全文获取类型
收费全文 | 5190篇 |
免费 | 878篇 |
国内免费 | 324篇 |
专业分类
化学 | 1387篇 |
晶体学 | 32篇 |
力学 | 480篇 |
综合类 | 29篇 |
数学 | 267篇 |
物理学 | 2191篇 |
无线电 | 2006篇 |
出版年
2024年 | 9篇 |
2023年 | 38篇 |
2022年 | 82篇 |
2021年 | 91篇 |
2020年 | 105篇 |
2019年 | 106篇 |
2018年 | 87篇 |
2017年 | 120篇 |
2016年 | 155篇 |
2015年 | 191篇 |
2014年 | 288篇 |
2013年 | 371篇 |
2012年 | 349篇 |
2011年 | 353篇 |
2010年 | 263篇 |
2009年 | 311篇 |
2008年 | 345篇 |
2007年 | 363篇 |
2006年 | 345篇 |
2005年 | 322篇 |
2004年 | 360篇 |
2003年 | 276篇 |
2002年 | 235篇 |
2001年 | 215篇 |
2000年 | 152篇 |
1999年 | 141篇 |
1998年 | 135篇 |
1997年 | 120篇 |
1996年 | 86篇 |
1995年 | 83篇 |
1994年 | 66篇 |
1993年 | 56篇 |
1992年 | 26篇 |
1991年 | 31篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有6392条查询结果,搜索用时 9 毫秒
991.
992.
在双轴晶体中,除光轴方向外,沿任一方向只存在2个具有不同偏振方向的平面波解,每个解有各自的传播常数。运用拉格朗日乘数法并借助双轴晶体的折射率椭球的概念,在主轴坐标系下求出双轴晶体的平面波解,得到每个解的空间色散关系,并从所得平面波解出发讨论平面波沿光轴方向传输的情况。最后将所得的结果运用到单轴晶体中检验其正确性。 相似文献
993.
994.
为了提取生物组织的色散信息,提出了一种基于Fourier变换以及多项式拟合的方法.该方法通过对光学相干层析术的干涉包络进行Fourier变换,再将得到的相位谱进行多项式拟合以实现色散信息的提取.通过数值模拟及相关实验验证了该方法的可行性.本文的分析结果不但有助于实现动态的色散补偿,而且可以用于区分不同的生物组织,以及同一生物组织的不同生理状态. 相似文献
995.
996.
997.
A 100 MeV H- compact cyclotron is under construction at China Institute of Atomic Energy (CYCIAE-100). The proton beams of 75 MeV-100 MeV at an intensity of 200 μA will be extracted in dual opposite directions by charge exchange stripping devices. The crossing point at the switching magnet center is fixed inside the magnet yoke and the stripping points for various extraction energies are calculated by the code CYCTRS. With the code GOBLIN, we can calculate the transfer matrix including the dispersion effects from the stripping point to the switch magnet. The beam distribution just after stripping foil can be obtained from the multi-particle tracking code COMA and the extracted beam parameters after the switch magnet such as emittance, envelope, dispersion, energy spread, bunch length, etc. are given by the extraction orbit simulations. 相似文献
998.
Measurement of optics for the SSRF storage ring in commissioning 总被引:1,自引:0,他引:1
The Shanghai Synchrotron Radiation Facility (SSRF) is a low emittance third-generation synchrotron radiation light source. Some optics parameters of the storage ring were measured when commissioning. This report presents the common methods for measuring some optics parameters of the storage ring, including the betatron tune, beta function, chromaticity, natural chromaticity and dispersion. The results and analysis of measurement for the optics parameters are given here, which are indispensable for the orbit correction of the accelerator and the nonlinear optimization. 相似文献
999.
Andrey N. Lagarkov 《Journal of magnetism and magnetic materials》2009,321(14):2082-2092
The paper reviews recent progress in the field of microwave magnetic properties of composites. The problem under discussion is developing composites with high microwave permeability that are needed in many applications. The theory of magnetic composites is briefly sketched with the attention paid to the laws governing the magnetic frequency dispersion in magnetic materials and basic mixing rules for composites. Recent experimental reports on the microwave performance of magnetic composites, as well as data on the agreement of the mixing rules with the measured permeability of composites that are available from the literature are discussed. From the data, a conclusion is made that the validity of a mixing rule is determined by the permeability contrast in the composite, i.e., the difference between permeability of inclusions and that of the host matrix. When the contrast is low, the Maxwell Garnet mixing rule is frequently valid. When the contrast is high, which is of the most interest for obtaining high microwave permeability of a composite, no conventionally accepted theory is capable of accurately predicting the permeability of the composites. Therefore, the mixing rules do not allow the microwave properties of magnetic composites to be predicted when the permeability of inclusions is high, that is the case of the most interest. Because of that, general limitations to the microwave performance of composites are of importance. In particular, an important relation constraining the microwave permeability of composites follows from Kittel's theory of ferromagnetic resonance and analytical properties of frequency dependence of permeability. Another constraint concerning the bandwidth of electromagnetic wave absorbers follows from the Kramers-Kronig relations for the reflection coefficient. The constraints are of importance in design and analysis of electromagnetic wave absorbers and other devices that employ the microwave magnetic properties of composites, such as magnetic substrates for microwave antennas, microwave inductors, etc. 相似文献
1000.
Yang Wang Jie Zhang Qinyu Zhang Naitong Zhang 《Wireless Communications and Mobile Computing》2009,9(2):169-179
In this paper, based on the analysis of the experimental data using a new post‐processing method for time‐domain channel measurements, a new double‐cluster statistical model for UWB systems with a bandwidth lower than 1 GHz in non‐line‐of‐sight (NLOS) indoor propagation environment is proposed. By using the proposed model, both the model itself and the parameter estimation of the corresponding model are simplified. By defining the polarity of a particular model parameter, the model has the flexibility to deal with both ‘soft NLOS’ and ‘hard NLOS’ indoor propagation environments. Therefore, the channel impulse responses (CIRs) generated by the proposed model ‘resemble’ the measured CIR better than the SV (Saleh‐‐Valenzuela)/IEEE 802.15.3a model not only in terms of the average values, but also in terms of the cumulative distribution functions (CDFs) of the small‐scale statistics. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献