全文获取类型
收费全文 | 2521篇 |
免费 | 7篇 |
国内免费 | 7篇 |
专业分类
航空 | 1237篇 |
航天技术 | 1006篇 |
综合类 | 5篇 |
航天 | 287篇 |
出版年
2021年 | 14篇 |
2019年 | 14篇 |
2018年 | 43篇 |
2017年 | 34篇 |
2016年 | 25篇 |
2015年 | 11篇 |
2014年 | 51篇 |
2013年 | 64篇 |
2012年 | 51篇 |
2011年 | 89篇 |
2010年 | 62篇 |
2009年 | 108篇 |
2008年 | 152篇 |
2007年 | 63篇 |
2006年 | 47篇 |
2005年 | 64篇 |
2004年 | 73篇 |
2003年 | 92篇 |
2002年 | 46篇 |
2001年 | 102篇 |
2000年 | 45篇 |
1999年 | 86篇 |
1998年 | 86篇 |
1997年 | 62篇 |
1996年 | 65篇 |
1995年 | 88篇 |
1994年 | 97篇 |
1993年 | 37篇 |
1992年 | 60篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 57篇 |
1988年 | 20篇 |
1987年 | 36篇 |
1986年 | 22篇 |
1985年 | 77篇 |
1984年 | 42篇 |
1983年 | 48篇 |
1982年 | 55篇 |
1981年 | 77篇 |
1980年 | 27篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 18篇 |
1974年 | 12篇 |
1972年 | 17篇 |
1969年 | 13篇 |
1966年 | 9篇 |
排序方式: 共有2535条查询结果,搜索用时 15 毫秒
231.
K Eguchi-Kasai M Murakami H Itsukaichi K Fukutsu F Yatagai T Kanai H Ohara K Sato 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(4):543-549
It has been suggested that it is not simple double-strand breaks (dsb) but the non-reparable breaks which correlate well with the high biological effectiveness of high LET radiations for cell killing (Kelland et al., 1988; Radford, 1986). We have compared the effects of charged particles on cell death in 3 pairs of cell lines which are normal or defective in the repair of DNA dsbs. For the cell lines SL3-147, M10, and SX10 which are deficient in DNA dsb repair, RBE values were close to unity for cell killing induced by charged particles with linear energy transfer (LET) up to 200 keV/micrometer and were even smaller than unity for the LET region greater than 300 keV/micrometer. The inactivation cross section (ICS) increased with LET for all 3 pairs. The ICS of dsb repair deficient mutants was always larger than that of their parents for all the LET ranges, but with increasing LET the difference in ICS between the mutant and its parent became smaller. Since a small difference in ICS remained at LET of about 300 keV/micrometer, dsb repair may still take place at this high LET, even if its role is apparently small. These results suggest that the DNA repair system does not play a major role in protection against the attack of high LET radiations and that a main muse of cell death is non-reparable dsb which are produced at a higher yield compared with low LET radiations. No correlation was observed between DNA content or nuclear area and ICS. 相似文献
232.
Clinorotation reduces number, but not size, of cartilaginous nodules formed in micromass cultures of mouse limbbud cells. 总被引:1,自引:0,他引:1
P J Duke D Montufar-Solis T Hamazaki A Sato 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1065-1072
In previous studies we used a ground based model to investigate the cellular responses to microgravity by exposing micromass cultures of embryonic limb cells to simulated weightlessness on a clinostat. Cultures set up in T-flasks and rotated at 30 rpm showed that clinostatted cultures had less chondrocyte differentiation than stationary or rotation controls, as assessed by number of nodules/culture stained with cartilage specific Alcian blue. In the current study, nodule size and shape of these nodules was assessed by interactive measurement of area, perimeter, circularity, and equivalent diameters, using the Optimas imaging software. Results show no significant difference in any of the measurements, indicating that clinorotation has no effect on expansion of the nodules either by differentiation of cells within the nodule, or by recruitment of cells into the nodule. The reduction in number of nodules without an alteration in size and shape indicates that the effect of simulated microgravity is to reduce the cell interactions required for the initial condensation of cells into a nodule, probably by interference with cell adhesion molecules. 相似文献
233.
