全文获取类型
收费全文 | 417篇 |
免费 | 11篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 36篇 |
地球物理 | 90篇 |
地质学 | 151篇 |
海洋学 | 42篇 |
天文学 | 86篇 |
综合类 | 1篇 |
自然地理 | 23篇 |
出版年
2022年 | 5篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 16篇 |
2012年 | 14篇 |
2011年 | 22篇 |
2010年 | 17篇 |
2009年 | 22篇 |
2008年 | 17篇 |
2007年 | 21篇 |
2006年 | 10篇 |
2005年 | 12篇 |
2004年 | 21篇 |
2003年 | 18篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1973年 | 6篇 |
1971年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有434条查询结果,搜索用时 0 毫秒
11.
Morgan Gopnik Clare Fieseler Laura Cantral Kate McClellan Linwood Pendleton Larry Crowder 《Marine Policy》2012
From 2009 to 2011, marine spatial planning (MSP) rapidly gained visibility in the United States as a promising ocean management tool. A few small-scale planning efforts were completed in state waters, and the Obama Administration proposed a framework for large-scale regional MSP throughout the U.S. Exclusive Economic Zone. During that same time period, the authors engaged a variety of U.S ocean stakeholders in a series of dialogs with several goals: to share information about what MSP is or could be, to hear stakeholder views and concerns about MSP, and to foster better understanding between those who depend on ocean resources for their livelihood and ocean conservation advocates. The stakeholder meetings were supplemented with several rounds of in-depth interviews and a survey. Despite some predictable areas of conflict, project participants agreed on a number of issues related to stakeholder engagement in MSP: all felt strongly that government planners need to engage outsiders earlier, more often, more meaningfully, and through an open and transparent process. Equally important, the project affirmed the value of bringing unlike parties together at the earliest opportunity to learn, talk, and listen to others with whom they rarely engage. 相似文献
12.
Jeffrey E. Moore Bryan P. Wallace Rebecca L. Lewison Ramúnas Žydelis Tara M. Cox Larry B. Crowder 《Marine Policy》2009
This paper reviews the available information (observer programs, estimates, statutes, regulations) for bycatch of marine mammals, sea turtles, and seabirds in fisheries of the United States. Goals of the review were to evaluate the state of knowledge of bycatch and the role of existing protective legislation in shaping bycatch management for different taxa. Pressing issues are identified, as well as knowledge gaps and policy limitations that hinder multi-species bycatch reduction. The USA has made important progress toward reducing bycatch in its fisheries, but the efficacy of its management has been limited somewhat by a focus on taxon- and fishery-specific regulation and the lack of consistent mandate across taxa for taking a cumulative perspective on bycatch. Applying consistent criteria across taxa for setting bycatch limits (e.g., extending the approach used for marine mammals to sea turtles and seabirds) would be the first step in a multi-species approach to bycatch reduction. A population-based multi-species multi-gear approach to bycatch would help identify priority areas where resources are needed most and can be used most effectively. 相似文献
13.
Patterns and controls of surface sediment distribution: west-central Florida inner shelf 总被引:2,自引:0,他引:2
Gregg R. Brooks Larry J. Doyle Richard A. Davis Nancy T. DeWitt Beau C. Suthard 《Marine Geology》2003,200(1-4):307-324
The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems. 相似文献
14.
Using a Markov chain model, we consider the regolith growth on a small body in orbit around Saturn, subject to meteoritic bombardment, and assuming all impact ejecta are re-collected. We calculate the growth of regolith and the fractional pollution, assuming an initial pure ice body and amorphous carbon as a pollutant. We extend the meteorite flux of Cuzzi and Estrada (Cuzzi, J., Estrada, P. [1998]. Icarus 132, 1-35) to larger sizes to consider the effect of disruption of the moonlet on other moonlets in the ensemble. This is a relatively small effect, completely negligible for moonlets of 1 m radius. For the given impact model, fractional pollution reaches 22% for 1 m bodies, but only 3% for 10 m bodies, 1.7% for 20 m bodies, and 1% for 30 m bodies after 4 byr. By considering an ensemble of moonlets, which have identical cross-sections for releasing and capturing ejecta, this analysis can be extended to a model of particles in Saturn’s rings, where the calculated spectra can be compared to observed ring spectra. The measured spectral reflectance of Saturn’s rings from Cassini observations therefore constrains the size and age of the ring particles. The comparison between 1 m, 10 m, 20 m, and 30 m particles confirms that for larger ring mass, the current rings would be less polluted; for the largest particles, we expect negligible changes in the UV spectrum after 4 byr of meteoritic bombardment. We consider two end members for mixing of the meteoritic material: areal and intimate. Given the uncertainties in the actual mixing of the meteoritic infall and in its composition (as a worst case, we assume the meteoritic material is 100% amorphous carbon, intimately mixed) initially pure ice 30 m ring particles would darken after 4 byr of exposure by 15%. 相似文献
15.
Remote sensing is a geographic analysis tool capable of producing large quantities of data in the spectral, temporal and spatial domains. Techniques for automating the image analysis process would be advanced by the inclusion of artificial intelligence techniques in the design of image processing systems. The remote sensing application which show promise for successful implementation of artificial intelligence techniques are intelligent onboard processing, advanced database interrogation, and the automated analysis of multispectral imagery. 相似文献
16.
