Solar Pro-ton Flare is,the greater the probability of high frequency and large runoff of debris flow is. On the contrary,the less active Solar Pro-ton Flare is,the greater the probability of low frequency,small runoff,and low sediment transport of debris flow is. 相似文献
28.
The unified chaotic system contains the Lorenz system and the Chen system as two dual systems at the two extremes of its parameter
spectrum. This paper presents the design of bang bang controller for unified system and multitude of numerical experiments
under various control parameters. Numerical experiments meet the theoretic proof perfectly and convincingly demonstrated the
controller can be effectively used for unified systems with uncertainty of the equilibrium points. The method enriches the
applications of chaotic control.
Foundation item: Supported by the National Natural Science Foundation of China(50209012)
Biography: Deng Xiao-ming (1980-), male, Master candidate, research direction: chaos control. 相似文献
29.
王心喜 《杭州师范学院学报(社会科学版)》2003,(2):89-93,100
五代十国时期,钱氏吴越国积极发展与日本的关系,但日本国对此却持消极的态度,双方的交往主要通过民间进行,局限在经济、文化领域。研究表明,此间中日交流出现了新的动向,即从以前中国方面的单方输出、日本方面的积极接受,开始变为中日双方的双向交流。尽管此时日本的"逆输出"在质和量上都不足道,但这毕竟是值得注意的历史现象,也可称为中日文化交流史上的一个转折点。 相似文献
30.
宋四海 《南京邮电大学学报(自然科学版)》1996,(4)
介绍了数字用户环路倍增设备用户开关电源的动态分析方法。在功率级和补偿网络拓扑给定时,应用最优控制理论,以动态误差平方积分最小为优化目标,建立非线性动态优化设计分析模型,用非线性不等式约束条件的最优化算法求出补偿网络的最优参数,并应用CAD辅助分析进行校核分析,以保证系统大、小信号的性能要求 相似文献