全文获取类型
收费全文 | 3932篇 |
免费 | 439篇 |
国内免费 | 133篇 |
专业分类
化学 | 375篇 |
晶体学 | 23篇 |
力学 | 1935篇 |
综合类 | 51篇 |
数学 | 892篇 |
物理学 | 1228篇 |
出版年
2024年 | 4篇 |
2023年 | 22篇 |
2022年 | 66篇 |
2021年 | 52篇 |
2020年 | 85篇 |
2019年 | 65篇 |
2018年 | 63篇 |
2017年 | 79篇 |
2016年 | 128篇 |
2015年 | 87篇 |
2014年 | 173篇 |
2013年 | 194篇 |
2012年 | 171篇 |
2011年 | 221篇 |
2010年 | 138篇 |
2009年 | 234篇 |
2008年 | 258篇 |
2007年 | 248篇 |
2006年 | 255篇 |
2005年 | 226篇 |
2004年 | 188篇 |
2003年 | 181篇 |
2002年 | 147篇 |
2001年 | 104篇 |
2000年 | 115篇 |
1999年 | 108篇 |
1998年 | 126篇 |
1997年 | 116篇 |
1996年 | 83篇 |
1995年 | 85篇 |
1994年 | 82篇 |
1993年 | 70篇 |
1992年 | 75篇 |
1991年 | 63篇 |
1990年 | 59篇 |
1989年 | 24篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4504条查询结果,搜索用时 46 毫秒
201.
202.
Microstructures are usually fabricated on the surface of optical sheets to improve the optical characteristics. In this study, a new fabrication process with UV (ultraviolet) laser direct writing method is developed to embed microstructures inside the glass. Then the optical properties of glass such as reflection and refraction indexes can be modified. Single- and multi-layer microstructures are designed and embedded inside glass substrate to modify the optical characteristics. Both luminance and uniformity can be controlled with the embedded microstructures. Thus, the glass with inside pattern can be used as a light guide plate to increase optical performance. First, an optical commercial software, FRED, is applied to design the microstructure configuration. Then, UV laser direct writing with output power 2.5-2.6 W, repetition rate 30 kHz, wave length: 355 nm, and pulse duration 15 ns is used to fabricate the microstructures inside the glass. The effect of dot pattern in the glass such as the dot pitch, the layer gap, and the number of layer on the optical performance is discussed. Machining capacity of UV laser ranges from micron to submicrometer; hence with this ultrafast laser pulse, objectives of various dimensions such as dot, line width, and layers can be easily embedded in the glass by one simple process. In addition, the embedded microstructures can be made with less contamination. Finally, the optical performance of the glasses with various configurations is measured using a Spectra Colorometer (Photo Research PR650) and compared with the simulated results. 相似文献
203.
Conventional triangulation techniques fail to correctly predict the acoustic source location in anisotropic plates due to the direction dependent nature of the elastic wave speeds. To overcome this problem, Kundu et al. [1] proposed an alternative method for acoustic source prediction based on optimizing an objective function. They defined an objective function that uses the time of flight information of the acoustic waves to the passive transducers attached to the plate and the wave propagation direction (θ) from the source point to the receiving sensors. Some weaknesses of the original algorithm proposed in Ref. [1] were later overcome by developing a modified objective function [2]. A new objective function is introduced here to further simplify the optimization procedure and improve the computational efficiency. A new algorithm for source location is also introduced here to increase the source location accuracy. The performance of the objective function and source location algorithm were experimentally verified on a homogeneous anisotropic plate and a non-homogeneous anisotropic plate with a doubler patch. Results from these experiments indicate that the new objective function and source location algorithm have improved performance when compared with those discussed in Refs. [1] and [2]. 相似文献
204.
205.
206.
207.
Two-dimensional photon counting imaging detector based on a Vernier position sensitive anode readout 总被引:1,自引:0,他引:1
A two-dimensional photon counting imaging detector based on a Vernier position sensitive anode is reported. The decode principle and design of a two-dimensional Vernier anode are introduced in detail. A photon counting imaging system was built based on a Vernier anode. The image of very weak optical radiation can be reconstructed by image processing in a period of integration time. The resolution is superior to 100 μm according to the resolution test. The detector may realize the imaging of very weak particle flow of high-energy photons, electrons and ions, so it can be used for high-energy physics, deep space exploration, spectral measurement and bio-luminescence detection. 相似文献
208.
Spatial‐skin effect for eigenvibrations of a thick cascade junction with ‘heavy’ concentrated masses
A spectral problem for the Laplace operator in a thick cascade junction with concentrated masses is considered. This cascade junction consists of the junction's body and a great number of ?‐alternating thin rods belonging to two classes. One class consists of rods of finite length, and the second one consists of rods of small length of order . The density of the junction is of order on the rods from the second class and outside of them. The asymptotic behavior of eigenvalues and eigenfunctions of this problem is studied as ? → 0. There exist five qualitatively different cases in the asymptotic behavior of eigenmagnitudes as ? → 0, namely the case of ‘light’ concentrated (α ∈ (0,1)), ‘middle’ concentrated (α = 1), and ‘heavy’ concentrated masses (α ∈ (1, + ∞ )) that we divide into ‘slightly heavy’ concentrated (α ∈ (1,2)), ‘intermediate heavy’ concentrated (α = 2), and ‘very heavy’ concentrated masses (α > 2). In the paper, we study in detail the influence of the concentrated masses on the asymptotic behavior if α ∈ (1,2). We construct the leading terms of asymptotic expansions both for the eigenvalues and eigenfunctions and prove the corresponding asymptotic estimates. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
209.
An analytical method is presented to study the non-linear buckling characteristic of rectangular local delamination near the surface of fiber-reinforced piezoelectric lamination shells under coupled mechanical and electric loads. The stacking sequence of fiber reinforced lamination shells with piezoelectric layers is considered as symmetry, but the stacking sequence of rectangular local delamination sub-shells is arbitrary. Based on the nonlinear displacement mode of delaminated sub-shells, the effects of electric fields, the geometrical, physical parameters and stacking sequences of piezoelectric laminated shells on the non-linear local buckling for rectangular delamination near the surface of piezoelectric laminated base-shells are solved. 相似文献
210.
《Applied Mathematical Modelling》2014,38(5-6):1737-1752