全文获取类型
收费全文 | 18065篇 |
免费 | 36篇 |
国内免费 | 122篇 |
专业分类
航空 | 9883篇 |
航天技术 | 5381篇 |
综合类 | 247篇 |
航天 | 2712篇 |
出版年
2021年 | 154篇 |
2018年 | 210篇 |
2016年 | 152篇 |
2014年 | 434篇 |
2013年 | 516篇 |
2012年 | 411篇 |
2011年 | 574篇 |
2010年 | 412篇 |
2009年 | 763篇 |
2008年 | 804篇 |
2007年 | 364篇 |
2006年 | 424篇 |
2005年 | 386篇 |
2004年 | 442篇 |
2003年 | 525篇 |
2002年 | 477篇 |
2001年 | 552篇 |
2000年 | 358篇 |
1999年 | 449篇 |
1998年 | 427篇 |
1997年 | 327篇 |
1996年 | 379篇 |
1995年 | 434篇 |
1994年 | 448篇 |
1993年 | 356篇 |
1992年 | 319篇 |
1991年 | 251篇 |
1990年 | 238篇 |
1989年 | 405篇 |
1988年 | 210篇 |
1987年 | 238篇 |
1986年 | 240篇 |
1985年 | 638篇 |
1984年 | 522篇 |
1983年 | 404篇 |
1982年 | 489篇 |
1981年 | 608篇 |
1980年 | 245篇 |
1979年 | 183篇 |
1978年 | 189篇 |
1977年 | 145篇 |
1976年 | 156篇 |
1975年 | 188篇 |
1974年 | 181篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
1970年 | 143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
151.
Recursive state equation estimation algorithms are derived to determine optimal estimation error covariance and state estimate for a linear dynamic system, driven by time-varying and positionverying (or angle-varying) functions whose a priori covariance are described. Retracing the same trajectory with the system measuring device causes the position varying function to repeat and can significantly reduce estimation errors. Applications for these algorithms include improving accuracy of a position dependent quantity to be mapped, or recursively processing radar or sonar data from repeating scans over the same area. Three types of return path patterns are considered: 1) multiple independent returns, 2) reverse returns, and 3) cyclical returns. 相似文献
152.
P W Barlow 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(6-7):69-72
The origin and subsequent evolution of life on Earth has taken place within an environment of which a 1g gravitational force is a part. Thus, all living organisms accommodate this variable in their structure and function. Evolution has also selected mechanisms to sense gravity which, in consequence, give particular orientations to living process. It is anticipated that the higher the evolutionary status of an organism, the greater the chance that it will possess multiple mechanisms of gravisensing because evolution discards nothing that assists fitness, but only adds to existing processes. A multiplicity of mechanisms permits gravity to participate in a wide range of developmental programmes, such as taxes, morphisms and tropisms, through the action of different sensors and distinct transduction/response pathways. 相似文献
153.
D J Grdina B A Garnes B Nagy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(2-3):257-263
Two thiophosphoroate compounds WR-2721 and WR-151327 were assessed for their ability to modify the deleterious effects (life shortening and carcinogenesis) of fission-spectrum neutrons (kerma-weighted mean energy of 0.85 MeV) or gamma rays on B6CF1 hybrid mice. Male and female mice, 200 of each sex per experimental group, were irradiated individually at 110 days of age. Radioprotectors (400 mg/kg of WR-2721 or 580 mg/kg of WR-151327) were administered intraperitoneally 30 min prior to irradiation. Neutron doses were 10 cGy or 40 cGy and gamma ray doses were 206 cGy or 417 cGy. Animals were housed five to a cage; cage locations in the holding rooms were randomized by computer. Animals were checked daily and all deceased animals were necropsied. WR-2721 afforded protection against both neutron- and gamma-ray-induced carcinogenesis and subsequent life shortening. Cumulative survival curves for unirradiated mice of either sex were unaffectecd by protectors. WR-2721 protected irradiated groups against life shortening by approximately 10 cGy of neutrons or 100 cGy of gamma rays. WR-151327 was as effective as WR-2721 against neutron irradiation. 相似文献
154.
A flat panel multifunction display (MFD) that offers the size and reliability benefits of liquid crystal display technology while achieving near-CRT display quality is presented. Display generation algorithms that provide exceptional display quality are being implemented in custom VLSI components to minimize MFD size. A high-performance processor converts user-specified display lists to graphics commands used by these components, resulting in high-speed updates of two-dimensional and three-dimensional images. The MFD uses the MIL-STD-1553B data bus for compatibility with virtually all avionics systems. The MFD can generate displays directly from display lists received from the MIL-STD-1553B bus. Complex formats can be stored in the MFD and displayed using parameters from the data bus. The MFD also accepts direct video input and performs special processing on this input to enhance image quality 相似文献
155.
