全文获取类型
收费全文 | 4871篇 |
免费 | 2篇 |
国内免费 | 12篇 |
专业分类
航空 | 2540篇 |
航天技术 | 1574篇 |
综合类 | 181篇 |
航天 | 590篇 |
出版年
2021年 | 32篇 |
2018年 | 69篇 |
2017年 | 39篇 |
2016年 | 40篇 |
2014年 | 72篇 |
2013年 | 106篇 |
2012年 | 111篇 |
2011年 | 160篇 |
2010年 | 103篇 |
2009年 | 184篇 |
2008年 | 199篇 |
2007年 | 114篇 |
2006年 | 88篇 |
2005年 | 88篇 |
2004年 | 115篇 |
2003年 | 140篇 |
2002年 | 179篇 |
2001年 | 198篇 |
2000年 | 94篇 |
1999年 | 123篇 |
1998年 | 153篇 |
1997年 | 99篇 |
1996年 | 139篇 |
1995年 | 168篇 |
1994年 | 148篇 |
1993年 | 95篇 |
1992年 | 126篇 |
1991年 | 57篇 |
1990年 | 63篇 |
1989年 | 125篇 |
1988年 | 58篇 |
1987年 | 60篇 |
1986年 | 51篇 |
1985年 | 156篇 |
1984年 | 122篇 |
1983年 | 109篇 |
1982年 | 117篇 |
1981年 | 154篇 |
1980年 | 57篇 |
1979年 | 46篇 |
1978年 | 58篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 48篇 |
1974年 | 39篇 |
1973年 | 25篇 |
1972年 | 49篇 |
1971年 | 47篇 |
1970年 | 30篇 |
1969年 | 33篇 |
排序方式: 共有4885条查询结果,搜索用时 15 毫秒
981.
Cosmic Research - Using the Meteor M2 low-orbit satellite, the dynamics of the boundaries of the auroral oval on the nightside during the magnetic storm observed from May 27 to 29, 2017, was... 相似文献
982.
Interim results of a study on use of the tethered propellant resupply technique on the space station are summarized. The acceleration produced by a gravity-gradient-stabilized tether can predictably settle propellants and thereby simplify propellant resupply of vehicles when compared to zero-g techniques. Separation of the gas and liquid phases by settling enables performance of liquid acquisition and gas venting without special hardware in the propellant tanks and without special procedures. The primary requirement for propellant transfer is control of liquid sloshing to maintain liquid over the supply tank outlet and gas over the receiver tank vent. Ultimately, the decision to use this technique on the space station may depend upon the capability to adjust depot logistic operations to a tether. 相似文献
983.
Alam E. Kherani Matheus Mascarenhas Eurico R. De Paula Jose H. A. Sobral Fernando Bertoni 《Space Science Reviews》2005,121(1-4):253-269
We present a three-dimensional simulation of collisional-interchange-instability in the equatorial-low-latitude F region of
ionosphere. The instability is responsible for the generation of large plasma density depletion or bubble. General 3D potential
and continuity equations are derived to simulate the phenomena. To understand the linear aspect of the instability, the general
3D linear growth rate is derived using 3D potential equation. The linear growth characteristics are compared with earlier
field-aligned-integrated growth analyses. The numerical simulation of bubble in the 3D spherical polar geometry is finally
presented. Distinct evolution characteristics of bubble in 3D and 2D simulation are further discussed. 相似文献
984.
N.V. Jorjio R.A. Kovrazhkin M.M. Mogilevsky J.M. Bosqued H. Rème J.A. Sauvaud C. Béghin J.L. Rauch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):141-144
The plasma diagnostic experiments on the AUREOL-3 satellite have revealed flows of low energy 0+ ions deep inside the night plasmasphere during a large substorm. Flux gradients of the 0+ ions were accompanied by enhancements of ELF electric field noise. The appearance of suprathermal ions at is interpreted within the framework of electrostatic ion-cyclotron acceleration of ionospheric ions in the diffuse auroral zone /12/ followed by a radial displacement of these ions inside the plasmasphere driven by azimuthal electric fields during substorm activity. Electrostatic oscillations observed inside the plasmasphere are apparently associated with gradient instability at the sharp boundaries of suprathermal ion flows. 相似文献
985.
