全文获取类型
收费全文 | 1264篇 |
免费 | 86篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 62篇 |
大气科学 | 103篇 |
地球物理 | 327篇 |
地质学 | 365篇 |
海洋学 | 89篇 |
天文学 | 285篇 |
综合类 | 2篇 |
自然地理 | 136篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 33篇 |
2020年 | 31篇 |
2019年 | 38篇 |
2018年 | 51篇 |
2017年 | 36篇 |
2016年 | 47篇 |
2015年 | 49篇 |
2014年 | 48篇 |
2013年 | 76篇 |
2012年 | 61篇 |
2011年 | 68篇 |
2010年 | 54篇 |
2009年 | 84篇 |
2008年 | 66篇 |
2007年 | 64篇 |
2006年 | 75篇 |
2005年 | 68篇 |
2004年 | 67篇 |
2003年 | 55篇 |
2002年 | 52篇 |
2001年 | 43篇 |
2000年 | 27篇 |
1999年 | 34篇 |
1998年 | 31篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1369条查询结果,搜索用时 15 毫秒
991.
Chris Kavalec 《Natural Resources Research》1998,7(2):123-127
This paper describes work undertaken and sponsored by the Energy Commission to improve transportation energy demand forecasting
and policy analysis for California. Two different, but related, modeling systems are presented: the Vehicle Transactions Simulator
and the Activity and Mobility Simulator. In addition, the paper discusses some of the important energy issues and analysis
that will be addressed in the next few years with the help of these models.
This paper was prepared as the result of work at the California Energy Commission. It does not necessarily represent the views
of the Energy Commission, its employees, or the State of California. 相似文献
992.
Chris Koen 《Monthly notices of the Royal Astronomical Society》1998,300(2):567-572
The results of 37 h of high-speed photometry of KPD 2109+4401 are described. At least five periodicities in the range 182–198 s are consistently present in the observations, with amplitudes in the range 1–6 mmag. Results of simultaneous multicolour high-speed photometry with the Stiening photometer are also presented; these data could in principle be used for mode identification of the periodicities. The results of a preliminary study suggest that the pulsations may all be ℓ = 1 and 2 modes. Properties of the star are compared with those of the other EC 14026 stars. 相似文献
993.
A U-series study of lavas from Kamchatka and the Aleutians: constraints on source composition and melting processes 总被引:1,自引:0,他引:1
Simon Turner Frank McDermott Chris Hawkesworth Pavel Kepezhinskas 《Contributions to Mineralogy and Petrology》1998,133(3):217-234
New data are presented for lavas from the Kamchatka Peninsula and the Aleutian arc. Radiogenic isotopes are strikingly homogeneous
in the Kamchatka lavas and although incompatible trace element ratios exhibit much greater variability, much of this appears
to result from shallow level, crystal fractionation. The data reveal little systematic across-arc change in radiogenic isotopes
or trace element ratios. The Nd and Pb isotope data overlap those for Pacific MORB and limit the amount of sediment that could
be incorporated in the mantle source region to <1% which is insufficient to account for the observed La/Ta ratios (50–68)
in the high-MgO lavas. The lack of a positive correlation between La/Ta and depth to the slab suggests that melt–wall rock
interaction was not important in controlling this ratio. Instead it is inferred that La/Ta increased during partial melting
and that DLa/DTa = 0.11–0.06, possibly due to residual amphibole. Ba, U, Sr and Pb were added to the source by an aqueous fluid from the subducting
slab and its inferred isotopic composition indicates that this fluid was derived from the altered oceanic crust. The addition
of U resulted in a large range of (238U/232Th) from 0.79–2.48 similar to that observed in the Mariana and Lesser Antilles island arcs. However, (230Th/232Th) = 0.79–2.34, and the majority of samples lie close to the equiline indicating that the time since U/Th fractionation is
generally ≥150 thousand years. The large width of the volcanic zone is assumed to reflect protracted fluid release from the
subducting slab over the depth interval 170–380 km possibly coupled with extension across the Central Kamchatka Depression.
