全文获取类型
收费全文 | 2055篇 |
免费 | 490篇 |
国内免费 | 358篇 |
专业分类
航空 | 1593篇 |
航天技术 | 445篇 |
综合类 | 221篇 |
航天 | 644篇 |
出版年
2024年 | 14篇 |
2023年 | 22篇 |
2022年 | 61篇 |
2021年 | 83篇 |
2020年 | 88篇 |
2019年 | 60篇 |
2018年 | 134篇 |
2017年 | 131篇 |
2016年 | 80篇 |
2015年 | 90篇 |
2014年 | 111篇 |
2013年 | 158篇 |
2012年 | 157篇 |
2011年 | 202篇 |
2010年 | 165篇 |
2009年 | 152篇 |
2008年 | 132篇 |
2007年 | 129篇 |
2006年 | 114篇 |
2005年 | 97篇 |
2004年 | 71篇 |
2003年 | 61篇 |
2002年 | 69篇 |
2001年 | 60篇 |
2000年 | 49篇 |
1999年 | 58篇 |
1998年 | 40篇 |
1997年 | 36篇 |
1996年 | 36篇 |
1995年 | 30篇 |
1994年 | 42篇 |
1993年 | 32篇 |
1992年 | 22篇 |
1991年 | 25篇 |
1990年 | 28篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1973年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有2903条查询结果,搜索用时 93 毫秒
911.
地球同步轨道长寿命卫星热控涂层太阳吸收率性能退化研究 总被引:14,自引:0,他引:14
文章介绍了15年地球同步轨道环境对卫星表面太阳吸收率性能影响的试验模拟研究,研究结果为长寿命卫星热设计及热控涂层选择和研制提供可靠依据;介绍自行研制的空间低能综合环境试验设备、太阳吸收率原位测试系统和空间低能综合环境模拟试验方法,并对航天器常用的S781白漆、SR107ZK白漆、F46镀银和OSR二次表面镜热控材料进行空间低能综合环境模拟试验,获得了这些热控涂层在地球同步轨道15年期间太阳吸收率性能退化模拟数据,与已有的飞行试验数据进行对比研究,取得满意的结果。 相似文献
912.
913.
914.
Anny-Chantal Levasseur-Regourd Jessica Agarwal Hervé Cottin Cécile Engrand George Flynn Marco Fulle Tamas Gombosi Yves Langevin Jérémie Lasue Thurid Mannel Sihane Merouane Olivier Poch Nicolas Thomas Andrew Westphal 《Space Science Reviews》2018,214(3):64
This review presents our understanding of cometary dust at the end of 2017. For decades, insight about the dust ejected by nuclei of comets had stemmed from remote observations from Earth or Earth’s orbit, and from flybys, including the samples of dust returned to Earth for laboratory studies by the Stardust return capsule. The long-duration Rosetta mission has recently provided a huge and unique amount of data, obtained using numerous instruments, including innovative dust instruments, over a wide range of distances from the Sun and from the nucleus. The diverse approaches available to study dust in comets, together with the related theoretical and experimental studies, provide evidence of the composition and physical properties of dust particles, e.g., the presence of a large fraction of carbon in macromolecules, and of aggregates on a wide range of scales. The results have opened vivid discussions on the variety of dust-release processes and on the diversity of dust properties in comets, as well as on the formation of cometary dust, and on its presence in the near-Earth interplanetary medium. These discussions stress the significance of future explorations as a way to decipher the formation and evolution of our Solar System. 相似文献
915.
Adrienn Luspay-Kuti Olivier Mousis Jonathan I. Lunine Yves Ellinger Françoise Pauzat Ujjwal Raut Alexis Bouquet Kathleen E. Mandt Romain Maggiolo Thomas Ronnet Bastien Brugger Ozge Ozgurel Stephen A. Fuselier 《Space Science Reviews》2018,214(8):115
The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument onboard the Rosetta spacecraft has measured molecular oxygen (O2) in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) in surprisingly high abundances. These measurements mark the first unequivocal detection of O2 in a cometary environment. The large relative abundance of O2 in 67P/C-G despite its high reactivity and low interstellar abundance poses a puzzle for its origin in comet 67P/C-G, and potentially other comets. Since its detection, there have been a number of hypotheses put forward to explain the production and origin of O2 in the comet. These hypotheses cover a wide range of possibilities from various in situ production mechanisms to protosolar nebula and primordial origins. Here, we review the O2 formation mechanisms from the literature, and provide a comprehensive summary of the current state of knowledge of the sources and origin of cometary O2. 相似文献
916.
