全文获取类型
收费全文 | 7389篇 |
免费 | 9篇 |
国内免费 | 16篇 |
专业分类
航空 | 3463篇 |
航天技术 | 2321篇 |
综合类 | 196篇 |
航天 | 1434篇 |
出版年
2021年 | 61篇 |
2019年 | 37篇 |
2018年 | 177篇 |
2017年 | 129篇 |
2016年 | 141篇 |
2015年 | 49篇 |
2014年 | 163篇 |
2013年 | 209篇 |
2012年 | 202篇 |
2011年 | 283篇 |
2010年 | 206篇 |
2009年 | 338篇 |
2008年 | 335篇 |
2007年 | 213篇 |
2006年 | 147篇 |
2005年 | 175篇 |
2004年 | 179篇 |
2003年 | 225篇 |
2002年 | 248篇 |
2001年 | 298篇 |
2000年 | 124篇 |
1999年 | 163篇 |
1998年 | 199篇 |
1997年 | 131篇 |
1996年 | 169篇 |
1995年 | 234篇 |
1994年 | 197篇 |
1993年 | 107篇 |
1992年 | 153篇 |
1991年 | 64篇 |
1990年 | 81篇 |
1989年 | 154篇 |
1988年 | 64篇 |
1987年 | 72篇 |
1986年 | 63篇 |
1985年 | 205篇 |
1984年 | 162篇 |
1983年 | 148篇 |
1982年 | 150篇 |
1981年 | 218篇 |
1980年 | 78篇 |
1979年 | 59篇 |
1978年 | 68篇 |
1977年 | 47篇 |
1976年 | 51篇 |
1975年 | 57篇 |
1974年 | 49篇 |
1972年 | 60篇 |
1971年 | 56篇 |
1969年 | 38篇 |
排序方式: 共有7414条查询结果,搜索用时 497 毫秒
881.
882.
Pulsone N.B. Raghavan R.S. 《IEEE transactions on aerospace and electronic systems》1999,35(3):903-916
Coherent signal detection in non-Gaussian interference is presently of interest in adaptive array applications. Conventional array detection algorithms inherently model the interference with a multivariate Gaussian random vector. However, non-Gaussian interference models are also under investigation for applications where the Gaussian assumption may not be appropriate. We analyze the performance of an adaptive array receiver for signal detection in interference modeled with a non-Gaussian distribution referred to as a spherically invariant random vector (SIRV). We first motivate this interference model with results from radar clutter measurements collected in the Mountain Top Program. Then we develop analytical expressions for the probability of false alarm and the probability of detection for the adaptive array receiver. Our analysis shows that the receiver has constant false alarm rate (CFAR) performance with respect to all the interference parameters. Some illustrative examples are included that compare the detection performance of this CFAR receiver with a receiver that has prior knowledge of the interference parameters 相似文献
883.
Large-scale Coronal Heating, Clustering of Coronal Bright Points, and Concentration of Magnetic Flux
By combining quiet-region Fe XII coronal images from SOHO/EIT with magnetograms from NSO/Kitt Peak and from SOHO/MDI, we show
that the population of network coronal bright points and the magnetic flux content of the network are both markedly greater
under the bright half of the large-scale quiet corona than under the dim half. These results (1) support the view that the
heating of the entire corona in quiet regions and coronal holes is driven by fine-scale magnetic activity (microflares, explosive
events, spicules) seated low in the magnetic network, and (2) suggest that this large-scale modulation of the magnetic flux
and coronal heating is a signature of giant convection cells.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
884.
T. Aramaki S.E. Boggs W.W. Craig H. Fuke F. Gahbauer C.J. Hailey J.E. Koglin N. Madden K. Mori R.A. Ong T. Yoshida 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The General AntiParticle Spectrometer (GAPS) is a novel approach for indirect dark matter searches that exploits cosmic antideuterons. GAPS complements existing and planned direct dark matter searches as well as other indirect techniques, probing a different and unique region of parameter space in a variety of proposed dark matter models. The GAPS method involves capturing antiparticles into a target material with the subsequent formation of an excited exotic atom. The exotic atom decays with the emission of atomic X-rays and pions from the nuclear annihilation, which uniquely identifies the captured antiparticle. This technique has been verified through the accelerator testing at KEK in 2004 and 2005. The prototype flight is scheduled from Hokkaido, Japan in 2011, preparatory for a long duration balloon flight from the Antarctic in 2014. 相似文献
885.
