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991.
Leistner G. M. E. 《GeoJournal》1981,2(2):85-93
It is widely held that the large majority of African countries are too small in terms of population and purchasing power to allow meaningful and rapid economic development to take place within the constraints of their domestic economies. Sub-regional groupings of states are called for in order to overcome the drawbacks of small size. Many attempt at establishing larger economic unions in Africa have failed. Particular interest therefore attaches to the southern African sub-region where South Africa, as the only industrial power south of the Sahara, functions as a powerhouse for neighbouring as well as more distant economies. The article provides a factual sketch of existing economic ties (infrastructure, trade, labour, tourism, finance and technology). Attention is paid to South Africa's efforts to create a constellation of states, and also to to the counter-measures of nine neighbouring states. 相似文献
992.
Hamidreza Ramazi Mohammad Reza Hossein Nejad Aenollah Azizzadeh Firoozi 《Journal of the Geological Society of India》2009,74(2):260-266
This paper is devoted to application of SP, resistivity and mise-a-la-masse method in Khenadarreh (Arak, Iran) graphite deposit
exploration. Mise-a-la-masse method is one of the main geophysical exploration methods used to investigate conductive bodies
with outcrops on the surface or in exploratory pits. By integrating mise-a-la-masse results with other geoelectrical methods,
such as self-potential and resistivity surveys, useful results can be acquired. Powerful survey design, data processing and
interpretation methods can make geoelectrical surveying results more reliable. Here, we applied integrated geoelectrical methods
to explore the Khenadarreh-bala graphite deposit in the Sarband region of the Markazi province, Iran. We present a new and
simple method for processing and interpreting mise-a-la-masse data, which corrects for the effect of distance from the current
electrode in the conductive body. After correction, the residual potential values corresponded with the SP results and the
apparent resistivity pseudosections. The geophysical results were confirmed by drill holes in the study area. 相似文献
993.
Holocene environmental history in the Tarim Basin and the Taklimakan Desert is known mainly from isolated eolian and lacustrine
deposits and remain puzzling. Here we present an adequately preserved loess section, covering the past 5000 years, at a highland
(2,850 m a.s.l) on the northern slope of Kunlun Mountains. Pollen preserved in the section reveal a drying trend with significant
moisture fluctuations around 3000–2600 cal yr BP and 1800 cal yr BP at the study site. Comparing the pollen, grain size from
the same section provides a different scene occurred in the Tarim basin and the Taklimakan desert. Comparison of grain size
to A/C ration of pollen suggests that active sand southward shifting in south margin of the desert is coincident with increasing
moisture condition at the section locality, implying a casual link. This moisture pattern occurred at the upper and lower
elevation of the slope is best explained by the vertical variation of local precipitation along the slope. 相似文献
994.
Since the launch of the first satellite in 1972, ecologists have been equipped with new tools to address the degradation of
tropical forests, previously limited by field-based methods. This article is a review of the state of remote sensing technology
in characterizing the degradation of tropical forest. The factors responsible for the structural and functional degradation
of the tropical forest and its likely impacts are described in view of generating remote sensing based inputs. In order to
assess the degradation and utility of geo-informatics tools, 32 parameters are identified. The research developments at different
levels of information extraction from the historic to recent periods are elaborated, and future challenges are predicted.
The article concludes that an additional momentum of research is required to answer many unresolved questions of tropical
forest degradation. 相似文献
995.
Air–water gas exchange is an important process in aquatic systems, including tidal rivers and estuaries. While there are now
reliable and routine methods for determining gas exchange over a range of temporal and spatial scales in the ocean and these
measurements have resulted in widely used wind speed parameterizations to calculate air–sea gas exchange, the same has not
been true for coastal inland waterways. Some studies have suggested that this difference is methodological, while others point
to the existence of additional drivers for gas exchange besides wind in rivers and estuaries. Here, we present gas transfer
velocities measured in the tidal Hudson River with a method widely used in oceanic studies, the 3He/SF6 dual tracer technique. Airside and waterside forcings were determined with an anemometer and an acoustic Doppler current
profiler, respectively. The results confirm that wind is the dominant driver of gas exchange in the tidal Hudson River, with
negligible contribution from bottom-generated turbulence. Furthermore, a parameterization between wind speed and gas exchange
developed for the ocean is able to predict gas exchange in this environment with high accuracy. It is hoped that by transferring
methodology used in oceanic studies to rivers and estuaries, robust data can be obtained that will eventually allow development
of widely applicable relationships between easily measured environmental variables and gas exchange in tidal inland waters. 相似文献
996.
