全文获取类型
收费全文 | 7591篇 |
免费 | 37篇 |
国内免费 | 14篇 |
专业分类
航空 | 3889篇 |
航天技术 | 2652篇 |
综合类 | 33篇 |
航天 | 1068篇 |
出版年
2021年 | 52篇 |
2019年 | 53篇 |
2018年 | 99篇 |
2017年 | 64篇 |
2016年 | 59篇 |
2014年 | 139篇 |
2013年 | 181篇 |
2012年 | 163篇 |
2011年 | 228篇 |
2010年 | 166篇 |
2009年 | 259篇 |
2008年 | 343篇 |
2007年 | 188篇 |
2006年 | 184篇 |
2005年 | 187篇 |
2004年 | 171篇 |
2003年 | 248篇 |
2002年 | 147篇 |
2001年 | 255篇 |
2000年 | 152篇 |
1999年 | 189篇 |
1998年 | 233篇 |
1997年 | 160篇 |
1996年 | 209篇 |
1995年 | 273篇 |
1994年 | 251篇 |
1993年 | 150篇 |
1992年 | 183篇 |
1991年 | 99篇 |
1990年 | 92篇 |
1989年 | 198篇 |
1988年 | 88篇 |
1987年 | 88篇 |
1986年 | 88篇 |
1985年 | 253篇 |
1984年 | 206篇 |
1983年 | 181篇 |
1982年 | 193篇 |
1981年 | 231篇 |
1980年 | 81篇 |
1979年 | 61篇 |
1978年 | 68篇 |
1977年 | 69篇 |
1976年 | 49篇 |
1975年 | 87篇 |
1974年 | 53篇 |
1973年 | 53篇 |
1972年 | 75篇 |
1971年 | 56篇 |
1970年 | 54篇 |
排序方式: 共有7642条查询结果,搜索用时 0 毫秒
271.
This paper presents the results of medical investigations performed in the Salyut-7 8-month mission in which a professional physician took part. The paper contains anthropometric measurements, results of investigating the vestibular function, cardiovascular function at rest and in response to multi-step tests (with emphasis on echocardiographic measurements), metabolic parameters and hormonal status. It also discusses medical aspects of the extravehicular activity. The medical investigations, although some new methods were applied, provided the continuity of methodical approaches and data accumulated in previous missions. 相似文献
272.
New one-axis magnetic attitude control is proposed. Only one attitude sensor providing any inertial direction measurements is necessary, magnetometer is not used. The control may be used as a backup capability in case main actuators or some attitude sensors fail. Sun pointing is achievable using only three-axis Sun sensor, so the control may be used to lower the power consumption during battery charging. Asymptotic stability of different equilibria depending on the satellite inertia tensor is summarized. In-flight results from “Chibis-M” microsatellite are provided proving general control performance. 相似文献
273.
Neri J. A. C. F. Dos Santos W. A. Rabay S. Fonseca I. M. De Souza P. N. Cividanes L. B. T. De Paula A. R. Oliveira Filho O. B. Almeida M. C. P. Francisco M. F. M. Varotto S. E. C. Ribeiro M. S. Saturno M. E. 《Acta Astronautica》1996,39(9-12):707-709
The National Space Research Institute (INPE) is developing the first Brazilian Scientific Microsatellite (SACI-1) based on the vanguard technology and on the experience acquired through projects developed by Brazilian Space Program. The SACI-1 is a 750km polar orbit satellite. The spacecraft will combine spin stabilization with geomagnetic control and has a total mass of 60 kg. The overall dimensions are 640×470×470 mm. The SACI-1 satellite shall be launched together with CBERS (China-Brazil Earth Resource Satellite). Its platform is being designed for multiple mission applications. The Brazilian Academy of Sciences has selected four scientific payloads that characterize the mission. The scientific experiments are: ORCAS (Solar and Anomalous Cosmic Rays Observation in the Magnetosphere), PLASMEX (Study of Plasma Bubbles), FOTSAT (Airglow Photometer), and MAGNEX (Geomagnetic Experiment). 相似文献
274.
