全文获取类型
收费全文 | 2993篇 |
免费 | 249篇 |
国内免费 | 467篇 |
专业分类
测绘学 | 262篇 |
大气科学 | 118篇 |
地球物理 | 249篇 |
地质学 | 888篇 |
海洋学 | 371篇 |
天文学 | 9篇 |
综合类 | 268篇 |
自然地理 | 1544篇 |
出版年
2024年 | 2篇 |
2023年 | 42篇 |
2022年 | 172篇 |
2021年 | 146篇 |
2020年 | 189篇 |
2019年 | 209篇 |
2018年 | 151篇 |
2017年 | 128篇 |
2016年 | 156篇 |
2015年 | 127篇 |
2014年 | 156篇 |
2013年 | 229篇 |
2012年 | 160篇 |
2011年 | 191篇 |
2010年 | 144篇 |
2009年 | 133篇 |
2008年 | 144篇 |
2007年 | 140篇 |
2006年 | 120篇 |
2005年 | 119篇 |
2004年 | 95篇 |
2003年 | 77篇 |
2002年 | 89篇 |
2001年 | 63篇 |
2000年 | 98篇 |
1999年 | 76篇 |
1998年 | 66篇 |
1997年 | 50篇 |
1996年 | 40篇 |
1995年 | 37篇 |
1994年 | 36篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有3709条查询结果,搜索用时 19 毫秒
61.
辽西义县组奔龙类化石一新种 总被引:4,自引:1,他引:4
在辽宁西部义县头台的义县组中新发现的1件奔龙类化石标本,显示出许多中国鸟龙属(Sinornithosaurus)所具有的特征,如上颌骨眶前窝侧面具有装饰性凹坑、前颌骨齿无边缘小锯齿、齿骨后缘二分叉、指节Ⅲ-1略长于指节Ⅲ-2的2倍、踱骨Ⅲ部分窄踱型形态等。但其头骨的部分骨骼与千禧中国鸟龙(S.millenii)有明显的区别:前颌骨主体部分相对较高,其长仅稍大于其高,前颌骨角大,前颌骨上颌突与鼻突均很长,上颌骨不参与外鼻孔的构成,上颌骨窗相对较小且为圆形,方颧骨上升突明显长于颧骨突,齿骨长高之比小等。此外,新标本肠骨的耻骨柄前后方向的宽度小于髋臼宽度。这些不同之处表明,义县头台的标本应为中国鸟龙属另一新种,将其命名为郝氏中国鸟龙(新种)(S.haoiana sp.nov.)。 相似文献
62.
The design of roadbed-abutment transition part is always a challenging problem in transportation engineering, especially in permafrost distribution zone. A new type of roadbed-abutment transition part on permafrost was presented, and long-term observation was conducted for the deformation and the thermal regime of a roadbed-abutment transition part in the constructing Qinghai-Tibet Railway. In this paper, a new structure was presented and the observed settlements both in the subgrade and the base and its dependency with the thermal regime (permafrost table) were analyzed. In conclusion the roadbed-a-butment transition method for permafrost distribution zone was evaluated. 相似文献
63.
64.
新材料是发展高新技术产业的基础。根据广西的矿产资源优势和在矿物材料方面的研究基础和技术力量,提出了加强工艺矿物学研究,大力发展广西新型矿物材料的研究开发方向,特别提出了超细改性矿物粉体材料、环保矿物材料、节能保温矿物材料、高技术陶瓷材料和合成矿物晶体材料等材料体系中的重点开发方向。 相似文献
65.
66.
