全文获取类型
收费全文 | 3688篇 |
免费 | 942篇 |
国内免费 | 1473篇 |
专业分类
测绘学 | 694篇 |
大气科学 | 546篇 |
地球物理 | 751篇 |
地质学 | 2638篇 |
海洋学 | 618篇 |
天文学 | 70篇 |
综合类 | 362篇 |
自然地理 | 424篇 |
出版年
2024年 | 54篇 |
2023年 | 167篇 |
2022年 | 350篇 |
2021年 | 388篇 |
2020年 | 350篇 |
2019年 | 400篇 |
2018年 | 361篇 |
2017年 | 352篇 |
2016年 | 371篇 |
2015年 | 333篇 |
2014年 | 338篇 |
2013年 | 335篇 |
2012年 | 357篇 |
2011年 | 298篇 |
2010年 | 234篇 |
2009年 | 228篇 |
2008年 | 172篇 |
2007年 | 144篇 |
2006年 | 121篇 |
2005年 | 79篇 |
2004年 | 68篇 |
2003年 | 68篇 |
2002年 | 56篇 |
2001年 | 72篇 |
2000年 | 52篇 |
1999年 | 36篇 |
1998年 | 31篇 |
1997年 | 34篇 |
1996年 | 37篇 |
1995年 | 28篇 |
1994年 | 30篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1958年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有6103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.
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.
8.
9.
位于准噶尔盆地西北缘中段的克-百断裂带,晚二叠世以来发育了一系列后撤式逆冲断层。长期以来,关于克-百断裂带高角度逆冲断层的成因机制一直处于争论当中,后撤式逆冲断层的物理模拟在国内尚未见文献报道。论文通过地震解释研究了克-百断裂带的构造变形特征及其演化阶段;应用断层"活动性系数"理论,半定量地描述了挤压条件下断层"活动性系数"、摩擦系数与断层倾角之间的关系,证明了挤压条件下也能形成高角度逆断层;结合"造山楔"理论解释了后撤式逆冲断层的成因机制。研究认为,克-百断裂带后撤式逆冲断层是印支期、燕山期持续挤压和扎伊尔山隆升效应综合作用的产物:挤压过程中发生"泊松效应",随着断层倾角增大,断层面上的正压力迅速增大、"活动性系数"降低,当倾角增大到一个临界值后断层停止活动,形成高角度的逆断层;同时扎伊尔山隆升造成挤压应力上移,为断层的后撤奠定了基础。最后利用砂箱物理实验模拟了克-百断裂带后撤式逆冲断层的形成过程。 相似文献
10.
正We studied the solid-liquid transformation of low-grade solid potash deposit in Dalangtan Basin and simplified the liquid phase system.We did experiments to optimize conditions of the solid-liquid transformation.The Suitable 相似文献