全文获取类型
收费全文 | 10315篇 |
免费 | 18篇 |
国内免费 | 31篇 |
专业分类
航空 | 4939篇 |
航天技术 | 3535篇 |
综合类 | 42篇 |
航天 | 1848篇 |
出版年
2021年 | 88篇 |
2019年 | 64篇 |
2018年 | 189篇 |
2017年 | 118篇 |
2016年 | 121篇 |
2015年 | 59篇 |
2014年 | 223篇 |
2013年 | 297篇 |
2012年 | 278篇 |
2011年 | 408篇 |
2010年 | 295篇 |
2009年 | 432篇 |
2008年 | 497篇 |
2007年 | 297篇 |
2006年 | 246篇 |
2005年 | 272篇 |
2004年 | 242篇 |
2003年 | 315篇 |
2002年 | 205篇 |
2001年 | 339篇 |
2000年 | 196篇 |
1999年 | 243篇 |
1998年 | 285篇 |
1997年 | 194篇 |
1996年 | 279篇 |
1995年 | 332篇 |
1994年 | 308篇 |
1993年 | 194篇 |
1992年 | 231篇 |
1991年 | 104篇 |
1990年 | 97篇 |
1989年 | 224篇 |
1988年 | 102篇 |
1987年 | 110篇 |
1986年 | 102篇 |
1985年 | 304篇 |
1984年 | 243篇 |
1983年 | 198篇 |
1982年 | 211篇 |
1981年 | 331篇 |
1980年 | 98篇 |
1979年 | 76篇 |
1978年 | 87篇 |
1977年 | 74篇 |
1975年 | 93篇 |
1974年 | 70篇 |
1973年 | 64篇 |
1972年 | 76篇 |
1971年 | 67篇 |
1970年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
561.
Yuming Fu Hui Liu Lingzhi Shao Minjuan Wang Yu A. Berkovich A.N. Erokhin Hong Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Vegetable cultivation plays a crucial role in dietary supplements and psychosocial benefits of the crew during manned space flight. Here we developed a ground-based prototype of horn-type sequential vegetable production facility, named Horn-type Producer (HTP), which was capable of simulating the microgravity effect and the continuous cultivation of leaf–vegetables on root modules. The growth chamber of the facility had a volume of 0.12 m3, characterized by a three-stage space expansion with plant growth. The planting surface of 0.154 m2 was comprised of six ring-shaped root modules with a fibrous ion-exchange resin substrate. Root modules were fastened to a central porous tube supplying water, and moved forward with plant growth. The total illuminated crop area of 0.567 m2 was provided by a combination of red and white light emitting diodes on the internal surfaces. In tests with a 24-h photoperiod, the productivity of the HTP at 0.3 kW for lettuce achieved 254.3 g eatable biomass per week. Long-term operation of the HTP did not alter vegetable nutrition composition to any great extent. Furthermore, the efficiency of the HTP, based on the Q-criterion, was 7 × 10−4 g2 m−3 J−1. These results show that the HTP exhibited high productivity, stable quality, and good efficiency in the process of planting lettuce, indicative of an interesting design for space vegetable production. 相似文献
562.
A. Antoniou E. Danezis E. Lyratzi L.Č. Popović D. Stathopoulos M.S. Dimitrijević 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
In this paper, using the Gauss-Rotation model (GR model), we analyse the UV C IV resonance lines in the spectra of 20 Oe-stars of different spectral subtypes, in order to detect the structure of C IV region. We study the presence and behavior of absorption clouds and analyse their characteristics. From this analysis we can calculate the values of a group of physical parameters, such as the apparent rotational and radial velocities, the random velocities of the thermal motions of the ions, the Full Width at Half Maximum (FWHM), the optical depth, as well as the absorbed energy and the column density of the independent regions of matter, which produce the main and the satellite clouds of the studied spectral lines. Finally, we present the relations between these physical parameters and the spectral subtypes of the studied stars and we give our results about the structure of the C IV region in their atmosphere. 相似文献
563.
