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   61578篇
  免费   688篇
  国内免费   419篇
测绘学   1353篇
大气科学   3765篇
地球物理   12142篇
地质学   22221篇
海洋学   5472篇
天文学   14756篇
综合类   132篇
自然地理   2844篇
  2022年   424篇
  2021年   719篇
  2020年   723篇
  2019年   794篇
  2018年   1740篇
  2017年   1615篇
  2016年   1829篇
  2015年   931篇
  2014年   1708篇
  2013年   3158篇
  2012年   1967篇
  2011年   2536篇
  2010年   2311篇
  2009年   3059篇
  2008年   2574篇
  2007年   2718篇
  2006年   2476篇
  2005年   1707篇
  2004年   1653篇
  2003年   1588篇
  2002年   1563篇
  2001年   1404篇
  2000年   1279篇
  1999年   1089篇
  1998年   1104篇
  1997年   1065篇
  1996年   897篇
  1995年   905篇
  1994年   816篇
  1993年   690篇
  1992年   671篇
  1991年   661篇
  1990年   740篇
  1989年   649篇
  1988年   591篇
  1987年   739篇
  1986年   626篇
  1985年   783篇
  1984年   857篇
  1983年   826篇
  1982年   738篇
  1981年   745篇
  1980年   636篇
  1979年   631篇
  1978年   613篇
  1977年   547篇
  1976年   533篇
  1975年   526篇
  1974年   503篇
  1973年   566篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Using the method of solar bidimensional spectroscopy based on the Universal Birefringent Filter (UBF), we have determined the bidimensional maps of moments of some chromospheric lines. The observational material, referring to a quiet region on the disk center, have been acquired with the UBF of the NSO at Sacramento Peak on Aug. 27,1985. In this note we present the work in progress and the new observational aspects arising from this diagnostic method.Visiting astronomers at the National Solar Observatory/Sacramento Peak, operated by the AURA under contract with the NSF  相似文献   
972.
973.
The equivalent width calculations for the fundamental vibration rotation band lines of HeH+ have been carried out for a non-DA white dwarf model with an effective temperature of 12 000 K. BothP andR branch lines with rotational quantum numbersJ=3 to 18 were included in the calculations. A search for these lines in helium rich white dwarfs is suggested.  相似文献   
974.
In memoriam     
  相似文献   
975.
The light curved in the CM field   总被引:1,自引:0,他引:1  
In this paper we introduce the CM field in Sections 2 and 3 based on the paper by Wang and Peng (1985), and calculate the light curved in the CM field in Section 4. The result shows thatP makes CM larger than C at , and smaller at . Under a special circumstance which source, CM lens, and observer are in the same line, if we get | 0=0 , and | =/2 , we can determine theP(M) andQ(M) of the CM lens,M is the mass of the CM lens.  相似文献   
976.
Results from a detailed isophotometric survey of NGC 5595, NGC 5597, NGC 5605, and NGC 7769 are given. It includes isophotic maps, luminosity profiles and ellipticity curves as well. Scanning of these galaxies was done in theB andV colours.  相似文献   
977.
The mean latitude of prominence samples referring to one boundary of the polarity division line of the large-scale magnetic field is calculated on the basis of H charts in the period 1955–1982. It is shown that the magnetic field in that period had a latitude zonal structure. The boundaries of the latitude zones of the magnetic field had no regular equatorwards migration. They either oscillated near the mean boundaries at 0°, ±20°, ±40°, or migrated polewards.  相似文献   
978.
G. Paubert  D. Gautier  R. Courtin 《Icarus》1984,60(3):599-612
The flux emitted by Titan's disk in millimeter lines of HCN, HC3N, CH3CN, and CO is calculated by means of a radiative transfer formulation which takes into account the sphericity of the atmosphere. It is demonstrated that the plane-parallel approximation for radiative transfer is no longer valid, especially in the core of emission lines, when Titan is not spatially resolved. The antenna temperatures which would be measured by large radiotelescopes observing Titan at frequencies of (1?0) and (2?1) transitions of CO, of (1?0), (2?1), and (3?2) transitions of HCN, and of selected transitions of HC3N and CH3CN in the range 80–300 GHz are calculated. The observability of these transitions is investigated. It is concluded that there is the possibility of inferring the vertical stratospheric distribution of these species from line shape measurements to be achieved with existing or forthcoming radioastronomical instrumentation. The determination of the CO abundance by D. O. Muhleman, G. L. Berge, and R. T. Clancy (1984, (Science (Washington, D.C.), 223, 393–396) from measurements at 115.3 GHz in two 200 MHz bands, is reinterpreted by means of this radiative transfer formulation. A CO mixing ratio between 3 × 10?5 and 18 × 10?5, with a most plausible value of 7.5 × 10?5, is found.  相似文献   
979.
In this paper we offer a model for the Earth's ionosphere and plasmasphere, allowing for the inertia and anisotropic energy distribution of thermal plasma. A procedure for simultaneous solution of equations of continuity and motion for the O+ and H+ ions, subject to inertia terms, is described. The model also includes transfer equations for longitudinal and transversal thermal energies. The system of simulating equations and the kinetic equation for superthermal electron spectra are concordantly solved along geomagnetic field lines. Within the framework of the model we developed a study is made of the dynamics of filling of the evacuated plasmaspheric reservoir after a magnetospheric disturbance. It is shown that the filling of the tubes offorce with L ? 3.5 proceeds with supersonic speeds during the first several days and the character of filling differs very much from a diffusion-equilibrium one. The spatio-temporal behavior of electron and ion temperature anisotropy that is formed in the process of filling, is considered. It is found that the value of electron anisotropy can be large. A brief analysis is made of the causes of electron and ion temperature anisotropy.  相似文献   
980.
Temperature and radiation effects of the 2010 summer fires are estimated on the basis of measurements at the Zvenigorod Scientific Station (ZSS) of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (RAS), in the Moscow region. The surface air temperature during the 2010 summer smoke varied in antiphase with the aerosol mass concentration, and the thermal radiation balance in the surface layer of the atmosphere varied in phase. Under extreme smoke of the surface layer in August 2010, the reduction in surface air temperature at ZSS has been found to reach 4 K with an increase in the downward flux of thermal radiation by an average of 20 W/m2 and a decrease in the difference between upward and downward fluxes of thermal radiation by an average of 24 W/m2.  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