全文获取类型
收费全文 | 892篇 |
免费 | 38篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 44篇 |
地球物理 | 201篇 |
地质学 | 531篇 |
海洋学 | 41篇 |
天文学 | 70篇 |
综合类 | 11篇 |
自然地理 | 34篇 |
出版年
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 16篇 |
2018年 | 63篇 |
2017年 | 72篇 |
2016年 | 68篇 |
2015年 | 39篇 |
2014年 | 57篇 |
2013年 | 72篇 |
2012年 | 54篇 |
2011年 | 49篇 |
2010年 | 30篇 |
2009年 | 48篇 |
2008年 | 51篇 |
2007年 | 23篇 |
2006年 | 28篇 |
2005年 | 18篇 |
2004年 | 26篇 |
2003年 | 24篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1966年 | 3篇 |
1960年 | 1篇 |
排序方式: 共有949条查询结果,搜索用时 625 毫秒
721.
Earthquake fault ruptures may emerge at the ground surface causing large differential movements. When fault ruptures emerge
at or adjacent to the position of existing foundations, significant damage can be caused. However, the study of recent faulting
events revealed that in some circumstances the fault-rupture emergence is deflected by the presence of buildings leaving the
buildings intact. A centrifuge modelling study has been conducted to investigate how normal faults interact with strip foundations
which run parallel to the strike direction. The study confirms that fault rupture may be deviated by the presence of the foundation
so that the foundation is protected from the most serious differential movements. However, whilst the fault propagates to
the soil surface the foundation has to withstand initial movements before the final fault rupture emergence mechanism is activated.
The centrifuge results suggest that it is the bearing pressure of the foundation which causes the deviation of the fault rather
than the kinematic restraint of the foundation. The interaction between the earthquake fault and the shallow foundation depends
on the foundation bearing pressure, foundation width, soil depth and position of the fault relative to the foundation and
these aspects should be considered in design. Results from the tests are used to validate a series of finite element analyses
as reported in an accompanying paper. 相似文献
722.
The response of shallow foundations under lateral cyclic loading is generally nonlinear and involves rocking, sliding, settlement, and may also involve foundation uplift and soil yielding. Unlike pile foundations, the nonlinear Winkler model is not widely used for modeling cyclic soil–footing–structure interaction (SFSI) problems. Nonetheless, it has some important features that make it more attractive than conventional finite element approaches, and is a recommended approach in the FEMA 356 design guideline. This paper explores the strengths and limitations of the FEMA 356 nonlinear Winkler modeling approach, when used in predicting the cyclic response of various recent SFSI experiments. The results of the study show that the model is capable of satisfactorily predicting all the different cyclic response quantities apart from permanent horizontal displacements. This should therefore be noted when using the approach in design. 相似文献
723.
In the last few decades, several integrated methods for marine sediment quality evaluation have been developed and applied to many coastal sites. This paper describes the development of a general integrated method based on the determination of organic and inorganic sediment contamination, lethal and sublethal toxicity assessments, in situ benthonic community structure alteration and bioaccumulation of contaminants. The proposed method was applied to sediments from Southern Spain's Atlantic coast where six rivers (Guadiana, Carreras, Piedras, Tinto, Odiel and Guadalquivir) drain pollutants from various anthropogenic sources. A series of experiments was conducted to determine the characteristics of the sediments: granulometry, organic matter content, etc. (1); metal contamination of sediments and Chamelea gallina (bivalves widely distributed in the area studied) (2); lethal and sublethal toxicity by a series of biological tests (3); and macrofauna distribution at the 16 stations included in the study (4). Ratio-to-reference values (RTR) calculated for each parameter were used to determine the organic and inorganic contamination indices, the lethal and sublethal toxicity indices, the index of bioavailability of metals in the organisms analyzed and the macrobenthic alteration index. The data were plotted on six-axis plots to describe better the relations between the physical, chemical and biological properties studied. A general integrated sediment quality index (ISQI) was determined and used as an indicator of pollution-induced degradation. The ISQI values summarize the main characteristics of the environmental situation at each sampling point and can be used for purposes of comparison. 相似文献
724.
