全文获取类型
收费全文 | 4521篇 |
免费 | 5篇 |
国内免费 | 21篇 |
专业分类
航空 | 2319篇 |
航天技术 | 1689篇 |
综合类 | 21篇 |
航天 | 518篇 |
出版年
2018年 | 54篇 |
2017年 | 36篇 |
2014年 | 64篇 |
2013年 | 99篇 |
2012年 | 75篇 |
2011年 | 125篇 |
2010年 | 91篇 |
2009年 | 151篇 |
2008年 | 242篇 |
2007年 | 91篇 |
2006年 | 98篇 |
2005年 | 107篇 |
2004年 | 130篇 |
2003年 | 147篇 |
2002年 | 83篇 |
2001年 | 114篇 |
2000年 | 90篇 |
1999年 | 87篇 |
1998年 | 138篇 |
1997年 | 91篇 |
1996年 | 117篇 |
1995年 | 131篇 |
1994年 | 151篇 |
1993年 | 86篇 |
1992年 | 121篇 |
1991年 | 56篇 |
1990年 | 56篇 |
1989年 | 133篇 |
1988年 | 47篇 |
1987年 | 55篇 |
1986年 | 73篇 |
1985年 | 172篇 |
1984年 | 115篇 |
1983年 | 106篇 |
1982年 | 111篇 |
1981年 | 155篇 |
1980年 | 66篇 |
1979年 | 47篇 |
1978年 | 44篇 |
1977年 | 41篇 |
1975年 | 53篇 |
1974年 | 39篇 |
1973年 | 46篇 |
1972年 | 40篇 |
1971年 | 43篇 |
1970年 | 38篇 |
1969年 | 45篇 |
1968年 | 30篇 |
1967年 | 30篇 |
1966年 | 30篇 |
排序方式: 共有4547条查询结果,搜索用时 78 毫秒
791.
W. I. Axford 《Space Science Reviews》1968,8(3):331-365
Observations bearing on the nature and properties of the interplanetary plasma are reviewed, and consideration is given to possible fruitful directions for further work. The observations are classified according as they involve traditional (comet tail, optical, geomagnetic, cosmic ray), radio (solar noise, radar, radio-source scattering and scintillation, space-probe transmission) or direct (space-probe) measurements. A fairly complete set of references up to September 1967 is given for the cases of comet tail, radar, radio-source scattering and scintillation, and space-probe measurements.An important development concerns observations of the composition of the solar wind. High-resolution measurements of the positive ion energy per charge spectra have been made using the Vela-3 satellites (Bame
et al., 1968). Ionic components other than H+ and He++ have been detected, notably the various ions of oxygen, O+5, O+6, O+7, (Hundhausen
et al., 1968). A promising technique for unambiguously distinguishing H+ and He++ ions, based on velocity as well as energy per unit charge, has been flown successfully on the satellite IMP-F by Ogilvie and Williamson (1968).This research was supported by the Advanced Research Projects Agency (Project DEFENDER) and was monitored by the U.S. Army Research Office — Durham under Contract DA-31-124-ARO-D-257. 相似文献
792.
The current status of the theoretical methods for producing the relevant atomic data is surveyed.Proceedings of the Conference Solar Physics from Space, held at at the Swiss Federal Institute of Technology Zurich (ETHZ), 11–14 November 1980. 相似文献
793.
794.
The Goddard Experiment Package will measure the ultraviolet spectral emittance of stars and nebulae. It has a spectral resolution of 2 ? in the 1050-? to 4000-? band. The telescope has a 38-inch clear aperture and automatically reduces the spectral data to digital form. Guidance accuracy is 1 of second arc. 相似文献
795.
Active control of a thin, deformable mirror is one approach to obtaining diffraction-limited performance from large orbiting telescopes. The control system design requires knowledge of the mirror reaction to the multiple forces used to maintain the desired mirror figure. A structural analysis program is used to obtain estimates of the static deflections of a point-loaded, thin, shallow, spherical primary mirror. The calculated deflections are compared to experimentally measured deflections for a specific configuration. 相似文献
796.
M. H. Rees 《Space Science Reviews》1969,10(3):413-441
Satellite and rocket measurements of auroral electrons (which have been made since Brown's (1966) and Pfister's (1967) papers have appeared) are reviewed, and the salient characteristics of auroral electrons which emerge from all types of measurements are summarized. Effects of the atmosphere on the energy distribution of electron fluxes are discussed. Ionization rates associated with typical fluxes are derived. Observable effects produced in the atmosphere and the fate of auroral electrons are briefly described.This paper does not discuss the role of auroral protons (or particles). A recent review on the subject has been given by Eather (1967). 相似文献
797.
The paper presents a method by which the zeros of the polynomial representing a Huffman (impulse-equivalent) pulse sequence can be chosen so as to exert a degree of control on the form of the energy distribution of the signal in the time-frequency plane. This makes it possible to design Huffman pulse sequences which are suitable for use as radar or sonar signals in situations where significant target velocity occurs. 相似文献
798.
H Follmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(11):33-38
Unlike ribose chemistry, the chemistry of 2-deoxyribose precludes its formation or at least its incorporation into nucleotides under accepted "primordial soup" conditions; therefore RNA and DNA could not develop in parallel during the evolution of protocells. However, deoxyribonucleotides might have been formed abiotically by direct reduction of ribonucleotides in a primitive version of the biochemical pathway. This sequence of events, in which DNA lagged behind RNA in the assembly of genetic information for an unknown--probably short--period of time is suggested by the primitive traits (i.e., nucleotide binding, thiol redox chemistry, and metal ion catalysis) of present-day enzyme systems of deoxyribonucleotide biosynthesis. The reaction should be amenable to experimental study. 相似文献
799.
Henderson IW 《Journal of the British Interplanetary Society》1989,42(7):363-366
Under conditions of microgravity severe alterations in body fluid composition and volume take place largely as a result of "cardiothoracic pooling" or headward shift of blood. Inappropriate endocrine, renal and cardiovascular responses result from the "misreading" of homeostatic signals by physiological receptors to produce an as yet incompletely defined syndrome under microgravitational conditions. 相似文献
800.
Kirkpatrick AW Nicolaou S Rowan K Liu D Cunningham J Sargsyan AE Hamilton D Dulchavsky SA 《Acta Astronautica》2005,56(9-12):831-838
The recent interest in the use of ultrasound (US) to detect pneumothoraces after acute trauma in North America was initially driven by an operational space medicine concern. Astronauts aboard the International Space Station (ISS) are at risk for pneumothoraces, and US is the only potential medical imaging available. Pneumothoraces are common following trauma, and are a preventable cause of death, as most are treatable with relatively simple interventions. While pneumothoraces are optimally diagnosed clinically, they are more often inapparent even on supine chest radiographs (CXR) with recent series reporting a greater than 50% rate of occult pneumothoraces. In the course of basic scientific investigations in a conventional and parabolic flight laboratory, investigators familiarized themselves with the sonographic features of both pneumothoraces and normal pulmonary ventilation. By examining the visceral–parietal pleural interface (VPPI) with US, investigators became confident in diagnosing pneumothoraces. This knowledge was subsequently translated into practice at an American and a Canadian trauma center. The sonographic examination was found to be more accurate and sensitive than CXR (US 96% and 100% versus US 74% and 36%) in specific circumstances. Initial studies have also suggested that detecting the US features of pleural pulmonary ventilation in the left lung field may offer the ability to exclude serious endotracheal tube malpositions such as right mainstem and esophageal intubations. Applied thoracic US is an example of a clinically useful space medicine spin-off that is improving health care on earth. 相似文献