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   3341篇
  免费   17篇
  国内免费   19篇
航空   1752篇
航天技术   1140篇
综合类   18篇
航天   467篇
  2019年   19篇
  2018年   40篇
  2017年   19篇
  2016年   23篇
  2014年   67篇
  2013年   84篇
  2012年   69篇
  2011年   122篇
  2010年   91篇
  2009年   118篇
  2008年   184篇
  2007年   94篇
  2006年   65篇
  2005年   81篇
  2004年   83篇
  2003年   110篇
  2002年   68篇
  2001年   116篇
  2000年   54篇
  1999年   88篇
  1998年   97篇
  1997年   74篇
  1996年   94篇
  1995年   125篇
  1994年   101篇
  1993年   67篇
  1992年   104篇
  1991年   42篇
  1990年   37篇
  1989年   88篇
  1988年   34篇
  1987年   31篇
  1986年   32篇
  1985年   91篇
  1984年   96篇
  1983年   63篇
  1982年   85篇
  1981年   97篇
  1980年   34篇
  1979年   42篇
  1978年   33篇
  1977年   22篇
  1976年   22篇
  1975年   40篇
  1974年   25篇
  1973年   18篇
  1972年   29篇
  1970年   17篇
  1969年   17篇
  1967年   20篇
排序方式: 共有3377条查询结果,搜索用时 62 毫秒
941.
The subsolar ionopause of Venus is expected to be stable to both the Kelvin-Helmholtz and flute instabilities. However, magnetic profiles obtained in the subsolar region indicate that the surface of the ionopause contains large amplitude corrugations, perhaps incipient flux ropes. A possible mechanism for destabilizing the boundary is suggested by the observation that the ion density does not drop abruptly at the ionopause but continues to decrease smoothly into the magnetosheath.  相似文献   
942.
Comet organics are traced to their origin in interstellar space. Possible sources of comet organics from solar nebula chemistry are briefly discussed. The infrared spectra of interstellar dust are compared with spectra of solar (space) irradiated laboratory organic residues and with meteorites. The spectra compare very favorably. The atomic composition of first generation laboratory organic residues compares favorably with that of comet Halley organics if divided into appropriate "volatile" (less refractory) and "refractory" (more refractory) complex organics.  相似文献   
943.
The preliminary results from optical search for light pulses associated with gamma ray bursts by means of the Czechoslovak Fireball Network plate collection at the Ondřejov observatory are given. Optical monitoring represents more than 7700 hours, but no real optical counterpart was found. Problems associated with the optical search for gamma ray bursts are discussed.  相似文献   
944.
Biological effects of heavy ions in Arabidopsis seeds.   总被引:1,自引:0,他引:1  
Irradiation of dry seeds of Arabidopsis with heavy ions (HZE-particles) produced by UNILAC-accelerator (GSI, Darmstadt) yielded aberrations in varied developmental endpoints such as survival rate and embryo vitality. The damage increased with particle density and charge. Cross sections in the range of 0.2-1.0 micrometer2 for Ne and Ar and 2.0-10.0 micrometers2 for Xe were estimated. Soaked seeds were more sensitive than dry seeds (cross-section 2.0-10.0 micrometers2 for Ar). The induced total damage in the irradiated seeds was estimated adding the different damages weighted by certain factors. These results will be used as base data for the interpretation and evaluation of spaceflight experiments on the biological effects of cosmic radiation.  相似文献   
945.
The charged particle spectrum for nuclei from protons to neon, (charge Z=10) was observed during the cruise phase and orbit around Mars by the MARIE charged particle spectrometer on the Odyssey spacecraft. The cruise data were taken between April 23, 2001 and mid-August 2001. The Mars orbit data were taken March 5, 2002 through May 2002 and are scheduled to continue until August 2004. Charge peaks are clearly separated for charges up to Z=10. Especially prominent are the carbon and oxygen peaks, with boron and nitrogen also clearly visible. Although heavy ions are much less abundant than protons in the cosmic ray environment, it is important to determine their abundances because their ionization energy losses (proportional to Z2) are far more dangerous to humans and to instruments. Thus the higher charged nuclei make a significant contribution to dose and dose equivalent received in space. Results of the charged particle spectrum measurements will be reported.  相似文献   
946.
