全文获取类型
收费全文 | 2445篇 |
免费 | 16篇 |
国内免费 | 6篇 |
专业分类
航空 | 1332篇 |
航天技术 | 873篇 |
综合类 | 19篇 |
航天 | 243篇 |
出版年
2018年 | 36篇 |
2017年 | 27篇 |
2014年 | 25篇 |
2013年 | 59篇 |
2012年 | 34篇 |
2011年 | 64篇 |
2010年 | 52篇 |
2009年 | 66篇 |
2008年 | 129篇 |
2007年 | 47篇 |
2006年 | 39篇 |
2005年 | 58篇 |
2004年 | 73篇 |
2003年 | 72篇 |
2002年 | 37篇 |
2001年 | 59篇 |
2000年 | 55篇 |
1999年 | 33篇 |
1998年 | 77篇 |
1997年 | 53篇 |
1996年 | 64篇 |
1995年 | 72篇 |
1994年 | 88篇 |
1993年 | 51篇 |
1992年 | 75篇 |
1991年 | 30篇 |
1990年 | 33篇 |
1989年 | 71篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 51篇 |
1985年 | 95篇 |
1984年 | 62篇 |
1983年 | 61篇 |
1982年 | 60篇 |
1981年 | 79篇 |
1980年 | 35篇 |
1979年 | 27篇 |
1978年 | 25篇 |
1977年 | 25篇 |
1975年 | 25篇 |
1974年 | 24篇 |
1973年 | 25篇 |
1972年 | 22篇 |
1971年 | 31篇 |
1970年 | 17篇 |
1969年 | 27篇 |
1968年 | 18篇 |
1967年 | 20篇 |
1966年 | 19篇 |
排序方式: 共有2467条查询结果,搜索用时 0 毫秒
271.
T. J. -L. Courvoisier A. Orr P. Bü hler A. Zchnder R. Henneck F. Stauffacher J. Biakhowski N. Schlumpf W. Schoeps A. Mchedlishvili R. Sunyaev V. Arefev A. Yascovich G. Babalyan M. Pavlinsky J. P. Delaboudini re T. Carone O. Siegmund J. Warren D. Leahy N. Salaschenko J. Platonov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):299-302
EUVITA is a set of 8 extreme UV normal incidence imaging telescopes, each of them sensitive in a narrow band (λ/Δλ = 15 to 80), centered at wavelengths between 50 and 175 Å. Each telescope has an effective area of a few cm2; a field of view of 1.2° and a spatial resolution of 10 arcsec.
EUVITA will be flown on the Russian mission SPECTRUM X-G. This satellite will be launched in a highly eccentric orbit with a period of 4 days, allowing long, uninterrupted observations (e.g. 105 seconds). EUVITA's narrow spectral bands allow the measurement of source parameters such as temperature or power law index as well as interstellar absorption, and will resolve groups of strong lines emitted by optically thin hot plasmas. 相似文献
272.
The effect of modulation nonlinearity on the range response of FM radars with harmonic processing and ?triangle? modulation is derived. The nonlinearity may be desirable or undesirable; that is, the sidelobe level of the range response may be decreased or increased depending on the shape and amount of nonlinearity. The results of this paper may be used to predict the actual range laws of existing ?linear? FM radars; or, alternately, to specify the desired amount of modulation nonlinearity for new FM radars so that superior sidelobe suppression can be realized. 相似文献
273.
Position-Location Solutions by Taylor-Series Estimation 总被引:12,自引:0,他引:12
Taylor-series estimation gives a least-sum-squared-error solution to a set of simultaneous linearized algebraic equations. This method is useful in solving multimeasurement mixed-mode position-location problems typical of many navigational applications. While convergence is not proved, examples show that most problems do converge to the correct solution from reasonable initial guesses. The method also provides the statistical spread of the solution errors. 相似文献
274.
275.
R.Z. Sagdeev G.G. Managadze A.A. Martinson Yu.A. Romanovsky R.I. Moisya W.K. Riedler M.F. Friedrich T.G. Adeishvily S.B. Lyakhov L.S. Novikov N.A. Leonov T.I. Gagua I.I. Slyusarenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):129-140
This paper describes two rocket experiments “Aelita” with high power lithium plasma injection. The results of onboard magnetometer, massspectrometer, photometer, plasma, corpuscular and ground radar measurements are given. Dynamics and structure of plasma formation are discussed. 相似文献
276.
Scharf L.L. Harthill W.P. Moose P.H. 《IEEE transactions on aerospace and electronic systems》1969,(4):672-673
The relative merits of intercept and pure pursuit homing are investigated by comparing the expected flight times to a nonmaneuvering target. The analysis is performed for the initial target heading angle uniformly distributed with arbitrary mean and variance. Two specific examples illustrate that intercept homing holds little statistical advantage over pure pursuit homing except when the speed advantage of the missile is very small. 相似文献
277.
278.
W. Nordberg 《Space Science Reviews》1967,7(5-6):539-578
279.
Mathematical representations of a state-plane switching boundary employed in a state-trajectory control law for dc-to-dc converters are derived. Several levels of approximation to the switching boundary equations are presented, together with an evaluation of the effects of nonideal operating characteristics of converter power stage components on the shape and location of the boundary and the behavior of a system controlled by it. Digital computer simulations ions of d-to-dc converters operating in conjunction with each of these levels of control are presented and evaluated with respect to changes in transient and steady-state performance. 相似文献
280.
Harry Y. McSween Jr. David W. Mittlefehldt Andrew W. Beck Rhiannon G. Mayne Timothy J. McCoy 《Space Science Reviews》2011,163(1-4):141-174
Howardite-eucrite-diogenite (HED) meteorites, thought to be derived from 4 Vesta, provide the best sampling available for any differentiated asteroid. However, deviations in oxygen isotopic composition from a common mass-fractionation line suggest that a few eucrite-like meteorites are from other bodies, or that Vesta was not completely homogenized during differentiation. The petrology and geochemistry of HEDs provide insights into igneous processes that produced a crust composed of basalts, gabbros, and ultramafic cumulate rocks. Although most HED magmas were fractionated, it is unresolved whether some eucrites may have been primary melts. The geochemistry of HEDs indicates that bulk Vesta is depleted in volatile elements and is relatively reduced, but has chondritic refractory element abundances. The compositions of HEDs may favor a magma ocean model, but inconsistencies remain. Geochronology indicates that Vesta accreted and differentiated within the first several million years of solar system history, that magmatism continued over a span of ??10 Myr, and that its thermal history extended for perhaps 100 Myr. The protracted cooling history is probably responsible for thermal metamorphism of most HEDs. Impact chronology indicates that Vesta experienced many significant collisions, including during the late heavy bombardment. The age of the huge south pole crater is controversial, but it probably ejected Vestoids and many HEDs. Continued impacts produced a regolith composed of eucrite and diogenite fragments containing only minor exotic materials. HED meteorites serve as ground truth for orbital spectroscopic and chemical analyses by the Dawn spacecraft, and their properties are critical for instrument calibration and interpretation of Vesta??s geologic history. 相似文献