El Arbi Toto Chakib Kerrouri Lahcen Zouhri Mohamed El Basri Aomar Ibenbrahim Hafid Mohamad Mohamed Benammi 《水文研究》2008,22(11):1675-1686
An area of about 30 km2 located in Ain Jouhra, south of Rabat, Morocco, was the subject of a geoelectric resistivity investigation. The main goal of the investigation was the assessment of the groundwater potential of the uppermost aquifer. The aquifer conditions such as depth, thickness and boundaries were also investigated. The obtained apparent resistivity curves were first analysed qualitatively and classified using simple curve shapes. Thereafter, the data were converted to resistivity and thickness pairs semi‐quantitatively by means of master curves and then quantitatively by computer modelling using ATO and Winsev software (Zohdy, 1989; Zohdy and Bisdrof, 1989). Lithological control from the available single well with a stratigraphic log aided in the correlation of the resistivity values to different rock units. Three different AB‐spacing iso‐resistivity maps, an isopach map of the main groundwater‐bearing horizon, the depth to the aquifer substratum map and five geoelectric cross‐sections were constructed. The interpretation of these soundings indicates the presence of an unconfined to semi‐confined sandy aquifer with relatively important extent and varying thickness. The maximal thickness of the aquifer is recorded in the central part of the investigated area and is thinning southwards to pinch out farther to the south. Geophysical as well as field data indicate a hydraulic connection between the upper and deeper aquifers. Indeed, the two aquifers are separated from each other by a marly substratum that is indicated throughout the area by the lowest values of the interpreted true resistivity. The value of this resistivity varies laterally, most likely due to the lateral variation in the shale‐to‐sand ratio. The altitude of the substratum decreases towards the north, and increases southwards. Regarding the availability of the groundwater in the study area, zones with high potential are theoretically expected to occur in the central part where the transversal resistance is greatest. However, sufficient water supply and high flow rates from wells intended to produce restrictively from the most upper aquifer are not likely to exist. This conclusion, which seems to be very pessimistic, is evidenced from two real field and experimental observations. The first is the rapid fall of the level of Gharnoug lake, despite the ongoing feeding by three wells. Hence, the amount of water level drop cannot be accounted for by the evaporation alone. That means that the deeper aquifer is continuously draining the upper aquifer at a high flow rate. Very low rates are recorded in all the wells that penetrated only the upper aquifer, the exception being the well that reached deeper into the lower aquifer. The flow rate in this lower aquifer measured 18 litre s?1. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
725.
726.
Neotectonic and seismotectonic investigation of seismically active regions in Tunisia: a multidisciplinary approach 总被引:1,自引:0,他引:1
N. Bahrouni S. Bouaziz A. Soumaya N. Ben Ayed K. Attafi Y. Houla A. El Ghali N. Rebai 《Journal of Seismology》2014,18(2):235-256
Due to its key position within the Africa–Europe convergence zone, Tunisia is marked by thrusting, folding, and faulting and has a major rupture zones associated with active faults. Consequently, most of Tunisian land is seismically active with significant active deformations, showing recent seismic events and their relative surface effects. This paper reports on several aspects of the seismotectonics, historical, and present-day seismicity and places them in the general tectonic and geodynamic framework of Tunisia. Field investigations, based on an integrated multidisciplinary approach, included (1) the identification of active faults, their motion and displacement, geomorphic aspects, and scarps and their relation with the general structural map of Tunisia and (2) an extensive analysis of brittle tectonic deformation affecting Quaternary deposits in several sites throughout Tunisia. The integration of field data within the existing data related to the seismic events that took place during the last decades allowed the establishment of an earthquake distribution map, as well as major seismic zones for better understanding of the seismicity database of Tunisia. To establish microzonation maps in seismic regions such as Gafsa and its surroundings, we have analyzed surface effects and secondary structures associated with active faults and correlated them with deformation rates, reconstructed for significant seismic events. Most faults exhibited typical left-stepping en-echelon with strike-slip component pattern suggesting that Tunisia is presently subjected to NNW–SSE compression. The focal mechanism of most Tunisia earthquakes combined with the existing tectonic and structural information and reconstruction of the Quaternary stress tensor allowed (a) better understanding of seismic zoning, (b) provided better assessment of the seismic hazard, and (c) facilitated the interpretation of the relationship between seismic zones and the geodynamic African–Eurasian plate boundary. 相似文献
727.
