全文获取类型
收费全文 | 354篇 |
免费 | 47篇 |
国内免费 | 47篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 36篇 |
地球物理 | 100篇 |
地质学 | 156篇 |
海洋学 | 23篇 |
天文学 | 13篇 |
综合类 | 40篇 |
自然地理 | 63篇 |
出版年
2024年 | 5篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 14篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 14篇 |
2016年 | 21篇 |
2015年 | 10篇 |
2014年 | 23篇 |
2013年 | 19篇 |
2012年 | 26篇 |
2011年 | 23篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 18篇 |
2007年 | 10篇 |
2006年 | 4篇 |
2005年 | 16篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 16篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 14篇 |
1995年 | 15篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有448条查询结果,搜索用时 15 毫秒
311.
混沌理论及其在地学中的应用前景 总被引:1,自引:0,他引:1
混沌理论作为一种普适性很强的新理论,在地球科学中的应用日前广泛,其意义已渐为人们所认识和关注。本文介绍了混沌在地球中的部分应用,认为混沌理论开阔了人们研究地学中复杂问题的思路;同时,地学中一些重大问题的解决也必将丰富和混沌理论。 相似文献
312.
Lucy J. Carpenter Stephen J. Andrews Richard T. Lidster Alfonso Saiz-Lopez Miguel Fernandez-Sanchez William J. Bloss Bin Ouyang Roderic L. Jones 《Journal of Atmospheric Chemistry》2017,74(2):145-156
Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH2I2) and chloro-iodomethane (CH2ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH2I2 and CH2ICl in air and of CH2I2 in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH2I2 was lower in amplitude than that of CH2ICl, despite its faster photolysis rate. We speculate that night-time loss of CH2I2 occurs due to reaction with NO3 radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k CH2I2+NO3 of ≤4 × 10?13 cm3 molecule?1 s?1; a previous kinetic study carried out at ≤100 Torr found k CH2I2+NO3 of 4 × 10?13 cm3 molecule?1 s?1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/? 0.8 nmol m?2 d?1 for CH2I2 and 3.7 +/? 0.8 nmol m?2 d?1 for CH2ICl), we show that the model overestimates night-time CH2I2 by >60 % but reaches good agreement with the measurements when the CH2I2 + NO3 reaction is included at 2–4 × 10?13 cm3 molecule?1 s?1. We conclude that the reaction has a significant effect on CH2I2 and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios. 相似文献
313.
The Yinyan Sn deposit, one of the three typical porphyry Sn deposits in China, is located in the western Guangdong province of the Cathaysia Block. Rhenium and osmium isotopes of molybdenites from the Yinyan deposit were first used to constrain the age of mineralization. Rhenium concentrations in molybdenite samples range from 0.13 to 1.3 µg g?1, indicating a crustal source for the ore‐forming materials. The Re–Os dating yield model ages ranging from 78.1 to 79.52 Ma, with an average of 78.65 ± 0.98 Ma, and give an isochron age of 78.8 ± 2.6 Ma. Evidently, isochron age is consistent with model ages in the error within the allowable range, so we can constrain the precise age of Yinyan Sn deposit at the Late Cretaceous. Based on the geological history and spatial‐temporal distribution of the Sn deposits, it is proposed that the formation of Sn deposits in the Cathaysia Block were related to lithospheric extension that are associated with a change in the polarity of the subduction of the Paleo‐Pacific Plate from oblique subduction to parallel the eastern margin of the Eurasian Plate after 135 Ma. 相似文献
314.
Yi-kang Li Jing-zheng Ouyang Li Lin Xing-liang Xu Fa-wei Zhang Yan-gong Du Shu-li Liu Guang-min Cao Fa Han 《山地科学学报》2016,13(11):1995-2005
Biological soil crusts (BSCs) are the important components of alpine meadow ecosystems. The extent and morphology of BSCs vary greatly with alpine meadow retrogressive succession due to grazing pressure. There is significant interest in impacts of crust composition on plant seed germination, especially in (semi-) arid environments. However, little is known about the influences of BSCs, and their associations with alpine meadow succession, on germination of typical alpine meadow vascular plant species. In a full factorial common-garden experiment, we studied effects of: (1) crust type, (2) seed position, and (3) surface texture on seed germination. We chose three typical alpine meadow plant species (i.e. Poa pratensis, Tibetia himalaica and Potentillen nivea), which belonged to different functional groups (graminoids, legumes, and forbs) and play important roles in all alpine meadow succession stages. Crust type and seed position influenced seed germination, and the inhibitory effects of BSCs depended on the crust type and seed species tested. The major factors influencing seed germination were BSC type, seed position, soil texture, and the interactions between BSC type and seed position; species and seed position; species and surface texture; and species, crust type, and surface texture. Cyanobacteria crust significantly inhibited germination of all seeds. Seed position also had a significant effect on seed germination (p < 0.001). Fewer seedlings germinated on the surface than below the surface, this was especially true for P. nivea. seeds within cyanobacteria and lichen crusts. Only germination rates of T. himalaica on the soil surface were significantly correlated with plant occurrence frequency within the alpine meadow community. The poor correlation for the other two species is possibly that they are perennials. Our results clearly demonstrated that BSCs can be biological filters during seed germination, depending on the BSC succession stage. Through their influences on seed germination, BSCs can strongly influence community assemblages throughout alpine meadow retrogressive succession. 相似文献
315.
