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21.
B. Valníček F. Fárník B. Sylwester J. Sylwester 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):121-123
X-ray data obtained by the Prognoz 5,6,7 and 8 hard X-ray photometers are compared with the measurements carried out by similar instruments aboard the Solrad 11, ISEE 3, SMM and Hinotori satellites. Using the method of relative amplitude analysis, the apparent disagreement in the energy discrimination level calibration between the instruments is pointed out. The results of the comparison and the possible sources of disagreement are given. We suggest an international effort be made to develop a system of uniform pre-launch calibration of photometers based on a reference calibration source. 相似文献
22.
23.
F. Fárník S. Fischer L. Křivský B. Valníček O.B. Likin V.N. Lutsenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(13):243-246
During the observation of solar cosmic rays on the Prognoz 6 and Helios 1 and 2 spacecrafts, several events with anomalous composition of accelerated particles (higher abundance of 3-He or Fe nuclei) occurred. We found seven such events from the period September to December 1977 for which data from the Prognoz 6 solar X-ray photometer are available. This material together with published optical and radio data from terrestrial observatories enabled us to identify more reliably the source flares and describe their characteristics. It turned out that the character of X-ray emission accompanying the emission of accelerated particles with anomalous composition shows no pronounced difference from other flares. No correlation has been found among the ratio 3-He/4-He and the angular distance between the field lines connected with the source flare and the place of observation. If a solar flare with anomalous ratio 3-He/4-He appears in a given active region, this region will probably produce other anomalous events. 相似文献
24.
Interplanetary origin of geomagnetic storms 总被引:8,自引:0,他引:8
Gonzalez Walter D. Tsurutani Bruce T. Clúa de Gonzalez Alicia L. 《Space Science Reviews》1999,88(3-4):529-562
Around solar maximum, the dominant interplanetary phenomena causing intense magnetic storms (Dst<−100 nT) are the interplanetary
manifestations of fast coronal mass ejections (CMEs). Two interplanetary structures are important for the development of storms,
involving intense southward IMFs: the sheath region just behind the forward shock, and the CME ejecta itself. Whereas the
initial phase of a storm is caused by the increase in plasma ram pressure associated with the increase in density and speed
at and behind the shock (accompanied by a sudden impulse [SI] at Earth), the storm main phase is due to southward IMFs. If
the fields are southward in both of the sheath and solar ejecta, two-step main phase storms can result and the storm intensity
can be higher. The storm recovery phase begins when the IMF turns less southward, with delays of ≈1–2 hours, and has typically
a decay time of 10 hours. For CMEs involving clouds the intensity of the core magnetic field and the amplitude of the speed
of the cloud seems to be related, with a tendency that clouds which move at higher speeds also posses higher core magnetic
field strengths, thus both contributing to the development of intense storms since those two parameters are important factors
in genering the solar wind-magnetosphere coupling via the reconnection process.
During solar minimum, high speed streams from coronal holes dominate the interplanetary medium activity. The high-density,
low-speed streams associated with the heliospheric current sheet (HCS) plasma impinging upon the Earth's magnetosphere cause
positive Dst values (storm initial phases if followed by main phases). In the absence of shocks, SIs are infrequent during
this phase of the solar cycle. High-field regions called Corotating Interaction Regions (CIRs) are mainly created by the fast
stream (emanating from a coronal hole) interaction with the HCS plasma sheet. However, because the Bz component is typically highly fluctuating within the CIRs, the main phases of the resultant magnetic storms typically have
highly irregular profiles and are weaker. Storm recovery phases during this phase of the solar cycle are also quite different
in that they can last from many days to weeks. The southward magnetic field (Bs) component of Alfvén waves in the high speed stream proper cause intermittent reconnection, intermittent substorm activity,
and sporadic injections of plasma sheet energy into the outer portion of the ring current, prolonging its final decay to quiet
day values. This continuous auroral activity is called High Intensity Long Duration Continuous AE Activity (HILDCAAs).
Possible interplanetary mechanisms for the creation of very intense magnetic storms are discussed. We examine the effects
of a combination of a long-duration southward sheath magnetic field, followed by a magnetic cloud Bs event. We also consider the effects of interplanetary shock events on the sheath plasma. Examination of profiles of very
intense storms from 1957 to the present indicate that double, and sometimes triple, IMF Bs events are important causes of such events. We also discuss evidence that magnetic clouds with very intense core magnetic
fields tend to have large velocities, thus implying large amplitude interplanetary electric fields that can drive very intense
storms. Finally, we argue that a combination of complex interplanetary structures, involving in rare occasions the interplanetary
manifestations of subsequent CMEs, can lead to extremely intense storms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
25.
