全文获取类型
收费全文 | 1462篇 |
免费 | 273篇 |
国内免费 | 137篇 |
专业分类
测绘学 | 97篇 |
大气科学 | 95篇 |
地球物理 | 549篇 |
地质学 | 950篇 |
海洋学 | 41篇 |
天文学 | 8篇 |
综合类 | 46篇 |
自然地理 | 86篇 |
出版年
2023年 | 5篇 |
2022年 | 27篇 |
2021年 | 26篇 |
2020年 | 44篇 |
2019年 | 52篇 |
2018年 | 34篇 |
2017年 | 60篇 |
2016年 | 44篇 |
2015年 | 48篇 |
2014年 | 92篇 |
2013年 | 58篇 |
2012年 | 61篇 |
2011年 | 108篇 |
2010年 | 62篇 |
2009年 | 119篇 |
2008年 | 110篇 |
2007年 | 106篇 |
2006年 | 99篇 |
2005年 | 55篇 |
2004年 | 71篇 |
2003年 | 53篇 |
2002年 | 48篇 |
2001年 | 45篇 |
2000年 | 41篇 |
1999年 | 45篇 |
1998年 | 39篇 |
1997年 | 39篇 |
1996年 | 42篇 |
1995年 | 32篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 22篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有1872条查询结果,搜索用时 15 毫秒
981.
中国东南地区岩石生热率分布特征 总被引:26,自引:0,他引:26
基于500余块岩石样品的生热率实测值和前人的研究成果,本文系统地分析了中国东南地区不同时代、不同岩性和不同大地构造单元岩石生热率的分布特征,揭示出华南沉积区地层在晚元古代一寒武纪和侏罗纪出现两次生热率高峰,花岗岩具有异常高的生热率背景。岩石生热率以粤中-赣南为核心,向外扩展呈下降趋势;政和-大埔断裂带西侧生热率明显高于东侧火山岩出露区;扬子沉积区明显低于华南区。按区域岩石生热率分布可以划分为三个区:南区生热率背景值超过2.8μW/m3,东区介于2.1~2.8μW/m3,北区普遍低于2.1μW/m3。岩石生热率分布在一定程度上反映了区域基底生热元素的丰度和岩浆活动的强度。 相似文献
982.
Frank Ahnert 《地球表面变化过程与地形》1987,12(1):3-15
The model SLOP3D is used to identify characteristic aspects of slope development under different conditions. A series of slopes along the Kall valley in the northern Eifel is reproduced by a developmental sequence of model slopes. The spatial and temporal variations of the components of slope development systems (relief, slope form, weathering rates, denudation rates) are discussed by means of mass movement and wash denudation models. The negative feedbacks between system components create a tendency towards the establishment of a dynamic equilibrium which is reached, however, only if the endogenic and exogenic conditions remain constant for the required relaxation time. The latter is shown to be a function of slope length, of the rate of uplift, of the denudational process type, and of the intensity of exogenic inputs (e.g. precipitation). Varying rock resistance leads to the development of shield inselbergs only if the rate of denudation becomes higher than the maximum possible weathering rate of the resistant bedrock. 相似文献
983.
984.
Monocyclic alkanes in Ordovician organic matter 总被引:1,自引:0,他引:1
The major compounds in the C15+ branched/cyclic alkane fractions of two Ordovician oils (Pine Unit and Midland Farms oils) and an immature Ordovician rock (Guttenberg Oil Rock) are monocyclics. One series of these compounds was identified as n-alkylcyclohexanes and another tentatively identified as methyl-n-alkylcyclohexanes. The carbon number distribution of these compounds resembled those of the n-alkanes found in these samples with an odd carbon number predominance. It is suggested that the monocyclic alkanes, in these Ordovician samples, may be principally derived from the cyclisation of straight-chain algal fatty acids, by mechanisms that involve decarboxylation. However, there is evidence from the m/z 97 fragmentograms of these samples, to indicate that methyl-n-alkylcyclohexanes can also be derived from fatty acids by a less preferred mechanism that does not involve decarboxylation or from other precursors.In addition, a sample of kerogen from the Guttenberg Oil Rock was hydrously pyrolysed. The saturated hydrocarbon products of this experiment showed very similar distributions (including monocyclics) to those observed in the Ordovician oils. This suggests that although the oils and the Guttenberg Oil Rock come from widely differing geographical locations, their precursor (algal derived) organic matter was very similar. 相似文献
985.
