全文获取类型
收费全文 | 17350篇 |
免费 | 50篇 |
国内免费 | 121篇 |
专业分类
航空 | 9752篇 |
航天技术 | 5052篇 |
综合类 | 247篇 |
航天 | 2470篇 |
出版年
2021年 | 158篇 |
2018年 | 169篇 |
2016年 | 151篇 |
2014年 | 434篇 |
2013年 | 515篇 |
2012年 | 400篇 |
2011年 | 554篇 |
2010年 | 386篇 |
2009年 | 746篇 |
2008年 | 774篇 |
2007年 | 344篇 |
2006年 | 417篇 |
2005年 | 357篇 |
2004年 | 408篇 |
2003年 | 476篇 |
2002年 | 456篇 |
2001年 | 535篇 |
2000年 | 345篇 |
1999年 | 440篇 |
1998年 | 397篇 |
1997年 | 299篇 |
1996年 | 345篇 |
1995年 | 413篇 |
1994年 | 376篇 |
1993年 | 351篇 |
1992年 | 276篇 |
1991年 | 249篇 |
1990年 | 232篇 |
1989年 | 374篇 |
1988年 | 201篇 |
1987年 | 230篇 |
1986年 | 226篇 |
1985年 | 636篇 |
1984年 | 511篇 |
1983年 | 398篇 |
1982年 | 485篇 |
1981年 | 608篇 |
1980年 | 243篇 |
1979年 | 184篇 |
1978年 | 189篇 |
1977年 | 144篇 |
1976年 | 156篇 |
1975年 | 184篇 |
1974年 | 181篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
1970年 | 143篇 |
1969年 | 147篇 |
1967年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
As commercial technology has become more embedded in the military community, there have been attendant effects caused by the rapid progress in technology and by obsolescence. Industry has generated many solutions to mitigate these effects, but their limitations are emerging with time. This is a discussion of higher-level approaches to obsolescence solutions and technology insertion problems that have not hitherto been addressed. 相似文献
152.
Khan M.H. Le-Ngoc T. Bhargava V.K. 《IEEE transactions on aerospace and electronic systems》1985,(4):547-558
Two hybrid schemes of time-frequency resource sharing to increase the rain margin of Ku-and Ka-band satellite systems are proposed. Scheme 1 requires sharing a small pool of bandwidth for adaptive forward error control coding, sharing a small pool of time frame for rate reduction, and sharing a portion of low frequency time-division multiple access (TDMA) back-up frame for downlink transmission to the rain affected stations. Scheme 2 utilizes variable rate modulation and forward error correction, shares a small pool of time frame for rate reduction, and shares a portion of low frequency TDMA back-up frame. Effective usable capacities of the system using these schemes are calculated. Distribution of resources in order to maximize the effective usable capacity is also analyzed. The results obtained are compared with other adaptive schemes. Preliminary analysis shows that the utilized capacity of scheme 1 exceeds 99 percent of the effective usable capacity possible if it never rains for an outage of 0.05 percent and fade margin of 2.5 dB. For scheme 2 similar performance is achievable at a fade margin of 1.5 dB. For higher outage objectives the loss of effective utilized capacity is higher for scheme 2. 相似文献
153.
Kottaras G. Sarris E. Paschalidis B. Stamatopoulos N. Paschalidis N. 《IEEE transactions on aerospace and electronic systems》2004,40(3):862-878
Several design and testing aspects of the TRIO smart sensor data acquisition chip, developed by JHU/APL for NASA spacecraft applications are presented. TRIO includes a 10 bit self-corrected analog-to-digital converter (ADC), 16/32 analog inputs, a front end multiplexer with selectable aquisition time, a current source, memory, serial and parallel bus, and control logic. So far TRIO is used in many missions including Contour, Messenger, Stereo, Pluto, and the generic JPL X2000 spacecraft bus. 相似文献
154.
K. Jahoda 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):231-240
A more appropriate title for this talk would have been “Measurements of Large Scale Structure from X-ray Background Fluctuations”. While it has long been recognized that the X-ray Background (XRB) is primarily of a cosmological origin (with z < a few), it has recently become apparent that surface brightness fluctuations in the surveys of the XRB can be used to trace the distribution of matter in much the same way as complete catalogs of individual objects. The distance which is probed is related to the angular resolution of the detector; for the HEAO-1 A2 experiment, which provides the best all-sky data base for the XRB in the 2–20 keV band, the effective depth is a few 100 Mpc. 相似文献
155.
H. Awaki K. Koyama 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):221-230
We observed twenty-eight Seyfert 2 galaxies with the Japanese X-ray satellite, Ginga, and found Seyfert 2 galaxies, in general, have the X-ray spectral characteristics of obscured Seyfert 1 nuclei. This result agrees with the predictions from Unified Seyfert model proposed by Antonucci and Miller /1/. However, among the observed Seyfert 2 galaxies, there are a few galaxies with no evidence of an obscuration, contrary to the general predictions of the unified model. We note that type 2 AGN will contribute to the Cosmic Diffuse X-ray Background, if the unified Seyfert model can be extended to the far distant AGN such as quasars. 相似文献
156.
The force exerted by the solar radiation, though very small in magnitude, produces significant effects, especially in the case of high altitude satellites. The solar radiation pressure represents one freely available environmental force that may be put to use for various purposes. This may lead to enhancement of the life of the satellite since it consumes a very nominal amount of on-board energy. The advantages offered by the solar radiation pressure have drawn the attention of several researchers. Various controllers were proposed for many space missions, particularly for attitude control and stabilization of satellites. A controller for achieving large angle pitch attitude maneuver is described. The proposed control law is very simple in its form and requires a minimum number of on-board computations. Varieties of cases are tried and the effect of various parameters is studied 相似文献
157.
V. Koblik E. Polyakhova L. Sokolov A. Shmyrov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,29(12):4431-2088
We present results of numerical simulations of trajectories of a space probe with a flat solar sail which moves from a circular Earth orbit to near-Sun regions. We consider the upper limit of the sail temperature as the basic restriction. We also examine the planar (ecliptic) solar sail transfer with gravity-assist flybys around planets. 相似文献
158.
D. L. Judge H. S. Ogawa D. R. McMullin P. Gangopadhyay J. M. Pap 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,29(12):502-1968
The SOHO Solar EUV Monitor has been in operation since December 1995 onboard the SOHO spacecraft. This instrument is a highly stable transmission grating solar extreme ultraviolet spectrometer. It has made nearly continuous full disk solar irradiance measurements both within an 8 nm bandpass centered at 30.4 nm and throughout the 0.1 to 50 nm solar flux region since launch. The 30.4 nm flux, the 0.1 to 50 nm flux and the extracted soft X-ray (0.1 to 5 nm) flux are presented and compared with the behavior of solar proxies. 相似文献
159.
A data fusion model consisting of several levels of parallel decision fusions is considered. Global optimization of such a model is discussed to obtain the fusion rules for overall optimal performance. The reliability analysis of the proposed model is carried out to establish its superiority over the existing parallel and serial fusion models 相似文献
160.
Geoffrey E. Perry 《Space Policy》1989,5(4):279-287
For many years the world-famous Kettering Group of amateur satellite observers have confounded many more ‘official’ organization with their accucary in tracking Soviet space launches. In this article the group's founder, Geoffrey E. Perry, MBE, presents his personal perspective on current developments in the Soviet space programme. The USSR's increased openness about non-sensitive issues is to be welcomed, he concludes, but the Kettering Group has work to do yet. 相似文献