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591.
Managing environmental problems in Cuban karstic aquifers 总被引:1,自引:0,他引:1
The study area is located along the Dead Sea Rift, the climate is considered arid in its southern margin near the Dead Sea,
which is the lowest water reservoir found on the globe (412 m BSL), to semiarid in its northern part. During the last few
decades, the water resources became depleted limiting the natural development of the agricultural settlements, which are the
most common type of communities in the region. Previous studies suggested that a large amount of freshwater is lost as the
result of salinization processes, which occur when fresh groundwater from the mountain aquifers, flow into the saline clastic
Neogene aquifer complex. In order to comprehend this complex system, a detailed outlining of the regional hydrogeological
system is essential. Since there are no boreholes, which penetrate the aquiferous rock sequences within the Rift, it was necessary
to interpolate a large variety of data from several fields of geosciences. The methods applied included geological mapping,
geophysical modeling based on interpretation of seismic profiles and geochemical modeling based on chemical and isotopic analysis
of runoff, sediments and groundwater. The combined modeling based on results from the different types of analyses implied
to several conclusions relevant to the regional water management policy: (1) groundwater becomes saline as it flows from the
margins of the Rift to its center. Therefore, it is recommended to exploit it along the foothills of the rift escarpment.
(2) Geophysical modeling indicated that the foothills and the Karstic mountain aquifer extend into the subsurface of the valley
and can be farther exploited (up to 15 mm3 per annum) by relatively shallow wells. (3) Several mechanisms of groundwater salinization were deciphered: (a) the dense
vertical faulting systems act as potential conduits for saline water, which flow-up from deep-seated sources and penetrate
into the fresh aquifers. (b) Fresh groundwater in the clastic aquifer complex is rare, furthermore, two evaporates bodies
were encountered (Auja and Zaharat el Qurein), also acting as sources for fresh water salinization. (c) Although the quantity
of runoff recharge to the Jordan Valley aquifer complex is negligible, the increase in its salt-content (TDS) turns this negligible
freshwater recharge to a significant contributor of salts. 相似文献
592.
Based on this preliminary study, existing sand and gravel mining regulations (in Maine, USA) can be inferred to provide some
protection to water resources. Sand and gravel deposits are important natural resources that have dual uses: mining for construction material and pumping for drinking water. How the mining of sand and gravel affects aquifers and change aquifer vulnerability to contamination
is not well documented. Mining regulations vary greatly by state and local jurisdiction. This study test metrics to measure
the effectiveness of mining regulations. The sand and gravel aquifer system studied is covered with former and active gravel
pits to nearly 25% of its areal extent. Data from homeowner interviews and field measurements found scant evidence of changes
in water quantity. Water quality analyses collected from springs, streams, ponds and wells indicate that the aquifer was vulnerable
to contamination by chloride and nitrate. However, water quality changes can not be related directly to mining activities. 相似文献
593.
Yvonne Thompson Brian C. Sandefur A. D. Karathanasis Elisa D’Angelo 《Aquatic Geochemistry》2009,15(3):349-370
Redox potentials (Eh) were monitored bimonthly and porewater chemistry was analyzed seasonally at three slightly-acidic, high-elevation
Kentucky wetlands that differed in hydrology, parent materials, and vegetation. At all sites, Eh values were below 300 mV,
which indicated that reducing conditions persisted within the upper 90 cm and fluctuated mainly within the range of iron and
sulfate reduction. Significant relationships of Eh values with depth were observed only at the Martins Fork wetland, where
precipitation was the primary water source. The strongest and most stable reducing conditions, observed at the Kentenia site,
reflected consistently high water levels, which were sustained by ground water. The third wetland (Four Level) was distinguished
by irregular Eh fluctuations coinciding with strong seasonal ground-water upwelling. Although Fe3+ and SO4
2− were the primary terminal electron acceptors in all wetlands, porewater chemistry also varied significantly by season and
soil depth in response to piezometric water level fluctuations. Additional factors that influenced porewater chemistry included:
(1) the presence of limestone parent materials that affected porewater pH, Ca2+, and Mg2+; and (2) the prevalence of sphagnum moss or graminoid species that influenced dissolved organic carbon, CO2, and CH4. Results from this study indicated the diverse range and importance of multiple factors in controlling biogeochemical processes
and properties in small, high-elevation Appalachian wetlands. 相似文献
594.
Jin Rui Li Xin Ma Mingguo Ge Yong Liu Shaomin Xiao Qing Wen Jianguang Zhao Kai Xin Xiaoping Ran Youhua Liu Qinhuo Zhang Renhua 《地球科学进展》2017,32(6):630-642
The validation is an important guarantee of quality, reliability and applicability of Remote Sensing Products (RSPs), and is also the foundation to improve the RSPs accuracy, extend the application domain and strength the application ability. This paper introduced the progresses and lessons learned from a project titled by ‘key technology of remote sensing products validation and its experimental evaluation’ supported by Ministry of Science and Technology of China. The progresses included: ①Formulating a series of national standards composed of general methods for the validation of terrestrial quantative RSPs, field-site selection and instrumentation for land surface RSPs, and other 24 individual standards of remote sensing variables; ②Building integral technique process system of RSPs validation; ③Developing some key methods from optimized spatial sampling, upscaling to validation strategy; ④Obtaining the multi-scale satellite-airborne-ground synchronized observation and evaluating systematically the validation standard and techniques; ⑤Setting up national validation network for RSPs, exploring multi-mode allied observation experiment and forming the prototype and operation mechanism for the validation network. 相似文献
595.
