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991.
In this study subsidence due to groundwater withdrawal was investigated. Kerman Province in Iran is struggling with land subsidence
problem due to extensive groundwater withdrawal mainly for farming. The rate and type of groundwater withdrawal has very important
impact on settlement rate. In this research, effective parameters on land subsidence caused by groundwater withdrawal were
determined by laboratory tests. Sampling had done up to depth of 300 m mainly with remolded specimens from Shams-abad, Nouq
plain in Kerman province. Similar to the field preconsolidation pressure was applied on specimens in the laboratory. Rate
of applied stress on prepared specimens was similar to effect of oscillation of groundwater level. In order to model the actual
soil behavior in the laboratory, one-dimensional consolidation device (odometer) was adopted for testing. In these tests,
the effect of loading caused by seasonal oscillation of groundwater table is considered by means of cyclic loading in the
testing which has great effect on rate of settlements. The results of tests show that when the water table level periodically
increases and decreases the amount of settlement decrease, comparing with the case when the groundwater table drop to a constant
level. In order to predict the further effects of groundwater level oscillation and actual field condition on land subsidence,
a finite element model based on Biots’ three-dimensional consolidation theory was developed. After calibration of finite element
model with laboratory tests, this model was used for prediction the effect of groundwater level oscillation on actual field
conditions. 相似文献
992.
Real-time monitoring and early warning of landslides at relocated Wushan Town,the Three Gorges Reservoir,China 总被引:6,自引:6,他引:6
A special monitoring and warning system has been established and improved in the Three Gorges Reservoir area since 1999. It
is necessary to develop a real-time monitoring system on landslides because there are dense populations centered in the reservoir
area and geo-hazards may be triggered by a 30-m water level fluctuation between 145 and 175 m in elevation during reservoir
operation; the regular monitoring could not be suitable to the early warning on landslides. Since 2003, the authors have carried
out a real-time monitoring and early warning project on landslides at the relocated Wushan town in the Three Gorges Reservoir
area. The monitoring station includes Global Positioning System with high-accuracy double frequency to monitor ground displacement,
time domain reflection technology, and immobile borehole, inclinometer to monitor deep displacement, piezometer to monitor
pore water pressure, and precipitation and reservoir water level monitoring. Compared with traditional methods, the real-time
monitoring is continuous and traceable in the acquisition process, and the cycle of data acquisition is very short, usually
within hours, minutes, or even shorter. Based on the landslide monitoring experience at the Three Gorges Reservoir area, the
early warning criteria on landslide are established in which the critical situation is classified into four levels: blue,
yellow, orange, and red, respectively, expressed by no, slight, moderate, and high risk situation. Comprehensive judgment
from multimonitoring data of Yuhuangge landslide in this area since 2004 suggested that the new Wushan town will be at the
blue early warning level, although some monitoring data of individual displacement at deep borehole showed that the displacement
was increased by 5 mm in 5 months with an average velocity of 1.0 mm/month, and the data of BOTDR also showed an obvious dislocation
along a stairway on the landslide. 相似文献
993.
Gyesoon Park Samgyu Park Myeong-Jong Yi Hyoungrae Rim Seong-Jun Cho Jung-Ho Kim 《Environmental Earth Sciences》2010,60(5):965-974
Two-dimensional (2-D) electrical resistivity and three-dimensional (3-D) gravity explorations were undertaken to estimate
the 3-D distribution of karst cavities at the area of Yongweol-ri in Korea where ground subsidence has occurred. Although
the gravity method is a low-cost way of analyzing a 3-D continuous structure, its vertical resolving power is poor. In contrast,
the electrical resistivity method can provide a 2-D and/or 3-D subsurface structure with a much higher lateral and vertical
resolution than the gravity method. Accordingly, geostatistical methods and density information were used to enhance the 2-D
resistivity structure revealed by the electrical resistivity method into a 3-D structure. The assumptions are, first, that
each data set senses the same underlying geological structure in terms of different material properties and, secondly, that
two different material properties are correlated locally or globally throughout the entire target area. As a result, the distribution
of limestone cavities can be estimated under the assumption that they are mostly filled with groundwater and clayey soils
and have abnormally low levels of resistivity and density. The estimated distribution corresponds with the grouting, borehole
imaging and monitoring data. In this example, it can be seen that the integration analysis of 2-D electrical resistivity and
3-D gravity methods is a very powerful tool for 3-D subsurface imaging and that the method can provide enhanced imaging capabilities
for 3-D cavities. 相似文献
994.
