全文获取类型
收费全文 | 206912篇 |
免费 | 32296篇 |
国内免费 | 20274篇 |
专业分类
化学 | 118966篇 |
晶体学 | 2033篇 |
力学 | 14694篇 |
综合类 | 2289篇 |
数学 | 46273篇 |
物理学 | 75227篇 |
出版年
2024年 | 131篇 |
2023年 | 6006篇 |
2022年 | 6980篇 |
2021年 | 7603篇 |
2020年 | 8792篇 |
2019年 | 6941篇 |
2018年 | 10897篇 |
2017年 | 11883篇 |
2016年 | 12295篇 |
2015年 | 10451篇 |
2014年 | 12231篇 |
2013年 | 17780篇 |
2012年 | 20987篇 |
2011年 | 18658篇 |
2010年 | 12227篇 |
2009年 | 10893篇 |
2008年 | 10951篇 |
2007年 | 13341篇 |
2006年 | 12971篇 |
2005年 | 9141篇 |
2004年 | 6190篇 |
2003年 | 5579篇 |
2002年 | 5142篇 |
2001年 | 5204篇 |
2000年 | 3325篇 |
1999年 | 4374篇 |
1998年 | 1984篇 |
1997年 | 962篇 |
1996年 | 840篇 |
1995年 | 754篇 |
1994年 | 492篇 |
1993年 | 537篇 |
1992年 | 525篇 |
1991年 | 393篇 |
1990年 | 388篇 |
1989年 | 282篇 |
1988年 | 208篇 |
1987年 | 182篇 |
1986年 | 230篇 |
1985年 | 218篇 |
1984年 | 120篇 |
1983年 | 90篇 |
1982年 | 70篇 |
1981年 | 27篇 |
1980年 | 10篇 |
1976年 | 16篇 |
1972年 | 10篇 |
1971年 | 32篇 |
1959年 | 36篇 |
1936年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Considering that the vibration signal of rolling bearing is very weak and difficult to be extracted under the working environment noise, a two-dimensional asymmetric bistable system (TDAB) is proposed. The system is coupled by two systems, and the weak signal is enhanced by adjusting the control system (monostable system) to adjust the controlled system (asymmetric bistable system). First, under the condition of adiabatic approximation system, the signal-to-noise ratio (SNR) is deduced, and analyzes the influence of different system parameters on the shape of potential function. Then the effects of each parameter on the SNR of the system are analyzed theoretically. Finally, combined with the adaptive intelligent algorithm, the parameters of the controlled system are optimized, and then the coupling coefficient and control system parameters are adjusted to obtain better system performance. The TDAB system obtained is applied to different bearing fault diagnosis and compared with different coupling systems. The experimental results show that the method can extract the characteristic frequency effectively and has good spectrum amplification performance and anti-noise capability. It is proved that the TDAB system can also have good detection effect in practical application. 相似文献
2.
3.
Some bouncing models are investigated in the framework of an extended theory of gravity. The extended gravity model is a simple extension of the General Relativity where an additional matter geometry coupling is introduced to account for the late time cosmic speed up phenomena. The dynamics of the models are discussed in the background of a flat FRW universe. Some viable models are reconstructed for specifically assumed bouncing scale factors. The behavior of the models are found to be decided mostly by the parameters of the respective models. The extended gravity based minimal matter-geometry coupling parameter has a role to remove the omega singularity occurring at the bouncing epoch. It is noted that the constructed models violate the energy conditions, however, in some cases this violation leads to the evolution of the models in phantom phase. The stability of the models are analyzed under linear homogeneous perturbations and it is found that, near the bounce, the models show instability but the perturbations decay out smoothly to provide stable models at late times. 相似文献
4.
5.
Wei Yuting Wang Qihua Liu Wei 《Annals of the Institute of Statistical Mathematics》2021,73(3):535-553
Annals of the Institute of Statistical Mathematics - In this paper, a model averaging approach is developed for the linear regression models with response missing at random. It is shown that the... 相似文献
6.
《Discrete Mathematics》2021,344(12):112601
7.
8.
9.
构建了一个制造商和一个零售商所组成的两级供应链模型,研究增值税税率下调对供应链决策和社会福利的影响.结果表明,下调制造商、零售商增值税税率都会使产品零售价降低,提高零售商和制造商的利润.下调增值税税率给制造商带来的利润增量大于给零售商带来的利润增量.制造商税率下调导致批发价降低,零售商税率下调反而提高批发价.社会福利的变化趋势与潜在需求规模有关.当潜在需求规模较高时,社会福利总是随降税幅度的增大而增大,且税率降低后的社会福利大于税率降低前;当潜在需求规模中等时,社会福利随降税幅度的增大而减小,但税率降低后的社会福利仍大于税率降低前;当潜在需求规模较小时,社会福利随降税幅度的增大而减小,增值税税率下调损害了社会福利. 相似文献
10.
Zhong Weizhou Zhang Zexiong Chen Xiaowei Wei Qiang Chen Gang Huang Xicheng 《Acta Mechanica Sinica》2021,37(7):1136-1151
Acta Mechanica Sinica - Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood... 相似文献