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51.
Extreme value analysis provides a semiparametric method for analyzing the extreme long tails of skew distributions which may be observed when handling mining data. The estimation of important tail characteristics, such as the extreme value index, allows for a discrimination between competing distribution models. It measures the thickness of such long tailed distributions, if only a limited sample is available. This paper stresses the practical implementation of extreme value theory, which is used to discriminate a lognormal from a mixed lognormal distribution in a case study of size distributions for alluvial diamonds. 相似文献
52.
Seismic hazard of Egypt 总被引:1,自引:0,他引:1
Earthquake hazard parameters such as maximum expected magnitude,M
max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas. 相似文献
53.
浙闽山区茶叶生产基地评价的探讨 总被引:6,自引:0,他引:6
茶叶基地的评价包括对基地的自然和经济条件的评估,应用系统分析方法,将自然和经济条件进行定量的综合评估,用综合评价值区分基地间的差异,最后定性与定量相结合,提出茶叶生产基地的合理布局. 相似文献
54.
Chang-Jo F. Chung 《Mathematical Geology》1993,25(7):851-865
Multivariate statistical analyses have been extensively applied to geochemical measurements to analyze and aid interpretation of the data. Estimation of the covariance matrix of multivariate observations is the first task in multivariate analysis. However, geochemical data for the rare elements, especially Ag, Au, and platinum-group elements, usually contain observations the below detection limits. In particular, Instrumental Neutron Activation Analysis (INAA) for the rare elements produces multilevel and possibly extremely high detection limits depending on the sample weight. Traditionally, in applying multivariate analysis to such incomplete data, the observations below detection limits are first substituted, for example, each observation below the detection limit is replaced by a certain percentage of that limit, and then the standard statistical computer packages or techniques are used to obtain the analysis of the data. If a number of samples with observations below detection limits is small, or the detection limits are relatively near zero, the results may be reasonable and most geological interpretations or conclusions are probably valid. In this paper, a new method is proposed to estimate the covariance matrix from a dataset containing observations below multilevel detection limits by using the marginal maximum likelihood estimation (MMLE) method. For each pair of variables, sayY andZ whose observations containing below detection limits, the proposed method consists of three steps: (i) for each variable separately obtaining the marginal MLE for the means and the variances,
,
,
, and
forY andZ: (ii) defining new variables by
and
and lettingA=C+D andB=C–D, and obtaining MLE for variances,
and
forA andB; (iii) estimating the correlation coefficient YZ by
and the covariance
YZ
by
. The procedure is illustrated by using a precious metal geochemical data set from the Fox River Sill, Manitoba, Canada. 相似文献
55.
56.
57.
Many stochastic process models for environmental data sets assume a process of relatively simple structure which is in some sense partially observed. That is, there is an underlying process (Xn, n 0) or (Xt, t 0) for which the parameters are of interest and physically meaningful, and an observable process (Yn, n 0) or (Yt, t 0) which depends on the X process but not otherwise on those parameters. Examples are wide ranging: the Y process may be the X process with missing observations; the Y process may be the X process observed with a noise component; the X process might constitute a random environment for the Y process, as with hidden Markov models; the Y process might be a lower dimensional function or reduction of the X process. In principle, maximum likelihood estimation for the X process parameters can be carried out by some form of the EM algorithm applied to the Y process data. In the paper we review some current methods for exact and approximate maximum likelihood estimation. We illustrate some of the issues by considering how to estimate the parameters of a stochastic Nash cascade model for runoff. In the case of k reservoirs, the outputs of these reservoirs form a k dimensional vector Markov process, of which only the kth coordinate process is observed, usually at a discrete sample of time points. 相似文献
58.
本文通过环境背景值、风化壳地球化学、对流层(大气气溶胶)地球化学和人为地球化学异常,初步探讨了南极长城站地区的现代环境地球化学特征。分析表明:环境要素固有的地球化学性质、区域环境条件和自然环境演变之间具有深刻的内在联系。 相似文献
59.
功能—技术矩阵,经众多工作者的努力研究,已渐趋成熟与实用。但如何利用功能—技术矩阵构造在广义现代设计领域中适用的科学模式,解决多学科设计方案的组成与评价问题,还存在薄弱环节。本文利用“使用价值分析优化”的概念,从设计方案技术先进性和经济合理性的协调统一的角度出发,较好地实现了功能—技术矩阵可行优化组合链的组成与评价,弥补了以往的缺陷。 相似文献
60.
A new earthquake catalogue for central, northern and northwestern Europe with unified Mw magnitudes, in part derived from chi-square maximum likelihood regressions, forms the basis for seismic hazard calculations
for the Lower Rhine Embayment. Uncertainties in the various input parameters are introduced, a detailed seismic zonation is
performed and a recently developed technique for maximum expected magnitude estimation is adopted and quantified. Applying
the logic tree algorithm, resulting hazard values with error estimates are obtained as fractile curves (median, 16% and 84%
fractiles and mean) plotted for pga (peak ground acceleration; median values for Cologne 0.7 and 1.2 m/s2 for probabilities of exceedence of 10% and 2%, respectively, in 50 years), 0.4 s (0.8 and 1.5 m/s2) and 1.0 s (0.3 and 0.5 m/s2) pseudoacclerations, and intensity (I0 = 6.5 and 7.2). For the ground motion parameters, rock foundation is assumed. For the area near Cologne and Aachen, maps
show the median and 84% fractile hazard for 2% probability of exceedence in 50 years based on pga (maximum median value about
1.5 m/s2), and 0.4 s (>2 m/s2) and 1.0 s (about 0.8 m/s2) pseudoaccelerations, all for rock. The pga 84% fractile map also has a maximum value above 2 m/s2 and shows similarities with the median map for 0.4 s. In all maps, the maximum values fall within the area 6.2–6.3° E and
50.8–50.9° N, i.e., east of Aachen. 相似文献