全文获取类型
收费全文 | 978篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
航空 | 363篇 |
航天技术 | 372篇 |
综合类 | 2篇 |
航天 | 244篇 |
出版年
2022年 | 5篇 |
2021年 | 22篇 |
2019年 | 9篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 35篇 |
2013年 | 47篇 |
2012年 | 41篇 |
2011年 | 42篇 |
2010年 | 34篇 |
2009年 | 60篇 |
2008年 | 72篇 |
2007年 | 22篇 |
2006年 | 21篇 |
2005年 | 31篇 |
2004年 | 22篇 |
2003年 | 28篇 |
2002年 | 20篇 |
2001年 | 38篇 |
2000年 | 21篇 |
1999年 | 13篇 |
1998年 | 27篇 |
1997年 | 11篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 27篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 4篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1972年 | 8篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有981条查询结果,搜索用时 15 毫秒
811.
I.S. Veselovsky V. Bothmer P. Cargill A.V. Dmitriev K.G. Ivanov E. Romashets A.N. Zhukov O.S. Yakovchouk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2460-2464
Times of sustained strong northward IMF can interrupt the magnetic storm development and lead to lower levels of geomagnetic activity for many hours. During 1997–2000 we have found two events of this kind observed on November 8, 1998 and October 13, 2000. In both cases, the storms started as usual after arrival of ejecta with a southward IMF component from the Sun to the Earth, but ceased after several hours due to the onset of sustained northward IMF leading to the faster recovery process. After the passage of this so-called positive domain, the storm development started again. The heliospheric magnetic field intensity remained enhanced and nearly constant. The solar origins of the geomagnetic storm interruptions have been investigated. Tentatively they may be related to strong nonlinear Alfvйn type solitary waves excited by non-stationary coronal current variations with a characteristic time-scale of about a day. 相似文献
812.
C Rodier O Vandenabeele-Trambouze R Sternberg D Coscia P Coll C Szopa F Raulin C Vidal-Madjar M Cabane G Israel M F Grenier-Loustalot M Dobrijevic D Despois 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(2):195-199
If there is, or ever was, life in our solar system beyond the Earth, Mars is the most likely place to search for. Future space missions will have then to take into account the detection of prebiotic molecules or molecules of biological significance such as amino acids. Techniques of analysis used for returned samples have to be very sensitive and avoid any chemical or biological contamination whereas in situ techniques have to be automated, fast and low energy consuming. Several possible methods could be used for in situ amino acid analyses on Mars, but gas chromatography would likely be the most suitable. Returned samples could be analyzed by any method in routine laboratory use such as gas chromatography, already successfully performed for analyses of organic matter including amino acids from martian meteorites. The derivatization step, which volatilizes amino acids to perform both in situ and laboratory analysis by gas chromatography, is discussed here. 相似文献
813.
This paper presents a review of geoid error characteristics of three satellite gravity missions in view of the general problem
of separating scientifically interesting signals from various noise sources. The problem is reviewed from the point of view
of two proposed applications of gravity missions, one is the observation of the mean oceanic circulation whereby an improved
geoid model is used as a reference surface against the long term mean sea level observed by altimetry. In this case we consider
the presence of mesoscale variability during assimilation of derived surface currents in inverse models. The other experiment
deals with temporal changes in the gravity field observed by GRACE in which case a proposed experiment is to monitor changes
in the geoid in order to detect geophysical interesting signals such as variations in the continental hydrology and non-steric
ocean processes. For this experiment we will address the problem of geophysical signal contamination and the way it potentially
affects monthly geoid solutions of GRACE.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
814.
P.O. Petrucci J. Ferreira G. Henri L. Sauge G. Pelletier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2909-2911
We present a unified accretion–ejection picture that explains the different spectral state of Black Hole X-ray binaries (BHXrB) from radio to X/γ-rays. In this view, the central region of BHXrB has a multi-flow configuration which consists in (1) an outer standard accretion disc, (2) an inner magnetized accretion disc driving, (3) a self-collimated electron–proton MHD jet, surrounding and (4) a relativistic electron–positron beam when adequate conditions are met. This picture provides a simple and unified explanation to the various canonical spectral states of BH X-ray binaries, by varying the transition radius rJ between the inner disc driving jets and the outer standard disc. In this framework, large rJ correspond to Quiescent and Hard states while small rJ correspond to Thermal Dominant ones. In between these two extremes, rJ can reach values that switches on the pair cascade process giving birth to a relativistic electron–positron beam. This would correspond to the bright intermediate state. 相似文献
815.