The data from the Aleutians contrast strongly with those from Kamchatka. Radiogenic isotope data indicate that the Aleutian
lavas contain a significant recycled sedimentary component, consistent with elevated 10Be/9Be ratios. The Aleutian lavas have (230Th/232Th) = 0.79–2.34 and exhibit a significant range of U/Th disequilibria [(238U/230Th) = 0.75–1.01]. However, 10Be/9Be is positively correlated with (238U/230Th) suggesting that the 10Be signal was carried by the aqueous fluid from the slab. The U/Th disequilibria for the Aleutian lavas lie close to a 30
thousand year reference line suggesting that this fluid was released from the slab ∼30 thousand years ago similar to recent
estimates from the Lesser Antilles, Marianas, and Tonga-Kermadec island arcs from which it is inferred that fluid addition
was the trigger for partial melting. Given that the rate of convergence in Kamchatka is similar to that in the Aleutians,
Marianas and Tonga-Kermadec the inferred greater time since␣fluid release in Kamchatka requires further investigation.
Received: 24 September 1997 / Accepted: 7 July 1998 相似文献
994.
Chris Roth 《Mathematical Geology》1998,30(8):999-1009
Lognormal kriging was developed early in geostatistics to take account of the often seen skewed distribution of the experimental mining data. Intuitively, taking the distribution of the data into account should lead to a better local estimate than that which would have been obtained when it is ignored. In practice however, the results obtained are sometimes disappointing. This paper tries to explain why this is so from the behavior of the lognormal kriging estimator. The estimator is shown to respect certain unbiasedness properties when considering the whole working field using the regression curve and its confidence interval for both simple or ordinary kriging. When examined locally, however, the estimator presents a behavior that is neither expected nor intuitive. These results lead to the question: is the theoretically correct lognormal kriging estimator suited to the practical problem of local estimation? 相似文献
995.
Data from the Halogen Occultation Experiment (HALOE) provide the first opportunity to examine solar center-to-limb relative intensity measured exoatmospherically at wavelengths from 2.4 to 10 m. The data were obtained from limb-to-limb scans across the solar equator on days of very low activity in May 1994. Coefficients for a function describing limb darkening are obtained at eight infrared wavelengths using a nonlinear least-squares fitting technique. Relative intensities produced by the limb-darkening functions are precise to 0.1% (2). From the limb-darkening coefficients, it is possible to calculate temperature information about the photosphere. At each of the eight HALOE wavelengths, the brightness temperature from the flux, T
b
disk(), and the temperature as a function of monochromatic optical depth, T(), are determined and normalized using Kondratyev et al. (1965) and calibrated Pierce (1954) central intensity measurements. The two temperature quantities are compared with the predictions of Vernazza, Avrett, and Loeser's (1976) model M, and in general there is good agreement. The largest differences occur between 2.4 and 3 m and suggest that the central intensities used in this spectral region are low. 相似文献
996.
997.
Dziak Robert P. Fox Christopher G. Bobbitt Andra M. Goldfinger Chris 《Marine Geophysical Researches》2001,22(4):235-250
Full-coverage multibeam bathymetric maps of the southern section of the Juan de Fuca Plate, also known as the Gorda Plate,
are presented. The bathymetric maps represent the compilation of multibeam surveys conducted by the National Oceanic and Atmospheric
Administration during the last 20 yrs, and illustrate the complex tectonic, volcanic, and geomorphologic features as well
as the intense deformation occurring within this region. The bathymetric data have revealed several major, previously unmapped
midplate faults. A series of gently curving faults are apparent in the Gorda Plate, with numerous faults offsetting the Gorda
Plate seafloor. The multibeam surveys have also provided a detailed view of the intense deformation occurring within the Gorda
Plate. A preliminary deformation model estimated from basement structure is discussed, where the southern part of the plate
(south of ∼42°30′ N) seems to be deforming through a series of left-lateral strike-slip faults, while the northern section
appears to be moving passively with the rest of the Juan de Fuca Plate. The bathymetry also demonstrates the Mendocino and
Eel Canyons are prominent morphologic features in the northern California margin. These canyons are active depositional features
with a large sediment fan present at the mouths of both the Mendocino and Eel canyons. The depositional lobes of these fan(s)
are evident in the bathymetry, as are the turbidite channels that have deposited sediment along the fans over time. The Trinidad
Canyon is readily evident in the margin morphology as well, with a large (∼10 km) plunge pool formed at the mouth of the canyon
as it enters the Gorda Plate sediments.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
998.
