全文获取类型
收费全文 | 3995篇 |
免费 | 9篇 |
国内免费 | 7篇 |
专业分类
航空 | 1679篇 |
航天技术 | 1088篇 |
综合类 | 20篇 |
航天 | 1224篇 |
出版年
2022年 | 15篇 |
2021年 | 42篇 |
2019年 | 19篇 |
2018年 | 227篇 |
2017年 | 172篇 |
2016年 | 130篇 |
2015年 | 52篇 |
2014年 | 116篇 |
2013年 | 148篇 |
2012年 | 142篇 |
2011年 | 242篇 |
2010年 | 198篇 |
2009年 | 263篇 |
2008年 | 253篇 |
2007年 | 204篇 |
2006年 | 84篇 |
2005年 | 139篇 |
2004年 | 105篇 |
2003年 | 121篇 |
2002年 | 86篇 |
2001年 | 120篇 |
2000年 | 42篇 |
1999年 | 58篇 |
1998年 | 65篇 |
1997年 | 45篇 |
1996年 | 46篇 |
1995年 | 81篇 |
1994年 | 62篇 |
1993年 | 40篇 |
1992年 | 49篇 |
1990年 | 21篇 |
1989年 | 44篇 |
1988年 | 12篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 78篇 |
1984年 | 63篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 83篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1972年 | 13篇 |
1967年 | 13篇 |
1966年 | 13篇 |
排序方式: 共有4011条查询结果,搜索用时 62 毫秒
941.
R. Harikumar S. Sampath V. Sasi Kumar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Rain drop size distribution (DSD) was measured at four places in Southern India {Thiruvananthapuram, Kochi, Munnar and Sriharikota (SHAR)} using a Joss–Waldvogel (JW) impact type disdrometer. The data for each minute were corrected for dead time errors and rain rate was computed from the corrected data. The data for a whole month were then sorted according to rain rate (R) into several classes ranging from 0.1 to >100 mm/h. The average DSD in each class was computed, and the lognormal distribution function was fitted to the average. In all the cases, the function fitted the data very well. The fit parameters were found to have dependence on rain rate. The total number of drops (NT), the geometric mean diameter (Dg) and the standard geometric deviation (σ) were also computed from the fit parameters. The standard geometric deviation (σ) was found to be more or less constant with rain rate at all the sites and in all months. The other two parameters (NT and Dg) were found to vary exponentially with rain rate except in Munnar, a high altitude station. At Thiruvananthapuram, in most of the months, NT increased exponentially with rain rate up to some value of R, which was different in different months, and then remained more or less constant or decrease slightly. In all cases, the variation of NT and Dg was such that NTDg3 increased linearly with rain rate. 相似文献
942.
I. G. Mitrofanov A. Bartels Y. I. Bobrovnitsky W. Boynton G. Chin H. Enos L. Evans S. Floyd J. Garvin D. V. Golovin A. S. Grebennikov K. Harshman L. L. Kazakov J. Keller A. A. Konovalov A. S. Kozyrev A. R. Krylov M. L. Litvak A. V. Malakhov T. McClanahan G. M. Milikh M. I. Mokrousov S. Ponomareva R. Z. Sagdeev A. B. Sanin V. V. Shevchenko V. N. Shvetsov R. Starr G. N. Timoshenko T. M. Tomilina V. I. Tretyakov J. Trombka V. S. Troshin V. N. Uvarov A. B. Varennikov A. A. Vostrukhin 《Space Science Reviews》2010,150(1-4):183-207
The design of the Lunar Exploration Neutron Detector (LEND) experiment is presented, which was optimized to address several of the primary measurement requirements of NASA’s Lunar Reconnaissance Orbiter (LRO): high spatial resolution hydrogen mapping of the Moon’s upper-most surface, identification of putative deposits of appreciable near-surface water ice in the Moon’s polar cold traps, and characterization of the human-relevant space radiation environment in lunar orbit. A comprehensive program of LEND instrument physical calibrations is discussed and the baseline scenario of LEND observations from the primary LRO lunar orbit is presented. LEND data products will be useful for determining the next stages of the emerging global lunar exploration program, and they will facilitate the study of the physics of hydrogen implantation and diffusion in the regolith, test the presence of water ice deposits in lunar cold polar traps, and investigate the role of neutrons within the radiation environment of the shallow lunar surface. 相似文献
943.
