全文获取类型
收费全文 | 13356篇 |
免费 | 2597篇 |
国内免费 | 1335篇 |
专业分类
化学 | 5249篇 |
晶体学 | 115篇 |
力学 | 1214篇 |
综合类 | 148篇 |
数学 | 776篇 |
物理学 | 9786篇 |
出版年
2024年 | 34篇 |
2023年 | 138篇 |
2022年 | 375篇 |
2021年 | 359篇 |
2020年 | 390篇 |
2019年 | 411篇 |
2018年 | 405篇 |
2017年 | 459篇 |
2016年 | 564篇 |
2015年 | 518篇 |
2014年 | 829篇 |
2013年 | 1073篇 |
2012年 | 821篇 |
2011年 | 985篇 |
2010年 | 701篇 |
2009年 | 861篇 |
2008年 | 873篇 |
2007年 | 922篇 |
2006年 | 844篇 |
2005年 | 720篇 |
2004年 | 578篇 |
2003年 | 533篇 |
2002年 | 553篇 |
2001年 | 528篇 |
2000年 | 435篇 |
1999年 | 331篇 |
1998年 | 299篇 |
1997年 | 246篇 |
1996年 | 196篇 |
1995年 | 197篇 |
1994年 | 153篇 |
1993年 | 144篇 |
1992年 | 113篇 |
1991年 | 110篇 |
1990年 | 77篇 |
1989年 | 61篇 |
1988年 | 57篇 |
1987年 | 50篇 |
1986年 | 42篇 |
1985年 | 54篇 |
1984年 | 50篇 |
1983年 | 24篇 |
1982年 | 34篇 |
1981年 | 27篇 |
1980年 | 25篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Huimin Xie Biao Li Robert Geer Bai Xu James Castracane 《Optics and Lasers in Engineering》2003,40(3):163-177
A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method. 相似文献
72.
M. I. Al-Jarallah Fazal-ur-Rehman F. Abu-Jarad A. Al-Shukri 《Radiation measurements》2003,36(1-6):445-448
An indoor radon survey of a total of 269 dwellings, with one dosimeter per house, distributed in four Saudi Arabian cities was carried out. The objective of this survey was to carry out indoor radon measurements of two cities in the Eastern Province, Khafji and Hafr Al-Batin and to compare this with two cities in the Western Province, Al-Madina and Taif. The survey provides additional information about indoor radon concentrations in Saudi Arabia. The results of the survey in these cities showed that the overall minimum, maximum and average radon concentration were 7,137 and 30 Bqm−3, respectively. The lowest average radon concentration (20 Bqm−3) was found in Hafr Al-Batin, while the highest average concentration was found in Khafji (40 Bqm−3). 相似文献
74.
75.
研究了三包层WⅠ和WⅡ型单模光纤的波导色散特性。结果发现在相同条件下,三包层WⅠ和WⅡ型单模光纤零色散点的调节范围比传统的双包层W型单模光纤明显增大。详细分析了几何参量P、Q和光学参量R1、R2对单模传输时的波导色散特性和低次模截止频率的影响。所得的研究结果为获得更为理想的色散补偿、色散平坦光纤及设计新型无源光器件提供了重要的依据。计算波导色散的方法可推广到多包层光纤。 相似文献
76.
An effect of Berry’s phase on the NQR spectrum of the rotating powder sample is described and applied for the determination of the electric field gradient asymmetry. The proposed method involves the analysis of the frequency singularities in the NQR powder patterns of the rotating samples. The Berry’s phases for the eigenstates, associated with an adiabatically changing quadrupole hamiltonian, are calculated for nuclei with a spin I = 3/2 and I = 1 as a function of the asymmetry parameter. 相似文献
77.
Rolando Cavazos-Cadena 《Annals of Operations Research》1991,28(1):169-184
We consider a class of Markov decision processes withfinite state and action spaces which, essentially, is determined by the following condition: The state space isirreducible under the action of any stationary policy. However, except by this restriction, the transition law iscompletely unknown to the controller. In this context, we find a set of policies under which thefrequency estimators of the transition law are strongly consistent and then, this result is applied to constructadaptive asymptotically discount-optimal policies.Dedicated to Professor Truman O. Lewis, on the occasion of his sixtieth birthdayThis research was supported in part by the Third World Academy of Sciences (TWAS) under Grant TWAS RG MP 898-152, and in part by the Consejo Nacional de Ciencia y Tecnología (CONACYT) under Grant A128CCOEO550 (MT-2). 相似文献
78.
根据广义Laguerre多项式的数学性质,导出了较为简单的三维各向同性谐振子径向矩阵元的普遍公式,并在这基础上计算了一些重要特殊情形的径向矩阵元: 矢径r整数次幂的平均值,电偶极跃迁矩阵元和电四极跃迁矩阵元.
关键词:
三维各向同性谐振子
径向矩阵元
广义Laguerre多项式
偶极跃迁
四极跃迁 相似文献
79.
80.
Charge density fluctuation of low frequency in a dusty plasma 总被引:2,自引:0,他引:2
The charge density fluctuation of low frequency in a dusty plasma, which is derived from the longitudinal dielectric permittivity
of the dusty plasma, has been studied by kinetic theory. The results show that theP value, which describes the relative charge density on the dust in the plasma, and the charging frequency of a dust particle
Ω
c
, which describes the ratio of charge changing of the dust particles, determine the character of the charge density fluctuation
of low frequency. For a dusty plasma ofP≪1, when the charging frequency Ω
c
, is much smaller than the dusty plasma frequency ωd, there is a strong charge density fluctuation which is of character of dust acoustic eigenwave. For a dusty plasma ofP≫1, when the frequency Ω
c
, is much larger than ω
d
there are weaker fluctuations with a wide spectrum. The results have been applied to the ionosphere and the range of radius
and density of dust particles is found, where a strong charge density fluctuation of low frequency should exist. 相似文献