全文获取类型
收费全文 | 3508篇 |
免费 | 429篇 |
国内免费 | 426篇 |
专业分类
测绘学 | 1087篇 |
大气科学 | 440篇 |
地球物理 | 840篇 |
地质学 | 924篇 |
海洋学 | 340篇 |
天文学 | 33篇 |
综合类 | 304篇 |
自然地理 | 395篇 |
出版年
2024年 | 18篇 |
2023年 | 36篇 |
2022年 | 68篇 |
2021年 | 89篇 |
2020年 | 112篇 |
2019年 | 161篇 |
2018年 | 129篇 |
2017年 | 166篇 |
2016年 | 191篇 |
2015年 | 175篇 |
2014年 | 217篇 |
2013年 | 247篇 |
2012年 | 191篇 |
2011年 | 220篇 |
2010年 | 177篇 |
2009年 | 178篇 |
2008年 | 197篇 |
2007年 | 201篇 |
2006年 | 172篇 |
2005年 | 160篇 |
2004年 | 152篇 |
2003年 | 131篇 |
2002年 | 95篇 |
2001年 | 88篇 |
2000年 | 94篇 |
1999年 | 83篇 |
1998年 | 90篇 |
1997年 | 81篇 |
1996年 | 67篇 |
1995年 | 57篇 |
1994年 | 43篇 |
1993年 | 51篇 |
1992年 | 31篇 |
1991年 | 33篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1973年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有4363条查询结果,搜索用时 9 毫秒
21.
22.
An important task in modern geostatistics is the assessment and quantification of resource and reserve uncertainty. This uncertainty
is valuable support information for many management decisions. Uncertainty at specific locations and uncertainty in the global
resource is of interest. There are many different methods to build models of uncertainty, including Kriging, Cokriging, and
Inverse Distance. Each method leads to different results. A method is proposed to combine local uncertainties predicted by
different models to obtain a combined measure of uncertainty that combines good features of each alternative. The new estimator
is the overlap of alternate conditional distributions. 相似文献
23.
应用探地雷达探测活动断层 总被引:1,自引:0,他引:1
在浅覆盖区采用探地雷达探测地震活动断层。通过实验确定出最佳的采集参数和数据处理流程,在雷达剖面上,能够清晰地显示出断层上部的形态特征、上断点埋深和岩土分层。结合钻孔资料,利用雷达剖面上对第四系覆盖的分层结果和上断点所在的层位可以分析和评价断层的活动性。 相似文献
24.
Erik Rüttener Juan José Egozcue Dieter Mayer-Rosa Stephan Mueller 《Natural Hazards》1996,14(2-3):165-178
Seismic hazard analysis is based on data and models, which both are imprecise and uncertain. Especially the interpretation of historical information into earthquake parameters, e.g. earthquake size and location, yields ambiguous and imprecise data. Models based on probability distributions have been developed in order to quantify and represent these uncertainties. Nevertheless, the majority of the procedures applied in seismic hazard assessment do not take into account these uncertainties, nor do they show the variance of the results. Therefore, a procedure based on Bayesian statistics was developed to estimate return periods for different ground motion intensities (MSK scale).Bayesian techniques provide a mathematical model to estimate the distribution of random variables in presence of uncertainties. The developed method estimates the probability distribution of the number of occurrences in a Poisson process described by the parameter . The input data are the historical occurrences of intensities for a particular site, represented by a discrete probability distribution for each earthquake. The calculation of these historical occurrences requires a careful preparation of all input parameters, i.e. a modelling of their uncertainties. The obtained results show that the variance of the recurrence rate is smaller in regions with higher seismic activity than in less active regions. It can also be demonstrated that long return periods cannot be estimated with confidence, because the time period of observation is too short. This indicates that the long return periods obtained by seismic source methods only reflects the delineated seismic sources and the chosen earthquake size distribution law. 相似文献
25.
