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991.
青藏高原的隆起,沙漠和黄土的形成,人类的起源与演化 总被引:4,自引:2,他引:4
青藏高原大幅度的隆起,地质历史由第三纪进入第四纪。西域组(或玉门组)底的不整合面应代表我国第四系的下限,约3.00Ma B.P.。随青藏高原的抬升,气候日趋干燥,塔克拉玛干沙漠形成。黄土是由北部戈壁、沙漠中细粒物质被风吹至南部,后经季雨冲洗堆积在盆地中形成的。青藏高原上不存在第四纪大冰盖。人类的起源和发展与青藏高原隆起关系密切,西瓦古猿在向北迁移中灭绝,其旁枝在高原东部形成真正的人属,然后再向北、东迁移,最终演化为智人。 相似文献
992.
Although the middle section of the Bangong-Nujiang suture zone has been intensively investigated, its tectonic framework and evolution is still controversy. The Pungco ophiolite has a relative complete ophiolitic complex, which is an ideal specimen for studying this tricky problem. LA-ICP-MS U-Pb dating of zircons from the diabasic rock yielded an age of 159.0±2.1 Ma. This age suggests that the Pungco ophiolite was formed in the Late Jurassic, indicating the development of the Late Jurassic ophiolite in the third ophiolitic subzone. The whole-rock major and trace element compositions of diabasic and basaltic rocks exhibit mixed arc and N-MORB geochemical characteristics. Two diabasic samples have (87Sr/86Sr)i values of 0.7055 and 0.7063 and εNd(t) values of 11.28 and 11.84, respectively. The geochemical signatures and formation age of the Pungco ophiolite suggest that this ophiolite was probably produced in an active continental fore-arc setting. It originated from a N-MORB-like depleted mantle source with the involvement of subducted-slab fluids. Considering the regional geological background, the Pungco ophiolite was likely generated during the southward subduction of the Bangong-Nujiang Tethyan oceanic lithosphere beneath the Lhasa terrane, and belongs to a regional archipelagic arc-basin system together with the other Early Jurassic-Early Cretaceous ophiolites from the northern Tibet Lake district. © 2018, Science Press. All right reserved. 相似文献
993.
994.
样品于1986年11月至1987年10月在福建省罗源湾10个站位采集。经鉴定有52种水母。它们可分为沿岸暖水、沿岸暖温和大洋广布三种生态类群。水母类总数量和种类数的季节分布呈单周期,两者高峰均出现在7月。低谷分别出现于11月和1月。在平面分布上,以拟细浅室水母Lensia subtiloides占优势的月份,数量从湾口向湾顶递减,而以球型侧腕水母Pleurobrachia globosa占优势的月份,数量却递增。文中还讨论了水母类的分布和环境因素的关系。 相似文献
995.
青海湖热力状况的模拟与未来情景之研究 总被引:3,自引:2,他引:3
运用基于湖泊热量收支与湍流扩散的湖泊热力学模型模拟了青海湖近30年来湖水热力状况,内容包括湖泊水面温度,温度沿深度的垂直分布,冬季结冰与融冰的起迄时间,冰盖厚度;积雪深度与天数等。在此基础上,运用4个GCMs模型输出的CO2倍增情景下该地区的气候状况,评价了湖泊热力状况在未来的可能变化情况。 相似文献
996.
You Lilan Liu Dajie Huang Jia'na Liu Xue Zhou KechangInstitute of Crustat Dynamics SSB Beijing China Wuhan Technical University of Surveying Mapping Wuhan China National Center for Seismic Data Inforraanon SSB Beijing China 《中国地震研究》1994,(3)
This paper makes a probe into the application of the Kalman filtering method to the data processing of across-fault measurements.On the basis of statistical regression,the mathematic and stochastic models of filtration are established by combining the regression method with Kalman filtering.In the filtering computation,not only the randomness of fault movements but also the time-dependent variation of environmental effects have been taken into consideration.By use of the adaptive filtering method,an estimation of the dynamic noise variance matrix is obtained through iteration.Models for one measuring line(leveling line or baseline),two measuring lines(both leveling lines or both baselines)and four measuring lines(two leveling lines and two baselines)are derived and established systematically.By means of these models,the data of across-fault measurements can be processed dynamically in real-time to provide the filtered values of height difference between benchmarks or baseline length at different time in 相似文献
997.
