全文获取类型
收费全文 | 7495篇 |
免费 | 34篇 |
国内免费 | 30篇 |
专业分类
航空 | 3784篇 |
航天技术 | 2629篇 |
综合类 | 27篇 |
航天 | 1119篇 |
出版年
2019年 | 50篇 |
2018年 | 94篇 |
2017年 | 66篇 |
2016年 | 58篇 |
2014年 | 136篇 |
2013年 | 192篇 |
2012年 | 165篇 |
2011年 | 239篇 |
2010年 | 164篇 |
2009年 | 269篇 |
2008年 | 332篇 |
2007年 | 202篇 |
2006年 | 179篇 |
2005年 | 206篇 |
2004年 | 165篇 |
2003年 | 238篇 |
2002年 | 144篇 |
2001年 | 251篇 |
2000年 | 149篇 |
1999年 | 182篇 |
1998年 | 209篇 |
1997年 | 155篇 |
1996年 | 214篇 |
1995年 | 269篇 |
1994年 | 261篇 |
1993年 | 143篇 |
1992年 | 167篇 |
1991年 | 95篇 |
1990年 | 80篇 |
1989年 | 195篇 |
1988年 | 80篇 |
1987年 | 82篇 |
1986年 | 86篇 |
1985年 | 248篇 |
1984年 | 213篇 |
1983年 | 170篇 |
1982年 | 180篇 |
1981年 | 242篇 |
1980年 | 70篇 |
1979年 | 59篇 |
1978年 | 69篇 |
1977年 | 70篇 |
1976年 | 49篇 |
1975年 | 75篇 |
1974年 | 55篇 |
1973年 | 55篇 |
1972年 | 63篇 |
1971年 | 55篇 |
1970年 | 57篇 |
1969年 | 54篇 |
排序方式: 共有7559条查询结果,搜索用时 0 毫秒
241.
242.
D. Abplanalp P. Wurz L. Huber I. Leya E. Kopp U. Rohner M. Wieser L. Kalla S. Barabash 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,44(7):870-878
The Polar Balloon Atmospheric Composition Experiment (P-BACE) is a new generation of neutral gas mass spectrometer based on the time-of-flight principle. P-BACE is the scientific experiment on the Mars Environment Analog Platform (MEAP) flown successfully on a balloon mission in summer 2008. The MEAP mission was flown with a 334,000 m3 helium balloon in the stratosphere on a semicircular trajectory from northern Sweden around the North Pole to Canada using the summer northern hemispheric wind current. The atmospheric conditions at an atmospheric altitude of 35–40 km are remarkably similar to those on the surface of Mars and thus the balloon mission was an ideal testbed for our mass spectrometer P-BACE. Originally this instrument was designed for in situ measurements of the chemical composition of the Martian atmosphere.P-BACE has a unique mass range from 0 to 1000 amu/q with a mass resolution m/Δm (FWHM) > 1000, and the dynamic range is at least six orders of magnitude. During this experiment, the acquisition of one mass spectrum is a sum of 65,535 single spectra, recorded in a time frame of 66 s.The balloon mission lasted 5 days and had successfully demonstrated the functionality of the P-BACE instrument during flight conditions. We had recorded more than 4500 mass spectra. With little modifications, P-BACE can be used on a planetary mission for Mars, but for example also for Venus or Mercury, if placed on a satellite. 相似文献
243.
We propose in this paper a method to analyse the efficiency of the direction pointed by an infrared sensor dedicated to forest fire detection on board of a space vehicle. The objective is to use these sensors to detect forest fires on a defined territory with a specified probability. One way to verify that the system stands this specification is to test each possible configuration (pointing direction of the sensor and number of space vehicles) and estimate the corresponding probability of forest fire detection. However, when the coverage territory is wide or when the number of vehicles is important, it is hardly possible to simulate every configuration in a reasonable amount of time. We propose to use kriging method for the prediction of forest fire detection probability for all possible configurations. 相似文献
244.
A typical approach and landing operation is described. The microwave landing system (MLS) is then examined, its design characteristics and how it works are shown, and how the MLS design fulfils the user's operational requirements by protecting the guidance signal from reflected signal interference is highlighted. MLS angle system accuracy is discussed in great detail, and its reliability, integrity, and coverage volume are briefly considered. MLS availability at any runway to all aircraft types and their landing scenarios, which is accomplished using narrow scanning beam antennas, is examined 相似文献
245.
