全文获取类型
收费全文 | 2056篇 |
免费 | 242篇 |
国内免费 | 426篇 |
专业分类
航空 | 1125篇 |
航天技术 | 599篇 |
综合类 | 464篇 |
航天 | 536篇 |
出版年
2024年 | 5篇 |
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 24篇 |
2020年 | 47篇 |
2019年 | 15篇 |
2018年 | 31篇 |
2017年 | 34篇 |
2016年 | 30篇 |
2015年 | 61篇 |
2014年 | 109篇 |
2013年 | 108篇 |
2012年 | 97篇 |
2011年 | 102篇 |
2010年 | 141篇 |
2009年 | 136篇 |
2008年 | 124篇 |
2007年 | 113篇 |
2006年 | 114篇 |
2005年 | 102篇 |
2004年 | 65篇 |
2003年 | 70篇 |
2002年 | 43篇 |
2001年 | 99篇 |
2000年 | 89篇 |
1999年 | 131篇 |
1998年 | 114篇 |
1997年 | 96篇 |
1996年 | 103篇 |
1995年 | 64篇 |
1994年 | 80篇 |
1993年 | 72篇 |
1992年 | 66篇 |
1991年 | 51篇 |
1990年 | 35篇 |
1989年 | 35篇 |
1988年 | 18篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1969年 | 1篇 |
1965年 | 2篇 |
1900年 | 1篇 |
排序方式: 共有2724条查询结果,搜索用时 15 毫秒
1.
D O'Sullivan D Zhou E Semones W Heinrich E Flood 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(6):1420-1423
Particle intensity, dose equivalent and absorbed dose have been measured on board the space shuttle Endeavour during STS-108 in December 2001 by Dublin Institute for Advanced Studies (DIAS). The dose estimates are based on very accurate measurements of recoils produced in CR-39 by cosmic ray primary and secondary protons and heavier nuclei and by secondary neutrons. The corresponding LET spectra were used to determine dose equivalent and absorbed dose values. Estimates of the total flux of Z > or = 2 nuclei have been undertaken and a preliminary charge spectrum was measured. Some comparisons are made with preliminary data obtained on STS-105 (ISS Expedition) and other missions using CR-39 detectors. 相似文献
2.
Molecular alterations in tumorigenic human bronchial and breast epithelial cells induced by high LET radiation. 总被引:3,自引:0,他引:3
T K Hei Y L Zhao D Roy C Q Piao G Calaf E J Hall 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(2):411-419
Carcinogenesis is a multi-stage process with sequence of genetic events governing the phenotypic expression of a series of transformation steps leading to the development of metastatic cancer. In the present study, immortalized human bronchial (BEP2D) and breast (MCF-10F) cells were irradiated with graded doses of either 150 keV/micrometer alpha particles or 1 GeV/nucleon 56Fe ions. Transformed cells developed through a series of successive steps before becoming tumorigenic in nude mice. Cell fusion studies indicated that radiation-induced tumorigenic phenotype in BEP2D cells could be completely suppressed by fusion with non-tumorigenic BEP2D cells. The differential expressions of known genes between tumorigenic bronchial and breast cells induced by alpha particles and their respective control cultures were compared using cDNA expression array. Among the 11 genes identified to be differentially expressed in BEP2D cells, three (DCC, DNA-PK and p21(CIP1)) were shown to be consistently down-regulated by 2 to 4 fold in all the 5 tumor cell lines examined. In contrast, their expressions in the fusion cell lines were comparable to control BEP2D cells. Similarly, expression levels of a series of genes were found to be altered in a step-wise manner among tumorigenic MCF-10F cells. The results are highly suggestive that functional alterations of these genes may be causally related to the carcinogenic process. 相似文献
3.
通用仪器接口总线标准及软件技术的发展 总被引:1,自引:0,他引:1
叙述了通用仪器接口总线标准和软件技术的现状和未来。介绍了GPIB、VXI总线,程控仪器校准命令和虚拟仪器,给出了GPIB标准关系图,GPIB软件结构以及虚拟仪器框图。 相似文献
4.
Hwu S.U. Loh Y.C. Dobbins J.A. Kroll Q.D. Sham C.C. 《Aerospace and Electronic Systems Magazine, IEEE》2005,20(10):9-14
Computational investigations and experimental measurements were performed to evaluate the Space Shuttle UHF communication system performance for payload bay antenna at the proposed new location. To insure adequate communication coverage at relocated new location, the link margin for the Extravehicular Activity (EVA) astronauts and between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous were analyzed. The multipath effects from the vehicle structures surrounding the antenna were investigated. The Radio Frequency (RF) electromagnetic radiation to the Orbiter Docking System (ODS) pyrotechnics was also analyzed to ensure the EMC/EMI compliances. 相似文献
5.
数据采集系统的总体评价 总被引:5,自引:0,他引:5
从性能指标出发,综述了数据采集系统总结评价技术的发展状况。并提出了对数据采集系统性能指标的两类分类方法 。 相似文献
6.
7.
8.
9.
随着车速的提高,汽车在行驶中受到的空气阻力便成为不可忽视的问题,因此与减阻节能相关的汽车优化造型也就显得越来越重要了。由于运动物体所受到的空气阻力系数的大小主要取决于它的头部的形状,因而我们对厢式大客车驾驶室前风窗区的几种不同造型在低速风洞中进行了测力的实验研究。实验结果表明,驾驶室前围不同形式的过渡是影响厢式客车空气阻力的重要因素。其中在适当的风窗倾角下,经过良好的圆化处理后,可使厢式大客车的空气阻力减小27%左右。这不仅节省了燃料的消耗,还可以提高汽车的最大行驶速度,改善其加速和爬坡能力。 相似文献
10.