全文获取类型
收费全文 | 2445篇 |
免费 | 368篇 |
国内免费 | 453篇 |
专业分类
测绘学 | 99篇 |
大气科学 | 253篇 |
地球物理 | 999篇 |
地质学 | 1344篇 |
海洋学 | 116篇 |
天文学 | 6篇 |
综合类 | 112篇 |
自然地理 | 337篇 |
出版年
2024年 | 6篇 |
2023年 | 32篇 |
2022年 | 38篇 |
2021年 | 38篇 |
2020年 | 78篇 |
2019年 | 86篇 |
2018年 | 52篇 |
2017年 | 94篇 |
2016年 | 147篇 |
2015年 | 136篇 |
2014年 | 167篇 |
2013年 | 149篇 |
2012年 | 114篇 |
2011年 | 176篇 |
2010年 | 113篇 |
2009年 | 204篇 |
2008年 | 192篇 |
2007年 | 159篇 |
2006年 | 176篇 |
2005年 | 135篇 |
2004年 | 126篇 |
2003年 | 92篇 |
2002年 | 88篇 |
2001年 | 108篇 |
2000年 | 70篇 |
1999年 | 61篇 |
1998年 | 68篇 |
1997年 | 50篇 |
1996年 | 41篇 |
1995年 | 44篇 |
1994年 | 41篇 |
1993年 | 30篇 |
1992年 | 24篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3266条查询结果,搜索用时 15 毫秒
41.
液化场地桩-土-桥梁结构动力相互作用振动台试验研究进展 总被引:20,自引:3,他引:20
本文在全面归纳与总结液化场地桩-土-桥梁结构动力相互作用振动台试验及与之相关领域的国内外研究进展基础上,直接针对我国桥梁工程中的主要震害问题,提出在我国开展液化场地桩-土-桥梁结构动力相互作用振动台试验研究的必要性,并阐述作者对液化场地桩-土-张桥梁结构动力相互作用振动台试验中若干问题的认识。 相似文献
42.
David K. Keefer 《Surveys in Geophysics》2002,23(6):473-510
Post-earthquake field investigations of landslide occurrence have provided a basis for understanding, evaluating, and mapping the hazard and risk associated withearthquake-induced landslides. This paper traces thehistorical development of knowledge derived from these investigations. Before 1783, historical accounts of the occurrence of landslides in earthquakes are typically so incomplete and vague that conclusions based on these accounts are of limited usefulness. For example, the number of landslides triggered by a given event is almost always greatly underestimated. The first formal, scientific post-earthquake investigation that included systematic documentation of the landslides was undertaken in the Calabria region of Italy after the 1783 earthquake swarm. From then until the mid-twentieth century, the best information on earthquake-induced landslides came from a succession ofpost-earthquake investigations largely carried out by formal commissions that undertook extensive ground-based field studies. Beginning in the mid-twentieth century, when the use of aerial photography became widespread, comprehensive inventories of landslide occurrence have been made for several earthquakes in the United States, Peru, Guatemala, Italy, El Salvador, Japan, and Taiwan. Techniques have also been developed for performing ``retrospective' analyses years or decades after an earthquake that attempt to reconstruct the distribution of landslides triggered by the event. The additional use of Geographic Information System (GIS) processing and digital mapping since about 1989 has greatly facilitated the level of analysis that can applied to mapped distributions of landslides. Beginning in 1984, syntheses of worldwide and national data on earthquake-induced landslides have defined their general characteristics and relations between their occurrence and various geologic and seismic parameters. However, the number of comprehensive post-earthquake studies of landslides is still relatively small, and one of the most pressing needs in this area of research is for the complete documentation of landslides triggered by many more earthquakes in a wider variety of environments. 相似文献
43.
R. A. SHAKESBY C. J. CHAFER S. H. DOERR W. H. BLAKE P. WALLBRINK G. S. HUMPHREYS 《The Australian geographer》2003,34(2):147-175
Soil water repellency can enhance overland flow and erosion and may be altered by fire. The Christmas 2001 bushfires near Sydney allowed investigation of the relationship between fire severity, water repellency and hydrogeomorphological changes. For two sub-catchments with differences in fire severities in Nattai National Park, south-west of Sydney, this paper considers: (1) the links between fire severity based on SPOT image analysis and ground observation of fire severity and repellency; (2) the textural and organic/minerogenic characteristics of eroded sediment; and (3) erodibility, erosion and deposition of soils in both catchments. Ground surveys show that image analysis reflects well the degree of vegetation consumption by fire, but cannot adequately predict the degree of ground litter consumption, associated soil heating and repellency effects. Fire had varying effects on repellency, leaving it unchanged, destroying it or enhancing it, depending on the soil temperature reached. The main post-fire hydrogeomorphological changes have been widespread erosion and colluvial and alluvial deposition of topsoil in foot-slope locations and river systems, but only localised redistribution of the highly erodible, repellent sandy subsurface layer. The fire did not trigger major geomorphological change in the study area, but fires probably cause important topsoil and nutrient depletion and may also affect water quality. 相似文献
44.
