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51.
振幅随偏移距变化是描述储层特征的重要方法之一,保幅偏移方法就是使偏移剖面能够反映出振幅随偏移距的变化.本论文中的保幅偏移是以走时为基础,主要的方法是采用走时的双曲线展开法,通过走时的二阶空间导数来确定波前曲率.该方法通过建立在大网格上的走时表来确定插值系数,将大网格插值成为较为精细的网格,这样就节省了数据的存储空间.对于相同的网格密度,通过插值来计算走时表比采用程函方程有限差分法直接计算走时要节省5至6倍的时间.走时的插值系数还可以用来计算几何扩散因子、权函数,不仅提高了成像质量,还大大节省了计算时间. 相似文献
52.
Fukun Chen Xiang-Hui Li Xiu-Li Wang Qiu-Li Li Wolfgang Siebel 《International Journal of Earth Sciences》2007,96(6):1179-1194
The Baoshan block of the Tethyan Yunnan, southwestern China, is considered as northern part of the Sibumasu microcontinent.
Basement of this block that comprises presumably greenschist-facies Neoproterozoic metamorphic rocks is covered by Paleozoic
to Mesozoic low-grade metamorphic sedimentary rocks. This study presents zircon ages and Nd–Hf isotopic composition of granites
generated from crustal reworking to reveal geochemical feature of the underlying basement. Dating results obtained using the
single zircon U–Pb isotopic dilution method show that granites exposed in the study area formed in early Paleozoic (about
470 Ma; Pingdajie granite) and in late Yanshanian (about 78–61 Ma, Late Cretaceous to Early Tertiary; Huataolin granite).
The early Paleozoic granite contains Archean to Mesoproterozoic inherited zircons and the late Yanshanian granite contains
late Proterozoic to early Paleozoic zircon cores. Both granites have similar geochemical and Nd–Hf isotopic charateristics,
indicating similar magma sources. They have whole-rock T
DM(Nd) values of around 2,000 Ma and zircon T
DM(Hf) values clustering around 1,900–1,800 and 1,600–1,400 Ma. The Nd–Hf isotopic data imply Paleoproterozoic to Mesoproterozoic
crustal material as the major components of the underlying basement, being consistent with a derivation from Archean and Paleoproterozoic
terrains of India or NW Australia. Both granites formed in two different tectonic events similarly originated from intra-crustal
reworking. Temporally, the late Yanshanian magmatism is probably related to the closure of the Neotethys ocean. The early
Paleozoic magmatism traced in the Baoshan block indicates a comparable history of the basements during early Paleozoic between
the SE Asia and the western Tethyan belt, such as the basement outcrops in the Alpine belt and probably in the European Variscides
that are considered as continental blocks drifting from Gondwana prior to or simultaneously with those of the SE Asia. 相似文献
53.
Preliminary study on assessment of nutrient transport in the Taihu Basin based on SWAT modeling 总被引:4,自引:0,他引:4
With the Taihu Basin as a study area, using the spatially distributed and mechanism-based SWAT model, preliminary simulations of nutrient transport in the Taihu Basin during the period of 1995-2002 has been carried out. The topography, soil, meteorology and land use with industrial point pollution discharge, the loss of agricultural fertilizers, urban sewerage, and livestock drainages were all considered in the boundary conditions of the simulations. The model was calibrated and validated against water quality monitoring data from 2001 to 2002. The results show that the annual total productions of nitrogen (TN) and phosphorus (TP) into Lake Taihu are 40000t and 2000t respectively. Nutrient from the Huxi Region is a major resource for Lake Taihu. The non-point source (surface source) pollution is the main form of catchment sources of nutrients into Lake Taihu, occupied TN 53% and TP 56% respectively. TN and TP nutrients from industrial point pollution discharge are 30% and 16%, and sewerage in both forms of point source and non-point source are TN 31 % and TP 47%. Both the loss of agricultural fertilizers and livestock drainages from the catchment should be paid more attention as an important nutrient source. The results also show that SWAT is an effective model for the simulation of temporally and spatially nutrient changes and for the assessment of the trends in a catchment scale. 相似文献
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中国大陆科学钻探主孔2000米以上脆性变形构造应力场 总被引:6,自引:6,他引:6
在主孔2000米之内,存在复杂的脆性破裂系统和构造应力场。根据其充填物的特征,可划分为由石英、方解石和绿泥石等矿物充填的微破裂,发育石英、方解石等矿物薄膜或擦痕线理的微破裂和既无矿物充填、也无矿物薄膜的微破裂等3种不同类型的脆性应变现象,它们依次代表早、中、晚和深、中、浅3个不同构造层次的脆性变形。初步分析表明脆性变形阶段存在有以南东东-北西西向为主导的挤压作用、北东-南西向的区域挤压作用、南北向挤压作用和垂向伸展作用等4期构造应力场。郯庐断裂东侧的现代构造应力场在区域上具有极大的稳定性。在脆性和脆-韧性转换带,制约苏鲁高压-超高压变质带侵位的主导应力作用方式为自南东东往北西西方向的挤压,它在时间和空间上具有一定的稳定性。 相似文献
60.
Strontium, neodymium isotopic compositions and trace elements of the detrital sediments of Core NS90-103 from South China
Sea were analyzed. The results show that the87Sr/86Sr ratios of the detritus during the last glacial range from 0.722 4 to 0.723 0. They are significantly higher than those
during the Holocene and the maximum of the last interglacial, which range from 0.721 0 to 0.721 7. This indicates stronger
continental weathering during the last glacial. On the other hand, the143Nd/144Nd ratios of these detritus are higher during the last glacial too, similar to the variation of the87Sr/86Sr ratios. The trace element geochemistry of these detritus indicates that more authigenic sediments, such as ferromanganese,
during the last glacial may partly contribute to the increase of143Nd/144Nd ratios. Furthermore, much more detritus from continent of South China to the north of the South China Sea may probably
contribute to143Nd/144Nd ratios increase during the last glacial, which was the result of the enhancement of northeast monsoon. 相似文献