全文获取类型
收费全文 | 4454篇 |
免费 | 6篇 |
国内免费 | 6篇 |
专业分类
航空 | 2116篇 |
航天技术 | 1256篇 |
综合类 | 181篇 |
航天 | 913篇 |
出版年
2021年 | 21篇 |
2019年 | 23篇 |
2018年 | 185篇 |
2017年 | 146篇 |
2016年 | 72篇 |
2015年 | 42篇 |
2014年 | 78篇 |
2013年 | 93篇 |
2012年 | 118篇 |
2011年 | 249篇 |
2010年 | 195篇 |
2009年 | 256篇 |
2008年 | 255篇 |
2007年 | 217篇 |
2006年 | 90篇 |
2005年 | 143篇 |
2004年 | 109篇 |
2003年 | 100篇 |
2002年 | 164篇 |
2001年 | 169篇 |
2000年 | 54篇 |
1999年 | 86篇 |
1998年 | 102篇 |
1997年 | 80篇 |
1996年 | 103篇 |
1995年 | 120篇 |
1994年 | 85篇 |
1993年 | 56篇 |
1992年 | 79篇 |
1991年 | 32篇 |
1990年 | 27篇 |
1989年 | 69篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1985年 | 114篇 |
1984年 | 99篇 |
1983年 | 62篇 |
1982年 | 85篇 |
1981年 | 109篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1978年 | 24篇 |
1977年 | 23篇 |
1975年 | 19篇 |
1974年 | 26篇 |
1972年 | 20篇 |
1971年 | 21篇 |
1970年 | 20篇 |
1969年 | 24篇 |
排序方式: 共有4466条查询结果,搜索用时 15 毫秒
991.
Harris PR 《Acta Astronautica》1995,36(7):399-408
The Space Age is causing new applications to the concept of culture, a human coping tool. The exploration and exploitation of outer space resources are altering human culture both on Earth and in orbit. For the first time in history, our species need not merely react and adapt to environment, but plan for a space culture appropriate for extraterrestrial migration. The impact of culture can be analyzed in terms of how space developments alter human perceptions and behavior on this planet; the emergence of a new culture to suit the orbital environment; the organizations that build spacecraft and deploy people aloft; and the technological systems created for spacefaring. This article presents a paradigm for analyzing some of the non-technical human factors involved in space undertakings. It also offers a method for classifying a culture according to ten categories which may be applied both to a macroculture, such as a lunar base; or a microculture, such as a space agency or crew. Human enterprise in space is viewed as both altering the species, and providing a challenge for expanded behavioral and biological scientific research on living and working in space. 相似文献
992.
R. P. Lepping M. H. Acũna L. F. Burlaga W. M. Farrell J. A. Slavin K. H. Schatten F. Mariani N. F. Ness F. M. Neubauer Y. C. Whang J. B. Byrnes R. S. Kennon P. V. Panetta J. Scheifele E. M. Worley 《Space Science Reviews》1995,71(1-4):207-229
The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and associated electronics. The dual configuration provides redundancy and also permits accurate removal of the dipolar portion of the spacecraft magnetic field. The instrument provides (1) near real-time data at nominally one vector per 92 s as key parameter data for broad dissemination, (2) rapid data at 10.9 vectors s–1 for standard analysis, and (3) occasionally, snapshot (SS) memory data and Fast Fourier Transform data (FFT), both based on 44 vectors s–1. These measurements will be precise (0.025%), accurate, ultra-sensitive (0.008 nT/step quantization), and where the sensor noise level is <0.006 nT r.m.s. for 0–10 Hz. The digital processing unit utilizes a 12-bit microprocessor controlled analogue-to-digital converter. The instrument features a very wide dynamic range of measurement capability, from ±4 nT up to ±65 536 nT per axis in eight discrete ranges. (The upper range permits complete testing in the Earth's field.) In the FTT mode power spectral density elements are transmitted to the ground as fast as once every 23 s (high rate), and 2.7 min of SS memory time series data, triggered automatically by pre-set command, requires typically about 5.1 hours for transmission. Standard data products are expected to be the following vector field averages: 0.0227-s (detail data from SS), 0.092 s (detail in standard mode), 3 s, 1 min, and 1 hour, in both GSE and GSM coordinates, as well as the FFT spectral elements. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the solar wind: (1) as a collisionless plasma laboratory, at all time scales, macro, meso and micro, but concentrating on the kinetic scale, the highest time resolution of the instrument (=0.022 s), (2) as a consequence of solar energy and mass output, (3) as an external source of plasma that can couple mass, momentum, and energy to the Earth's magnetosphere, and (4) as it is modified as a consequence of its imbedded field interacting with the moon. Since the GEOTAIL Inboard Magnetometer (GIM), which is similar to the MFI instrument, was developed by members of our team, we provide a brief discussion of GIM related science objectives, along with MFI related science goals. 相似文献
993.