A. N. Kusyumov E. V. Romanova A. S. Batrakov R. R. Nurmukhametov G. N. Barakos 《Russian Aeronautics (Iz VUZ)》2012,55(3):263-268
We consider a problem of a stationary incompressible viscous fluid flow around a flat circular cylinder. In the vicinity of the critical Reynolds number Re cr a stepwise drop of the cylinder drag takes place, which is called the drag crisis. 相似文献
886.
V. V. Tsatiashvili 《Russian Aeronautics (Iz VUZ)》2013,56(1):50-58
The results of analyzing an impact of mixing velocity on the stoichiometric surface of a laminar diffusion methane-air flame on nitric oxides formation are presented. The conclusion about the nonlinear and steady decrease of nitric oxides emission at the increase of mixing velocity is made. The relationship is presented, showing that at the expense of non-equilibrium effects it is possible to provide a significant decrease of nitric oxides emission in diffusion combustion. 相似文献
887.
This paper presents the results of three-dimensional numerical studies of hydrodynamics and heat exchange on the models of flat plates in the jet airflow. These results are compared with the experimental data. A three-dimensional model for determining the thermal condition of the nozzle clusters in the conjugated formulation is proposed. Also presented are the data on optimization of the system used for the jet airflow around the duct platforms of the nozzle clusters. 相似文献
888.
R. P. Lin 《Space Science Reviews》2011,159(1-4):421-445
RHESSI measurements relevant to the fundamental processes of energy release and particle acceleration in flares are summarized. RHESSI??s precise measurements of hard X-ray continuum spectra enable model-independent deconvolution to obtain the parent electron spectrum. Taking into account the effects of albedo, these show that the low energy cut-off to the electron power-law spectrum is typically ?tens of keV, confirming that the accelerated electrons contain a large fraction of the energy released in flares. RHESSI has detected a high coronal hard X-ray source that is filled with accelerated electrons whose energy density is comparable to the magnetic-field energy density. This suggests an efficient conversion of energy, previously stored in the magnetic field, into the bulk acceleration of electrons. A new, collisionless (Hall) magnetic reconnection process has been identified through theory and simulations, and directly observed in space and in the laboratory; it should occur in the solar corona as well, with a reconnection rate fast enough for the energy release in flares. The reconnection process could result in the formation of multiple elongated magnetic islands, that then collapse to bulk-accelerate the electrons, rapidly enough to produce the observed hard X-ray emissions. RHESSI??s pioneering ??-ray line imaging of energetic ions, revealing footpoints straddling a flare loop arcade, has provided strong evidence that ion acceleration is also related to magnetic reconnection. Flare particle acceleration is shown to have a close relationship to impulsive Solar Energetic Particle (SEP) events observed in the interplanetary medium, and also to both fast coronal mass ejections and gradual SEP events. New instrumentation to provide the high sensitivity and wide dynamic range hard X-ray and ??-ray measurements, plus energetic neutral atom (ENA) imaging of SEPs above ??2 R??, will enable the next great leap forward in understanding particle acceleration and energy release is large solar eruptions??solar flares and associated fast coronal mass ejections (CMEs). 相似文献
889.
The problem of fracture mechanics for the solid propellant deteriorated by a crack-shaped cavity, the surface of which burns
is considered. It is assumed that the propellant reagents are uniformly distributed in the solid phase while the combustion
products are gaseous. The sufficient condition for the “combustion -fracture” stability regime is obtained. 相似文献
890.
R. Govind J.J. Valette F.G. Lemoine 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The Lambert–Amery System is the largest glacier–ice shelf system in East Antarctica, draining a significant portion of the ice sheet. Variation in ice sheet discharge from Antarctica or Greenland has an impact on the rate of change in global mean sea level; which is a manifestation of climate change. In conjunction with a measure of ice thickness change, ice sheet discharge can be monitored by determining the absolute velocities of these glaciers. 相似文献