全文获取类型
收费全文 | 5149篇 |
免费 | 16篇 |
国内免费 | 15篇 |
专业分类
航空 | 2235篇 |
航天技术 | 1694篇 |
综合类 | 26篇 |
航天 | 1225篇 |
出版年
2021年 | 51篇 |
2019年 | 25篇 |
2018年 | 195篇 |
2017年 | 145篇 |
2016年 | 125篇 |
2015年 | 51篇 |
2014年 | 145篇 |
2013年 | 175篇 |
2012年 | 156篇 |
2011年 | 237篇 |
2010年 | 175篇 |
2009年 | 265篇 |
2008年 | 267篇 |
2007年 | 162篇 |
2006年 | 105篇 |
2005年 | 150篇 |
2004年 | 147篇 |
2003年 | 164篇 |
2002年 | 112篇 |
2001年 | 159篇 |
2000年 | 72篇 |
1999年 | 91篇 |
1998年 | 117篇 |
1997年 | 80篇 |
1996年 | 103篇 |
1995年 | 148篇 |
1994年 | 108篇 |
1993年 | 75篇 |
1992年 | 100篇 |
1991年 | 39篇 |
1990年 | 38篇 |
1989年 | 84篇 |
1988年 | 33篇 |
1987年 | 36篇 |
1986年 | 35篇 |
1985年 | 141篇 |
1984年 | 105篇 |
1983年 | 93篇 |
1982年 | 96篇 |
1981年 | 142篇 |
1980年 | 43篇 |
1979年 | 42篇 |
1978年 | 37篇 |
1977年 | 39篇 |
1976年 | 32篇 |
1975年 | 29篇 |
1974年 | 29篇 |
1972年 | 27篇 |
1970年 | 22篇 |
1969年 | 24篇 |
排序方式: 共有5180条查询结果,搜索用时 15 毫秒
1.
2.
Minakshi Devi S. Patgiri A.K. Barbara Koh-Ichiro Oyama K. Ryu V. Depuev A. Depueva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(6):1444-1455
The earthquake (EQ) time coupling processes between equator-low-mid latitude ionosphere are complex due to inherent dynamical status of each latitudinal zone and qualified geomagnetic roles working in the system. In an attempt to identify such process, the paper presents temporal and latitudinal variations of ionization density (foF2) covering 45°N to 35°S, during a number of earthquake events (M?>?5.5). The approaches adopted for extraction of features by the earthquake induced preparatory processes are discussed in the paper through identification of parameters like the ‘EQ time modification in density gradient’ defined by δ?=?(foF2 max???foF2 min)∕τmm, where τmm – time span (in days) between EQ modified density maximum and minimum, and the Earthquake time Equatorial Anomaly, i.e. EEA, one of the most significant phenomenon which develops even during night time irrespective of epicenter position. Based on the observations, the paper presents the seismic time coupling dynamics through anomaly like manifestations between equator, low and mid latitude ionosphere bringing in the global Total Electron Content (TEC) features as supporting indices. 相似文献
3.
Giulio L. Marco B. Aldo F. Domenico T.P. Mario M. 《Aerospace and Electronic Systems Magazine, IEEE》2002,17(9):22-27
This paper reviews the results of the thermal and static analysis of small motor aerospace technology (SMART) propulsion system, constituted of a microthrusters array realised by MEMS technology on silicon wafers. This system has been studied using FEM (NASTRAN) and the results have been verified by the electro-thermic analogy and the FDM method, using, respectively, SPICE and MATLAB codes. The simulation results demonstrated the feasibility of SMART systems for aerospace applications such as attitude control and deorbiting missions for small satellite station-keeping. A theoretical impulse of 20 mNs has been calculated for the SMART system. 相似文献
4.
A review of common switching techniques for dc/dc power conversion is presented. The evolution of the forward converter is discussed, leading naturally to the introduction of the double forward converter. Technical details for a series of radiation-hardened converters are then provided. This series was designed for space power management and distribution (PMAD) applications. The successful development of the PMAD converter demonstrated the viability of high voltage bus. 相似文献
5.
Significant advances in and applications of battery technology are outlined. Factors driving future developments are identified 相似文献
6.
7.
8.
S I Bartsev V V Mezhevikin V A Okhonin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):201-204
Any attempt to create LSS for practical applications must take into account the possibility of castastrophic consequences if the problem of LSS reliability and stability is not solved. An integrated conception of CELSS studies development as a possible way to increase its reliability is considered. The BIOS-4 facility project is developed in the context of the conception. Three principles of highly effective experimental CELSS facility design are proposed. Some details of BIOS-4 design and its exploitation features are presented. 相似文献
9.
K Eguchi-Kasai M Murakami H Itsukaichi K Fukutsu T Kanai Y Furusawa K Sato H Ohara F Yatagai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):109-118
It can be noted that it is not simple double strand breaks (dsb) but the non-reparable breaks that are associated with high biological effectiveness in the cell killing effect for high LET radiation. Here, we have examined the effectiveness of fast neutrons and low (initial energy = 12 MeV/u) or high (135 MeV/u) energy charged particles on cell death in 19 mammalian cell lines including radiosensitive mutants. Some of the radiosensitive lines were deficient in DNA dsb repair such as LX830, M10, V3, and L5178Y-S cells and showed lower values of relative biological effectiveness (RBE) for fast neutrons if compared with their parent cell lines. The other lines of human ataxia-telangiectasia fibroblasts, irs 1, irs 2, irs 3 and irs1SF cells, which were also radiosensitive but known as proficient in dsb repair, showed moderated RBEs. Dsb repair deficient mutants showed low RBE values for heavy ions. These experimental findings suggest that the DNA repair system does not play a major role against the attack of high linear energy transfer (LET) radiations. Therefore, we hypothesize that a main cause of cell death induced by high LET radiations is due to non-reparable dsb, which are produced at a higher rate compared to low LET radiations. 相似文献
10.
D F Smart M A Shea 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(2):113-116
We find that the heliolongitudinal distribution of solar flares associated with earth-observed solar proton events is a function of the particle measurement energy. For solar proton events containing fluxes with energies exceeding 1 GeV, we find a Gaussian distribution about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun. This distribution is modified as the detection threshold is lowered. For > 100 MeV solar proton events with fluxes > or = 10 protons (cm2-sec-ster)-1 we find the distribution becomes wider with a secondary peak near the solar central meridian. When the threshold is lowered to 10 MeV the distribution further evolves. For > 10 MeV solar proton events having a flux threshold at 10 protons (cm2-sec-ster)-1 the distribution can be considered to be a composite of two Gaussians. One distribution is centered about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun, and the other is centered about the solar central meridian. For large flux solar proton events, those with flux threshold of 1000 (cm2-sec-ster)-1 at energies > 10 MeV, we find the distribution is rather flat for about 40 degrees either side of central meridian. 相似文献