全文获取类型
收费全文 | 5863篇 |
免费 | 14篇 |
国内免费 | 18篇 |
专业分类
航空 | 2832篇 |
航天技术 | 2032篇 |
综合类 | 191篇 |
航天 | 840篇 |
出版年
2019年 | 35篇 |
2018年 | 87篇 |
2017年 | 44篇 |
2016年 | 49篇 |
2014年 | 109篇 |
2013年 | 142篇 |
2012年 | 122篇 |
2011年 | 199篇 |
2010年 | 140篇 |
2009年 | 226篇 |
2008年 | 296篇 |
2007年 | 153篇 |
2006年 | 125篇 |
2005年 | 148篇 |
2004年 | 148篇 |
2003年 | 180篇 |
2002年 | 204篇 |
2001年 | 239篇 |
2000年 | 91篇 |
1999年 | 149篇 |
1998年 | 174篇 |
1997年 | 130篇 |
1996年 | 174篇 |
1995年 | 208篇 |
1994年 | 165篇 |
1993年 | 109篇 |
1992年 | 157篇 |
1991年 | 69篇 |
1990年 | 59篇 |
1989年 | 135篇 |
1988年 | 54篇 |
1987年 | 50篇 |
1986年 | 57篇 |
1985年 | 185篇 |
1984年 | 170篇 |
1983年 | 106篇 |
1982年 | 153篇 |
1981年 | 171篇 |
1980年 | 57篇 |
1979年 | 53篇 |
1978年 | 47篇 |
1977年 | 40篇 |
1976年 | 34篇 |
1975年 | 51篇 |
1974年 | 45篇 |
1973年 | 31篇 |
1972年 | 44篇 |
1971年 | 36篇 |
1970年 | 33篇 |
1969年 | 39篇 |
排序方式: 共有5895条查询结果,搜索用时 8 毫秒
111.
A new current injected equivalent circuit approach (CIECA) to modeling switching dc-dc converter power stages is developed, which starts with the current injected approach and results in either a set of equations which completely describe input and out-put properties or an equivalent linear circuit model valid at small signal, low frequency levels. This approach to modeling switching dc-dc converter power stages has the merits but not the demerits of both the electronic equivalent circuit state space average approach and the current injected control type approach, namely, 1) the modeling is very clear and is simple whether the converter operates in continuous or discontinuous inductor conduction modes, 2) the modeling results in an equivalent circuit which is very close to the actual converter, and 3) the equivalent circuit can be used directly in the computer for theoretical predictions like SPICE, etc. 相似文献
112.
C. G. Page 《Space Science Reviews》1985,40(3-4):387-390
The EXOSAT Medium Energy instrument has been used with the new HER6 mode to study the rapid variability of Cygnus X-1. It was found that the fluctuations in the higher energy band (5–14 keV) lagged behind those in the lower band (2–5 keV) by about 6 milliseconds. This confirms predictions of the inverse Compton model and gives an upper limit to the scale-size of the hot gas clouds. 相似文献
113.
114.
115.
In general, circuit reliability can be enhanced by either incorporating redundancy or by minimizing a circuits component count. Conventional nonregulating converters generally require two active devices, whereas in regulating converters or switching regulators as many as 10 transistors, either integrated or discrete, is not uncommon. A regulating dc-to-dc converter which provides useful regulation and which can be constructed with either two or three transistors is described. 相似文献
116.
A study of the effect of observation errors on the best least squares estimate of satellite attitude based on two sets of direction measurements, where one set contains two independent measurements which are corrupted by zero-mean normally distributed additive errors, is summarized. Using Monte-Carlo techniques, the statistics of the estimated rotation of the satellite, from a known reference, were obtained. It was found that one of the parameterizations of the rotation, namely, the vector z, is best suited for estimation, since ?z is normally distributed with zero mean and its standard deviation is independent of the two direction measurements. 相似文献
117.
The Discrete Address Beacon System (DABS) is scheduled to replace the Air Traffic Control Beacon System (ATCRBS) as the prime sensing tool for air traffic control in the 1980's. The design of DABS requires knowledge of the tracking accuracy obtainable as a function of various system parameters. In particular, the potential value of air-to-ground telemetry of turn-rate data and its effect on intermittent positive control (IPC) must be assessed. The design of DABS tracking algorithms is discussed, and the results obtained with a Kalman tracker simulation are given. The major finding is that turn-rate telemetry of moderate accuracy can improve tracking by a factor of 6 to 10. 相似文献
118.
Two new methods of landmark navigation were recently presented. The landmarks are assumed to be within sight of the navigator but with unknown positions. Both methods require computations which are time consuming when a computer is not available. This correspondence presents the concept of a new navigation device called ?landmark navigation rule? which eliminates all the computation effort required in both new methods. The device is simple in construction, lightweight, and consumes no power. 相似文献
119.
120.
Flutter and time errors are critical factors in all instrumentation recording. This paper presents analytically the relationship between flutter, time base error, and time base error difference (sometimes called jitter), and the effects of these factors on direct and FM recording. Methods of measuring these quantities are discussed and experimental examples are given. Finally, a measurement method for the interchannel time error is presented, and some trends of correlation among all channels are discussed. 相似文献