Yong Wang Qi-Long Miao Chong-Yi E Jian-Kang Han Yuan-Yuan Ding 《Environmental Earth Sciences》2010,60(6):1257-1266
The δ18O data obtained from an 18.7 m ice core drilled in Chongce Ice Cap at an elevation of 6,530 m a.s.l. in the West Kunlun Mountains
on the northern Tibetan Plateau show a strong correlation with the summer temperature of the middle to upper troposphere over
the mid-high latitudes of Eurasia. Based on this, the δ18O record can be used as a proxy of the June–September mean temperature of the mid-upper troposphere (MUT) from 1903 to 1992.
The time span of the ice core record is much longer than the meteorological data available only after 1948. Using the empirical
mode decomposition method (EMD), the δ18O record is decomposed into various frequency components and compared with the solar irradiance variations of the same period.
The results show that (1) The June–September mean temperature of the MUT over Eurasian mid-high latitudes is completely decomposed
into four IMF (intrinsic mode function) components and an increasing trend. (2) Solar irradiance is decomposed into the Schwabe
cycle, the Hale cycle, the Gleissberg cycle, and an increasing trend. (3) The correlation coefficients between the June and
September mean temperatures of the MUT over Eurasian mid-high latitudes and solar irradiance on the longer timescales (at
least more than 11-year) show the significant correlations; their phase changes are basically identical in general, and (4)
the 11-year Schwabe cycle exists in the June–September mean temperature of the MUT over Eurasian mid-high latitudes during
most of the time from 1903 to 1992, and only in the two high-temperature phases (1929–1944 and from 1975 to the present) may
global warming disturb this relation. A full understanding of this phenomenon would shed insight into the potential consequence
of global warming on the MUT. 相似文献
995.
Bing Wang Shengtian Yang Changwei Lü Jing Zhang Yujuan Wang 《Environmental Earth Sciences》2010,59(6):1337-1347
Green plants play an important role in energy flows and material cycles. The net primary productivity (NPP) reflects the capability
of vegetation to convert solar energy into photosynthate (fixed carbon). Understanding the factors that contribute to variations
in NPP is of key importance for improving the rock-desertification environment in karst areas. In this paper, the NPP model
(Light Use Efficiency model) is modified on the basis of remote sensing data [moderate resolution imaging spectroradiometer
(MODIS)], climate data and observed information. Then the model is employed to estimate the spatial–temporal variations of
NPP in the Guizhou Province, China. Finally, the NPP differences between karst area and non-karst area, and the relationships
between NPP and climate factors are analyzed. The results show that the NPP estimated using MODIS data are reasonable. The
mean NPP of territorial vegetation is 421.46 gC m−2 year−1; the NPP in the non-karst area is 13.3% higher than that in the karst area; the correlation degree between NPP and precipitation
is better in southeastern and western districts. 相似文献
996.
Mechanism and geochemical implications of the Late Holocene organic carbon burial event: an example from the southwest coast of India 总被引:1,自引:0,他引:1
B. Ajaykumar Mahesh Mohan M. S. Shylesh Chandran K. K. Jayasooryan K. S. Unni A. P. Thomas 《Environmental Earth Sciences》2010,59(7):1409-1416
Carbonaceous clay found in the palaeo-deposits of Meenachil River basin was analysed for the total organic carbon, nitrogen
and textural characters. Radiocarbon dating of this clay formation and the embedded carbonized wood fragments was also done.
The values obtained for the organic carbon, nitrogen and C/N ratio of the carbonaceous clay exhibited a very remarkable range,
suggestive of different environmental conditions of formation. It is evident from the present study that since the lignin
and cellulose are the dominant components of terrestrial higher plants, allochthonous and submerged organic matter have high
C/N ratio. The radio carbon dating of the sediment and wood samples suggested that the palaeo-deposits of Meenachil River
basin were formed as result of many transgrassive–regressive episodes, which had started even before the formation of Vembanad
Lake. The formation of carbonaceous clay, as found sandwiched in palaeo-deposits, was due to the global eustatic sea-level
fluctuations and tectonism. 相似文献
997.
