全文获取类型
收费全文 | 83726篇 |
免费 | 8841篇 |
国内免费 | 5744篇 |
专业分类
化学 | 19052篇 |
晶体学 | 639篇 |
力学 | 2529篇 |
综合类 | 593篇 |
数学 | 5663篇 |
物理学 | 22832篇 |
综合类 | 47003篇 |
出版年
2024年 | 279篇 |
2023年 | 786篇 |
2022年 | 1762篇 |
2021年 | 1832篇 |
2020年 | 1789篇 |
2019年 | 1684篇 |
2018年 | 1577篇 |
2017年 | 2175篇 |
2016年 | 2467篇 |
2015年 | 2649篇 |
2014年 | 4009篇 |
2013年 | 5269篇 |
2012年 | 4819篇 |
2011年 | 5177篇 |
2010年 | 4148篇 |
2009年 | 4482篇 |
2008年 | 4817篇 |
2007年 | 6012篇 |
2006年 | 5402篇 |
2005年 | 4843篇 |
2004年 | 4233篇 |
2003年 | 3915篇 |
2002年 | 3626篇 |
2001年 | 3017篇 |
2000年 | 2696篇 |
1999年 | 2234篇 |
1998年 | 1837篇 |
1997年 | 1686篇 |
1996年 | 1418篇 |
1995年 | 1249篇 |
1994年 | 1064篇 |
1993年 | 910篇 |
1992年 | 804篇 |
1991年 | 669篇 |
1990年 | 561篇 |
1989年 | 501篇 |
1988年 | 489篇 |
1987年 | 349篇 |
1986年 | 246篇 |
1985年 | 183篇 |
1984年 | 141篇 |
1983年 | 61篇 |
1982年 | 105篇 |
1981年 | 64篇 |
1980年 | 63篇 |
1979年 | 66篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 14篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
M. R. McEwen J. P. Sephton P. H. G. Sharpe D. R. Shipley 《Radiation Physics and Chemistry》2003,68(6):1017-1022
A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level). 相似文献
82.
网络股泡沫大小测度研究 总被引:1,自引:0,他引:1
网络股泡沫是最能反映网络泡沫本质的表现形式,本文利用理性预期理论,构建了网络股泡沫大小的测度模型,说明网络股泡沫的存在,在此基础上确定了网络股泡沫大小的测度指标,并以雅虎公司股票为例对泡沫的大小进行了测度,结果符合网络泡沫的实际情况。 相似文献
83.
本文提出从高分辨电子显微像中,利用光学、全息和部分相干等方法,提取传递函数,制作相位和振幅滤波器,实现解卷,提高高分辨电子显微像的分辨率. 相似文献
84.
85.
86.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
87.
光纤传感振动检测系统及其实验研究 总被引:3,自引:0,他引:3
实际工程结构中的振动检测是十分重要的,也是十分复杂的,常用的结构振动检测传感器易受工程现场恶劣环境的影响.而光纤传感器具有小巧、抗电磁干扰、灵敏度高、适合长期监测等优点。本文建立了基于马赫—曾德(Mech-Zehnder)干涉原理的光纤传感振动检测系统.研制了运用先进的数字信号处理技术采集和处理数据的专用软件,并在典型结构件——钢制悬臂梁结构上进行了外加信号作用下的强迫振动检测和冲击载荷作用下的自由衰减振动检测,测量了该结构件的频率及振幅,其结果与同时进行的成熟的电测结果相近,说明光纤传感器用于结构件的振动测量是可靠的。本文为光纤传感器应用于实际工程的振动检测提供了新的技术装置,具有工程应用前景。 相似文献
88.
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
89.
Takeshi Murashige Hideo Fujikake Hiroto Sato Hiroshi Kikuchi Taiichiro Kurita Fumio Sato 《Optical Review》2004,11(6):349-352
We have confirmed light diffraction of aligned polymer fibers obtained by a phase separation of an anisotropic-phase solution of liquid crystal and polymer. He—Ne laser light passing through the polymer fibers was scattered in the axis vertical to the fibers, and had two peaks of light intensity symmetrical to the center of the transmitting laser spot. The two peaks were found to be caused by light diffraction due to the periodic polymer-fiber dispersion because the peaks corresponded to values calculated by intervals between the fibers. The periodical fiber networks are considered to be formed by anisotropic spinodal decomposition. This effect can be used to measure the dispersion order of the polymer fibers. © 2004 The Optical Society of Japan 相似文献
90.
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