全文获取类型
收费全文 | 74328篇 |
免费 | 12411篇 |
国内免费 | 7359篇 |
专业分类
化学 | 51234篇 |
晶体学 | 659篇 |
力学 | 4753篇 |
综合类 | 313篇 |
数学 | 8241篇 |
物理学 | 28898篇 |
出版年
2024年 | 281篇 |
2023年 | 1613篇 |
2022年 | 2733篇 |
2021年 | 2942篇 |
2020年 | 3123篇 |
2019年 | 2919篇 |
2018年 | 2579篇 |
2017年 | 2348篇 |
2016年 | 3584篇 |
2015年 | 3491篇 |
2014年 | 4154篇 |
2013年 | 5325篇 |
2012年 | 6761篇 |
2011年 | 6756篇 |
2010年 | 4483篇 |
2009年 | 4268篇 |
2008年 | 4608篇 |
2007年 | 4119篇 |
2006年 | 3770篇 |
2005年 | 3142篇 |
2004年 | 2441篇 |
2003年 | 1920篇 |
2002年 | 1759篇 |
2001年 | 1478篇 |
2000年 | 1360篇 |
1999年 | 1537篇 |
1998年 | 1311篇 |
1997年 | 1295篇 |
1996年 | 1291篇 |
1995年 | 1058篇 |
1994年 | 927篇 |
1993年 | 770篇 |
1992年 | 683篇 |
1991年 | 588篇 |
1990年 | 502篇 |
1989年 | 386篇 |
1988年 | 336篇 |
1987年 | 277篇 |
1986年 | 251篇 |
1985年 | 204篇 |
1984年 | 143篇 |
1983年 | 103篇 |
1982年 | 80篇 |
1981年 | 67篇 |
1980年 | 65篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 40篇 |
1976年 | 30篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Wenping Deng Gang Xu Lei Wan Anwen Liu Bo Gao Junhe Du Shuiming Hu Yang Chen 《Acta Physico》2008,24(8):1329-1334
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (ν=0←0, J=6←0) line around 2410 cm−1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-helium temperature was studied. 相似文献
122.
Retractable structures which alter their geometries according to practical requirements are widely used in roof structures of stadiums for their versatility. A retractable structure based on threefold-symmetric Bricard linkages and rotating rings of tetrahedra is proposed and developed in this paper. By replacing each link of a threefold-symmetric Bricard linkage with a tetrahedron, a retractable structure is obtained which can repeatedly open and close by rotating the tetrahedra. The geometric relationship between the retractable structure and the threefold-symmetric Bricard linkage is derived and ranges of main geometric parameters are determined to ensure a continuous and smooth movement in the deployment of the structure. Then the relative displacement of the support and the open rate of the structure, two main parameters concerned in practical applications, are investigated. Preferred ranges of main geometric parameters are proposed and a physical model is manufactured to verify them. A discussion on some possible improvements and modifications of the structure is also presented. 相似文献
123.
Tie-Jun Liu Yue-Sheng Wang Chuanzeng Zhang 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(4):267-282
The main interest of this study is a new method to solve the axisymmetric frictionless contact problem of functionally graded
materials (FGMs). Based on the fact that an arbitrary curve can be approached by a series of continuous but piecewise linear
curves, the FGM is divided into a series of sub-layers with shear modulus varying linearly in each sub-layer and continuous
at the sub-interfaces. With this model, the axisymmetric frictionless contact problem of a functionally graded coated half-space
is investigated. By using the transfer matrix method and Hankel integral transform technique, the problem is reduced to a
Cauchy singular integral equation. The contact pressure, contact region and indentation are calculated for various indenters
by solving the equations numerically.
An erratum to this article can be found at 相似文献
124.
Starting from the vectorial Rayleigh diffraction integral formula and using a simple expansion of the nucleus in the Rayleigh formula, an analytical propagation equation of vectorial nonparaxial Gaussian beams in free space is derived, which permits us to perform numerical calculations in comparison with the expression derived by Ciattoni et al. and with the direct numerical integration of the Rayleigh formula. It is found that as usual the use of expansion of vectorial Rayleigh diffraction integral is sufficient to provide satisfactory numerical results as compared with the direct integration of the Rayleigh formula. The above two analytical expressions are valid under certain conditions, however both are applicable in the far field. 相似文献
125.
In this paper we obtain some sufficient conditions for the existence of non-constant periodic solutions of the following planar system with six delaysOur approach is based on the continuation theorem of the coincidence degree. 相似文献
126.
For the minimal surfaces in Rn with Plateau boundary condition and establish the global existence and uniqueness of the flow as well as the continuous dependence of the initial datum. 相似文献
127.
Q. H. Liu W. H. Qi T. G. Liu Z. H. Zhu 《International Journal of Theoretical Physics》2003,42(4):783-791
Expectation values of physical quantities in a wave packet involving few stationary states in an infinite square well are calculated. Explicit results show that the expectation values in the classical limit go over to the corresponding classical quantity in the form of the arithmetic mean (in mathematical term, the Fejér's average) of the partial Fourier series converging to the classical quantity. The number of the stationary states is that of the partial Fourer series in the Fejér's average. The quantum uncertainty is then demonstrated to have a classical counterpart. 相似文献
128.
研究了在均匀分层介质中构成标准矢量波函数的必要条件。研究结果表明在均匀分层介质中构成标准矢量波函数一般需遵循Morse-Feshbach判据外,领示矢量只能选取与折射率变化方向一致的那根坐标轴单位矢量。但在某些特定的条件下,对领示矢量的选取条件可以放宽为只需遵循Morse-Feshbach判据即可。 相似文献
129.
软x射线近贴显微技术 总被引:1,自引:0,他引:1
软x射线近贴显微技术不但可使活的生物样品成象,分辨率高于光学显微镜,而且人为的样品准备程序在该技术中都可避免。本文描述了用高功率激光打靶产生的等离子体作为软x射线源而进行的近贴显微研究,并得到了分辨率好于1μm的结果。 相似文献
130.