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911.
Harry O. Ruppe 《Space Policy》1987,3(2)
Fearing that mistaken decisions may be made, the author offers his comments to clarify the future possibilities for Ariane, Hermes and Columbus. The decisions soon to be taken on the manned spaceflight programme will affect the future of the entire European space programme. The possibilities for air-breathing propulsion are also reviewed. 相似文献
912.
C. Murakami Y. Ohkami O. Okamoto A. Nakajima M. Inoue J. Tsuchiya K. Yabu-uchi S. Akishita T. Kida 《Acta Astronautica》1984,11(9):613-619
A new type of magnetically suspended gimbal momentum wheel utilizing permanent magnets is described. The bearing was composed of four independent thrust actuators which control the rotor thrust position and gimbal angles cooperatively, so that the bearing comes to have a simple mechanism with high reliability and light weight. The high speed instability problem due to the internal damping was easily overcome by introducing anisotropic radial stiffness. A momentum flywheel with the 3-axis controlled magnetic bearing displays good performance for attitude control of satellite with biased momentum. 相似文献
913.
O. M. Alifanov S. A. Budnik A. V. Nenarokomov D. M. Titov 《Russian Aeronautics (Iz VUZ)》2016,59(4):548-553
This paper is devoted to the development of heat transfer models that are adequate to the real processes by using the experimental and computational methodology based on the theory of inverse heat transfer problems. 相似文献
914.
Biological dosimetry in Russian and Italian astronauts. 总被引:1,自引:0,他引:1
O Greco M Durante G Gialanella G Grossi M Pugliese P Scampoli G Snigiryova G Obe 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(6):1495-1503
Large uncertainties are associated with estimates of equivalent dose and cancer risk for crews of long-term space missions. Biological dosimetry in astronauts is emerging as a useful technique to compare predictions based on quality factors and risk coefficients with actual measurements of biological damage in-flight. In the present study, chromosomal aberrations were analyzed in one Italian and eight Russian cosmonauts following missions of different duration on the MIR and the international space station (ISS). We used the technique of fluorescence in situ hybridization (FISH) to visualize translocations in chromosomes 1 and 2. In some cases, an increase in chromosome damage was observed after flight, but no correlation could be found between chromosome damage and flight history, in terms of number of flights at the time of sampling, duration in space and extra-vehicular activity. Blood samples from one of the cosmonauts were exposed in vitro to 6 MeV X-rays both before and after the flight. An enhancement in radiosensitivity induced by the spaceflight was observed. 相似文献
915.
P.O. Petrucci J. Ferreira G. Henri L. Sauge G. Pelletier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2909-2911
We present a unified accretion–ejection picture that explains the different spectral state of Black Hole X-ray binaries (BHXrB) from radio to X/γ-rays. In this view, the central region of BHXrB has a multi-flow configuration which consists in (1) an outer standard accretion disc, (2) an inner magnetized accretion disc driving, (3) a self-collimated electron–proton MHD jet, surrounding and (4) a relativistic electron–positron beam when adequate conditions are met. This picture provides a simple and unified explanation to the various canonical spectral states of BH X-ray binaries, by varying the transition radius rJ between the inner disc driving jets and the outer standard disc. In this framework, large rJ correspond to Quiescent and Hard states while small rJ correspond to Thermal Dominant ones. In between these two extremes, rJ can reach values that switches on the pair cascade process giving birth to a relativistic electron–positron beam. This would correspond to the bright intermediate state. 相似文献
916.
In September 1995, NASA-Goddard held a workshop on low-cost access to space for science missions. The workshop provided briefings on balloons, sounding rockets, Shuttle payloads, and low-cost free-flyer concepts, to provide options of getting experiments into space. This report is the result of a panel session organized with the aim of generating new ideas beyond those presented in the workshop. In addition to the authors, Orlando Figueroa and Paul Ondrus of NASA-Goddard and Richard Zwirnbaum of Computer Sciences Corp. participated in the discussions. The ideas presented do not necessarily reflect the current thinking of NASA managers. Although the panel discussion was focused on the kinds of science missions usually funded by NASA, most of the ideas that were generated are relevant to military and commercial missions as well. 相似文献
917.
In this study, in-plane mixed mode-I/II fatigue crack growth simulations and experiments are performed for the Al 7075-T651 aluminum alloy which is widely used in the aerospace industry. Tests are carried out under different mode mixity ratios to evaluate the applicability of a fracture criterion developed in a previous study to mixed mode-I/II fatigue crack growth tests. Results obtained from the analyses and experiments are compared with existing and developed criteria in terms of crack growth lives. Compact Tension Shear (CTS) specimens, which enable mixed mode loading with loading devices under different loading angles, are used in the simulations and experiments. In an effort to model and simulate the actual conditions in the experiments, crack surfaces of fractured specimens are scanned, crack paths are modeled exactly, and contacts are defined between the contact surfaces of a specimen and the loading device for each crack propagation step in the analyses. Having computed the mixed mode stress intensity factors from the numerical analyses, propagation life cycles are predicted by existing and the developed mixed mode-I/II criteria and then compared with experimental results. 相似文献
918.
This paper presents a review of geoid error characteristics of three satellite gravity missions in view of the general problem
of separating scientifically interesting signals from various noise sources. The problem is reviewed from the point of view
of two proposed applications of gravity missions, one is the observation of the mean oceanic circulation whereby an improved
geoid model is used as a reference surface against the long term mean sea level observed by altimetry. In this case we consider
the presence of mesoscale variability during assimilation of derived surface currents in inverse models. The other experiment
deals with temporal changes in the gravity field observed by GRACE in which case a proposed experiment is to monitor changes
in the geoid in order to detect geophysical interesting signals such as variations in the continental hydrology and non-steric
ocean processes. For this experiment we will address the problem of geophysical signal contamination and the way it potentially
affects monthly geoid solutions of GRACE.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
919.
Becker R.H. Clayton R.N. Galimov E.M. Lammer H. Marty B. Pepin R.O. Wieler R. 《Space Science Reviews》2003,106(1-4):377-410
Variations in the isotopic ratios of volatile elements in different reservoirs on the terrestrial planets carry information
about processes that operated on the planets since their formation. Comparisons between primordial planetary compositions,
to the extent they can be determined, may help us understand the planetary formation process. This working group report summarizes
our knowledge of terrestrial planet volatile inventories.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
920.
Pyrhonen J. Niemela M. Kaukonen J. Luukko J. Pyrhonen O. 《Aerospace and Electronic Systems Magazine, IEEE》1998,13(4):23-27
Synchronous motors are important in large drives. The application of the direct flux linkage control (DFLC) in synchronous machine drives is examined. This control method guarantees the best possible dynamics for the drive. Torque steps the height of which correspond to the motor nominal torque are achieved within a few milliseconds 相似文献