The first intercontinental satellite communication link, which involved the NASA Echo I balloon, a transmitting station on the Island of Trinidad, and a receiving station at Floyd, NY, is discussed. Rome Air Development Center (RADC) experimental stations were set up using a great deal of ingenuity and makeshift equipment and on a very small budget. Much of the equipment was salvaged from unrelated systems, while some was hand-built for this project. The implementation of the system, the testing of the system using moon bounce, the first orbital launch of the Echo I balloon, and the early difficulties encountered in the project are reviewed 相似文献
986.
A pure-Cartesian formulation is presented for angle-only and angle-plus-range tracking filters. Unlike conventional angle-only filters, which use target elevation and bearing as measurements, the filter expresses the sensor measurements in Cartesian coordinates. Consequently, the filter performs equally well for any line-of-sight (LOS) geometry, even when target elevation approaches or is equal to ±90° 相似文献
987.
R.K. Shevgaonkar M.R. Kundu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):247-250
Simultaneous observations of a microwave burst at 2 and 6 cm wavelengths were carried out with the Very Large Array (VLA). The 6 cm burst source is located close to a magnetic neutral line, presumably near the top of a flaring loop, while the 2 cm emission originates from the footpoints of the loop. It is concluded that the 6 cm emission is dominated by gyrosynchrotron radiation of the thermal electrons in the bulk heated plasma at a temperature of ~ 4 × 107 K, while the 2 cm emission is due to nonthermal particles released and accelerated during the flare process. From the observed low degree of polarization and the lack of the 2 cm source cospatiality with the 6 cm source a magnetic field of 200–350 G and δ ? 4 are estimated in the flare energy release site. A DC electric field flare model is invoked to explain the long delay between the peaks at the two wavelengths. From the delay, the strength of the electric field is estimated to be 0.2–4 μ statvolt cm?1 in the flaring region. 相似文献
988.
W R Schwingel J C Sager 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):293-297
An anaerobic reactor seeded with organisms from an anaerobic lagoon was used to study the degradation of inedible crop residues from potato and wheat crops grown in a closed environment. Conversion of this biomass into other products was also evaluated. Degradation of wheat volatile solids was about 25% where that of potato was about 50%. The main product of the anaerobic fermentation of both crops was acetic acid with smaller quantities of propionate and butyrate produced. Nitrate, known to be high in concentration in inedible potato and wheat biomass grown hydroponically, was converted to ammonia in the anaerobic reactor. Both volatile fatty acid and ammonia production may have implications in a crop production system. 相似文献
989.
B Fu P E Nelson R Irvine L L Kanach 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):241-250
A controlled ecological life-support system (CELSS) is required to sustain life for long-duration space missions. The challenge is preparing a wide variety of tasty, familiar, and nutritious foods from CELSS candidate crops under space environmental conditions. Conventional food processing technologies will have to be modified to adapt to the space environment. Extrusion is one of the processes being examined as a means of converting raw plant biomass into familiar foods. A nutrition-improved pasta has been developed using cowpea as a replacement for a portion of the durum semolina. A freeze-drying system that simulates the space conditions has also been developed. Other technologies that would fulfill the requirements of a CELSS will also be addressed. 相似文献
990.
The 1990s have been stressful for commercial airline industry: fierce competition has caused the demise of several carriers. The resulting drive to slash operating expenses has bolstered development of avionics industry standards for automated test equipment. Rockwell's Collins Air Transport Division (CATD) has begun to market compliant test gear that airline maintenance departments wishing to acquire modern high performance test systems without the development cost penalty have eagerly received. A similar situation now confronts the military. The various branches can no longer justify the maintenance of independent autotest architectures. This paper describes the CATD implementation of the commercial-standard architecture; shows how we have designed the system to avoid obsolescence; and indicates the considerations that are necessary for adapting it to military scenarios 相似文献