Numerous Fe–Cu deposits are hosted in the late Paleoproterozoic Dongchuan and Dahongshan Groups in the Kangdian region, SW
China. The Dongchuan Group is composed of siltstone, slate, and dolostone with minor volcanic rocks, whereas the Dahongshan
Group has undergone lower amphibolite facies metamorphism and consists of quartz mica-schist, albitite, quartzite, marble
and amphibolite with local migmatite. Deposits in the Dongchuan Group are commonly localized in the cores of anticlines, in
fault bends and intersections, and at lithological contacts. Orebodies are closely associated with breccias, which are locally
derived from the host rocks. Fe-oxides (magnetite and/or hematite) and Cu-sulfides (chalcopyrite, bornite) form disseminated,
vein-like and massive ores, and typically fill open spaces in the host rocks. The deposits have extensive albite alteration
and local K-feldspar alteration overprinted by quartz, carbonate, sericite and chlorite. Deposits in the Dahongshan Group
have orebodies sub-parellel to stratification and show crude stratal partitioning of metals. Fe-oxide ores occur as massive
and/or banded replacements within the breccia pipes, whereas Cu-sulfide ores occur predominantly as disseminations and veinlets
within mica schists and massive magnetite ores. Ore textures suggest that Cu-sulfides formed somewhat later than Fe-oxides,
but are possibly within the same mineralization event. Both ore minerals predated regional Neoproterozoic metamorphism. Both
orebodies and host rocks have undergone extensive alteration of albite, scapolite, amphibole, biotite, sericite and chlorite.
Silica and carbonate alterations are also widespread. Ore-hosting strata have a LA-ICP-MS zircon U–Pb age of 1681 ± 13 Ma,
and a dolerite dyke cutting the Fe-oxide orebodies has an age of 1659 ± 16 Ma. Thus, the mineralization age of the Dahongshan
deposit is constrained at between the two. All ores from the two groups have high Fe and low Ti, with variable Cu contents.
Locally they are rich in Mo, Co, V, and REE, but all are poor in Pb and Zn. Sulfides from the Fe–Cu deposits have δ34S values mostly in the range of +2 to +6 per mil, suggesting a mix of several sources due to large-scale leaching of the strata
with the involvement of evaporites. Isotopic dating and field relationships suggest that these deposits formed in the late
Paleoproterozoic. Ore textures, mineralogy and alteration characteristics are typical of IOCG-type deposits and thus define
a major IOCG metallogenic province with significant implications for future exploration. 相似文献
997.
998.
Neo-rural populations and their relations with local decision makers in rural Québec: collaboration or conflict? 总被引:1,自引:0,他引:1
The socio-demographic recomposition of the countryside is affecting local interactions and power relations. Understanding these relationships remains a challenge, as the studies to date are often limited to conflicts between neo-rural populations (newcomers) and long-time country residents over partial issues, without including decision makers. To go beyond this conflictual and fragmentary perspective, the objective of this article is to present an overall picture of both cooperative and oppositional relations between four groups, namely, newcomers, long-time rural residents, leaders of local organizations and municipal officials, in regard to all the issues that concern them. The data are based on interviews with these various actors in two contrasting rural areas of Québec (Canada). After looking at the newcomers’ mixed assessment of their participation in community life, we concentrate on areas of collaboration and/or conflict between all the actors regarding demographic, economic, sociocultural, political, environmental and agricultural issues. Three main trends emerge, revealing unexpected ways of interacting, complex power relations and antagonistic conceptions of rural spaces and their future development. 相似文献
999.
In the paper, a novel inversion approach is used for the solution of the problem of factor analysis. The float-encoded genetic algorithm as a global optimization method is implemented to extract factor variables using open-hole logging data. The suggested statistical workflow is used to give a reliable estimate for not only the factors but also the related petrophysical properties in hydrocarbon formations. In the first step, the factor loadings and scores are estimated by Jöreskog’s fast approximate method, which are gradually improved by the genetic algorithm. The forward problem is solved to calculate wireline logs directly from the factor scores. In each generation, the observed and calculated well logs are compared to update the factor population. During the genetic algorithm run, the average fitness of factor populations is maximized to give the best fit between the observed and theoretical data. By using the empirical relation between the first factor and formation shaliness, the shale volume is estimated along the borehole. Permeability as a derived quantity also correlates with the first factor, which allows its determination from an independent source. The estimation results agree well with those of independent deterministic modeling and core measurements. Case studies from Hungary and the USA demonstrate the feasibility of the global optimization based factor analysis, which provides a useful tool for improved reservoir characterization. 相似文献
1000.