全文获取类型
收费全文 | 1253篇 |
免费 | 150篇 |
国内免费 | 51篇 |
专业分类
化学 | 176篇 |
晶体学 | 1篇 |
力学 | 53篇 |
综合类 | 8篇 |
数学 | 36篇 |
物理学 | 1180篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 34篇 |
2020年 | 26篇 |
2019年 | 12篇 |
2018年 | 31篇 |
2017年 | 47篇 |
2016年 | 57篇 |
2015年 | 46篇 |
2014年 | 108篇 |
2013年 | 82篇 |
2012年 | 101篇 |
2011年 | 103篇 |
2010年 | 65篇 |
2009年 | 77篇 |
2008年 | 76篇 |
2007年 | 84篇 |
2006年 | 73篇 |
2005年 | 35篇 |
2004年 | 45篇 |
2003年 | 44篇 |
2002年 | 36篇 |
2001年 | 32篇 |
2000年 | 30篇 |
1999年 | 28篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1454条查询结果,搜索用时 15 毫秒
991.
Achromatic objectives are constructed by combining two or more lenses with properly chosen powers made of materials with different dispersions. We present a new approach that simplifies the design of multilens achromatic combinations as well as the choice of materials for them and show how this method can be applied to the design of a four-lens superachromatic combination. 相似文献
992.
993.
CCD camera system design for the beam diagnostic by using OTR 总被引:1,自引:0,他引:1
In this paper, a new CCD camera system used in the OTR beam measurement is presented, the basic principle of OTR beam measurement and the application of CCD chips-ICX208CL and AD9929 in camera system design are introduced in detail. 相似文献
994.
摄像机标定精度研究中的图像及数据处理问题 总被引:1,自引:0,他引:1
在计算机视觉测量系统中,摄像机的标定精度对保证测量结果的可靠性起着至关重要的作用,本文利用数学形态学探讨了图像处理的精度,并论述了豪斯荷尔德矩阵分解法在确保求解数值稳定性中的作用,最后通过对标定块上特征点进行三维重建的精度分析,验证了摄像机的标定精度。 相似文献
995.
Surface roughness and color characteristics of wood treated with preservatives after accelerated weathering test 总被引:2,自引:0,他引:2
Ali Temiz Umit C. Yildiz Ismail Aydin Morten Eikenes Gry Alfredsen Gürsel olakoglu 《Applied Surface Science》2005,250(1-4):35-42
Wood samples treated with ammonium copper quat (ACQ 1900 and ACQ 2200), chromated copper arsenate (CCA), Tanalith E 3491 and Wolmanit CX-8 have been studied in accelerated weathering experiments. The weathering experiment was performed by cycles of 2 h UV-light irradiation followed by water spray for 18 min. The changes on the surface of the weathered samples were characterized by roughness and color measurements on the samples with 0, 200, 400 and 600 h of total weathering.
The objective of this study was to investigate the changes created by weathering on impregnated wood with several different wood preservatives. This study was performed on the accelerated weathering test cycle, using UV irradiation and water spray in order to simulate natural weathering.
Surface roughness and color measurement was used to investigate the changes after several intervals (0–200–400–600 h) in artificial weathering of treated and untreated wood. 相似文献
996.
Data processing technique applied to the calibration of a high performance FPA infrared camera 总被引:3,自引:0,他引:3
The present work deals with the calibration of a focal plane array infrared camera whose detector is a matrix of 320×244 PtSi sensors active in the range 3.6–5 μm. The calibration curve has been obtained by measuring the energy emitted by a blackbody, consisting in a copper cylindric cavity with isothermal walls. The results, obtained in the temperature range 10–70 °C, enable us to investigate the nature of the noise which affects the measurements. The aim is to suggest a data processing and a calibration technique in order to enhance the image quality and the instrument response as well. The effects of random uncertainties have been reduced by using Wiener filtration, which enables us to improve the signal to noise ratio. The problem caused by the nonuniform response of the detector array has been handled by using a different calibration curve for each sensor. The effectiveness of this procedure has been checked by comparing the frequency histograms of the raw and the processed signal. The investigation enables us to highlight some peculiar features of the new focal plane array technology employed in the new generation infrared cameras. 相似文献
997.
998.
CCD摆动提高摄象机性能的研究 总被引:1,自引:0,他引:1
本文提出用摆动方法提高CCD摄象机二维空间分辨率的因素及可能达到最大分辨极限。本文还描述了自行设计的实现水平、垂直分辨率各提高一倍的悬臂型压电双晶片微摆动机构;并且详述了水平和垂直分辨率各提高一倍的信号处理方法及产生与现有制式相兼容的高清晰图像信号的再生过程,分析了提高二维清晰度的图象信号系统。 相似文献
999.
1000.
本文选用了波长为1.054μm的磷酸盐钕玻璃锁模激光器输出的单个PS激光脉冲,经KDP晶体倍频后的绿光(λ=0.527μm)做激发光源。用条纹相机测定了血卟琳、核黄素有机生物大分子的激发单态S_1的寿命。并就氧分子的猝灭效应对寿命的影响进行了初步讨论。 相似文献