全文获取类型
收费全文 | 8118篇 |
免费 | 15篇 |
国内免费 | 23篇 |
专业分类
航空 | 3631篇 |
航天技术 | 2723篇 |
综合类 | 25篇 |
航天 | 1777篇 |
出版年
2021年 | 80篇 |
2019年 | 48篇 |
2018年 | 230篇 |
2017年 | 169篇 |
2016年 | 137篇 |
2015年 | 61篇 |
2014年 | 201篇 |
2013年 | 243篇 |
2012年 | 250篇 |
2011年 | 401篇 |
2010年 | 293篇 |
2009年 | 414篇 |
2008年 | 452篇 |
2007年 | 295篇 |
2006年 | 179篇 |
2005年 | 233篇 |
2004年 | 214篇 |
2003年 | 245篇 |
2002年 | 173篇 |
2001年 | 265篇 |
2000年 | 144篇 |
1999年 | 176篇 |
1998年 | 206篇 |
1997年 | 125篇 |
1996年 | 191篇 |
1995年 | 224篇 |
1994年 | 200篇 |
1993年 | 135篇 |
1992年 | 163篇 |
1991年 | 54篇 |
1990年 | 58篇 |
1989年 | 158篇 |
1988年 | 66篇 |
1987年 | 66篇 |
1986年 | 76篇 |
1985年 | 216篇 |
1984年 | 168篇 |
1983年 | 122篇 |
1982年 | 136篇 |
1981年 | 238篇 |
1980年 | 59篇 |
1979年 | 50篇 |
1978年 | 54篇 |
1977年 | 51篇 |
1975年 | 56篇 |
1974年 | 48篇 |
1973年 | 40篇 |
1972年 | 36篇 |
1971年 | 38篇 |
1970年 | 40篇 |
排序方式: 共有8156条查询结果,搜索用时 31 毫秒
71.
F. S. Khairullin 《Russian Aeronautics (Iz VUZ)》2009,52(4):480-483
We consider a possibility to apply the method of analyzing the complex-shaped shells, proposed in [1], for determining the
stress strain state of thin shells with a degenerating domain. The results of numerical calculations are presented. 相似文献
72.
A. Sh. Dzhabrailov Yu. V. Klochkov S. S. Marchenko A. P. Nikolaev 《Russian Aeronautics (Iz VUZ)》2007,50(2):115-120
We demonstrate that it is possible to express each component of the displacement vector for the interior point of the finite element (FE) through all components of nodal unknowns in curvilinear coordinates. The effectiveness of the valid technique of vector approximation for displacement fields has been verified on an example. 相似文献
73.
The fastest pulsar and the slowest nova; the oldest galaxies and the youngest stars; the weirdest life forms and the commonest
dwarfs; the highest energy particles and the lowest energy photons. These were some of the extremes of Astrophysics 2006.
We attempt also to bring you updates on things of which there is currently only one (habitable planets, the Sun, and the Universe)
and others of which there are always many, like meteors and molecules, black holes and binaries. 相似文献
74.
N. N. Makarov 《Russian Aeronautics (Iz VUZ)》2008,51(1):60-66
The problem is formulated and a technique is revealed for synthesizing the optimal strategy of troubleshooting and constructing an operation algorithm for the information-control system of inspection and diagnostics of the aircraft equipment state. 相似文献
75.
The characteristics of the insulator wear process in the discharge chamber of a stationary plasma thruster (SPT) are analyzed. The results of studying the erosion resistance to ionic spraying of different ceramic compositions are presented. It is shown experimentally that the integral characteristics (the value of thrust and thrust efficiency) as well as the SPT lifetime can be improved in changing from the conventional hot-pressed boron silicate (BN + SiO2) ceramics to the BN + Si3N4 ceramic compositions. 相似文献
76.
V. A. Ovchinnikov 《Russian Aeronautics (Iz VUZ)》2007,50(2):146-149
We analyze the effect of injection both of uniformly distributed over the entire cylinder surface and of the optimal one on the velocity distribution at the outer border of the boundary layer and, as a result, on friction. 相似文献
77.
The results of studying an incompressible gas flow field in a periodic element of the porous structure made up of the same radius spheres are presented; the studies were based on the solution of the Navier-Stokes equations using FLUENT software. The possibilities to accelerate the solution process with the use of parallel calculations are investigated and the calculation results under changes of pressure differential in the periodic element are given. 相似文献
78.
T. Yu. Gainutdinova 《Russian Aeronautics (Iz VUZ)》2007,50(2):215-217
In this paper, a program package for solving problems in the field of thin-walled three-dimensional FV structure design is described. 相似文献
79.
介绍了NIST开展的微波散射参数(S参数)及功率测量业务。包括在这两项业务中的各自的测量内容,系统的校准技术,对系统及所用的标准件的描述和对于不同测量所考虑的测量不确定度。此外还介绍了在S参数测量及功率测量的未来工作方向。 相似文献
80.
Mercury’s unusually high mean density has always been attributed to special circumstances that occurred during the formation of the planet or shortly thereafter, and due to the planet’s close proximity to the Sun. The nature of these special circumstances is still being debated and several scenarios, all proposed more than 20 years ago, have been suggested. In all scenarios, the high mean density is the result of severe fractionation occurring between silicates and iron. It is the origin of this fractionation that is at the centre of the debate: is it due to differences in condensation temperature and/or in material characteristics (e.g. density, strength)? Is it because of mantle evaporation due to the close proximity to the Sun? Or is it due to the blasting off of the mantle during a giant impact? In this paper we investigate, in some detail, the fractionation induced by a giant impact on a proto-Mercury having roughly chondritic elemental abundances. We have extended the previous work on this hypothesis in two significant directions. First, we have considerably increased the resolution of the simulation of the collision itself. Second, we have addressed the fate of the ejecta following the impact by computing the expected reaccretion timescale and comparing it to the removal timescale from gravitational interactions with other planets (essentially Venus) and the Poynting–Robertson effect. To compute the latter, we have determined the expected size distribution of the condensates formed during the cooling of the expanding vapor cloud generated by the impact. We find that, even though some ejected material will be reaccreted, the removal of the mantle of proto-Mercury following a giant impact can indeed lead to the required long-term fractionation between silicates and iron and therefore account for the anomalously high mean density of the planet. Detailed coupled dynamical–chemical modeling of this formation mechanism should be carried out in such a way as to allow explicit testing of the giant impact hypothesis by forthcoming space missions (e.g. MESSENGER and BepiColombo). 相似文献