全文获取类型
收费全文 | 9745篇 |
免费 | 1678篇 |
国内免费 | 2334篇 |
专业分类
化学 | 7981篇 |
晶体学 | 183篇 |
力学 | 611篇 |
综合类 | 213篇 |
数学 | 1267篇 |
物理学 | 3502篇 |
出版年
2024年 | 5篇 |
2023年 | 131篇 |
2022年 | 209篇 |
2021年 | 264篇 |
2020年 | 380篇 |
2019年 | 360篇 |
2018年 | 364篇 |
2017年 | 346篇 |
2016年 | 431篇 |
2015年 | 489篇 |
2014年 | 690篇 |
2013年 | 753篇 |
2012年 | 792篇 |
2011年 | 876篇 |
2010年 | 772篇 |
2009年 | 748篇 |
2008年 | 814篇 |
2007年 | 698篇 |
2006年 | 692篇 |
2005年 | 618篇 |
2004年 | 547篇 |
2003年 | 411篇 |
2002年 | 483篇 |
2001年 | 417篇 |
2000年 | 385篇 |
1999年 | 252篇 |
1998年 | 140篇 |
1997年 | 92篇 |
1996年 | 85篇 |
1995年 | 76篇 |
1994年 | 55篇 |
1993年 | 53篇 |
1992年 | 60篇 |
1991年 | 50篇 |
1990年 | 46篇 |
1989年 | 29篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1971年 | 3篇 |
1966年 | 4篇 |
1964年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
An easy-to-prepare chemosensor, 2-(4-formylphenyl)phenanthroimidazole 1, synthesized by facile one-step condensation under microwave irradiation, has been indicated to be a colorimetric and fluorometric
probe for fluoride anion with good sensitivity and high selectivity. This probe shows obvious red shift and absorbance intensity
changes in UV absorption and fluorescence spectra in the presence of fluoride anions. Such color and absorbance intensity
changes are attributed to the deprotonation of N-H on the imidazole moiety with fluoride anion. 相似文献
992.
This paper focuses on multistability theory for discontinuous dynamical systems having a set of multiple isolated equilibria and/or a continuum of equilibria. Multistability is the property whereby the solutions of a dynamical system can alternate between two or more mutually exclusive Lyapunov stable and convergent equilibrium states under asymptotically slowly changing inputs or system parameters. In this paper, we extend the definition and theory of multistability to discontinuous autonomous dynamical systems. In particular, nontangency Lyapunov-based tests for multistability of discontinuous systems with Filippov and Carathéodory solutions are established. The results are then applied to excitatory and inhibitory biological neuronal networks to explain the underlying mechanism of action for anesthesia and consciousness from a multistable dynamical system perspective, thereby providing a theoretical foundation for general anesthesia using the network properties of the brain. 相似文献
993.
A model to modulate acoustic field in a regenerator of a thermoacoustic system by the double loudspeakers method is presented in this paper. The equations are derived for acoustic field modulation. They represent the relations among acoustic field (complex pressure p(0), complex velocity u(0), and acoustic impedance Z(0)), driving parameters of loudspeakers (voltage amplitude and its phase difference), and operating parameters involved in a matrix H (frequency, temperature of regenerator). The range of acoustic field is adjustable and limited by the maximal driving voltages of loudspeakers according to driving parameters. The range is simulated and analyzed in the amplitude-phase and complex coordinate planes for a given or variable H. The simulated results indicate that the range has its intrinsic characteristics. The expected acoustic field in a regenerator can be obtained feasibly by the modulation. 相似文献
994.
In this paper, a new type of circular photonic crystal (CPC) with a geometrical distribution of concentric layers is presented. A broad and isotropic photonic band gap is achieved using this geometrically distributed CPC (GCPC). Also, the influence of the number of concentric layers to the overall band gap of GCPC is studied. It is demonstrated that the band gap broadens with a red shift when the number of concentric layers is increased. The reason for the red shift of the band gap is further investigated. 相似文献
995.
The optical characteristics of transparent lead magnesium niobate titanate (PMNT) electro-optic ceramic, including the electro-optic phase modulation, electric hysteresis property and thermo-optic coefficient, are investigated in detail. Based on this novel ceramic, a polarization independent electro-optic switch by using fiber Sagnac interferometer (FSI) structure is realized. An initial π-shift is introduced into the Sagnac loop to eliminate the effect of the polarization orientation of the incident light on the switch performance. Then an electrically controllable PMNT phase retarder is used to switch the optical signal between the reflection and transmission ports. Some theoretical analyses are given and the switch performances are also discussed, including the thermal characteristic and different switching frequency response. 相似文献
996.
We setup an ultrafast noncollinear optical parametric amplification system for fluorescence spectral dynamics study. The simultaneous broadband amplifying ability makes it suitable as an ultrafast spectrometer with femtosecond time-resolution. By real-time fluctuation correction, femtosecond fluorescence spectra are obtained efficiently by a single scan. With this technique, the solvation dynamics of DCM dye in four solvents are measured to demonstrate the performance of the system. We show that this ultrafast time-resolved spectrometer is very useful and efficient in studying ultrafast spectral dynamics. 相似文献
997.
998.
999.
1000.