全文获取类型
收费全文 | 1462篇 |
免费 | 250篇 |
国内免费 | 176篇 |
专业分类
测绘学 | 88篇 |
大气科学 | 48篇 |
地球物理 | 648篇 |
地质学 | 704篇 |
海洋学 | 100篇 |
天文学 | 85篇 |
综合类 | 71篇 |
自然地理 | 144篇 |
出版年
2024年 | 12篇 |
2023年 | 39篇 |
2022年 | 69篇 |
2021年 | 49篇 |
2020年 | 64篇 |
2019年 | 67篇 |
2018年 | 62篇 |
2017年 | 56篇 |
2016年 | 57篇 |
2015年 | 67篇 |
2014年 | 79篇 |
2013年 | 82篇 |
2012年 | 74篇 |
2011年 | 98篇 |
2010年 | 61篇 |
2009年 | 82篇 |
2008年 | 66篇 |
2007年 | 94篇 |
2006年 | 106篇 |
2005年 | 84篇 |
2004年 | 71篇 |
2003年 | 67篇 |
2002年 | 49篇 |
2001年 | 65篇 |
2000年 | 37篇 |
1999年 | 41篇 |
1998年 | 30篇 |
1997年 | 41篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1888条查询结果,搜索用时 10 毫秒
31.
Ricardo J. Elia 《Natural Resources Research》1997,6(2):85-98
Archaeological sites, the material remnants of our human past, are finite and nonrenewable cultural resources that are under
constant threat from environmental forces, development activities, warfare, vandalism, and looting. Site looting is the destructive
removal of archaeological objects to supply the art market. Looting is part of an economic system, the antiquities market,
that works to supply the demand of collectors for archaeological objects. The destruction of archaeological resources by looters
is an international crisis and threatens to obliterate the world’s cultural heritage and our ability to understand past cultures.
The scale and intensity of the looting problem can be estimated by studying the extent of site destruction in countries of
origin and by investigating the sources of antiquities held by collectors. Finding a solution to the problem of looting will
require a focus on the demand side of the market (i.e., collectors) instead of the traditional focus on the supply side (looters,
dealers) 相似文献
32.
33.
Catalogues of actual observed intensities are constructed for three towns in the Ionian Islands. They are used for seismic hazard assessment and the results are compared with those obtained by standard approaches; that is, by statistics applied to the data computed from epicentral parameters. The results show that seismic hazard is better assessed using observed rather than computed data, but preparation of the local catalogue presents non-trivial difficulties. 相似文献
34.
沈冠军 《中国地球化学学报》1996,15(4):303-313
Calculations,according to some open-system models,point out that while a statistically significant discrepancy between the results of two U-series methods,^230Th/^234U and ^227Th/^220Th(or ^231Pa/^235U),attests a relatively recent and important uranium migration,concordant dates cannot guarantee closes-system behavior of sample.The results of 20 fossil bones from 10 Chinese sites,19 of which are determined by two U-series methods,are given,Judging from independent age controls,8 out of the 11 concordant age sets are unacceptable,The results in this paper suggest that uranium may cycle into or out of fossil bones,such geochemical events may take place at any time and no known preserving condition may securely protect them from being affected.So for the sitew we have studied,the U-series dating of fossil bones is of limited reliability. 相似文献
35.
论述了钻孔灌注桩常见现场事故的预防,分析和治理等方面的几个问题,叙述了钢筋笼上浮,导管堵塞,钢筋笼掉入孔内,导管提出混凝土面,掉钻头,串孔等事故的原因和处理方法及预防措施。 相似文献
36.
37.
钻孔岩芯饼状断裂破坏机制 总被引:2,自引:1,他引:2
本文首先阐述岩芯饼状断裂及其特征, 进而用断裂力学的理论与方法对岩饼破坏进行了断裂扩张机制的分析, 不但合理地解释了断裂特征及断裂破坏机制, 且以二滩坝址为例, 分析了产生钻孔岩饼的微裂纹条件及应力条件, 为定量地评价坝址地应力状态, 包括其大小及方向提供了一种新的方法。上述不仅具有重要的理论意义, 而且具有重要的工程实际意义。 相似文献
38.
About 70% of its land area as mountains and plateaus,China is the largest mountain countryin the world.Thanks to its vast territory (9.6 million km2),outstanding relief and varied climates,China boasts extremely plenty of ecosystems and landscapes.From south to north,it traverses almostall the temporal zones from tropical rainforest in the southernmost to frigid-temperate needle-leavedforest in the northernmost; from east to west,it sees a gradual transition fro humid forest landscape toextremely arid desert landscape; vertical change of landscapes is most striking owing to the existenceof many high mountains (above 6000-7000 m,e.g.,the Himalayas,the Kunlun,the Tianshan,theHengduan,etc.) and plateaus,especially the immense Tibetan Plateau (averagely 4500 m above sealevel).All of this give rise to the richness and diversity of ecosystems and landscape in China.Some ofthe ecosystems are endemic to China,e.g.,alpine desert and alpine steppe in the Tibetan Plateau.As aresult,China bears a great responsibility in the protection of global ecosystems and landscape. 相似文献
39.
Green''''s functions for uniformly distributed loads acting on an inclined line in a poroelastic layered site 总被引:4,自引:0,他引:4
Based on one type of practical Biot's equation and the dynamic-stiffness matrices of a poroelastic soil layer and half-space, Green's functions were derived for uniformly distributed loads acting on an inclined line in a poroelastic layered site. This analysis overcomes significant problems in wave scattering due to local soil conditions and dynamic soil-structure interaction. The Green's functions can be reduced to the case of an elastic layered site developed by Wolf in 1985. Parametric studies are then carried out through two example problems. 相似文献
40.