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81.
用NCEP/NCAR再分析辐射资料估算月平均地表反照率 总被引:16,自引:1,他引:15
本文利用1979年 ̄1995年17年平均的NCEP/NCAR(National Center for Environmen-tal Prediction/National Center for Atmospheric Research,美国国家环境预报中心/美国国家大气研究中心)再分析辐射资料估算了全球月平均地表反照率.从所得结果的时空分布来看,用NCEP/NCAR辐射资料得到的全球地表反照率基本 相似文献
82.
Explicit formula for the geoid-quasigeoid separation 总被引:1,自引:0,他引:1
The explicit formula for the geoid-to-quasigeoid correction is derived in this paper. On comparing the geoidal height and
height anomaly, this correction is found to be a function of the mean value of gravity disturbance along the plumbline within
the topography. To evaluate the mean gravity disturbance, the gravity field of the Earth is decomposed into components generated
by masses within the geoid, topography and atmosphere. Newton’s integration is then used for the computation of topography-and
atmosphere-generated components of the mean gravity, while the combined solution for the downward continuation of gravity
anomalies and Stokes’ boundary-value problem is utilized in computing the component of mean gravity disturbance generated
by mass irregularities within the geoid. On application of this explicit formulism a theoretical accuracy of a few millimetres
can be achieved in evaluation of the geoid-to-quasigeoid correction. However, the real accuracy could be lower due to deficiencies
within the numerical methods and to errors within the input data (digital terrain and density models and gravity observations). 相似文献
83.
84.
P. J. G. Teunissen 《Journal of Geodesy》2007,81(12):759-780
In this contribution, we extend the existing theory of minimum mean squared error prediction (best prediction). This extention
is motivated by the desire to be able to deal with models in which the parameter vectors have real-valued and/or integer-valued
entries. New classes of predictors are introduced, based on the principle of equivariance. Equivariant prediction is developed
for the real-parameter case, the integer-parameter case, and for the mixed integer/real case. The best predictors within these
classes are identified, and they are shown to have a better performance than best linear (unbiased) prediction. This holds
true for the mean squared error performance, as well as for the error variance performance. We show that, in the context of
linear model prediction, best predictors and best estimators come in pairs. We take advantage of this property by also identifying
the corresponding best estimators. All of the best equivariant estimators are shown to have a better precision than the best
linear unbiased estimator. Although no restrictions are placed on the probability distributions of the random vectors, the
Gaussian case is derived separately. The best predictors are also compared with least-squares predictors, in particular with
the integer-based least-squares predictor introduced in Teunissen (J Geodesy, in press, 2006). 相似文献
85.
研究了复平面上 ,广义 Hermite-Fejer插值多项式的收敛性。得到了其在空间 lp(| z| =1 ) (0
相似文献
86.
P. Goovaerts 《Mathematical Geology》1998,30(5):511-534
This paper presents both estimation and simulation as optimization problems that differ in the optimization criteria, minimization of a local expected loss for estimation and reproduction of global statistics (semivariogram, histogram) for simulation. An intermediate approach is proposed whereby an initial random image is gradually modified using simulated annealing so as to better match both local and global constraints. The relative weights of the different constraints in the objective function allow the user to strike a balance between smoothness of the estimated map and reproduction of spatial variability by simulated maps. The procedure is illustrated using a synthetic dataset. The proposed approach is shown to enhance the influence of observations on neighboring simulated values, hence the final realizations appear to be better conditioned to the sample information. It also produces maps that are more accurate (smaller prediction error) than stochastic simulation ignoring local constraints, but not as accurate as E-type estimation. Flow simulation results show that accounting for local constraints yields, on average, smaller errors in production forecast than a smooth estimated map or a simulated map that reproduces only the histogram and semivariogram. The approach thus reduces the risk associated with the use of a single realization for forecasting and planning. 相似文献
87.
Information concerning a total number of 13700 instrumentally recorded earthquakes is used to study the geographical and the vertical distribution of the Earth's seismicity. From these earthquakes, which form four complete samples of data (M 7.0, 1894–1992; M 6.5, 1930–1992; M 6.0, 1953–1992; M 5.5, 1966–1992), 11511 are shallow (h 60 km), 2085 are of intermediate focal depth (61 h 300 km) and 564 are deep focus earthquakes (301 h 720 km). The parameters a and b of the frequency-magnitude relationship were calculated in a grid of equally spaced points at 1° by using the data of earthquakes located inside circles centered at each point. The radius of the circles increased from 30 km with a step of 10 km until the information for the earthquakes located inside the circle fulfil three criteria which concern the size of the sample used to compute these parameters at each point of the grid. The results are given in a qualitative way (epicenter maps) as well as in a quantitative way (mean return periods). 相似文献
88.
A detailed barotropic, baroclinic and combined barotropic-baroclinic stability analysis has been carried out with mean monsoon
zonal currents over western India, eastern India and S.E. Asia. The lower and middle tropospheric zonal wind profiles over
western India are barotropically unstable. The structure and growth rate of these modes agree well with the observed features
of the midtropospheric cyclones. Similar profiles over eastern India and S.E. Asia, however, are barotropically stable. This
is attributed to weak horizontal shear, inherent to these profiles. The upper tropospheric profiles, on the other hand, are
barotropically unstable throughout the whole region. The features of these unstable modes agree with those of observed easterly
waves. The baroclinic and combined barotropic-baroclinic stability analyses show that the baroclinic effects are not important
in tropics.
Though the barotropic instability of the mean zonal current seems to be res ponsible for the initial growth of the mid-tropospheric
cyclones, neither barotropic nor baroclinic instability of the mean zonal current seem to explain the observed features of
the monsoon depressions. 相似文献
89.
The approach to remote sensing of water vapor by using global positioning systems(GPS)isdiscussed.In order to retrieve the vertical integrated water vapor(IWV)or the precipitable water(PW),the weighted“mean temperature”of the atmosphere,T_m would be estimated to the specificarea and season.T_m depends on surface temperature,tropospheric temperature profile,and thevertical distribution of water vapor.The surface temperature dependence is borne out by acomparison of T_m and the values of surface temperature T_s using radiosonde profiles of BeijingStation(No.54511)throughout 1992.The analysis of radiosonde profiles spanning a one-yearinterval(1992)from sites in eastern region of China with a latitude range of 20-50°N and alongitude range of 100-130°E yields the coefficients α and b of a linear regression equation T_m=α bT_s. 相似文献
90.
江苏省近百年汛期旱涝变化的诊断分析 总被引:8,自引:2,他引:6
本文应用历史气候资料和现代降水记录,对近百年来汛期江苏省各区域各年代进行旱涝诊断分析,采用滑动平均方法探讨其变化趋势,并用最大搞谱方法提取显著周期。得出以下三个比较有意义的结论:(1)近百年来,汛期全省较易发生旱的灾害,20-30年代为旱灾濒发期;(2)淮北地区近年有向早年发展的趋势,江淮之间及苏南地区进入90年代以来向旱年发展的趋势则愈来愈明显;(3)全省具有2-3年、5-6年的旱涝周期。 相似文献