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991.
The problem of computing the translational velocity and position relative to earth, which has to be solved by the processor of a strapdown inertial navigation system is discussed. Several approaches are briefly examined with consideration given to the form in which the sensor data are generated and to the computational burden involved in each approach. A computational scheme is finally selected in which the computation is divided into three rate levels. The differential equations of this scheme are developed and the assumptions on which the development is founded are stated. Three variants of the basic scheme are presented, each based on a different level of simplifying assumptions. The main purpose of this work is to develop the differential equations to be solved at each stage of the computation, rather than the numerical implementation of the solution. This work supplies the theoretical background for some of the numerical methods which are now being used. 相似文献
992.
A suboptimal Kalman filter design method is presented for the problem of tracking a maneuvering target. The design method is essentially based on linear target dynamics and linear-like structured measurements called pseudomeasurements. The pseudomeasurements are obtained by manipulating the original nonlinear measurements algebraically. The resulting filter has computational advantages over other filters with similar performance. Also, a variant of the Berg model is proposed as a target acceleration model under the assumption of a coordinated turn maneuver. The proposed model is consistent with the underlying assumption. Monte Carlo computer simulation results are included to demonstrate the effectiveness of the proposed suboptimal filter associated with the target acceleration model 相似文献
993.
Multipath fading often poses a serious hindrance in radiocommunication. The application of a least-mean-square (LMS)adaptive array to the problem of multipath fading reduction is discussed. However, it is known that multipath components are in general correlated with one another. We examine the effect of the correlation on the performance of the LMS adaptive array. When the correlation coefficient does not equal or approximate 1, the LMS adaptive array suppresses the multipath signals significantly by nulling. On the other hand, when the correlation coefficient nearly equals 1, the LMS adaptive array prevents the output signalpower from decreasing. Therefore, the LMS adaptive array mayreduce the multipath fading effectively for any correlation coefficient value. A reference signal in the LMS adaptive array is also discussed. It is shown that synchronization in the referencesignal generation must be extremely accurate. Moreover, aprocessor configuration is proposed which may generate thereference signal with the required accuracy. 相似文献
994.
The effects of interference on frequency-locked Doppler tracking loops are investigated. Conditions for jump from locking on the desired signal to locking on the interfering signal are established. Parasitic frequency modulation of the desired signal results when the other signal interferes with it. The index of this parasitic modulation as a function of the interference-to-desired signal amplitude ratio is computed. Both critical amplitude ratio and critical parasitic modulation index at the occurrence of jump are derived. Comparing frequency-locked loops with phase-locked loops with phase-locked loops in the presence of interference shows the former performs better for most cases of practical importance in Doppler tracking systems. 相似文献
995.
A detailed development is presented of the psi-angle vector differential equation as applied to the error analysis of strapdown inertial navigation systems. The coordinate systems involved and the psi misalignment vector are clearly defined. It is proven that apart from a sign change the psi-angle differential equation in the error analysis of strapdown inertial navigation systems is identical to the one used in conventional gimbaled inertial navigation systems. 相似文献
996.
A Coradini F. Capaccioni P. Drossart G. Arnold E. Ammannito F. Angrilli A. Barucci G. Bellucci J. Benkhoff G. Bianchini J. P. Bibring M. Blecka D. Bockelee-Morvan M. T. Capria R. Carlson U. Carsenty P. Cerroni L. Colangeli M. Combes M. Combi J. Crovisier M. C. Desanctis E. T. Encrenaz S. Erard C. Federico G. Filacchione U. Fink S. Fonti V. Formisano W. H. Ip R. Jaumann E. Kuehrt Y. Langevin G. Magni T. Mccord V. Mennella S. Mottola G. Neukum P. Palumbo G. Piccioni H. Rauer B. Saggin B. Schmitt D. Tiphene G. Tozzi 《Space Science Reviews》2007,128(1-4):529-559
The VIRTIS (Visual IR Thermal Imaging Spectrometer) experiment has been one of the most successful experiments built in Europe
for Planetary Exploration. VIRTIS, developed in cooperation among Italy, France and Germany, has been already selected as
a key experiment for 3 planetary missions: the ESA-Rosetta and Venus Express and NASA-Dawn. VIRTIS on board Rosetta and Venus
Express are already producing high quality data: as far as Rosetta is concerned, the Earth-Moon system has been successfully
observed during the Earth Swing-By manouver (March 2005) and furthermore, VIRTIS will collect data when Rosetta flies by Mars
in February 2007 at a distance of about 200 kilometres from the planet. Data from the Rosetta mission will result in a comparison
– using the same combination of sophisticated experiments – of targets that are poorly differentiated and are representative
of the composition of different environment of the primordial solar system. Comets and asteroids, in fact, are in close relationship
with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The Rosetta mission payload is designed
to obtain this information combining in situ analysis of comet material, obtained by the small lander Philae, and by a long lasting and detailed remote sensing of the
comet, obtained by instrument on board the orbiting Spacecraft. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the “in situ” measurements will provide “ground-truth” for the remote sensing information, and, in turn, the locally collected data will
be interpreted in the appropriate context provided by the remote sensing investigation. VIRTIS is part of the scientific payload
of the Rosetta Orbiter and will detect and characterise the evolution of specific signatures – such as the typical spectral
bands of minerals and molecules – arising from surface components and from materials dispersed in the coma. The identification
of spectral features is a primary goal of the Rosetta mission as it will allow identification of the nature of the main constituent
of the comets. Moreover, the surface thermal evolution during comet approach to sun will be also studied. 相似文献
997.
