全文获取类型
收费全文 | 6221篇 |
免费 | 48篇 |
国内免费 | 33篇 |
专业分类
航空 | 2723篇 |
航天技术 | 2099篇 |
综合类 | 88篇 |
航天 | 1392篇 |
出版年
2022年 | 28篇 |
2021年 | 65篇 |
2018年 | 149篇 |
2017年 | 139篇 |
2016年 | 129篇 |
2015年 | 69篇 |
2014年 | 163篇 |
2013年 | 208篇 |
2012年 | 181篇 |
2011年 | 283篇 |
2010年 | 214篇 |
2009年 | 304篇 |
2008年 | 355篇 |
2007年 | 218篇 |
2006年 | 164篇 |
2005年 | 201篇 |
2004年 | 152篇 |
2003年 | 195篇 |
2002年 | 153篇 |
2001年 | 202篇 |
2000年 | 120篇 |
1999年 | 142篇 |
1998年 | 153篇 |
1997年 | 127篇 |
1996年 | 122篇 |
1995年 | 162篇 |
1994年 | 159篇 |
1993年 | 89篇 |
1992年 | 114篇 |
1991年 | 48篇 |
1990年 | 58篇 |
1989年 | 100篇 |
1988年 | 45篇 |
1987年 | 44篇 |
1986年 | 46篇 |
1985年 | 158篇 |
1984年 | 128篇 |
1983年 | 113篇 |
1982年 | 92篇 |
1981年 | 169篇 |
1980年 | 46篇 |
1979年 | 42篇 |
1978年 | 42篇 |
1977年 | 38篇 |
1976年 | 34篇 |
1975年 | 50篇 |
1974年 | 29篇 |
1972年 | 45篇 |
1971年 | 34篇 |
1967年 | 27篇 |
排序方式: 共有6302条查询结果,搜索用时 115 毫秒
881.
G Fogleman J L Huntington G C Carle J A Nuth 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(2):91-94
In the gravitational field on Earth, the large settling rate of micron-sized particles and the effects of gravity-induced convection prohibit many interesting studies of phenomena such as coagulation, collisions, and mutual interactions of droplets, dust grains and other particles. Examples of exobiology experiments involving these phenomena are the simulation of organic aerosol formation in Titan's atmosphere, studies of the role of comets in prebiotic chemical evolution, and simulations of carbon grain interactions in various astrophysical environments. The Gas-Grain Simulation Facility (GGSF) is a proposed Earth-orbital laboratory that will allow present ground-based experimental programs which study processes involving small particles and weak interactions to be extended to a new domain. Physics issues that scientists wishing to propose GGSF experiments must consider are reviewed in this paper. Specifically, coagulation, motion in gases and vacua, and wall deposition of particles in a microgravity environment are discussed. 相似文献
882.
Ramachandra K.V. Division R.C. 《IEEE transactions on aerospace and electronic systems》1987,(5):705-708
A one-dimensional tracking filter based on the Kalman filtering techniques for tracking of a dynamic target such as an aircraft is discussed. The target is assumed to be moving with constant acceleration and is acted upon by a plant noise which perturbs its constant acceleration motion. The plant noise accounts for maneuvers and/or other random factors. Analytical results for estimating optimum steady state position, velocity, and acceleration of the target are obtained. 相似文献
883.
T. Muoz-Darias I.G. Martínez-Pais J. Casares T.R. Marsh R. Cornelisse D. Steeghs V.S. Dhillon P.A. Charles 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2762-2764
We present preliminary results of a simultaneous X-ray/optical campaign of the prototypical LMXB Sco X-1 at 1–10 Hz time resolution. Lightcurves of the high excitation Bowen/HeII emission lines and a red continuum at λc 6000 Å were obtained through narrow interference filters with ULTRACAM, and these were cross-correlated with simultaneous RXTE X-ray lightcurves. We find evidence for correlated variability, in particular when Sco X-1 enters the Flaring branch. The Bowen/HeII lightcurves lag the X-ray lightcurves with a light travel time which is consistent with reprocessing in the companion star while the continuum lightcurves have shorter delays consistent with reprocessing in the accretion disc. 相似文献
884.
