全文获取类型
收费全文 | 1769篇 |
免费 | 360篇 |
国内免费 | 95篇 |
专业分类
化学 | 343篇 |
晶体学 | 15篇 |
力学 | 180篇 |
综合类 | 36篇 |
数学 | 369篇 |
物理学 | 1281篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 39篇 |
2021年 | 62篇 |
2020年 | 49篇 |
2019年 | 31篇 |
2018年 | 45篇 |
2017年 | 48篇 |
2016年 | 75篇 |
2015年 | 66篇 |
2014年 | 114篇 |
2013年 | 123篇 |
2012年 | 96篇 |
2011年 | 127篇 |
2010年 | 127篇 |
2009年 | 86篇 |
2008年 | 122篇 |
2007年 | 104篇 |
2006年 | 97篇 |
2005年 | 104篇 |
2004年 | 81篇 |
2003年 | 76篇 |
2002年 | 57篇 |
2001年 | 47篇 |
2000年 | 60篇 |
1999年 | 60篇 |
1998年 | 42篇 |
1997年 | 41篇 |
1996年 | 36篇 |
1995年 | 21篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2224条查询结果,搜索用时 15 毫秒
21.
对G.Ladas的一个开问题的解答 总被引:3,自引:0,他引:3
本文获得了一个高阶非线性差分方程具有无界正解的充分条件,所得结果解决了G.Ladas提出的一个开问题。 相似文献
22.
M.Yu. Tretyakov V.V. Parshin M.A. Koshelev A.P. Shkaev A.F. Krupnov 《Journal of Molecular Spectroscopy》2006,238(1):91-97
Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′ka′, kc′-Jka, kc = 51,5-42,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 31,3-22,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given. 相似文献
23.
针对二聚物三能级蒸气激光系统增益相对于泵浦光方向显著的不对称特性,本文设计了一种稳定的能够充分利用介质增益特性的环形谐振腔,给出了象散和慧差补偿及泵浦激光与谐振腔匹配的条件。文中还给出了Na_2B~1Ⅱ_u-X~1∑_g~+跃迁激光谐振腔设计数据。 相似文献
24.
双电极对双脉冲激光器结构分析 总被引:1,自引:0,他引:1
本文对双电极对双脉冲激光器的谐振腔结构进行了分析,结果表明采用双非稳腔和增大反射镜的曲率半径可分别获得单纵模和基横模输出。为使输出能量稳定,则双电极对的间距有一最小值的限制。 相似文献
25.
A. Waksberg 《International Journal of Infrared and Millimeter Waves》2002,23(9):1327-1335
Coupling losses have been calculated for laser resonators with unequal apertures and extended Fresnel Numbers. This was done using both, diffraction theory and a simple linear model.A close form expression was derived to calculate coupling losses with reasonable accuracies for a limited range of paramters. This should help in the preliminary design of hole coupling laser resonators. 相似文献
26.
27.
S. Sasa A. Nakashima Y. Nakajima M. Inoue 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):224
We fabricated nanoscale open-dot structures in an InAs surface inversion layer using an atomic-force-microscope oxidation process. Due to its superior nanofabrication capability, small open-dot structures with the feature size ranging between 100 and 300 nm were successfully fabricated. The magnetoresistance signal measured at 4.2 K showed reproducible fluctuations and a periodic oscillation component that varies in both amplitude and periodicity depending on the dot size. We show that the period of the oscillations corresponds to that of the Aharonov–Bohm effect and propose that the possible mechanism for the oscillations is due to the formation of a one-dimensional electron channel enclosing the open-dot structure as a result of the electron transfer from the InAs oxide to InAs. 相似文献
28.
High power industrial multibeam CO2 lasers consist of a large number of closely packed parallel glass discharge tubes sharing a common plane parallel resonator.
Every discharge tube forms an independent resonator. When discharge tubes of smaller diameter are used and the Fresnel numberN ≪ 1 for all resonators, they operate in waveguide mode. Waveguide modes have excellent discrimination of higher order modes.
A DC excited waveguide multibeam CO2 laser is reported having six glass discharge tubes. Simultaneous excitation of DC discharge in all sections is achieved by
producing pre-ionization using an auxiliary high frequency pulsed discharge along with its other advantages. Maximum 170 W
output power is obtained with all beams operating in EH11 waveguide mode. The specific power of 28 W/m is much higher as compared to similar AC excited waveguide multibeam CO2 lasers. Theoretical analysis shows that all resonators of this laser will support only EH11 mode. This laser is successfully used for woodcutting 相似文献
29.
Victor Alexandrov 《Geometriae Dedicata》2004,107(1):169-186
Classical H. Minkowski theorems on existence and uniqueness of convex polyhedra with prescribed directions and areas of faces as well as the well-known generalization of H. Minkowski uniqueness theorem due to A.D. Alexandrov are extended to a class of nonconvex polyhedra which are called polyhedral herissons and may be described as polyhedra with injective spherical image. 相似文献
30.