全文获取类型
| 收费全文 | 3151篇 |
| 免费 | 13篇 |
| 国内免费 | 6篇 |
专业分类
| 航空 | 1670篇 |
| 航天技术 | 1080篇 |
| 综合类 | 9篇 |
| 航天 | 411篇 |
出版年
| 2018年 | 37篇 |
| 2017年 | 19篇 |
| 2016年 | 23篇 |
| 2014年 | 54篇 |
| 2013年 | 78篇 |
| 2012年 | 59篇 |
| 2011年 | 105篇 |
| 2010年 | 82篇 |
| 2009年 | 112篇 |
| 2008年 | 176篇 |
| 2007年 | 90篇 |
| 2006年 | 60篇 |
| 2005年 | 77篇 |
| 2004年 | 78篇 |
| 2003年 | 100篇 |
| 2002年 | 52篇 |
| 2001年 | 99篇 |
| 2000年 | 48篇 |
| 1999年 | 79篇 |
| 1998年 | 93篇 |
| 1997年 | 73篇 |
| 1996年 | 91篇 |
| 1995年 | 124篇 |
| 1994年 | 98篇 |
| 1993年 | 66篇 |
| 1992年 | 101篇 |
| 1991年 | 42篇 |
| 1990年 | 36篇 |
| 1989年 | 87篇 |
| 1988年 | 33篇 |
| 1987年 | 28篇 |
| 1986年 | 32篇 |
| 1985年 | 87篇 |
| 1984年 | 91篇 |
| 1983年 | 59篇 |
| 1982年 | 82篇 |
| 1981年 | 92篇 |
| 1980年 | 34篇 |
| 1979年 | 42篇 |
| 1978年 | 32篇 |
| 1977年 | 22篇 |
| 1976年 | 21篇 |
| 1975年 | 37篇 |
| 1974年 | 24篇 |
| 1973年 | 18篇 |
| 1972年 | 29篇 |
| 1969年 | 17篇 |
| 1968年 | 16篇 |
| 1967年 | 20篇 |
| 1966年 | 16篇 |
排序方式： 共有3170条查询结果，搜索用时 15 毫秒
801.
802.
T. G. Forbes J. A. Linker J. Chen C. Cid J. Kóta M. A. Lee G. Mann Z. Mikić M. S. Potgieter J. M. Schmidt G. L. Siscoe R. Vainio S. K. Antiochos P. Riley 《Space Science Reviews》2006,123(1-3):251-302
This chapter provides an overview of current efforts in the theory and modeling of CMEs. Five key areas are discussed: (1) CME initiation; (2) CME evolution and propagation; (3) the structure of interplanetary CMEs derived from flux rope modeling; (4) CME shock formation in the inner corona; and (5) particle acceleration and transport at CME driven shocks. In the section on CME initiation three contemporary models are highlighted. Two of these focus on how energy stored in the coronal magnetic field can be released violently to drive CMEs. The third model assumes that CMEs can be directly driven by currents from below the photosphere. CMEs evolve considerably as they expand from the magnetically dominated lower corona into the advectively dominated solar wind. The section on evolution and propagation presents two approaches to the problem. One is primarily analytical and focuses on the key physical processes involved. The other is primarily numerical and illustrates the complexity of possible interactions between the CME and the ambient medium. The section on flux rope fitting reviews the accuracy and reliability of various methods. The section on shock formation considers the effect of the rapid decrease in the magnetic field and plasma density with height. Finally, in the section on particle acceleration and transport, some recent developments in the theory of diffusive particle acceleration at CME shocks are discussed. These include efforts to combine self-consistently the process of particle acceleration in the vicinity of the shock with the subsequent escape and transport of particles to distant regions. 相似文献
803.
Hiroshi Matsui John C. Foster Donald L. Carpenter Iannis Dandouras Fabien Darrouzet Johan De Keyser Dennis L. Gallagher Jerry Goldstein Pamela A. Puhl-Quinn Claire Vallat 《Space Science Reviews》2009,145(1-2):107-135
The electric field and magnetic field are basic quantities in the plasmasphere measured since the 1960s. In this review, we first recall conventional wisdom and remaining problems from ground-based whistler measurements. Then we show scientific results from Cluster and Image, which are specifically made possible by newly introduced features on these spacecraft, as follows. 1. In situ electric field measurements using artificial electron beams are successfully used to identify electric fields originating from various sources. 2. Global electric fields are derived from sequences of plasmaspheric images, revealing how the inner magnetospheric electric field responds to the southward interplanetary magnetic fields and storms/substorms. 3. Understanding of sub-auroral polarization stream (SAPS) or sub-auroral ion drifts (SAID) are advanced through analysis of a combination of magnetospheric and ionospheric measurements from Cluster, Image, and DMSP. 4. Data from multiple spacecraft have been used to estimate magnetic gradients for the first time. 相似文献
804.
