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排序方式: 共有433条查询结果,搜索用时 31 毫秒
201.
H Aiginger V Andersen F Ballarini G Battistoni M Campanella M Carboni F Cerutti A Empl W Enghardt A Fassò A Ferrari E Gadioli M V Garzelli K Lee A Ottolenghi K Parodi M Pelliccioni L Pinsky J Ranft S Roesler P R Sala D Scannicchio G Smirnov F Sommerer T Wilson N Zapp 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(2):214-222
202.
Jeongwoo Lee 《Space Science Reviews》2007,133(1-4):73-102
Solar active region coronae are known for strong magnetic fields permeating tenuous plasma, which makes them an ideal astronomical
laboratory for magnetohydrodynamics research. It is, however, relatively less known that this physical condition also permits
a very efficient radiation mechanism, gyro-resonant emission, produced by hot electrons gyrating in the coronal magnetic field.
As a resonant mechanism, gyro-emission produces high enough opacity to fully reveal the coronal temperature, and is concentrated
at a few harmonics of the local gyrofrequency to serve as an excellent indicator of the magnetic field. In addition, the polarization
of the ubiquitous free–free emission and a phenomenon of depolarization due to mode coupling extend the magnetic field diagnostic
to a wide range of coronal heights. The ability to measure the coronal temperature and magnetic field without the complications
that arise in other radiative inversion problems is a particular advantage for the active region radio emissions available
only at these wavelengths. This article reviews the efforts to understand these radiative processes, and use them as diagnostic
tools to address a number of critical issues involved with active regions. 相似文献
203.
Equivalent ARMA model representation for RLG random errors 总被引:2,自引:0,他引:2
Sang Man Seong Jang Gyu Lee Chan Gook Park 《IEEE transactions on aerospace and electronic systems》2000,36(1):286-290
It is shown that a mixture of random noises can be represented by a single equivalent ARMA (autoregressive moving average) model that is simple to implement. We applied the scheme to model RLG (ring laser gyroscope) random errors. An identification result from real test data confirms the validity of this approach 相似文献
204.
Lee Hartmann 《Space Science Reviews》2000,92(1-2):55-68
Currently available observational constraints on transport mechanisms in pre-main sequence disks are reviewed. The main observable
quantity accessable by imaging the spatial structure of disks is the mass accretion rate, which constrains angular momentum
transport, and migration and diffusion of disk material.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
205.
Sabate J.A. Farrington R.W. Jovanovic M.M. Lee E.C. 《IEEE transactions on aerospace and electronic systems》1996,32(1):255-266
The analysis of resonant converters including the capacitance of the switches is presented. New dc characteristics are obtained for the series, parallel, and series-parallel resonant converters (SPRC). The operating regions where the converters operate with zero-voltage switching (ZVS) are determined as a function of the switch capacitance. The more pronounced effect can be seen in the series resonant converter (SRC), while the parallel resonant converter (PRC) is the most insensitive. The results of the analysis have been verified on an experimental prototype 相似文献
206.
A digital quadrature demodulation system 总被引:1,自引:0,他引:1
Ho K.C. Chan Y.T. Inkol R. 《IEEE transactions on aerospace and electronic systems》1996,32(4):1218-1227
Existing digital quadrature demodulation techniques sample the input at either 2B Hz or 4B Hz, select the even samples as the in-phase (I), and interpolate the odd samples to give the quadrature (Q), output. The signal bandwidth is B. We propose a demodulation system to produce I and Q samples at arbitrary sampling rate greater than 2B Hz. The system eliminates the IF downconversion step with a special sampling scheme. The even samples correspond to the I component, while the Q components are the filtered output. The filter can be a lowpass or least squares (LS) filter. The lowpass filter design is based on trade-offs between the filter length and the degree of oversampling. It produces similar results as previous work when the sampling rate is 2B Hz or 4B Hz. Unlike existing methods which assume the input is white, a LS filter, on the other hand, can make use of input signal characteristics to achieve a better result. The higher the correlation in the input the larger the improvement. The cost for LS filtering is a coefficient update step if the input is time varying. A scheme to cancel dc offset from analog to digital (A/D) converters is also given 相似文献
207.
A neural network approach to pulse radar detection 总被引:2,自引:0,他引:2
A multilayer feedforward neural network is applied to pulse compression. The 13-element Barker code and the maximum-length sequences (m -sequences) with lengths 15, 31, and 63 b were used as the signal codes, and four networks were implemented, respectively. In each of these networks, the number of input units was the same as the signal length while the number of hidden units was three and the number of output units was one. In training each of these networks, backpropagation learning was used and the number of training epochs was 500. Using this approach, a more than 40 dB output peak signal-to-sidelobe ratio can be achieved. These fault-tolerant neural networks can provide a robust means for pulse radar detection 相似文献
208.
Shiuh-Jeng Wang Hung-Jui Ke Jia-Hung Huang Chien-Lung Chan 《Aerospace and Electronic Systems Magazine, IEEE》2007,22(1):3-7
In the Crypto 2004 Conference (Wang et al., 2004), one of the big news was that a fundamental technique in cryptography - one of the hash algorithms, Message Digest 5 (MD5) had been cracked. Soon after this event, it was announced that the secure hash algorithm (SHA-1) had been cracked as well. This series of information shocked the researches in the field of cryptography, and raised the attention of every related organization of security application mechanisms. Most agencies are still looking into the impact this may have, and are considering their future responses and solutions in the wake of these developments in the hash structure of cryptanalysis. Based on this information, this paper will discuss in detail the broken MD5 and SHA-1, which both are reported to have been cracked, and will investigate any impact, and propose recommendations for the applications in cyber-space, such as password authentication and forensic software, when using a hash algorithm 相似文献
209.
Receiver autonomous integrity monitoring (RAIM), a GPS integrity monitoring scheme that uses redundant ranging signals to detect a satellite malfunction that results in a large range error, involves two functions: detection of the presence of a malfunctioning satellite and identification of which satellite (or satellites) is malfunctioning. An analysis is presented of GPS RAIM capability for sole-means navigation in the oceanic phase of flight, where the position protection limit requirement for the integrity function is not as stringent as for nonprecision approaches, and yet both detection and identification function may be required if GPS is to be used as a sole-means system. For this purpose, a detection and identification algorithm is developed which takes advantage of the fact that for the oceanic phase of flight, a much larger position error is acceptable than for the nonprecision approach phase of flight. The performance of this algorithm and an algorithm proposed previously by others is estimated via simulation and compared. On the basis of the results, recommendations are made on how RAIM may be used if GPS is to be coupled with an inertial system to provide a sole-means capability in the oceanic phase of flight 相似文献
210.
Although considerations of discourse coherence and cognitive processing suggest that communicators should adopt consistent perspectives when describing spatial scenes, in many cases they switch perspectives. Ongoing research examining cognitive costs indicates that these are small and exacted in establishing a mental model of a scene but not in retrieving information from a well-known scene. A perspective entails a point of view, a referent object, and terms of reference. These may change within a perspective, exacting cognitive costs, so that the costs of switching perspective may not be greater than the costs of maintaining the same perspective. Another project investigating perspective choice for self and other demonstrates effects of salience of referent object and ease of terms of reference. Perspective is mixed not just in verbal communications but also in pictorial ones, suggesting that at times, switching perspective is more effective than maintaining a consistent one. 相似文献