全文获取类型
收费全文 | 1290篇 |
免费 | 67篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 37篇 |
大气科学 | 83篇 |
地球物理 | 381篇 |
地质学 | 497篇 |
海洋学 | 143篇 |
天文学 | 158篇 |
综合类 | 9篇 |
自然地理 | 70篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 30篇 |
2020年 | 29篇 |
2019年 | 34篇 |
2018年 | 50篇 |
2017年 | 55篇 |
2016年 | 74篇 |
2015年 | 39篇 |
2014年 | 54篇 |
2013年 | 76篇 |
2012年 | 72篇 |
2011年 | 105篇 |
2010年 | 71篇 |
2009年 | 96篇 |
2008年 | 77篇 |
2007年 | 63篇 |
2006年 | 63篇 |
2005年 | 51篇 |
2004年 | 51篇 |
2003年 | 36篇 |
2002年 | 37篇 |
2001年 | 21篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1970年 | 4篇 |
1969年 | 1篇 |
排序方式: 共有1378条查询结果,搜索用时 453 毫秒
391.
392.
Roberto De Propris Matthew Colless Simon P. Driver Warrick Couch John A. Peacock Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Nicholas Cross Gavin B. Dalton George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren S. Madgwick Peder Norberg Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2003,342(3):725-737
393.
Carlos E. Mendoza 《Mathematical Geology》1986,18(3):307-322
Data, each consisting of a unit vector and a position, are modeled as a smooth unit vector field plus random directional errors; the smooth unit vector field is estimated by fitting a spline to observations. The estimate is nonlinear; it is obtained with an iterative procedure in which, at each step, a least-squares smoothing spline is fitted to a set of pseudovalues. The resulting estimate is exemplified with a data set extracted from the literature in geology. The proposed estimate is compared, using the same data set with that obtained through suggestions of other authors, and is found to have attractive qualities. The use of plots of the resulting estimate to find the appropriate value of the smoothing parameter is emphasized throughout. 相似文献
394.
Chris Blake Michael B. Pracy Warrick J. Couch Kenji Bekki Ian Lewis Karl Glazebrook Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Carole Jackson Ofer Lahav Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,355(3):713-727
395.
Vanessa Cerqueira Koppe João Felipe Coimbra Leite Costa Jair Carlos Koppe Fernando Gambin Gary Fallon Nick Davies 《Natural Resources Research》2007,16(4):293-303
Seismic reflection methods measure the time a seismic wave takes to travel through the ground, from the user defined source
to a series of signal monitoring sensors known as geophones. The measured times need to be depth converted to allow for integration
with other geological data. In order to convert from time to depth, an estimate of the rock volume velocity field must be
made. The velocity field estimate can be made by assignment of velocity estimates to a geological model independent of the
seismic processing. This article presents the results of using the acoustic geophysical log data extrapolated via sequential
Gaussian simulation to derive the velocity field. The uncertainties associated with the velocity estimates were significant
and provided the means to assess confidence limits for the actual depth determination. The technique is assessed by application
to a major coal deposit, approximately 2.1 m thick and 210 m deep. Considering only the uncertainty associated with estimating
the velocity field, half of the confidence interval values showed approximately 1 m of uncertainty in depth. The application
of sequential Gaussian simulation to model the 3D distribution of acoustic velocity can be extended to other geophysical log
parameters or derived estimates. 相似文献
396.
Sea level measurements along the southeastern Brazilian coast, between 20° S and 30° S, show the effect of the Sumatra Tsunami
of December 26, 2004. Two records from stations, one located inside an estuary and other inside a bay, shows oscillations
of about 0.20 m range; one additional record from a station facing the open sea shows up to 1.2 m range oscillations. These
oscillations have around 45 min period, starting 20–22 h after the Sumatra earthquake in the Indian Ocean (00:59 UTC) and
lasting for 2 days. A computer modelling of the event reproduces the time of arrival of long shallow-water tsunami waves at
the southeastern Brazilian coast but with slight longer period and amplitudes smaller than observed at the coast, probably
due to its coarse resolution (1/4 of a degree). The high amplitudes observed at the coast suggest a mechanism of amplification
of these waves over the southeastern Brazilian shelf. 相似文献
397.
Carlos M. Duarte Núria Marbà Dorte Krause-Jensen María Sánchez-Camacho 《Estuaries and Coasts》2007,30(4):652-656
The power of equations predicting seagrass depth limit (Zc) from light extinction (K
z) was tested on data on seagrass depth limits collected from the literature. The test data set comprised 424 reports of seagrass
colonization depth and water transparency, including data for 10 seagrass species. This data set confirmed the strong negative
relationship betweenZ
c andK
z. The regression equation in Duarte (1991) overestimated the realized seagrass colonization depths at colonization depths
< 5 m, while there was no prediction bias above this threshold. These results indicated that seagrass colonizing turbid waters
(K
z 0.27 m-1) have higher apparent light requirements than those growing in clearer waters. The relationship between seagrass colonization
depth and light attenuation shifts at a threshold of light attenuation of 0.27 m-1, requiring separate equations to predictZ
c for seagrass growing in more turbid waters and clearer waters, and to set targets for seagrass restoration and conservation
efforts. 相似文献
398.