M. H. Acuña D. Curtis J. L. Scheifele C. T. Russell P. Schroeder A. Szabo J. G. Luhmann 《Space Science Reviews》2008,136(1-4):203-226
The magnetometer on the STEREO mission is one of the sensors in the IMPACT instrument suite. A single, triaxial, wide-range, low-power and noise fluxgate magnetometer of traditional design—and reduced volume configuration—has been implemented in each spacecraft. The sensors are mounted on the IMPACT telescoping booms at a distance of ～3 m from the spacecraft body to reduce magnetic contamination. The electronics have been designed as an integral part of the IMPACT Data Processing Unit, sharing a common power converter and data/command interfaces. The instruments cover the range ±65,536 nT in two intervals controlled by the IDPU (±512 nT; ±65,536 nT). This very wide range allows operation of the instruments during all phases of the mission, including Earth flybys as well as during spacecraft test and integration in the geomagnetic field. The primary STEREO/IMPACT science objectives addressed by the magnetometer are the study of the interplanetary magnetic field (IMF), its response to solar activity, and its relationship to solar wind structure. The instruments were powered on and the booms deployed on November 1, 2006, seven days after the spacecraft were launched, and are operating nominally. A magnetic cleanliness program was implemented to minimize variable spacecraft fields and to ensure that the static spacecraft-generated magnetic field does not interfere with the measurements. 相似文献
805.
We analyze the immediate negative acknowledgment (NAK) mode of the consultative committee for space data systems (CCSDS) file delivery protocol for the single-hop file transfer operation. We propose a timer setting rule that minimizes the expected time taken to transfer a file under the constraint that the throughput efficiency is maximized. Then, we derive the expected file delivery time and compare it with that of the deferred NAK mode. The main contribution is the closed-form expression for evaluating the performance metrics. 相似文献
806.
Peckham C.D. Haimovich A.M. Ayoub T.F. Goldstein J.S. Reid I.S. 《IEEE transactions on aerospace and electronic systems》2000,36(2):664-676
The space-time radar problem is well suited to the application of techniques that take advantage of the low-rank property of the space-time covariance matrix. It is shown that reduced-rank (RR) methods outperform full-rank space-time adaptive processing (STAP) when the space-time covariance matrix is estimated from a data set with limited support. The utility of RR methods is demonstrated by theoretical analysis, simulations and analysis of real data. It is shown that RR processing has two opposite effects on the performance: increased statistical stability which tends to improve performance, and introduction of a bias which lowers the signal-to-noise ratio (SNR). A method for evaluating the theoretical conditioned SNR for fixed RR transforms is also presented. It Is shown that while best performance is obtained using data-dependent transforms, the loss incurred by the application of fixed transforms (such as the discrete cosine transform) may be relatively small. The main advantage of fixed transforms is the availability of efficient computational procedures for their implementation. These findings suggest that RR methods could facilitate the development of practical, real-time STAP technology 相似文献
807.
A. J. Kliore J. D. Anderson J. W. Armstrong S. W. Asmar C. L. Hamilton N. J. Rappaport H. D. Wahlquist R. Ambrosini F. M. Flasar R. G. French L. Iess E. A. Marouf A. F. Nagy 《Space Science Reviews》2004,115(1-4):1-70
Cassini radio science investigations will be conducted both during the cruise (gravitational wave and conjunction experiments) and the Saturnian tour of the mission (atmospheric and ionospheric occultations, ring occultations, determinations of masses and gravity fields). New technologies in the construction of the instrument, which consists of a portion on-board the spacecraft and another portion on the ground, including the use of the Ka-band signal in addition to that of the S- and X-bands, open opportunities for important discoveries in each of the above scientific areas, due to increased accuracy, resolution, sensitivity, and dynamic range.This revised version was published online in July 2005 with a corrected cover date. 相似文献
808.
C. Elachi M. D. Allison L. Borgarelli P. Encrenaz E. Im M. A. Janssen W. T. K. Johnson R. L. Kirk R. D. Lorenz J. I. Lunine D. O. Muhleman S. J. Ostro G. Picardi F. Posa C. G. Rapley L. E. Roth R. Seu L. A. Soderblom S. Vetrella S. D. Wall C. A. Wood H. A. Zebker 《Space Science Reviews》2004,115(1-4):71-110
The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn’s icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn’s atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as −40 dB.RADAR Team LeaderThis revised version was published online in July 2005 with a corrected cover date. 相似文献
809.
We address the problem of loading as much freight as possible in an aircraft while balancing the load in order to minimize fuel consumption and to satisfy stability/safety requirements. Our formulation methodology permits to solve the problem on a PC, within ten min, by off-the-shelf integer linear programming software. This method decides which containers to load (and in which compartment) and which to leave on the ground. 相似文献
810.
A utility-type, 20-kHz, AC power distribution system for the space station employing resonant power-conversion techniques is presented. The system converts raw DC voltage from photovoltaic cells or three-phase, low-frequency AC voltage from a solar dynamic generator into a regulated, 20-G kHz AC voltage for distribution among various loads. Operations of the components of the system such as driver inverter, DC receiver, bidirectional receiver, and three-phase AC receiver are discussed. EASY5 computer modeling and simulations were performed to study the local and global performance of the system. Simulation results show that the system has fast response and good transient behavior. The AC bus voltage is effectively regulated using the phase-control scheme, which is demonstrated with both line and load variations. The feasibility of paralleling the outputs of driver modules is illustrated with the driver modules synchronized and sharing a common feedback loop. A high-frequency, sinusoidal AC voltage is generated in the three-phase, AC input case, when the driver modules are phased 120° away from one another and their outputs are connected in series 相似文献