全文获取类型
收费全文 | 4513篇 |
免费 | 8篇 |
国内免费 | 10篇 |
专业分类
航空 | 1790篇 |
航天技术 | 1494篇 |
综合类 | 20篇 |
航天 | 1227篇 |
出版年
2022年 | 16篇 |
2021年 | 48篇 |
2019年 | 21篇 |
2018年 | 200篇 |
2017年 | 145篇 |
2016年 | 127篇 |
2015年 | 50篇 |
2014年 | 144篇 |
2013年 | 165篇 |
2012年 | 145篇 |
2011年 | 228篇 |
2010年 | 176篇 |
2009年 | 264篇 |
2008年 | 275篇 |
2007年 | 171篇 |
2006年 | 100篇 |
2005年 | 128篇 |
2004年 | 135篇 |
2003年 | 148篇 |
2002年 | 109篇 |
2001年 | 167篇 |
2000年 | 62篇 |
1999年 | 79篇 |
1998年 | 84篇 |
1997年 | 63篇 |
1996年 | 77篇 |
1995年 | 104篇 |
1994年 | 85篇 |
1993年 | 51篇 |
1992年 | 70篇 |
1991年 | 18篇 |
1990年 | 30篇 |
1989年 | 66篇 |
1988年 | 21篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 118篇 |
1984年 | 78篇 |
1983年 | 66篇 |
1982年 | 64篇 |
1981年 | 119篇 |
1980年 | 33篇 |
1979年 | 21篇 |
1978年 | 19篇 |
1977年 | 25篇 |
1976年 | 20篇 |
1975年 | 24篇 |
1974年 | 23篇 |
1972年 | 15篇 |
1971年 | 14篇 |
排序方式: 共有4531条查询结果,搜索用时 718 毫秒
631.
I.A. Daglis 《Space Science Reviews》2001,98(3-4):343-363
In this paper I am reviewing recent advances and open disputes in the study of the terrestrial ring current, with emphasis on its storm-time dynamics. The ring current is carried by energetic charged particles flowing toroidally around the Earth, and creating a ring of westward electric current, centered at the equatorial plane and extending from geocentric distances of about 2 R
E to roughly 9 R
E. This current has a permanent existence due to the natural properties of charged particles in the geospace environment, yet its intensity is variable. It becomes more intense during global electromagnetic disturbances in the near-Earth space, which are known as space (or magnetic or geomagnetic) storms. Changes in this current are responsible for global decreases in the Earth's surface magnetic field, which is the defining feature of geomagnetic storms. The ring current is a critical element in understanding the onset and development of space weather disturbances in geospace. Ring current physics has long been driven by several paradigms, similarly to other disciplines of space physics: the solar origin paradigm, the substorm-driver paradigm, the large-scale symmetry paradigm, the charge-exchange decay paradigm. The paper addresses these paradigms through older and recent important investigations. 相似文献
632.
W F Blakely A C Miller M B Grace C B McLeland L Luo J M Muderhwa V L Miner P G Prasanna 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(6):1487-1493
The multiparametric dosimetry system that we are developing for medical radiological defense applications could be adapted for spaceflight environments. The system complements the internationally accepted personnel dosimeters and cytogenetic analysis of chromosome aberrations, considered the best means of documenting radiation doses for health records. Our system consists of a portable hematology analyzer, molecular biodosimetry using nucleic acid and antigen-based diagnostic equipment, and a dose assessment management software application. A dry-capillary tube reagent-based centrifuge blood cell counter (QBC Autoread Plus, Becton [correction of Beckon] Dickinson Bioscience) measures peripheral blood lymphocytes and monocytes, which could determine radiation dose based on the kinetics of blood cell depletion. Molecular biomarkers for ionizing radiation exposure (gene expression changes, blood proteins) can be measured in real time using such diagnostic detection technologies as miniaturized nucleic acid sequences and antigen-based biosensors, but they require validation of dose-dependent targets and development of optimized protocols and analysis systems. The Biodosimetry Assessment Tool, a software application, calculates radiation dose based on a patient's physical signs and symptoms and blood cell count analysis. It also annotates location of personnel dosimeters, displays a summary of a patient's dosimetric information to healthcare professionals, and archives the data for further use. These radiation assessment diagnostic technologies can have dual-use applications supporting general medical-related care. 相似文献
633.
