全文获取类型
收费全文 | 5302篇 |
免费 | 766篇 |
国内免费 | 693篇 |
专业分类
测绘学 | 1005篇 |
大气科学 | 540篇 |
地球物理 | 1134篇 |
地质学 | 1920篇 |
海洋学 | 968篇 |
天文学 | 7篇 |
综合类 | 440篇 |
自然地理 | 747篇 |
出版年
2024年 | 29篇 |
2023年 | 78篇 |
2022年 | 153篇 |
2021年 | 223篇 |
2020年 | 235篇 |
2019年 | 260篇 |
2018年 | 193篇 |
2017年 | 243篇 |
2016年 | 274篇 |
2015年 | 253篇 |
2014年 | 369篇 |
2013年 | 406篇 |
2012年 | 320篇 |
2011年 | 364篇 |
2010年 | 289篇 |
2009年 | 317篇 |
2008年 | 360篇 |
2007年 | 375篇 |
2006年 | 320篇 |
2005年 | 226篇 |
2004年 | 211篇 |
2003年 | 179篇 |
2002年 | 171篇 |
2001年 | 154篇 |
2000年 | 130篇 |
1999年 | 102篇 |
1998年 | 99篇 |
1997年 | 75篇 |
1996年 | 79篇 |
1995年 | 54篇 |
1994年 | 56篇 |
1993年 | 47篇 |
1992年 | 35篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1977年 | 1篇 |
排序方式: 共有6761条查询结果,搜索用时 203 毫秒
31.
32.
33.
34.
Using benthic macrofauna to assess environmental quality of four intertidal mudflats in Hong Kong and Shenzhen Coast 总被引:4,自引:0,他引:4
Cai Lizhe Nora F. Y. Tam Teresa W. Y. Wong Ma Li Gao Yang Yuk-Shan Wong 《海洋学报(英文版)》2003,22(2):309-319
Abstract-Intertidal zone is a significant wetland between land and ocean. It plays an important rolein maintaining local ecological balance. Both Mai Po and Futian intertidal mudflats are located in Shen-zhen Bay and are important "refueling" point along the East Asian/Australian flyway of migratory birds.The environmental quality of Mai Po and Futian mudflats have aroused great concern due to rapid eco-nomic developments in Hong Kong and Shenzhen in recent decades. Microinfauna of Mai Po and Futianmudflats was investigated in December 2000 and the faunal data were used to assess their environmentalquality. Two other mudflats, namely Ma Wan Typhoon Shelter (a more disturbed area) and Luk Kengintertidal mudflat (a place with relatively less human disturbance), were also sampled for macroinfaunaand used as reference mudflats. Shannon-Weaver species diversity index (I_(sd)), biotic coefficient (C_b)and macrofaunal pollution index (I_(mp)) of the macrofauna community on four intertidal mudflats wereused to 相似文献
35.
36.
37.
Miriam J. Doyle Kathryn L. Mier Morgan S. Busby Richard D. Brodeur 《Progress in Oceanography》2002,53(2-4)
The coastal regions of the northeast Pacific support large, economically valuable fishery resources and provide nursery areas for many fish species. Over the last few decades, there have been dramatic shifts in species abundance and composition in this area. In this paper, we examine the springtime spatial patterns in the ichthyoplankton of three oceanographically different regions, the Southeast Bering Sea, the Gulf of Alaska and the U.S. West Coast. The data examined are a subset of a larger database (comprising data from cruises conducted from 1972 to 1997) that is being used to investigate spatial, seasonal and interannual patterns in ichthyoplankton of the northeast Pacific in relation to environmental conditions. Ichthyoplankton were collected during seven cruises using 60-cm bongo nets. Spatial patterns of ichthyoplankton were examined using both classification and ordination techniques. Relative Bray-Curtis dissimilarity coefficients calculated from the log10 (n+1) of abundance data were used as input to the numerical classification of species and stations. Nonmetric multidimensional scaling was also applied to the abundance data to examine geometric patterns in the data. The numerical analyses of the species abundance data sets for each cruise revealed spatial patterns in the ichthyoplankton that suggest the occurrence of geographically distinct assemblages of fish larvae in each region. For all three sampling regions, the assemblage structure is primarily related to bathymetry, and Shelf, Slope, and Deep-Water assemblages are described. This shallow to deep-water gradient in species occurrence and abundance reflects the habitat preference and spawning location of the adult fish. Another degree of complexity is superimposed on this primary assemblage structure in each region and seems to be related to local topography and the prevailing current patterns. The patterns in ichthyoplankton assemblages of the three regions in the northeast Pacific Ocean described here form the basis for future investigations of spatial and temporal patterns in the ichthyoplankton of the subarctic Pacific.Regional Index Terms: Northeast Pacific Ocean, Southeast Bering Sea, Gulf of Alaska, U.S. West Coast. 相似文献
38.
INTRODUCTIONTheDenglouCape ,inthesouthwestoftheLeizhouPeninsula ,isatthenorthmarginoftropicalzone .SeveralresearchesandcartographiesoftheregionalgeomorphologyandQuater narygeology ,whichwerecarriedoutinthepast,allincludethisarea (MGL ,SCSIO ,CAS ,1 978;GPCSGRCZT… 相似文献
39.
40.
第二次土地调查建库过程中数据质量的控制方法 总被引:1,自引:0,他引:1
第二次全国土地调查工作正在广泛开展,其中数据库如实、高效、精确的建立是最主要的任务,而数据质量控制程度的高低直接影响了数据库的建设状况。本文以山西省大同市新荣区为例简要叙述了本次土地利用现状调查数据质量的误差来源及影响因素,同时针对这些问题提出了各阶段的数据质量控制方法与措施,从而对本次土地调查建库过程中的数据质量控制方法进行了探究。 相似文献