全文获取类型
收费全文 | 29062篇 |
免费 | 1269篇 |
国内免费 | 2084篇 |
专业分类
测绘学 | 1829篇 |
大气科学 | 2794篇 |
地球物理 | 5756篇 |
地质学 | 14190篇 |
海洋学 | 1596篇 |
天文学 | 1916篇 |
综合类 | 2522篇 |
自然地理 | 1812篇 |
出版年
2024年 | 20篇 |
2023年 | 69篇 |
2022年 | 209篇 |
2021年 | 260篇 |
2020年 | 193篇 |
2019年 | 266篇 |
2018年 | 4997篇 |
2017年 | 4248篇 |
2016年 | 2811篇 |
2015年 | 485篇 |
2014年 | 373篇 |
2013年 | 346篇 |
2012年 | 1309篇 |
2011年 | 3048篇 |
2010年 | 2315篇 |
2009年 | 2591篇 |
2008年 | 2153篇 |
2007年 | 2587篇 |
2006年 | 286篇 |
2005年 | 420篇 |
2004年 | 581篇 |
2003年 | 590篇 |
2002年 | 468篇 |
2001年 | 258篇 |
2000年 | 235篇 |
1999年 | 202篇 |
1998年 | 186篇 |
1997年 | 148篇 |
1996年 | 123篇 |
1995年 | 86篇 |
1994年 | 94篇 |
1993年 | 88篇 |
1992年 | 67篇 |
1991年 | 52篇 |
1990年 | 42篇 |
1989年 | 30篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 26篇 |
1980年 | 22篇 |
1976年 | 6篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1958年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
291.
292.
遥感技术在煤炭资源开发状况监督管理中的应用研究 总被引:1,自引:0,他引:1
利用高分辨率遥感图象可以快速查明煤炭资源开发状况以及煤炭资源开发的合法性(界内开采、界外开采、越界开采)等,对煤矿安全生产及维护矿业秩序具有重要意义。以我国中部某煤炭开采密集区为试验区,选择不同分辨率的遥感数据,从矿山铺助设施、道路、矿堆、矸石的特征出发,进行矿山开采状况遥感解译;以地理信息系统技术(GIS)为支撑实现采矿权数据、规划数据图层与遥感专题数据的叠加分析和相关分析,判断非法与越界矿山,评价矿产资源开发与保护规划执行情况。 相似文献
293.
An iterative inverse method, the sequential self-calibration method, is developed for mapping spatial distribution of a hydraulic
conductivity field by conditioning on nonreactive tracer breakthrough curves. A streamline-based, semi-analytical simulator
is adopted to simulate solute transport in a heterogeneous aquifer. The simulation is used as the forward modeling step. In
this study, the hydraulic conductivity is assumed to be a deterministic or random variable. Within the framework of the streamline-based
simulator, the efficient semi-analytical method is used to calculate sensitivity coefficients of the solute concentration
with respect to the hydraulic conductivity variation. The calculated sensitivities account for spatial correlations between
the solute concentration and parameters. The performance of the inverse method is assessed by two synthetic tracer tests conducted
in an aquifer with a distinct spatial pattern of heterogeneity. The study results indicate that the developed iterative inverse
method is able to identify and reproduce the large-scale heterogeneity pattern of the aquifer given appropriate observation
wells in these synthetic cases. 相似文献
294.
The Tau Model for Data Redundancy and Information Combination in Earth Sciences: Theory and Application 总被引:3,自引:0,他引:3
Sunderrajan Krishnan 《Mathematical Geosciences》2008,40(6):705-727
Many decision-making processes in the Earth sciences require the combination of multiple data originating from diverse sources.
These data are often indirect and uncertain, and their combination would call for a probabilistic approach. These data are
also partially redundant with each other or with all others taken jointly. This overlap in information arises due to a variety
of reasons—because the data arises from the same geology, because they originate from the same location or the same measurement
device, etc. The proposed tau model combines partially redundant data, each taking the form of a prior probability for the
event being assessed to occur given that single datum. The parameters of that tau model measure the additional contribution
brought by any single datum over that of all previously considered data; they are data sequence-dependent and also data value-dependent.
Data redundancy depends on the sequence in which the data is considered and also on the data values themselves. However, for
a given sequence, averaging the tau model parameters over all possible data values leads to exact analytical expressions and
corresponding approximations and inference avenues. Information on multiple-point connectivity of permeability arrives from
core data, well-test data and seismic data which are defined over varying supports with complex redundancy between these information
sources. In order to compute these tau weights for determining connectivity, one needs a model of data redundancy, here expressed
as a vectorial training image (Ti) constructed using a prior conceptual knowledge of geology and the physics of data measurement.
From such a vectorial Ti, the tau weights can be computed exactly. Neglecting data redundancy leads to an over-compounding
of individual data information and the possible risk of making extreme decisions. 相似文献
295.
Fu-Ping Liu Rui-Zhong Li Jin-yao Li Hui-Guo Chen Chang-Chun Yang 《Mathematical Geosciences》2008,40(7):813-829
The group time delay (GTD) formulae of quasi-total reflection of inhomogeneous P-polarized electromagnetic waves (P-PEW, whose electric field parallels to the plane of incidence), caused by the Goos–Hänchen effect, is derived by the phase shift of the wave. A numerical example where the frequency equals to 1 GHz is given. The curves of calculating results show that there are three discontinuous points at the critical angle of phase shift vector, the critical angle of attenuation vector and 90○. When the angle of incidence is equal to one of these three angles, the GTD will become infinite, and the electromagnetic wave will propagate along the interface. The GTD will be very large, when the angle of incidence is close to one of these three angles. The results indicate that there is an important relationship between the two critical angles and the conductivity and permittivity of the two strata, and that the GTD has an important relationship with the angle of incidence. These results can be used to determine the lithology of the strata and to delimit the interfaces of strata more effectively. It is suggested that this research may prove useful in electromagnetic logging analysis and, perhaps, in the design of logging instruments. 相似文献
296.