Rectangular blocks of York Stone and of concrete placed on a sodium chloride sabkha in southern Tunisia for six years suffered very severe breakdown, thereby indicating the power of salt weathering as a process in sabkha environments. 相似文献
986.
On May 7, 1986, the residents of Tuscaloosa, Alabama, felt a seismic event of local magnitude 3.6 that occurred at the same time as a rock burst and roof collapse in an active longwall coal mine. Visual inspection of the seismograms reveals a deficiency in energy at frequencies above 20 Hz compared to tectonic earthquakes or surface blasts. The predominance of energy below 5 Hz may explain reports of body wave magnitudes (m
b
) greater than 4.2. Also, 1.0 Hz surface waves were more strongly excited than body waves and may explain local felt effects more typically associated with greater epicentral distances. All recorded first motions were dilatational. The concentration of stations in the northern hemisphere allows reverse motion on an east-trending near-vertical plane or strike-slip motion on northwest or southeast trending planes. The reverse focal mechanism is preferred, because the area of roof collapse and the area of active longwall mining are located between two east-striking loose vertical fracture zones. The characteristics of the seismic event suggest that it might have been sudden shear failure resulting from accumulated strain energy in overlying strata behind an active longwall. Although an alternate interpretation of the focal mechanism as an implosion or shear failure in the strata above previously mined out areas is also allowed by the first motion data, this alternate intepretation is not supported by geological data. 相似文献
987.
在本文中,用实验的方法确定了由取样数据再建地形表面的误差和取样间隔之间的线性关系。正是这一关系的简单性和稳定性,为数字地面模型数据扶取的在线质量控制提供了一个可靠的方案。 相似文献
988.
以45年生酥梨树为试材,分析测定塑料薄膜覆盖、树盘覆草、自然生草、定期灌水、清耕等不同土壤水分管理措施对土壤水分和酥梨品质的影响,结果表明:不同处理间以塑料薄膜覆盖处理效果最好,不但果个较大,果实的固酸比值和产量也较高;树盘覆草次之,且具有土壤水分变化幅度较小和省工、省时等优点。 相似文献
989.
High resolution carbon isotopic records in millennial, centennial and decadal timescales from three stalagmites from three different caves under a similar monsoon climate in Guangxi–Guizhou, China, provided detailed information on the paleo-ecological environmental conditions in the past 15,000 years. The results indicate that during the glacial period, or cold-dry period, such as Heinrich event H1 and Younger Dryas event karst development was poor as was pedogenesis, C3 vegetation didn’t grow well, resulting in C4 plants dominating and with heavy δ13C values in stalagmites. In a warm-humid stage, C3 vegetation grew well and predominated with negative δ13C values. The δ13C records from stalagmites could be indicative of sensitive vegetation changes and reflective of climate changes in precipitation, temperature, etc. The δ13C records may also be used to distinguish different effects from nature or human activity. Particularly since the late Holocene, human activities have increased disturbances to environment, even more than natural factors. Forest vegetation was destroyed, C4 plants became dominant, and rock desertification was aggravated because of severe water and soil loss, all resulting in sharply increasing δ13C values of stalagmites that are heavier than pre-middle Holocene δ13C values. 相似文献
990.
This paper investigates the role played by the fumarolic plume of a passive degassing volcano in the genesis of rock coatings
(RC) and in the introduction and re-distribution of metals and trace elements in the surficial environment. At La Fossa active
volcano (Vulcano Island) and in the surrounding environment RC develop owing to exposure of the ground surface to the volcanic
acid plume produced by the passive degassing of La Fossa. Significant positive anomalies of a wide variety of metals and trace
elements (including Bi, Ag, Se, Te, Sb, Pb, As, Cu, Tl and Cd) were observed either in distal and proximal RC. Most of these
anomalies are interpreted to be the result of the transport and subsequent deposition of trace elements, likely to form volatile
compounds, in the fumarolic plume. Two main processes seem to control the geochemistry of RC: one is represented by the leaching
and subsequent deposition of elements from the proximal toward the distal RC; the other is the direct input of trace elements
carried by the emitted volcanic aerosol. The fact that most of the trace elements (particularly Pb, As, Tl, Bi, Te, Se, Cd)
enriched in the RC of Vulcano are highly toxic and potentially dangerous to health in high concentration, indicates that the
atmospheric metal injection by the quiescently degassing La Fossa volcano together with the subsequent deposition and remobilization
by means of surficial waters may represent an environmental hazard that should be taken into account in evaluating the potential
impact of volcanic air pollution on human health. 相似文献