全文获取类型
收费全文 | 844篇 |
免费 | 20篇 |
国内免费 | 37篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 42篇 |
地球物理 | 208篇 |
地质学 | 315篇 |
海洋学 | 78篇 |
天文学 | 97篇 |
综合类 | 3篇 |
自然地理 | 136篇 |
出版年
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 21篇 |
2017年 | 19篇 |
2016年 | 22篇 |
2015年 | 12篇 |
2014年 | 42篇 |
2013年 | 53篇 |
2012年 | 21篇 |
2011年 | 57篇 |
2010年 | 32篇 |
2009年 | 48篇 |
2008年 | 50篇 |
2007年 | 32篇 |
2006年 | 22篇 |
2005年 | 33篇 |
2004年 | 25篇 |
2003年 | 31篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 20篇 |
1995年 | 11篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有901条查询结果,搜索用时 15 毫秒
31.
32.
Impact of the Montreal protocol and its amendments on the rate of change of global radiative forcing
Increases in chlorinated and brominated halocarbons are believed to be responsible for the depletion of stratospheric ozone observed over much of the globe in the past decade or so. Ozone depletion is in turn believed to lead to a negative radiative forcing, tending to cool the stratosphere and the surface. We show that the increasing atmospheric concentrations of ozone-depleting halocarbons and onset of related ozone depletion likely led to a negative forcing of the climate system in the 1980s that slowed significantly the rate of change of total anthropogenic radiative forcing due to the combined effect of all greenhouse gases over that decade. Within the next decade, emissions of these halocarbons are expected to rapidly decrease, with corresponding impacts on ozone and radiative forcing. As the emissions of ozone-depleting gases are reduced and eventually phased out, the rate of ozone depletion is expected to decrease and eventually reverse. All other things being equal, we show that the change from deepening ozone depletion in the 1980s to ozone increases in the future should lead to a pronounced increase in the decadal rate of change of anthropogenic greenhouse forcing of the next few decades, perhaps to levels unprecedented in this century. 相似文献
33.
David L. Huston Jorge M. R. S. Relvas J. Bruce Gemmell Susan Drieberg 《Mineralium Deposita》2011,46(5-6):473-507
Assessment of geological, geochemical and isotopic data indicates that a significant subgroup of volcanic-hosted massive sulphide (VHMS) deposits has a major or dominant magmatic?Chydrothermal source of ore fluids and metals. This group, which is typically characterised by high Cu and Au grades, includes deposits such as those in the Neoarchean Doyon-Bousquet-LaRonde and Cambrian Mount Lyell districts. These deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones. In many of these deposits, ??34Ssulphide is low, with a major population below ?3??; ??34Ssulphate differs from coexisting seawater and ??34Ssulphate?Csulphide????20?C30??. These characteristics are interpreted as the consequence of disproportionation of magmatic SO2 as magmatic?Chydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic?Chydrothermal contribution. Other characteristics that we consider diagnostic of significant magmatic?Chydrothermal input into VHMS ore fluids include uniformly high (>3 times modern seawater values) salinities or very 18O-enriched (??18O?>?5??) ore fluids. We do not consider other criteria [e.g. variable salinity, moderately high ??18Ofluid (2?C5??), ??34Ssulphide near 0??, metal assemblages or a spatial association with porphyry Cu or other clearly magmatic-hydrothermal deposits] that have been used previously to advocate significant magmatic?Chydrothermal contributions to be diagnostic as they can be produced by non-magmatic processes known to occur in VHMS mineral systems. However, in general, a small magmatic?Chydrothermal contribution cannot be excluded in most VHMS systems considered. Conclusive data that imply minimal magmatic?Chydrothermal contributions are only available in the Paleoarchean Panorama district where coeval seawater-dominated and magmatic?Chydrothermal systems appear to have been physically separated. This district, which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages, is typical of many VHMS deposits around the world, suggesting that for ??garden variety?? VHMS deposits, a significant magmatic?Chydrothermal contribution is not