Kathleen Crane Lynn Johnson Bruce Appelgate Clyde Nishimura Roger Buck Chris Jones Peter Vogt Rubin Kos’yan 《Marine Geophysical Researches》1997,19(4):319-338
On 21 May 1989, a major earthquake swarm on the Reykjanes Ridge at59°44 N, 29°32 W at a water depth of about 1000 m andabout 500 km southwest of Iceland was detected on both the WorldwideStandard Seismic Network (WWSSN) and Icelandic seismic networks. As part ofa multi-institutional response to this swarm, the Naval ResearchLaboratory arranged for a P3 Orion Aircraft to deploy sonobuoys and AXBTs inthe immediate vicinity of the swarm activity. The detection of the swarmmotivated a survey of the region in 1990, using the towed SeaMARC IIside-looking sonar system. In 1990–1991 the Russian ShirshovInstitute of Oceanology offered the use of its MIR deep-divingsubmersibles to investigate the rise axis for recent volcanism. During 1992,a scientific team comprised of five US and ten Russian scientists mobilizedthe twin, deep diving Russian submersibles to study the spreading axis ofthe Reykjanes Ridge. The resulting data analyses allows us to conclude thatthe 1989 seismic swarm event occurred adjacent to and east of the largeaxial high in the center of our survey area. The length, width and depthrange of the earthquakes were very similar to major seismic swarm eventsconfined to fissure systems in the Krafla region of Iceland. It is likelythat the earthquake swarm was located on a fresh, well-defined systemof fissures and faults extending south of the northernmost axial highstudied. The earthquake swarm was probably associated with an emanation oflava creating a region of high backscatter, located just to the east of thecentral axial high. In addition, the region of high-backscatterremains unsampled because it lay underneath the nadir of the processedSeaMARC tracks used to plan the submersible survey. However many sampleswere taken and structural studies of the evolving Reykjanes Ridge werecarried out. 相似文献
999.
James P. Barry Kurt R. Buck Chris F. Lovera Linda Kuhnz Patrick J. Whaling Edward T. Peltzer Peter Walz Peter G. Brewer 《Journal of Oceanography》2004,60(4):759-766
Purposeful deep-sea carbon dioxide sequestration by direct injection of liquid CO2 into the deep waters of the ocean has the potential to mitigate the rapid rise in atmospheric levels of greenhouse gases.
One issue of concern for this carbon sequestration option is the impact of changes in seawater chemistry caused by CO2 injection on deep-sea ecosystems. The effects of deep-sea carbon dioxide injection on infaunal deep-sea organisms were evaluated
during a field experiment in 3600 m depth off California, in which liquid CO2 was released on the seafloor. Exposure to the dissolution plume emanating from the liquid CO2 resulted in high rates of mortality for flagellates, amoebae, and nematodes inhabiting sediments in close proximity to sites
of CO2 release. Results from this study indicate that large changes in seawater chemistry (i.e. pH reductions of ∼0.5–1.0 pH units)
near CO2 release sites will cause high mortality rates for nearby infaunal deep-sea communities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1000.
Cities in the USA engage in action on climate change, even as the federal government remains resistant to comprehensive climate policy. While experts generally agree that local level adaptation and mitigation policies are critical to avoiding the worst climate impacts, the degree to which cities communicate climate change issues to their constituents has yet to be fully explored. In this article, we evaluate how US cities communicate climate change-related issues, problems, and policies. We use a computer-assisted approach to evaluate climate change efforts by cities by examining the full text of press releases of 82 large cities in the USA. We first identify who discusses climate change, finding that many large cities in the USA address climate change in their public communication. Second, we examine the content of these discussions. Many cities discuss weather-related concerns in conjunction with broad collaborative efforts to address global warming, while city-based policy discussions focus more on energy and transportation efforts. Third, we evaluate the local factors associated with these discussions. We find that the city’s climate vulnerability is particularly influential in shaping the level and timing of climatic communication. 相似文献