T I Pisman L A Somova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(7):1757-1761
This study addresses competition between the Paramecium bursaria and zoochlorella-endosymbiosis and the infusoria Paramecium caudatum in a closed aquatic system. The system is a natural model of a simple biotic cycle. P. bursaria consumes glucose and oxygen released by its zoochlorella and releases nitrogenous compounds and carbon dioxide necessary for algal photosynthesis. P. caudatum was fed on bacteria. It was shown that the infusoria P. bursaria united in one cycle with Chlorella had a higher competitive ability than P. caudatum. With any initial percentage of the infusoria in the mixed culture, the end portion of P. bursaria reached 90-99%, which was significantly higher than the end potion of the P. caudatum population. It is assumed that the sustenance expenditures of P. caudatum were greater than those of the endosymbiotic paramecium, i.e. the closing of the components into a biotic cycle leads to a decrease in sustenance expenditures. 相似文献
634.
A.V Yakovenko 《Space Policy》2000,16(1):39
Despite its straightened circumstances and doubts about how much political support it receives, Russia's space programme continues — and continues to plan for new activities and applications. This edited version of the National Paper of the Russian Federation, presented at Unispace III in July 1999, details some of the country's major achievements in space in recent years and sets out the main areas it intends to pursue for the early twentieth-first century. While emphasis is placed on communications, remote sensing, navigation and space science, the commitment to manned flight remains. 相似文献
635.
636.
L Y Popova T I Lobova T Y Krylova T V Kargatova E E Maksimova A N Boyandin N S Pechurkin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(9):1571-1579
The role of key environmental factors in adaptation of spore-forming and non-spore-forming transgenic microorganisms (TM) have been studied in model ecosystems. Model TM Escherichia coli Z905 (bearing plasmid genes of bacterial luminescence Ap (r) Lux+) has been found to have a higher adaptation potential than TM Bacillus subtilis 2335/105 (bearing genes of human alpha 2-interferon Km (r) Inf+), planned for employment as a living vaccine under varying environmental conditions. Effects of abiotic factors on migration of natural and recombinant plasmids between microorganisms under model ecosystem conditions has been estimated. The transgenic microorganisms with low copy number survived better under introduction conditions in the microcosms studied. This trend has been shown to be independent of the microcosm type and its complexity. Grant numbers: 99-04-96017, 25, 00-07-9011. 相似文献
637.
Reed I.S. Gagliardi R.M. Stotts L.B. 《IEEE transactions on aerospace and electronic systems》1990,26(3):434-440
A recursive track-before-detect algorithm, producing potentially large signal-to-noise ratio (SNR) gains under realizable conditions, is described. The basic relation has the form of a linear, constant-coefficient difference equation with a unity magnitude damping factor. Known as recursive moving-target-indication (RMTI), this procedure adapts easily to digital processing and achieves SNR gains comparable to those from other robust track-before-detect algorithms. Examples are given to demonstrate the performance of the moving target indicator (MTI) procedure 相似文献
638.
An update of a phased array radar project with the experimental system ELRA (electronic steerable radar) is given with respect to the extended and improved possibilities for performing measurements and evaluations for different types of radar operation. The variability of waveforms for solid-state transmitters is described. Flexible control of multifunction operation with various search and localization tasks is achieved with a network of microcomputers. Different means of signal processing are used for target detection and estimation. The active receiving array is divided into subarrays, and offers digital beamforming for pattern shaping and adaptive jammer suppression. Experimental results are presented 相似文献
639.
The enhancements of solar protons with an energy of more than 30 MeV, originating from flares in one active region and observed simultaneously aboard three spacecraft Vega-1, 2 and Prognoz-10 in July 1985, are analyzed and approximated in this work by using the reflection model [2]. The numerical values of several physical parameters (the parameters of distribution of solar cosmic ray (SCR) particles inside heliosphere traps, the coefficients of trap transparency) that are not observed by direct measurements are estimated. 相似文献
640.
The benefits of using transmitting phased array antennas for radar systems are examined. Accurate performance prediction for the transmitting phased array antennas requires theories describing both the antenna system and the power generation devices. These theories were created and applied to the design and performance evaluation of the Russian 3-D mobile solid-state surveillance radar 67N6E (GAMMA-DE), a PAA designed for long-range air defense. 相似文献