全文获取类型
收费全文 | 2357篇 |
免费 | 5篇 |
国内免费 | 4篇 |
专业分类
航空 | 1282篇 |
航天技术 | 844篇 |
综合类 | 13篇 |
航天 | 227篇 |
出版年
2018年 | 27篇 |
2017年 | 23篇 |
2014年 | 24篇 |
2013年 | 47篇 |
2012年 | 29篇 |
2011年 | 62篇 |
2010年 | 50篇 |
2009年 | 63篇 |
2008年 | 129篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 50篇 |
2004年 | 71篇 |
2003年 | 74篇 |
2002年 | 37篇 |
2001年 | 55篇 |
2000年 | 51篇 |
1999年 | 30篇 |
1998年 | 77篇 |
1997年 | 57篇 |
1996年 | 62篇 |
1995年 | 69篇 |
1994年 | 90篇 |
1993年 | 56篇 |
1992年 | 70篇 |
1991年 | 29篇 |
1990年 | 35篇 |
1989年 | 71篇 |
1988年 | 27篇 |
1987年 | 29篇 |
1986年 | 50篇 |
1985年 | 90篇 |
1984年 | 57篇 |
1983年 | 60篇 |
1982年 | 57篇 |
1981年 | 70篇 |
1980年 | 35篇 |
1979年 | 28篇 |
1978年 | 27篇 |
1977年 | 25篇 |
1975年 | 26篇 |
1974年 | 24篇 |
1973年 | 24篇 |
1972年 | 22篇 |
1971年 | 32篇 |
1970年 | 17篇 |
1969年 | 26篇 |
1968年 | 18篇 |
1967年 | 20篇 |
1966年 | 20篇 |
排序方式: 共有2366条查询结果,搜索用时 15 毫秒
201.
S B Curtis E G Luebeck W D Hazelton S H Moolgavkar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):937-944
When applied to the Colorado Plateau miner population, the two-stage clonal expansion (TSCE) model of radiation carcinogenesis predicts that radiation-induced promotion dominates radiation-induced initiation. Thus, according to the model, at least for alpha-particle radiation from inhaled radon daughters, lung cancer induction over long periods of protracted irradiation appears to be dominated by radiation-induced modification of the proliferation kinetics of already-initiated cells rather than by direct radiation-induced initiation (i.e., mutation) of normal cells. We explore the possible consequences of this result for radiation exposures to space travelers on long missions. Still unknown is the LET dependence of this effect. Speculations of the cause of this phenomenon include the suggestion that modification of cell kinetics is caused by a "bystander" effect, i.e., the traversal of normal cells by alpha particles, followed by the signaling of these cells to nearby initiated cells which then modify their proliferation kinetics. 相似文献
202.
A commonly accepted view is that life began in a marine environment, which would imply the presence of inorganic ions such as Na+, Cl-, Mg2+, Ca2+, and Fe2+. We have investigated two processes relevant to the origin of life--membrane self-assembly and RNA polymerization--and established that both are adversely affected by ionic solute concentrations much lower than those of contemporary oceans. In particular, monocarboxylic acid vesicles, which are plausible models of primitive membrane systems, are completely disrupted by low concentrations of divalent cations, such as magnesium and calcium, and by high sodium chloride concentrations as well. Similarly, a nonenzymatic, nontemplated polymerization of activated RNA monomers in ice/eutectic phases (in a solution of low initial ionic strength) yields oligomers with > 80% of the original monomers incorporated, but polymerization in initially higher ionic strength aqueous solutions is markedly inhibited. These observations suggest that cellular life may not have begun in a marine environment because the abundance of ionic inorganic solutes would have significantly inhibited the chemical and physical processes that lead to self-assembly of more complex molecular systems. 相似文献
203.
Avdeev S Bidoli V Casolino M De Grandis E Furano G Morselli A Narici L De Pascale MP Picozza P Reali E Sparvoli R Boezio M Carlson P Bonvicini W Vacchi A Zampa N Castellini G Fuglesang C Galper A Khodarovich A Ozerov Y Popov A Vavilov N Mazzenga G Ricci M Sannita WG Spillantini P 《Acta Astronautica》2002,50(8):511-525
The phenomenon of light flashes (LF) in eyes for people in space has been investigated onboard Mir. Data on particles hitting the eye have been collected with the SilEye detectors, and correlated with human observations. It is found that a nucleus in the radiation environment of Mir has roughly a 1% probability to cause an LF, whereas the proton probability is almost three orders of magnitude less. As a function of LET, the LF probability increases above 10 keV/micrometer, reaching about 5% at around 50 keV/micrometer. 相似文献
204.
Education and public outreach are viewed by NASA as significant undertakings for all of its space missions. The IMAGE satellite is one of the first missions to explicitly include `E&PO in its original proposal to NASA in 1996. We will discuss what IMAGE has accomplished in this area to date, and what new activities it will conduct following a successful launch. 相似文献
205.
