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861.
W Trettnak C Kolle F Reininger C Dolezal P O'Leary R A Binot 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(10):1465-1474
Optical oxygen sensors are mainly based on the principle of luminescence quenching. In contrast to arready existing intensity-based systems, the measurement of the luminescence lifetime provides certain advantages, such as insensitivity to photobleaching or leaching of the dye, or changes in the intensity of excitation light. This facilitates the use of simple optical systems or optical fibres. A new family of oxygen-sensitive dyes, the porphyrin-ketones, has been introduced, which exhibits favorable spectral properties and decay times in the order of tens and hundreds of microseconds. This allows the use of simple optoelectronic circuitry and low-cost processing electronics. An optical oxygen sensor module has been developed with the dimensions of only 120 x 60 x 30 mm. The prototype is based on the measurement of the decay time of the luminophore by measuring the phase shift between the square-wave excitation and the detected square-wave of the emission coming from the sensor. The instrument is based on semiconductor devices (light-emitting diodes, photodiodes) and may be used for the detection of oxygen in gaseous or liquid samples. The measurement range of the device is from 0 to 200 hPa oxygen partial pressure with a resolution of < 1 hPa over the whole measurement range. The overall measurement accuracy of < +/- 1 hPa has been obtained for periods of 24 h of continuous measurement in a thermostatted environment. The sensor response times t90 are typically < 1 s for gases and 0.5 to 5 min for liquid samples. 相似文献
862.
The most important sensors for gathering target information onboard a submarine are passive sonars. Problems concerning fusion of these passive sonars are discussed. Three typical passive sonars-passive noise sonar, passive ranging sonar and acoustic pulse surveillance sonar-constitute a passive sonar system for data fusion. This paper is concerned mainly with problems of significance in system development, such as tactical application background, special fusion techniques and own-ship maneuver considerations 相似文献
863.
This paper deals with the performance of pulse Doppler radar in the presence of random fading. The behavior of this radar is studied as a statistical problem to bring out the limiting bounds of the ambiguity diagram and the nature of variance with respect to the Doppler frequency. The performance of the radar insofar as the first sidelobe is concerned, is shown to be better in the presence of fading than in the normal case. In a particular case where 75 pulses out of an aggregate of 250 pulses are missing, the first sidelobe level is 20.0 dB down from the main lobe with a probability of 23 percent. 相似文献
864.
Soil carbon distribution and site characteristics in hyper-arid soils of the Atacama Desert: A site with Mars-like soils 总被引:1,自引:0,他引:1
Julio E. Valdivia-Silva Rafael Navarro-González Lauren Fletcher Saúl Perez-Montaño Reneé Condori-Apaza Christopher P. Mckay 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The soil carbon content and its relation to site characteristics are important in evaluating current local, regional, and global soil C storage and projecting future variations in response to climate change. In this study we analyzed the concentration of organic and inorganic carbon and their relationship with in situ climatic and geological characteristics in 485 samples of surface soil and 17 pits from the hyper-arid area and 51 samples with 2 pits from the arid–semiarid region from the Atacama Desert located in Peru and Chile. The soil organic carbon (SOC) in hyperarid soils ranged from 1.8 to 50.9 μg C per g of soil for the 0–0.1 m profile and from 1.8 to 125.2 μg C per g of soil for the 0–1 m profile. The analysis of climatic (temperature and precipitation), elevation, and some geologic characteristics (landforms) associated with hyper-arid soils explained partially the SOC variability. On the other hand, soil inorganic carbon (SIC) contents, in the form of carbonates, ranged from 200 to 1500 μg C per g of soil for the 0–0.1 m profile and from 200 to 3000 μg C per g of soil for the 0–1.0 m profile in the driest area. The largest accumulations of organic and inorganic carbon were found near to arid–semiarid areas. In addition, the elemental carbon concentrations show that the presence of other forms of inorganic carbon (e.g. graphite, etc.) was negligible in these hyperarid soils. Overall, the top 1 m soil layer of hyperarid lands contains ∼11.6 Tg of organic carbon and 344.6 Tg of carbonate carbon. The total stored carbon was 30.8-fold the organic carbon alone. To our knowledge, this is the first study evaluating the total budget carbon on the surface and shallow subsurface on ∼160,000 km2 of hyperarid soils. 相似文献
865.
