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991.
992.
2   总被引:3,自引:0,他引:3  
Configurationaerodynamicdesignconceptsareaimedatthedefinitionoffindingairframeandpropulsioncomponentgeometrieswithacontroledf...  相似文献   
993.
The use of commercial-off-the-shelf (COTS) microprocessors for safety-critical applications usually implies derating of the device to make it work in harsh environments. We discuss derating concerns for state-of-the-art microprocessors. Issues addressed herein include noise margins due to low voltage levels, multiple power supplies, frequency and current derating concerns, error sources, timing degradation, power-aware architectures, and new advanced microprocessor derating features.  相似文献   
994.
995.
ARTEMIS Science Objectives   总被引:1,自引:0,他引:1  
NASA??s two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of the Earth??s magnetotail; reconnection, particle acceleration, and turbulence in the Earth??s magnetosphere, at the bow shock, and in the solar wind; and the formation and structure of the lunar wake. Planetary topics include the lunar exosphere and its relationship to the composition of the lunar surface, the effects of electric fields on dust in the exosphere, internal structure of the Moon, and the lunar crustal magnetic field. This paper describes the expected contributions of ARTEMIS to these baseline scientific objectives.  相似文献   
996.
To establish a large deployable antenna, monitoring and collimation are essential for reliable and precise deployment. We have developed an analysis method to detect shifts in several images, in which the combination of cross-correlations between images and approximations at subpixel precision enables us to detect shifts in images with a precision of up to 0.01 pixels. The LDREX mission; which was a preliminary experiment for a large deployable antenna, ETS-VIII, was performed in December 2000. During this experiment, anomalies occurred in the antenna, and deployment was aborted. To understand the cause of the anomalies, we used our visual analysis method. Using this analysis, we detected vibrating features in the antenna, which were useful for explaining the anomalies. We outline our visual analysis method and discuss its application in monitoring the deployable antenna.  相似文献   
997.
We have investigated the effect of microgravity during spaceflight on body-wall muscle fiber size and muscle proteins in the paramyosin mutant of Caenorhabditis elegans. Both mutant and wild-type strains were subjected to 10 days of microgravity during spaceflight and compared to ground control groups. No significant change in muscle fiber size or quantity of the protein was observed in wild-type worms; where as atrophy of body-wall muscle and an increase in thick filament proteins were observed in the paramyosin mutant unc-15(e73) animals after spaceflight. We conclude that the mutant with abnormal muscle responded to microgravity by increasing the total amount of muscle protein in order to compensate for the loss of muscle function.  相似文献   
998.
    
General principles are outlined for the design of space infrared telescopes intended to cool by radiation to the lowest temperatures attainable without the use of on-board cryogens, and assuming on-orbit cooling after a warm launch. Maximum protection from solar and earth heating, maximum radiating area and efficiency and minimum absorbing area and absorptivity are the obvious basic criteria. The optimised design is a short, fat telescope surrounded by a series of radiation shields, each cooled by its own radiator. Maximising the longitudinal conductivity of the radiation shields and of the telescope tube itself is important both to the on-orbit cooling time and the final achieveable temperature. Realistic designs take between 80 and 200 days to cool to within a few degrees of equilibrium temperatures, depending on the materials used. Great advantages accrue from the use of an orbit distant from earth. Both simple models and detailed simulations suggest that temperatures of 30 to 40 K are attainable in high earth orbits. Placing a radiatively cooled telescope in a halo orbit around the Lagrangian point L2 is a particularly attractive option and significantly lower temperatures can be achieved there than in Earth orbit. Optimised radiative cooling is an important element of the small Japanese mission SMIRT. We suggest that a combination of an ESA Medium-sized Mission with a NASA Explorer to send a 2m+ telescope to an L2 halo orbit would provide a cost-effective and powerful long-duration facility for the early 21st century.  相似文献   
999.
We examined two consecutive plasma sheet oscillation and dipolarization events observed by Cluster in the magnetotail, which are associated with a pseudo-breakup and a small substorm monitored by the IMAGE spacecraft. Energy input from the solar wind and an associated enhancement of the cross-tail current lead to current sheet thinning and plasma sheet oscillations of 3–5 min periods, while the pseudo-breakups occur during the loading phase within a spatially limited area, accompanied by a localized dipolarization observed by DSP TC1 or GOES 12. That is, the so-called “growth phase” is a preferable condition for both pseudo-breakup and plasma sheet oscillations in the near-Earth magnetotail. One of the plasma sheet oscillation events occurs before the pseudo-breakup, whereas the other takes place after pseudo-breakup. Thus there is no causal relationship between the plasma sheet oscillation events and pseudo-breakup. As for the contribution to the subsequent small substorm, the onset of the small substorm took place where the preceding plasma sheet oscillations can reach the region.  相似文献   
1000.
The problem of the post-buckling behavior of the supported cylindrical panel under uniform axial compression is solved. The cylindrical supported panel is considered as a beam on the Winkler elastic foundation, the stiffness coefficient of which is calculated at the known value of buckling load. The criteria for post-buckling estimation are introduced, namely, vanishing of the determinant of the resolving system of equations and going to infinity of the deflection and strain energy in the implementation of post buckling. A good agreement of the post-buckling load obtained in this work with the experimental results is shown.  相似文献   
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