陇东地区是黄河上游水土流失严重区 ,也是国家重点治理的地区之一。由于特殊的岩土体的存在 ,加重了这一地区水土流失作用的危害性。本文通过水土流失现象与地质作用的关系进行偿试性探讨 ,旨在从中找到防治水土流失的有效措施 ,开展治理工作 相似文献
45.
46.
云南省癌死亡率与土壤环境中化学元素的关系 总被引:3,自引:0,他引:3
癌病严重危害人类生命。研究表明:土壤环境中微量元素与肿病发生发展以及治疗相关,个别地区的地方病与元素含量关系密切。对土壤中元素含量研究证实:云南癌死亡率低于全国平均水平。文章详细讨论云南9种频发、52种常见癌症与元素的关系。 相似文献
47.
Yulin DENG Yan PENG Yukuan WANG Zongting YANG Institute of Mountain Hazards Environment Chinese Academy of Sichuan P. R. China College of Forestry Horticulture of Sichuan Agricultural University Sichuan P. R. China. Water Resources Administration in Ya''''an Sichuan P. R. China. 《国际泥沙研究》2003,18(4)
Converting farming slope land into artificial forestland or grassland is a major measure of soil/water conservation. Five conversion practices, namely, 1) a control plot still tilled with a crop (maize), 2) a folder grass-growing plot seeded with Lolium perenne , 3) a young alder tree-growing plot, 4) a pear orchard plot and 5)a bamboo plot intercropped with folder grass, were monitored to compare the soil conservation efficiency of those changes in Ya'an, Sichuan for 3 years between September 1998 and August 2001. Results showed that the 5 designed converting models functioned differently in erosion control. The most effective model was bamboo groves intercropped with folder grass (Lolium perenne). The folder grass (Lolium perenne) growing model was more effective than the pure pear orchard model. The least effective model was the young alder tree-growing slope, which was even less effective than the control (a slope without converted cultivation). Meanwhile, changes in the soil's physical properties r 相似文献
48.
Electrical, seismic, and electromagnetic methods can be used for noninvasive determination of subsurface physical and chemical properties. In particular, we consider the evaluation of water salinity and the detection of surface contaminants. Most of the relevant properties are represented by electric conductivity, P-wave velocity, and dielectric permittivity. Hence, it is important to obtain relationships between these measurable physical quantities and soil composition, saturation, and frequency. Conductivity in the geoelectric frequency range is obtained with Pride's model for a porous rock. (The model considers salinity and permeability.) White's model of patchy saturation is used to calculate the P-wave velocity and attenuation. Four cases are considered: light nonaqueous phase liquid (LNAPL) pockets in water, dense nonaqueous phase liquid (DNAPL) pockets in water, LNAPL pockets in air, and DNAPL pockets in air. The size of the pockets (or pools), with respect to the signal wavelength, is modeled by the theory. The electromagnetic properties in the GPR frequency range are obtained by using the Hanai–Bruggeman equation for two solids (sand and clay grains) and two fluids (LNAPL or DNAPL in water or air). The Hanai–Bruggeman exponent (1/3 for spherical particles) is used as a fitting parameter and evaluated for a sand/clay mixture saturated with water.Pride's model predicts increasing conductivity for increasing salinity and decreasing permeability. The best-fit exponent of the Hanai–Bruggeman equation for a sand/clay mixture saturated with water is 0.61, indicating that the shape of the grains has a significant influence on the electromagnetic properties. At radar frequencies, it is possible to distinguish between a water-saturated medium and a NAPL-saturated medium, but LNAPL- and DNAPL-saturated media have very similar electromagnetic properties. The type of contaminant can be better distinguished from the acoustic properties. P-wave velocity increases with frequency, and has dissimilar behaviour for wet and dry soils. 相似文献
49.
Hubert Hellmann 《洁净——土壤、空气、水》2003,31(2):85-96
A Recent Contamination Trend: Polycylic Aromatic Hydrocarbons (PAHs) in Aquatic and Terrestrial Sediments Concentrations of polycylic aromatic hydrocarbons (PAHs) measured in aquatic sediments of small, medium‐sized or very large inland lakes, of estuaries as well as in terrestrial sediments from Germany, the UK, Finland, and the USA were plotted in 10 trend curves over the period from 1800 to 1990. The segments of the bore cores were dated for their deposition age. For comparability of the results, the trend is preferentially shown by the guide parameter fluoranthene. Until the 19th century, a constant background value of CFluo = 10…50 μg/kg was observed in all regions. Then a steep increase in concentration followed, reaching in the aquatic sediments a maximum in the period 1940 to 1965, while the individual fluoranthene values ranged widely from 90 to 2400 μg/kg. In several regions, a more or less distinct decrease superseded this maximum, although this development did not appear in terrestrial sediments, in one estuary, and in remote forest lakes in Finland. The trend curves reflect the atmospheric deposition of PAHs in airborne dust and in some cases the import through runoff via rivers. Thus, the sediment profiles depict the development of air pollution by pyrogenic contaminants over more than a century. Sediment profiles from rivers can be used only with a high degree of reservation, because of the irregularity and low representativity of the sedimentation. 相似文献
50.