首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2510篇
  免费   2篇
  国内免费   6篇
航空   1247篇
航天技术   991篇
综合类   7篇
航天   273篇
  2021年   13篇
  2019年   14篇
  2018年   40篇
  2017年   34篇
  2016年   25篇
  2015年   11篇
  2014年   50篇
  2013年   60篇
  2012年   50篇
  2011年   87篇
  2010年   62篇
  2009年   106篇
  2008年   149篇
  2007年   62篇
  2006年   46篇
  2005年   65篇
  2004年   75篇
  2003年   98篇
  2002年   51篇
  2001年   110篇
  2000年   45篇
  1999年   86篇
  1998年   85篇
  1997年   62篇
  1996年   63篇
  1995年   88篇
  1994年   97篇
  1993年   37篇
  1992年   59篇
  1991年   22篇
  1990年   28篇
  1989年   56篇
  1988年   20篇
  1987年   35篇
  1986年   19篇
  1985年   74篇
  1984年   42篇
  1983年   46篇
  1982年   55篇
  1981年   77篇
  1980年   26篇
  1979年   24篇
  1978年   22篇
  1977年   18篇
  1976年   15篇
  1975年   18篇
  1974年   12篇
  1972年   17篇
  1969年   13篇
  1966年   8篇
排序方式: 共有2518条查询结果,搜索用时 31 毫秒
981.
The Advanced Thin Ionization Calorimeter (ATIC) Balloon Experiment had a successful test flight and a science flight in 2000–01 and 2002–03 and an unsuccessful launch in 2005–06 from McMurdo, Antarctica, returning 16 and 19 days of flight data. ATIC is designed to measure the spectra of cosmic rays (protons to iron). The instrument is composed of a Silicon matrix detector followed by a carbon target interleaved with scintillator tracking layers and a segmented BGO calorimeter composed of 320 individual crystals totaling 18 radiation lengths to determine the particle energy. BGO (Bismuth Germanate) is an inorganic scintillation crystal and its light output depends not only on the energy deposited by particles but also on the temperature of the crystal. The temperature of balloon instruments during flight is not constant due to sun angle variations as well as differences in albedo from the ground. The change in output for a given energy deposit in the crystals in response to temperature variations was determined.  相似文献   
982.
On January 20, 2005 there was an X 7.1 solar flare at 0636 UT with an accompanied halo coronal mass ejection (CME). The resultant interplanetary shock impacted earth ∼36 h later. Near earth, the Advanced Composition Explorer (ACE) spacecraft observed two impulses with a staircase structure in density and pressure. The estimated earth-arrival times of these impulses were 1713 UT and 1845 UT on January 21, 2005. Three MINIature Spectrometer (MINIS) balloons were aloft on January 21st; one in the northern polar stratosphere and two in the southern polar stratosphere. MeV relativistic electron precipitation (REP) observed by all three balloons is coincident (<3 min) with the impulse arrivals and magnetospheric compression observed by both GOES 10 and 12. Balloon electric field data from the southern hemisphere show no signs of the impulse electric field directly reaching the ionosphere. Enhancement of the balloon-observed convection electric field by as much as 40 mV/m in less than 20 min during this time period is consistent with typical substorm growth. Precipitation-induced ionospheric conductivity enhancements are suggested to be (a) the result of both shock arrival and substorm activity and (b) the cause of rapid (<6 min) decreases in the observed electric field (by as much as 40 mV/m). There is poor agreement between peak cross polar cap potential in the northern hemisphere calculated from Super Dual Auroral Radar Network (SuperDARN) echoes and horizontal electric field at the MINIS balloon locations in the southern hemisphere. Possible reasons for this poor agreement include (a) a true lack of north–south conjugacy between measurement sites, (b) an invalid comparison between global (SuperDARN radar) and local (MINIS balloon) measurements and/or (c) radar absorption resulting from precipitation-induced D-region ionosphere density enhancements.  相似文献   
983.
