全文获取类型
收费全文 | 5388篇 |
免费 | 7篇 |
国内免费 | 15篇 |
专业分类
航空 | 2297篇 |
航天技术 | 1935篇 |
综合类 | 15篇 |
航天 | 1163篇 |
出版年
2021年 | 46篇 |
2018年 | 108篇 |
2017年 | 91篇 |
2016年 | 82篇 |
2015年 | 37篇 |
2014年 | 118篇 |
2013年 | 151篇 |
2012年 | 139篇 |
2011年 | 230篇 |
2010年 | 167篇 |
2009年 | 250篇 |
2008年 | 294篇 |
2007年 | 161篇 |
2006年 | 117篇 |
2005年 | 161篇 |
2004年 | 176篇 |
2003年 | 178篇 |
2002年 | 123篇 |
2001年 | 187篇 |
2000年 | 87篇 |
1999年 | 111篇 |
1998年 | 137篇 |
1997年 | 102篇 |
1996年 | 106篇 |
1995年 | 143篇 |
1994年 | 151篇 |
1993年 | 79篇 |
1992年 | 101篇 |
1991年 | 39篇 |
1990年 | 52篇 |
1989年 | 93篇 |
1988年 | 42篇 |
1987年 | 43篇 |
1986年 | 58篇 |
1985年 | 173篇 |
1984年 | 133篇 |
1983年 | 108篇 |
1982年 | 103篇 |
1981年 | 195篇 |
1980年 | 45篇 |
1979年 | 39篇 |
1978年 | 43篇 |
1977年 | 40篇 |
1976年 | 36篇 |
1975年 | 47篇 |
1974年 | 43篇 |
1973年 | 37篇 |
1972年 | 43篇 |
1971年 | 25篇 |
1970年 | 25篇 |
排序方式: 共有5410条查询结果,搜索用时 0 毫秒
871.
J Huttermann A Schaefer G Kraft 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):35-44
Free radical formation after heavy-ion bombardment was studied in solid, polycristalline pellets of DNA-constituents by analysing the dose-yield curves and the spectra obtained by ESR-spectroscopy at low (< 100 K) and ambient temperatures. The dose-yield curves were found to correlate with those found after X-irradiation but shifted to higher doses and lower saturation concentrations. The corresponding radical yields (per 100 eV) exhibit values which are one to two orders of magnitudes lower. The structural aspects as revealed from powder ESR-spectra gave a complex inter-relation between substance, LET, dose and irradiation temperature, which is discussed in terms of mechanistic models. 相似文献
872.
J F Bottollier-Depois Q Chau P Bouisset G Kerlau L Plawinski L Lebaron-Jacobs 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(1):59-66
The assessment of exposure to cosmic radiation on board aircraft is one of the preoccupations of organizations responsible for radiation protection. The cosmic radiation particle flux increases with altitude and latitude and depends on the solar activity. The radiation exposure has been estimated on several airlines using transatlantic, Siberian and transequatorial routes on board subsonic and supersonic aircraft, to illustrate the effect of these parameters. Measurements have been obtained with a tissue equivalent proportional counter using the microdosimetric technique. Data have been collected at maximum solar activity in 1991-92 and at minimum in 1996-98. The lowest mean dose rate measured was 3 microSv/h during a Paris-Buenos Aires flight in 1991; the highest was 6.6 microSv/h during a Paris-Tokyo flight using a Siberian route and 9.7 microSv/h on Concorde in 1996-97. The mean quality factor is around 1.8. The corresponding annual effective dose, based on 700 hours of flight for subsonic aircraft and 300 hours for Concorde, can be estimated between 2 mSv for least-exposed routes and 5 mSv for more exposed routes. 相似文献
873.
B Shukitt-Hale G Casadesus I Cantuti-Castelvetri B M Rabin J A Joseph 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(1):119-126
Exposing rats to particles of high energy and charge (e.g., 56Fe) disrupts neuronal systems and the behaviors mediated by them; these adverse behavioral and neuronal effects are similar to those seen in aged animals. Because cognition declines with age, and our previous study showed that radiation disrupted Morris water maze spatial learning and memory performance, the present study used an 8-arm radial maze (RAM) to further test the cognitive behavioral consequences of radiation exposure. Control rats or rats exposed to whole-body irradiation with 1.0 Gy of 1 GeV/n high-energy 56Fe particles (delivered at the alternating gradient synchrotron at Brookhaven National Laboratory) were tested nine months following exposure. Radiation adversely affected RAM performance, and the changes seen parallel those of aging. Irradiated animals entered baited arms during the first 4 choices significantly less than did controls, produced their first error sooner, and also tended to make more errors as measured by re-entries into non-baited arms. These results show that irradiation with high-energy particles produces age-like decrements in cognitive behavior that may impair the ability of astronauts to perform critical tasks during long-term space travel beyond the magnetosphere. 相似文献
874.