required. Other than deposits associated with advanced argillic alteration assemblages, the only deposit for which we ascribe a major magmatic?Chydrothermal contribution is the Devonian Neves Corvo deposit. This deposit differs from other deposits in the Iberian Pyrite Belt and around the world in being extremely Sn-rich, with the Sn closely associated with Cu and in having formed from high 18O-rich fluids (??18Ofluid ??8.5??). We consider these characteristics, particularly the last, as diagnostic of a significant magmatic hydrothermal contribution. Our analysis indicates that two subgroups of VHMS deposits have a major magmatic?Chydrothermal contribution: Cu/Au-rich deposits with aluminous alteration assemblages and reduced, very Sn-rich deposits in which Sn was introduced in a high-temperature ore assemblage. Comparison with ??normal?? VHMS deposits suggests that these subgroups of VHMS deposits may form in specialised tectonic environments. The Cu/Au-rich deposits appear to form adjacent to magmatic arcs, an environment conducive to the generation of hydrous, oxidised melts by melting metasomatised mantle in the wedge above the subducting slab. This contrasts with the back-arc setting of ??normal?? VHMS deposits in which relatively dry granites (In this contribution, we use the term granite sensu latto) formed by decompression melting drive seawater-dominated hydrothermal circulation. The tectonic setting of highly Sn-rich VHMS deposits such as Neves Corvo is less clear; however, thick continental crust below the ore-hosting basin may be critical, as it is in other Sn deposits. 相似文献
34.
35.
SUN Bainian XIAO Liang XIE Sanping DENG Shenghui WANG Yongdong JIA Hui Susan?Turner 《《地质学报》英文版》2007,81(6):931-939
A better theoretical and practical understanding of the linkage between paleo-CO2 and climate during geological history is important to enhance the sustainable development of modern human society. Development in plant physiology since the 1980s has led to the realization that fossil plants can serve as a proxy for paleoatmosphere and paleobiosphere. As a relict gymnosperm with evolutionary stasis, Ginkgo is well suited for paleoenvironmental reconstruction. This paper analyzes fossil Ginkgo species from integrated strata in the north of China using anatomic data of plant physiology. Using stomatal parameters, a trend for the paleo-CO2 level during the Early-Middle Jurassic and the Early Cretaceous was obtained, which is consistent with the estimates by GEOCARB. The trend is also similar to that of Mean Global Surface Temperature in geological time. Compared with three other atmospheric CO2 concentration parameters, the trend of paleo-CO2 level based on the stomatal parameter of the fossil Ginkgo specimens from three contiguous strata is more exact. 相似文献
36.
37.
William D. Robertson James W. Roy Susan J. Brown Dale R. Van Stempvoort Greg Bickerton 《Ground water》2014,52(1):63-70
Monitoring of a well‐defined septic system groundwater plume and groundwater discharging to two urban streams located in southern Ontario, Canada, provided evidence of natural attenuation of background low level (ng/L) perchlorate (ClO4?) under denitrifying conditions in the field. The septic system site at Long Point contains ClO4? from a mix of waste water, atmospheric deposition, and periodic use of fireworks, while the nitrate plume indicates active denitrification. Plume nitrate (NO3?‐N) concentrations of up to 103 mg/L declined with depth and downgradient of the tile bed due to denitrification and anammox activity, and the plume was almost completely denitrified beyond 35 m from the tile bed. The ClO4? natural attenuation occurs at the site only when NO3?‐N concentrations are <0.3 mg/L, after which ClO4? concentrations decline abruptly from 187 ± 202 to 11 ± 15 ng/L. A similar pattern between NO3?‐N and ClO4? was found in groundwater discharging to the two urban streams. These findings suggest that natural attenuation (i.e., biodegradation) of ClO4? may be commonplace in denitrified aquifers with appropriate electron donors present, and thus, should be considered as a remediation option for ClO4? contaminated groundwater. 相似文献
38.
