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   1007篇
  免费   128篇
  国内免费   216篇
测绘学   41篇
大气科学   422篇
地球物理   220篇
地质学   95篇
海洋学   74篇
天文学   418篇
综合类   26篇
自然地理   55篇
  2024年   4篇
  2023年   4篇
  2022年   15篇
  2021年   14篇
  2020年   11篇
  2019年   16篇
  2018年   21篇
  2017年   13篇
  2016年   12篇
  2015年   16篇
  2014年   23篇
  2013年   52篇
  2012年   18篇
  2011年   26篇
  2010年   37篇
  2009年   83篇
  2008年   91篇
  2007年   109篇
  2006年   113篇
  2005年   82篇
  2004年   70篇
  2003年   57篇
  2002年   58篇
  2001年   47篇
  2000年   63篇
  1999年   46篇
  1998年   52篇
  1997年   31篇
  1996年   33篇
  1995年   23篇
  1994年   17篇
  1993年   19篇
  1992年   15篇
  1991年   8篇
  1990年   7篇
  1989年   11篇
  1988年   9篇
  1987年   1篇
  1986年   5篇
  1985年   3篇
  1984年   3篇
  1983年   4篇
  1982年   3篇
  1980年   2篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
排序方式: 共有1351条查询结果,搜索用时 15 毫秒
51.
氯化钠-溴水封闭溶样碘量法测定矿石中的金   总被引:2,自引:0,他引:2  
采用NaCl-溴水为溶剂、封闭溶样法分解试样,泡塑抽滤吸附以及碘量法测定矿石中Au。方法简单快速、准确、不污染环境,适用于测定矿石中0.x~xxg/t的Au。  相似文献   
52.
Based on steady semi-geostrophic model equations,analysis is carried out of the linear and nonlinear modification/response of the tropical atmosphere to the forcing of ideal paired heat sources of contrasting nature.Resuits show that the linear part is dominant in the steady response but the nonlinear modification is quite noticable in the neighborhood of the heat source and between the paired sources,and the barotropic mode and second baroclinic mode play a different role in the modification,with the barotropic(second baroclinic)mode modification depending largely on the Rossby wave self-interaction(the magnitude due to the Kelvin-Rossby wave interaction)between the paired sources.  相似文献   
53.
Airborne measurements made during August 1985 over Greenland and its environs show that both accumulation-mode (0.1 m D2.0 m) and giant (D2 m) particles were present in relatively high concentrations in arctic haze layers and that the accumulation-mode particles dominated light scattering. Particles with diameters (D) between 1 and 4 m consisted predominately of mixed materials, small and dense inclusions, and probably organic compounds containing sulfur. Many of the particles from 0.1 to 1 m in diameter were also of mixed composition, with sulfuric acid, ammonium sulfate and organics probably the dominant constituents.  相似文献   
54.
The adiabatic, quasi-geostraphic, 25-layer, numerical, linear model with Ekman boundary layer friction is utilised to perform the baroclinic stability analysis of the mean monsoon zonal wind profile. It is shown thec i is a function of the resultant wavenumber alone. This relation is able to explain the effects of the lateral walls on the unstable waves.The energetics and zonal plane distribution of the short and long preferred viscous waves are computed. The upward motion of the short wave together with the warm (cold) core lies to the west of the surface trough position above (below) 850 mb. Further, it is shown that the main source of kinetic energy for the wave lies in the middle layer (850–700 mb) which is transported to the lower and upper layers. Computed is found to be in good agreement with observed values.  相似文献   
55.
进一步讨论了大中尺度Rossby波与惯性重力波的非线性相互作用问题.从共振相互作用曲线来看,Rossby波和惯性重力波可以在相当广泛的角谱范围内发生共振非线性相互作用.在一定条件下,一个大振幅波包可以激发两个小振幅波包不稳定增长而出现参量不稳定现象,这三个波包可以是同种类型或不同类型的波包.当两个大振幅波包发生相互作用时,非线性过程会产生另一个波包并使它增长,并且增长速度大于仅有一个大振幅波包时的增长速度.大尺度Rossby波包税发两个较小尺度惯性重力波的过程是一种重要的能量串级(cascade)过程.  相似文献   
56.
