全文获取类型
收费全文 | 3945篇 |
免费 | 720篇 |
国内免费 | 202篇 |
专业分类
化学 | 1191篇 |
晶体学 | 4篇 |
力学 | 515篇 |
综合类 | 80篇 |
数学 | 1675篇 |
物理学 | 1402篇 |
出版年
2024年 | 7篇 |
2023年 | 40篇 |
2022年 | 71篇 |
2021年 | 131篇 |
2020年 | 139篇 |
2019年 | 107篇 |
2018年 | 95篇 |
2017年 | 186篇 |
2016年 | 196篇 |
2015年 | 147篇 |
2014年 | 181篇 |
2013年 | 386篇 |
2012年 | 270篇 |
2011年 | 253篇 |
2010年 | 210篇 |
2009年 | 215篇 |
2008年 | 213篇 |
2007年 | 236篇 |
2006年 | 191篇 |
2005年 | 179篇 |
2004年 | 184篇 |
2003年 | 153篇 |
2002年 | 140篇 |
2001年 | 129篇 |
2000年 | 121篇 |
1999年 | 117篇 |
1998年 | 88篇 |
1997年 | 86篇 |
1996年 | 74篇 |
1995年 | 65篇 |
1994年 | 42篇 |
1993年 | 35篇 |
1992年 | 25篇 |
1991年 | 25篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 16篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4867条查询结果,搜索用时 328 毫秒
991.
992.
Considering the properties of slow change and quasi-periodicity of
magnetocardiography (MCG) signal, we use an integrated technique of adaptive
and low-pass filtering in dealing with two-channel MCG data measured by high
$T_{\rm c}$ SQUIDs. The adaptive filter in the time domain is based on a noise feedback
normalized least-mean-square (NLMS) algorithm, and the low-pass filter with
a cutoff at 100Hz in the frequency domain characterized by Gaussian functions is
combined with a notch at the power line frequency. In this way, both
relevant and irrelevant noises in original MCG data are largely eliminated.
The method may also be useful for other slowly varying quasi-periodical
signals. 相似文献
993.
We investigate the phenomena of spontaneous symmetry breaking
for φ4 model on a square lattice in the parameter space by using
the potential importance sampling method, which was proposed by Milchev,
Heermann, and Binder [J. Stat. Phys. 44 (1986) 749]. The critical
values of the parameters allow us to determine the phase diagram of the
model. At the same time, some relevant quantities such as
susceptibility and specific heat are also obtained. 相似文献
994.
995.
F. Fang C. C. Pain I. M. Navon M. D. Piggott G. J. Gorman P. A. Allison A. J. H. Goddard 《国际流体数值方法杂志》2009,59(8):827-851
A novel proper orthogonal decomposition (POD) model has been developed for use with an advanced unstructured mesh finite‐element ocean model, the Imperial College Ocean Model (ICOM, described in detail below), which includes many recent developments in ocean modelling and numerical analysis. The advantages of the POD model developed here over existing POD approaches are the ability:
- 1. To increase accuracy when representing geostrophic balance (the balance between the Coriolis terms and the pressure gradient). This is achieved through the use of two sets of geostrophic basis functions where each one is calculated by basis functions for velocities u and v.
- 2. To speed up the POD simulation. To achieve this a new numerical technique is introduced, whereby a time‐dependent matrix in the discretized equation is rapidly constructed from a series of time‐independent matrices. This development imparts considerable efficiency gains over the often‐used alternative of calculating each finite element over the computational domain at each time level.
- 3. To use dynamically adaptive meshes in the above POD model.
996.
In this paper, the synchronization and the parameter identification
of the chaotic Pikovsky--Rabinovich (PR) circuits are investigated.
The linear error of the second corresponding variables is used to
change the driven chaotic PR circuit, and the complete
synchronization of the two identical chaotic PR circuits is realized
with feedback intensity k increasing to a certain threshold. The
Lyapunov exponents of the chaotic PR circuits are calculated by
using different feedback intensities and our results are confirmed.
The case where the two chaotic PR circuits are not identical is also
investigated. A general positive Lyapunov function V, which
consists of all the errors of the corresponding variables and
parameters and changeable gain coefficient, is constructed by using
the Lyapunov stability theory to study the parameter identification
and complete synchronization of two non-identical chaotic circuits.
The controllers and the parameter observers could be obtained
analytically only by simplifying the criterion dV/dt<0
(differential coefficient of Lyapunov function V with respect to
time is negative). It is confirmed that the two non-identical
chaotic PR circuits could still reach complete synchronization and
all the unknown parameters in the drive system are estimated exactly
within a short transient period. 相似文献
997.
Adaptive projective synchronization of unified chaotic systems and its application to secure communication 下载免费PDF全文
In this paper, a simple adaptive linear feedback control method is proposed for controlling the scaling factor between two coupled unified chaotic systems to a desired value, based on the invarianee principle of differential equations. Under this control strategy, one can arbitrarily select the scaling factor. Numerical simulations are given to support the effectiveness of the proposed method and show the robustness against noise. Furthermore, a secure communication scheme based on the adaptive projective synchronization of unified chaotic systems is presented and numerical simulation shows its feasibility.[第一段] 相似文献
998.
Synchronization between two different noise-perturbed chaotic systems with unknown parameters 下载免费PDF全文
In this paper, a general method of synchronizing noise-perturbed chaotic systems with unknown parameters is proposed. Based on the LaSalle-type invariance principle for stochastic differential equations and by employing a combination of feedback control and adaptive control, some sufficient conditions of chaos synchronization between these noise-perturbed systems with unknown parameters are established. The model used in the research is the chaotic system, but the method is also applicable to the hyperchaotic systems. Unified system and noise-perturbed RSssler system, hyperchaotic Chen system and nolse-perturbed hyperchaotic RSssler system are taken for illustrative examples to demonstrate this technique.[第一段] 相似文献
999.
爆炸性物质太赫兹时间分辨光谱测量 总被引:6,自引:0,他引:6
利用自由空间电光取样方法,研究了四种炸药在太赫兹(THz)频段的光学特性。通过太赫兹时间分辨光谱测量,作者得到了四种炸药DNT(2,4-二硝基甲苯)、钝化的RDX(黑索今)、HMX(奥克托金)和TNT(2,4,6-三硝基甲苯)的透射光谱,进而计算得出它们在0.2~2.5 THz频段的吸收系数和折射率。作者发现,2,4-DNT在1.08 THz,HMX在1.82 THz存在显著的吸收尖峰,RDX在此频段存在多个吸收峰,TNT的吸收谱线相对其他三种样品比较平缓,这种共振吸收一般认为是由分子间相互作用或声子共振模式引起的。四种炸药对太赫兹波独特的吸收性质说明,太赫兹时间分辨光谱测量技术在炸药特征识别及安全检测领域具有潜在应用价值。作者对致癌物质偶氮苯进行了太赫兹光谱研究,发现了国产偶氮苯和进口偶氮苯在太赫兹波段均存在特征吸收峰,可用于物质鉴别。 相似文献
1000.