994.
P Ehrenfreund B H Foing 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(7):1033-1042
The discovery and synthesis of fullerenes led to the hypothesis that they may be present and stable in interstellar space. Fullerenes have been reported in an impact crater on the LDEF spacecraft. Investigations of fullerenes in carbonaceous meteorites have yielded only small upper limits. Fullerene compounds and their ions could be interesting carrier molecules for some of the "diffuse interstellar bands" (DIBs), a long standing mystery in astronomy. We have detected two new diffuse bands that are consistent with laboratory measurements of the C60+, as first evidence for the largest molecule ever detected in space. Criteria for this identification are discussed. The inferred abundance (up to 0.9 % of cosmic carbon locked in C60+) suggests that fullerenes may play an important role in interstellar chemistry. We present new observations on DIB substructures consistent with fullerene compounds, and the search for neutral C60 in the diffuse medium. 相似文献
995.
M.?HesseEmail author N.?Aunai J.?Birn P.?Cassak R.?E.?Denton J.?F.?Drake T.?Gombosi M.?Hoshino W.?Matthaeus D.?Sibeck S.?Zenitani 《Space Science Reviews》2016,199(1-4):577-630
The Magnetospheric Multiscale (MMS) mission will provide measurement capabilities, which will exceed those of earlier and even contemporary missions by orders of magnitude. MMS will, for the first time, be able to measure directly and with sufficient resolution key features of the magnetic reconnection process, down to the critical electron scales, which need to be resolved to understand how reconnection works. Owing to the complexity and extremely high spatial resolution required, no prior measurements exist, which could be employed to guide the definition of measurement requirements, and consequently set essential parameters for mission planning and execution. Insight into expected details of the reconnection process could hence only been obtained from theory and modern kinetic modeling. This situation was recognized early on by MMS leadership, which supported the formation of a fully integrated Theory and Modeling Team (TMT). The TMT participated in all aspects of mission planning, from the proposal stage to individual aspects of instrument performance characteristics. It provided and continues to provide to the mission the latest insights regarding the kinetic physics of magnetic reconnection, as well as associated particle acceleration and turbulence, assuring that, to the best of modern knowledge, the mission is prepared to resolve the inner workings of the magnetic reconnection process. The present paper provides a summary of key recent results or reconnection research by TMT members. 相似文献
996.
Proton Events and X-ray Flares in the Last Three Solar Cycles 总被引:3,自引:0,他引:3
A database joining the available information about proton enhancements near the Earth and their possible solar sources is organized on the basis of proton measurements of the GOES and IMP-8 satellites, the data of neutron monitors, and GOES X-ray measurements. One thousand one hundred and forty-four proton events with energy > 10 MeV have been selected in the period from 1975 to 2003. More than a half of these events can be reliably related to X-ray solar flares. A statistical analysis shows the probability of observing solar protons near the Earth and their maximum flux value to be strongly dependent on the importance of a flare and its heliolongitude. Proton events are recorded after all suitably located (western) flares with X-ray importance > X5. The heliolongitude of a flare predetermines the character of the time profile of proton events in many respects. The relationship of proton events with the other characteristics of flares is established. The flares associated with proton enhancements are characterized by longer duration, slower rise to the X-ray maximum, smaller temperature, and larger length of the X-ray loops.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 3, 2005, pp. 171–185.Original Russian Text Copyright © 2005 by Belov, Garcia, Kurt, Mavromichalaki. 相似文献
997.
