全文获取类型
收费全文 | 4064篇 |
免费 | 865篇 |
国内免费 | 1194篇 |
学科分类
地球科学 | 6123篇 |
出版年
2024年 | 42篇 |
2023年 | 125篇 |
2022年 | 256篇 |
2021年 | 308篇 |
2020年 | 244篇 |
2019年 | 292篇 |
2018年 | 242篇 |
2017年 | 240篇 |
2016年 | 286篇 |
2015年 | 284篇 |
2014年 | 266篇 |
2013年 | 308篇 |
2012年 | 299篇 |
2011年 | 356篇 |
2010年 | 292篇 |
2009年 | 291篇 |
2008年 | 296篇 |
2007年 | 258篇 |
2006年 | 249篇 |
2005年 | 188篇 |
2004年 | 126篇 |
2003年 | 114篇 |
2002年 | 113篇 |
2001年 | 111篇 |
2000年 | 78篇 |
1999年 | 85篇 |
1998年 | 53篇 |
1997年 | 63篇 |
1996年 | 31篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 21篇 |
1992年 | 32篇 |
1991年 | 25篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1984年 | 2篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1964年 | 1篇 |
1958年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有6123条查询结果,搜索用时 0 毫秒
1.
2.
This study uses a comparative approach to examine responses of marine ecosystems to climatic regime shifts. The three seas surrounding the Korean peninsula, the Japan/East Sea, the East China Sea and the Yellow Sea represent three contiguous but distinct ecosystems. Sampling has been carried out by the National Fisheries Research and Development Institute of South Korea since 1965, using the same methods in all three seas. Sampling was generally synoptic. Amplitude time series of 1st EOF modes for temperature, salinity, zooplankton biomass and concentrations of four major zooplankton taxa were used to determine whether the three marine ecosystems respond in a similar manner to climate variations. Temporal patterns of the variables were strongly similar among the three seas at decadal time scales, but very weakly similar at interannual scales. All three seas responded to a climatic regime shift that occurred in 1989. Temperature, zooplankton biomass and copepod concentrations increased in the late 1980s or early 1990s in all three seas. Concentrations of amphipods, chaetognaths and euphausiids also increased in the Japan/East Sea and the East China Sea, but not the Yellow Sea. The Yellow Sea ecosystem differs strongly from the other two seas, and water exchange between the Yellow Sea and the East China Sea is much weaker than that between the East China Sea and Japan/East Sea. Spatial patterns of zooplankton determined by the EOF analysis were closely related to currents and fronts in each of the three seas. 相似文献
3.
用切比雪夫多项式标准化GPS卫星轨道 总被引:1,自引:0,他引:1
根据精密星历提供的等时间间隔点上的卫星坐标,采用切比雪夫多项式拟合的方法,选用达到精度要求的最佳拟合多项式阶数,对GPS卫星轨道进行标准化,从中得出:选用不同的多项式阶数直接影响到拟合的精度。 相似文献
4.
5.
高校自然地理实践教学改革探讨 总被引:7,自引:0,他引:7
从现代自然地理学综合性和应用性的特点出发,结合自然地理教学现状,分析了自然地理实践教学改革的必要性。阐述了加强实践教学应遵循的基本原则。提出了改革的主要途径,即调整课程内容,优化自然地理课程体系;创新实践教学手段和方法;营造良好的学术氛围和加强横向科研合作。 相似文献
6.
Geomorphic effects of rural-to-urban land use conversion on three streams in the Central Redbed Plains of Oklahoma 总被引:2,自引:1,他引:2
This research evaluates the impact of rural-to-urban land use conversion on channel morphology and riparian vegetation for three streams in the Central Redbed Plains geomorphic province (central Great Plains ecoregion) of Oklahoma. The Deep Fork Creek watershed is largely urbanized; the Skeleton Creek watershed is largely rural; and the Stillwater Creek watershed is experiencing a rapid transition from rural to urban land cover. Each channel was divided into reaches based on tributary junctions, sinuosity, and slope. Field surveys were conducted at transects in a total of 90 reaches, including measurements of channel units, channel cross-section at bankfull stage, and riparian vegetation. Historical aerial photographs were available for only Stillwater Creek watershed, which were used to document land cover in this watershed, especially changes in the extent of urban areas (impervious cover).The three streams have very low gradients (< 0.001), width-to-depth ratios < 10, and cohesive channel banks, but have incised into red Permian shales and sandstone. The riparian vegetation is dominated by cottonwoods, ash, and elm trees that provide a dense root mat on stream banks where the riparian vegetation is intact. Channels increased in width and depth in the downstream direction as is normally expected, but the substrate materials and channel units remained unchanged. Statistical analyses demonstrated that urbanization did not explain spatial patterns of changes in any variables. These three channels in the central Redbed Plains are responding as flumes during peak flows, funneling runoff and the wash-load sediment downstream in major runoff events without any effect on channel dimensions. Therefore, local geological conditions (similar bedrock, cohesive substrates and similar riparian vegetation) are mitigating the effects of urbanization. 相似文献
7.
遥感技术在煤炭地质中的应用现状及前景 总被引:6,自引:0,他引:6
介绍了遥感技术在煤炭资源调查和评价、煤矿区地质灾害调查和评估、生态环境及污染调查评价和监测以及煤矿三维可视化仿真规划系统建设方面的应用研究现状及所取得的主要成果,并结合遥感技术的发展方向,展望了其在煤炭地质中的应用前景。 相似文献
8.
西南某电站右岸倾坡内夹泥裂隙成因探讨 总被引:1,自引:0,他引:1
西南某拟建大型水电站的右岸岩体中存在倾向坡内的夹泥裂隙,通过对其的发育情况以及所处的地质环境进行系统的研究和认真剖析,认为该区内的倾坡内夹泥裂隙的成因并非正常卸荷引起,而是在构造的基础上,穹隆挽近期隆起的结果,为右岸坝肩稳定性评价提供了可靠的依据。 相似文献
9.
10.