Helen Ruth Aspaas 《GeoJournal》2004,61(3):281-289
Women in many rural areas of the US often engage in small-scale businesses as one of several avenues for contributing to household
incomes. In those geographical areas that contain a significant minority population, many of the women's businesses display
the cultural diversity of the regions in which they live. Likewise, women's roles as economic providers as well as wives and
mothers are reflected in the manner in which they operate their businesses. Candida Brush suggests that women's strategies
for operating their businesses are highly integrative because women's business decisions are intertwined with familial responsibilities,
household economic demands and desires to contribute to their communities. Hispanic and Native American women in the Four
Corners region of southwestern US and African American women in central Virginia participated in interviews in which they
responded to numerous short answer and open-ended questions about their businesses and decision-making strategies. From these
interviews an image emerges of rural minority business women who are operating their businesses at the nexus of family obligations,
economic necessities, cultural ties and with a commitment for serving their communities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
Problems associated with tourism development in Southern Africa: The case of Transfrontier Conservation Areas 总被引:2,自引:0,他引:2
Sanette Ferreira 《GeoJournal》2004,60(3):301-310
Tourism in Southern Africa is synonymous with the wildlife safari. In the post-colonial era the establishment of so-called
‘peaceparks’ that straddle the borders of states has come to be seen as a key not only to increasing tourism in the Southern
African region, but also to the modernizing of conservation policies and the development of rural economies. This paper focuses
on the global and continental presence of transfrontier conservation areas, the link between conservation and tourism development,
and the current factors that constrain and influence the realization of an ‘African Dream’ — ‘establishment of the greatest
animal kingdom’. The unstable political situation in Zimbabwe and how this negatively affects wildlife conservation and tourism
in the Gonarezhou part of the Greater Limpopo Transfrontier Park, serves as a case study.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
68.
根据新土地分类在南海区1∶1000土地利用现状调查中的应用,采用文献分析法和实例验证法,探讨其在大比例尺土地利用现状调查中的适用性。结果表明:新土地分类在使用中存在诸如分类层次数目少且略显粗糙以及界线不严谨等问题。提出建议:增加分类层次熏进一步细化分类;更清晰表达地类涵义以及统一分类标准等。 相似文献
69.
Weights of Evidence Modeling of Mineral Potential: A Case Study Using Small Number of Prospects,Abra, Philippines 总被引:9,自引:1,他引:9
Weights of evidence (WofE) modeling usually is applied to map mineral potential in areas with large number of deposits/prospects. In this paper, WofE modeling is applied to a case study area measuring about 920 km2 with 12 known porphyry copper prospects. A pixel size of 100 m × 100 m was used in the spatial data analyses to represent in a raster-based GIS lateral extents of prospects and of geological features considered as spatial evidence. Predictor maps were created based on (a) estimates of studentized values of positive spatial association between prospects and spatial evidence; (b) proportion of number of prospects in zones where spatial evidence is present; and (c) geological interpretations of positive spatial association between prospects and spatial evidence. Uncertainty because of missing geochemical evidence is shown to have an influence on tests of assumption of conditional independence (CI) among predictor maps with respect to prospects. For the final predictive model, assumption of CI is rejected based on omnibus test but is accepted based on a new omnibus test. The final predictive model, which delineates 30% of study area as zones with potential for porphyry copper, has 83% success rate and 73% prediction rate. The results demonstrate plausibility of WofE modeling of mineral potential in large areas with small number of mineral prospects. 相似文献
70.
Targeting seasonal climate forecasts for integration into household level decisions: the case of smallholder farmers in Lesotho 总被引:2,自引:0,他引:2
Gina Ziervogel 《The Geographical journal》2004,170(1):6-21
Seasonal climate forecasts have been promoted as a means to increase the resilience of marginal groups in Africa. The manifestations of this are still to be seen. This paper argues that successful dissemination and adoption of the forecast requires an in-depth profile of the characteristics and needs of user groups. The case study of a mountainous village in southern Lesotho is used to highlight the decisions which one group of marginal users – smallholder farmers – might make in response to the forecast. A participatory role-play exercise explores what information households presently receive and how new climate forecast information could be integrated into seasonal decision making. Results show that there are a number of low-input options available to these farmers for responding to the forecast. Adoption, however, is going to require repeated exposure to the forecast in conjunction with forecast development that is suited to users' needs. The case study is linked back to the larger scale by suggesting paths that seasonal climate forecast development could take if it is to contribute to improving livelihood sustainability among marginal groups. 相似文献