In developing radio-electronic devices (RED) of spacecraft operating in the fields of ionizing radiation in space, one of the most important problems is the correct estimation of their radiation tolerance. The “weakest link” in the element base of onboard microelectronic devices under radiation effect is the integrated microcircuits (IMC), especially of large scale (LSI) and very large scale (VLSI) degree of integration. The main characteristic of IMC, which is taken into account when making decisions on using some particular type of IMC in the onboard RED, is the probability of non-failure operation (NFO) at the end of the spacecraft’s lifetime. It should be noted that, until now, the NFO has been calculated only from the reliability characteristics, disregarding the radiation effect. This paper presents the so-called “reliability” approach to determination of radiation tolerance of IMC, which allows one to estimate the probability of non-failure operation of various types of IMC with due account of radiation-stimulated dose failures. The described technique is applied to RED onboard the Spektr-R spacecraft to be launched in 2007. 相似文献
885.
An approach to knowledge-aided covariance estimation 总被引:1,自引:0,他引:1
Melvin W.L. Showman G.A. 《IEEE transactions on aerospace and electronic systems》2006,42(3):1021-1042
This paper introduces a parametric covariance estimation scheme for use with space-time adaptive processing (STAP) methods operating in heterogeneous clutter environments. The approach blends both a priori knowledge and data observations within a parameterized model to capture instantaneous characteristics of the cell under test (CUT) and reduce covariance errors leading to detection performance loss. We justify this method using both measured and synthetic data. Performance potential for the specific operating conditions examined herein include: 1) averaged behavior within roughly 2 dB of the optimal filter, 2) 1 dB improvement in exceedance characteristic relative to the optimal filter, highlighting improved instantaneous capability, and 3) impervious ness to corruptive target-like signals in the secondary data (no additional signal-to-interference-plus-noise ratio (SINK) loss, compared with 10 dB or greater loss for the standard STAP implementation), with corresponding detections comparable to the optimal filter case 相似文献
886.
N. F. Blagoveshchenskaya A. D. Andreev V. A. Kornienko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):45-48
Effects of ionospheric modification produced by powerful high frequency radio waves are studied using the method of field-aligned scattering of diagnostic HF radio signals. Observations of scattered HF signals have been made by the Doppler spectrum method. Analysis of the experimental data shows the appearance of quasiperiodic variations in Doppler frequency shift fd, with periods 30–60 s during the heating cycles. Powerful HF waves are assumed to excite the Alfvén resonator generating oscillations of the magnetic field lines in the heated region and giving rise to fd artificial variations and magnetic pulsations. In the case of continuous action of the powerful HF transmitter ionospheric waves are sometimes observed with periods 12–25 min, typical of medium-scale travelling ionospheric disturbances. 相似文献
887.
As a circuit is tested, the current drawn from a power supply can vary as different functions are invoked by the test. The current draw can be plotted against time, showing a characteristic trace for the test performed. Sensors in the ATS power supply can be used to monitor the current flow during test execution. Defective components can be classified using a Neural Network according to the pattern of variation from the “trace” of a good card. This can be performed as a background function, with the network gaining in accuracy over time. This paper discusses the Neural Network Routine for diagnosing circuit faults using monitored power supply current 相似文献
888.
889.
Diane Sonya Wong Ryan Chornock Alexei V. Filippenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2813-2815
We present results of optical follow-up observations of candidate ultra-luminous X-ray sources (ULXs). Using Keck optical spectroscopy, 17 of the candidates from the Colbert and Ptak [Colbert, E.J.M., Ptak, A.F. A catalog of candidate intermediate-luminosity X-ray objects. ApJS 143, 25–45, 2002] catalog have been identified; this is one of the largest sets of optical identifications of such objects thus far. Fifteen are background active galactic nuclei (AGN); two are foreground stars in our Galaxy. These findings are consistent with background and foreground object expectations, as derived from log N–log S relations. Also, the results are briefly discussed in terms of the spiral-galaxy/ULX connection. 相似文献
890.