全文获取类型
收费全文 | 2672篇 |
免费 | 599篇 |
国内免费 | 886篇 |
专业分类
测绘学 | 358篇 |
大气科学 | 666篇 |
地球物理 | 857篇 |
地质学 | 1274篇 |
海洋学 | 546篇 |
天文学 | 36篇 |
综合类 | 201篇 |
自然地理 | 219篇 |
出版年
2024年 | 20篇 |
2023年 | 71篇 |
2022年 | 87篇 |
2021年 | 101篇 |
2020年 | 78篇 |
2019年 | 127篇 |
2018年 | 95篇 |
2017年 | 102篇 |
2016年 | 84篇 |
2015年 | 104篇 |
2014年 | 151篇 |
2013年 | 124篇 |
2012年 | 136篇 |
2011年 | 162篇 |
2010年 | 172篇 |
2009年 | 193篇 |
2008年 | 194篇 |
2007年 | 183篇 |
2006年 | 183篇 |
2005年 | 175篇 |
2004年 | 169篇 |
2003年 | 160篇 |
2002年 | 139篇 |
2001年 | 102篇 |
2000年 | 124篇 |
1999年 | 100篇 |
1998年 | 93篇 |
1997年 | 115篇 |
1996年 | 98篇 |
1995年 | 96篇 |
1994年 | 96篇 |
1993年 | 87篇 |
1992年 | 63篇 |
1991年 | 40篇 |
1990年 | 54篇 |
1989年 | 41篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4157条查询结果,搜索用时 218 毫秒
171.
172.
173.
The variability in global oceanic evaporation data sets was examined for the period 1988-2000. These data sets are satellite estimates based on bulk aerodynamic formulations and include the NASA/Goddard Space Flight Center Satellite-based Surface Turbulent Flux version 2 ( GSSTF2), the Japanese-ocean flux using remote sensing observations (J-OFURO), and the Hamburg Ocean-Atmosphere Parameters and Fluxes from Satellite version 2 (HOAPS2). The National Center for Environmental Prediction (NCEP) reanalysis is also included for comparison. An increase in global average surface latent heat flux (SLHF) can be observed in all the data sets. Empirical mode decomposition (EMD) shows long-term increases that started around 1990 for all remote sensing data sets. The effect of Mt. Pinatubo eruption in 1991 is clearly evident in HOAPS2 but is independent of the longterm increase. Linear regression analyses show increases of 9.4%, 13.0%, 7. 3%, and 3.9% for GSSTF2, J-OFURO, HOAPS2 and NCEP, for the periods of the data sets. Empirical orthogonal function (EOF) analyses show that the pattern of the first EOF of all data sets is consistent with a decadal variation associated with the enhancement of the tropical Hadley circulation, which is supported by other satellite observations. The second EOF of all four data sets is an ENSO mode, and the correlations between their time series and an SO1 are 0.74, 0.71,0.59, and 0.61 for GSSTF2, J-OFURO, HOAPS2, and NCEP in that order. When the Hadley modes are removed from the remote sensing data, the residue global increases are reduced to 2.2% , 7. 3%, and 〈 1% for GSSTF2, J-OFURO and HOAPS, respectively. If the ENSO mode is used as a calibration standard for the data sets, the Hadley mode is at least comparable to, if not larger than, the ENSO mode during our study period. 相似文献
174.
175.
176.
177.
Rossby waves with linear topography in barotropic fluids 总被引:1,自引:0,他引:1
Rossby waves are the most important waves in the atmosphere and ocean, and are parts of a large-scale system in fluid. The theory and observation show that, they satisfy quasi-geostrophic and quasi-static equilibrium approximations. In this paper, solitary Rossby waves induced by linear topography in barotropic fluids with a shear flow are studied. In order to simplify the problem, the topography is taken as a linear function of latitude variable y, then employing a weakly nonlinear method and a perturbation method, a KdV (Korteweg-de Vries) equation describing evolution of the amplitude of solitary Rossby waves induced by linear topography is derived. The results show that the variation of linear topography can induce the solitary Rossby waves in barotropic fluids with a shear flow, and extend the classical geophysical theory of fluid dynamics. 相似文献
178.
Sensitivity of penman-monteith reference crop evapotranspiration in Tao’er River Basin of northeastern China 总被引:1,自引:0,他引:1
A non-dimensional relative sensitivity coefficient was employed to predict the responses of reference crop evapotranspiration (ET0) to perturbation of four climate variables in Tao'er River Basin of the northeastern China. Mean monthly ET0 and yearly ET0 from 1961 to 2005 were estimated with the FAO-56 Penman-Monteith Equation. A 45-year historical dataset of average monthly maximum/minimum air temperature, mean air temperature, wind speed, sunshine hours and relative humidity from 15 meteorological stations was used in the analysis. Results show that: 1) Sensitivity coefficients of wind speed, air temperature and sunshine hours were positive except for those of air temperature of Arxan Meteorological Station, while those of relative humidity were all negative. Relative humidity was the most sensitive variable in general for the Tao'er River Basin, followed by sunshine hours, wind speed and air temperature. 2) Similar to climate variable, monthly sensitivity coefficients exhibit large annual fluctuations. 3) Sensitivity coefficients for four climate variables all showed significant trends in seasonal/yearly series. Also, sensitivity coefficients of air temperature, sunshine hours and wind speed all showed significant trends in spring. 4) Among all sensitivity coefficients, the average yearly sensitivity coefficient of relative humidity was highest throughout the basin and showed largest spatial variability. Longitudinal distribution of sensitivity coefficients for air temperature, relative humidity and sunshine hours was also found, which was similar to the distribution of the three climate variables. 相似文献
179.
为了获取常用超短波信号的特征参数,采取一种非线性变换的方法。根据信号参数的分布信息,对信号特征不够明显的参数进行二次变换,使所有信号的特征参数都具有较好的区分度,并利用BP网对这些特征参数进行识别。大量的仿真实验表明,该方法参数提取容易,计算量较小,在较低信噪比下能够较好地识别常用的超短波信号。识别的信号为2FSK、MSK、QAM、DPSK和FM。 相似文献
180.
介绍了一种经济实用的 16通道铂热电阻测温巡检显示仪 ,并论述了铂热电阻的引线消除和用正反馈实现非线性校正的方法。 相似文献