H.J. Völk E.G. Berezhko L.T. Ksenofontov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):473-476
For the case of Tycho’s supernova remnant (SNR), we present the relation between the blast wave and contact discontinuity radii calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is very close to the shock radius. Therefore a consistent explanation of these observations can be given in terms of efficient CR acceleration which makes the medium more compressible. 相似文献
234.
C.-F. Shih T.H. Vonder Haar G.G. Campbell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(6):197-201
The extraordinary El-Nino event of 1982–83 started to fade out in the late spring of 1983. However the sea surface temperature of the Eastern Equatorial Pacific still remained warmer than normal in the following summer. To investigate the characteristics of this late transition phase of the 1982–83 El-Nino, the GOES-West satellite data of July and August of 1983 are analyzed. The outgoing longwave radiation field and the distribution of cloudiness, which was derived by using a new threshold technique, are obtained. The longwave radiation field is compared to monthly average climatic indices commonly used at the Climatic Analysis Center. The results of cloud analysis showed some interesting features during the decaying phase of the 1982–83 El-Nino. The diurnal variation of cloudiness indicates that total cloud amounts decrease from 8 GMT to 20 GMT over most of the area. This overall study demonstrates preliminary results of the International Satellite Cloud Climatology Project of the World Climate Research Program. 相似文献
235.
T W Tibbitts S M Bennett R C Morrow R J Bula 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(8):53-59
Potatoes (Solanum tuberosum) have a strong potential as a useful crop species in a functioning CELSS. The cultivar Denali has produced 37.5 g m-2 d-1 when grown for 132 days with the first 40 days under a 12-h photoperiod and a light:dark temperature cycle of 20 degrees C:16 degrees C, and then 92 days under continuous irradiance and a temperature of 16 degrees C. Irradiance was at 725 micromoles m-2 s-1 PPF and carbon dioxide at 1000 micromoles mol-1. The dried tubers had 82% carbohydrates, 9% protein and 0.6% fat. Other studies have shown that carbon dioxide supplementation (1000 micromoles mol-1) is of significant benefit under 12-h irradiance but less benefit under 24 h irradiance. Irradiance cycles of 60 minutes light and 30 minutes dark caused a reduction of more than 50% in tuber weight compared to cycles of 16 h light and 8 h dark. A diurnal temperature change of 22 degrees C for the 12-h light period to 14 degrees C during the 12-h dark period gave increased yields of 30% and 10% for two separate cultivars, compared with plants grown under a constant 18 degrees C temperature. Cultivar screening under continuous irradiance and elevated temperatures (28 degrees C) for 8 weeks of growth indicated that the cvs Haig, Denali, Atlantic, Desiree and Rutt had the best potential for tolerance to these conditions. Harvesting of tubers from plants at weekly intervals, beginning at 8 weeks after planting, did not increase yield over a single final harvest. Spacing of plants on 0.055 centers produced greater yield per m2 than spacing at 0.11 or 0.22 m2. Plants maintained 0.33 meters apart (0.111 m2 per plant) in beds produced the same yields when separated by dividers in the root matrix as when no separation was made. 相似文献
236.
N. Kolachevsky A. Matveev J. Alnis C. G. Parthey T. Steinmetz T. Wilken R. Holzwarth T. Udem T. W. Hänsch 《Space Science Reviews》2009,148(1-4):267-288
In this review we discuss the progress of the past decade in testing for a possible temporal variation of the fine structure constant α. Advances in atomic sample preparation, laser spectroscopy and optical frequency measurements led to rapid reduction of measurement uncertainties. Eventually laboratory tests became the most sensitive tool to detect a possible variation of α at the present epoch. We explain the methods and technologies that helped to make this possible. 相似文献
237.
