全文获取类型
收费全文 | 1071篇 |
免费 | 274篇 |
国内免费 | 206篇 |
专业分类
航空 | 797篇 |
航天技术 | 296篇 |
综合类 | 135篇 |
航天 | 323篇 |
出版年
2024年 | 6篇 |
2023年 | 16篇 |
2022年 | 41篇 |
2021年 | 47篇 |
2020年 | 44篇 |
2019年 | 41篇 |
2018年 | 39篇 |
2017年 | 49篇 |
2016年 | 27篇 |
2015年 | 50篇 |
2014年 | 64篇 |
2013年 | 69篇 |
2012年 | 84篇 |
2011年 | 84篇 |
2010年 | 82篇 |
2009年 | 108篇 |
2008年 | 70篇 |
2007年 | 56篇 |
2006年 | 51篇 |
2005年 | 37篇 |
2004年 | 42篇 |
2003年 | 43篇 |
2002年 | 51篇 |
2001年 | 41篇 |
2000年 | 38篇 |
1999年 | 36篇 |
1998年 | 28篇 |
1997年 | 24篇 |
1996年 | 41篇 |
1995年 | 22篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有1551条查询结果,搜索用时 985 毫秒
641.
E.V. Nesterenko V.A. Kozlov S.V. Khizhnyak N.S. Manukovsky V.S. Kovalev Yu.L. Gurevich Hong Liu Yidong Xing Enzhu Hu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The object of this research is to study a soil-like substrate (SLS) to grow plants in a Bioregenerative Life Support System (BLSS). Wheat and rice straw were used as raw materials to prepare SLS. Anti-fungal activity of SLS using test cultures of Bipolaris sorokiniana, a plant-pathogenic fungus which causes wheat root rot was studied. Experiments were conducted with SLS samples, using natural soil and sand as controls. Infecting the substrates, was performed at two levels: the first level was done with wheat seeds carrying B. sorokiniana and the second level with seeds and additional conidia of B. sorokiniana from an outside source. We measured wheat disease incidence and severity in two crop plantings. Lowest disease incidence values were obtained from the second planting, SLS: 26% and 41% at the first and the second infection levels, respectively. For soil the values were 60% and 82%, respectively, and for sand they were 67% and 74%, respectively. Wheat root rot in the second crop planting on SLS, at both infection levels was considerably less severe (9% and 13%, respectively) than on natural soil (20% and 33%) and sand (22% and 32%). SLS significantly suppressed the germination of B. sorokiniana conidia. Conidia germination was 5% in aqueous SLS suspension, and 18% in clean water. No significant differences were found regarding the impact on conidia germination between the SLS samples obtained from wheat and rice straw. The anti-fungal activity in SLS increased because of the presence of worms. SLS also contained bacteria stimulating and inhibiting B. sorokiniana growth. 相似文献
642.
曲洪波 《沈阳航空工业学院学报》2010,27(6):65-67
银冈书院是清代辽宁地区重要的教育与学术文化机构,它由清初流人郝浴建立,由清初到近代,经历了200余年的发展,成为清代辽宁地区最负盛名的传统书院。银冈书院以传统文化教育为主要内容,主张关注社会发展,讲求经世致用,为地方培育了大量社会需求的人才,促进了辽宁地区学术文化的发展。 相似文献
643.
644.
本文对矩阵特征值估计和定位问题的两个重要结论,Gerschgorin圆盘定理和Ostrowski圆盘定理进行深入研究,并给出便于应用的定理1,定理2和定理3。 相似文献
645.
646.
高温高湿高日照环境对发射场与测控设备影响分析 总被引:1,自引:0,他引:1
以我国海南文昌新一代运载火箭发射场建设为背景,以高温、高湿、高日照气象环境为主要分析对象,对影响的范围与特征,各要素的生成与分布、演变规律,对发射场和测控系统地面设施、设备的主要影响内容,进行了较全面的分析论述,旨在能对发射场系统和测控系统设施、设备的防护与可靠性设计提供参考性技术依据。 相似文献
647.
装备的保障过程由于受到保障活动参数的影响存在着较大的不确定性.针对保障过程的不确定性问题,建立了基于方差的保障活动不确定性重要度作为保障过程全局敏感性分析指标;根据保障过程工期的GERT(Graphic Evaluation and Review Technique)模型,设计了一种基于方差的保障时间不确定分析方法来计算保障活动的时间不确定性重要度,并对该方法进行解析求解,给出了具体步骤.最后,将舰载机航空保障作为案例,验证了方法的有效性. 相似文献
648.
649.
650.
Chin-Chun Wu K. Liou Shao-Ju Shan C.-L. Tseng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(4):611-616
The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionospheric anomaly (EIA) region is studied by analyzing dual-frequency signals of the Global Position System (GPS) acquired from a chain of nine observational sites clustered around Taiwan (21.9–26.2°N, 118.4–112.6°E). In this study, we present results from a statistical study of seasonal and geomagnetic effects on the EIA during solar cycle 23: 1994–2003. It is found that TEC at equatorial anomaly crests yield their maximum values during the vernal and autumnal months and their minimum values during the summer (except 1998). Using monthly averaged Ic (magnitude of TEC at the northern anomaly crest), semi-annual variations is seen clearly with two maxima occurring in both spring and autumn. In addition, Ic is found to be greater in winter than in summer. Statistically monthly values of Ic were poorly correlated with the monthly Dst index (r = −0.22) but were well correlated with the solar emission F10.7 index (r = 0.87) for the entire database for the period during 1994–2003. In contrast, monthly values of Ic were correlated better with Dst (r ? 0.72) than with F10.7 (r ? 0.56) in every year during the low solar activity period (1994–1997). It suggests that the effect of solar activity on Ic is a longer term (years), whereas the effect of geomagnetic activity on Ic is a shorter term (months). 相似文献