进一步讨论了大中尺度Rossby波与惯性重力波的非线性相互作用问题.从共振相互作用曲线来看,Rossby波和惯性重力波可以在相当广泛的角谱范围内发生共振非线性相互作用.在一定条件下,一个大振幅波包可以激发两个小振幅波包不稳定增长而出现参量不稳定现象,这三个波包可以是同种类型或不同类型的波包.当两个大振幅波包发生相互作用时,非线性过程会产生另一个波包并使它增长,并且增长速度大于仅有一个大振幅波包时的增长速度.大尺度Rossby波包税发两个较小尺度惯性重力波的过程是一种重要的能量串级(cascade)过程.  相似文献   
57.
Summary The total ozone response to strong major geomagnetic storms (Ap≥60) in winter along the 50° N latitudinal circle is studied. The results add to the recent results of Laštovička et al. (1992) obtained for European middle latitudes (∼50°N) and to the results of Mlch (1994). A significant response of total ozone is only observed in winter under high solar activity/E-phase of QBO conditions (E-max) and seems to be caused by geomagnetic storm-induced changes of atmospheric dynamics. There are two sectors along latitude 50°N, which are sensitive to forcing by geomagnetic storms both in total ozone and the troposphere — north-eastern Atlantic-European and eastern Siberia-Aleutian sectors. The total ozone response under E-max conditions manifests itself mainly as a large decrease in the longitudinal variation of ozone after the storm, which means an increase of ozone in Europe. The observed effects in total ozone consist in redistribution, not production or loss of ozone.  相似文献   
58.
Mean growing season soil PCO2 data were obtained for 19 regions of the world in nine countries. Bivariate and multiple linear regression analysis with soil log(PCO2) as the dependent variable and TEMP, PRECIP, log(AET), and log(PET) as the four climatic independent variables demonstrated that AET was the best independent predictor of soil PCO2. An improved soil PCO2-AET model was developed by assuming (1) that as AET approaches zero, soil PCO2 approaches the atmospheric value and (2) that there is an upper limit to soil PCO2 at very high AET. This model has the form log(PCO2) = ?3·47 + 2·09 (1 ?e?0·0172 AET) where AET is in mm. It explains 67 per cent of the initial variation in the soil PCO2 data, predicts a soil log(PCO2) of ? 3·47 at AET = 0, and an upper limit of 3·5 per cent (log(PCO2) = ? 1·45) for mean growing season soil PCO2 at AET values of 2000 mm and above. The results of this study suggest that soil PCO2 levels in tropical areas are, on average, higher than those in temperate, alpine, and arctic regions.  相似文献   
59.
Tropical airglow work during the last few years is reviewed. Airglow instrumentation is becoming more complex. Some of these sophisticated airglow experiments giving important information about the upper atmosphere such as ionospheric F region electron density, height of maximum electron density, dynamics of and irregularities in the F region, mesospheric neutral temperature and its variation, dynamics of mesospheric, etc. are mentioned. At the end some problems which could be tackled in near future with airglow techniques have been suggested. Invited Review paper, Commission 21, IAU, Patras, Greece, August, 1982.  相似文献   
60.
将流的标准化变差度概念应用到各年南海夏季风建立研究中去,并用其作为大气环流调整的客观定量指标。用该指标定义的南海夏季风建立的预兆日期与用传统天气气候学方法确定的南海夏季风的来临日期,在绝大多数具体年份两者均很接近,故可作南海夏季风建立的先兆指标。但有一些年份,南海季风的建立不伴随着低空环流的突变过程,两种方法都可能不准确,可靠的方法也许是用场相似度作指标。此外,南海夏季风建立前,对流层顶和平流层下层就出现了环流调整,该调整为南海夏季风建立打下基础,而南海夏季风爆发则表现为低空环流的大调整。南海夏季风的爆发是高、低空全球大气环流发生显著调整的结果,并非限于南海范围局部,南海夏季风建立不能看作是发生在南海的局部现象。  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