T.P. Dachev B. Tomov Yu. Matviichuk Pl. Dimitrov N. Bankov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The paper presents observation of relativistic electrons. Data are collected by the Radiation Risk Radiometer-Dosimeters (R3D) B2/B3 modifications during the flights of Foton M2/M3 satellites in 2005 and 2007 as well as by the R3DE instrument at the European Technology Exposure Facility (EuTEF) on the Columbus External Payload Adaptor at the International Space Station (ISS) in the period February 20 – April 28, 2008. On the Foton M2/M3 satellites relativistic electrons are observed more frequently than on the ISS because of higher (62.8°) inclination of the orbit. At both Foton satellites the usual duration of the observations are a few minutes long. On the ISS the duration usually is about 1 min or less. The places of observations of high doses due to relativistic electrons are distributed mainly at latitudes above 50° geographic latitude in both hemispheres on Foton M2/M3 satellites. A very high maximum is found in the southern hemisphere at longitudinal range 0°–60°E. At the ISS the maximums are observed between 45° and 52° geographic latitude in both hemispheres mainly at longitudes equatorward from the magnetic poles. The measured absolute maximums of dose rates generated by relativistic electrons are found to be as follows: 304 μGy h−1 behind 1.75 g cm−2 shielding at Foton M2, 2314 μGy h−1 behind 0.71 g cm−2 shielding at Foton M3 and 19,195 μGy h−1 (Flux is 8363 cm−2 s−1) behind les than 0.4 g cm−2 shielding at ISS. 相似文献
238.
Lehman D. Clark K. Cook B. Gavit S. Kayali S. McKinney J. Milkovich D. Reh K. Taylor R. Casani J. Griebel T. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(3):12-21
Congress authorized NASA's Prometheus Project in February 2003, with the first Prometheus mission slated to explore the icy moons of Jupiter. The project had two major objectives: 1) to develop a nuclear reactor that would provide unprecedented levels of power and show that it could be processed safely and operated reliably in space for long-duration, deep-space exploration; and 2) to explore the three icy moons of Jupiter - Callisto, Ganymede, and Europa - and return science data that would meet the scientific goals as set forth in the Decadal Survey Report of the National Academy of Sciences. Early in project planning, it was determined that the development of the Prometheus nuclear-powered spaceship would be complex and require the intellectual knowledge residing at numerous organizations across the country. In addition, because of the complex nature of the project and the multiple partners, approaches beyond those successfully used to manage a typical JPL project would be needed. This describes the key experiences in managing Prometheus, which should prove useful for future projects of similar scope and magnitude. 相似文献
239.
Kuroki F. Wagatsuma Y. Yoneyama T. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(7):42-45
An FM-CW radar front-end was fabricated in an integrated manner at 60 GHz by using the NRD guide. The main emphasis was placed on compactness in size and high-precise operation in performance. The fabricated radar consists of an FM Gunn oscillator, a balanced mixer, and a planar antenna fed by a leaky NRD guide with a mechanically beam-scanning performance. All circuit components and the antenna were contained in a compact housing of 170 x 140 mm in area and 25 mm in thickness, and thus, a thin type of millimeter-wave radar front-end was successfully developed. Moreover, an error of distance estimation was measured to be less than a distance of 0.7 m. 相似文献
240.
S. Suresh S. N. Omkar V. Mani T. N. Guru Prakash 《Aerospace Science and Technology》2003,7(8):2114-602
In this paper, identification of dynamic stall effect of rotor blade is considered. Recurrent Neural Networks have the ability to identify the nonlinear dynamical systems from training data. This paper describes the use of recurrent neural networks for predicting the coefficient of lift (CZ) at high angle of attack. In our approach, the coefficient of lift (CZ) obtained from the experimental results (wind tunnel data) at different mean angle of attack θmean is used to train the recurrent neural network. Then the recurrent neural network prediction is compared with experimental ONERA OA212 airfoil data. The time and space complexity required to predict CZ in the proposed method is less and it is easy to incorporate in any commercially available rotor code. 相似文献