全文获取类型
| 收费全文 | 8579篇 |
| 免费 | 36篇 |
| 国内免费 | 23篇 |
专业分类
| 航空 | 3939篇 |
| 航天技术 | 3053篇 |
| 综合类 | 29篇 |
| 航天 | 1617篇 |
出版年
| 2021年 | 81篇 |
| 2019年 | 56篇 |
| 2018年 | 172篇 |
| 2017年 | 115篇 |
| 2016年 | 117篇 |
| 2015年 | 53篇 |
| 2014年 | 205篇 |
| 2013年 | 256篇 |
| 2012年 | 239篇 |
| 2011年 | 366篇 |
| 2010年 | 263篇 |
| 2009年 | 392篇 |
| 2008年 | 451篇 |
| 2007年 | 247篇 |
| 2006年 | 190篇 |
| 2005年 | 219篇 |
| 2004年 | 222篇 |
| 2003年 | 262篇 |
| 2002年 | 183篇 |
| 2001年 | 265篇 |
| 2000年 | 161篇 |
| 1999年 | 208篇 |
| 1998年 | 240篇 |
| 1997年 | 138篇 |
| 1996年 | 214篇 |
| 1995年 | 246篇 |
| 1994年 | 247篇 |
| 1993年 | 152篇 |
| 1992年 | 187篇 |
| 1991年 | 70篇 |
| 1990年 | 72篇 |
| 1989年 | 195篇 |
| 1988年 | 83篇 |
| 1987年 | 81篇 |
| 1986年 | 85篇 |
| 1985年 | 254篇 |
| 1984年 | 188篇 |
| 1983年 | 154篇 |
| 1982年 | 159篇 |
| 1981年 | 289篇 |
| 1980年 | 79篇 |
| 1979年 | 67篇 |
| 1978年 | 66篇 |
| 1977年 | 58篇 |
| 1975年 | 76篇 |
| 1974年 | 53篇 |
| 1973年 | 49篇 |
| 1972年 | 49篇 |
| 1970年 | 55篇 |
| 1969年 | 48篇 |
排序方式： 共有8638条查询结果，搜索用时 15 毫秒
561.
Tether Satellite System Collision Study 总被引：1，自引：0，他引：1
A study was performed to determine the probability of collision with resident space objects and untrackable debris for the tether component of the Tethered Satellite System (TSS) after it broke away from the Space Shuttle orbiter (mission STS-75) in February 1996. Both an analytical and a numerical approach were used in this study, and the results obtained with these two methods were found to be in good agreement. These results show that the deployed tether is expected to have been impacted by several particles 0.1mm or larger in size. The probability of collision with objects 10cm in size or larger was on the order of 10–3 per month. Since the severed tether reentered within one month after deployment, the collision hazard to other objects while in orbit was small. The analytical methods used in this study are useful for tether collision evaluations in general. 相似文献
562.
B.A. Conway 《Acta Astronautica》1983,10(8):581-584
The lunar orbit is presently expanding due, we believe, to tidal friction, i.e. the attraction of the moon for the tides it raises on the rotating Earth. The Moon may therefore have been significantly closer to the Earth in the distant past, a point of great interest to those studying the lunar origin. This work presents the results of the integration of the equations which govern the rates of change of the lunar orbit elements and the angular momentum of the Earth. Results are presented for both the past and future of the Earth-Moon system. 相似文献
563.
A problem of determining a shape of the airfoil being streamlined by a potential incompressible inviscid flow is solved by the successive approximation method using a specified chord velocity diagram. It is shown that a closed airfoil that possesses a specified chord velocity diagram can be constructed with a sufficient accuracy; if the chord diagram is unsuccessfully specified, the closed airfoil may prove to be not univalent, that is, physically unrealizable. 相似文献
564.
565.
566.
567.
This paper analyzes the state of the ionosphere during two geomagnetic storms of a different intensity evolving in different sectors of local time in different seasons. There were used the data from a network of ionospheric stations located in the opposite longitudinal sectors of 80°-150° E and 250°-310° E.This analysis has permitted us to conclude that the detected differences in the variations of the disturbances are likely to be determined by the local time difference of the geomagnetic storm development, its intensity and by the different illumination conditions of the ionosphere. 相似文献
568.
The general differential equations for the circuits of a homopolar inductor alternator are established. The system of equations is modified for the case of nonsymmetrical subtransient operation. The Runge-Kutta and Adams-Moulton methods are used to solve the system of differential equations with variable coefficients. The solution is obtained for different initial conditions. Several damper winding designs are analyzed. A step-by-step correction method in the time domain is used to improve the approximate initial value of the subtransient reactance. This method takes care of saturation, which changes greatly during a subtransient. The analysis of the most advantageous design of the axial damper winding located in the armature slots is given in this paper. All calculations were carried out for the same alternator as used in the companion paper [1]. 相似文献
569.
A. Hovhannisyan A. Chilingarian 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Particle detectors of worldwide networks are continuously measuring various secondary particle fluxes incident on Earth surface. At the Aragats Space Environmental Center (ASEC), the data of 12 cosmic ray particle detectors with a total of ∼280 measuring channels (count rates of electrons, muons and neutrons channels) are sent each minute via wireless bridges to a MySQL database. These time series are used for the different tasks of off-line physical analysis and for online forewarning services. Usually long time series contain several types of errors (gaps due to failures of high or low voltage power supply, spurious spikes due to radio interferences, abrupt changes of mean values of several channels or/and slowly trends in mean values due to aging of electronics components, etc.). To avoid erroneous physical inference and false alarms of alerting systems we introduce offline and online filters to “purify” multiple time-series. In the presented paper we classify possible mistakes in time series and introduce median filtering algorithms for online and off-line “purification” of multiple time-series. 相似文献
570.
A review of some of the underlying reasons for crime is presented, together with a perspective-setting view of the present status of crime in the United States. A statistical analysis of the number of repeaters is presented as the basis for a crime control system consisting of a transponder carried by each convicted person after he is released from confinement. Real-time tracking of these transponders is done by a computer-radio system; when a crime is committed a quick check shows at least who was not involved. Countermeasures and some social implications are also covered. 相似文献