Lateral variation in Moho depth around the southern Tanlu fault zone and its adjacent area 下载免费PDF全文
We estimated Moho depth beneath the southern Tanlu fault zone and its adjacent area using common-conversion-point(CCP)stacking of receiver fun-ctions,which were computed from teleseismic records of the CEArray.Our estimated Moho depth matches well with 2-D profiles derived from active-source deep seismic reflection surveys,suggesting that the calculated the Moho depth map is likely accurate beyond the 2-D profiles.Overall,the estimated Moho depth map showed a high spatial correlation with tectonic provinces,i.e.,Moho topographic boundaries are in good agreement with geological boundaries.Beneath the Dabie orogenic belt and the mountainous areas in southern Anhui Province,the Moho lies relatively deep,and there is an obvious difference in Moho depth between the two sides of this segment of the Tanlu fault.We further selected four depth profiles with dense instrumentation to show Moho depth changes across different tectonic blocks in the study area.We saw two step-like changes in Moho depth beneath the Xiangfan-Guangji and Gushi-Feizhong,which run parallel along the WNW-ESE direction and delineate the southern and northern bounds of the northern Dabie orogenic belt,which is likely the suture zone between the North China Block and South China Block.Crust beneath the northeast corner of the study area is significantly thinner than other areas,which is consistent with the crustal detachment model proposed for suturing between the North and South China blocks in the region east to the Tanlu fault. 相似文献
998.
香港地区断裂构造的新活动性 总被引:1,自引:0,他引:1
香港地区主要分布有北东东-近东西、北东和北西向三维断裂。北东向断裂分布全区,燕山期有过强烈活动,第四纪早-中期仍有过活动,以后的活动性不明显。其余两组构造虽然具有不同的发展历史,但在新构造运动中为一组共轭构造。在晚更新世(距今9-11万年)仍有明显活动全新世以来活动性相对较弱,全新世滑动速度为0.6-0.9mm/a 相似文献
999.
1000.
Rui Liu Yun Chen Jianping Wu Lei Gao Damian Barrett Tingbao Xu Linyi Li Chang Huang Jia Yu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(6):1575-1590
Flooding hazard evaluation is the basis of flooding risk assessment which has significances to natural environment, human life and social economy. This study develops a spatial framework integrating naïve Bayes (NB) and geographic information system (GIS) to assess flooding hazard at regional scale. The methodology was demonstrated in the Bowen Basin in Australia as a case study. The inputs into the framework are five indices: elevation, slope, soil water retention, drainage proximity and density. They were derived from spatial data processed in ArcGIS. NB as a simplified and efficient type of Bayesian methods was used, with the assistance of remotely sensed flood inundation extent in the sampling process, to infer flooding probability on a cell-by-cell basis over the study area. A likelihood-based flooding hazard map was output from the GIS-based framework. The results reveal elevation and slope have more significant impacts on evaluation than other input indices. Area of high likelihood of flooding hazard is mainly located in the west and the southwest where there is a high water channel density, and along the water channels in the east of the study area. High likelihood of flooding hazard covers 45 % of the total area, medium likelihood accounts for about 12 %, low and very low likelihood represents 19 and 24 %, respectively. The results provide baseline information to identify and assess flooding hazard when making adaptation strategies and implementing mitigation measures in future. The framework and methodology developed in the study offer an integrated approach in evaluation of flooding hazard with spatial distributions and indicative uncertainties. It can also be applied to other hazard assessments. 相似文献