Aiming at a 1-cm Orbit for Low Earth Orbiters: Reduced-Dynamic and Kinematic Precise Orbit Determination 总被引:1,自引:0,他引:1
The computation of high-accuracy orbits is a prerequisite for the success of Low Earth Orbiter (LEO) missions such as CHAMP,
GRACE and GOCE. The mission objectives of these satellites cannot be reached without computing orbits with an accuracy at
the few cm level. Such a level of accuracy might be achieved with the techniques of reduced-dynamic and kinematic precise
orbit determination (POD) assuming continuous Satellite-to-Satellite Tracking (SST) by the Global Positioning System (GPS).
Both techniques have reached a high level of maturity and have been successfully applied to missions in the past, for example
to TOPEX/POSEIDON (T/P), leading to (sub-)decimeter orbit accuracy. New LEO gravity missions are (to be) equipped with advanced
GPS receivers promising to provide very high quality SST observations thereby opening the possibility for computing cm-level
accuracy orbits. The computation of orbits at this accuracy level does not only require high-quality GPS receivers, but also
advanced and demanding observation preprocessing and correction algorithms. Moreover, sophisticated parameter estimation schemes
need to be adapted and extended to allow the computation of such orbits. Finally, reliable methods need to be employed for
assessing the orbit quality and providing feedback to the different processing steps in the orbit computation process.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
156.
Lithium ion battery technology is being introduced into power supplies used by our armed forces for a variety of applications. In many cases, the same cells and design parameters that support commercial battery packs are being used in military battery packs. This approach is expected to result in a major decrease in the total life cycle cost of the equipment these batteries support. On June 13, 1991, NAVSEA issued INST9310.1B1, which states that all lithium battery powered equipment must undergo safety evaluation and approval prior to fleet use. This safety program governs a process whereby approvals are issued for lithium batteries to be used in specific equipment on ground facilities, surface combatants, air combatants, and/or submarines. The Naval Ordnance Safety and Security Activity (NOSSA) manages the program. The chief technical advisors are Code 644 at NSWC Carderock Division and Code 609A at NSWC Crane Division. This paper describes three battery designs that incorporate lithium ion technology, and the results of battery safety tests conducted in accordance with navy requirements. 相似文献
157.
Stratton D.A. Stengel R.F. 《IEEE transactions on aerospace and electronic systems》1993,29(4):1185-1194
Severe low-altitude wind shear is a threat to aviation safety. Newly developed airborne sensors measure the radial component of wind along a line directly in front of an aircraft. The authors use optimal estimation theory to define a detection algorithm to warn of hazardous wind shear from these sensors. To achieve robustness, a wind shear detection algorithm must distinguish threatening wind shear from less hazardous gustiness, despite variations in wind shear structure. Statistical analysis methods to refine wind shear detection algorithm robustness are presented. Computational methods predict the ability to warn of severe wind shear and avoid false warning. Comparative capability of the detection algorithm as a function of its design parameters is determined, identifying designs that provide robust detection of severe wind shear 相似文献
158.
K. Uesugi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1991,11(12):19-27
A chronological review of studies in ISAS concerning collisions in space is presented. The collision probability in space with artificial orbiting bodies was estimated, and a Space Traffic Control System was proposed, in 1971. The design of a space station for safety against collision hazards was discussed in 1972. A trajectory optimization technique for low-thrust multiple rendezvous mission in order ti sweep space debris around the earth was developed in 1977. In 1984, the collision probability was reestimated using space bedris data accumulated for more than a decade. Several experimental projects in ISAS, such as hypervelocity impact experiments using a railgun system, sampling and measuring of alumina particles in exhaust plume of solid-propellant propellant rocket motors, and a result of analysis on the behavior of such alumina particles in orbit are also introduced. 相似文献
159.
Intersecting spheres are useful in the design of pressure vessels for weight limited situations as in the case of space or ocean applications. This paper treats the general problem of N intersecting spheres demonstrating that mass reduction can be achieved in relation to the single sphere that encloses the same internal volume. It is shown that this reduction approaches asymptotically the value of 39.5%. 相似文献
160.
Loran-C is a pulsed, hyperbolic radio aid for long-range marine, air, and land navigation. The worldwide expansion of Loran-C, especially in Europe, has focused attention on carrier-wave interference to the system. The effects of a multiplicity of carrier-wave interferers (CWIs) on receiver timing measurement accuracy are considered. Both the phase tracking and the cycle-selection performance of receivers are quantified in terms of the probabilities that they will operate correctly within the arbitrarily set error limits. Characteristic functions (CFs) are used to compute these probabilities. Analyses and results are presented for typical situations. The relative sensitivity of the phase tracking and cycle-selection functions to interfering signals are discussed 相似文献