O. L. Vaisberg A. V. Leibov V. N. Smirnov L. A. Avanov J. -J. Bertelier K. Torcar F. Leblan V. F. Babkin V. A. Grishin V. Baumjohann F. Escoubet 《Cosmic Research》2006,44(3):202-208
A numerical model of an ion mass-spectrometer is developed based on the new type of charged-particle analyzer CAMERA suggested previously [1–3]. The spectrometer provides for complete instantaneous imaging of the flux distribution of various ions in a hemisphere. Such a type of the mass-spectrometer is chosen, which allows one to analyze a conelike beam of ions at the exit of the CAMERA. The mathematical model of the CAMERA with this time-of-flight mass-analyzer ensures sufficiently high mass resolution (M/ΔM > 100) at conserved imaging capabilities of the CAMERA. Such an instrument can find a wide application both in magnetospheric studies and in studying various objects of the solar system. 相似文献
816.
The purpose of this work is to form transparent parametric patterns for 5-axis machining of blade rings of GTE blisks. The algorithms were developed for geometry correction of control surfaces by the results of measuring the geometry of the airfoil blade processed with the use of smoothing algorithms based on the bicubic spline interpolation. 相似文献
817.
Erwin O. Flückiger Rolf Bütikofer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
This review summarizes the history of cosmic ray research at Jungfraujoch, the installation of three neutron monitors in Switzerland, and highlights a few of the main results by the Cosmic Ray Group of the Physikalisches Institut, Universität Bern, Switzerland. In addition, the outstanding scientific and personal contribution of the late Hermann Debrunner, the longtime leader of the Bern Cosmic Ray Group, is honored. 相似文献
818.
J.O. Adeniyi B.O. Adebesin I.A. Adimula O.A. Oladipo A.O. Olawepo S.O. Ikubanni B.W. Reinisch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The Incoherent Scatter Radar measurement over Jicamarca, together with the IRI model-2007 measurements were compared with ground-based digisonde inferred E × B drift over Ilorin in the African region during year of solar minima (F10.7 = 81). Seasonally, Ilorin pre-reversal enhancement (PRE) had peak drift velocities of 7.2, 3.7 and 7.9 m/s for March equinox, September equinox and December solstice respectively, while Jicamarca drifts indicated 13.0, 10.5 and 5.2 m/s; as well as the IRI model with 14.3, 8.4 and 0.7 m/s in similar order. PRE value was insignificant during June solstice. The PRE magnitude of the IRI-model during the equinoxes is twice the value obtained at Ilorin. The daytime E × B drift peaked over Ilorin 1–2 h earlier than both the modeled and Jicamarca observations. This could be due to the difference in sunset time at the conjugate points corresponding to the altitude of the observation. During the evening time PRE, the respective correlation coefficients (R) for Vz–F10.7 relation over Jicamarca, Ilorin and the modeled observations are −0.5559, 0.4796 and −0.4979. Similarly, the Vz–Ap relation exhibit excellent anti-correlation coefficient (R = −0.8637) for the IRI-model, −0.4827 over Jicamarca and 0.3479 for Ilorin. Annual mean drift velocities over Jicamarca, Ilorin and IRI model measurements respectively are 10, 5.6 and 10 m/s for the peak PRE observation; 15, 16 and 21 m/s for the daytime pre-sunrise peak values; and −21, −9 and −16 m/s for the nighttime downward reversals. The root-mean square (RMS) deviation between IRI-model and the Ilorin drift between 2000 and 0500 h is 4.37, 2.03, 3.71 and 2.42 m/s for March equinox, June solstice, September equinox and December solstice respectively. For Jicamarca–Ilorin drift relation, RMS deviation is 5.48, 2.30, 3.47 and 1.27 m/s in the same order respectively. Annual hmF2 inferred drift over Ilorin during daytime is higher by a factor of ≈2 and 3 at Jicamarca and IRI model measurements respectively; and by a factor of ≈5 for both during the night-time period. The limitations in using hmF2 to infer drifts are discussed. 相似文献
819.
In this paper, a problem of ensuring the helicopter flight safety in off-optimum situations is considered. We describe the most typical critical regimes and flight limitations imposed on the helicopter motion parameters. Also presented are some dependences that determine the operating regime limits with respect to the basic flight parameters of the critical flight regimes warning system. 相似文献
820.
A.O. Alothman M.A. Alsubaie M.E. Ayhan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The ionosphere is a dispersive medium for radio waves with the refractive index which is a function of frequency and total electron content (TEC). TEC has a strong diurnal variation in addition to monthly, seasonal and solar cycle variations and small and large scale irregularities. Dual frequency GPS observations can be utilized to obtain TEC and investigate its spatial and temporal variations. We here studied short term TEC variations over the Kingdom of Saudi Arabia (KSA). A regional GPS network is formed consisting of 16 sites in and around KSA. GPS observations, acquired between 1st and 11th February 2009, were processed on a daily basis by using the Bernese v5.0 software and IGS final products. The geometry-free zero difference smoothed code observables were used to obtain two hour interval snapshots of TEC and their RMS errors at 0.5 × 0.5 degree grid nodes and regional ionosphere models in a spherical harmonics expansion to degree and order six. The equatorial ionized anomaly (EIA) is recovered in the south of 20°N from 08:00 to 12:00 UT. We found that day-by-day TEC variation is more stable than the night time variation. 相似文献