全文获取类型
收费全文 | 19819篇 |
免费 | 3122篇 |
国内免费 | 2056篇 |
专业分类
化学 | 14643篇 |
晶体学 | 211篇 |
力学 | 1252篇 |
综合类 | 153篇 |
数学 | 2244篇 |
物理学 | 6494篇 |
出版年
2023年 | 365篇 |
2022年 | 376篇 |
2021年 | 573篇 |
2020年 | 746篇 |
2019年 | 761篇 |
2018年 | 599篇 |
2017年 | 600篇 |
2016年 | 871篇 |
2015年 | 871篇 |
2014年 | 1075篇 |
2013年 | 1326篇 |
2012年 | 1747篇 |
2011年 | 1798篇 |
2010年 | 1221篇 |
2009年 | 1084篇 |
2008年 | 1274篇 |
2007年 | 1121篇 |
2006年 | 1129篇 |
2005年 | 928篇 |
2004年 | 724篇 |
2003年 | 668篇 |
2002年 | 651篇 |
2001年 | 518篇 |
2000年 | 406篇 |
1999年 | 422篇 |
1998年 | 328篇 |
1997年 | 298篇 |
1996年 | 324篇 |
1995年 | 268篇 |
1994年 | 233篇 |
1993年 | 173篇 |
1992年 | 187篇 |
1991年 | 190篇 |
1990年 | 141篇 |
1989年 | 131篇 |
1988年 | 94篇 |
1987年 | 82篇 |
1986年 | 89篇 |
1985年 | 72篇 |
1984年 | 66篇 |
1983年 | 50篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 37篇 |
1979年 | 23篇 |
1978年 | 27篇 |
1977年 | 33篇 |
1976年 | 26篇 |
1974年 | 27篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
71.
72.
How to choose an optimal threshold is a key problemin the generalized Pareto distribution (GPD) model.This paper attains the exactthreshold by testing for GPD,and shows that GPD model allows the actuary to easily estimate high quantiles and the probable maximum loss from the medical insurance claims data. 相似文献
73.
74.
75.
Jing Cheng 《量子光学学报》2006,12(B08):71-72
The effect of finite control beam on the transverse spatial profile of the slow light propagation in an electromagnetically induced transparency medium is studied. From the second-order wave equation and linear response of an EIT medium to the signal field, we find it is possible to produce an effective waveguide for the signal field. The existence and properties of a set of localized, stationary transverse modes are demonstrated. Especially, by carefully manipulating the profile of the control beam, we can realize single-mode propagation for the signal field, which may be important for potential applications. 相似文献
76.
The implementation of a nonzero-order joint transform correlator using the double port Mach-Zehnder interferometric technique is proposed and demonstrated. This approach provides on-line processing for directly removing the zero-order components of a joint power spectrum in one step and performs the nonzero-order optical correlation. Experimental results are presented and discussed. 相似文献
77.
在分析红外图象和视图象差异的基础上,研究了一种适用于可视图像序列的运动小目标检测算法。受目标影响的象素点具有较弱的时间相关性,即相对普通象素点有较大的时间方差,根据此特征,用管道更新的方法产生新方差图象序列,再用管道更新的方法累积,增加信噪比,然后用基于统计均值的自适应门限方法分割出目标,最后将原图象的梯度倒数作为象素点强度的加权,有效地抑制灰度突变边界的传感器噪音,保存目标点。 相似文献
78.
79.
The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased. 相似文献
80.
This study investigates a holographic recording effect of biphotonic polarization gratings (BPGs) written on dye-doped liquid crystal (DDLC) films. One linearly polarized green light (λG = 514.5 nm) and a polarization-modulated interference pattern formed by two mutually coherent orthogonal (±45° with respect to the polarization of the green light) polarized red lights simultaneously excite the DDLC films to generate a BPG. The formation of BPGs depends primarily on the dichroism of the dye molecules and a sequence of mechanisms: photoisomerization, anisotropic adsorption and inhibition of dye adsorption. The cis-isomer absorbance-modulated distribution associated with the red polarization-modulation pattern induces the dye adsorption-modulated pattern, in turn, yielding the permanent BPG which generates a modulated twisted nematic (TN) structure pattern in the sample. It is found that each BPG is verified to be electrically switchable and thermally erasable. The switching time is in the order of milliseconds. Additionally, the recording time to form a BPG decreases with increasing intensity of the green pump beam. 相似文献