全文获取类型
收费全文 | 33228篇 |
免费 | 1530篇 |
国内免费 | 1517篇 |
专业分类
系统科学 | 2293篇 |
丛书文集 | 824篇 |
教育与普及 | 600篇 |
理论与方法论 | 375篇 |
现状及发展 | 963篇 |
研究方法 | 78篇 |
综合类 | 31139篇 |
自然研究 | 3篇 |
出版年
2024年 | 89篇 |
2023年 | 302篇 |
2022年 | 521篇 |
2021年 | 503篇 |
2020年 | 371篇 |
2019年 | 150篇 |
2018年 | 916篇 |
2017年 | 991篇 |
2016年 | 728篇 |
2015年 | 671篇 |
2014年 | 942篇 |
2013年 | 957篇 |
2012年 | 1296篇 |
2011年 | 1981篇 |
2010年 | 1828篇 |
2009年 | 1570篇 |
2008年 | 1706篇 |
2007年 | 1925篇 |
2006年 | 1116篇 |
2005年 | 1124篇 |
2004年 | 1004篇 |
2003年 | 969篇 |
2002年 | 939篇 |
2001年 | 957篇 |
2000年 | 974篇 |
1999年 | 1516篇 |
1998年 | 1263篇 |
1997年 | 1363篇 |
1996年 | 1221篇 |
1995年 | 955篇 |
1994年 | 952篇 |
1993年 | 812篇 |
1992年 | 747篇 |
1991年 | 659篇 |
1990年 | 628篇 |
1989年 | 566篇 |
1988年 | 509篇 |
1987年 | 325篇 |
1986年 | 139篇 |
1985年 | 58篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1967年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
91.
用边界积分方法分析了表面裂纹在接触载荷作用下的张开位移和应力强度因子,该方法将埋在无穷大弹性介质中裂纹模拟为连续分布的位错环,根据两个位错环之间的相互作用能可以得到弹性体的应变能,对弹性体的势能取极值,可以得到关于裂纹张开位移的边界积分方程,通过把半空间的边界模拟成一个包含在无穷大弹性介质中大裂纹,该方法能用已有的边界积分方法很好的处理具有任意表面形状的表面裂纹,文中算例分析了不同倾角的表面裂纹在法向和切向接触载荷作用下,裂纹尖端的应力强度因子,其结果对于分析路面表面裂纹的扩展具有重要意义。 相似文献
92.
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
93.
The aim of this study is to identify the brain activity associated with amphetamine craving for understanding the neurobiology of addiction by watching pictures of happy, sad or amphetamine. Brain activity was measured in 12 amphetamine addicts and 12 healthy subjects by fMRI while the subjects watched pictures designed to elicit happy feelings, sad feelings, or the desire to use amphetamine. The result demonstrated that amphetamine cues led to abnormally high cingulate and low frontal lobe activation in amphetamine addicts, who showed abnormalities in affect-related brain activation. 相似文献
94.
95.
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
96.
97.
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
98.
Kang J.Y. Xu F.C. 《中国科学基金(英文版)》2004,(2):57-58,64
1 Introduction
Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].
…… 相似文献
99.
100.
固体超强酸催化剂研究进展 总被引:3,自引:0,他引:3
徐少华 《太原师范学院学报(自然科学版)》2003,2(3):63-65
概括介绍了固体超强酸催化剂的合成进展,并对固体超强酸催化剂在有机合成反应中的应用做了简要评述. 相似文献