首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2064篇
  免费   58篇
  国内免费   13篇
化学   1334篇
晶体学   40篇
力学   65篇
综合类   2篇
数学   180篇
物理学   514篇
  2023年   21篇
  2022年   88篇
  2021年   78篇
  2020年   50篇
  2019年   76篇
  2018年   75篇
  2017年   70篇
  2016年   70篇
  2015年   56篇
  2014年   86篇
  2013年   129篇
  2012年   144篇
  2011年   121篇
  2010年   98篇
  2009年   92篇
  2008年   88篇
  2007年   73篇
  2006年   66篇
  2005年   59篇
  2004年   37篇
  2003年   42篇
  2002年   40篇
  2001年   24篇
  2000年   25篇
  1999年   19篇
  1998年   19篇
  1997年   17篇
  1996年   14篇
  1995年   15篇
  1994年   12篇
  1993年   16篇
  1992年   23篇
  1991年   19篇
  1990年   13篇
  1989年   14篇
  1988年   13篇
  1987年   14篇
  1986年   10篇
  1985年   21篇
  1984年   11篇
  1983年   14篇
  1982年   12篇
  1981年   11篇
  1980年   12篇
  1979年   12篇
  1978年   12篇
  1977年   14篇
  1976年   15篇
  1974年   11篇
  1973年   9篇
排序方式: 共有2135条查询结果,搜索用时 15 毫秒
941.
942.
In this paper, the effects of carbon nanotubes (CNT) implantation and sisal fibre size on the electrical properties of sisal fibre-reinforced epoxy composites are reported. For this purpose, the epoxy composites reinforced with CNT-implanted sisal fibre of 5 mm and 10 mm lengths were prepared by hand moulding and samples characterized for their electrical properties, such as dielectric constant (ε′), dielectric dissipation factor (tan δ) and AC conductivity (σac) at different temperatures and frequencies. It was observed that the dielectric constant increases with increase in temperature and decreases with increase in frequency from 500 Hz to 5 KHz. Interestingly, the sample having CNT-implanted sisal fibre of 5 mm length exhibited the highest value of dielectric constant than the one with length 10 mm. This is attributed to the increased surface area of sisal fibre and enhancement of the interfacial polarization. At a constant volume and a length of 5 mm of the fibres, the number of interfaces per unit volume element is high and results in a higher interfacial polarization. The interfaces decrease as the fibre length increases, and therefore, the value of ε′ decreases at 10 mm fibre length. The peak value of the dielectric constant decreases with increasing frequency. A continuous decrease in dissipation factor (tan δ) with increasing frequency for all samples was observed, while at lower temperatures, the values of tan δ remains approximately same. The AC conductivity for 5 mm length sisal epoxy composite and 10 mm length sisal fibre–epoxy composites is higher than that of pure epoxy at all the frequencies.  相似文献   
943.
The compound CeRh3B2 orders magnetically with a low saturation moment of about 0.4 microB per formula unit but a very high Curie temperature of 115 K. On replacing Rh with Os, it is observed that in the Ce(Rh1?xOsx)3B2 (0 ? x ? 0.167) series, both the magnetic moment and the Curie temperature decrease rapidly with increasing x. The compound CeRh2.5Os0.5B2 (x = 0.167) does not appear to be ordered magnetically down to 5 K. This behavior is thought to arise from the changes in the hybridization of Ce 4f levels with sp type conduction electrons and/or with Rh and Os derived d bands.  相似文献   
944.
This paper obtains solutions to the Zakharov-Kuznetsov modified equal width equation with power law nonlinearity. The Lie symmetry approach and the simplest equation method are used to obtain these solutions. Moreover, conservation laws are derived for the underlying equation by employing two approaches: the new conservation theorem and the multiplier method.  相似文献   
945.
Using the method of strained coordinates, a weakly nonlinear theory of the breakup of a gravitating column is presented. It is shown that the self-gravitating column breaks into the main celestial bodies and their satellites whose dimensions are sensitive to the wavenumbers.  相似文献   
946.
