全文获取类型
收费全文 | 19204篇 |
免费 | 39篇 |
国内免费 | 127篇 |
专业分类
航空 | 10231篇 |
航天技术 | 5713篇 |
综合类 | 242篇 |
航天 | 3184篇 |
出版年
2021年 | 157篇 |
2018年 | 273篇 |
2017年 | 154篇 |
2016年 | 176篇 |
2014年 | 434篇 |
2013年 | 516篇 |
2012年 | 442篇 |
2011年 | 653篇 |
2010年 | 480篇 |
2009年 | 837篇 |
2008年 | 861篇 |
2007年 | 445篇 |
2006年 | 439篇 |
2005年 | 429篇 |
2004年 | 471篇 |
2003年 | 553篇 |
2002年 | 496篇 |
2001年 | 625篇 |
2000年 | 368篇 |
1999年 | 473篇 |
1998年 | 466篇 |
1997年 | 339篇 |
1996年 | 417篇 |
1995年 | 497篇 |
1994年 | 482篇 |
1993年 | 367篇 |
1992年 | 354篇 |
1991年 | 250篇 |
1990年 | 243篇 |
1989年 | 424篇 |
1988年 | 214篇 |
1987年 | 244篇 |
1986年 | 247篇 |
1985年 | 645篇 |
1984年 | 528篇 |
1983年 | 422篇 |
1982年 | 493篇 |
1981年 | 624篇 |
1980年 | 247篇 |
1979年 | 194篇 |
1978年 | 189篇 |
1977年 | 146篇 |
1976年 | 156篇 |
1975年 | 195篇 |
1974年 | 181篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
1970年 | 143篇 |
1969年 | 147篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
761.
The basic steps of an algorithm are given for calculating the parameters of the limiting state of a helicopter main rotor
blade. To estimate the static strength, a technique of elastic constants variation is used; it is based on the limit equilibrium
theory and enables us to obtain the upper and lower bounds for the critical load simultaneously. An iterative technique is
proposed to determine the lower bound of the allowable load on the root section of the composite blade depending on the azimuthal
angle of its turn in the helicopter hovering mode. 相似文献
762.
A technique of analyzing the flutter initiation in flat plate compressor cascades was developed. The viscous and inviscid
flow study was carried out using the COBRA solver based on the modified implicit Godunov method and unsteady implicit method
updated for using. The flutter conditions were revealed and the effect of taking into account viscosity, angles of attack
and time steps was investigated. 相似文献
763.
V. A. Futin 《Russian Aeronautics (Iz VUZ)》2011,54(2):165-169
The influence of the clearance between the case and blade ends of the semi-open impeller on the centrifugal stage characteristics
is considered using the experimental data and numerical calculation results. 相似文献
764.
The influence of geometry and operating conditions of the centrifugal compressor stage on the radial gas force is determined
on the basis of the theoretical method and calculation program using experimental boundary conditions. 相似文献
765.
M. V. Usanin A. A. Siner A. M. Sipatov L. Yu. Gomzikov V. G. Avgustinovich 《Russian Aeronautics (Iz VUZ)》2011,54(1):34-42
The application of the low dissipative high-order accurate scheme for numerical solution of the Euler and Navier-Stokes equations
in the two-dimensional statement is considered. The scheme of calculating space derivatives is the seven-point central-difference
approximation of the fourth order with the coefficients optimized to reduce the dispersion errors. The optimized six-step
Runge-Kutta method is used for evaluating the time derivatives. By means of filtration, spurious pulsations are suppressed
and shocks are processed. The results of verifying the calculation scheme realized on the stationary problem of flow around
the model turbine blades are presented. 相似文献
766.
767.
I. Martínez J.M. Perales 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The experimental results obtained in experiment “STACO” made on board the Spacelab D-2 are re-visited, with image-analysis tools not then available. The configuration consisted of a liquid bridge between two solid supporting discs. An expected breakage occurred during the experiment. The recorded images are analysed and the measured behaviour compared with the results of a three dimensional model of the liquid dynamics, obtaining a much better fit than with linear models. 相似文献
768.
The results of the interplanetary scintillation observations performed in the period of the maximum of solar activity from April 2013 to April 2014 on the BSA LPI radio telescope at the frequency 111MHz are presented. Fluctuations of the radio emission flux were recorded round the clock for all sources with a scintillating flux of more than 0.2 Jy falling in a strip of sky with a width of 50° over declinations corresponding to a 96-beam directional pattern of the radio telescope. The total number of sources observed during the day reaches 5000. The processing of the observational data was carried out on the assumption that a set of scintillating sources represents a homogeneous statistical ensemble. Daily two-dimensional maps of the distribution of the level of scintillations, whose analysis shows the strong nonstationarity and large-scale irregularity of the spatial distribution of solar wind parameters, were constructed. According to maps of the distribution of the level of scintillations averaged over monthly intervals, the global structure of the distribution of the solar wind was investigated in the period of the maximum of solar activity, which was found to be on the average close to spherically symmetric. The data show that on a spherically symmetric background an east–west asymmetry is observed, which indicates the presence of a large-scale structure of a spiral type in the solar wind. 相似文献
769.
M.R. Saradjian M. Hosseini 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In the past studies, different soil moisture estimation models were developed for bare soil areas by using remotely-sensed data. However, there are few models that can be used to estimate soil moisture in vegetated areas. Water Cloud Model (WCM) model is a widely used soil moisture estimation model has been developed for vegetated areas. In this study, the WCM model was extended to take soil roughness parameter into consideration. The modeling and its accuracy assessment were done by using multi-polarization Airborne Synthetic Aperture Radar (AIRSAR) images and ground data collected during field Soil Moisture Experiments. 相似文献
770.