J T Lett A B Cox M D Story 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):99-104
Theories of cellular radiation sensitivity that preclude a significant role for cellular repair processes in the final biological expression of cellular damage induced by ionizing radiation are unsound. Experiments are discussed here in which the cell-cycle dependency of the repair deficiency of the S/S variant, of the L5178Y murine leukemic lymphoblast was examined by treatment with the heavy ions, 20Ne, 28Si, 40Ar, 56Fe and 93Nb. Evidence from those studies, which will be described in detail elsewhere, provide support for the notion that as the linear energy transfer (LET infinity) of the incident radiation increases the ability of the S/S cell to repair radiation damage decreases until effectively it is eliminated around 500 keV/micrometer. In the region of the latter LET infinity value, the behavior of the S/S cell approximates the ideal case of target theory where post-irradiation metabolism (repair) does not influence cell survival. The expression of this phenomenon among different cell types and tissues will depend upon the actual repair systems involved and other considerations. 相似文献
246.
In this paper, a process of flanging to create thin-walled axisymmetrical shells with the shape of truncated cone is analyzed. Also presented are some dependences that make it possible to determine the relative depth of a formed piece at the given piece-blank thickness ratio. 相似文献
247.
E. V. Kasumov 《Russian Aeronautics (Iz VUZ)》2013,56(3):224-228
A possibility of evaluating dynamic response of a mechanical system to controlling actions of the automatic stabilization and control system is considered on the basis of a numerical experiment. Examples of design analysis are presented for a light-weight helicopter in which an autopilot is part of the control system. The finite element analysis is used in this paper. 相似文献
248.
Ch. I. Chaban R. T. Ripetskyj E. L. Kordyum N. A. Kit 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(12):2011-2016
Under gravistimulation, dark-grown protonemata of Pottia intermedia revealed negative gravitropism with a growth rate of approximately 28 μm·h−1 at room temperature (20 °C). In 7 days, the protonema formed a bundle of vertically oriented filaments. At an elevated temperature (30 °C), bundles of vertically growing filaments were also formed. However, both filament growth rate and amplitude of the gravicurvature were reduced. Red light (RL) irradiation induced a positive phototropism of most apical protonemal cells at 20 °C. In a following period of darkness, approximately two-thirds of such cells began to grow upward again, recovering their negative gravitropism. RL irradiation at the elevated temperature caused a partial increase in the number of protonemal cells with negative phototropism, but the protonemata did not exhibit negative gravitropism after transfer to darkness. The negative gravitropic reaction was renewed only when protonemata were placed at 20 °C. A dramatic decrease in starch amount in protonemal apical cells, which are sensitive to both gravity and light, occurred at the higher temperature. Such a decrease may be one of the reasons for the inhibition of the protonemal gravireaction at the higher temperature. The observation has a bearing on the starch-statolith theory. 相似文献
249.
N S Pechurkin A V Brilkov V V Ganusov T V Kargatova E E Maksimova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(3):335-341
The possibility of introducing genetically engineered microorganisms (GEM) into simple biotic cycles of laboratory water microcosms was investigated. The survival of the recombinant strain Escherichia coli Z905 (Apr, Lux+) in microcosms depends on the type of model ecosystems. During the absence of algae blooming in the model ecosystem, the part of plasmid-containing cells E. coli decreased fast, and the structure of the plasmid was also modified. In conditions of algae blooming (Ankistrodesmus sp.) an almost total maintenance of plasmid-containing cells was observed in E. coli population. A mathematics model of GEM's behavior in water ecosystems with different level of complexity has been formulated. Mechanisms causing the difference in luminescent exhibition of different species are discussed, and attempts are made to forecast the GEM's behavior in water ecosystems. 相似文献
250.
A. N. Kusyumov E. V. Romanova A. S. Batrakov R. R. Nurmukhametov G. N. Barakos 《Russian Aeronautics (Iz VUZ)》2012,55(3):263-268
We consider a problem of a stationary incompressible viscous fluid flow around a flat circular cylinder. In the vicinity of the critical Reynolds number Re cr a stepwise drop of the cylinder drag takes place, which is called the drag crisis. 相似文献