In this article we develop a power computation code in the R language which provides an easy to use tool to researchers in designing Shewhart control charts. It enables researchers to use different existing and newly introduced sensitizing rules and runs rules schemes designed for Shewhart-type control charts for location and spread. The code provides researchers to compute the power for different options of r out of m rules/schemes. The code is flexible to apply for any sample size, false alarm rate, type of control limits (one- or two-sided), amount of shift in the process parameters and a variety of popular distributions for commonly used Shewhart-type control charts (i.e. ${\bar{{X}} ,R ,S}$ and S 2 charts). These mentioned benefits of the developed functional code are only partially found in features of the existing software packages and these programs may be enhanced by adding the features of the developed code as a function in their libraries dealing with quality control charting.  相似文献   
947.
Let R be a prime ring with center Z(R). For a fixed positive integer n, a permuting n-additive map ${\Delta : R^n \to R}$ is known to be permuting n-derivation if ${\Delta(x_1, x_2, \ldots, x_i x'_{i},\ldots, x_n) = \Delta(x_1, x_2, \ldots, x_i, \ldots, x_n)x'_i + x_i \Delta(x_1, x_2, \ldots, x'_i, \ldots, x_n)}$ holds for all ${x_i, x'_i \in R}$ . A mapping ${\delta : R \to R}$ defined by δ(x) = Δ(x, x, . . . ,x) for all ${x \in R}$ is said to be the trace of Δ. In the present paper, we have proved that a ring R is commutative if there exists a permuting n-additive map ${\Delta : R^n \to R}$ such that ${xy + \delta(xy) = yx + \delta(yx), xy- \delta(xy) = yx - \delta(yx), xy - yx = \delta(x) \pm \delta(y)}$ and ${xy + yx = \delta(x) \pm \delta(y)}$ holds for all ${x, y \in R}$ . Further, we have proved that if R is a prime ring with suitable torsion restriction then R is commutative if there exist non-zero permuting n-derivations Δ1 and Δ2 from ${R^n \to R}$ such that Δ1(δ 2(x), x, . . . ,x) =  0 for all ${x \in R,}$ where δ 2 is the trace of Δ2. Finally, it is shown that in a prime ring R of suitable torsion restriction, if ${\Delta_1, \Delta_2 : R^n \longrightarrow R}$ are non-zero permuting n-derivations with traces δ 1, δ 2, respectively, and ${B : R^n \longrightarrow R}$ is a permuting n-additive map with trace f such that δ 1 δ 2(x) =  f(x) holds for all ${x \in R}$ , then R is commutative.  相似文献   
948.
An efficient multi-wavelength Brillouin-erbium fiber laser utilizing low stimulated Brillouin scattering threshold highly nonlinear photonic crystal fiber (PCF) is presented. A Fabry-Perot pre-amplified Brillouin pump configuration was used which consists of 100 m PCF and 10 m erbium doped fiber (EDF). Up to 28 output channels with SNR of more than 20 dB could be generated with modest pump power.  相似文献   
949.
We present a general and fascinating problem of quantum entanglement (QE) that is calculated with the help of quantum Fisher information (QFI) and von Neumann entropy (VNE) for moving two-level atomic systems. We calculate numerically the temporal evolution of the state vector of the entire system under the influence of intrinsic decoherence for a moving two-level atom. We demonstrate that the phase shifts of an estimator parameter, intrinsic decoherence, and the atomic motion play an important and prominent role during the time evolution of the atomic system. We observe that there is a monotonic relation between the atomic quantum Fisher information (QFI) and quantum entanglement (QE) in the absence of atomic motion. We also show that at the revival time the local maximum values of QFI decreases gradually. A periodic behavior of QFI is observed in the presence of atomic motion, which becomes more important and remarkable for two-level atomic systems. Moreover, the atomic quantum Fisher information and entanglement demonstrate an opposite response during the time evolution in the presence of atomic motion. We show that the evolution of entanglement is more susceptible to the intrinsic decoherence; a considerable change occurs in the degree of entanglement when the intrinsic decoherence parameter increases. Intrinsic decoherence in the atom–field interaction represses the nonclassical effects of the atomic systems. Both the entanglement and the quantum Fisher information saturate to their lower levels for longer time scales in the presence of intrinsic decoherence. For larger values of intrinsic decoherence, the sudden death of entanglement is observed.  相似文献   
950.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号