Robert M. Haberle Francois Forget James Schaeffer Nora J. Kelly 《Planetary and Space Science》2008,56(2):251-255
The mostly carbon dioxide (CO2) atmosphere of Mars condenses and sublimes in the polar regions, giving rise to the familiar waxing and waning of its polar caps. The signature of this seasonal CO2 cycle has been detected in surface pressure measurements from the Viking and Pathfinder landers. The amount of CO2 that condenses during fall and winter is controlled by the net polar energy loss, which is dominated by emitted infrared radiation from the cap itself. However, models of the CO2 cycle match the surface pressure data only if the emitted radiation is artificially suppressed suggesting that they are missing a heat source. Here we show that the missing heat source is the conducted energy coming from soil that contains water ice very close to the surface. The presence of ice significantly increases the thermal conductivity of the ground such that more of the solar energy absorbed at the surface during summer is conducted downward into the ground where it is stored and released back to the surface during fall and winter thereby retarding the CO2 condensation rate. The reduction in the condensation rate is very sensitive to the depth of the soil/ice interface, which our models suggest is about 8 cm in the Northern Hemisphere and 11 cm in the Southern Hemisphere. This is consistent with the detection of significant amounts of polar ground ice by the Mars Odyssey Gamma Ray Spectrometer and provides an independent means for assessing how close to the surface the ice must be. Our results also provide an accurate determination of the global annual mean size of the atmosphere and cap CO2 reservoirs, which are, respectively, 6.1 and 0.9 hPa. They also indicate that general circulation models will need to account for the effect of ground ice in their simulations of the seasonal CO2 cycle. 相似文献
596.
597.
There are many arguments on energy sources and main controlling factors of geothermal fields, so a systematic study on the distribution of ground temperature fields shall be necessary. In this paper the thermal conduction forward method of geothermal field is used to simulate cooling rate of abnormal heat sources and heat transfer of the paleo-uplift model. Combined with a large number of geothermal field exploration cases and oil exploration well temperature curves of domestic and foreign, the following conclusions are drawn:(1) According to the magmatic activity time, the magmatism activities are divided into two categories: Magma active areas(activity time 500 000 years) and weak/magma inactive areas(activity time 500 000 years). The latter has a fast cooling rate(the cooling time of the magma pocket buried around 10 km is less than 200 000 years) after it has intruded into the shallow layer and it has no direct contribution to modern geothermal fields;(2) China belongs to a weak/magma inactive area such as Tengchong region and Qinghai-Tibet region because the chronological data of these regions show that its magma activity time is more than 500 000 years;(3) The temperature of most geothermal fields can be obviously divided into three segments in the vertical direction: A high geothermal gradient segment(Segment H) at the surface, then a low geothermal gradient segment(Segment L) at a secondary depth, and finally a lower temperature segment(Segment D) at a deeper depth. The temperature isoline presents a mirror reflection relation on the temperature profile, indicating that geothermal field is dominated by heat conduction, rather than having an abnormally high temperature "heat source" to provide heat;(4) Near-surface(0-5 km) materials' lateral heterogeneity caused by tectonic movement shall probably be the main controlling factor of ground temperature fields. 相似文献
598.
The paper describes a case history where during two rock music concerts the audience at the large outdoor stadium Nya Ullevi, Gothenburg, Sweden, started to jump in time to the music. Violent vibration levels occurred in the ground and a part of the audience observed considerable motion in the structure. Based on finite element analysis, it is concluded that the underlying soft clay of the structure was excited with the same frequency as the beat of the music. The whole clay deposit under the stadium started, therefore, to vibrate with great variations in amplitudes over the field due to the complex geometry. Through interaction with the basement of the structure as well as its deep foundation the waves were transmitted to the superstructure. Parts of the structure framework have natural frequencies close to those of the beat. Consequently they started to vibrate violently. 相似文献
599.
Soft mud can be found in many large size reclaimed lands. Such soils present extremely high settlement potential that needs to be alleviated by means of effective ground improvement techniques. Current knowledge on applying small cement content to reduce settlement potential of soft mud is limited. This study concerns the consolidation behavior and settlement potential of soft mud treated with small cement content. Based on the pH values of soft mud–cement mixtures, oedometer specimens with cement content of 6% were prepared for consolidation tests. The test results show that preconsolidation pressure is rapidly developed and secondary compression is reduced. The ratio of secondary compression index to compression index is also reduced, indicating a change in grain size characteristics. The coefficient of consolidation is increased for consolidation pressures smaller than the preconsolidation pressure. This indicates that treating the soft mud with a small cement content can be very effective for reducing settlements in cases where new loads are small to medium and the time for ground improvement is limited. 相似文献
600.
用山西地电台网的资料,从震前变化的一些现象入手,找到识别和消除非地震异常及背景影响的方法,对地电阻率背景变化场作了初步的物理解释,并将此方法用于1991年震情分析中,取得较好结果。 相似文献