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   3257篇
  免费   417篇
  国内免费   479篇
测绘学   138篇
大气科学   933篇
地球物理   535篇
地质学   370篇
海洋学   253篇
天文学   1505篇
综合类   111篇
自然地理   308篇
  2024年   11篇
  2023年   34篇
  2022年   51篇
  2021年   77篇
  2020年   64篇
  2019年   72篇
  2018年   63篇
  2017年   61篇
  2016年   65篇
  2015年   106篇
  2014年   128篇
  2013年   136篇
  2012年   128篇
  2011年   140篇
  2010年   121篇
  2009年   247篇
  2008年   223篇
  2007年   253篇
  2006年   220篇
  2005年   223篇
  2004年   182篇
  2003年   188篇
  2002年   186篇
  2001年   153篇
  2000年   157篇
  1999年   146篇
  1998年   126篇
  1997年   90篇
  1996年   85篇
  1995年   86篇
  1994年   77篇
  1993年   53篇
  1992年   33篇
  1991年   38篇
  1990年   26篇
  1989年   27篇
  1988年   23篇
  1987年   17篇
  1986年   8篇
  1985年   4篇
  1984年   7篇
  1983年   1篇
  1982年   4篇
  1981年   4篇
  1980年   4篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1954年   1篇
排序方式: 共有4153条查询结果,搜索用时 15 毫秒
991.
西部山区总辐射气候学计算及分布   总被引:11,自引:1,他引:11  
根据西部山区太阳总辐射的实测资料分析,指出,西部山区总辐射的气候学计算必须考虑日照,水汽分布及海拔高度的影响。为此研制了适宜于西部山区的总辐射气候学计算公式Q=Q0(a+bs1+cs1^2),进而讨论了西部山区总辐射的时,空分布。  相似文献   
992.
应用1979年5-8月季风试验期间印度8个陆地辐射探空站资料,通过多种方案试验,得出适用于各种云量条件下各等压面大气有效辐射的气候计算式,并计算和讨论了全国104站500hPa大气有效辐射的时空分布特征。  相似文献   
993.
烟雾层的长波辐射效应以及对边界层温度层结的影响   总被引:2,自引:1,他引:2  
本文利用一个简化的长波辐射方案,计算了兰州城市烟雾层大气的辐射效应.计算表明:烟雾层气溶胶增加了到达地面的大气逆辐射和气层的冷却率,平均污染状况时,增加量分别为15.2%和0.073℃/h.与烟雾层对太阳辐射吸收加热率相比,冷却率量值较小,但对全天边界层能量平衡所起作用不可忽略.对比分析了兰州和郊区夜晚的平均温度廓线演变情况,可以看出烟雾层长波辐射效应增加了低层大气中上部的冷却.  相似文献   
994.
Series of high-resolution infrared solar spectra recorded at the International Scientific Station of the Jungfraujoch, Switzerland, between 06/1986 and 11/1992, and at Kitt Peak National Observatory, Tucson, Arizona (U.S.A.), from 12/1980 to 04/1992, have been analyzed to provide a comprehensive ensemble of vertical column abundances of CHCIF2 (HCFC-22; Freon-22) above the European and the North American continents. The columns were derived from nonlinear least-squares curve fittings between synthetic spectra and the observations containing the unresolved 2v 6 Q-branch absorption of CHCIF2 at 829.05 cm–1. The changes versus time observed in these columns were modeled assuming both an exponential and a linear increase with time. The exponential rates of increase at one-sigma uncertainties were found equal to (7.0±0.35)%/yr for the Junfraujoch data and (7.0±0.23)%/yr for the Kitt Peak data. The exponential trend of 7.0%/yr found at both stations widely separated in location can be considered as representative of the global increase of the CHCIF2 burden in the Earth's atmosphere during the period 1980 to 1992. When assuming two realistic vertical volume mixing ratio profiles for CHCIF2 in the troposphere, one quasi constant and the other decreasing by about 13% from the ground to the tropopause, the concentrations for mid-1990 were found to lie between 97 and 111 pptv (parts per trillion by volume) at the 3.58 km altitude of the Jungfraujoch and between 97 and 103 pptv at Kitt Peak, 2.09 km above sea level. Corresponding values derived from calculations using a high vertical resolution-2D model and recently compiled HCFC-22 releases to the atmosphere, were equal to 107 and 105 pptv, respectively, in excellent agreement with the measurements. The model calculated lifetime of CHCIF2 was found equal to 15.6 years. The present results are compared critically with similar data found in the literature. On average, the concentrations found here are lower by 15–20% than those derived from in situ investigations; this difference cannot be explained by the absolute uncertainty of ±11% assigned presently to the infrared remote measurements.  相似文献   
995.