W.D. Apel J.C. Arteaga-Velázquez K. Bekk M. Bertaina J. Blümer H. Bozdog I.M. Brancus E. Cantoni A. Chiavassa F. Cossavella K. Daumiller V. de Souza F. Di Pierro P. Doll R. Engel J. Engler M. Finger B. Fuchs D. Fuhrmann H.J. Gils R. Glasstetter C. Grupen A. Haungs D. Heck J.R. Hörandel D. Huber T. Huege K.-H. Kampert D. Kang H.O. Klages K. Link P. Łuczak M. Ludwig H.J. Mathes H.J. Mayer M. Melissas J. Milke B. Mitrica C. Morello J. Oehlschläger S. Ostapchenko N. Palmieri M. Petcu T. Pierog H. Rebel M. Roth H. Schieler S. Schoo F.G. Schröder O. Sima 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
564.
S. Narendranath P.S. Athiray P. Sreekumar V. Radhakrishna A. Tyagi B.J. Kellett the CLASS team 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS. 相似文献
565.
J.R. Souza W.D. Asevedo Jr. P.C.P. dos Santos A. Petry G.J. Bailey I.S. Batista M.A. Abdu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
We describe a new version of the Parameterized Regional Ionospheric Model (PARIM) which has been modified to include the longitudinal dependences. This model has been reconstructed using multidimensional Fourier series. To validate PARIM results, the South America maps of critical frequencies for the E (foE) and F (foF2) regions were compared with the values calculated by Sheffield Plasmasphere-Ionosphere Model (SUPIM) and IRI representations. PARIM presents very good results, the general characteristics of both regions, mainly the presence of the equatorial ionization anomaly, were well reproduced for equinoctial conditions of solar minimum and maximum. The values of foF2 and hmF2 recorded over Jicamarca (12°S; 77°W; dip lat. 1°N; mag. declination 0.3°) and sites of the conjugate point equatorial experiment (COPEX) campaign Boa Vista (2.8°N; 60.7°W; dip lat. 11.4°; mag. declination −13.1°), Cachimbo (9.5°S; 54.8°W; dip lat. −1.8°; mag. declination −15.5°), and Campo Grande (20.4°S; 54.6°W; dip lat. −11.1°; mag. declination −14.0°) have been used in this work. foF2 calculated by PARIM show good agreement with the observations, except during morning over Boa Vista and midnight-morning over Campo Grande. Some discrepancies were also found for the F-region peak height (hmF2) near the geomagnetic equator during times of F3 layer occurrences. IRI has underestimated both foF2 and hmF2 over equatorial and low latitude sectors during evening-nighttimes, except for Jicamarca where foF2 values were overestimated. 相似文献
566.
在机体结构维修中,飞机舱门经常因腐蚀和碰撞而使维修项目较多。但当前许多创新材料和作动系统正在让舱门维修项目减少,维修变得简易化。如新型热塑性材料、先进的机电作动系统和传感器技术、环保的表面处理技术等。一般来说,客舱和货舱门及其部件极易因腐蚀和碰撞造成损伤,如客机和货机前后舱门的下部在装卸行李和货物过程中容易被地面服务车辆和单元装载设备损坏,因此维修项目较多。令人欣慰的是,原始制造商和供应商正在从材料和部件方面引入创新技术,提高产品的损伤容限,降低维修强度。 相似文献
567.
B. Sylwester J. Sylwester K.J.H. Phillips E. Landi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We present the observations of He-like Ar triplet lines obtained by RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios between triplet lines of lower Z elements is known to provide useful diagnostics of plasma conditions within the emitting source. Here, we investigate whether triplet line ratios are useful for interpretation of higher Z element spectra. A high sensitivity, low background and precise absolute calibration of RESIK allow to consider in addition also the continuum contribution. This provides a way to determine the Ar absolute abundance from the observed triplet component ratios. The method is presented and the results are shown for two selected flares. Derived values of Ar absolute abundance for these flares are found to be similar: 2.6 × 10−6 and 2.9 × 10−6. They fall in the range between presently accepted Ar photospheric and coronal abundances. 相似文献
568.
