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511.
Identifying Nonstationarity in Turbulence Series 总被引:1,自引:1,他引:0
Edgar L Andreas Cathleen A. Geiger George Treviño Kerry J. Claffey 《Boundary-Layer Meteorology》2008,127(1):37-56
Because of rapid forcing by varying cloud and sky conditions, turbulence time series collected in the atmospheric surface
layer over land may often be nonstationary. The meteorological community, however, has no consensus definition of what nonstationarity
is and, thus, no consensus method for how to identify it. This study, therefore, adopts definitions for first-order and second-order
stationarity taken from the time series analysis literature and implements new analysis techniques and probabilistic tests
to quantify first-order and second-order nonstationarity. First-order nonstationarity manifests as a change in the series
mean; second-order nonstationarity, as a change in the variance. The analysis identifies nonstationarity in surface-level
turbulent temperature and water vapour series collected during two sample days with solar forcing influenced by cirrus and
cirrostratus clouds, but that nonstationarity is not as severe as expected despite the rapid thermal forcing by these clouds.
On the other hand, even with negligible cloud forcing, both sample days exhibited severe nonstationarity at night. 相似文献
512.
P. Nurmi 《Monthly notices of the Royal Astronomical Society》2001,323(4):911-922
Two long-term simulation methods for cometary orbits, a Monte Carlo method and a direct integration method, are compared with each other. The comparison is done in seven inclination and perihelion distance intervals, and shows differences in dynamical lifetime and capture probabilities for the following main reasons. We use a finite energy step approximation in the Monte Carlo method and the method considers only close approaches with the planets. The differences can be taken into account statistically and it is possible to calculate the correction factors for the capture probability and dynamical lifetime in the Monte Carlo method. Both corrections depend on the inclination and on the value of the minimum energy step. The capture probabilities of the short-period comets originating in the Oort Cloud are calculated by the corrected Monte Carlo method and compared with published results. 相似文献
513.
本文阐述大气中重要的“痕量气体”之一——臭氧(平流层臭氧)对地球表面和低层大气的温室效应及其全球气候的反馈影响;指出了云的辐射力的概念及其重要性,并讨论了“南极臭氧洞”现象。 相似文献
514.
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516.
Admir C. Targino Kevin J. Noone Frank Drewnick Johannes Schneider Radovan Krejci Gustavo Olivares Silke Hings Stephan Borrmann 《Atmospheric Research》2007,86(3-4):225-240
During June and July 2003 the Sources and Origins of Atmospheric Cloud Droplets experiment (SOACED) was carried out on a mountain-top site in central Sweden. The main objective of the experiment was to characterise the microphysical and chemical properties of cloud droplet residuals and interstitial aerosol particles in continental clouds and to understand the processes controlling cloud properties at this location.Interstitial and residual aerosol size distributions, cloud liquid water content and species- and size-resolved aerosol mass concentrations are the main variables employed to address questions pertaining to the cloud droplet number concentration and scavenging efficiency during a stratocumulus cloud event observed on July 28, 2003. In this cloud event, about 56% of the aerosol mass was associated with organic species, whilst SO4 accounted for 23% and NH4 for 14%. NO3 and Cl made up about 7% of the total mass.The partitioning of the aerosol particles between cloud droplets and interstitial air has been studied in terms of their microphysical properties. The scavenging efficiency, defined as the fraction of particles activated into cloud elements compared to the total amount of particles, was investigated as a function of size. The scavenging efficiency curves displayed different shapes during the cloud event, from an S-shaped curve, with low scavenging efficiency in the Aitken mode and larger scavenging efficiency in the accumulation mode, to more unusual shapes where Aitken-mode particles were either solely activated or activated in addition to accumulation-mode particles.This study suggests that alterations of the aerosol chemical composition occurred during the measurement period, changing the hygroscopic nature of the CCN and decreasing their activation diameter. It is also hypothesized that entrainment of drier air aloft may have introduced inhomogeneities in the supersaturation field and modified the S-shaped scavenging curves. 相似文献
517.
This research examines the influence of cloud on the cataract effective UV (UVCat) irradiances on a horizontal plane over an extended period of 12months that included the range of cloud conditions, solar zenith angle (SZA) and ozone conditions experienced over that time. The data were collected at five minute intervals. Cloud modification factors were determined from the influence of clouds on the global broadband solar radiation and these were applied to the cloud free cataract effective UV to evaluate the UVCat irradiances on a horizontal plane for all cloud conditions. A comparison of the measured and calculated UVCat irradiances for the 2004 data set in the range of SZA of 70° or less provided an R2 value of 0.85. The data in the first 6months of 2005 for an SZA of 70° or less that were at a different time to that when the technique was developed provided an R2 value of 0.83 for the comparison of the measured and calculated UVCat irradiances. 相似文献
518.
L. Alados-Arboledas I. Alados I. Foyo-Moreno F. J. Olmo A. Alcntara 《Atmospheric Research》2003,66(4):273-290
The purpose of this study is to examine the effect of clouds on the ultraviolet erythemal irradiance. The study was developed at three stations in the Iberian Peninsula: Madrid and Murcia, using data recorded in the period 2000–2001, and Zaragoza, using data recorded in 2001. In order to determine the cloud effect on ultraviolet erythemal irradiance, we considered a cloud modification factor defined as the ratio between the measured values of ultraviolet erythemal irradiance and the corresponding clear-sky ultraviolet erythemal irradiance, which would be expected for the same time period and atmospheric conditions. The dependence of this cloud modification factor on total cloud amount, cloud type and solar elevation angle was investigated. The results suggest that the effect of cloud on ultraviolet erythemal irradiance can be parameterized in a simple way in terms of the cloud amount. Our results suggest that the same cloud modification factor model can be used at the three analysed locations estimating the ultraviolet erythemal irradiance with mean bias deviation (MBD) in the range of the expected experimental errors. This cloud modification factor is lower than that associated to the whole solar spectral range, indicating that the attenuation for the ultraviolet erythemal irradiance is lower than that associated to other solar spectral ranges. The cloud modification factor for ultraviolet erythemal irradiance presents dependence with solar elevation, with opposite dependencies with solar elevation for overcast and partial cloud cover conditions, a fact that can be explained in terms of the influence of reflection-enhancement of the ultraviolet irradiance in the last case. Concerning the influence of cloud type, a limited study of two cloud categories, low and medium level and high level, indicated that for overcast conditions, lower clouds presents an attenuation of ultraviolet erythemal irradiance 20% greater than that associated to high level clouds. 相似文献
519.
520.
中川地区一次负地闪的起始过程研究 总被引:14,自引:7,他引:7
利用GPS同步的多点慢天线电场变化仪在甘肃中川地雷暴过程中测量得到的资料,对一次负地闪的起始过程进行了分析。发现地闪产和在击发之前常有持续170-300ms的去2内放电过程发生,它可有数据不等的K变化组成。 相似文献