全文获取类型
收费全文 | 4884篇 |
免费 | 899篇 |
国内免费 | 961篇 |
专业分类
化学 | 2801篇 |
晶体学 | 37篇 |
力学 | 595篇 |
综合类 | 45篇 |
数学 | 167篇 |
物理学 | 3099篇 |
出版年
2024年 | 18篇 |
2023年 | 54篇 |
2022年 | 130篇 |
2021年 | 161篇 |
2020年 | 145篇 |
2019年 | 147篇 |
2018年 | 131篇 |
2017年 | 180篇 |
2016年 | 192篇 |
2015年 | 183篇 |
2014年 | 214篇 |
2013年 | 370篇 |
2012年 | 298篇 |
2011年 | 345篇 |
2010年 | 244篇 |
2009年 | 334篇 |
2008年 | 339篇 |
2007年 | 353篇 |
2006年 | 324篇 |
2005年 | 290篇 |
2004年 | 280篇 |
2003年 | 244篇 |
2002年 | 239篇 |
2001年 | 203篇 |
2000年 | 211篇 |
1999年 | 175篇 |
1998年 | 168篇 |
1997年 | 112篇 |
1996年 | 98篇 |
1995年 | 98篇 |
1994年 | 80篇 |
1993年 | 73篇 |
1992年 | 66篇 |
1991年 | 39篇 |
1990年 | 34篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1974年 | 2篇 |
1973年 | 4篇 |
排序方式: 共有6744条查询结果,搜索用时 281 毫秒
51.
平台框架部件刚度的简化计算 总被引:1,自引:1,他引:0
利用卡氏定理,对惯性平台框架部件的刚度进行简化计算。通过微机编程获得数据,为结构设计初期合理选取结构参数提供参考。 相似文献
52.
Investigation on chaotic motion in hysteretic non-linear suspension system with multi-frequency excitations 总被引:3,自引:0,他引:3
This paper presents the investigation on possible chaotic motion in a vehicle suspension system with hysteretic non-linearity, which is subjected to the multi-frequency excitation from road surface. The Melnikov’s function is used to derive the critical condition for the chaotic motion, and then it is investigated that the effects of parameters in non-linear damping on the chaotic field. The path from quasi-periodic to chaotic motion is found via Poincaré map and Lyapunov exponents. 相似文献
53.
Software Cold Test Simulation of Coupled Cavity Slow-Wave Structure in Millimeter Wave TWT 总被引:2,自引:0,他引:2
In this paper, the software cold-test simulation method to obtain RF dispersion, interaction impedance by MAFIA software is discussed considering effect of the conducting barrel in the millimeter-wave TWT. The dispersion simulation result is obtained more consistent with experiment data than the method that ignoring effect of the conducting barrel. By changing the structure parameter, high frequency characteristic will be affected. The change relationship of high frequency characteristic with structure parameter is obtained. The different calculation methods of the interaction impedance are discussed. These results are received and are consistent with experiment data. 相似文献
54.
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
55.
The presented work offers new algorithms for phase evaluation in interferometric measurements. Several phase-shifting algorithms with an arbitrary but constant phase-shift between captured intensity frames are proposed. These phase calculation algorithms need to measure five frames of the intensity of the interference field. The algorithms are similarly derived as so called Carré algorithm. The phase evaluation process then does not depend on the linear phase shift errors. Furthermore, the detailed analysis of the algorithms with respect to most important factors, which affect interferometric measurements, is carried out. It is also studied the dependency of the evaluation algorithms on the phase shift values, and the proposed phase calculation algorithms are compared with respect to the resulting phase errors. The influence of most important factors in the measurement and evaluation process was simulated as systematic and random errors using a proposed mathematical model. 相似文献
56.
Dynamic systems described by nonlinear differential equations of the second order are studied. It is assumed that certain
preliminary information on the dissipative or elastic characteristics of systems is known. A new approach is demonstrated
to obtaining full information on unknown or partially known characteristics of a system from measurements of not only displacements
but also velocities and accelerations
__________
Published in Prikladnaya Mekhanika, Vol. 41, No. 6, pp. 139–143, June 2005. 相似文献
57.
58.
Yu. M. Smirnov 《Journal of Russian Laser Research》2003,24(2):121-128
Excitation of rhenium atoms by electron impact is investigated by the method of extended crossing beams. At electron energies of 50 eV, the excitation cross sections of 36 resonance and competing transitions in ReI are measured. Within the energy range from the threshold value to 250 eV, six optical excitation functions are detected. The reliability of data on transition probabilities in ReI has been analyzed. 相似文献
59.
电子离子碰撞激发速率系数在超组态碰撞辐射模型中真实模拟非局域热动力学平衡Au激光等离子体M带谱 5f 3d跃迁中各种复杂电荷态离子的电离态特性 (譬如离子的平均电离度 ,相对丰度和能级布居数 )是必不可少的。基于准相对论多组态Hartree Fock方法和扭曲波玻恩交换近似 ,采用自编的扭曲波程序ACDW (9)和Fit(9) ,从头计算了Au等离子体M带 5f 3d电子离子碰撞激发速率系数。结果表明 :在“神光II”实验装置诊断的电子温度约 2keV ,电子密度约 6× 10 2 1cm-3 范围内 ,这些电子离子碰撞激发参数有利于采用超组态碰撞辐射模型模拟Au的激光等离子体M带 5f~ 3d细致谱的平均电离度和电荷态分布。 相似文献
60.