全文获取类型
收费全文 | 8378篇 |
免费 | 59篇 |
国内免费 | 51篇 |
专业分类
航空 | 3739篇 |
航天技术 | 2856篇 |
综合类 | 41篇 |
航天 | 1852篇 |
出版年
2021年 | 97篇 |
2019年 | 60篇 |
2018年 | 219篇 |
2017年 | 141篇 |
2016年 | 159篇 |
2015年 | 67篇 |
2014年 | 223篇 |
2013年 | 282篇 |
2012年 | 264篇 |
2011年 | 379篇 |
2010年 | 283篇 |
2009年 | 412篇 |
2008年 | 435篇 |
2007年 | 276篇 |
2006年 | 189篇 |
2005年 | 236篇 |
2004年 | 222篇 |
2003年 | 282篇 |
2002年 | 226篇 |
2001年 | 285篇 |
2000年 | 146篇 |
1999年 | 188篇 |
1998年 | 221篇 |
1997年 | 136篇 |
1996年 | 188篇 |
1995年 | 243篇 |
1994年 | 223篇 |
1993年 | 128篇 |
1992年 | 169篇 |
1991年 | 54篇 |
1990年 | 61篇 |
1989年 | 159篇 |
1988年 | 68篇 |
1987年 | 66篇 |
1986年 | 74篇 |
1985年 | 221篇 |
1984年 | 177篇 |
1983年 | 135篇 |
1982年 | 141篇 |
1981年 | 247篇 |
1980年 | 65篇 |
1979年 | 55篇 |
1978年 | 58篇 |
1977年 | 51篇 |
1975年 | 58篇 |
1974年 | 46篇 |
1973年 | 37篇 |
1972年 | 46篇 |
1971年 | 44篇 |
1970年 | 42篇 |
排序方式: 共有8488条查询结果,搜索用时 240 毫秒
391.
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
392.
Devajyoti Dutta Sanjay Sharma G.K. Sen B.A.M. Kannan S. Venketswarlu R.M. Gairola J. Das G. Viswanathan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
By using a Doppler Weather Radar (DWR) at Shriharikota (13.66°N & 80.23°E), an Artificial Neural Network (ANN) based technique is proposed to improve the accuracy of rain intensity estimation. Three spectral moments of a Doppler spectra are utilized as an input data to an ANN. Rain intensity, as measured by the tipping bucket rain gauges around the DWR station, are considered as a target values for the given inputs. Rain intensity as estimated by the developed ANN model is validated by the rain gauges measurements. With the help of a developed technique, reasonable improvement in the estimation of rain intensity is observed. By using the developed technique, root mean square error and bias are reduced in the range of 34–18% and 17–3% respectively, compared to Z–R approach. 相似文献
393.
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
394.
V. G. Dmitriev V. I. Biryukov O. V. Egorova S. I. Zhavoronok L. N. Rabinskii 《Russian Aeronautics (Iz VUZ)》2017,60(2):169-176
The discretization of the boundary value problem for laminated composite shells is based on the finite difference approach using the regular mesh with the constant grid step and the difference operators of the second order of accuracy. The dynamic relaxation method is proposed for the solution of the nonlinear problem. The evolutionary equations of the dynamic relaxation are constructed, and the optimum parameters of the converging linear iterative process are estimated. 相似文献
395.
This paper presents a brief review of activities in laminar flow control being performed at the Central Aerohydrodynamic Institute named after Prof. N.E. Zhukovsky (TsAGI). These efforts are focused on the improvement of the existing laminar flow control methods and on the development of new ones. The investigations have demonstrated the effectiveness of aircraft surface laminarization applications with the aim of friction drag reduction. The opportunity of considerable delaying of laminar-turbulent transition due to special wing profile geometry and using boundary layer suction and surface cooling has been verified at sub- and supersonic speeds through various wind tunnel testing at TsAGI and during flying laboratory experiments at the Flight Research Institute (LII). The investigations on using hybrid laminar flow control systems for friction drag reduction were also carried out. New techniques of laminar flow control were proposed, in particular, the method of local heating of the wing leading edge, boundary layer laminarization by means of receptivity control, and electrohydrodynamic methods of boundary layer stability control. 相似文献
396.
For an interception strategy of a removable target by a return space vehicle (RSV), we propose a structure of the control law by the aerodynamic efficiency that determines a chain of the three standard trajectories: nosing-up–free flight–nosing-down. A solution of the terminal problem is to determine numerical values of the control parameters that define moments to switch the RSV flight from one standard trajectory to another. 相似文献
397.
A problem of modeling the incompressible viscous flow between two disks taking into account the rotation of one of them is
considered. We study the effect of the disk angular velocity (flow regimes) in the interdisk spacing, finiteness (infiniteness)
of disk radiuses, calculation region configuration as well as distances between disks on the flow characteristics, particularly,
on the resistance moment coefficient. Numerical simulation is performed with the aid of Maple and ANSYS Fluent software. 相似文献
398.
N. D. Akhmetov M. M. Gimadeev V. N. Drulis V. A. Krivosheev T. V. Rzaeva 《Russian Aeronautics (Iz VUZ)》2011,54(1):108-113
A technique for calculating the energy parameters of shock waves at electrical discharge in water is presented for the transition
region of discharge channel expansion using as the base the predetermined characteristics of discharge circuit. The technique
is based on the solution of energy transport equation that is similar in form to that of radiative transfer. The validity
of the presented approach was experimentally verified. 相似文献
399.
Systems for the indication and display of secondary information in avionics and autobasing complexes
A. A. Bagdasarov R. V. Anitropov O. V. Bagdasarova I. L. Livshits 《Russian Aeronautics (Iz VUZ)》2011,54(2):185-191
We consider the peculiarities of application for the cabin indicating systems of secondary information display, formulate
and systematize the compositional and technical requirements for display systems and their elements. The tendencies and lines
in the development of head-up displays for avionics and autobasing complexes were determined. The technique of calculating
optics of such display systems with the use of electronic distortion compensation is presented. 相似文献
400.
Aerodynamic characteristics of two-dimensional smart flap under the ground effect have been assessed by a numerical simulation. In this process, a pressure-based implicit procedure to solve Navier–Stokes equations on a nonorthogonal mesh with collocated finite volume formulation is used. The boundedness criteria for this procedure are determined from the Normalized Variable Diagram (NVD) scheme. The procedure incorporates the k–ε eddy–viscosity turbulence model. Cantilever beam with uniformly varying load with roller support at the free end is considered for the configuration of the smart flap. The method is first validated against experimental data. Then, the algorithm is applied for turbulent aerodynamic flows around airfoil with smart and conventional flaps for different attack angle, flap angle and ground clearance where the results of two flaps are compared. The comparisons show that the quality of the solution is considerable. 相似文献