全文获取类型
收费全文 | 6195篇 |
免费 | 652篇 |
国内免费 | 483篇 |
专业分类
航空 | 3178篇 |
航天技术 | 1706篇 |
综合类 | 445篇 |
航天 | 2001篇 |
出版年
2024年 | 15篇 |
2023年 | 47篇 |
2022年 | 115篇 |
2021年 | 178篇 |
2020年 | 129篇 |
2019年 | 120篇 |
2018年 | 280篇 |
2017年 | 240篇 |
2016年 | 217篇 |
2015年 | 190篇 |
2014年 | 280篇 |
2013年 | 297篇 |
2012年 | 303篇 |
2011年 | 364篇 |
2010年 | 384篇 |
2009年 | 437篇 |
2008年 | 377篇 |
2007年 | 299篇 |
2006年 | 220篇 |
2005年 | 240篇 |
2004年 | 176篇 |
2003年 | 205篇 |
2002年 | 225篇 |
2001年 | 214篇 |
2000年 | 134篇 |
1999年 | 152篇 |
1998年 | 127篇 |
1997年 | 117篇 |
1996年 | 102篇 |
1995年 | 141篇 |
1994年 | 113篇 |
1993年 | 72篇 |
1992年 | 82篇 |
1991年 | 44篇 |
1990年 | 45篇 |
1989年 | 56篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 82篇 |
1984年 | 61篇 |
1983年 | 51篇 |
1982年 | 48篇 |
1981年 | 89篇 |
1980年 | 26篇 |
1979年 | 18篇 |
1978年 | 18篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1972年 | 14篇 |
排序方式: 共有7330条查询结果,搜索用时 118 毫秒
251.
R.V. Semenyshyn A.N. VeklichI.L. Babich V.F. Boretskij 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Plasma of the free burning electric arc between Ag–SnO2–ZnO composite electrodes as well as brass electrodes were investigated. The plasma temperature distributions were obtained by Boltzmann plot method involving Cu I, Ag I or Zn I spectral line emissions. The electron density distributions were obtained from the width and from absolute intensity of spectral lines. The laser absorption spectroscopy was used for measurement of copper atom concentration in plasma. Plasma equilibrium composition was calculated using two independent groups of experimental values (temperature and copper atom concentration, temperature and electron density). It was found that plasma of the free burning electric arc between brass electrodes is in local thermodynamical equilibrium. The experimental verification of the spectroscopic data of Zn I spectral lines was carried out. 相似文献
252.
A.D. Danilov A.V. Konstantinova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):359-370
Long-term changes in the E-layer critical frequency, foE, at three stations of the European region (Juliusruh, Slough and Rome) and also at Moscow and Wakkanai stations are analyzed by the method developed by the authors and described in detail in the previous papers. It is found that Juliusruh and Slough stations demonstrate a well-pronounced change in foE (a trend) during two previous decades. At the same time, the same features of the behavior of the aforementioned trend k(foE) are obtained. The trend is positive and negative in the morning and evening hours, respectively. Similar diurnal behavior of k(foE) is found also for Moscow station but with lower absolute values of the trends. A well-pronounced seasonal behavior of k(foE) is detected at Juliusruh and Slough: the trend is minimal and maximal in the summer period and at the end of fall—beginning of winter, respectively. The maximal amplitude in the morning hours reaches +0.04?MHz per year, whereas the minimal amplitude in evening hours is ?0.06?MHz per year. No systematic changes exceeding by the magnitude 0.01?MHz per year are found for Rome and Wakkanai stations. It is assumed that the observed trends are related to changes (trends) in the meridional wind bringing NO molecules from the auroral oval to lower latitudes. 相似文献
253.
Cosmic Research - An Erratum to this paper has been published: https://doi.org/10.1134/S0010952521120017 相似文献
254.
Based on an integrated approach, we solve the optimization problem for energy content and weight-dimensional characteristics of the electric servo drive by synthesis of structure and analysis of characteristics for different power supplies. The generalized power supply model, developed for different power supply of drive control systems, is given. 相似文献
255.
E. O. Ariskin A. V. Nikitin V. V. Soldatkin V. M. Soldatkin 《Russian Aeronautics (Iz VUZ)》2015,58(4):454-460
The problem and features of measuring the speed and the direction angle of the wind vector relative to the longitudinal helicopter axis during parking, starting and takeoff-landing modes by onboard means are considered. The construction principles, information processing algorithms and advantages of onboard system for measuring the wind vector parameters based on ion-beacon and aerometric measuring channels, are disclosed. 相似文献
256.
We consider the stability of stationary motions of a model of a spacecraft as a system of coaxial bodies with small asymmetry caused by the shift of the axes of dynamic symmetry of bodies relative to the axis of rotation. We determine the stationary motions of the system; their stability is studied with respect to both the projections of angular velocity and the position of the axis of rotation. The sufficient conditions for the stability of these stationary motions are obtained by constructing a Lyapunov function, and the necessary conditions are obtained by analyzing the corresponding linearized equations of perturbed motion. 相似文献
257.
258.
A weak but statistically reliable dependence of the diurnal activity of oscillations in the ionospheric Alfvén resonator on orientation of the interplanetary magnetic field ahead of the magnetospheric front has been detected based on observations of ULF oscillations at Sayan solar observatory Mondy of the Institute of Solar–Terrestrial Physics. The interpretation of the result has been proposed. The essence is that the electromagnetic fluctuations penetrate into the magnetosphere from the interplanetary environment and influence the ionospheric resonator. The formulation of the problem and the method of solving it are part of the broad program of the experimental and theoretical study of the influence of the interplanetary magnetic field on the oscillation regime of ULF oscillations of the magnetosphere. 相似文献
259.
本文通过对该型教练机现有航空电子系统构型、驾驶员操作程序、接口控制文件深入研究,结合未来功能扩展需求,给出了合理的系统构型分析、功能分配、数据流规划、原相关系统软件改动分析,在此基础上还设计出了嵌入式训练系统技术方案.依据方案研制的嵌入式训练系统原理样机通过系统动态试验、航电系统地面综合试验和飞机地面通电试验,证明系统... 相似文献
260.
The requirements for skid landing gear static strength ensuring are examined based on the comparative analysis of the Airworthiness Standards requirements. Probabilistic principle of determining the safety factor of the skid landing gear is presented. The analysis of the experimental data on bench and flight tests is performed for calculating the actual value of this factor. 相似文献