Anand K. Singh A.K. Sinha Rahul Rawat Bulusu Jayashree B.M. Pathan Ajay Dhar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Magnetic data from a newly commissioned Indian Antarctic station Bharati (corrected geomagnetic (CGM) coordinates 74.7°S, 97.2°E) and closely-spaced IMAGE chain observatories (∼100° magnetic meridian in Northern hemisphere) has been analyzed to study the climatology of substorms which were localized poleward of the standard auroral oval. We considered four austral summers (year 2007–2010) when data from Bharati was available. Several very high latitude substorms were observed in this duration when the solar activity remained unexpectedly low for a long time. Various features of very high latitude substorms, e.g., local time dependence, interplanetary state, hemispherical asymmetry and their nightside low latitude signatures are examined. Events studied here, suggested the following properties of substorms occurring at very high latitudes: (1) maximum occurrence was observed near magnetic midnight (21:00–02:00 MLT). (2) In contradiction to earlier reports, many substorms were observed even during negative IMF Bz condition. In addition, majority of substorms occurred during low or moderate solar wind streams. (3) Magnetic signatures were often pronounced in the winter hemisphere. (4) Even if widely used standard AE indices fail to monitor very high latitude substorms, their low latitude signatures are often evident. 相似文献
569.
Z. Peeters D. Vos I.L. ten Kate F. Selch C.A. van Sluis D.Yu. Sorokin G. Muijzer H. Stan-Lotter M.C.M. van Loosdrecht P. Ehrenfreund 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Halophilic archaea are of interest to astrobiology due to their survival capabilities in desiccated and high salt environments. The detection of remnants of salty pools on Mars stimulated investigations into the response of haloarchaea to martian conditions. Natronorubrum sp. strain HG-1 is an extremely halophilic archaeon with unusual metabolic pathways, growing on acetate and stimulated by tetrathionate. We exposed Natronorubrum strain HG-1 to ultraviolet (UV) radiation, similar to levels currently prevalent on Mars. In addition, the effects of low temperature (4, −20, and −80 °C), desiccation, and exposure to a Mars soil analogue from the Atacama desert on the viability of Natronorubrum strain HG-1 cultures were investigated. The results show that Natronorubrum strain HG-1 cannot survive for more than several hours when exposed to UV radiation equivalent to that at the martian equator. Even when protected from UV radiation, viability is impaired by a combination of desiccation and low temperature. Desiccating Natronorubrum strain HG-1 cells when mixed with a Mars soil analogue impaired growth of the culture to below the detection limit. Overall, we conclude that Natronorubrum strain HG-1 cannot survive the environment currently present on Mars. Since other halophilic microorganisms were reported to survive simulated martian conditions, our results imply that survival capabilities are not necessarily shared between phylogenetically related species. 相似文献
570.
A. Damiani M. Storini C. Rafanelli P. Diego 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The low background values at nighttime of the mesospheric hydroxyl (OH) radical make it easier to single out the atmospheric response to the external solar forcing in Polar Regions. Because of the short lifetime of HOx, it is possible to follow the trails of Solar Energetic Particle (SEP) events in the terrestrial atmosphere, as shown by Storini and Damiani (2008). The sensitivity of this indicator makes discernible not only extreme particle events with a flux peak of several thousand pfu [1 pfu = 1 particle/(cm2 s sr)] at energies >10 MeV, but also those with lower flux up to about 300 pfu. Using data from the Microwave Limb Sounder (MLS) on board the EOS AURA satellite, we examined the correlation of OH abundance vs. solar proton flux for almost all the identified SEP events spanning from November 2004 to December 2006 (later on no more SEP events occurred during Solar Cycle no. 23). The channels at energies greater than 5 MeV and 10 MeV showed the best correlation values (r ∼ 0.90–0.95) at altitudes around 65–75 km whereas, as expected, the most energetic channels were most highly correlated at lower altitudes. Therefore, it is reasonably possible to estimate the solar proton flux from values of mesospheric OH (and viceversa) and it could be useful in studying periods with gaps in the records of solar particles. 相似文献