全文获取类型
收费全文 | 14020篇 |
免费 | 1166篇 |
国内免费 | 1287篇 |
专业分类
航空 | 7489篇 |
航天技术 | 4392篇 |
综合类 | 1146篇 |
航天 | 3446篇 |
出版年
2022年 | 132篇 |
2021年 | 205篇 |
2020年 | 187篇 |
2019年 | 141篇 |
2018年 | 262篇 |
2017年 | 219篇 |
2016年 | 227篇 |
2015年 | 296篇 |
2014年 | 525篇 |
2013年 | 573篇 |
2012年 | 675篇 |
2011年 | 804篇 |
2010年 | 761篇 |
2009年 | 879篇 |
2008年 | 925篇 |
2007年 | 691篇 |
2006年 | 568篇 |
2005年 | 578篇 |
2004年 | 462篇 |
2003年 | 482篇 |
2002年 | 404篇 |
2001年 | 493篇 |
2000年 | 376篇 |
1999年 | 462篇 |
1998年 | 477篇 |
1997年 | 375篇 |
1996年 | 327篇 |
1995年 | 365篇 |
1994年 | 407篇 |
1993年 | 263篇 |
1992年 | 296篇 |
1991年 | 201篇 |
1990年 | 164篇 |
1989年 | 227篇 |
1988年 | 127篇 |
1987年 | 114篇 |
1986年 | 94篇 |
1985年 | 200篇 |
1984年 | 187篇 |
1983年 | 155篇 |
1982年 | 156篇 |
1981年 | 244篇 |
1980年 | 70篇 |
1979年 | 63篇 |
1978年 | 63篇 |
1977年 | 52篇 |
1976年 | 54篇 |
1975年 | 53篇 |
1974年 | 50篇 |
1972年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
101.
102.
D.I. Kosenko S.I. Blinnikov K.A. Postnov P. Lundqvist E.I. Sorokina 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2705-2710
Time-dependent thermal X-ray spectra are calculated from physically plausible conditions around GRB. It is shown that account for time-dependent ionization processes strongly affects the observed spectra of hot rarefied plasma. These calculations may provide an alternative explanation to the observed X-ray lines of early GRBs afterglows (such as GRB 011211). Our technique will allow one to obtain independent constraints on the GRB collimation angle and on the clumpiness of circumstellar matter. 相似文献
103.
104.
从防空导弹地面电源--热电池的热设计和工艺角度出发,分析影响电池工作寿命的因素,提出延长电池工作寿命的三条途径:合理控制热电池的内部热量;提高加热片的均匀性;合理选择外保温材料。实践证明,这些途径是可行的。 相似文献
105.
Superiority of canards in homing missiles 总被引:3,自引:0,他引:3
We suggest a first-order model to distinguish between nose control (canards) and tail control. We present optimal guidance strategies and demonstrate the superiority of nose control. This simple model enables us to develop simple and robust guidance strategies based on three approaches: unconstrained optimal control, constrained optimal control, and constrained differential games. It turns out that nose control requires low gain and is capable of forcing small miss distance in the presence of a maneuvering target. 相似文献
106.
A.G. Lyne 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2716-2720
A recent multibeam pulsar survey of the outer Galactic plane at Parkes has discovered the first-known double-pulsar binary, a very compact double neutron star system in which both stars are observable as radio pulsars. In this review, we briefly describe the discovery and the studies which have been enabled by the unique properties of the system. These range from the most precise confirmation yet of the theory of general relativity, with the possibility of even more new tests and the measurement of second-order post-Newtonian effects, to studies of the magnetospheres and emission properties of the two pulsars. The discovery also results in a significant increase in the expected rate of occurrence of the mergers of double neutron star systems, and hence the rate of detection of such events by the new ground-based gravitational wave detectors. 相似文献
107.
Liu S. Singer C.H. Dougal R.A. 《IEEE transactions on aerospace and electronic systems》2006,42(2):612-624
Electric power anomalies or disturbances can disrupt the normal operation of equipment, accelerate aging, or even cause outright failures thus resulting in increased costs of maintenance and reduced system reliability. Past research on the effects caused by power anomalies has been mostly focused on industrial, commercial, or residential systems, or on power distribution equipment. A literature survey reveals that there is no comprehensive review related to low-voltage (LV) power systems and utilization equipment applicable to military combat vehicles, such as aircraft and ships. This paper summarizes the results of a new literature survey that focused on the causes, effects, and mitigation methods for power anomalies typical of LV mobile power systems. Electric power anomaly cost data collected from the literature are also presented, from which the costs of anomalies to the national defense are estimated using some simple rationales. 相似文献
108.
H. Sakurai Y. Shouji M. Osaki T. Aoki T. Gandou W. Kato Y. Takahashi S. Gunji F. Tokanai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2492-2496
Daily Be-7 concentrations in air at the height of 15 m are continuously observed at 38°15.2′N, 140°20.9′E, between 2000 and 2001. The average concentration and the relative standard deviation were 4.0 mBq/m3 and 50% in 2000–2001, respectively. The Be-7 concentrations increased 2.5% with the decrease in the sunspot numbers by 6.7% for the term of two years. From the power spectral analysis, the periodicity of 26 days is shown for the daily Be-7 concentrations. The folding analysis indicates that the time variation of the Be-7 concentration is similar to that of the ground-based neutron counting rate, and the phase delay for the minimum portion of Be-7 concentration was roughly 8 days to the maximum sunspot number. These results indicate that the Be-7 concentrations in the air at ground level have 26 day periodicity as a component of time variations and the time variation is caused by the solar modulation of galactic cosmic rays, which corresponds to the variation of the sunspot number due to the rotation of the sun. 相似文献
109.
110.
A mathematical model of the high-latitude F-region, taking the ionospheric plasma convection into account, is used for modeling a response of the auroral F-region to irradiation by powerful high-frequency (HF) radiowaves. The model enables us to calculate the time variations in the profiles of the electron concentration, the velocity of positive ions, and the ion and electron temperatures in the part of a magnetic-flux tube moving over an artificial ionospheric heater under the action of a convective electric field. The modeling was carried out for a part of the magnetic flux tube intersecting the F-layer irradiated by the Norwegian heater at Tromsö when it is located near the midnight magnetic meridian. The calculations were made for the equinox conditions under the high solar and low geomagnetic activity. The results of our modeling show that substantial variations in the profiles of the electron temperature, the velocity of positive ions, and the electron concentration can be produced in the nighttime high-latitude F-layer due to HF heating. The perturbation caused by a 20 s rectangular pulse should exist for about 20 min at the level of the F-layer maximum. The disturbed plasma volume can leave the region irradiated by the heater and move away for over 500 km within the above-mentioned time period. 相似文献