全文获取类型
收费全文 | 18043篇 |
免费 | 33篇 |
国内免费 | 126篇 |
专业分类
航空 | 9863篇 |
航天技术 | 5398篇 |
综合类 | 251篇 |
航天 | 2690篇 |
出版年
2021年 | 156篇 |
2018年 | 206篇 |
2016年 | 154篇 |
2014年 | 435篇 |
2013年 | 516篇 |
2012年 | 411篇 |
2011年 | 568篇 |
2010年 | 398篇 |
2009年 | 760篇 |
2008年 | 797篇 |
2007年 | 370篇 |
2006年 | 429篇 |
2005年 | 390篇 |
2004年 | 440篇 |
2003年 | 518篇 |
2002年 | 485篇 |
2001年 | 563篇 |
2000年 | 364篇 |
1999年 | 456篇 |
1998年 | 425篇 |
1997年 | 313篇 |
1996年 | 379篇 |
1995年 | 447篇 |
1994年 | 427篇 |
1993年 | 358篇 |
1992年 | 321篇 |
1991年 | 251篇 |
1990年 | 234篇 |
1989年 | 389篇 |
1988年 | 206篇 |
1987年 | 246篇 |
1986年 | 238篇 |
1985年 | 643篇 |
1984年 | 521篇 |
1983年 | 410篇 |
1982年 | 488篇 |
1981年 | 615篇 |
1980年 | 247篇 |
1979年 | 184篇 |
1978年 | 189篇 |
1977年 | 145篇 |
1976年 | 155篇 |
1975年 | 187篇 |
1974年 | 180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 0 毫秒
1.
The Role and Contributions of Energetic Neutral Atom (ENA) Imaging in Magnetospheric Substorm Research 总被引:2,自引:0,他引:2
Pollock C.J. C:son-Brandt P. Burch J.L. Henderson M.G. Jahn J.-M. McComas D.J. Mende S.B. Mitchell D.G. Reeves G.D. Scime E.E. Skoug R.M. Thomsen M. Valek P. 《Space Science Reviews》2003,109(1-4):155-182
Energetic Neutral Atom (ENA) imaging has contributed substantially to substorm research. This technique has allowed significant advances in areas such as observation and quantification of injected particle drift as a function of energy, observation of dynamics in the tail that are directly related to the effects of imposed (growth phase) and induced (expansion phase) electric fields on the plasma, the prompt extraction of oxygen from the ionosphere during substorms, the relationship between storms and substorms, and the timing of substorm ENA signatures. We present discussion of the advantages and shortcomings of the ENA technique for studying space plasmas. Although the technique is in its infancy, it is yielding results that enrich our understanding of the substorm process and its effects. 相似文献
2.
Giulio L. Marco B. Aldo F. Domenico T.P. Mario M. 《Aerospace and Electronic Systems Magazine, IEEE》2002,17(9):22-27
This paper reviews the results of the thermal and static analysis of small motor aerospace technology (SMART) propulsion system, constituted of a microthrusters array realised by MEMS technology on silicon wafers. This system has been studied using FEM (NASTRAN) and the results have been verified by the electro-thermic analogy and the FDM method, using, respectively, SPICE and MATLAB codes. The simulation results demonstrated the feasibility of SMART systems for aerospace applications such as attitude control and deorbiting missions for small satellite station-keeping. A theoretical impulse of 20 mNs has been calculated for the SMART system. 相似文献
3.
We have taken an inventory of the elemental and isotopic abundances of major carbon- and nitrogen-bearing components in different
groups of meteorites. Primary phases, inherited from the solar nebula, are frequently isotopically heterogeneous, and surprisingly
resistant to modification through parent body processing. Even melted and recrystallised meteorites retain primordial carbon
and nitrogen isotopic signatures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
This study introduces a field oriented controlled (FOC) induction machine based flywheel energy storage (FES) system fed from a 20 kHz high frequency (HF) ac link and pulse density modulated (PDM) Converter. The feasibility of FES system is investigated both in software and hardware and is demonstrated successfully in both cases. The investigated system offers a good potential as a temporary energy storage system for various applications from automobile industry to aerospace applications. 相似文献
5.
A review of common switching techniques for dc/dc power conversion is presented. The evolution of the forward converter is discussed, leading naturally to the introduction of the double forward converter. Technical details for a series of radiation-hardened converters are then provided. This series was designed for space power management and distribution (PMAD) applications. The successful development of the PMAD converter demonstrated the viability of high voltage bus. 相似文献
6.
Snyder S. Schipper B. Vallot L. Parker N. Spitzer C. 《Aerospace and Electronic Systems Magazine, IEEE》1992,7(5):3-11
In November 1990, a differential GPS/inertial flight test was conducted to acquire a system performance database and demonstrate automatic landing using an integrated differential GPS/INS with barometric and radar altimeters. Flight test results obtained from postflight data analysis are presented. These results include characteristics of DGPS/inertial error, using a laser tracker as a reference. In addition, data are provided on the magnitude of the differential correlations and vertical channel performance with and without radar altimeter augmentation. Flight test results show one sigma DGPS/inertial horizontal errors of 9 ft and one sigma DGPS inertial vertical errors of 15 ft. Without selective availability effects, the differential corrections are less than 10 ft and are dominated by receiver unique errors over the time period of an approach. Therefore, the one sigma performance of the autonomous GPS (8-ft horizontal and 20-ft vertical) is very similar to the DGPS/inertial performance. Postprocessed results also demonstrate significant improvements in vertical channel performance when GPS/inertial is aided with radar altimeter along with a low-resolution terrain map 相似文献
7.
Significant advances in and applications of battery technology are outlined. Factors driving future developments are identified 相似文献
8.
9.
U Seitzer M Bodo P K Muller 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,16(7):235-238
Quantitative and qualitative aspects of collagen synthesis under microgravity, normal gravity and hypergravity conditions were investigated during the spacelab D-2 mission by incubating human fibroblast cultures with [3H]-proline for 0, 4, 7, 10 and 20 hours. Quantitative analysis revealed an increase of collagen synthesis under microgravity conditions, being 40% higher than 1g controls. Hypergravity samples at 1.44g, 6.6g and 10g showed a decrease in collagen synthesis with increasing g, being down to about 15% at 10g. The relative proportion of collagen from total protein synthesized, the secretion of collagen by the cells, proline hydroxylation of individual collagen alpha-chains and the relative proportions of collagens I, III and V synthesized were not affected at any of the applied conditions. 相似文献
10.
P.L. Israelevich A.I. Ershkovich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(12):99-103
Plasma and magnetic field disturbances accompanying dust particle impacts are explained by means of creation of a secondary cloud around the spacecraft. Cold cometary ions impinging upon the cloud are scattered by atoms of the cloud. This scattering changes initial angular distribution of cometary ions. Magnetic field perturbation is created by the friction between the electron component of the cometary plasma flow and the cloud. 相似文献