全文获取类型
收费全文 | 6936篇 |
免费 | 301篇 |
国内免费 | 387篇 |
专业分类
航空 | 3780篇 |
航天技术 | 2266篇 |
综合类 | 450篇 |
航天 | 1128篇 |
出版年
2021年 | 53篇 |
2019年 | 43篇 |
2018年 | 77篇 |
2017年 | 45篇 |
2016年 | 66篇 |
2015年 | 66篇 |
2014年 | 156篇 |
2013年 | 206篇 |
2012年 | 181篇 |
2011年 | 278篇 |
2010年 | 259篇 |
2009年 | 259篇 |
2008年 | 385篇 |
2007年 | 256篇 |
2006年 | 186篇 |
2005年 | 211篇 |
2004年 | 194篇 |
2003年 | 244篇 |
2002年 | 152篇 |
2001年 | 233篇 |
2000年 | 177篇 |
1999年 | 222篇 |
1998年 | 276篇 |
1997年 | 207篇 |
1996年 | 222篇 |
1995年 | 245篇 |
1994年 | 243篇 |
1993年 | 184篇 |
1992年 | 207篇 |
1991年 | 121篇 |
1990年 | 107篇 |
1989年 | 171篇 |
1988年 | 69篇 |
1987年 | 84篇 |
1986年 | 81篇 |
1985年 | 170篇 |
1984年 | 138篇 |
1983年 | 116篇 |
1982年 | 134篇 |
1981年 | 150篇 |
1980年 | 66篇 |
1979年 | 64篇 |
1978年 | 50篇 |
1977年 | 38篇 |
1975年 | 54篇 |
1974年 | 44篇 |
1973年 | 40篇 |
1972年 | 48篇 |
1971年 | 43篇 |
1969年 | 39篇 |
排序方式: 共有7624条查询结果,搜索用时 46 毫秒
171.
STUDIESONAIRCRAFTTOTALENERGYFLIGHTCONTROLSYSTEM:NONLINEARSYSTEMINTEGRATIONANDSIMULATIONWuShufan;ShenYongzhang;GuoSuofeng(Dept... 相似文献
172.
介绍1种用标准长度作基准,以自扫描光电二极管列阵作光电传换器,微型计算机进行数据处理,对基准浮动的非刚性工件宽度进行在线测量的测量装置。 相似文献
173.
吴昌忠%陈静%陈怀宁%林泉洪 《宇航材料工艺》2005,35(3):17-20,30
综述了钛及钛合金高温钎焊结构在现代工业中的应用。在分析了钛基钎料应用和发展的基础上,重点分析了钎焊接头的组织与接头性能的关系以及影响因素。指明接头组织中脆性金属间化合物相的存在形态是决定接头性能的主要因素,接头间隙和钎焊时间决定了接头的组织形态,从而影响接头的性能。钛及钛合金高温钎焊接头的拉伸性能、高温性能和疲劳性能是优越的,而接头氧化后的性能急剧下降。并展望了钛基材料连接的发展方向。 相似文献
174.
175.
武迪蒙%曾科%唐文睿%杨刚 《宇航材料工艺》2007,37(2):17-21
合成了三种AB型聚酰亚胺单体:4-(4-氨基苯氧基)邻苯二甲酸(单体4),4-(3-氨基苯氧基)邻苯二甲酸(单体7)和对(间)乙基4-(3-氨基苯氧基)邻苯二甲酸酯(单体8或9)。利用热失重分析(TGA)对比研究了这三种AB型聚酰亚胺单体的热行为。结果表明,单体4、单体7和单体8(9)在升温的过程中能发生热聚合生成聚酰亚胺。将单体4用于气相沉积聚合设备,得到了均匀透明的聚酰亚胺薄膜。对分子结构的修饰使单体8(9)较之单体7有更好的挥发性。 相似文献
176.
随着计算机在分析与仿真中的广泛应用,固体火箭发动机工作过程中许多复杂而难以观察的现象已能得到揭示.因此,计算机的应用已成为设计与研制高性能固体火箭发动机的十分重要的手段.本文综述了应用计算机在一些固体火箭发动机的性能预示、设计优化、性能检验和故障分析等方面所取得的成就,并就今后我国在设计与研制固体火箭发动机中如何加强计算机化提出了若干建议. 相似文献
177.
This work is concerned with binary systems that we call ‘moderately close’. These are systems in which the primary (by which we mean the initially more massive star) fills its Roche lobe when it is on the giant branch with a deep convective envelope but before helium ignition (late case B). We find that if the mass ratio q(= M 1/M 2) < q crit = 0.7 when the primary fills its Roche lobe positive feedback will lead to a rapid hydrodynamic phase of mass transfer which will probably lead to common envelope evolution and thence to either coalescence or possibly to a close binary in a planetary nebula. Although most Algols have probably filled their Roche lobes before evolving off the main-sequence we find that some could not have and are therefore ‘moderately close’. Since rapid overflow is unlikely to lead to an Algol-like system there must be some way of avoiding it. The most likely possibility is that the primary can lose sufficient mass to reduce q below q crit before overflow begins. Ordinary mass loss rates are insufficient but evidence that enhanced mass loss does take place is provided by RS CVn systems that have inverted mass ratios but have not yet begun mass transfer. We postulate that the cause of enhanced mass loss lies in the heating of the corona by by magnetic fields maintained by an α — ω dynamo which is enhanced by tidal effects associated with corotation. In order to model the the effects of enhanced mass loss we ignore the details and adopt an empirical approach calibrating a simple formula with the RS CVn system Z Her. Using further empirical relations (deduced from detailed stellar models) that describe the evolution of red giants we have investigated the effect on a large number of systems of various initial mass ratios and periods. These are notable in that some systems can now enter a much gentler Algol-like overflow phase and others are prevented from transferring mass altogether. We have also investigated the effects of enhanced angular momentum loss induced by corotation of the wind in the strong magnetic fields and consider this in relation to observed period changes. We find that a typical ‘moderately close’ Algol-like system evolves through an RS CVn like system and then possibly a symbiotic state before becoming an Algol and then goes on through a red giant-white dwarf state which may become symbiotic before ending up as a double white dwarf system in either a close or wide orbit depending on how much mass is lost before the secondary fills its Roche lobe. 相似文献
178.
179.
A scheme is presented for the identification of naval vessels via active multiple-frequency radar interrogation. A major virtue of the described method is the use of a response waveform synthesized using amplitude data only. A prediction correlation using natural resonances associated with substructures on the vessels is applied to synthetically generated matched-filter response waveforms. The identification scheme is tested using measured model data for 8 vessels on a simulated sea surface. A correct identification probability of roughly 77 percent is obtained. 相似文献
180.
This paper describes the architecture and calibration design of the experimental ground based radar station MERIC. This full-polarimetric radar is conceived for the analysis and the recognition of non cooperative aircraft in flight.We carefully study how the full-polarimetric capability is obtained for a simultaneous transmit (simultaneous transmission of two linear FM with opposite slopes) radar system, using analogue deramping with a replica.The phase distortions of the signal propagating in the four polarimetric channels are carefully estimated. We define a phase calibrating method compatible with the outdoor measurements conditions and few constraints on reference targets.We show the phase accuracy obtained with the proposed calibration method on real measurements. 相似文献