全文获取类型
收费全文 | 7096篇 |
免费 | 1809篇 |
国内免费 | 2981篇 |
专业分类
测绘学 | 1266篇 |
大气科学 | 1105篇 |
地球物理 | 1453篇 |
地质学 | 5166篇 |
海洋学 | 1321篇 |
天文学 | 103篇 |
综合类 | 589篇 |
自然地理 | 883篇 |
出版年
2024年 | 102篇 |
2023年 | 299篇 |
2022年 | 638篇 |
2021年 | 733篇 |
2020年 | 608篇 |
2019年 | 684篇 |
2018年 | 594篇 |
2017年 | 613篇 |
2016年 | 610篇 |
2015年 | 617篇 |
2014年 | 570篇 |
2013年 | 618篇 |
2012年 | 686篇 |
2011年 | 621篇 |
2010年 | 547篇 |
2009年 | 494篇 |
2008年 | 463篇 |
2007年 | 402篇 |
2006年 | 358篇 |
2005年 | 281篇 |
2004年 | 223篇 |
2003年 | 167篇 |
2002年 | 164篇 |
2001年 | 158篇 |
2000年 | 137篇 |
1999年 | 75篇 |
1998年 | 46篇 |
1997年 | 41篇 |
1996年 | 45篇 |
1995年 | 35篇 |
1994年 | 39篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 16篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1958年 | 3篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Kunde Yang Yuanliang Ma Chao Sun Miller J.H. Potty G.R. 《Oceanic Engineering, IEEE Journal of》2004,29(4):964-972
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data. 相似文献
2.
3.
鄂尔多斯盆地黄陵、东胜地区地温场对比 总被引:2,自引:0,他引:2
鄂尔多斯盆地黄陵、东胜铀矿区分别处于盆地南部渭北隆起的北侧边缘和盆地北部伊盟隆起的东部,赋矿层位都是中侏罗统直罗组。盆地南、北铀矿区在现今地温场及古地温场都存在明显差异,南部现今大地热值及热演化程度明显高于北部。对于下侏罗统延安组和石炭—二叠系煤层,黄陵地区镜质体反射率都高于东胜地区。通过镜质体反射率资料得出同一埋深的一套地层经历的最大古地温和对应的古地温梯度也有南部高于北部的现象。由于早白垩世后期盆地普遍整体抬升使得现今地温相对古地温降低,南部黄陵地区抬升剥蚀量大于北部东胜地区,导致古、今地温差异也大于后者。盆地南部庆阳—富县一带局部构造热运动,导致南部异常地温场的形成,使得南部热演化程度高于北部。 相似文献
4.
A one-dimensional model for thinning of the plasma sheet is developed on the basis of launching a fast mode MHD rarefaction wave propagating in the tailward direction along the plasma sheet. Behind the rarefaction wave the pressure is reduced, leading to thinning of the plasma sheet and also to an Earthward plasma flow with a speed on the order of the sound speed a0. The plasma sheet thickness is reduced by a factor of 2 if an Earthward plasma flow speed of 0.8a0 is induced. The predictions of the model are in reasonable agreement with observations. 相似文献
5.
Debris flows have caused serious loss of human lives and a lot of damage to properties in Taiwan over the past decades. Moreover, debris flows have brought massive mud causing water pollution in reservoirs and resulted in water shortage for daily life locally and affected agricultural irrigation and industrial usages seriously. A number of methods for prediction of debris flows have been studied. However, the successful prediction ratio of debris flows cannot always maintain a stable and reliable level. The objective of this study is to present a stable and reliable analytical model for occurrence predictions of debris flows. This study proposes an Artificial Neural Networks (ANN) model that was constructed by seven significant factors using back-propagation (BP) algorithm. These seven factors include (1) length of creek, (2) average slope, (3) effective watershed area, (4) shape coefficient, (5) median size of soil grain, (6) effective cumulative rainfall, and (7) effective rainfall intensity. A total of 178 potential cases of debris flows collected in eastern Taiwan were fed into the ANN model for training and testing. The average ratio of successful prediction reaching 93.82% demonstrates that the presented ANN model with seven significant factors can provide a stable and reliable result for the prediction of debris flows in hazard mitigation and guarding systems. 相似文献
6.
7.
PreliminaryresultsonkinematicmodeloftectonicblocksderivedfromhighprecisionGPSobservationsinSouthwestChinaLIRENHUANG1)(黄立人)... 相似文献
8.
9.
This paper designs three quasi-geostrophic barotropic models with a radial/horizontal grid length being 2 kin,one in the polar coordinates,one on a stationary typhoon circulation condition and another on a non-stationary typhoon circulation condition in the Cartesian coordinates,to investigate the effects of azimuthal and radial linear advections,and nonlinear advection on the inward propagation of mesoscale vorticity and the changes of typhoon intensity.Results show that the azimuthal linear advection may result in the formation of spiral vorticity bands;the radial linear advection in a certain parameter set is able to transfer vorticity inwards,leading to a slight enhancement of typhoon;the nonlinear advection of perturbation vorticity on a stationary typhoon circulation condition may transfer more vorticities inwards,thus resulting in a distinct enhancement of typhoon;and the nonlinear advection on a non-stationary typhoon circulation condition possesses duality,i.e.on the one hand,the advection increases the vorticity of inward propagation,thus favorable to the intensification of typhoon,and on the other hand,in the inward propagation process of vorticity the originally concentric and axisymmetric structure of typhoon basic flow is damaged,and a complex flow pattern forms,which in turn tends to weaken the circulation of typhoon.At last the paper discusses the possible applications of those results in typhoon intensity prediction. 相似文献
10.