广州地区太阳分光辐射的某些变化特征   总被引:1,自引:0,他引:1       下载免费PDF全文
利用广州地区1985—1990年的太阳分光辐射的连续观测资料(观测角度为23°11′),研究了广州地区紫外辐射、可见光辐射(光合有效辐射)、近红外辐射的某些特征。结果指出,每年7—10月份各分光辐射及总辐射总量较大。月总辐射中可见光辐射占总辐射的百分比年平均为47.3%,相应的紫外辐射和近红外辐射分别占7.1%和45.6%。文中还分析了晴天条件下分光辐射的变化和1990年紫外辐射变化的某些特征,并分析和讨论了分光辐射与云量、日照时间等因子的相关。  相似文献   
996.
与地震预报有关的电磁现象国际讨论会概况   总被引:3,自引:0,他引:3  
与地震预报有关的电磁现象国际学术讨论会已于1993年9月6-8日在东京召开。这次学术讨论会的宗旨是,为世界各国学者提供一个公开讲坛以讨论与地震有关的电磁现象,并通过交叉学科与多科学相关领域相结合的方式探讨地震预报等问题。本文较详细地介绍了各国学者在这一领域中的最新成果。  相似文献   
997.
I.observedResultsandtheEmpiricalEstimatedFormulasforDirect'UltraviolctRadiationl.observedresultsofdirectultravioletradiationDuetostrongabsorptionofo2,N2,O,N,andO3inthehighlayeroftheatmosphere,solarradiationatwavelengthlessthan29onmcannotarriveateartl1suthee.Betweenthewavelength29Onmand4Oonm,thedirectultravioletirradia11ceSuvcanbewrittenas:Where,S.xissolarsPectralirradiancearrivedattopofatmosphere,Tlxisoptlcalthicknessofatmosphericmolecularabovesea1evel,Whicl1isaknownfunctiollofwavelengt…  相似文献   
998.
Saltern crystallizer ponds are coloured red due to the presence of dense communities of red halophilic archaea (family Halobacteriaceae). Little quantitative information exists on the species distribution within the archaeal community in such ponds. As the different genera of the Halobacteriaceae differ in polar lipid content, and especially in the types of glycolipids, lipid analysis can be used to obtain information on the nature of the organisms present. Analysis of the polar lipids extracted from the biomass collected from the saltern crystallizer ponds in Eilat, Israel, showed one major glycolipid to be present, co-chromatographing with the sulfated diglycosyl diether lipid characteristic of the genusHaloferax. No indications were found for the presence of significant amounts of those glycolipids that would indicate the presence of large numbers of other archaea such asHalobacterium species (H. cutirubrum andH. salinarium, characterized by sulfated triglycosyl and tetraglycosyl diethers), orHaloarcula species (possessing a triglycosyl diether). Phosphatidyl glycerosulfate, a polar lipid absent inHaloferax species, was present in the lipid extract from the crystallizer ponds, suggesting that the dominant microorganism present may be related to strains which are presently classified in the genusHalobacterium but are awaiting a taxonomic reappraisal (H. sodomense, H. saccharovorum, andH. trapanicum). Organisms of the latter group are characterized by sulfated diglycosyl diethers, and the presence of phosphatidyl glycerosulfate. Attempts to isolate the dominant type of bacterium on agar plates yielded relatively low counts (1–2 orders of magnitude lower than the numbers observed microscopically) of bacteria, and most of the isolates had a polar lipid composition characteristic of theH. salinarium group or theH. sodomense-H. saccharovorum-H. trapanicum group.  相似文献   
999.
Solar radiance measurements covering over seventeen months are analysed for a location beside the Lagos Lagoon. The aerosol extinction coefficient was generally higher in the dusty months than in the wet months. Clean air estimates of the coefficient are made. Data on its wavelength dependence are also presented.  相似文献   
1000.
Summary A three-stream infra-red radiation scheme for use particularly in boundary layer models is described. Local uniformity of the atmosphere (i.e. a generalization of the cooling to space approximation in clear air) is assumed, and the radiation equation is solved by simple collocation rather than by the full discrete ordinate method. In clear air the scheme corresponds to the usual approximation, which incorporates the Elsasser factor in the transmission function to account for diffuse radiation. The band models of Goody for water vapour and Elsasser for carbon dioxide are used for the band averaging of the transmission functions. Consistent with this, the band averaging of the radiation flux in cloud is undertaken by replacing the rapidly varying absorption coefficients for the gases by the actual band-averaged values of those coefficients. The band averaging is precise in the limits of strong and weak gaseous absorption.  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