Plagiogranites as late-stage immiscible liquids in ophiolite and mid-ocean ridge suites: An experimental study 总被引:1,自引:0,他引:1
Chemical studies of two ophiolite suites and of selected mid-oceanic rift (MOR) regions indicate the presence of certain magmatic compositions: basalt, Fe-enriched basalt, and sodium granite (plagiogranite). There is a notable lack of evidence for melts of intermediate composition (i.e. 50–60 wt.% SiO2). To determine possible relationships between basic rocks (basalts and gabbros) and acidic rocks (plagiogranites) a primitive basalt was fractionated at low pressure, under anhydrous conditions, and at different oxygen fugacities near the iron-wustite buffer and slightly above the quartz-fayalite-magnetite buffer. Samples of this basalt were taken to slightly above liquidus temperatures and then cooled at rates ranging from 1 to 2°C/hr. A liquid line of descent characterized by an Fe enrichment was delineated by quenching these experiments from a final temperature in the range of 1200 to 1000°C and analyzing the residual liquid (glass). After 95% crystallization of olivine, plagioclase, calcium pyroxene, and ilmenite, the residual liquid was an Fe-enriched basalt. This Fe-enriched basalt became immiscible at a temperature of about 1010°C. The immiscible phases produced were a more Fe-enriched basaltic liquid and a granitic liquid. The granitic liquid is similar in composition to the naturally occurring plagiogranites found in small volumes in ophiolites and in certain MOR regions. It is therefore concluded that silicate liquid immiscibility could be the petrogenetic process responsible for producing plagiogranite in some MOR regions and in some ophiolites. On the other hand, plagiogranites in ophiolites and MOR rock suites having andesitic and dacitic composition rocks may have evolved under conditions more closely approximating equilibrium crystallization and/or they may have evolved at high water pressures. The available experimental data suggest that amphibole would crystallize early and yield SiO2-enriched liquids at depths greater than 4.5 km for PH2O's in the range 0.6–1.0 Ptotal.The major problem in interpreting any of the natural plagiogranites as products of silicate liquid immiscibility is the fact that neither the Fe-enriched conjugate liquid or its crystalline equivalent has been described in the ophiolite or MOR literature. The identification of this Fe-rich conjugate magma is essential in any rock suite if a completely convincing case for silicate liquid immiscibility is to be made. 相似文献
39.
A. Rob MacKenzie Stefan Krause Kris M. Hart Richard M. Thomas Phillip J. Blaen R. Liz Hamilton Giulio Curioni Susan E. Quick Angeliki Kourmouli David M. Hannah Sophie A. Comer-Warner Nicolai Brekenfeld Sami Ullah Malcolm C. Press 《水文研究》2021,35(3):e14096
The ecosystem services provided by forests modulate runoff generation processes, nutrient cycling and water and energy exchange between soils, vegetation and atmosphere. Increasing atmospheric CO2 affects many linked aspects of forest and catchment function in ways we do not adequately understand. Global levels of atmospheric CO2 will be around 40% higher in 2050 than current levels, yet estimates of how water and solute fluxes in forested catchments will respond to increased CO2 are highly uncertain. The Free Air CO2 Enrichment (FACE) facility of the University of Birmingham's Institute of Forest Research (BIFoR) is the only FACE in mature deciduous forest. The site specializes in fundamental studies of the response of whole ecosystem patches of mature, deciduous, temperate woodland to elevated CO2 (eCO2). Here, we describe a dataset of hydrological parameters – seven weather parameters at each of three heights and four locations, shallow soil moisture and temperature, stream hydrology and CO2 enrichment – retrieved at high frequency from the BIFoR FACE catchment. 相似文献
40.
The present study examines the benthos within western inner Swansea Bay (Wales, UK), for the period before, during and immediately after the cessation of a major, sewage discharge from Mumbles Head. There have been significant improvements in seawater quality and changes in the species composition of the benthic communities following the cessation of the sewage discharge. There has been an increase in the diversity of deposit feeders, especially the amphipods, and a decrease in the diversity of the filter feeders, especially the polychaetes. Changes are not attributable either to sediment organic matter content or to gross changes in sediment type, but are related to the significant reduction in suspended particulate organic material and sewage contaminants discharged to the Bay. A recovery model has been proposed to describe how soft sediment benthic communities in a shallow, sublittoral, high tidal energy environment respond to the abrupt cessation of a major sewage discharge. 相似文献