全文获取类型
收费全文 | 4684篇 |
免费 | 44篇 |
国内免费 | 28篇 |
专业分类
航空 | 2367篇 |
航天技术 | 1321篇 |
综合类 | 71篇 |
航天 | 997篇 |
出版年
2021年 | 35篇 |
2018年 | 194篇 |
2017年 | 177篇 |
2016年 | 66篇 |
2015年 | 55篇 |
2014年 | 75篇 |
2013年 | 104篇 |
2012年 | 117篇 |
2011年 | 280篇 |
2010年 | 231篇 |
2009年 | 259篇 |
2008年 | 293篇 |
2007年 | 243篇 |
2006年 | 110篇 |
2005年 | 165篇 |
2004年 | 95篇 |
2003年 | 116篇 |
2002年 | 90篇 |
2001年 | 108篇 |
2000年 | 88篇 |
1999年 | 102篇 |
1998年 | 107篇 |
1997年 | 101篇 |
1996年 | 88篇 |
1995年 | 104篇 |
1994年 | 107篇 |
1993年 | 69篇 |
1992年 | 76篇 |
1991年 | 39篇 |
1990年 | 44篇 |
1989年 | 74篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 34篇 |
1985年 | 113篇 |
1984年 | 79篇 |
1983年 | 79篇 |
1982年 | 59篇 |
1981年 | 103篇 |
1980年 | 25篇 |
1979年 | 27篇 |
1978年 | 33篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1975年 | 39篇 |
1974年 | 20篇 |
1972年 | 33篇 |
1971年 | 25篇 |
1969年 | 22篇 |
1967年 | 23篇 |
排序方式: 共有4756条查询结果,搜索用时 31 毫秒
921.
L. M. Bartolone K. Carney S. B. Cohen J. Erickson J. Gutbezahl P. H. Knappenberger Jr. D. J. McComas 《Space Science Reviews》2009,146(1-4):353-369
The IBEX mission includes a comprehensive Education and Public Outreach (E/PO) program that develops programs and products in exciting themes from astronomy and space physics. With the active involvement of the Principal Investigator and several science team partners, it is overseen and implemented by the Adler Planetarium & Astronomy Museum. The program includes an internationally distributed planetarium show with accompanying informal education materials that are also accessible to individuals with special needs; a national Space Science Core Curriculum for grades 6–8 in collaboration with other NASA missions; a professional development program for teachers; and workshops that engage Hispanic and Native American students. Materials are made available for download or for order via the IBEX website: http://www.ibex.swri.edu/. Our program is developed, implemented and monitored for effectiveness by organizations with proven capabilities and experience in their respective areas of E/PO. This paper describes these program elements in detail and includes the rationale and design process for this E/PO program. 相似文献
922.
Maxim L. Khodachenko Valerii V. Zaitsev Albert G. Kislyakov Alexander V. Stepanov 《Space Science Reviews》2009,149(1-4):83-117
Coronal loops, which trace closed magnetic field lines, are the primary structural elements of the solar atmosphere. Complex dynamics of solar coronal magnetic loops, together with action of possible subphotospheric dynamo mechanisms, turn the majority of the coronal loops into current-carrying structures. In that connection none of the loops can be considered as isolated from the surroundings. The current-carrying loops moving relative to each other interact via the magnetic field and currents. One of the ways to take into account this interaction consists in application of the equivalent electric circuit models of coronal loops. According to these models, each loop is considered as an equivalent electric LCR-circuit with variable inductive coefficients L, capacitance C, and resistance R, which depend on shape, scale, position of the loop with respect to neighbouring loops, as well as on the plasma parameters in the magnetic tube. Such an approach enables to describe the process of electric current dynamics in the groups of coronal loops, as well as the related dynamical, energy release and radiation processes. In the present paper we describe the major principles of LCR-circuit models of coronal magnetic loops, and show their application for interpretation of the observed oscillatory phenomena in the loops and in the related radiation. 相似文献
923.
924.
A mathematical model for the annular gas-liquid mixture flow in the cylindrical channel is described. The influence of an upward turbulent gas flow on the downward liquid film is considered. The problem is numerically solved and the calculation results are compared with the experimental data. 相似文献
925.
