全文获取类型
收费全文 | 16651篇 |
免费 | 3827篇 |
国内免费 | 1132篇 |
专业分类
化学 | 4416篇 |
晶体学 | 597篇 |
力学 | 1380篇 |
综合类 | 128篇 |
数学 | 732篇 |
物理学 | 14357篇 |
出版年
2024年 | 57篇 |
2023年 | 146篇 |
2022年 | 427篇 |
2021年 | 427篇 |
2020年 | 450篇 |
2019年 | 350篇 |
2018年 | 393篇 |
2017年 | 570篇 |
2016年 | 678篇 |
2015年 | 599篇 |
2014年 | 965篇 |
2013年 | 1464篇 |
2012年 | 1120篇 |
2011年 | 1137篇 |
2010年 | 848篇 |
2009年 | 1031篇 |
2008年 | 1157篇 |
2007年 | 1076篇 |
2006年 | 1049篇 |
2005年 | 940篇 |
2004年 | 808篇 |
2003年 | 755篇 |
2002年 | 672篇 |
2001年 | 618篇 |
2000年 | 588篇 |
1999年 | 509篇 |
1998年 | 442篇 |
1997年 | 424篇 |
1996年 | 321篇 |
1995年 | 316篇 |
1994年 | 275篇 |
1993年 | 218篇 |
1992年 | 179篇 |
1991年 | 115篇 |
1990年 | 95篇 |
1989年 | 77篇 |
1988年 | 65篇 |
1987年 | 53篇 |
1986年 | 35篇 |
1985年 | 39篇 |
1984年 | 29篇 |
1983年 | 13篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1973年 | 4篇 |
1971年 | 4篇 |
1970年 | 3篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
11.
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
12.
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
13.
14.
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
15.
The thermal and thermo-elastic-plastic response of newly developed ceramic-metalfunctionally graded materials under a thermal shock load is studied.The materials are heated at the ce-ramic surface with a sudden high-intensity heat flux input,and cooled at the metal surface with aflowing liquid nitrogen.Emphasis is placed on two aspects:(1)the influence of the graded composi-tion of the materials on the temperature and stress response;and(2)the optimum design of the gradedcomposition from a unified viewpoint of the heat insulation property and stress relaxation property.Moreover,a comparison between the thermoelastic stress and the thermo-elastic-plastic stress is alsomade to indicate the plasticity effect. 相似文献
16.
17.
横向放大率法确定复合光学系统的基点 总被引:2,自引:0,他引:2
介绍了应用测量横向放大率确定两薄透镜组成的复合光学系统基点的方法。由于采用线阵光电耦合器件(CCD)测量物经光学系统成像的横向放大率,提高了测量精度。 相似文献
18.
Linear and nonlinear optical properties of racemic (±)2-(α-methylbenzylamino)-5-nitropyridine ((±)MBANP) single crystals have been comprehensively investigated and compared with those of the enantiomorph (–)2-(α-methylbenzylamino)-5-nitropyridine ((–)MBANP) crystals. (±)MBANP crystal exhibits very high chemical and physical stability, but relatively small nonlinear optical coefficients (d31 = 6.8 pm/V, d32 = 4.7 pm/V, d33 = 0.84 pm/V). A comparison between the nonlinear optical coefficients of (±)MBANP and (–)MBANP demonstrates the validity of the oriented-gas model in molecular crystals that neglects all the contributions from intermolecular interaction. 相似文献
19.
设计一种用归零码及多重相关解调技术的传输方案,并给了所需的几种抗干扰单元电路,最后结合实验说明了此方案可提高不良环境下传输数据的置信率。 相似文献
20.