全文获取类型
收费全文 | 14019篇 |
免费 | 10119篇 |
国内免费 | 2265篇 |
专业分类
航空 | 20597篇 |
航天技术 | 1885篇 |
综合类 | 632篇 |
航天 | 3289篇 |
出版年
2024年 | 149篇 |
2023年 | 298篇 |
2022年 | 615篇 |
2021年 | 687篇 |
2020年 | 773篇 |
2019年 | 1348篇 |
2018年 | 1499篇 |
2017年 | 1478篇 |
2016年 | 1432篇 |
2015年 | 1422篇 |
2014年 | 1312篇 |
2013年 | 1345篇 |
2012年 | 1356篇 |
2011年 | 1328篇 |
2010年 | 1274篇 |
2009年 | 1329篇 |
2008年 | 1141篇 |
2007年 | 968篇 |
2006年 | 850篇 |
2005年 | 589篇 |
2004年 | 547篇 |
2003年 | 442篇 |
2002年 | 477篇 |
2001年 | 385篇 |
2000年 | 346篇 |
1999年 | 358篇 |
1998年 | 269篇 |
1997年 | 236篇 |
1996年 | 188篇 |
1995年 | 160篇 |
1994年 | 172篇 |
1993年 | 215篇 |
1992年 | 153篇 |
1991年 | 323篇 |
1990年 | 274篇 |
1989年 | 304篇 |
1988年 | 215篇 |
1987年 | 92篇 |
1986年 | 38篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1962年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
H. Thiemann R. W. Schunk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(12):143-146
Heavy emission caused by impacting plasma ions results in a fast discharging effect of the initially large surface potentials on the dielectric solar cells. This eventually counteracts the energization process of the plasma ions to the cover glasses and leaves no significant electric fields. Thus, with an existing thermal plasma, electrons are again able to reach dielectric surfaces. Strong localized electric fields of the order of several 10 kV/cm form near the interconnector-cover glass interface. 相似文献
12.
针对中国加入WTO对航空货物运输的影响,从溢出效应、竞争、辅助市场的开放、市场准入、管理、WTO规则和机制6个方面进行了分析。强调要全面和发展地看待WTO给航空货物运输带来的影响,以及要更加注重掌握WTO的规则和机制,才能更好地理解WTO对航空货物运输企业经营环境和约束条件的影响。 相似文献
13.
T. J. Ponman A. M. Read 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):361-364
Using data from the Wide Field Camera EUV all-sky survey, we have established upper limits to the EUV flux from a sample of 30 bright, nearby, non-active spiral galaxies. These galaxies were chosen to be those most likely to be detected in the EUV on the basis of (i) low interstellar absorption within our own galaxy, (ii) brightness in other wavebands, (iii) high star formation activity, and (iv) proximity. The derived EUV upper limits are restrictive, and establish for the first time that the EUV flux escaping from galaxies does not constitute a major component of their bolometric luminosity, and in particular that it cannot be the sink for the energy injected into the interstellar medium by supernova explosions, as had been suggested following the failure to detect this power in the X-ray band. 相似文献
14.
15.
The authors present a new scientific space mission consisting of a satellite carrying a receiving- only SAR which receives the signal transmitted by the ENVISAT-1 SAR. The integration of ENVISAT-1 SAR and bistatic radar data offers an improved potentiality of surface classification, three-dimensional observation, and the opportunity of advanced scientific experiments in the field of bistatic scattering. The small satellite nominal orbit and the attitude manoeuvres are designed in order to maintain an adequate overlap between the two radar swaths along the whole orbit, taking into account the ENVISAT-1 attitude and pointing. A preliminary satellite design (2-year lifetime) is then performed to evaluate the orbit decay and to determine the appropriate orbit manoeuvres (every 4 days) to control the satellites relative phase. The numerical simulation shows that a spacecraft of about 584kg is able to meet the mission requirements. 相似文献
16.
本文主要对固定资产税金计算中存在的问题入手,继而阐述固定资产各种交易中所涉及的税种以及税金的计算步骤,目的在于揭示固定资产具体税种税金计算的过程。 相似文献
17.
In extension to common applications such as groundtrack displays and antenna steering, the SGP4 orbit model is proposed for operational orbit determination in small satellite missions. SGP4 is an analytical orbit model for Low-Earth orbiting satellites that is widely used for the propagation of NORAD twoline elements. Twoline elements may hence be generated completely independent of NORAD. Their use as exclusive source of orbital information simplifies the operations concept and reduces mission costs through the extensive use of existing low-cost mission support software. Due to small computer resource requirements of 8–10kByte, the SGP4 model may also be applied for onboard orbit computations making use of e.g. a 80186 processor, thus ensuring full compatibility of ground-based and onboard operations. The proposed approach is particularly suited in combination with a space-borne GPS receiver, were the C/A-code navigation solutions are treated as measurements that are adjusted in a least-squares sense using the SGP4 model. As consequence, inherent drawbacks of the pure navigation solutions such as data gaps and scatter as well as limited velocity accuracy are avoided, while the operational navigation activities are kept at a minimum. The feasibility of the concept is illustrated based on real GPS navigation data from the TOPEX/Poseidon and the MIR space station with an inherent data quality of 50–100 m. It is shown that 3 hours of data within a 4 day period are sufficient to keep the position error within 4 km, that is considered sufficient for most applications. 相似文献
18.
19.
随机抽取广州市2 905家企业人事经理的管理信念、劳动关系和谐度、企业经济绩效和非经济绩效的问卷调查数据进行多重回归,检验中介效应,并比较守法企业与非守法企业的差异.结果发现:(1)守法企业与非守法企业在管理信念、劳动关系和谐度、企业经济绩效和非经济绩效的表现上均存在极其显著的差异;(2)管理信念对企业经济绩效和非经济绩效都有正向性的影响;(3)企业的劳动关系和谐度发挥积极的中介作用. 相似文献
20.
文章阐述RFID物流配送系统的构成及其信息处理过程,探讨RFID电子标签在物流配送全过程中的信息识别作用,提出了RFID技术在现代物流配送中的一种新型应用模型和方法。 相似文献