全文获取类型
收费全文 | 8871篇 |
免费 | 1942篇 |
国内免费 | 3128篇 |
专业分类
测绘学 | 1176篇 |
大气科学 | 1127篇 |
地球物理 | 1803篇 |
地质学 | 6093篇 |
海洋学 | 1512篇 |
天文学 | 308篇 |
综合类 | 826篇 |
自然地理 | 1096篇 |
出版年
2024年 | 112篇 |
2023年 | 300篇 |
2022年 | 627篇 |
2021年 | 745篇 |
2020年 | 622篇 |
2019年 | 654篇 |
2018年 | 654篇 |
2017年 | 597篇 |
2016年 | 656篇 |
2015年 | 648篇 |
2014年 | 666篇 |
2013年 | 693篇 |
2012年 | 722篇 |
2011年 | 714篇 |
2010年 | 671篇 |
2009年 | 595篇 |
2008年 | 550篇 |
2007年 | 474篇 |
2006年 | 531篇 |
2005年 | 388篇 |
2004年 | 298篇 |
2003年 | 250篇 |
2002年 | 235篇 |
2001年 | 222篇 |
2000年 | 184篇 |
1999年 | 192篇 |
1998年 | 134篇 |
1997年 | 121篇 |
1996年 | 100篇 |
1995年 | 94篇 |
1994年 | 79篇 |
1993年 | 75篇 |
1992年 | 59篇 |
1991年 | 40篇 |
1990年 | 38篇 |
1989年 | 38篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 28篇 |
1985年 | 25篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1958年 | 3篇 |
1957年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
Based on the land surface temperature (LST), the land cover classification map,vegetation coverage, and surface evapotranspiration derived from EOS-MODIS satellite data, and by the use of GIS spatial analytic technique and multivariate statistical analysis method, the urban heat island (UHI) spatial distribution of the diurnal and seasonal variabilities and its driving forces are studied in Beijing city and surrounding areas in 2001. The relationships among UHI distribution and landcover categories, topographic factor, vegetation greenness, and surface evapotranspiration are analyzed. The results indicate that: (i) The significant UHI occur in Beijing city areas in the four seasons due to high heat capacity and multi-reflection of compression building, as well as with special topographic features of its three sides surrounded by mountains,especially in the summer. The UHI spatial distribution is corresponding with the urban geometry structure profile. The LST difference is approximately 4-6℃ between Beijing city and suburb areas, comparatively is 8- 10℃ between Beijing city area and outer suburb area in northwestern regions. (ii) The UHI distribution and intensity in daytime are different from nighttime in Beijing city area, the nighttime UHI is obvious. However, in the daytime, the significant UHI mainly appears in the summer, the autumn takes second place, and the UHI in the winter and the spring seem not obvious. The surface evapotranspiration in suburb areas is larger than that in urban areas in the summer, and high latent heat exchange is evident, which leads to LST difference between city area and suburb area. (iii) The reflection of surface landcover categories is sensitive to the UHI, the correlation between vegetation greenness and UHI shows obviously negative.The scatterplot shows that there is the negative correlation between NDVI and LST (R2 = 0.6481).The results demonstrate that the vegetation greenness is an important factor for reducing the UHI,and large-scale construction of greenbelts can considerably reduce the UHI effect. 相似文献
155.
介绍了东海大桥钻孔灌注桩基础的施工技术 ,对一些关键技术做了详细说明 ,还讨论了海上钻孔灌注桩施工成孔设备的选择及所用的淡水泥浆的配制 相似文献
156.
157.
Climatic response of thick leaf spruce (Picea crassifolia) tree-ring width at different elevations over Qilian Mountains, northwestern China 总被引:3,自引:0,他引:3
Tree-ring cores of thick leaf spruce (Picea crassifolia) taken from four sites at different elevations, in the middle of the Qilian Mountains, in the arid and semi-arid region of northwestern China, were used to develop four tree-ring width chronologies using standard dendrochronological methods. Results indicate that with increasing altitude the chronologies’ year-to-year variations decreased. Hence, the sensitivity of the tree-ring chronologies to climate decreases with altitude. Further analysis showed that the significant limiting factor on tree growth is spring precipitation. Measurements of stomata density and leaf dry weight suggest the species’ ecological adaptation strategy changes with elevation. At high elevation the metabolic rate of thick leaf spruce decreases, thus showing the effect of the climate. 相似文献
158.
在准噶尔盆地西北缘,寻找岩性圈闭油气藏已是至关重要的问题。但人们几乎还是用常规的手段来寻找岩性油气藏,没有实质性进展。本文是以利用宽方位角采集的地震数据为基础,对数据进行高保真资料处理和参考标准层的层拉平解释。利用前人的区域地质研究成果和钻井解释成果对侏罗系的沉积环境进行了精细的描述,确定了拐19井区在下侏罗统三工河组的出油层段附近的沉积环境由湖泊相-三角洲前缘相-河流相-湖泊相的演化过程。利用地震属性解释的结果也能较好地反映目标区的沉积环境变迁,并且与区域地质、测井解释结果相吻合,为寻找油气提供了很好的依据。由此得出利用地震属性可以进行沉积环境变迁分析,为油田寻找岩性圈闭及油气藏做出贡献。 相似文献
159.
160.