全文获取类型
收费全文 | 18322篇 |
免费 | 38篇 |
国内免费 | 122篇 |
专业分类
航空 | 9938篇 |
航天技术 | 5501篇 |
综合类 | 244篇 |
航天 | 2799篇 |
出版年
2021年 | 156篇 |
2018年 | 221篇 |
2016年 | 158篇 |
2014年 | 433篇 |
2013年 | 513篇 |
2012年 | 416篇 |
2011年 | 590篇 |
2010年 | 416篇 |
2009年 | 760篇 |
2008年 | 793篇 |
2007年 | 376篇 |
2006年 | 426篇 |
2005年 | 386篇 |
2004年 | 448篇 |
2003年 | 536篇 |
2002年 | 487篇 |
2001年 | 564篇 |
2000年 | 364篇 |
1999年 | 457篇 |
1998年 | 441篇 |
1997年 | 324篇 |
1996年 | 404篇 |
1995年 | 478篇 |
1994年 | 447篇 |
1993年 | 360篇 |
1992年 | 342篇 |
1991年 | 253篇 |
1990年 | 238篇 |
1989年 | 417篇 |
1988年 | 211篇 |
1987年 | 238篇 |
1986年 | 236篇 |
1985年 | 642篇 |
1984年 | 523篇 |
1983年 | 419篇 |
1982年 | 491篇 |
1981年 | 617篇 |
1980年 | 250篇 |
1979年 | 187篇 |
1978年 | 189篇 |
1977年 | 146篇 |
1976年 | 156篇 |
1975年 | 191篇 |
1974年 | 180篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
1970年 | 144篇 |
1969年 | 147篇 |
1967年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
Ground penetrating radar VIY-2 总被引:2,自引:0,他引:2
Prokhorenko V.P. Ivashchuk V.E. Korsun S.V. 《Aerospace and Electronic Systems Magazine, IEEE》2005,20(7):16-18
VIY-2 ground penetrating radar (GPR) with unique sounding possibilities and use simplicity is presented at this paper. VIY-2 GPR combines all units (synchronizer, transmitting and receiving modules, powering, and antenna system) into single case. The VIY-2 GPR communicates with computer via standard interface RS232 or USB1.0. Technical solutions utilized by the VIY-2 GPR reduce deployment time and simplify surveying process. The VIY-2 GPR design features and its components interaction are considered at this paper. Some field results are also presented here. The VIY-2 GPR design concept allows reducing the data acquisition time,, optimizing the time-varying gain control function, applying depth-stacking dependence, controlling the surveying window position and interference reducing by pulse repetition frequency randomizing. 相似文献
973.
Track-before-detect procedures for early detection of moving target from airborne radars 总被引:2,自引:0,他引:2
Buzzi S. Lops M. Venturino L. 《IEEE transactions on aerospace and electronic systems》2005,41(3):937-954
In this paper we present a family of track-before-detect (TBD) procedures for early detection of moving targets from airborne radars. Upon a sectorization of the coverage area, the received echoes are jointly processed in the azimuth-range-Doppler domain and in the time domain through a Viterbi-like algorithm that exploits the physically admissible target transitions between successive illuminations, in order to collect all of the energy back-scattered during the time on target (TOT). A reduced-complexity implementation is derived assuming, at the design stage, that the target does not change resolution cell during the TOT in each scan. The constant false alarm rate (CFAR) constraint is also englobed in the proposed procedures as well as the possibility of working with quantized data. Simulation results show that the proposed algorithms have good detection and tracking capabilities even for high target velocities and low quantization rates. 相似文献
974.
We review observations from Voyager 2 of CIRs and merged CIRs in the outer heliosphere. The rather simple characteristics
of the CIR-associated changes in plasma, magnetic field, and particles become more complex as observations are made at greater
and greater distances. Pickup ions from charge exchange undoubtedly play an important role in the structure, but the full
details are not yet understood.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
975.
976.
单晶铝纳米级硬度试验研究 总被引:1,自引:0,他引:1
使用纳米硬度计对单晶铝进行了纳米压痕试验,利用原子力显微镜对压痕形貌进行扫描并计算硬度值,重点观察和分析了纳米级条件下单晶铝的硬度性质,结果表明,当压痕深度小于2000nm时,单晶铝纳米硬度存在尺寸效应现象;从材料性质的角度分析了纳米硬度尺寸效应现象;探讨了纳米硬度和传统硬度本质上的区别,指出其根本原因在于不同尺度下人们对材料性质的关注点不同。 相似文献
977.
The results of research in a process of a probe rocket berthing to an asteroid are presented. Control laws were obtained as solutions of three problems, namely berthing considering transient processes in a rocket engine, fastest berthing with regard to fuel consumption and berthing in a scheduled time considering fuel consumption. A program trajectory obtained at solving of the first problem is suitable for mathematical modeling of berthing with the feedback control law and stabilization of angular motion. The solutions of the problems are reduced to simple formulas for controlling parameters calculation in the corresponding structures of control laws. The results can be applied in designing promising space vehicles intended for berthing to other space objects. 相似文献
978.
Yu. V. Klochkov A. P. Nikolaev A. A. Shubovich S. S. Marchenko 《Russian Aeronautics (Iz VUZ)》2013,56(4):327-334
In this paper, we present an algorithm for geometrically nonlinear finite element analysis of the shells of revolution. Use is made of the most proper algorithms for vector interpolation of displacements through the nodal unknowns and an efficient algorithm for obtaining the stress-strain increment relation at a step of loading. By comparing the results of analyzing a geometrically nonlinear shell of revolution obtained on the basis of the ANSYS software with the scalar interpolation of displacements with those obtained on the basis of an author-developed finite element, it has been shown that application of the FEM vector displacement interpolation leads to increasing the accuracy of the finite element solutions in analyzing the stress-strain state of the geometrically nonlinear shells. 相似文献
979.
直升机旋翼气动机械稳定性的一个重要方面是空中与地面稳定性问题。本文从旋翼桨叶的结构型式、气动模型和分析方法几个方面对直升机空中与地面稳定性研究进行了回顾与展望。在简单分析方法的基础上 ,也对更精确的分析方法进行探讨 相似文献
980.
Messenger S. Stadermann F.J. Floss C. Nittler L.R. Mukhopadhyay S. 《Space Science Reviews》2003,106(1-4):155-172
Interplanetary dust particles collected in the stratosphere frequently exhibit enrichments in deuterium (D) and 15N relative to terrestrial materials. These effects are most likely due to the preservation of presolar interstellar materials.
While the elevated D/H ratios probably resulted from mass fractionation during chemical reactions at very low < 100 K temperatures,
the origin of the N isotopic anomalies remains unresolved. The bulk of the N-bearing material may have obtained its isotopic
signatures from low temperature chemistry, but a nucleosynthetic origin is also possible.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献