The Advanced Thin Ionization Calorimeter (ATIC) experiment is designed to investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 1011 to 1014 eV during Long Duration Balloon (LDB) flights from McMurdo, Antarctica. Currently, analysis from the ATIC-1 test flight and ATIC-2 science flight is underway and preparation for a second science flight is in progress. Charge identification of the incident cosmic ray is accomplished, primarily, by a pixilated Silicon Matrix detector located at the very top of the instrument. While it has been shown that the Silicon Matrix detector provides good charge identification even in the presence of electromagnetic shower backscatter from the calorimeter, the detector only measures the charge once. In this paper, we examine use of the top scintillator hodoscope detector to provide a second measure of the cosmic ray charge and, thus, improve the ATIC charge identification.  相似文献   
984.
The Cosmic-Ray Energetics And Mass balloon-borne experiment has been launched twice in Antarctica, first in December 2004 and again in December 2005. It circumnavigated the South Pole three times during the first flight, which set a flight duration record of 42 days. A cumulative duration of 70 days within 13 months was achieved when the second flight completed 28 days during two circumnavigations of the Pole on 13 January 2006. Both the science instrument and support systems functioned extremely well, and a total 117 GB of data including 67 million science events were collected during these two flights. Preliminary analysis indicates that the data extend well above 100 TeV and follow reasonable power laws. The payload recovered from the first flight has been refurbished for the third flight in 2007, whereas the payload from the second flight is being refurbished to be ready for the fourth flight in 2008. Each flight will extend the reach of precise cosmic-ray composition measurements to energies not previously possible.  相似文献   
985.
Gamma-ray spectrometer (GRS) is included in the payload of Chinese first lunar mission Chang’E-1 that will be launched in 2007. Specific objectives of the GRS are to map abundance of O, Si, Fe, Ti, U, Th, K, and perhaps, Mg, Al, and Ca to depths of about 20 cm. There are remarkable advantages for GRS application to remote sensing elemental materials over the entire lunar surface: large effective area and good ability for background rejection. We will describe the design of GRS and present its performance in this paper. Moreover, the GRS calibration will also be introduced.  相似文献   
986.
The finite element algorithm developed by the authors has been used for solving the strength and stability problems of shells. The effect of deformation nonlinearity, stiffness of stringer set, shell thickness on critical loads has been determined.  相似文献   
987.
This paper examines the impact of the external field intensity of white noise on the nonlinear dynamics of square plates under the longitudinal load. It is shown that in some cases, the noise of high intensity is able to reduce the number of frequencies in the oscillation spectrum of the system.  相似文献   
988.
989.
The effects on 17 different structural parameters of mouse small intestine three days after treatment with three types of heavy ion (neon, iron and niobium) are compared, the first two being of particular relevance to space flight. The data for niobium are given in full, showing that changes after niobium ion treatment are not standard and are concentrated in the epithelial compartment, with few of the parameters having a response which is dose dependent. When comparisons are made for the three types of heavy ion, the damage is greatest after neon ion irradiation, implying that the additional non-epithelial damage produced as LET rises from X rays through neutrons to neon ions is not necessarily maintained as LET continues to rise. Further understanding is therefore needed of the balance between changes affecting the vascular and absorptive components of the organ. Variation from group to group is also important, as is variation of strain or gastrointestinal status. All such factors are important in the understanding of changes in multicellular organs after exposure to heavy ion radiation.  相似文献   
990.
This paper presents a perturbation theory for hypersonic flows past pointed-nose slender bodies of revolution at small angles of attack. The theory presents the counter part of other theories on two-dimensional flow, axisymmetric flow, and flow past delta wings, in the case of bodies of revolution. Further restricting the analysis to Newtonian flow, a straightforward perturbation in the angle of attack is applied to the equations obtained and the resulting equations are solved only for circular cones. A striking feature of this approach is the absence of a vortical layer and a uniformally valid solution at body surface and all over the flowfield. In spite of the yaw angle, conical streamlines at cone surface are predicted which bend around towards the leeward plane. Results obtained for the surface pressure and the shock wave of a circular cone compare very well with other approximate calculations and experiment.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号