全文获取类型
收费全文 | 143165篇 |
免费 | 15323篇 |
国内免费 | 18339篇 |
专业分类
化学 | 101013篇 |
晶体学 | 1705篇 |
力学 | 4255篇 |
综合类 | 1132篇 |
数学 | 19212篇 |
物理学 | 49510篇 |
出版年
2023年 | 1220篇 |
2022年 | 2314篇 |
2021年 | 3532篇 |
2020年 | 4309篇 |
2019年 | 4084篇 |
2018年 | 3331篇 |
2017年 | 4507篇 |
2016年 | 4882篇 |
2015年 | 4395篇 |
2014年 | 6487篇 |
2013年 | 11318篇 |
2012年 | 9681篇 |
2011年 | 8928篇 |
2010年 | 7400篇 |
2009年 | 9457篇 |
2008年 | 9768篇 |
2007年 | 10250篇 |
2006年 | 9005篇 |
2005年 | 7360篇 |
2004年 | 6697篇 |
2003年 | 5920篇 |
2002年 | 5165篇 |
2001年 | 4303篇 |
2000年 | 3801篇 |
1999年 | 3407篇 |
1998年 | 2987篇 |
1997年 | 2562篇 |
1996年 | 2243篇 |
1995年 | 2277篇 |
1994年 | 2022篇 |
1993年 | 1739篇 |
1992年 | 1618篇 |
1991年 | 1089篇 |
1990年 | 864篇 |
1989年 | 800篇 |
1988年 | 640篇 |
1987年 | 571篇 |
1986年 | 522篇 |
1985年 | 542篇 |
1984年 | 487篇 |
1983年 | 272篇 |
1982年 | 484篇 |
1981年 | 632篇 |
1980年 | 568篇 |
1979年 | 594篇 |
1978年 | 476篇 |
1977年 | 359篇 |
1976年 | 298篇 |
1974年 | 120篇 |
1973年 | 197篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Dariusz Marek Adam Domaski Joanna Domaska Jakub Szygua Tadeusz Czachrski Jerzy Klamka 《Entropy (Basel, Switzerland)》2021,23(5)
In this article, a way to employ the diffusion approximation to model interplay between TCP and UDP flows is presented. In order to control traffic congestion, an environment of IP routers applying AQM (Active Queue Management) algorithms has been introduced. Furthermore, the impact of the fractional controller and its parameters on the transport protocols is investigated. The controller has been elaborated in accordance with the control theory. The TCP and UDP flows are transmitted simultaneously and are mutually independent. Only the TCP is controlled by the AQM algorithm. Our diffusion model allows a single TCP or UDP flow to start or end at any time, which distinguishes it from those previously described in the literature. 相似文献
2.
《中国物理 B》2021,30(5):56501-056501
Thermal expansion control is always an obstructive factor and challenging in high precision engineering field. Here,the negative thermal expansion of Nb F_3 and Nb OF_2 was predicted by first-principles calculation with density functional theory and the quasi-harmonic approximation(QHA). We studied the total charge density, thermal vibration, and lattice dynamic to investigate the thermal expansion mechanism. We found that the presence of O induced the relatively strong covalent bond in Nb OF_2, thus weakening the transverse vibration of F and O in Nb OF_2, compared with the case of Nb F_3.In this study, we proposed a way to tailor negative thermal expansion of metal fluorides by introducing the oxygen atoms.The present work not only predicts two NTE compounds, but also provides an insight on thermal expansion control by designing chemical bond type. 相似文献
3.