T G Guzik S Albergo C X Chen S Costa H J Crawford J Engelage P Ferrando I Flores L Greiner F C Jones C N Knott S Ko P J Lindstrom J Mazotta J W Mitchell J Romanski R Potenza A Soutoul O Testard C E Tull C Tuve C J Waddington W R Webber J P Wefel X Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):825-830
The Transport Collaboration, consisting of researchers from institutions in France, Germany, Italy and the USA, has established a program to make new measurements of nuclear interaction cross sections for heavy projectiles (Z > or = 2) in targets of liquid H2, He and heavier materials. Such cross sections directly affect calculations of galactic and solar cosmic ray transport through matter and are needed for accurate radiation hazard assessment. To date, the collaboration has obtained data using the LBL Bevalac HISS facility with 20 projectiles from 4He to 58Ni in the energy range 393-910 MeV/nucleon. Preliminary results from the analysis of these data are presented here and compared to other measurements and to cross section prediction formulae. 相似文献
875.
W.F. Hoffmann G.G. Fazio D.A. Harper 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(1):117-120
A NASA supported design study is being carried out for a three-meter balloon-borne far infrared and submillimeter telescope. The goal of this project is to provide a facility for frequent flights for photometry, spectroscopy, and imaging in the spectral region 30 micrometers to 1 millimeter. It is intended to provide a scientific and technical step on the way to a large submillimeter telescope in space in the future. The study is concentrating on areas where technical advances are required: materials and fabrication techniques for lightweight primary mirrors, telescope and gondola structure, and pointing and stabilization. We are carrying out a design optimization and environmental test program of state-of-the-art carbon fiber reinforced plastic sandwich panels in collaboration with Dornier Systems. Similar efforts are being pursued for very lightweight molded glass mirrors. Innovative approaches to the telescope support and stabilization are being explored for achieving the required 1 arcsecond pointing stability. 相似文献
876.
S. Azouggagh-McBride L.A. Roe M.A. Franzen J.A. Buffington D.W.G. Sears 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Laboratory impact tests have been performed on experimental versions of a proposed robotic sample collector for extraterrestrial samples. The collector consists of a retractable aluminum ring containing an impregnable silicone compound that is pressed into the surface of the body to be sampled. As part of a comprehensive program to evaluate this idea, we have performed tests to determine if the samples embedded in the collector medium can survive the impact forces experienced during direct reentry, such as that of the recent Genesis sample return mission. For the present study, samples of sand, rock, glass, and chalk were subjected to decelerations of 1440–2880 g using drop tests. We found that even the most fragile samples, chosen to be representative of a wide range of the types of materials found on the surface of asteroids that have currently been studied, can withstand impacts of the intensity experienced by a sample return capsule during direct reentry. 相似文献
877.
J.S. Halekas D.A. BrainR.P. Lin J.G. LuhmannD.L. Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1347-1352
We investigate accelerated electrons observed by Mars Global Surveyor (MGS), using data from the Electron Reflectometer (ER) instrument. We find three different types of accelerated electron events. Current sheet events occur over regions with weak or no crustal fields, have the highest electron energy fluxes, and are likely located on draped magnetotail fields. Extended events occur over regions with moderate crustal magnetic fields, and are most often observed on closed magnetic field lines. Localized events have the lowest energy fluxes, occur in strong magnetic cusp regions, and are the most likely kind of event to be found on open magnetic field lines. Some localized events have clear signatures of field-aligned currents; these events have much higher electron fluxes, and are preferentially observed on radially oriented open magnetic field lines. Electron acceleration events, especially localized events, are similar in many ways to events observed in the terrestrial auroral zone. However, physical processes related to those found in the terrestrial cusp and/or plasmasheet could also be responsible for accelerating electrons at Mars. 相似文献
878.
Hardware-in-the-loop testing technology for automatic control, condition monitoring and diagnostics systems of gas turbine engines is described. The technology proposed makes it possible to simulate combinations and chains of unexpected and gradual failures of engines, transducers and actuators. 相似文献
879.
I. Sh. Sharafeev 《Russian Aeronautics (Iz VUZ)》2009,52(2):255-258
A set of systems for labor standard computer-aided design is described, namely, initial developments, advance and state-of-the art. 相似文献
880.
Yu. G. Kutsenko 《Russian Aeronautics (Iz VUZ)》2009,52(2):208-213
A modification of the Zimont turbulent combustion model is presented; the modification makes it possible to describe processes in diffusion and homogeneous flame fronts as well as to take into account the influence of different factors that cause flame destabilization. The model is based on the equation for a reaction completeness extent (completeness of combustion). The model realization to simulate the premixed combustion is described and the modification of the turbulent combustion model is applied to simulate a process of flameout downstream of the flameholder. 相似文献