全文获取类型
收费全文 | 3788篇 |
免费 | 651篇 |
国内免费 | 1023篇 |
专业分类
测绘学 | 469篇 |
大气科学 | 146篇 |
地球物理 | 1258篇 |
地质学 | 2656篇 |
海洋学 | 313篇 |
天文学 | 8篇 |
综合类 | 305篇 |
自然地理 | 307篇 |
出版年
2024年 | 19篇 |
2023年 | 65篇 |
2022年 | 144篇 |
2021年 | 157篇 |
2020年 | 166篇 |
2019年 | 208篇 |
2018年 | 183篇 |
2017年 | 159篇 |
2016年 | 218篇 |
2015年 | 209篇 |
2014年 | 286篇 |
2013年 | 288篇 |
2012年 | 239篇 |
2011年 | 251篇 |
2010年 | 227篇 |
2009年 | 266篇 |
2008年 | 273篇 |
2007年 | 266篇 |
2006年 | 256篇 |
2005年 | 200篇 |
2004年 | 219篇 |
2003年 | 173篇 |
2002年 | 137篇 |
2001年 | 144篇 |
2000年 | 112篇 |
1999年 | 108篇 |
1998年 | 82篇 |
1997年 | 78篇 |
1996年 | 59篇 |
1995年 | 44篇 |
1994年 | 40篇 |
1993年 | 27篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有5462条查询结果,搜索用时 640 毫秒
151.
《Marine Policy》2016
Marine minerals such as manganese nodules, Co-rich ferromanganese crusts, and seafloor massive sulfides are commonly seen as possible future resources that could potentially add to the global raw materials supply. At present, a proper assessment of these resources is not possible due to a severe lack of information regarding their size, distribution, and composition. It is clear, however, that manganese nodules and Co-rich ferromanganese crusts are a vast resource and mining them could have a profound impact on global metal markets, whereas the global resource potential of seafloor massive sulfides appears to be small. These deep-sea mineral commodities are formed by very different geological processes resulting in deposits with distinctly different characteristics. The geological boundary conditions also determine the size of any future mining operations and the area that will be affected by mining. Similarly, the sizes of the most favorable areas that need to be explored for a global resource assessment are also dependent on the geological environment. Size reaches 38 million km2 for manganese nodules, while those for Co-rich crusts (1.7 million km2) and massive sulfides (3.2 million km2) are much smaller. Moreover, different commodities are more abundant in some jurisdictions than in others. While only 19% of the favorable area for manganese nodules lies within the Exclusive Economic Zone of coastal states or is covered by proposals for the extension of the continental shelf, 42% of the favorable areas for massive sulfides and 54% for Co-rich crusts are located in EEZs. 相似文献
152.
153.
154.
Norhakim Yusof Raul Zurita-Milla Menno-Jan Kraak Bas Retsios 《International journal of geographical information science》2016,30(8):1486-1506
Wind speed and direction vary over space and time due to the interactions between different pressures and temperature gradients within the atmospheric layers. Near the earth’s surface, these interactions are modulated by topography and artificial structures. Hence, characterizing wind behaviour over large areas and long periods is a complex but essential task for various energy-related applications. In this study, we present a novel approach to discover wind patterns by integrating sequential pattern mining and interactive visualization techniques. The approach relies on the use of the Linear time Closed pattern Miner sequence algorithm in conjunction with a time sliding window that allows the discovery of all sequential patterns present in the data. These patterns are then visualized using integrated 2D and 3D coordinated multiple views and visually explored to gain insight into the characteristics of the wind from a spatial, temporal and attribute (type of wind pattern) point of view. This proposed approach is used to analyse 10 years of hourly wind speed and direction data for 29 weather stations in the Netherlands. The results show that there are 15 main sequential patterns in the data. The spatial task shows that weather stations located in the same region do not necessarily experience similar wind pattern. For within the selected time interval, similar wind patterns can be observed in different stations and in the same station at different times of occurrence. The attribute task discovered that the repetitive occurrences of chosen pattern indicate as regular wind behaviour at different weather stations that persisted continuously over time. The results of these tasks show that the proposed interactive discovery facilitates the understanding of wind dynamics in space and time. 相似文献
155.
156.
157.
In order to understand the mechanical behaviours of the surrounding rocks in the underground caverns of the Wudongde hydropower plant, triaxial tests are performed on a type of dolomite. It is revealed that damage induced by crack development is the main factor controlling the nonlinear plastic deformation and failure behaviour of the dolomite in both pre- and post-peak regimes. Based on this understanding, a coupled elastoplastic damage model is developed for capturing the dolomite’s mechanical behaviours. In the model, the effects of plasticity and damage on rocks is described by introducing plastic hardening and damage softening commonly in the plastic yield surface. Which are both derived from a suitable Helmholtz free energy function. The model is used to simulate the triaxial tests. Comparisons between test results and the numerical modelling show that the developed model is capable of describing the macro mechanical behaviours of the Wudongde dolomite. 相似文献
158.
Anil B. Valsangkar 《Marine Georesources & Geotechnology》2016,34(6):542-549
Regional scale morphological studies on different-sized polymetallic nodules from the Central Indian Basin show that only 2–5 cm sized nodules have highest occurrence per station (92–94% along latitudes; 88–94% along longitudes). A nodule size shows an inverse relationship with the nodule distribution, grade, and abundance. Interestingly, only 3–4 and 4–5 cm sized nodules have highest grade, abundance, and distribution percentages along longitudes in P1, first generation mine site and relinquished area, which further implies that the nodule mining along the longitude would be beneficial. Different-sized nodule groups suggest their formation under variable environmental conditions that existed in the Central Indian Basin. The coexistence of different-sized nodules suggests different environmental conditions existed in the Central Indian Basin. 相似文献
159.
160.
将不同浓度PM_(2.5)降尘作用于A549细胞后,利用MTT法检测其存活率,W-G染色观察细胞形态,荧光探针法检测细胞ROS和MMP相对水平,以探讨PM_(2.5)降尘对A549细胞线粒体氧化损伤的影响及作用机制。结果显示,经12. 5μg/m L的PM_(2.5)降尘作用A549细胞3 h后,细胞存活率为(81. 77±6. 15)%,并随作用浓度及时间增加呈递减趋势。PM_(2.5)染毒后可观察到细胞形态不规则,胞膜溶解破坏,细胞微核出现。PM_(2.5)降尘作用于细胞24 h后,胞内ROS相对含量随暴露浓度增加呈递增趋势,细胞MMP相对水平随染毒浓度增加而降低,且胞内ROS和MMP两者间存在显著相关关系(R2=0. 878)。提示PM_(2.5)降尘处理A549细胞后可通过刺激ROS的产生,诱导细胞MMP下降,造成细胞线粒体氧化损伤。 相似文献