全文获取类型
收费全文 | 2589篇 |
免费 | 32篇 |
国内免费 | 12篇 |
专业分类
航空 | 1020篇 |
航天技术 | 956篇 |
综合类 | 12篇 |
航天 | 645篇 |
出版年
2022年 | 13篇 |
2021年 | 31篇 |
2019年 | 28篇 |
2018年 | 78篇 |
2017年 | 62篇 |
2016年 | 51篇 |
2015年 | 24篇 |
2014年 | 81篇 |
2013年 | 99篇 |
2012年 | 77篇 |
2011年 | 152篇 |
2010年 | 108篇 |
2009年 | 149篇 |
2008年 | 151篇 |
2007年 | 83篇 |
2006年 | 65篇 |
2005年 | 81篇 |
2004年 | 79篇 |
2003年 | 84篇 |
2002年 | 60篇 |
2001年 | 77篇 |
2000年 | 39篇 |
1999年 | 48篇 |
1998年 | 52篇 |
1997年 | 50篇 |
1996年 | 46篇 |
1995年 | 59篇 |
1994年 | 35篇 |
1993年 | 38篇 |
1992年 | 54篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 42篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 62篇 |
1984年 | 59篇 |
1983年 | 46篇 |
1982年 | 43篇 |
1981年 | 59篇 |
1980年 | 34篇 |
1979年 | 16篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1974年 | 12篇 |
1971年 | 7篇 |
1969年 | 7篇 |
排序方式: 共有2633条查询结果,搜索用时 0 毫秒
151.
Parker D. E. Basnett T. A. Brown S. J. Gordon M. Horton E. B. Rayner N. A. 《Space Science Reviews》2000,94(1-2):309-320
A survey is given of the available instrumental data for monitoring and analysis of climatic variations. We focus on temperature measurements, both over land and ocean, at the surface and aloft.Over land, the older observations were subject to exposure changes which may not have been fully compensated. The effects of urbanization have been largely avoided in studies of climatic change over the last 150 years. There are few records for pre-1850 outside Europe and eastern North America, and the global network shows a recent decline. Over the ocean, sea surface temperature (SST) has been measured using buckets, engine intakes, hull sensors, buoys, and satellites. Many of these data have been effectively homogenized, but new challenges arise as observing systems evolve. Available SST and marine air temperature datasets begin in the 1850s. The data are concentrated in shipping lanes especially before 1900, and very sparse during the world wars, but additional historical data are being digitized.The radiosonde record is short (40 years) and has major gaps over the oceans, tropics and Southern Hemisphere. Instrumental heterogeneities are beginning to be assessed and removed using physical and statistical techniques. The MSU record is complete but only began in 1979, and is not highly resolved in the vertical: major biases, mainly affecting the lower-tropospheric retrieval, have been reduced as a result of recent analyses.Advanced interpolation or data-assimilation techniques are being applied to these data, but the results must be interpreted with care. 相似文献
152.
Recent observational evidence has suggested that variations in solar activity may affect winter stratospheric polar ozone and temperature levels. The paucity of direct sunlight available during this season points strongly to a dynamical mechanism. We have carried out several large ensemble experiments within the middle atmosphere and the coupled middle atmosphere and lower thermosphere to simulate the radiative/dynamical coupling via planetary waves for a range of solar fluxes. In the former case, the model response in the winter stratosphere was linear and of the order of the summer stratopause forcing, whilst in the latter, the level of correlation in the winter stratosphere remained high, but was diluted over a wider volume. The inclusion of the upper atmosphere enhanced the winter polar stratospheric response by a factor of three. 相似文献
153.
154.
Clark R.N. Masreliez C.J. Burrows J.W. 《IEEE transactions on aerospace and electronic systems》1976,(4):459-463
A scheme to provide redundant sensor data in an automatic control system using the principle of functional redundancy is described. Normally there are three redundant radar altimeters used in the terminal phase of automatic landing of jet transport airplanes. This scheme replaces one of these altimeters with a data processing scheme based on a Kalman filter. The filter is driven by altitude rate and acceleration signals from the air data computer and vertical accelerometer. A special initialization technique employs the two altimeter signals. The feasibility of this scheme is indicated by tests in which data obtained from these several sensors during flight tests are used to drive the functionally redundant altimeter. 相似文献
155.
E. H. B. M. Gronenschild R. Mewe N. J. Westergaard J. Heise F. D. Seward T. Chlebowski N. P. M. Kuin A. C. Brinkman J. H. Dijkstra H. W. Schnopper 《Space Science Reviews》1981,30(1-4):185-189
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
156.
B. Aschenbach H. Bräuninger U. Briel W. Brinkmann H. Fink N. Heinecke H. Hippmann G. Kettenring G. Metzner A. Ondrusch E. Pfeffermann P. Predehl G. Reger K. -H. Stephan J. Trümper H. U. Zimmermann 《Space Science Reviews》1981,30(1-4):569-573
The primary scientific objective of the ROSAT mission is to perform the first all sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. Consequently a large number of new sources (> 105) will be discovered and located with an accuracy of 1 arcmin. After completion of the survey which will take about half a year the instrument will be used for detailed observations of selected targets.The X-ray telescope consists of a fourfold nested Wolter type I mirror system with 80 cm aperture and 240 cm focal length, and three focal plane detectors. In the baseline version these will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 20 × 20. 相似文献
157.
G. Branduardi-Raymont R. Corbet A. N. Parmar P. G. Murdin K. O. Mason 《Space Science Reviews》1981,30(1-4):279-286
We report photometric observations of the optical counterpart of the X-ray source 2S0921-630. The data, obtained at the South African Astronomical Observatory during 3 weeks in 1980 and 1981, are consistent with a 17.9 day periodic modulation of the flux in the B band. Correlated variability of the (B-V) and (U-B) colour indices with the B mag. is demonstrated and quantified. The observed B mag. and colours at maximum and minimum light are used to compute some of the system parameters. A model of 2S0921-630 is proposed in terms of a binary system in which the variable inclination of a luminous accretion disc produces the long-term modulation of the optical flux. 相似文献
158.
159.
We present the results of a continuous 18 hour observation of 4U1755-33 made with the European Space Agency's EXOSAT Observatory. Four 50 min dips in X-ray intensity were observed equally spaced with a period of 4.4 hrs, confirming the periodicity first suggested in White et al. (1984). The dips are spectrally independent. We examine the properties of 4U1755-33 and conclude that the source is most probably point-like and that the metallicity of the absorbing material is at least 600 times less than cosmic values. 相似文献
160.
von Steiger R. Zurbuchen T.H. Geiss J. Gloeckler G. Fisk L.A. Schwadron N.A. 《Space Science Reviews》2001,97(1-4):123-127
The source region of solar wind plasma is observed to be directly reflected in the compositional pattern of both elemental
and charge state compositions. Slow solar wind associated with streamers shows higher freeze-in temperatures and larger FIP
enhancements than coronal hole associated wind. Also, the variability of virtually all compositional parameters is much higher
for slow solar wind compared to coronal hole associated wind. We show that these compositional patterns persist even though
stream-stream interactions complicate the identification based on in situ plasma parameters.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献