全文获取类型
收费全文 | 24115篇 |
免费 | 4507篇 |
国内免费 | 4837篇 |
专业分类
化学 | 18464篇 |
晶体学 | 607篇 |
力学 | 1372篇 |
综合类 | 490篇 |
数学 | 2609篇 |
物理学 | 9917篇 |
出版年
2024年 | 60篇 |
2023年 | 350篇 |
2022年 | 642篇 |
2021年 | 769篇 |
2020年 | 853篇 |
2019年 | 985篇 |
2018年 | 796篇 |
2017年 | 842篇 |
2016年 | 1063篇 |
2015年 | 1217篇 |
2014年 | 1375篇 |
2013年 | 1842篇 |
2012年 | 2226篇 |
2011年 | 2185篇 |
2010年 | 1813篇 |
2009年 | 1814篇 |
2008年 | 2019篇 |
2007年 | 1701篇 |
2006年 | 1727篇 |
2005年 | 1528篇 |
2004年 | 1274篇 |
2003年 | 946篇 |
2002年 | 1013篇 |
2001年 | 846篇 |
2000年 | 742篇 |
1999年 | 556篇 |
1998年 | 332篇 |
1997年 | 253篇 |
1996年 | 238篇 |
1995年 | 206篇 |
1994年 | 224篇 |
1993年 | 177篇 |
1992年 | 115篇 |
1991年 | 128篇 |
1990年 | 93篇 |
1989年 | 83篇 |
1988年 | 84篇 |
1987年 | 50篇 |
1986年 | 41篇 |
1985年 | 50篇 |
1984年 | 32篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 28篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1959年 | 5篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
本文利用武汉电离层观象台的加密频高图和三站Doppler图记录及新近提出的短波扰动反演方法,分析了1985年全球大气重力波联测(WAGS)期间10月18日这天白天的重力波扰动,发现在该日扰动中有两列不同形态的波列分别属于中尺度的内重力波和大尺度的导制重力波。本文还进一步估算了这两列重力波的水平传播参量,深入分析了它们的频谱结构的高度变化特征,发现了重力波功率谱谱峰的分裂和偏移等重要现象。本文结果表明,新的反演方法使电离层无线电汉诊断的简易短波实验系统,也能成为探测和研究重力波一类大尺度电离层动力过程的有效手段。 相似文献
42.
Let ? be a primitive substitution on a two-letter alphabet {a,b} having two fixed points ξa and ξb. We show that the substitution ? is invertible if and only if one has ξa=abξ and ξb=baξ. To cite this article: Z.-X. Wen et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 727–731. 相似文献
43.
潘继斌 《数学的实践与认识》2006,36(2):182-185
研究了基于支持向量机的后验概率的应用,提出了对样本集进行分解,以产生局部后验概率,根据模式的稳健性对局部后验概率进行凸组合融合的方法. 相似文献
44.
使用参数Dioid模块网络法,把含大量摄动参数的在普通极大代数意义下非线性状态空间模型在参数Dioid意义下线性化,在此基础上研究一类过程摄动系统的无阻塞鲁棒性.给出了有限缓冲串行生产系统在没有缓冲器下无阻塞的充要条件和充分条件. 相似文献
45.
46.
Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, while the high-frequency one was independent of it. The cell shape effect was simulated by an ellipsoidal cell model but the comparison between theory and experiment was far from being satisfactory. Prompted by the discrepancy, we proposed the use of spectral representation to analyze more realistic cell models. We adopted a shell-spheroidal model to analyze the effects of the cell membrane. It is found that the dielectric property of the cell membrane has only a minor effect on the dispersion magnitude ratio and the characteristic frequency ratio. We further included the effect of rotation of dipole induced by an external electric field, and solved the dipole-rotation spheroidal model in the spectral representation.Good agreement between theory and experiment has been obtained. 相似文献
47.
枸橼酸莫沙必利的合成 总被引:1,自引:0,他引:1
分别以邻羟基对氨基苯甲醇钠,对氟苯甲醛,邻苯二甲酰亚胺为起始原料,制得3个中间体,用其中2个中间体经偶合,环化后与第3个中间体反应,再经成盐制得产品,其摩尔总收率为31.5%。 相似文献
48.
49.
Wang Jingxiu Zhang Jun Deng Yuanyong Li Jingqun Tian Lirong Yang Xiulan 《中国科学A辑(英文版)》2002,45(1):57-64
Based on the studies on the source regions of a group of coronal mass ejections, we have identified two types of large-scale magnetic structures, and suggested that they are intrinsic components of solar magnetism, their destabilization, expansion, and eruption into the interplanetary space are the basic physical processes which lead to the coronal mass ejections. These two types of large-scale structures are giant magnetic loops connecting the two active belts on the opposite hemispheres of the Sun, and the giant filaments (filament channels) and their related magnetic structures. The latter often appear as two parallel rows of sunspots and plage fields, which align side by side in the full disk daily and synoptic magnetograms. The magnetic neutral lines of these large-scale structures are usually longer than 50 heliographic degrees. We name this type of structure “super A configuration”. Sometimes, they are shown as very long filaments and related large-scale magnetic fields. As these magnetic structures are of very large scale, they extend to a great altitude into the corona, they are not easily recognized in magnetic field observations which are usually aimed at solar flare studies. To identify these large-scale structures becomes a key to understanding and predicting coronal mass ejections. 相似文献
50.
Jun Xiang Ge 《International Journal of Infrared and Millimeter Waves》1994,15(10):1681-1688
In 1991, we developed a new type of quasi-optical power combiner, called a compound quasi-optical power combiner, at Ka-band. In this paper, the circuit of such a compound quasi-optical power combiner is analysed. Its equivalent circuit model is proposed. The circuit equations, the balance condition, the injection locking and the stabilized condition of the compound quasi-optical power combiner are studed by the equivalent circuit model. As an example, a compound quasi-optical power combiner which consists of two single—cavity, two—device power combiners is analysed 相似文献