全文获取类型
收费全文 | 5101篇 |
免费 | 155篇 |
国内免费 | 259篇 |
专业分类
化学 | 1631篇 |
晶体学 | 28篇 |
力学 | 37篇 |
综合类 | 5篇 |
数学 | 33篇 |
物理学 | 2456篇 |
无线电 | 1325篇 |
出版年
2024年 | 6篇 |
2023年 | 82篇 |
2022年 | 66篇 |
2021年 | 89篇 |
2020年 | 62篇 |
2019年 | 74篇 |
2018年 | 94篇 |
2017年 | 159篇 |
2016年 | 206篇 |
2015年 | 171篇 |
2014年 | 295篇 |
2013年 | 353篇 |
2012年 | 243篇 |
2011年 | 270篇 |
2010年 | 220篇 |
2009年 | 330篇 |
2008年 | 298篇 |
2007年 | 329篇 |
2006年 | 278篇 |
2005年 | 232篇 |
2004年 | 229篇 |
2003年 | 170篇 |
2002年 | 156篇 |
2001年 | 117篇 |
2000年 | 105篇 |
1999年 | 99篇 |
1998年 | 95篇 |
1997年 | 107篇 |
1996年 | 109篇 |
1995年 | 93篇 |
1994年 | 42篇 |
1993年 | 50篇 |
1992年 | 66篇 |
1991年 | 64篇 |
1990年 | 27篇 |
1989年 | 30篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有5515条查询结果,搜索用时 0 毫秒
81.
82.
The analysis of changes in the vibrational spectrum of infrared active molecules adsorbed on a ionic surface containing point or extended defects can be an efficient method to determine the nature and density of surface defects. We study the infrared response of ammonia molecules deposited on a ionic surface of MgO containing charge vacancies and dipolar defects in various concentrations and distributions and show significant changes assigned to the defects signature. A Monte Carlo approach is used to randomly deposit the probe molecules on the surface displaying random or regularly arranged defects at low temperature. 相似文献
83.
O.M. Lyulin V.I. Perevalov H. Tran J.-Y. Mandin V. Dana L. Rgalia-Jarlot X. Thomas D. Dcatoire 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(17):1815-1824
Using the Fourier transform spectra of the acetylene molecule recorded near 1.5-μm, the intensities of 111 lines belonging to seven hot bands of the main isotopologue 12C2H2 have been retrieved by means of a multispectrum fitting procedure. Considering the density of lines in the spectra, and the fact that the measured bands are the weakest observed, the accuracy of the measurements is around 10%. At first stage, an empirical treatment of these data has been performed, leading to the vibrational transition dipole moment squared and some Herman–Wallis coefficients. Then the measured line intensities of this work and collected ones from the literature have been treated simultaneously within the framework of the effective operator approach. 相似文献
84.
Polyamide-imide (PAI) fibrous mats were fabricated through electrospinning and further treated with atmospheric-pressure plasma. The surface characteristics of the PAI fibrous mats were examined to determine the effect of plasma treatment on the hydrophilic properties. FT-IR, X-ray photoelectron spectroscopy, and contact-angle analysis indicated that the hydrophilicity of the PAI fibrous mats increased upon the introduction of hydrophilic groups by plasma treatment. The concentration of functional groups, including oxygen, and the surface roughness of the PAI fibrous mats increased with increasing treatment time. The optimum plasma treatment time for surface modification of the PAI fibrous mats under atmospheric pressure was 120 s. 相似文献
85.
针对双波段红外探测设备不同波段的探测要求,利用曳光管双波段辐射特性,提出无人机加载曳光管作为低空移动光电靶,实现同一靶标满足双波段测试要求;通过对无人机航路距离和航向的统筹设计,实现同一个飞行航次满足作用距离和目标数据精度等多个测试项目;文中对目标航迹真值精度进行深入分析,总结出在不同条件下,航路、航向及布站等相关参数的关联和设置方法,为该测试项目组织实施提供充分的技术准备和选择空间。 相似文献
86.
87.
88.
Scene-based non-uniformity correction (SBNUC) algorithms are an important part of infrared image processing; however, SBNUC algorithms usually cause two defects: (1) ghosting artifacts and (2) over-correction. In this paper, we use the absolute difference based on guided image filter (AD-GF) method to validate the performance of SBNUC algorithms. We obtain a self-separation source using the improved guided image filter to process the input image, and use the self-separation source to obtain the space-high-frequency parts of the input image and the corrected image. Finally, we use the absolute difference between the two space-high-frequency parts as the evaluation result. Based on experimental results, the AD-GF method has better robustness and can validate the performance of SBNUC algorithms even if ghosting artifacts or over-correction occur. Also the AD-GF method can measure how SBNUC algorithms perform in the time domain, it’s an effective evaluation method for SBNUC algorithm. 相似文献
89.
90.
Real-time infrared simulation technology can provide a large number of infrared images under different conditions to support the design, test and evaluation of a system having infrared imaging equipment with very low costs. By synthesizing heat transfer, infrared physics, fluid mechanics and computer graphics, a real-time infrared simulation method is proposed based on the method of characteristics to predict the infrared feature of aircraft plumes, which tries to obtain a good balance between simulation precision and computation efficiency. The temperature and pressure distribution in the under-expansion status can be rapidly solved with dynamically changing flight statuses and engine working states. And a modified C–G (Curtis–Godson) spectral band model that combines the plume streamlines with the conventional C–G spectral band model was implemented to calculate the non-uniformly distributed radiation parameters inside a plume field. The simulation result was analyzed and compared with the CFD++, which validates the credibility and efficiency of the proposed simulation method. 相似文献