IMM estimator with out-of-sequence measurements 总被引:3,自引:0,他引:3
In multisensor tracking systems that operate in a centralized information processing architecture, measurements from the same target obtained by different sensors can arrive at the processing center out of sequence. In order to avoid either a delay in the output or the need for reordering and reprocessing an entire sequence of measurements, such measurements have to be processed as out-of-sequence measurements (OOSMs). Recent work developed procedures for incorporating OOSMs into a Kalman filter (KF). Since the state of the art tracker for real (maneuvering) targets is the interacting multiple model (IMM) estimator, the algorithm for incorporating OOSMs into an IMM estimator is presented here. Both data association and estimation are considered. Simulation results are presented for two realistic problems using measurements from two airborne GMTI sensors. It is shown that the proposed algorithm for incorporating OOSMs into an IMM estimator yields practically the same performance as the reordering and in-sequence reprocessing of the measurements. Also, it is shown how the range rate from a GMTI sensor can be used as a linear velocity measurement in the tracking filter. 相似文献
998.
In target tracking systems measurements are typically collected in "scans" or "frames" and then they are transmitted to a processing center. In multisensor tracking systems that operate in a centralized manner, there are usually different time delays in transmitting the scans or frames from the various sensors to the center. This can lead to situations where measurements from the same target arrive out of sequence. Such "out-of-sequence" measurement (OOSM) arrivals can occur even in the absence of scan/frame communication time delays. The resulting "negative-time measurement update" problem, which is quite common in real multisensor systems, was solved previously only approximately in the literature. The exact state update equation for such a problem is presented. The optimal and two suboptimal algorithms are compared on a number of realistic examples, including a GMTI (ground moving target indicator) radar case. 相似文献
999.
Chan Y.T. Lee B.H. Inkol R. Yuan Q. 《IEEE transactions on aerospace and electronic systems》2001,37(4):1155-1162
The conventional analog Adcock-Butler matrix (ABM) antenna array direction finder suffers from systemic errors, component matching problems, and bandwidth limitations. Three digital bearing estimators are developed as candidates to replace the analog signal processing portion of the ABM. Using the same antenna array, they perform all signal processing in the frequency domain, thereby benefitting from the computational efficiency of the fast Fourier transform (FFT) algorithm. The first estimator requires two analog-to-digital converters (A-D) and three antenna elements. It multiplies the difference between the discrete Fourier transforms (DFTs) of the output signals from two antenna elements with that from a third antenna element. At each frequency component, the phase of this product is a function of the bearing. A weighted least squares (LS) fit through all the phase components then gives a bearing estimate. The second estimator is similar to the first but uses three A-D and all four antenna elements. The output signal from the additional antenna element provides an independent estimate of the weights for the LS fit, giving an improvement in accuracy. The third estimator applies the physical constraint existing between the time-difference-of-arrival (TDOA) of a signal intercepted by two perpendicular sets of antenna elements. This yields a better estimator than simple averaging of the bearing from each set of antenna elements. The simulation studies used sinusoids and broadband signals to corroborate the theoretical treatment and demonstrate the accuracy achievable with these estimators. All three direction finders have superior performance in comparison with the analog ABM 相似文献
1000.
Gamow was one of the pioneers who studied the possible variability of fundamental physical constants. Some versions of modern Grand Unification theories do predict such variability. The paper is concerned with three of the constants: the fine-structure constant , the ratio of the proton massm
p to the electron massm
e, and the ratio of the neutron massm
n tom
e. It is shown on the basis of the quasar spectra analysis, that all the three constants revealed no statistically significant variation over the last 90% of the life time of the Universe. At the 2 significance level, the following upper bounds are obtained for the epoch corresponding to the cosmological redshiftsz2–3: /<1.5×10–3, m
p/m
p<2×10–3, and m/m<3×10–4, where x is a possible deviation of a quantityx from its present value,m=m
p+m
n, and the nucleon masses are in units ofm
e. (According to new observational data which became known most recently, m
p/m
p<2×10–4) In addition a possible anisotropy of the high-redshift fine splitting over the celestial sphere is checked. Within the relative statistical error 3 < 1% the values of turned out to be the same in various quadrants of the celestial sphere, which corresponds to their equality in causally disconnected areas. However, at the 2 level a tentative anisotropy of estimated / values is found in directions that approximately coincide with the direction of the relic microwave background anisotropy.The revealed constraints serve as criteria for selection of those theoretical models which predict variation of ,m
p orm
n with the cosmological time. 相似文献