全文获取类型
收费全文 | 33681篇 |
免费 | 5912篇 |
国内免费 | 2126篇 |
专业分类
化学 | 5117篇 |
晶体学 | 611篇 |
力学 | 439篇 |
综合类 | 181篇 |
数学 | 979篇 |
物理学 | 16009篇 |
无线电 | 18383篇 |
出版年
2024年 | 122篇 |
2023年 | 327篇 |
2022年 | 665篇 |
2021年 | 774篇 |
2020年 | 875篇 |
2019年 | 667篇 |
2018年 | 726篇 |
2017年 | 1071篇 |
2016年 | 1194篇 |
2015年 | 1442篇 |
2014年 | 2147篇 |
2013年 | 2506篇 |
2012年 | 2557篇 |
2011年 | 2299篇 |
2010年 | 1730篇 |
2009年 | 1907篇 |
2008年 | 2233篇 |
2007年 | 2231篇 |
2006年 | 2160篇 |
2005年 | 1959篇 |
2004年 | 1703篇 |
2003年 | 1642篇 |
2002年 | 1328篇 |
2001年 | 1278篇 |
2000年 | 1100篇 |
1999年 | 873篇 |
1998年 | 740篇 |
1997年 | 635篇 |
1996年 | 547篇 |
1995年 | 472篇 |
1994年 | 395篇 |
1993年 | 339篇 |
1992年 | 266篇 |
1991年 | 212篇 |
1990年 | 140篇 |
1989年 | 111篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 44篇 |
1985年 | 37篇 |
1984年 | 37篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1975年 | 9篇 |
1974年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO3, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO3 crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent. 相似文献
25.
We measured the entire region of mesopic and photopic vision to determine the color zone covering the visual field with unique red, yellow, green, and blue hue components. Eight kinds of test stimuli in the natural color system (NCS) color notation system were used. These stimuli were presented at horizontal and vertical meridians, and at meridians inclined at 45° angles. The illuminance level was set at six levels: 0.01 lx-1000 lx. The evaluation method measured chromatic, white, and black components as well as the hue component of the stimuli. Results show that the color zone of the retina extended further into the periphery with increasing illuminance; the response of opponent colors y-b was shown to be greater than that of the opponent colors r-g. 相似文献
26.
The problem of investigation of the amplitude and phase structure of a time-varying probing optical signal and the structure of time-varying inhomogeneities of a substance tested by this signal is considered. The analysis is concerned, in particular, with determination of the structure of signals and processes with resolution in the pico- and femtosecond range. The scheme used for the analysis is based on registration of four spatially separated spectra of the studied radiation. The spectra are formed in a four-channel scheme with a twin-wave Michelson interferometer and a spectral device. Modulators based on electrooptical crystals (perovskites) are placed in the channels. The sum spectra are formed: without modulators, with the effect of either of the modulators, and with both of them affecting the radiation. The effect of the studied substance implies either modulating the radiation (in this case it is described by multiplication) or redistributing the radiation (then it is described by convolution). 相似文献
27.
Tracing is a method of assigning flows in an electricity network to particular generators and loads, assuming perfect mixing at each node. It can be used to assign costs to transmission users. We show that the resulting allocation is equal to the Shapley value of an equivalent co-operative game. 相似文献
28.
29.
An all-optical fiber nonlinear Fabry-Perot resonator is proposed. The steady-state model for describing this resonator is developed. The transmission and refection bistabilities are shown numerically. Our results show that the bistability in this system is similar to that in a normal nonlinear Fabry-Perot etalon, except that the characteristics of the bistability can be changed not only by the cavity length but also by the phase shifts of the fiber loop mirrors. 相似文献
30.