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771.
Raup DM 《Acta Astronautica》1992,26(3-4):257-261
Animals lacking humanoid intelligence have evolved systems indistinguishable in function, if not in structure, from systems built by humans. Although radio communication has never been verified in animals, it is completely feasible biologically. If such systems are present in non-intelligent organisms on other planets, then our chances of detecting life in the universe by current SETI methods are greatly enhanced. 相似文献
772.
Artur D. Chernin 《Space Science Reviews》1995,74(3-4):447-454
George Gamow (1904–1968) was a man with boundless interests and imagination that took him from relativity theory to quantum mechanics and nuclear physics, back to cosmology and then to genetics. He had made seminal contributions to these key areas of modern knowledge which ensured him an enduring place among the giants of twentieth-century science. 相似文献
773.
Lombardo P. Pastina D. Bucciarelli T. 《IEEE transactions on aerospace and electronic systems》2001,37(4):1207-1220
For pt. I see ibid., vol. 37, no. 4, pp. 1194-1206 (2001).This paper presents the derivation of a polarimetric coherent adaptive scheme to detect a radar target against a non-Gaussian background. This completes the results presented in Part I for the Gaussian background. A Texture Free-Generalized Likelihood Ratio Test (TF-GLRT) detector is derived that exploits the polarimetric characteristics of the received radar echoes to improve the detection performance. The proposed polarimetric detector is shown to have Constant False Alarm Rate (CFAR) when operating against compound-Gaussian clutter with unknown parameters. Its performance is fully characterized by both theoretical analysis and simulation. Moreover, the application to recorded radar data demonstrates the performance improvement achievable in practice 相似文献
774.
Vonbun F.O. Argentiero P.D. Schmid P.E. 《IEEE transactions on aerospace and electronic systems》1978,(6):834-842
The results are reported of the ATS-6/GEOS-3 and the ATS-6 NIMBUS-6 satellite-to-satellite orbit determination experiments. NASA intends to use the tracking data relay satellite system for operational orbit determination of NASA satellites. Hence, in the near future, satellite-to-satellite tracking data will be routinely processed to obtain orbits. The satellite-to-satellite tracking system used in the ATS-6/NIMBUS-6 and ATS-6/GEOS-3 experiments performed with a resolution of 1 to 2 m in range and less than 1 mm/s in range rate for a 10-s averaging. A Bayesian least squares estimation technique utilizing independent ranging to the synchronous relay satellite was determined to be the most effective procedure for estimating orbits from satellite-to-satellite tracking data. The use of this technique yields estimates of user satellite orbits which are comparable in accuracy to what is usually obtained from ground based systems. 相似文献
775.
E.M. Apostolov L.F. Alberca D. Pancheva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(12):47-50
In this paper we intend to enlarge the fof2 long-term prediction accuracy taking into account the systematic variations of the hysteresis and secular-time phenomena. 相似文献
776.
777.
Recent determinations of the primordial He abundance have given significantly different results. We are attempting to identify some of the causes of these differences and propose observational solutions. Here we identify a systematic difference in how the data are interpreted (differences in corrections for the presence of neutral helium) and the importance of a systematic bias towards lower derived helium abundances (underestimating the presence of underlying stellar absorption). 相似文献
778.
V. N. Oraevsky Yu. Ya. Ruzhin Kh. D. Kanonidi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(12):147-150
Here are presented experimental results concerning the registration by ground magnetometers of artificial MHD echo generated by powerful pulse current in ground loop contour. Data analysis was made of several magnetic stations for 16 experiments with giant loop-current contour giving magnetic flux 106nT/km2 (the current attained 20 kA). Only several rather weak bursts were registered which appeared 78±2s after main switch impulse. Echo signal was a few nanotesla. Taking into account real magnetosphere tube configuration for L ≈ 5,5 and Kp≤2 it was shown that the signal with such a delay corresponds to propagation of artificial excited Alfven echo, returning back from a magnetoconjugate ionospheric region. Meanwhile, the amplitude exceed by one order the theoretically calculated one. 相似文献
779.
P.S. Dobreva M.D. Kartalev D. Koitchev V.I. Keremidarska M. Kaschiev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1279-1285
This article presents some preliminary features of a new self consistent model of the system magnetosheath–magnetosphere, recently developed in the Institute of Mechanics, Sofia, Bulgaria. The flow in the magnetosheath is governed by 3D ideal gas-dynamic equations. The positions and the shapes of the bow shock and the magnetopause are calculated iteratively as a part of the solution. These surfaces are essentially three-dimensional (generally non-axially-symmetric). The self-consistency between the regions is ensured via the boundary conditions. The magnetopause cusp indentations are formed, influencing essentially the magnetosheath flow. Prediction of the position and the shape of the bow shock for different values of the sonic Mach number are derived. Distribution of some flow parameters in the magnetosheath is presented. 3D numerical finite element model, calculating the field due to the magnetopause currents for an arbitrary magnetopause geometry, is used in the magnetosphere. The fields due to the current systems inside the magnetosphere(cross-tail current, ring current, and Birkeland current) are taken from the Tsyganenko empirical model. The magnetopause surface is calculated from the requirement the outside gas-dynamic pressure to be balanced by the magnetic pressure inside. The magnetosphere model can be viewed as an improved version of the empirical model but with more realistic magnetopause form and shielding field. Not a final but a beta version is used in this approach. The final model version as well the model details will be presented elsewhere. 相似文献
780.
D. Kucharski G. Kirchner E. Cristea 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,42(8):1424-1428
Using kHz Satellite LASER Ranging (SLR) data of the SLR station Graz only, we determined the spin periods of the two ETALON satellites – launched into high orbits of about 20,000 km – and their spin period increase during 3 years. The determined spin period values and spin period increase rates at 2004-01-01 are: TET1 = 63 s + 0.484 s/year, and TET2 = 65.5 s + 0.401 s/year. 相似文献