The results of analyzing axisymmetric forced vibrations of an elastic circular sandwich plate connected with an elastic foundation under different surface loads are presented. The hypotheses of a broken normal are accepted to describe the kinematics of a package that is nonsymmetrical over the thickness. The analytical solutions of a problem for plates with a light filler are obtained and numerical analysis is carried out. 相似文献
926.
In the framework of the general theory for unsteady weakly disturbed fluid flows with free boundaries, a problem is solved to calculate a jet flow around the cascade of plates executing the harmonic oscillations. We developed a program that enables us for the first time to carry out systematic calculations of flow characteristics depending on arbitrary values of determining parameters. 相似文献
927.
I. M. Zakirov K. A. Alekseev R. A. Kayumov I. R. Gainutdinov 《Russian Aeronautics (Iz VUZ)》2009,52(3):347-350
We consider some general problems of improving the strength characteristics of folded cores as well as the corresponding techniques
for modifying the core material polymer surfaces with the use of nanotechnologies and the “mass-strength” criteria. 相似文献
928.
Yu. F. Gortyshov V. M. Gureev R. Sh. Misbakhov I. F. Gumerov A. P. Shaikin 《Russian Aeronautics (Iz VUZ)》2009,52(4):488-490
We present the results of experimental studies of the fuel hydrogen additive influence on the characteristics of a gas-piston
engine converted for operation by natural gas under changes of an ignition advance angle (IAA). The results of investigations
were used to determine the influence of the hydrogen additive on the effective engine efficiency and fuel consumption under
IAA changes. 相似文献
929.
提出了一种新的时变系统健康监控的损伤分类方法。将函数级数时变自回归平滑时序模型应用于时变系统的振动信号,以估计TAR/TMA参数和革新方差。这些参数是时间的函数,将它们在以特定的基函数构成的某种函数子空间上展开得到相应的投影系数组。所估计得到的TAR/TMA参数和革新方差可进一步用来计算潜在成分(LCs),将LCs用于健康评估比原来的参数更具信息。并将LCs联合并归化为数值得到特征集,输入概率神经网络(PNN)进行损伤分类。为了评价该方法,对一个时变系统进行了仿真,以各种不同的质量和刚度减少来模拟不同的损伤类别。算例表明:该方法能够在时变系统的背景下对损伤进行归类。 相似文献
930.
Lawrence D. Huebner R. Marshall Smith John R. Campbell Terry L. Taylor 《Acta Astronautica》2009,65(11-12):1706-1716
The Ares I–X Flight Test Vehicle is the first in a series of flight test vehicles that will take the Ares I Crew Launch Vehicle design from development to operational capability. Ares I–X is scheduled for a 2009 flight date, early enough in the Ares I design and development process so that data obtained from the flight can impact the design of Ares I before its Critical Design Review. Decisions on Ares I–X scope, flight test objectives, and FTV fidelity were made prior to the Ares I systems requirements being baselined. This was necessary in order to achieve a development flight test to impact the Ares I design. Differences between the Ares I–X and the Ares I configurations are artifacts of formulating this experimental project at an early stage and the natural maturation of the Ares I design process. This paper describes the similarities and differences between the Ares I–X Flight Test Vehicle and the Ares I Crew Launch Vehicle. Areas of comparison include the outer mold line geometry, aerosciences, trajectory, structural modes, flight control architecture, separation sequence, and relevant element differences. Most of the outer mold line differences present between Ares I and Ares I–X are minor and will not have a significant effect on overall vehicle performance. The most significant impacts are related to the geometric differences in Orion Crew Exploration Vehicle at the forward end of the stack. These physical differences will cause differences in the flow physics in these areas. Even with these differences, the Ares I–X flight test is poised to meet all five primary objectives and six secondary objectives. Knowledge of what the Ares I–X flight test will provide in similitude to Ares I—as well as what the test will not provide—is important in the continued execution of the Ares I–X mission leading to its flight and the continued design and development of Ares I. 相似文献