V Bidoli M Casolino M P De Pascale G Furano A Morselli L Narici P Picozza E Reali R Sparvoli A M Galper A V Ozerov YuVPopov N R Vavilov A P Alexandrov S V Avdeev Y u Baturin Y u Budarin G Padalko V G Shabelnikov G Barbellini W Bonvicini A Vacchi N Zampa S Bartalucci G Mazzenga M Ricci O Adriani P Spillantini M Boezio P Carlson C Fuglesang G Castellini W G Sannita 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2000,25(10):2075-2079
The SilEye experiment aims to study the cause and processes related to the anomalous Light Flashes (LF) perceived by astronauts in orbit and their relation with Cosmic Rays. These observations will be also useful in the study of the long duration manned space flight environment. Two PC-driven silicon detector telescopes have been built and placed aboard Space Station MIR. SilEye-1 was launched in 1995 and provided particles track and LF information; the data gathered indicate a linear dependence of FLF(Hz) ( 4 2) 10(3) 5.3 1.7 10(4) Fpart(Hz) if South Atlantic Anomaly fluxes are not included. Even though higher statistic is required, this is an indication that heavy ion interactions with the eye are the main LF cause. To improve quality and quantity of measurements, a second apparatus, SilEye-2, was placed on MIR in 1997, and started work from August 1998. This instrument provides energetic information, which allows nuclear identification in selected energy ranges; we present preliminary measurements of the radiation field inside MIR performed with SilEye-2 detector in June 1998. 相似文献
206.
207.
C. Satirapod I. Trisirisatayawong L. Fleitout J.D. Garaud W.J.F. Simons 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Following previous findings from ongoing GPS research in Thailand since 2004 we continue to exploit the GPS technique to monitor and model land motions induced by the Sumatra–Andaman Earthquake. Our latest results show that up to the end of 2010, Thailand has been co-seismically displaced and is subsequently undergoing a post-seismic horizontal deformation with total displacements (co-seismic plus post-seismic) ranging from 10.5 to 74.7 cm. We observed the largest horizontal displacements in the southern part of Thailand and moderate and small displacements in the central and northern parts. In addition to horizontal displacements throughout Thailand, continuous GPS measurements show that large parts of Thailand are subsiding at rates up to 1 cm/yr. It is the first time that such vertical post-seismic deformations at large distances (650–1500 km away from the Earthquake’s epicentre) have been recorded. We have investigated the physical processes leading to the observed subsidence. While after-slip on the subduction interface induces negligible or even slightly positive vertical motions, relaxation in the asthenosphere is associated with a sizable subsidence. Predictions from a 3D finite element model feature an asthenosphere with an effective viscosity of the order of 3 * 1018 Pas, fit the horizontal post-seismic data and the observed subsidence well. This model is then used to predict the subsidence over the whole seismic cycle. The subsidence should go on with a diminishing rate through the next two decades and its final magnitude should not exceed 10 cm in the Bangkok area. 相似文献
208.
W. Menn O. Adriani G.C. Barbarino G.A. Bazilevskaya R. Bellotti M. Boezio E.A. Bogomolov L. Bonechi M. Bongi V. Bonvicini S. Borisov S. Bottai A. Bruno F. Cafagna D. Campana R. Carbone P. Carlson M. Casolino G. Castellini L. Consiglio M.P. De Pascale C. De Santis N. De Simone V. Di Felice A.M. Galper W. Gillard L. Grishantseva G. Jerse A.V. Karelin S.V. Koldashov S.Y. Krutkov A.N. Kvashnin A. Leonov V. Malakhov V. Malvezzi L. Marcelli A.G. Mayorov V.V. Mikhailov E. Mocchiutti A. Monaco N. Mori N. Nikonov G. Osteria F. Palma P. Papini M. Pearce P. Picozza C. Pizzolotto M. Ricci S.B. Ricciarini 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
209.
The conventional ambiguity function is extended to include the Doppler distortions of the modulation function. The distinctive features of the extension are the use of the complex notation for wideband signals, and inclusion of the Doppler effect on the signal amplitude. The result is an ambiguity function from which Woodward's form can be found by inspection. It is shown that the well-known volume constraint also applies, in unchanged form, to the generalized ambiguity function. For the volume to be constant, it is not required that the distortions of the modulation function be neglected. Rather, the volume constancy is related to the sinusoidal fluctuations of a modulated carrier-type signal and thus is strictly a matter of the percentage bandwidth of the signal. 相似文献
210.
Previous calculations of the accumulation of small (∼10 km) planetesimals at ∼1 AU to form Mars-sized bodies assumed that
the initial assemblage of planetesimals were all present at the outset. This is an obviously reasonable assumption in systems
in which the time scale for growth time of ∼1026 g planetary bodies is long compared to estimates of the evolutionary time scale of a protosolar disk, as was the case in
the pioneering work of Safronov (1969). It is now found that as a result of the preplanetary assemblage being unstable with
respect to the runaway growth of the largest bodies, this is unlikely to be the case. The more realistic alternative of adding
the initial planetesimals on a ∼105 year time scale is considered here, as well as the consequences of the initial planetesimals being considerably smaller than
those assumed previously. It is found that although the time scale for runaway growth is now actually controlled by the availability
of planetesimals, for planetesimal production time scales of ∼105 yrs, the final consequences are very similar. These calculations do show, however, that as a consequence of continuous infall
during the runaway growth process, the late initial planetesimals are likely to be catastrophically disrupted by mutual collisions.
For this reason, a more detailed treatment of the growth of planetesimals into planetary embryos will require a better understanding
of the difficult problem of formation of the initial planetesimals themselves.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献