P.V.S. Rama Rao K. VenkateshD.S.V.V.D. Prasad K. Niranjan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The Indian sector encompasses the equatorial and low latitude regions where the ionosphere is highly dynamic and is characterized by the equatorial ionization anomaly (EIA) resulting in large latitudinal electron density gradients causing errors and uncertainties in the estimation of range delays in satellite based navigation systems. The diurnal and seasonal variations of standard deviations in the TEC data measured during the low sunspot period 2004–2005 at 10 different Indian stations located from equator to the anomaly crest region and beyond are examined and presented. The day-to-day variability in TEC is found to be lowest at the equatorial station and increases with latitude up to the crest region of EIA and decreases beyond. 相似文献
866.
C Schimek P Eibel T Horie P Galland T Ootaki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(6):687-696
The sporangiophores of the zygomycete fungus Phycomyces blakesleeanus contain octahedral crystals with diameters of up to 5 micrometers in their vacuole. The crystals are associated with the intracellular membrane system. In tilted or horizontally placed sporangiophores, the crystals sediment to the respective lower face of the vacuole with a velocity of up to 100 micrometers per minute. The sedimentation is completed within about 2 minutes, well within the latency period for the negative gravitropic response of Phycomyces. Crystal-lacking mutant strains display a smaller maximal bending angle and a reduced gravitropic bending rate in comparison to the wild type. We therefore conclude that the crystals serve as statoliths for gravitropism in Phycomyces. 相似文献
867.
We review the observations of supernova remnants (SNRs) and pulsar-wind nebulae (PWNe) that give information on the strength and orientation of magnetic fields. Radio polarimetry gives the degree of order of magnetic fields, and the orientation of the ordered component. Many young shell supernova remnants show evidence for synchrotron X-ray emission. The spatial analysis of this emission suggests that magnetic fields are amplified by one to two orders of magnitude in strong shocks. Detection of several remnants in TeV gamma rays implies a lower limit on the magnetic-field strength (or a measurement, if the emission process is inverse-Compton upscattering of cosmic microwave background photons). Upper limits to GeV emission similarly provide lower limits on magnetic-field strengths. In the historical shell remnants, lower limits on B range from 25 to 1000?μG. Two remnants show variability of synchrotron X-ray emission with a timescale of years. If this timescale is the electron-acceleration or radiative loss timescale, magnetic fields of order 1?mG are also implied. In pulsar-wind nebulae, equipartition arguments and dynamical modeling can be used to infer magnetic-field strengths anywhere from ~5?μG to 1?mG. Polarized fractions are considerably higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field geometries often suggest a toroidal structure around the pulsar, but this is not universal. Viewing-angle effects undoubtedly play a role. MHD models of radio emission in shell SNRs show that different orientations of upstream magnetic field, and different assumptions about electron acceleration, predict different radio morphology. In the remnant of SN 1006, such comparisons imply a magnetic-field orientation connecting the bright limbs, with a substantial density gradient across the remnant. 相似文献
868.
Glisson T.H. Black C.I. Sage A.P. 《IEEE transactions on aerospace and electronic systems》1970,(1):37-50
Systems which utilize acoustic energy to explore an undersea environment are called sonars. This introductory and tutorial paper presents a discussion of active sonar signal analysis concentrating upon sinusoidal, linear FM, and pseudorandom echolocation pulses. Many previously published results concerning sonar signals and their haracteristics are integrated, collected, and presented in a unified form such as to portray typical signal design considerations. 相似文献
869.
A class of simple and efficient digital sequential detectors is presented, which are particularly suitable for application to radar systems where the antenna dwell time is easily varied. A methematical method, based on the random walk model, is developed to evaluate the DFTSD (digital fixed-thresholds sequential detector) performance. The DFTSD has a loss of 0.2 to 0.3 dB with respect to the digital SPRT (sequential probability ratio test) in the case of a single-range-bin system. Finally, results for the multiple-range-bin case are presented and compared with the performance of a moving-window detector. 相似文献
870.