Heinrich Eichhorn 《Celestial Mechanics and Dynamical Astronomy》1996,64(3):273-275
The autodependence, (a special case of the — now quite obsolete — dependences, which had been introduced for very specialized astrometric purposes) is proportional to the parameter variance which is the expectation of the variance of the systematic error of a function evaluated with estimated parameters. 相似文献
26.
参数的期望估计及其在形变分析中的应用 总被引:1,自引:0,他引:1
利用“参数的期望估计”能准确定位、定量粗差及参数的期望估计不受粗差影响折特殊性质,寻找地壳变形区域和不变形区域,以确定拟稳点,进而进行拟稳变换,分析地菜变,将是一种有效方法。 相似文献
27.
本文对成都市总人口、建成区面积等11个因子、作了主成份回归L-S估计和M-估计,讨论了成都城市发展对“热岛”强度的主要影响因子。结果表明,城区房屋建筑面积及总人口数是影响城市气候(气温)的主要因子,其次为城市人口总户数、建成面积等。 文中,对回归方程进行了拟合计算,回归效果比较满意(尤其是稳健回归)。 相似文献
28.
Two different goals in fitting straight lines to data are to estimate a true linear relation (physical law) and to predict values of the dependent variable with the smallest possible error. Regarding the first goal, a Monte Carlo study indicated that the structural-analysis (SA) method of fitting straight lines to data is superior to the ordinary least-squares (OLS) method for estimating true straight-line relations. Number of data points, slope and intercept of the true relation, and variances of the errors associated with the independent (X) and dependent (Y) variables influence the degree of agreement. For example, differences between the two line-fitting methods decrease as error in X becomes small relative to error in Y. Regarding the second goal—predicting the dependent variable—OLS is better than SA. Again, the difference diminishes as X takes on less error relative to Y. With respect to estimation of slope and intercept and prediction of Y, agreement between Monte Carlo results and large-sample theory was very good for sample sizes of 100, and fair to good for sample sizes of 20. The procedures and error measures are illustrated with two geologic examples. 相似文献
29.
Spatial and temporal variability of Holocene temperature in the North Atlantic region 总被引:1,自引:0,他引:1
The early Holocene climate of the North Atlantic region was influenced by two boundary conditions that were fundamentally different from the present: the presence of the decaying Laurentide Ice Sheet (LIS) and higher than present summer solar insolation. In order to assess spatial and temporal patterns of Holocene climate evolution across this region, we collated quantitative paleotemperature records at sub-millennial resolution and synthesized their temporal variability using principal components analysis (PCA). The analysis reveals considerable spatial variability, most notably in the time-transgressive expression of the Holocene thermal maximum (HTM). Most of the region, but especially areas peripheral to the Labrador Sea and hence closest to the locus of LIS disintegration, experienced maximum Holocene temperatures that lagged peak summer insolation by 1000-3000 years. Many sites from the northeastern North Atlantic sector, including the Nordic Seas and Scandinavia, either warmed in phase with maximum summer insolation (11,000-9000 years ago) or were less strongly lagged than the Baffin Bay-Labrador Sea region. These spatially complex patterns of Holocene climate development, which are defined by the PCA, resulted from the interplay between final decay of the LIS and solar insolation forcing. 相似文献
30.
In this study, hydrogeologic and hydrochemical information from the Mersin-Erdemli groundwater system were integrated and
used to determine the main factors and mechanisms controlling the chemistry of groundwaters in the area and anthropogenic
factors presently affecting them. The PHREEQC geochemical modeling demonstrated that relatively few phases are required to
derive water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area
fall into four categories: (1) silicate weathering reactions; (2) dissolution of salts; (3) precipitation of calcite, amorphous
silica and kaolinite; (4) ion exchange. As determined by multivariate statistical analysis, anthropogenic factors show seasonality
in the area where most contaminated waters related to fertilizer and fungicide applications that occur during early summer
season. 相似文献