全文获取类型
收费全文 | 8882篇 |
免费 | 1404篇 |
国内免费 | 1962篇 |
专业分类
测绘学 | 513篇 |
大气科学 | 1551篇 |
地球物理 | 1873篇 |
地质学 | 3478篇 |
海洋学 | 2143篇 |
天文学 | 139篇 |
综合类 | 622篇 |
自然地理 | 1929篇 |
出版年
2024年 | 48篇 |
2023年 | 144篇 |
2022年 | 299篇 |
2021年 | 351篇 |
2020年 | 373篇 |
2019年 | 465篇 |
2018年 | 343篇 |
2017年 | 399篇 |
2016年 | 413篇 |
2015年 | 435篇 |
2014年 | 546篇 |
2013年 | 630篇 |
2012年 | 580篇 |
2011年 | 577篇 |
2010年 | 518篇 |
2009年 | 549篇 |
2008年 | 545篇 |
2007年 | 574篇 |
2006年 | 514篇 |
2005年 | 460篇 |
2004年 | 403篇 |
2003年 | 366篇 |
2002年 | 329篇 |
2001年 | 279篇 |
2000年 | 299篇 |
1999年 | 257篇 |
1998年 | 215篇 |
1997年 | 227篇 |
1996年 | 185篇 |
1995年 | 148篇 |
1994年 | 140篇 |
1993年 | 115篇 |
1992年 | 123篇 |
1991年 | 76篇 |
1990年 | 75篇 |
1989年 | 52篇 |
1988年 | 37篇 |
1987年 | 27篇 |
1986年 | 31篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 711 毫秒
941.
942.
943.
944.
The use of meiofauna as an indicator of benthic organic enrichment associated with salmonid aquaculture 总被引:4,自引:1,他引:3
Sutherland TF Levings CD Petersen SA Poon P Piercey B 《Marine pollution bulletin》2007,54(8):1249-1261
Sediment chemistry and meiofaunal samples were collected in the Broughton Archipelago, British Columbia, to examine the relationship between sediment variables and meiofauna diversity across near- and far-field gradients surrounding several finfish aquaculture operations. The sediment variables examined consisted of free sulfide concentrations, redox potential (E(NHE)), organic content, and sediment grain size. A strong trend between sediment texture and organic content was observed across all sampling locations, which reflected a wide range of sediment types (sand-silt) that exist within the Broughton Archipelago. The abundance of certain meiofaunal groups (kinorhynchs, crustaceans, polychaetes) declined in an asymptotic fashion with increasing free sulfide concentrations, an indicator of benthic organic enrichment. Within these relationships, low meiofaunal abundances occurred in fine sediments associated with higher organic contents. Although other groups (nematodes, foraminifera) showed a slight decline in abundance with increasing organic enrichment, a high amount of variability in abundance was observed at high free sulfide concentrations, rendering these groups not suitable as indicators of organic enrichment. This study reports both horizontal and vertical trends in meiofaunal distributions relative to free sulfide concentrations. The abundance of nematode and crustacean taxa decreased with sediment depth as well as increasing sulfide concentration, while polycheate abundance increased with increasing free sulfide concentration. The ratio of nematodes to copepods was also shown to represent the degree of organic loading associated with aquaculture operations and its application as an indicator of benthic impact is discussed. 相似文献
945.
Bathymetric segregation of sea urchins on reefs of the Canarian Archipelago: Role of flow-induced forces 总被引:1,自引:0,他引:1
F. Tuya J. Cisneros-Aguirre L. Ortega-Borges R.J. Haroun 《Estuarine, Coastal and Shelf Science》2007,73(3-4):481-488
We examined whether adults of three species of sea urchins species (Diadema antillarum, Arbacia lixula, and Paracentrotus lividus) exhibit a consistent depth-dependent partitioning pattern on rocky reefs of the Canarian Archipelago (eastern Atlantic). Hydrodynamic experiments were carried out to quantify the resistance to flow-induced dislodgement in these three species. We tested the model that different morphology can result in habitat partitioning among these sea urchins. Abundances of D. antillarum increased with depth. In contrast, A. lixula and P. lividus showed the opposite zonation pattern, coexisting in high abundances in the shallowest depths (<5 m), and occurring in low densities in the deepest part of reefs (>7 m). Both A. lixula and P. lividus had greater adhesion-surface to body-height ratios than D. antillarum. Similarly, A. lixula and P. lividus showed a greater ability to resist flow-induced dislodgement compared with D. antillarum. The mean “velocity of dislodgement” was 300% and 50% greater for A. lixula and P. lividus, respectively, relative to D. antillarum, for any particular size. As a result, A. lixula and P. lividus are better fitted to life in high-flow environments than D. antillarum. We conclude that the risk of dislodgement by water motion likely play a relevant role in the vertical distribution patterns of these sea urchins in the eastern Atlantic. 相似文献
946.
Journal of Geographical Sciences - Due to the atmospheric nuclear weapon tests carried out, terrestrial environments have been extensively contaminated by global fallout of plutonium (Pu)... 相似文献
947.
板桥凹陷钱圈地区沙河街组物源主要来自北部陡坡带增幅台地区和南部北大港潜山地区,在研究区北部陡坡带形成了扇三角洲沉积,在南部缓坡带形成了辫状河三角洲沉积。利用层序地层学和地震沉积学的研究思路和方法,在波阻抗数据体的基础上采用地层切片技术,在等时层序地层格架内结合单井岩-电关系,对三角洲体系砂体的展布特征进行了分析。研究结果表明:①南部缓坡带沙三上亚段沉积时期,物源主要来自北大港潜山地区,辫状河三角洲的砂体呈进积特征,展布范围逐渐变大,反映湖盆基准面下降的特征,在沙二段沉积时期,辫状河三角洲沉积物源来自增幅台和北大港潜山2个地区;陡坡带沙二段至沙一上亚段沉积时期,扇三角洲砂体呈退积特征,砂体展布范围逐渐变小,反映湖盆基准面上升的特征;②以地震波阻抗数据体为基础的地层切片技术可以清晰地刻画三角洲沉积体系的砂体沉积相带平面展布,砂体预测结果得到了钻井资料的进一步证实。 相似文献
948.
949.
950.
西昌市地质灾害发育分布规律及防灾建议 总被引:1,自引:0,他引:1
西昌市地处川西的安宁河流域,区内地质条环境件复杂,生态环境脆弱,泥石流、滑坡等地质灾害发育,给当地居民生命财产安全及经济发展带来了较大影响。本文通过对西昌市目前发育的153处不同类型的地质灾害进行统计,总结了地质灾害在流域、高程、时段等方面的分布规律;对影响或控制西昌市地质灾害发育的地形地貌、构造、岩土体结构、地震、降雨及人类工程活动等因素进行了分析、总结;并针对西昌市的地质灾害类型及发育分布特征提出了适用于该地区的科学、合理的地质灾害防灾建议。 相似文献