Dynamical analysis,circuit realization,and application in pseudorandom number generators of a fractional-order laser chaotic system 下载免费PDF全文
Chenguang Ma 《中国物理 B》2021,30(12):120504-120504
A new five-dimensional fractional-order laser chaotic system (FOLCS) is constructed by incorporating complex variables and fractional calculus into a Lorentz-Haken-type laser system. Dynamical behavior of the system, circuit realization and application in pseudorandom number generators are studied. Many types of multi-stable states are discovered in the system. Interestingly, there are two types of state transition phenomena in the system, one is the chaotic state degenerates to a periodical state, and the other is the intermittent chaotic oscillation. In addition, the complexity of the system when two parameters change simultaneously is measured by the spectral entropy algorithm. Moreover, a digital circuit is design and the chaotic oscillation behaviors of the system are verified on this circuit. Finally, a pseudo-random sequence generator is designed using the FOLCS, and the statistical characteristics of the generated pseudo-random sequence are tested with the NIST-800-22. This study enriches the research on the dynamics and applications of FOLCS. 相似文献
4.
Due to their intrinsic link with nonlinear Fokker-Planck equations and many other applications, distribution dependent stochastic differential equations (DDSDEs) have been intensively investigated. In this paper, we summarize some recent progresses in the study of DDSDEs, which include the correspondence of weak solutions and nonlinear Fokker-Planck equations, the well-posedness, regularity estimates, exponential ergodicity, long time large deviations, and comparison theorems. 相似文献
5.
We propose a conjecture on the relative twist formula of l-adic sheaves, which can be viewed as a generalization of Kato—Saito's conjecture. We verify this conjecture under some transversal assumptions. We also define a relative cohomological characteristic class and prove that its formation is compatible with proper push-forward. A conjectural relation is also given between the relative twist formula and the relative cohomological characteristic class. 相似文献
6.
7.
8.
《Mendeleev Communications》2022,32(4):520-522
Investigations of nanocomposite thin films based on polyarylene- phthalide, single-walled carbon nanotubes and graphene oxide have been carried out. Using these films as a transport layer, field-effect transistors were assembled and their output and transfer characteristics were measured. The mobility of charge carriers was estimated and the obtained values are as follows: μPAP/GO = 0.020 cm2 V?1 s?1 and μPAP/SWCNT = 0.071 cm2 V?1 s?1. 相似文献
9.
移动加热器法(THM)生长碲锌镉晶体时,界面稳定性对晶体生长的质量有很大影响。本文基于多物理场有限元仿真软件Comsol建立了THM生长碲锌镉晶体的数值模拟模型,讨论了Te边界层与组分过冷区之间的关系,对不同生长阶段的物理场、Te边界层与组分过冷区进行仿真研究,最后讨论了微重力对物理场分布的影响,并对比了微重力与正常重力下的生长界面形貌。模拟结果表明,Te边界层与组分过冷区的分布趋势是一致的,在不同生长阶段,流场中次生涡旋的位置会发生移动,从而导致生长界面的形貌随着生长的进行发生变化,同时微重力条件下形成的生长界面形貌最有利于单晶生长。因此,在晶体生长的中前期,对次生涡旋位置的控制和对组分过冷的削弱,是THM生长高质量晶体的有效方案。 相似文献
10.
Evolution of electrical conductivity and semiconductor to metal transition of iron oxides at extreme conditions 下载免费PDF全文
Yukai Zhuang 《中国物理 B》2022,31(8):89101-089101
Iron oxides are widely found as ores in Earth's crust and are also important constituents of its interiors. Their polymorphism, composition changes, and electronic structures play essential roles in controlling the structure and geodynamic properties of the solid Earth. While all-natural occurring iron oxides are semiconductors or insulators at ambient pressure, they start to metalize under pressure. Here in this work, we review the electronic conductivity and metallization of iron oxides under high-pressure conditions found in Earth's lower mantle. We summarize that the metallization of iron oxides is generally controlled by the pressure-induced bandgap closure near the Fermi level. After metallization, they possess much higher electrical and thermal conductivity, which will facilitate the thermal convection, support a more stable and thicker D$\prime\prime$ layer, and formulate Earth's magnetic field, all of which will constrain the large-scale dynamos of the mantle and core. 相似文献