Geomagnetic Core Field Secular Variation Models 总被引:1,自引:0,他引:1
We analyse models describing time changes of the Earth’s core magnetic field (secular variation) covering the historical period (several centuries) and the more recent satellite era (previous decade), and we illustrate how both the information contained in the data and the a priori information (regularisation) affect the result of the ill-posed geomagnetic inverse problem. We show how data quality, frequency and selection procedures govern part of the temporal changes in the secular variation norms and spectra, which are sometimes difficult to dissociate from true changes of the core state. We highlight the difficulty of resolving the time variability of the high degree secular variation coefficients (i.e. the secular acceleration), arising for instance from the challenge to properly separate sources of internal and of external origin. In addition, the regularisation process may also result in artificial changes in the model norms and spectra. Model users should keep in mind that such features can be mis-interpreted as the signature of physical mechanisms (e.g. diffusion). Finally, we present perspectives concerning core field modelling: imposing dynamical constraints (e.g. by means of data assimilation) reduces the non-uniqueness of the geomagnetic inverse problem. 相似文献
944.
A. P. Paramonov 《Russian Aeronautics (Iz VUZ)》2010,53(2):121-125
Problems of improving the efficiency of design works in the process of space-rocket complex (SRC) updating are considered.
The methodical foundation for the expert system application to form promising technical solutions in studying the flight vehicle
(FV) modification is presented. 相似文献
945.
Basic principles of a mathematical model for disk-wing aircraft balancing and evaluation of power expenditure for flight as
compared with a helicopter are presented. 相似文献
946.
Methodology of constructing a stationary multichannel flow aerometric receiver using the effects of deceleration and throttling
of an incoming airflow and their circular transformation in the yaw plane is considered. The mathematical models and algorithms
for processing primary informative signals entering along the channels of speed, altitude, angles of attack and slip of the
helicopter air data system constructed on the basis of the aerometric receiver being proposed are obtained. 相似文献
947.
E. N. Bogomolov S. M. Piotukh I. A. Simonov V. A. Uglov 《Russian Aeronautics (Iz VUZ)》2010,53(4):416-420
A method for calculating the flowrate of the gas flowing through the cellular insert cells over the labyrinth seal strip is
proposed. The gas density is taken to be average with respect to the decisive section. It is assumed that jets flowing out
of cells disrupt the direct flow of the labyrinth seal. A practical implementation of the method is confirmed by the known
experimental data. 相似文献
948.
A. I. Golovanov 《Russian Aeronautics (Iz VUZ)》2010,53(2):161-166
A technique for numerical finite element analysis of large elastoplastic strains is proposed. A problem is formulated in terms
of principal stretches and their logarithms in the current basis of the left distortion tensor. It is shown that the “classical”
multiplicative decomposition of the total strain gradient into the product of elastic and plastic strain gradients is equivalent
to the presentation of total stretches as a product of elastic and plastic stretches. 相似文献
949.
We reveal a functional diagram, design features of a receiver electrode system, a principle of forming primary informative
signals, a technique for synthesizing angular characteristics and estimating indicated errors, channel realization and algorithms
of forming output signals of an ionmarking aerodynamic angle and airspeed sensor with logometric informative signals and interpolation
processing scheme. 相似文献
950.
Using the results of numerical modeling of nonstationary gas hydrodynamic working processes in the gas conduit variable section
channel when removing and cooling hot gases of different purpose technical plants, an engineering technique has been developed
to provide the gas conduit operation under limitations on the flow temperature in the outlet plant section. A multiparametric
area of permissible gas conduit operation connecting the characteristics of technical plants, gas conduit and water feeding
system is presented. 相似文献