首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6373篇
  免费   15篇
  国内免费   30篇
航空   2889篇
航天技术   2393篇
综合类   21篇
航天   1115篇
  2021年   69篇
  2019年   46篇
  2018年   191篇
  2017年   113篇
  2016年   81篇
  2015年   30篇
  2014年   149篇
  2013年   190篇
  2012年   179篇
  2011年   255篇
  2010年   176篇
  2009年   293篇
  2008年   343篇
  2007年   178篇
  2006年   154篇
  2005年   188篇
  2004年   186篇
  2003年   213篇
  2002年   135篇
  2001年   207篇
  2000年   136篇
  1999年   150篇
  1998年   176篇
  1997年   130篇
  1996年   167篇
  1995年   204篇
  1994年   195篇
  1993年   99篇
  1992年   155篇
  1991年   52篇
  1990年   52篇
  1989年   136篇
  1988年   48篇
  1987年   50篇
  1986年   61篇
  1985年   193篇
  1984年   145篇
  1983年   113篇
  1982年   137篇
  1981年   168篇
  1980年   47篇
  1979年   31篇
  1978年   41篇
  1977年   37篇
  1976年   33篇
  1975年   32篇
  1974年   40篇
  1973年   27篇
  1972年   28篇
  1970年   29篇
排序方式: 共有6418条查询结果,搜索用时 0 毫秒
81.
We consider the peculiarities of application for the cabin indicating systems of secondary information display, formulate and systematize the compositional and technical requirements for display systems and their elements. The tendencies and lines in the development of head-up displays for avionics and autobasing complexes were determined. The technique of calculating optics of such display systems with the use of electronic distortion compensation is presented.  相似文献   
82.
Aerodynamic characteristics of two-dimensional smart flap under the ground effect have been assessed by a numerical simulation. In this process, a pressure-based implicit procedure to solve Navier–Stokes equations on a nonorthogonal mesh with collocated finite volume formulation is used. The boundedness criteria for this procedure are determined from the Normalized Variable Diagram (NVD) scheme. The procedure incorporates the kε eddy–viscosity turbulence model. Cantilever beam with uniformly varying load with roller support at the free end is considered for the configuration of the smart flap. The method is first validated against experimental data. Then, the algorithm is applied for turbulent aerodynamic flows around airfoil with smart and conventional flaps for different attack angle, flap angle and ground clearance where the results of two flaps are compared. The comparisons show that the quality of the solution is considerable.  相似文献   
83.
Observations of galactic cosmic rays (GCRs) from the two Voyager spacecraft inside the heliosheath indicate significant differences between them, suggesting that in addition to a possible global asymmetry in the north–south dimensions (meridional plane) of the heliosphere, it is also possible that different modulation (turbulence) conditions could exist between the two hemispheres of the heliosphere. We focus on illustrating the effects on GCR Carbon of asymmetrical modulation conditions combined with a heliosheath thickness that has a significant dependence on heliolatitude. To reflect different modulation conditions between the two heliospheric hemispheres in our numerical model, the enhancement of both polar and radial perpendicular diffusion off the ecliptic plane is assumed to differ from heliographic pole to pole. The computed radial GCR intensities at polar angles of 55° (approximating the Voyager 1 direction) and 125° (approximating the Voyager 2 direction) are compared at different energies and for both particle drift cycles. This is done in the context of illustrating how different values of the enhancement of both polar and radial perpendicular diffusion between the two hemispheres contribute to causing differences in radial intensities during solar minimum and moderate maximum conditions. We find that in the A > 0 cycle these differences between 55° and 125° change both quantitatively and qualitatively for the assumed asymmetrical modulation condition as reflected by polar diffusion, while in the A < 0 cycle, minute quantitative differences are obtained. However, when both polar and radial perpendicular diffusion have significant latitude dependences, major differences in radial intensities between the two polar angles are obtained in both polarity cycles. Furthermore, significant differences in radial intensity gradients obtained in the heliosheath at lower energies may suggest that the solar wind turbulence at and beyond the solar wind termination shock must have a larger latitudinal dependence.  相似文献   
84.
85.
We use simultaneous observations from RESIK and RHESSI instruments to compare plasma properties of a major solar flare in its rise and gradual phase. This event occurred on 2002 August 3 (peak time at 19:06 UT). The flare had a very good coverage with RESIK data and well-resolved soft and hard X-ray sources were seen in RHESSI images. Spectra of X-ray radiation from RHESSI images are studied and compared with RESIK measurements in different flare phases. Result shows large differences in flare morphology and spectra between flare rise and gradual phase.  相似文献   
86.
The binary system Capella (G6 III + F9 III) has been observed on 1979 March 15 and on 1980 March 15–17 with the Objective Grating Spectrometer (OGS) onboard theEinstein Observatory. The spectrum measured with the 1000 l/mm grating covers the range 5–30 Å with a resolution < 1 Å. The spectra show evidence for a bimodal temperature distribution of emission measure in an optically thin plasma with one component 5 million degrees and the other one 10 million degrees. Spectral features can be identified with line emissions from O VIII, Fe XVII, Fe XVIII, Fe XXIV, and Ne X ions. Good spectral fits have been obtained assuming standard cosmic abundances. The data are interpreted in terms of emission from hot static coronal loops rather similar to the magnetic arch structures found on the Sun. It is shown that the conditions required by this model exist on Capella. Mean values of loop parameters are derived for both temperature components.  相似文献   
87.
88.
We report the results of a 1.4 104s observation of the region of 4U 1323-62 with the EXOSAT ME. The source has a flux of 7–8 10-11 erg/cm2s (2–10 keV) and a power-law spectrum with 1.1 < < 1.8. During our observation, the source showed a symmetric 60% dip in its X-ray flux of R~1 hr. The spectrum hardens during the dip. Inside the dip we observed an X-ray burst with a 2–10 keV peak flux of 7 10-10 erg/cm2s. The burst spectrum is black-body, and shows evidence of cooling during the burst decay. The discovery of a burst from 4U 1323-62 settles the classification of the source; the observation of a dip suggests that we may be able to measure its orbital period in the near future.  相似文献   
89.
Ergun  R.E.  Carlson  C.W.  Mozer  F.S.  Delory  G.T.  Temerin  M.  McFadden  J.P.  Pankow  D.  Abiad  R.  Harvey  P.  Wilkes  R.  Primbsch  H.  Elphic  R.  Strangeway  R.  Pfaff  R.  Cattell  C.A. 《Space Science Reviews》2001,98(1-2):67-91
We describe the electric field sensors and electric and magnetic field signal processing on the FAST (Fast Auroral SnapshoT) satellite. The FAST satellite was designed to make high time resolution observations of particles and electromagnetic fields in the auroral zone to study small-scale plasma interactions in the auroral acceleration region. The DC and AC electric fields are measured with three-axis dipole antennas with 56 m, 8 m, and 5 m baselines. A three-axis flux-gate magnetometer measures the DC magnetic field and a three-axis search coil measures the AC magnetic field. A central signal processing system receives all signals from the electric and magnetic field sensors. Spectral coverage is from DC to 4 MHz. There are several types of processed data. Survey data are continuous over the auroral zone and have full-orbit coverage for fluxgate magnetometer data. Burst data include a few minutes of a selected region of the auroral zone at the highest time resolution. A subset of the burst data, high speed burst memory data, are waveform data at 2×106 sample s–1. Electric field and magnetic field data are primarily waveforms and power spectral density as a function of frequency and time. There are also various types of focused data processing, including cross-spectral analysis, fine-frequency plasma wave tracking, high-frequency polarity measurement, and wave-particle correlations.  相似文献   
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号