全文获取类型
收费全文 | 7292篇 |
免费 | 1609篇 |
国内免费 | 2094篇 |
专业分类
测绘学 | 1085篇 |
大气科学 | 1034篇 |
地球物理 | 1513篇 |
地质学 | 4158篇 |
海洋学 | 1172篇 |
天文学 | 271篇 |
综合类 | 796篇 |
自然地理 | 966篇 |
出版年
2024年 | 57篇 |
2023年 | 160篇 |
2022年 | 492篇 |
2021年 | 558篇 |
2020年 | 479篇 |
2019年 | 505篇 |
2018年 | 518篇 |
2017年 | 473篇 |
2016年 | 557篇 |
2015年 | 512篇 |
2014年 | 537篇 |
2013年 | 580篇 |
2012年 | 545篇 |
2011年 | 540篇 |
2010年 | 552篇 |
2009年 | 475篇 |
2008年 | 441篇 |
2007年 | 396篇 |
2006年 | 400篇 |
2005年 | 305篇 |
2004年 | 216篇 |
2003年 | 189篇 |
2002年 | 169篇 |
2001年 | 165篇 |
2000年 | 134篇 |
1999年 | 174篇 |
1998年 | 115篇 |
1997年 | 112篇 |
1996年 | 91篇 |
1995年 | 93篇 |
1994年 | 78篇 |
1993年 | 75篇 |
1992年 | 56篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 38篇 |
1988年 | 18篇 |
1987年 | 19篇 |
1986年 | 27篇 |
1985年 | 23篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1965年 | 2篇 |
1958年 | 3篇 |
1957年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
261.
262.
263.
Landslide susceptibility modeling based on ANFIS with teaching-learning-based optimization and Satin bowerbird optimizer 总被引:1,自引:0,他引:1
As threats of landslide hazards have become gradually more severe in recent decades,studies on landslide prevention and mitigation have attracted widespread attention in relevant domains.A hot research topic has been the ability to predict landslide susceptibility,which can be used to design schemes of land exploitation and urban development in mountainous areas.In this study,the teaching-learning-based optimization(TLBO)and satin bowerbird optimizer(SBO)algorithms were applied to optimize the adaptive neuro-fuzzy inference system(ANFIS)model for landslide susceptibility mapping.In the study area,152 landslides were identified and randomly divided into two groups as training(70%)and validation(30%)dataset.Additionally,a total of fifteen landslide influencing factors were selected.The relative importance and weights of various influencing factors were determined using the step-wise weight assessment ratio analysis(SWARA)method.Finally,the comprehensive performance of the two models was validated and compared using various indexes,such as the root mean square error(RMSE),processing time,convergence,and area under receiver operating characteristic curves(AUROC).The results demonstrated that the AUROC values of the ANFIS,ANFIS-TLBO and ANFIS-SBO models with the training data were 0.808,0.785 and 0.755,respectively.In terms of the validation dataset,the ANFISSBO model exhibited a higher AUROC value of 0.781,while the AUROC value of the ANFIS-TLBO and ANFIS models were 0.749 and 0.681,respectively.Moreover,the ANFIS-SBO model showed lower RMSE values for the validation dataset,indicating that the SBO algorithm had a better optimization capability.Meanwhile,the processing time and convergence of the ANFIS-SBO model were far superior to those of the ANFIS-TLBO model.Therefore,both the ensemble models proposed in this paper can generate adequate results,and the ANFIS-SBO model is recommended as the more suitable model for landslide susceptibility assessment in the study area considered due to its excellent accuracy and efficiency. 相似文献
264.
265.
Preliminary seismic anisotropy in the upper crust of the south segment of Xiaojiang faults and its tectonic implications 下载免费PDF全文
The Xiaojiang faults,striking north-to-south(NS),and the Honghe faults,striking north-to-west(NW),are first-order block boundaries that intersect to form a concentrated stress zone at an acute angle in the southern part of the Sichuan-Yunnan rhombic block(SYB).It is also a crucial zone for material escaping from the Tibetan Plateau(TP)due to the collision between the Indian Plate and the Eurasian Plate.In December 2017,the Institute of Earthquake Forecasting of the China Earthquake Administration(CEA)deployed a linear temporary seismic broadband array,the Honghe-Xiaojiang temporary Seismic Array(HX Array),across first-order block boundaries in the southern SYB.By using the waveform data of small earthquakes recorded by stations in the HX Array across Xiaojiang faults from 2017 to 2019,and by permanent seismic stations of the China National Earthquake Networks from 2012 to 2019,this paper adopts the systematic analysis method of shear-wave splitting(SWS),SAM method,to obtain preliminary results for seismic anisotropy in the upper crust.The study area can be divided into two subzones according to the spatial distribution of the directions of polarization of the fast shear-wave(PFS)at the stations:the northern zone(zone A,where the HX Array is located)and the southern zone(zone B,to the south of the HX Array).The results show that the directions of the PFS at stations in zone A were highly consistent,dominant in the NE direction,correlated with the in-situ principal compressive stress,and were seemingly unaffected by the Xiaojiang faults.The directions of the PFS as recorded at stations in zone B were more complicated,and were dominant in the NS direction parallel to that of the regional principal compressive stress.This suggests the joint influence of complex tectonics and regional stress in this narrow wedge area.By referring to the azimuthal anisotropy derived from seismic ambient noise in the southeast margin of the TP,the NS direction of the PFS in the middle and lower crust,and its EW direction in the upper mantle,this paper concludes that azimuthal anisotropy in the upper crust differed from that in the lower crust in the south segment of Xiaojiang faults,at least beneath the observation area,and azimuthal anisotropy in the crust was different from that in the upper mantle.The results support the pattern of deformation of ductile flow in the lower crust,and the decoupling between the upper and lower crusts as well as that between the crust and the mantle in the study area.The crustal directions of the PFS appeared to be independent of the Xiaojiang faults,suggesting that the influence of the South China block on the SYB passed through the Xiaojiang faults to the Yimen region.The results of this study indicate that anisotropic studies based on data on the dense temporary seismic array can yield clearer tectonic information,and reveal the complex spatial distribution of stress and deformation in the upper crust of the south segment of Xiaojiang faults. 相似文献
266.
基于分布式检测与决策融合的海底油气管线检漏 总被引:3,自引:0,他引:3
利用多传感器的信息融合思想,提出分布式检测与决策融合方法进行长距离海底管线泄漏监测。试验水管和天然气/凝析油管线现场数据分析表明此算法不仅降低了误报警概率,且对流体在输送过程中动态变化具有稳健性。 相似文献
267.
268.
269.
270.