Rorik A. Peterson 《Mathematical Geosciences》2008,40(3):277-298
Differential frost heave is often implicated in the formation of patterned ground in regions subject to recurrent freezing
and thawing. A linear stability analysis (LSA) indicates that a continuum model of frost heave is linearly unstable under
typical natural freezing conditions of silty-clay soils. A two-dimensional non-linear numerical analysis corroborates the
frozen time LSA results, and also indicates the importance of non-linear and time-dependent terms that ultimately lead to
a preferred mode, which the LSA fails to predict. Instability of the one-dimensional solution occurs at shallow freezing depths
and near-zero surface loads when positive perturbations in the ice content at the freezing front lead to a concomitant increase
in thermomolecular pressure and upward ice velocity. Differential frost heave can then occur because of the increased heat
flux from the perturbed surfaces. A three-dimensional model using random initial surface perturbations indicates that regular
surface patterns will evolve with a length scale in the order of 2–4 meters, which corresponds quite closely with naturally-occurring
non-sorted patterned ground. 相似文献
297.
Non-Linear Theory and Power-Law Models for Information Integration and Mineral Resources Quantitative Assessments 总被引:7,自引:0,他引:7
Qiuming Cheng 《Mathematical Geosciences》2008,40(5):503-532
Singular physical or chemical processes may result in anomalous amounts of energy release or mass accumulation that, generally,
are confined to narrow intervals in space or time. Singularity is a property of different types of non-linear natural processes
including cloud formation, rainfall, hurricanes, flooding, landslides, earthquakes, wildfires, and mineralization. The end
products of these non-linear processes can be modeled as fractals or multifractals. Hydrothermal processes in the Earth’s
crust can result in ore deposits characterized by high concentrations of metals with fractal or multifractal properties. Here
we show that the non-linear properties of the end products of singular mineralization processes can be applied for prediction
of undiscovered mineral deposits and for quantitative mineral resource assessment, whether for mineral exploration or for
regional, national and global planning for mineral resource utilization. In addition to the general theory and framework for
the non-linear mineral resources assessment, this paper focuses on several power-law models proposed for characterizing non-linear
properties of mineralization and for geoinformation extraction and integration. The theories, methods, and computer system
discussed in this paper were validated using a case study dealing with hydrothermal Au mineral potential in southern Nova
Scotia, Canada. 相似文献
298.
Inversely-Mapped Analytical Solutions for Flow Patterns around and within Inclined Elliptic Inclusions in Fluid-Saturated Rocks 总被引:1,自引:0,他引:1
Chongbin Zhao Bruce E. Hobbs Alison Ord Shenglin Peng Liangming Liu 《Mathematical Geosciences》2008,40(2):179-197
In this paper, an inverse mapping is used to transform the previously-derived analytical solutions from a local elliptical
coordinate system into a conventional Cartesian coordinate system. This enables a complete set of exact analytical solutions
to be derived rigorously for the pore-fluid velocity, stream function, and excess pore-fluid pressure around and within buried
inclined elliptic inclusions in pore-fluid-saturated porous rocks. To maximize the application range of the derived analytical
solutions, the focal distance of an ellipse is used to represent the size of the ellipse, while the length ratio of the long
axis to the short one is used to represent the geometrical shape of the ellipse. Since the present analytical solutions are
expressed in a conventional Cartesian coordinate system, it is convenient to investigate, both qualitatively and quantitatively,
the distribution patterns of the pore-fluid flow and excess pressure around and within many different families of buried inclined
elliptic inclusions. The major advantage in using the present analytical solution is that they can be conveniently computed
in a global Cartesian coordinate system, which is widely used in many scientific and engineering computations. As an application
example, the present analytical solutions have been used to investigate how the dip angle of an inclined elliptic inclusion
affects the distribution patterns of the pore-fluid flow and excess pore-fluid pressure when the permeability ratio of the
elliptic inclusion is of finite but nonzero values. 相似文献
299.
300.
西江主洼是珠江口盆地一个低勘探程度洼陷,油气差异聚集特征明显,但其机理不清。本文在断陷盆地油气成藏理论指导下,利用研究区地质、地球物理和地球化学等资料,开展了烃源岩、断盖组合、储集体系和运聚模式等方面的研究。结果表明,裂陷期沉降、沉积中心有序迁移,造成主力烃源岩自东向西由文四段迁移至文三段、文一+二段,控制东、西部油气差异分布。恩平组区域性泥岩发育且晚期断裂缺乏,导致油气纵向上更易聚集于下构造层;区域泥岩减薄尖灭或晚期断裂切开盖层的区域,上构造层有一定油气分布。"源-汇"类型从宏观上控制储层优劣,影响下构造层油气富集程度;"仓储"运移是控制上构造层油气规模聚集的主要模式。下构造层古近系应作为重点部署方向,东部围绕文四段、西部围绕文三段、文一+二段烃源岩构成的含油气系统展开;上构造层勘探需关注珠海组,在隆起周边寻找具备"仓储"运移模式的有利区带。 相似文献