Lick Observatory's Optical SETI (search for extraterrestrial intelligence) program has been in regular operation for 4.5 years. We have observed 4,605 stars of spectral types F-M within 200 light-years of Earth. Occasionally, we have appended objects of special interest, such as stars with known planetary systems. We have observed 14 candidate signals ("triple coincidences"), all but one of which are explained by transient local difficulties. Additional observations of the remaining candidate have failed to confirm arriving pulse events. We now plan to proceed in a more economical manner by operating in an unattended drift scan mode. Between operational and equipment modifications, efficiency will more than double. 相似文献
998.
Arbeille Ph Lebouard D Massabuau M Pottier JM Patat F Pourcelot L Guell A 《Acta Astronautica》1991,25(7):415-418
Cardiovascular assessment by ultrasound methods was performed during two long duration (1 month) Head Down Tilt (HDT) on 6 healthy volunteers. On a first 1 month HDT session, 3 of the 6 subjects (A, B, C) had daily several lower body negative pressure tests (LBNP), whereas the 3 subjects remaining (D, E, F) rested without LBNP. On a second 1 month HDT session subjects D, E, and F had daily LBNP tests and the A, B and C subjects did not. The cardiac function was assessed by Echocardiography, (B mode, TM mode). On all the "6 non LBNP" subjects the left ventricule diastolic volume (LVDV), the stroke volume (SV) and the cardiac output (CO) increase (+10%, -15%) after HDT then decrease and remain inferior (-5%, -5%) or equal to the basal value during the HDT. Immediately after the end of the HDT the heart rate (HR) increase (+10%, +30%) whereas the cardiac parameters decrease weakly (-5%, -10%) and normalize after 3 days of recovery. On the "6 LBNP" subjects the LVDV, SV and CO increase (+10%, 15%) after 1 h HDT as in the previous group then decrease but remain superior (+5%, +15%) or equal to the basal value. After the HDT session, the HR is markedly increased (+20%, +40%) the LVDV and SV decrease (-15%, -20%) whereas the CO increases or decreases depending on the amplitude of the HR variations. These parameters do not completely normalize after 3 day's recovery. Repeated LBNP sessions have a significant effect on the cardiovascular function as it maintains all cardiac parameters above the basal value. The LBNP manoeuvre can be considered as an efficient countermeasure to prevent cardiac disadaptation induced by HDT position and probably microgravity. 相似文献
999.
Brownlee DE Tsou P Atkins KL Yen CW Vellinga JM Price S Clark BC 《Acta Astronautica》1996,39(1-4):51-60
The STARDUST Discovery mission will collect samples of cometary coma and interstellar dust and return them to Earth. Five years after launch in February 1999, coma dust in the 1- to 100-micrometers size range will be captured by impact into ultra-low-density silica aerogel during a 6 kms-1 flyby of Comet Wild 2. The returned samples will be investigated at laboratories where the most critical information on these primitive materials is retained. The Jet Propulsion Laboratory will provide project management with Lockheed Martin Astronauts as the spacecraft industrial partner. STARDUST management will aggressively and innovatively achieve cost control through the use of Total Quality Management principles, the chief of which will be organization in a Project Engineering and Integration Team that "flattens" the traditional hierarchical structure by including all project elements from the beginning, in a concurrent engineering framework focusing on evolving Integrated Mission Capability. 相似文献
1000.
This paper proposes a framework for the integrated development of space products. The framework is called ‘total view framework’ because it provides the total set of product, process and organisation elements and their interactions from the outset in the development process. It uses systems engineering (SE) and concurrent engineering (CE) in an integrated manner, as part of the same framework. The framework extends the application of the SE process to life cycle processes and their performing organisations and applies CE at all levels of the hierarchical product breakdown structure. The ‘total view framework’ is supported by a method, called ‘concurrent structured analysis method’, that consists of the three analysis processes: requirements, functional and physical. These processes mirror the bulk of the SE process and are applied concurrently to product, process and organisations. The outputs of the method are requirements, functional attributes, physical attributes and the interactions among them. These outputs are then analysed using a clustering algorithm and a complexity metric based on cohesion and coupling shows the clustering effects. 相似文献