L. Metcalfe M. Aberasturi E. Alonso R. Álvarez M. Ashman I. Barbarisi J. Brumfitt A. Cardesín D. Coia M. Costa R. Fernández D. Frew J. Gallegos J. J. García Beteta B. Geiger D. Heather T. Lim P. Martin C. Muñoz Crego M. Muñoz Fernandez A. Villacorta H. Svedhem 《Space Science Reviews》2018,214(4):78
The ExoMars Trace Gas Orbiter (TGO) Science Ground Segment (SGS), comprised of payload Instrument Team, ESA and Russian operational centres, is responsible for planning the science operations of the TGO mission and for the generation and archiving of the scientific data products to levels meeting the scientific aims and criteria specified by the ESA Project Scientist as advised by the Science Working Team (SWT). The ExoMars SGS builds extensively upon tools and experience acquired through earlier ESA planetary missions like Mars and Venus Express, and Rosetta, but also is breaking ground in various respects toward the science operations of future missions like BepiColombo or JUICE. A productive interaction with the Russian partners in the mission facilitates broad and effective collaboration. This paper describes the global organisation and operation of the SGS, with reference to its principal systems, interfaces and operational processes. 相似文献
26.
Nellore S. Venkataraman Ana M. Vélez García Vikram Venkataraman Heberth Diestra-Cruz 《Acta Astronautica》2014
Thermal control of spacecrafts plays an important role in space missions. In the design stage the preliminary thermal analysis of the spacecraft requires an estimate of the conductive thermal resistance between the various spacecraft components. With this in mind, the fully three dimensional problem of determining the thermal field in a conducting sphere with an asymmetric split ring current carrying heating source is resolved in an analytical or almost analytical form, implying either a closed form solution or utmost expressions involving a simple numerical integration. This has immediate application for evaluation of thermal resistance in spacecrafts. Green's function integral techniques are used. Comparisons are made with series solutions and also with purely numerical solutions to contrast the simplicity and highlight the elegance of the present method. Parametric studies reveal expected behavior. 相似文献
27.
Modeling and Optimal Design of 3 Degrees of Freedom Helmholtz Resonator in Hydraulic System 总被引:1,自引:0,他引:1
Three degrees of freedom (3-DOF) Helmholtz resonator which consists of three cylindrical necks and cavities connected in series (neck-cavity-neck-cavity-neck-cavity) is suitable to reduce flow pulsation in hydraulic system. A novel lumped parameter model (LPM) of 3-DOF Helmholtz resonator in hydraulic system is developed which considers the viscous friction loss of hydraulic fluid in the necks. Applying the Newton’s second law of motion to the equivalent mechanical model of the resonator, closed-form expression of transmission loss and resonance frequency is presented. Based on the LPM, an optimal design method which employs rotate vector optimization method (RVOM) is proposed. The purpose of the optimal design is to search the resonator’s unknown parameters so that its resonance frequencies can coincide with the pump-induced flow pulsation harmonics respectively. The optimal design method is realized to design 3-DOF Helmholtz resonator for a certain type of aviation piston pump hydraulic system. The optimization result shows the feasibility of this method, and the simulation under optimum parameters reveals that the LPM can get the same precision as transfer matrix method (TMM). 相似文献
28.
LEE Kok Meng 《中国航空学报》2012,25(4):566-574
Effective thermal control systems are essential for reliable operation of spacecraft.A dual-driven intelligent combination control strategy is proposed to improve the temperate control and heat flux tracking effects.Both temperature regulation and heat flux tracking errors are employed to generate the final control action;their contributions are adaptively adjusted by a fuzzy fusing policy of control actions.To evaluate the control effects,describe a four-nodal mathematical model for analyzing the dynamic characteristics of the controlled heat pipe space cooling system(HP-SCS) consisting of an aluminum-ammonia heat pipe and a variable-emittance micro-electromechanical-system(MEMS) radiator.This dynamical model calculates the mass flow-rate and condensing pressure of the heat pipe working fluid directly from the systemic nodal temperatures,therefore,it is more suitable for control engineering applications.The closed-loop transient performances of four different control schemes have been numerically investigated.The results conclude that the proposed intelligent combination control scheme not only improves the thermal control effects but also benefits the safe operation of HP-SCS. 相似文献
29.
Vázquez-Mayagoitia Á Horton SR Sumpter BG Šponer J Šponer JE Fuentes-Cabrera M 《Astrobiology》2011,11(2):115-121
The RNA-world theory hypothesizes that early Earth life was based on the RNA molecule. However, the notion that ribose, the sugar in RNA, is unstable still casts a serious doubt over this theory. Recently, it has been found that the silicate-mediated formose reaction facilitates the stabilization of ribose. Using accurate quantum chemical calculations, we determined the relative stability of the silicate complexes of arabinose, lyxose, ribose, and xylose with the intent to determine which would form predominantly from a formose-like reaction. Five stereoisomers were investigated for each complex. The stereoisomers of 2:1 ribose-silicate are the more stable ones, to the extent that the least stable of these is even more stable than the most stable stereoisomer of the other 2:1 sugar-silicate complexes. Thus, thermodynamically, a formose-like reaction in the presence of silicate minerals should preferentially form the silicate complex of ribose over the silicate complex of arabinose, lyxose, and xylose. 相似文献
30.