No two rocky bodies offer a better laboratory for exploring the conditions controlling interior dynamics than Venus and Earth. Their similarities in size, density, distance from the sun, and young surfaces would suggest comparable interior dynamics. Although the two planets exhibit some of the same processes, Venus lacks Earth’s dominant process for losing heat and cycling volatiles between the interior and the surface and atmosphere: plate tectonics. One commonality is the size and number of mantle plume features which are inferred to be active today and arise at the core mantle boundary. Such mantle plumes require heat loss from the core, yet Venus lacks a measurable interior dynamo. There is evidence for plume-induced subduction on Venus, but no apparent mosaic of moving plates. Absent plate tectonics, one essential question for interior dynamics is how did Venus obtain its young resurfacing age? Via catastrophic or equilibrium processes? Related questions are how does it lose heat via past periods of plate tectonics, has it always had a stagnant lid, or might it have an entirely different mode of heat loss? Although there has been no mission dedicated to surface and interior processes since the Magellan mission in 1990, near infrared surface emissivity data that provides information on the iron content of the surface mineralogy was obtained fortuitously from Venus Express. These data imply both the presence of continental-like crust, and thus formation in the presence of water, and recent volcanism at mantle hotspots. In addition, the study of interior dynamics for both Earth and exoplanets has led to new insights on the conditions required to initiate subduction and develop plate tectonics, including the possible role of high temperature lithosphere, and a renewed drive to reveal why Venus and Earth differ. Here we review current data that constrains the interior dynamics of Venus, new insights into its interior dynamics, and the data needed to resolve key questions. 相似文献
917.
将高超声速飞行器双重不确定性因素建模为未知干扰输入项,针对状态演化方程和量测方程含有不同未知干扰输入的高超声速飞行器控制系统状态估计问题开展研究,提出一种基于自适应方差极小化的递推状态估计器(Adaptive variance minimization based Recursive Estimator, AVMRE)。首先建立了状态估计递推滤波器模型,实现滤波误差中的量测未知干扰解耦,之后引入自适应调整因子刻画状态未知干扰并推导了最小上界估计误差协方差矩阵,最后,基于最小方差估计准则设计了滤波器中的量测增益反馈矩阵。以外部突风和传感器故障为例,受内外部双重不确定性因素影响下的高超声速飞行器仿真实验验证了本文算法的有效性,与相关算法的仿真对比反映了本文算法的优越性。 相似文献
918.
Superluminous supernovae are a new class of supernovae that were recognized about a decade ago. Both observational and theoretical progress has been significant in the last decade. In this review, we first briefly summarize the observational properties of superluminous supernovae. We then introduce the three major suggested luminosity sources to explain the huge luminosities of superluminous supernovae, i.e., the nuclear decay of 56Ni, the interaction between supernova ejecta and dense circumstellar media, and the spin down of magnetars. We compare these models and discuss their strengths and weaknesses. 相似文献
919.
基于编辑距离相似度的文本校验技术研究与应用 总被引:1,自引:0,他引:1
树形结构的文本配置在分布式的测控数据处理软件中使用广泛,它的正确性对数据处理而言至关重要。为了实现树形结构的文本配置自动检查和纠错,通过引入LD(Levenshtein Distance)编辑距离算法,把字符串的编辑操作推广到多叉树之间。在此基础上定义了多叉树之间的编辑距离,建立了衡量多叉树之间相似度的方法,设计了基于模糊匹配的文本配置自动校对流程,解决了精确匹配时由字符的多义性导致的查全率失真和误判的问题。根据实验结果,查全率和查准率分别达到了87.5%和100%,有效提高了基于树形结构的文本配置自动校验时的可靠性。 相似文献
920.