全文获取类型
收费全文 | 13840篇 |
免费 | 2012篇 |
国内免费 | 1368篇 |
专业分类
化学 | 7108篇 |
晶体学 | 238篇 |
力学 | 940篇 |
综合类 | 146篇 |
数学 | 1317篇 |
物理学 | 7471篇 |
出版年
2024年 | 17篇 |
2023年 | 118篇 |
2022年 | 217篇 |
2021年 | 347篇 |
2020年 | 341篇 |
2019年 | 302篇 |
2018年 | 306篇 |
2017年 | 441篇 |
2016年 | 532篇 |
2015年 | 458篇 |
2014年 | 675篇 |
2013年 | 1069篇 |
2012年 | 934篇 |
2011年 | 878篇 |
2010年 | 737篇 |
2009年 | 881篇 |
2008年 | 877篇 |
2007年 | 1053篇 |
2006年 | 821篇 |
2005年 | 795篇 |
2004年 | 685篇 |
2003年 | 626篇 |
2002年 | 563篇 |
2001年 | 423篇 |
2000年 | 396篇 |
1999年 | 399篇 |
1998年 | 309篇 |
1997年 | 321篇 |
1996年 | 255篇 |
1995年 | 223篇 |
1994年 | 215篇 |
1993年 | 186篇 |
1992年 | 139篇 |
1991年 | 142篇 |
1990年 | 84篇 |
1989年 | 80篇 |
1988年 | 54篇 |
1987年 | 38篇 |
1986年 | 40篇 |
1985年 | 34篇 |
1984年 | 36篇 |
1983年 | 14篇 |
1982年 | 36篇 |
1981年 | 19篇 |
1980年 | 26篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
91.
P.S Erdman M Fajardo K.M Sando W.C Stwalley 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,88(4):447-481
Experimental results are reported for a unique spectroscopic device called the Plasma Spectroscopy Cell. Optical absorption of lithium metal vapor was observed at high density and temperature. Absorption spectra are analyzed using theoretical calculations of absorption cross sections for lithium-helium interactions, and singlet and triplet state transitions of diatomic lithium in the visible spectral range. This is believed to be the most complex example yet calculated in which absolute bound-bound, bound-free, free-bound, and free-free contributions for all possible optically allowed transitions are all included, in quite respectable agreement with experiment. 相似文献
92.
A. López-Ortega 《General Relativity and Gravitation》2004,36(6):1299-1319
We show that the Dirac equation is separable in the circularly symmetric metric in three dimensions and when the background spacetime is de Sitter we find exact solutions to the radial equations. Using these results we show that the de Sitter horizon has a cross section equal to zero for the massless Dirac field, as in the case of the scalar field. Also, using the improved brick wall model we calculate the fermionic entropy associated with the de Sitter horizon and we compare it with some results previously published. 相似文献
93.
An experimentally validated finite element method is used to model the sound level in rooms at low frequencies. It is demonstrated that the dimensions of rectangular rooms strongly influence the sound pressure level difference. Additional factors were investigated which are not normally considered in the frequency range where diffuse sound field conditions can be assumed. Three effects were investigated: room damping due to wall vibrations, furniture, the effect of small deviations from simple rectangular shapes. It is confirmed by field measurements that the vibrations of masonry walls and floors introduce less damping than surfaces of lightweight construction. Assigning to the FE model a damping equivalent to a surface absorption of 0.02 reproduces the effect of walls of heavyweight construction. Damping equivalent to a surface absorption of 0.15 reproduces the effects of plastered timber-frame walls, floors and ceilings. The work was briefly extended to a room pair built with heavyweight and lightweight material of construction. The modification of the shape of the room frequency response highlights well the effect of material of construction. In-situ and laboratory measurements show that furniture has little effect on steady-state room response below 100 Hz. Modelling a wall recess smaller than 0.5 m improved the agreement between prediction and measurements but the assumption of a simple rectangular room remains appropriate. 相似文献
94.
In this paper, we have developed an analytical model to study the temperature distributions in IR optical materials heated by laser pulses. Our model takes into account the two-photon absorption (TPA). The calculations are based on a three-dimensional model of heat diffusion in solids using the integral transform method. We find out the rigorous analytical expression of the thermal field when one considers both one- and two-photon absorption. The model is valid for any laser–solid system whose interaction can be described by the generalized Beer–Lambert law. Specific results are presented for an application of the model to ZnSe sample. We find out that TPA can produce detectable temperature variation. 相似文献
95.
96.
97.
A.D. Bykov V.N. Saveliev C. Camy-Peyret A. Valentin 《Journal of Molecular Spectroscopy》2004,224(2):164-175
Forty-seven N2 broadened water vapor line-widths have been measured in the 1845-2140 cm−1 spectral range with a Fourier Transform spectrometer in the 258-330 K temperature range at a spectral resolution of 0.005 cm−1 for the lines with upper state rotational quantum number up to 16. The measured exponents of the temperature dependence of the width exhibit a large range of values from 1.60 to −0.86. Theoretical calculations were made using a semi-empirical technique based on the Anderson theory. The calculated broadening coefficients as well as the temperature exponents for the half-width agree satisfactory with measured values. 相似文献
98.
主要研究在高空核爆的双指数类型电磁脉冲平面波入射时,地面附近的电磁脉冲环境。计算给出了在不同入射波状态,不同地表介质电气特性和距地面不同高度等条件下的电磁脉冲环境参数,归纳了一些规律性认识。结果显示:地面附近的电场会随距地面高度的不同而发生显著的变化,对于水平场分量,其反射场总是试图抵消入射场,而对于垂直场分量,其反射场叠加在入射场上,使得地面附近的垂直场强幅值一般大于入射波场强幅值;当入射波仰角增大时,合成电场波形的脉冲宽度会变宽;地表介质的电气特性参数不同也会对地面附近电场的波形和幅值造成一定的影响。 相似文献
99.
100.