Using a novel space platform-based manipulator with slewing and deployable links, the paper addresses two issues of considerable importance: (a) How important is it to model flexibility of the system? (b) How many modes are needed to adequately represent the elastic character? Results suggest that the fundamental mode is able to capture physics of the response quite accurately. Due to its massive character, the platform dynamics is virtually unaffected, even by severe maneuvers of the manipulator. Hence, treating the platform as rigid would save the computational cost without affecting the accuracy. Although the link flexibility does affect the manipulator's tip vibration, the joint and platform vibrations remain negligible. The revolute joint flexibility appears to be an important parameter affecting both the joint as well as tip responses. The information should prove useful in the design of this new class of manipulators. 相似文献
275.
276.
277.
Modern 4th generation air-to-air missiles are quite capable of dealing with today's battlefield needs. Advanced aerodynamics, highly efficient warheads and smart target acquisition systems combine to yield higher missile lethality than ever. However, in order to intercept highly maneuverable targets, such as future unmanned combat air vehicles (UCAV), or to achieve higher tracking precision for missiles equipped with smaller warheads, further improvement in the missile guidance system is still needed. A new concept is presented here for deriving improved differential-game-based guidance laws that make use of information about the target orientation, which is acquired via an imaging seeker. The underlying idea is that of using measurements of the target attitude as a leading indicator of target acceleration. Knowledge of target attitude reduces the reachable set of target acceleration, facilitating the computation of an improved estimate of the zero-effort miss (ZEM) distance. In consequence, missile guidance accuracy is significantly improved. The new concept is applied in a horizontal interception scenario, where it is assumed that the target maneuver direction, constituting a partial attitude information, can be extracted via processing target images, acquired by an imaging sensor. The derivation results in a new guidance law that explicitly exploits the direction of the target acceleration. The performance of the new guidance law is studied via a computer simulation, which demonstrates its superiority over existing state-of-the-art differential-game-based guidance laws. It is demonstrated that a significant decrease in the miss distance can be expected via the use of partial target orientation information. 相似文献
278.
A New Mathematical Formulation for Strapdown Inertial Navigation 总被引:12,自引:0,他引:12
A differential equation is developed for the orientation vector relating the body frame to a chosen reference frame. The time derivative of this vector is the sum of the inertially measurable angular velocity vector and of the inertially nonmeasurable noncommutativity rate vector. It is precisely this noncommutativity rate vector that causes the computational problems when numerically integrating the direction cosine matrix. The orientation vector formulation allows the noncommutativity contribution to be isolated and, therefore, treated separately and advantageously. An orientation vector mechanization is presented for a strap down inertial system. Further, an example is given of the applica tion of this formulation to a typical rigid body rotation problem. 相似文献
279.
The equations derived by A. J. Rainal for the probability density function of the angle error output of a monopulse radar excited by a Gaussian signal and Gaussian thermal noise are generalized to include the presence of multiple targets. The examples given demonstrate the radar's behavior for various combinations of target and noise parameters. 相似文献
280.
Louise M. Prockter Rosaly M. C. Lopes Bernd Giese Ralf Jaumann Ralph D. Lorenz Robert T. Pappalardo Gerald W. Patterson Peter C. Thomas Elizabeth P. Turtle Roland J. Wagner 《Space Science Reviews》2010,153(1-4):63-111
The surfaces of the Solar System’s icy satellites show an extraordinary variety of morphological features, which bear witness to exchange processes between the surface and subsurface. In this paper we review the characteristics of surface features on the moons of Jupiter, Saturn, Uranus and Neptune. Using data from spacecraft missions, we discuss the detailed morphology, size, and topography of cryovolcanic, tectonic, aeolian, fluvial, and impact features of both large moons and smaller satellites. 相似文献