Seismic attenuation of coda waves in the eastern region of Cuba 总被引:1,自引:0,他引:1
Cuba's seismic attenuation had never been studied in detail. In this paper we present the results of the research on the seismic attenuation of Cuba's eastern zone based upon the information collected by the seismological Cuban network from 1998 to 2003. 581 earthquakes were selected from the Cuban catalogue to make this study. All of them, recorded by at least three seismic stations, had their epicenters located in the eastern Cuban region (19.3–22 N, 79–73 W), epicentral distances between 15 km and 213 km, their coda duration magnitudes ranging from 2 and 4.1 and their focal depths reaching up to 30 km. The seismic wave attenuation was studied using coda waves. The single scattering method proposed by Sato in 1977 was applied, the attenuation and frequency dependency for different paths and the correlation of the results with the geotectonics of the region are presented in this paper.The mean Qc value calculated was Qc = (64 ± 2)f0.84 ± 0.01. The relatively low Q0 and the high frequency dependency agree with the values of a region characterized by a high tectonic activity. The Qc values of seven subregions of eastern Cuba were calculated and correlated with the geology and tectonics of the area. 相似文献
399.
Gladys V. Melián Inés Galindo Nemesio M. Pérez Pedro A. Hernández Mario Fernández Carlos Ramírez Raúl Mora Guillermo E. Alvarado 《Pure and Applied Geophysics》2007,164(12):2465-2487
We report the results of four soil H2 surveys carried out in 2000–2003 at Poás volcano, Costa Rica, to investigate the soil H2 distribution and evaluate the diffuse H2 emission as a potential surveillance tool for Poás volcano. Soil gas H2 contents showed a wide range of concentration from 0.2 to 7,059 ppmV during the four surveys. Maps of soil gas H2 based on Sequential Gaussian Simulation showed low H2 concentration values in the soil atmosphere (<0.7 ppmV) for most of the study area, whereas high soil gas H2 values were observed inside the active crater of Poás. A significant increase in soil gas H2 concentration was observed inside the active crater during 2001 and 2002 with respect to year 2000, followed by a decrease
in 2003. The observed spatial and temporal variations of soil H2 concentration have been well correlated with seismicity, microgravimetry and fumarolic chemistry changes which occurred during
this study. These observations evidence changes in the shallow magmatic-hydrothermal system of Poás, and it might be related
to a potential magmatic intrusion during the period 1998–2004. Therefore, monitoring diffuse H2 emission of Poás has become an important geochemical tool for the monitoring of its volcanic activity. 相似文献
400.
Anomalous Emissions of SO2 During the Recent Eruption of Santa Ana Volcano, El Salvador, Central America 总被引:1,自引:0,他引:1
Rodolfo Olmos José Barrancos Claudia Rivera Francisco Barahona Dina L. López Benancio Henriquez Agustín Hernández Efrain Benitez Pedro A. Hernández Nemesio M. Pérez Bo Galle 《Pure and Applied Geophysics》2007,164(12):2489-2506
Santa Ana volcano in western El Salvador, Central America, had a phreatic eruption at 8:05 am (local time) on October 1, 2005,
101 years after its last eruption. However, during the last one hundred years this volcano has presented periods of quiet
degassing with fumarolic activity and an acidic lake within its crater. This paper presents results of frequent measurements
of SO2 degassing using the MiniDOAS (Differential Optical Absorption Spectroscopy) system and a comparison with the volcanic seismicity
prior to the eruption, during, and after the eruption. Vehicle measurements of SO2 flux were taken every hour during the first nine days of the eruption and daily after that. The period of time reported here
is from August to December, 2005. Three periods of degassing are distinguished: pre-eruptive, eruptive, and post-eruptive
periods. The intense activity at Santa Ana volcano started in July 2005. During the pre-eruptive period up to 4306 and 5154
ton/day of SO2 flux were recorded on October 24 and September 9, 2005, respectively. These values were of the same order of magnitude as
the recorded values just after the October 1st eruption (2925 ton/day at 10:01 am). Hourly measurements of SO2 flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase
in SO2 flux and that this parameter reaches a peak after the explosion took place. This behavior suggests that increasing accumulation
of exsolved magmatic gases occurs within the magmatic chamber before the explosions, increasing the pressure until the point
of explosion. A correlation between SO2 fluxes and RSAM (Real Time Seismic Amplitude Measurements) is observed during the complete sampling period. Periodic fluctuations
in the SO2 and RSAM values during the entire study period are observed. One possible mechanism explaining these fluctuations it that
convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels, allowing increasing
degasification and then decreasing degasification as the batch of magma lowers its gas content, becomes denser, and sinks
to give space to a new magma pulse. These results illustrate that the measurements of SO2 flux can provide important warning signals for incoming explosive activity in active volcanoes. 相似文献