全文获取类型
收费全文 | 916篇 |
免费 | 239篇 |
国内免费 | 260篇 |
专业分类
化学 | 248篇 |
晶体学 | 40篇 |
力学 | 464篇 |
综合类 | 26篇 |
数学 | 77篇 |
物理学 | 560篇 |
出版年
2024年 | 9篇 |
2023年 | 40篇 |
2022年 | 35篇 |
2021年 | 44篇 |
2020年 | 35篇 |
2019年 | 44篇 |
2018年 | 23篇 |
2017年 | 38篇 |
2016年 | 36篇 |
2015年 | 47篇 |
2014年 | 95篇 |
2013年 | 59篇 |
2012年 | 63篇 |
2011年 | 49篇 |
2010年 | 59篇 |
2009年 | 56篇 |
2008年 | 89篇 |
2007年 | 56篇 |
2006年 | 59篇 |
2005年 | 48篇 |
2004年 | 71篇 |
2003年 | 69篇 |
2002年 | 34篇 |
2001年 | 40篇 |
2000年 | 37篇 |
1999年 | 21篇 |
1998年 | 20篇 |
1997年 | 24篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有1415条查询结果,搜索用时 15 毫秒
101.
Mechanical model study of relationship of molecular configuration and multiphase in liquid crystal materials 总被引:3,自引:0,他引:3 下载免费PDF全文
A mechanical model of liquid crystals (LCs) is applied to
study the polymorphism of homologous series of terphenyl compounds. With
a semi-experimental molecular orbit method, we calculate the moment of inertia
which represents the rotation state to describe the phase transition
temperature obtained from experimental data. We propose a novel
explanation of the phase sequence or polymorphism of LC materials using
the two key
parameters, the moment of inertia and critical rotational velocity. The effect
of molecular polarity on the appearance of liquid crystalline is also discussed. 相似文献
102.
The aim of this paper is to present a theoretical study of the aerosol penetration
through an electret fibrous filter, using a numerical approach. The aerosol sizes
considered in this study were in the submicron range, and in the numerical model,
the conventional mechanical mechanisms (impaction, interception, diffusion and
gravitationally settling) were taken into consideration along with the electrostatic
mechanisms, including the Coulombic and dielectrophoretic effects. The aerosol
penetration through an electret fibrous filter is heavily dependent on the aerosol
penetration of a single fibre. The aerosol penetration through a single electret
fibre under various filtration conditions was calculated. The effects of aerosol
diameter, aerosol and fibre charge state, face velocity, packing density and aerosol
dielectric constant on the aerosol penetration were investigated. 相似文献
103.
Chaotic time series prediction using fuzzy sigmoid kernel-based support vector machines 总被引:1,自引:0,他引:1 下载免费PDF全文
Support vector machines (SVM) have been widely used in chaotic time series
predictions in recent years. In order to enhance the prediction efficiency
of this method and implement it in hardware, the sigmoid kernel in SVM is
drawn in a more natural way by using the fuzzy logic method proposed in this
paper. This method provides easy hardware implementation and straightforward
interpretability. Experiments on two typical chaotic time series predictions
have been carried out and the obtained results show that the average CPU
time can be reduced significantly at the cost of a small decrease in
prediction accuracy, which is favourable for the hardware implementation for
chaotic time series prediction. 相似文献
104.
ZHANGHu ParvizAyaziShamlou 《高等学校化学研究》2004,20(4):489-493
Three approaches based on computational fluid dynamics(CFD) techniques have been assessed for their ability to describe the engineering flow environment in a miniaturized mechanically agitated bioreactor. The three approaches tested were the source-sink(SS), the multiple reference frames (MRF) and the sliding grids(SG). In all the cases, the predictions of the velocity components agree with reported experimental data. However, the analysis of the results of the turbulent intensities predicted by the three approaches indicates the MRF and the SG techniques under predicted turbulent intensities are comparable to both experimental measurements and the SS method. The predicted power number and pumping number based on the SS ap-proach are closer to typical reported experimental values compared to those obtained from the MRF and SG methods. 相似文献
105.
We propose a scheme for implementing the Grover search algorithm
with two superconducting quantum interference devices (SQUIDs) in a
cavity. Our scheme only requires single resonant interaction of the
SQUID-cavity system and the required interaction time is very short.
The simplicity of the process and the reduction of the interaction
time are important for restraining decoherence. 相似文献
106.
107.
108.
109.
两温区气相输运和机械振荡合成ZnGeP2多晶材料 总被引:3,自引:2,他引:1
ZnGeP2多晶的合成是其单晶生长的前提和基础,多晶材料的质量是生长高质量单晶的关键.因此,要获得高质量的ZnGeP2单晶体,必须提供高质量的ZnGeP2多晶材料.对两温区气相输运机械振荡法合成ZnGeP2多晶材料的工艺进行了研究,利用高纯(6N)P、Ge、Zn单质为原料,采用两温区气相输运和机械振荡合成出了ZnGeP2多晶材料.合成出的多晶材料经比重测试和X射线粉末衍射测试证明与标准值一致.采用改进的布里奇曼法生长出外观完整、无裂纹的φ15 mm × 25 mm单晶体,在2.5~10 μm范围内红外透过率达50;以上. 相似文献
110.
Lattice materials have been attractive over the last decade for use as load-carrying structures, energy absorbing elements and heat exchanging structures because of their excellent mechanical properties and multifunctional characters. However, the quantitative analysis accounting for high order deformations upon the collapse of lattice materials, which is important for their applications, has not been reported. An analytical investigation of yield surfaces with respect to the high order deformations was carried out for two typical planar lattice materials: triangular and Kagome lattices separately. The analytical results were validated by the finite element method (FEM) simulations. It was found that the effect of high order deformation on the yield strength increases with the relative density. The bending effect of the Kagome lattice is more obvious than that of the triangular one with the same relative density and stress state. The yield strength of the Kagome lattice calculated by neglecting the bending effect overestimates the result by more than 10% when the relative density is higher than about 11.1%, which may not be ignored in engineering applications. The yielding surfaces of the two lattice materials demonstrated in the paper also confirm the analytical results. 相似文献