Observations of turbulent dissipation rates measured by two independent instruments are compared with numerical model runs to investigate the injection of turbulence generated by sea surface gravity waves. The near-surface observations are made by a moored autonomous instrument, fixed at approximately 8 m below the sea surface. The instrument is equipped with shear probes, a high-resolution pressure sensor, and an inertial motion package to measure time series of dissipation rate and nondirectional surface wave energy spectrum. A free-falling profiler is used additionally to collect vertical microstructure profiles in the upper ocean. For the model simulations, we use a one-dimensional mixed layer model based on a k–ε type second moment turbulence closure, which is modified to include the effects of wave breaking and Langmuir cells. The dissipation rates obtained using the modified k–ε model are elevated near the sea surface and in the upper water column, consistent with the measurements, mainly as a result of wave breaking at the surface, and energy drawn from wave field to the mean flow by Stokes drift. The agreement between observed and simulated turbulent quantities is fairly good, especially when the Stokes production is taken into account. 相似文献
728.
The Importance of the Precipitation and the Susceptibility of the Slopes for the Triggering of Landslides Along the Roads 总被引:3,自引:1,他引:2
Clemente Irigaray Francisco Lamas Rachid El Hamdouni Tomás Fernández José Chacón 《Natural Hazards》2000,21(1):65-81
In order to characterise the influence of the heavyrains on the observed landslides during the 1996–1997hydrological cycle, rainfall records for the last 100years are analysed from 104 stations in easternAndalusia. Regarding the amounts of rain recordedbetween October 1996 and March 1997 in the 104stations studied, 31 presented new all-time records;15 presented values that were 80–100% of thepre-1995 record; 49 stations, 80–50%; and 9stations, < 50%. A map has been devised of thesusceptibility of the materials through which thesouth-eastern Andalusian road network crosses,together with an inventory of the damage caused byinstability phenomena on banks and cuttings of theroad network during the winter of 1996–1997. Therelationships between the rainfall during the studyperiod, the damage caused to the road network and thesusceptibility of the materials affected are analysed.The results indicate that there is a clearcorrespondence between the rainfall recorded and thesusceptibility of the materials with the inventorieddamage. It is concluded that the widespread seriousdamage caused in early 1997 to the roads andsurrounding areas in the Alpujarra region and thecoast of the Province of Granada was mainly caused bythe extraordinarily heavy rains. However, considerablyless damage was observed where the susceptibility ofthe terrain is low, thus highlighting the extremeusefulness of terrain-susceptibility maps for riskprevention and territorial planning. 相似文献
729.
通过对球粒陨石的天然和实验冲击特征加以比较,探讨用实验结果来校正H- 和L-群球粒陨石天然冲击特征的可行性.实验中对吉林陨石(H5)样品施加的冲击载荷 分别为 12, 27, 39,53, 78, 83, 93和 133 GPa.当压力大于 78 GPa时球粒陨石质熔体开始 产生,压力达133 GPa时形成占体积约60%的熔体.在所有受冲击样品中,无论在陨石 的变形区或熔融区,均未发现高压相矿物.实验冲击样品的结构特征和矿物组合可与 天然受强烈冲击岩庄陨石(H6)相比较,但显然与天然受强烈冲击的L6球粒陨石不相同. L6球粒陨石冲击脉体包含橄榄石和辉石的高压多型以及高压液态相。 相似文献
730.