全文获取类型
收费全文 | 11775篇 |
免费 | 2106篇 |
国内免费 | 721篇 |
专业分类
化学 | 1826篇 |
晶体学 | 44篇 |
力学 | 2249篇 |
综合类 | 98篇 |
数学 | 613篇 |
物理学 | 4346篇 |
无线电 | 5426篇 |
出版年
2024年 | 41篇 |
2023年 | 112篇 |
2022年 | 261篇 |
2021年 | 331篇 |
2020年 | 349篇 |
2019年 | 261篇 |
2018年 | 283篇 |
2017年 | 423篇 |
2016年 | 503篇 |
2015年 | 482篇 |
2014年 | 798篇 |
2013年 | 841篇 |
2012年 | 772篇 |
2011年 | 828篇 |
2010年 | 618篇 |
2009年 | 657篇 |
2008年 | 713篇 |
2007年 | 702篇 |
2006年 | 700篇 |
2005年 | 622篇 |
2004年 | 534篇 |
2003年 | 530篇 |
2002年 | 445篇 |
2001年 | 421篇 |
2000年 | 349篇 |
1999年 | 303篇 |
1998年 | 235篇 |
1997年 | 227篇 |
1996年 | 224篇 |
1995年 | 167篇 |
1994年 | 130篇 |
1993年 | 129篇 |
1992年 | 109篇 |
1991年 | 89篇 |
1990年 | 72篇 |
1989年 | 56篇 |
1988年 | 26篇 |
1987年 | 37篇 |
1986年 | 38篇 |
1985年 | 31篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 41篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
81.
Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice
coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized
soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method
of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities,
temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which
compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease
with electric field. 相似文献
82.
Modern trends in designing mechatronic systems call for a synergic design of the separated subsystems (mechanic, electronic parts, control modules, etc.) concurring to the overall performance. Following this point of view, this paper presents a control oriented model and a nonlinear control design for a Common Rail injection system. First a model is developed, which is tuned in a virtual simulation environment, representing the injection system in details in a reliable replication of reality. Then a sliding mode control is developed. Both the model of the injection process and of the control law are validated by a virtual detailed simulation environment. The prediction capability of the model and the control efficiency are clearly shown. 相似文献
83.
本文用石蜡模拟油垢,用^60Co放射源的1.25MeV平均能量的γ射线垂直入射,以一定的散射角和不同的探测立体角接收散射γ光子敫.发现散射γ计数与被测石蜡厚度之间存在不同的线性关系.结果发现,放射源与探测器之间屏蔽的好坏和合理的探测距离对提高线性度有很大关系.本实验测得最佳线性相关系数平方值为0.9981,平均测量精度为1.26mm.这对研究散射法检测油垢厚度和选择合适的探测距离提供了实验基础. 相似文献
84.
The stress-strain state of multilayered plates on an undeformable foundation is investigated. The design diagram of a transversely
loaded plate is formed by supplementing it with a symmetric one about the contact surface of the foundation. The double-thickness
plate obtained becomes loaded bilaterally and symmetrically about its midsurface. In such a way, only unflexural deformations
can be modeled, which reduces the number of unknowns and the general order of differentiation of the resolving system of equations.
The refined continual model developed takes into account the deformations of transverse shear and transverse compression in
high iterative approximations. The cases of a rigid contact between the foundation and the plate and frictionless slip of
the plate over the foundation are considered. Calculations confirm the efficiency of such an approach, which allows one to
obtain solutions qualitatively and quantitatively close to three-dimensional ones.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 643–654, September–October, 2006. 相似文献
85.
切变模量和转动惯量实验的改进 总被引:2,自引:1,他引:1
设计了一种基于垂直轴定理的新型吊钩,对切变模量和转动惯量实验进行了改进,使之成为既可测定金属丝切变模量和环、柱等刚体的转动惯量,又可验证反映转动惯量重要性质的平行轴定理及垂直轴定理的多功能实验仪. 相似文献
86.
Stability of tokamak plasmas with internal transport barriers against high n ideal magnetohydrodynamic ballooning mode
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A ballooning mode equation for tokamak plasma, with the toroidicity and the Shafranov shift effects included, is derived for a shift circular flux tokamak configuration. Using this equation, the stability of the plasma configuration with an internal transport barrier (ITB) against the high n (the toroidal mode number) ideal magnetohydrodynamic (MHD) ballooning mode is analysed. It is shown that both the toroidicity and the Shaftanov shift effects are stabilizing. In the ITB region, these effects give rise to a low shear stable channel between the first and the second stability regions. Out of the ITB region towards the plasma edge, the stabilizing effect of the Shaftanov shift causes the unstable zone to be significantly narrowed. 相似文献
87.
基于将Maxwell方程与四能级原子系统速率方程相结合而建立起随机激光时域理论,并利用有限时域差分法,研究了二维随机介质中激光模式的输出特性与介质尺寸、外形及抽运速率等参数的关系.结果表明,与传统激光模式相似,随机激光模式的强度随抽运速率的变化不仅具有阈值特性,而且具有饱和特性.基于模式特性对介质及抽运参数的依赖关系,提出了二维随机激光器的选模方式,在很大程度上不同于传统激光器的选模方式.
关键词:
随机激光器
模式选择
无序介质中的光学特性 相似文献
88.
运用一种新的动力学突变检测方法——排列熵(permutation entropy,PE)算法,计算并分析了中国华北地区52个站点1960年—2000年逐日平均气温资料的排列熵演化情况,发现中国华北地区气温在20世纪70年代中期、80年代初均发生了较大突变;进一步用经验模态分解(empirical mode decomposition,EMD)方法对排列熵序列进行逐级平稳化处理,结果发现这一地区的气温突变与准10年这一年代际时间尺度的周期变率密切相关,其原因与太阳黑子活动有着密切联系.
关键词:
华北
突变
排列熵算法
经验模态分解 相似文献
89.
Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the material's structure. There appears a relatively large change in structure of the material at about 273K, The anharmonic potential of the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes at around 312 cm^-1 and 464cm^-1 indicate that the latter phonon mode is more anharmonic than the former one. 相似文献
90.