全文获取类型
收费全文 | 18038篇 |
免费 | 37篇 |
国内免费 | 124篇 |
专业分类
航空 | 9943篇 |
航天技术 | 5259篇 |
综合类 | 241篇 |
航天 | 2756篇 |
出版年
2021年 | 155篇 |
2018年 | 220篇 |
2016年 | 166篇 |
2014年 | 433篇 |
2013年 | 514篇 |
2012年 | 425篇 |
2011年 | 595篇 |
2010年 | 422篇 |
2009年 | 772篇 |
2008年 | 813篇 |
2007年 | 388篇 |
2006年 | 424篇 |
2005年 | 398篇 |
2004年 | 431篇 |
2003年 | 515篇 |
2002年 | 467篇 |
2001年 | 570篇 |
2000年 | 351篇 |
1999年 | 453篇 |
1998年 | 420篇 |
1997年 | 315篇 |
1996年 | 364篇 |
1995年 | 432篇 |
1994年 | 406篇 |
1993年 | 355篇 |
1992年 | 306篇 |
1991年 | 249篇 |
1990年 | 234篇 |
1989年 | 381篇 |
1988年 | 202篇 |
1987年 | 235篇 |
1986年 | 224篇 |
1985年 | 639篇 |
1984年 | 514篇 |
1983年 | 406篇 |
1982年 | 486篇 |
1981年 | 610篇 |
1980年 | 244篇 |
1979年 | 188篇 |
1978年 | 189篇 |
1977年 | 146篇 |
1976年 | 156篇 |
1975年 | 186篇 |
1974年 | 180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 15 毫秒
831.
Analysis based on the state-plane diagram is given for series resonant converters operating in the frequency range 0.5 ? fs/fo ? 1.0. When the voltages and currents in the converter are normalized, design parameters take on special geometric meanings in the normalized state diagram. Examples of converter design using graphical methods are given for the cases of ? and ? control. Control characteristics of the converter operating in the continuous conduction mode are derived. The concept of the energy reflection coefficient is introduced as a measure of power transfer efficiency in the converter design. 相似文献
832.
An adaptive antenna array is defined as an antenna array whose output is the weighted sum of the signals received at the antennas, with signal-dependent automatic adjustment of the weights to optimize some criterion. This open-literature bibliography of papers on the subject is intended to provide a brief overview of the field, and the authors involved, up to the end of 1985. Papers are listed both by subject area and by sole/primary/secondary author. 相似文献
833.
This note deals with the effect of the common process noise on the fusion (combination) of the state estimates of a target based on measurements obtained by two different sensors. This problem arises in a multisensor environment where each sensor has its information processing (tracking) subsystem. In the case of an ?-? tracking filter the effect of the process noise is that, over a wide range of its variance, the uncertainty area corresponding to the fused estimates is about 70 percent of the single-sensor uncertainty area as opposed to 50 percent obtained if the dependence is ignored. 相似文献
834.
835.
836.
Andrew P. Ingersoll 《Space Science Reviews》1976,18(5-6):603-639
Current information on the neutral atmosphere of Jupiter is reviewed, with approximately equal emphasis on composition and thermal structure on the one hand, and markings and dynamics on the other. Studies based on Pioneer 10 and 11 data are used to refine the atmospheric model. Data on the interior are reviewed for the information they provide on the deep atmosphere. The markings and dynamics are discussed with emphasis on qualitative relationships and analogies with phenomena in the Earth's atmosphere.Contribution No. 2652 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, Calif. 91125, U.S.A. 相似文献
837.
Edward J. Smith 《Space Science Reviews》1976,19(4-5):661-686
A review is presented of the interplanetary magnetic field observations acquired in early August 1972 when four solar flares erupted in McMath Plage region 11976. Measurements of the interplanetary field were obtained by Earth satellites, HEOS-2 and Explorer 41, and by Pioneers 9 and 10 which, by good fortune, were radially aligned and only 45° east of the Earth-Sun direction. In response to the four flares, four interplanetary shocks were seen at Earth and at Pioneer 9, which was then at a heliocentric distance of 0.78 AU. However, at Pioneer 10, which was 2.2 AU from the Sun, only two forward shocks and one reverse shock were seen. The available magnetic field data acquired in the vicinity of the shocks are presented. Efforts to identify corresponding shocks at the several locations and to deduce their velocities of propagation between 0.8 and 2.2 AU are reviewed. The early studies were based on average velocities between the Sun and Pioneer 9, the Sun and Earth and the Sun and Pioneer 10. A large deceleration of the shocks between the Sun and 0.8 AU as well as between 0.8 and 2.2 AU was inferred. More recently the local velocities of the shocks at Pioneers 9 and 10 have become available. A comparison of these velocities shows little, if any, deceleration between 0.8 and 2.2 AU and implies that most or all of the deceleration actually occurred nearer the Sun. Evidence is also presented that shows a significant departure of the flare-generated shock fronts from spherical symmetry. 相似文献
838.
In [1] a scheme for forming a rectangular FIR filter bank is described using only a few percent of the number of multiplications required by straightforward procedures. The sidelobe level suffers degradation. Attention is drawn to a different scheme published in [2] and [3] which needs even fewer multiplications without degradationvof the sidelobe level. 相似文献
839.
This paper demonstrates and tests a new algorithm for extracting velocity information from a pulse Doppler radar signal. The system is adaptive and performs weil in the presence of target scintillation. This paper also shows a special steady-state version of the adaptive algorithm. lt is computationally attractive and produces near optimal velocity estimates. 相似文献
840.
Echoes from complex targets due to chirp waveforms show different time responses for different chirp rates, because of the ambiguity of range and radial velocity information. A graphical method is described which enables the derivation of the time response for an arbitrary chirp rate when the scattering cross-section distribution in the range and radial velocity plane is known for complex targets. The graphical method can also be used to generate an approximately realistic scattering cross-section distribution when the time responses for two different chirp rates are given. An example is shown which applies to the computer simulation of the radar echo from a waking reentry space vehicle. 相似文献