Micro computers have been demonstrated to be a most valuable, cost-effective means of long- and short-term data acquisition for ground water investigations and installations. A system can readily be assembled for the cost of labor saved in the field, or for the same cost as other conventional instruments, which perform only a fraction of the functions of the computer system
Documented in this article are systems which have been developed and used for simultaneous monitoring of several wells during aquifer tests, and systems installed for long-term monitoring of piezometric surface fluctuations. Both systems can be contained in a small suitcase or insulated cooler. Specific features of the systems include multiple channel capacity, one-month maintenance period, variable computer controlled reading intervals, magnetic tape data storage, data reduction and analysis capabilities while maintaining monitoring, graphic display of time and measurements, hard copy capability and barometric pressure change corrections.
Other applications are examined for the complete control of pumping tests, including pumping rate; in situ permeability tests; monitoring changes; and even strain. The pressure transducer system may also be applied for river gauging and current measurement. 相似文献
Documented in this article are systems which have been developed and used for simultaneous monitoring of several wells during aquifer tests, and systems installed for long-term monitoring of piezometric surface fluctuations. Both systems can be contained in a small suitcase or insulated cooler. Specific features of the systems include multiple channel capacity, one-month maintenance period, variable computer controlled reading intervals, magnetic tape data storage, data reduction and analysis capabilities while maintaining monitoring, graphic display of time and measurements, hard copy capability and barometric pressure change corrections.
Other applications are examined for the complete control of pumping tests, including pumping rate; in situ permeability tests; monitoring changes; and even strain. The pressure transducer system may also be applied for river gauging and current measurement. 相似文献
17.
Positive-displacement piston pumps that minimize sample agitation have no apparent advantage over centrifugal submersible pumps when used to collect ground water samples for analysis of low concentrations of purge-able organic compounds. Analytical uncertainties inherent in laboratory environments appear to influence analytical results of low-concentration purgeable organic compound samples more than either pump type or sampling team. Centrifugal submersible pumps are at least equally efficient as positive-displacement piston pumps in the recovery of carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, and chloroform after sampling and analytical influences are made constant. 相似文献
18.
Philip A. Helmke Douglas P. Blanchard Larry A. Haskin Karen Telander Charles Weiss Jeffrey W. Jacobs 《Earth, Moon, and Planets》1973,8(1-2):129-148
The concentrations of major and trace elements have been determined in igneous rocks from Apollo 15. All materials analyzed have typical depletions of Eu except for minerals separated from sample 15085. Four samples have concentrations of trace elements that are similar to those of KREEP. The samples of mare basalt from Apollo 15 have higher concentrations of FeO, MgO, Mn, and Cr and lower concentrations of CaO, Na2O, K2O, and rare-earth elements (REE) as compared to the samples of mare basalt from Apollos 11, 12, and 14. The samples can be divided into two groups on the basis of their normative compositions. One group is quartz normative and has low concentrations of FeO while the other is olivine normative and has high concentrations of FeO. The trace element data indicate that the samples of olivine normative basalt could be from different portions of a single lava flow. At least two and possible three parent magmas can be identified from the samples of the quartz normative group on the basis of their concentration ratios of Sm to Eu. Within each group, the compositions of the samples appear to be related by crystallization of olivine or pyroxene. Significant variations of the ratio of concentration of Sm to Eu cannot be produced without plagioclase-liquid equilibrium. The source material of mare basalt may be depleted in Eu. Alternatively, the magmas may have assimilated a small volume of material similar to KREEP.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. 相似文献
19.
Larry K. Stephenson 《Geoforum》1979,10(2):195-201
An attempt is made in this paper to complement existing analyses of voluntary groups by outlining some additional explicitly spatial dimensions which, it is argued, can be useful in examining those organizations with a land use or environmental focus. The distinction is drawn between groups which have direct spatial links and those with indirect spatial links; the hierarchical subdivision of space is considered; the role of scale and its relation to perception and desired use of areas is addressed; and the importance of considering the resolution scale of land use and environmental conflicts noted. 相似文献
20.
Roger K. Ulrich Larry Webster John E. Boyden Nick Magnone Richard S. Bogart 《Solar physics》1991,135(2):211-241
We describe enhancements to the hardware and software for the 150-foot tower system on Mt. Wilson which make possible the acquisition of high precision line profile measurements. This system utilizes the 75-foot pit spectrograph with a photomultiplier detector system to scan line profiles repeatedly in order to study variations induced by the passage of waves vertically through the solar atmosphere. Oscillations of line profile parameters with an amplitude as low as 1.7 m s–1 have been detected with this system using integrated sunlight. Phase relations between oscillations of different parts of the line profile are appropriate to upward energy transport. Consistent with the previous conclusion by Mein and Schmieder (1981), we find that the magnitude of the energy transport is compatible with the 5-min oscillations making an important contribution to the heating of the low chromosphere.The Mount Wilson Observatory is operated by the Mount Wilson Institute under agreement with the Carnegie Institution of Washington. 相似文献