The CELSS Test Facility (CTF) is a device for measuring crop plant productivity in the micro-gravity environment of Space Station Freedom. It will allow us to address questions of crop productivity in space, versus that on the ground. The crop productivity factors that will be measured are rates of: 1) biomass production, 2) food production, 3) O2 and CO2 exchange, and 4) water transpiration. In addition, other productivity factors of specific crops will be determined, such as : 1) the ratio of edible to inedible biomass (harvest index), 2) leaf area exposed to and collecting light (leaf area index), 3) ratio of root mass to total biomass, and 4) photosynthetic efficiency (ratio of moles of CO2 fixed (or O2 produced), per mole of photons of specific energies used). Plant and crop morphology, at several levels, ranging from the community to the sub-cellular, will also be evaluated.  相似文献   
947.
针对传统静态自由网平差进行自主定轨存在的秩亏问题,提出一种卫星动力学短弧段定轨和自由网伪逆平差理论相结合的自主定轨算法。该算法以导航星座星间链路(ISL)双向测距为基础,利用伪逆平差法,解决整网位置解算起算数据不足带来的秩亏问题;同时,利用轨道动力学建立不同历元之间状态转移关系,解决单历元平差无法对速度分量进行有效估计的问题。仿真结果表明,自主运行90天,平均用户测距精度(URE)小于1 m(2σ),优于导航星座自主运行指标要求,验证了本文算法的有效性。  相似文献   
948.
Camprubí  E.  de Leeuw  J. W.  House  C. H.  Raulin  F.  Russell  M. J.  Spang  A.  Tirumalai  M. R.  Westall  F. 《Space Science Reviews》2019,215(8):1-35

The Rosetta observations have greatly advanced our knowledge of the cometary nucleus and its immediate environment. However, constraints on the mission (both planned and unplanned), the only partially successful Philae lander, and other instrumental issues have inevitably resulted in open questions. Surprising results from the many successful Rosetta observations have also opened new questions, unimagined when Rosetta was first planned. We discuss these and introduce several mission concepts that might address these issues. It is apparent that a sample return mission as originally conceived in the 1980s during the genesis of Rosetta would provide many answers but it is arguable whether it is technically feasible even with today’s technology and knowledge. Less ambitious mission concepts are described to address the suggested main outstanding scientific goals.

  相似文献   
949.
Loto’aniu  T. M.  Redmon  R. J.  Califf  S.  Singer  H. J.  Rowland  W.  Macintyre  S.  Chastain  C.  Dence  R.  Bailey  R.  Shoemaker  E.  Rich  F. J.  Chu  D.  Early  D.  Kronenwetter  J.  Todirita  M. 《Space Science Reviews》2019,215(4):1-25
Space Science Reviews - The Modular Multispectral Imaging Array (MMIA) is a suite of optical sensors mounted on an external platform of the European Space Agency’s Columbus Module on the...  相似文献   
950.
The Juno Radiation Monitoring (RM) Investigation   总被引:1,自引:0,他引:1  
The Radiation Monitoring Investigation of the Juno Mission will actively retrieve and analyze the noise signatures from penetrating radiation in the images of Juno’s star cameras and science instruments at Jupiter. The investigation’s objective is to profile Jupiter’s \(>10\mbox{-MeV}\) electron environment in regions of the Jovian magnetosphere which today are still largely unexplored. This paper discusses the primary instruments on Juno which contribute to the investigation’s data suite, the measurements of camera noise from penetrating particles, spectral sensitivities and measurement ranges of the instruments, calibrations performed prior to Juno’s first science orbit, and how the measurements may be used to infer the external relativistic electron environment.  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