全文获取类型
收费全文 | 5707篇 |
免费 | 1400篇 |
国内免费 | 198篇 |
专业分类
化学 | 2811篇 |
晶体学 | 453篇 |
力学 | 94篇 |
综合类 | 17篇 |
数学 | 68篇 |
物理学 | 3862篇 |
出版年
2024年 | 12篇 |
2023年 | 44篇 |
2022年 | 82篇 |
2021年 | 92篇 |
2020年 | 200篇 |
2019年 | 147篇 |
2018年 | 192篇 |
2017年 | 231篇 |
2016年 | 349篇 |
2015年 | 222篇 |
2014年 | 315篇 |
2013年 | 927篇 |
2012年 | 351篇 |
2011年 | 374篇 |
2010年 | 290篇 |
2009年 | 371篇 |
2008年 | 370篇 |
2007年 | 403篇 |
2006年 | 376篇 |
2005年 | 301篇 |
2004年 | 256篇 |
2003年 | 218篇 |
2002年 | 199篇 |
2001年 | 132篇 |
2000年 | 108篇 |
1999年 | 130篇 |
1998年 | 100篇 |
1997年 | 62篇 |
1996年 | 73篇 |
1995年 | 45篇 |
1994年 | 42篇 |
1993年 | 34篇 |
1992年 | 32篇 |
1991年 | 20篇 |
1990年 | 32篇 |
1989年 | 13篇 |
1988年 | 26篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 21篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1977年 | 4篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 7篇 |
排序方式: 共有7305条查询结果,搜索用时 912 毫秒
31.
32.
Tunable microlens arrays using polymer network liquid crystal 总被引:1,自引:0,他引:1
A tunable-focus microlens array based on polymer network liquid crystal (PNLC) is demonstrated. The PNLC was prepared using an ultraviolet (UV) light exposure through a patterned photomask. The photocurable monomer in each of the UV exposed spot forms an inhomogeneous centro-symmetrical polymer network which acts as a lens when a homogeneous electric field is applied to the cell. The focal length of the microlens arrays is tunable with the applied voltage. 相似文献
33.
高斯光束计算平板波导自由传输区远场分布及其修正 总被引:2,自引:2,他引:0
对近轴近似条件下求解亥姆霍兹方程得到的高斯光束显式传播公式做了分析,同时,基于基尔霍夫衍射理论,在菲涅耳近似的条件下给出了相应的高斯光束在远场的传播公式,在此基础上,对近轴近似条件做出了定量分析,给出了这个近似条件引入的误差,提出了一种计算高斯光束远场分布的修正方法,并采用有限差分-光束传播方法(FD-BPM)来检验各种方法的准确性。把这种修正方法应用到平面光集成波导器件,如阵列波导光栅(AWG)、蚀刻衍射光栅(EDG)等器件的设计和模拟中,可以大大降低工作的复杂性,同时可以得到精确的结果。 相似文献
34.
The present paper reports the dislocation unpinning model of acoustic emission (AE) from alkali halide crystals. Equations
are derived for the strain dependence of the transient AE pulse rate, peak value of the AE pulse rate and the total number
of AE pulse emitted. It is found that the AE pulse rate should be maximum for a particular strain of the crystals. The peak
value of the AE pulse rate should depend on the volume and strain rate of the crystals, and also on the pinning time of dislocations.
Since the pinning time of dislocations decreases with increasing strain rate, the AE pulse rate should be weakly dependent
on the strain rate of the crystals. The total number of AE should increase linearly with deformation and then it should attain
a saturation value for the large deformation. By measuring the strain dependence of the AE pulse rate at a fixed strain rate,
the time constantτ
s for surface annihilation of dislocations and the pinning timeτ
p of the dislocations can be determined. A good agreement is found between the theoretical and experimental results related
to the AE from alkali halide crystals. 相似文献
35.
Ottokar Leminger 《Optical and Quantum Electronics》2002,34(5-6):435-443
Photonic crystals exhibit band gaps, meaning that electromagnetic fields cannot propagate in them for specific ranges of wavelengths
and directions. The calculation of band structure diagrams has been intensively studied and is now well understood. In contrast
to that, so-called wave-vector diagrams (i.e. dispersion surfaces, depicting the loci of all relevant wave vectors at a fixed
wavelength) are less known and used. In principle, they show how the effective index of the structure depends on the direction
of propagation. A method to calculate explicitly wave-vector diagrams for two-dimensional photonic crystals is derived which
leads finally to quadratic eigenvalue problems. Results for square and triangular lattices are presented and some applications
are discussed. 相似文献
36.
阐述了紫外无机非线性光学晶体分子工程学探索方法的基本特点,具体分析深紫外无机非线性光学晶体硼铍酸锶(SBBO)以氟硼铍酸钾(KBBF)为主要参考晶体的分子设计方法,随后根据晶体结构研究、单晶培养、和非线性光学性能测定等实验结果讨论SBBO作为新型深紫外无机晶体的主要优点,即它既具有更短的紫外吸收边(接近155nm)和较大的非线性光学系数(d22(SBBO)=06×d22(BBO)=138pm/V),同时晶体无明显层状习性,并肯有良好的化学稳定性和机械性能 相似文献
37.
38.
P.A. Postigo A.R. Alija L.J. Martínez M.L. Dotor D. Golmayo J. Snchez-Dehesa C. Seassal P. Viktorovitch M. Galli A. Politi M. Patrini L.C. Andreani 《Photonics and Nanostructures》2007,5(2-3):79-85
Two-dimensional photonic crystal lasers have been fabricated on III–V semiconductor slabs. Tuning of the spontaneous emission in micro and nanocavities has been achieved by accurate control of the slab thickness. Different structures, some of them of new application to photonic crystal lasers, have been fabricated like the Suzuki-phase or the coupled-cavity ring-like resonators. Laser emission has been obtained by pulsed optical pumping. Optical characterization of the lasing modes have been performed showing one or more laser peaks centred around 1.55 μm. Far field characterization of the emission pattern has been realized showing different patterns depending on the geometrical shape of the structures. These kinds of devices may be used as efficient nanolaser sources for optical communications or optical sensors. 相似文献
39.
By means of improved ligand-field theory, the "pure electronic" pressure-induced shifts (PS's) and the PS's due to electron-phonon interaction (EPI) of R1 line and R2 line of YAG:Cr3 have been calculated, respectively.The calculated results are in very good agreement with the experimental data. It is demonstrated that the admixture of |t22(3T1)e4T2> and |t322E> bases in the wavefunction of R1 level of YAG:Cr3 and its change with pressure play a key role for the PS of R1 line. The behaviors of the "pure electronic" PS of R1 line and the PS of R1 line due to EPI are different. It is the combined effect of them that gives rise to the total PS of R1 line, which has satisfactorily explained the experimental results. The systematic analyses and comparisons between the feature of R1-line PS of YAG:Cr3 and the ones of three laser crystals (GSGG:Cr3 , GGG:Cr3 and ruby) have been made, and the origin of the difference between them has been revealed. 相似文献
40.
HANG Chao HUANG Guo-Xiang 《理论物理通讯》2006,46(1):149-154
We investigate the nonlinear localized structures of optical pulses propagating in a one-dimensional photonic crystal with a quadratic nonlinearity. Using a method of multiple scales we show that the nonlinear evolution of a wave packet, formed by the superposition of short-wavelength excitations, and long-wavelength mean fields, generated by the self-interaction of the wave packet, are governed by a set of coupled high-dimenslonal nonlinear envelope equations, which can be reduced to Davey-Stewartson equations and thus support dromionlike high-dimensional nonlinear excitations in the system. 相似文献