In the middle of 2007, a severe flood affected the People’s Republic of Bangladesh. This is a natural disaster that takes
people’s lives, destroys livestock, infrastructures and communication systems and, damages crops and fish ponds. Despite many
adverse impacts, the flood situation is an accepted phenomenon to the citizens of Bangladesh, due to the immense increase
of soil fertility due to the flood, plus, the recharge of aquifer, ecosystem and fish. The flood of 2007 was the 5th major
flood of the last 20 years when more than thirty-five percent of the area of the country was inundated with flood water. As
in the past, the flood of 2007 had its own significance. The geography of the country contains a floodplain delta of three
major river basins: the Ganges, the Brahmaputra and the Meghna (GBM). The mean monthly rainfall plot from the TRMM satellite
data has shown that for both the Meghna and Brahmaputra basins, the rainfall was higher during July 2007 than any other months
of the last 2 years. This excess rainfall had accumulated in the Brahmaputra and Meghna rivers and carried downstream to Bangladesh.
This was the main cause of the flooding in 2007. The first crossing above the danger level of the river waters was observed
at Durgapur station of the Someswari and at Sunamganj station of the Surma on the nineteenth of July, 2007 inside Bangladesh.
In terms of magnitude of the peak and duration of the flood, the Brahmaputra was higher in 2007 than during 2004. However,
the Ganges river water level never crossed the danger level during flood of 2007. The Meghna was lower during the flood peak
for the duration of the flood in 2007. The year–to-year variability in both the magnitude and duration of the flood suggests
changes in rainfall and landuse pattern of the catchment. 相似文献
998.
Jagadish Prasad Sahoo Pradip Kumar Pradhan 《Geotechnical and Geological Engineering》2010,28(6):889-897
An experimental investigation was undertaken to study the effects of lime-stabilized soil-cushion on the strength behavior
of expansive soil. In the present investigation, a series of laboratory tests (Unconfined compression tests and CBR tests)
were conducted on both expansive soil alone and expansive soil cushioned with lime-stabilized non-expansive cohesive soil.
Lime contents of 2, 4, 6, 8 and 10% by dry weight of cohesive non-swelling soil was used in the stabilized soil cushion. Both
expansive soil and lime stabilized soil cushion were compacted to Standard Proctor’s optimum condition with thickness ratio
2:1. Tests on cushioned expansive soils were conducted at different curing and soaking periods i.e., 7, 14, 28 and 56 days.
The test results revealed that maximum increase in strength was achieved after 14 days of curing or soaking period with 8%
of lime content. 相似文献
999.
Rebecca J. Howard 《Estuaries and Coasts》2010,33(1):127-138
Genetic diversity within plant populations can influence plant community structure along environmental gradients. In wetland
habitats, salinity and soil type are factors that can vary along gradients and therefore affect plant growth. To test for
intraspecific growth variation in response to these factors, a greenhouse study was conducted using common plants that occur
in northern Gulf of Mexico brackish and salt marshes. Individual plants of Distichlis spicata, Phragmites australis, Schoenoplectus californicus, and Schoenoplectus robustus were collected from several locations along the coast in Louisiana, USA. Plant identity, based on collection location, was
used as a measure of intraspecific variability. Prepared soil mixtures were organic, silt, or clay, and salinity treatments
were 0 or 18 psu. Significant intraspecific variation in stem number, total stem height, or biomass was found in all species.
Within species, response to soil type varied, but increased salinity significantly decreased growth in all individuals. Findings
indicate that inclusion of multiple genets within species is an important consideration for marsh restoration projects that
include vegetation plantings. This strategy will facilitate establishment of plant communities that have the flexibility to
adapt to changing environmental conditions and, therefore, are capable of persisting over time. 相似文献
1000.
The Mullipallam creek in Muthupet mangroves region is the only E-W trending coastal strip in the SE coast of India and is
very important, as the mangrove acts as a barrier to natural diasters. Natural, anthropogenic signals and accumulation of
elements were made by collecting sediment samples at various depths in a core. All sediments were analyzed for carbonates
(CaCO3), organic carbon (OC), major (Si, Al, Fe, Na, K, Ca, Mg, P), and trace (Mn, Cr, Cu, Ni, Co, Pb, Zn). Normalization with Al
values has been done for all the major and trace elements and enrichment factors have been calculated. The calculated enrichment
factors and comparison indicate that the trace metals (especially Pb) are enriched mainly due to the external (anthropogenic)
activities in the land as well as in the coastal zone (Palk Strait). 相似文献