Water plays an important role in nearly every aspect of geological processes as well as in the evolution of planetary bodies. Chang E-3 NIR spectra appeared weak peak of OH in the vicinity of signal 1.4 μm, it may represent the presence of water. In order to quantitatively calculate the water content, apatite as the research object in the paper. Through analyzing and validating the infrared spectrum correlation between 1.4 μm and 2.8 μm of the structure water in the apatite, we obtained its molar absorption coefficient in the infrared spectrum of 1.4 μm. IR spectra were collected on oriented. When the light vector E is parallel to the c-axis of the apatite crystal, H2O concentration in apatite can be related to measured IR absorbance as follows: C=ωA/ερd, which based on Beer-Lambert’s law. This result can provide reference for the interpretation of Chang E-3 near-infrared spectral data of water signal. This method can provide the basis for the quantitative calculation of structure water in the near infrared spectrum in other moon minerals. 相似文献
316.
Natural landscapes consist of the natural substances, environment, and phenomena, all of which provide many benefits to people, including a sense of place, sightseeing, relaxing, and recuperating. However, the economic value of natural landscapes has only been recognized in recent decades, and the resulting large-scale decline and degradation of ecosystems now severely threatens the sustainable provision of their services to society. There is an emerging consensus that natural capital should be incorporated into the current socioeconomic accounting system. Many studies valuated natural resources at local and regional scales, but there are very few empirical studies at a national level. To provide a benchmark for natural landscape management on a national scale, we use the travel cost method(TCM) and the contingent valuation method(CVM) to determine the economic value and the spatial distribution of natural landscapes across China. Our results show that the total economic value of China′s natural landscape was 9.75 × 10~(11) U.S. dollars(USD) in 2012. Of this value, the highest proportion was in the eastern and southwestern regions of China, which accounts for 23.7% and 18.3%, respectively. The provinces of Guangdong, Sichuan, Yunnan, Inner Mongolia, and Heilongjiang were the top five in terms of the largest number of natural landscapes and largest economic values. Together, these five provinces accounted for 32.9% of the total number of natural landscapes and 29.4% of the total economic value in 2012. We believe this study will increase awareness of the value of natural landscapes, and more importantly provide a scientific basis for resolving conflicts between development and resource conservation. 相似文献
317.
Carbon isotopic fractionation in the process of Fischer-Tropsch reaction in primitive solar nebula 总被引:1,自引:1,他引:0
Carbon isotopic fractionation of low-weight molecules of the products of Fischer-Tropsch reaction under the conditions of
Earth's accumulation region in primitive solar nebula has been experimentally studied. Among the reaction products, carbon
dioxide has the heaviest isotopic composition; carbon isotopic composition of methane has a large variation; different from
biogenic natural gases, carbon isotopic compositions among ethane, propane and butane yield a reverse distribution pattern.
It suggests that primordial hydrocarbons that were captured in the interior of the Earth during its accretion possess a reverse
carbon isotopic distribution pattern.
Project supported by the National Natural Science Foundation of China (Grant No. 49233060). 相似文献
318.
319.
~~AN EXPERIMENTAL STUDY ON SEDIMENT FLUSHING OF DONGZHUANG RESERVOIR ON THE JINGHE RIVER@Hongwu ZHANG$Department of Hydraulic Engineering,Tsinghua University!Beijing100084
@Ouyang ZHANG$Department of Hydraulic Engineering,Tsinghua University!Beijing100084
@Junhua ZHANG$Institute of Hydraulic Research of Yellow River Conservation Commission!zhengzhou 450003
@Guodong WANG$Institute of Hydraulic Research of Yellow River Conservation Comm… 相似文献
320.
Mass movements caused by recent tectonic activity: The 1999 Chi-chi earthquake in central Taiwan 总被引:10,自引:0,他引:10
Wen-Neng Wang Huei-Long Wu Hiroyuki Nakamura Shang-Chih Wu Shoung Ouyang Ming-Fang Yu 《Island Arc》2003,12(4):325-334
Abstract The Chi‐chi earthquake (MS = 7.7), which occurred in September 1999, seriously damaged central Taiwan. Approximately 2 years later (July 2001), the Toraji typhoon brought a heavy rainstorm (650 mm rain/day) and triggered widespread landslides in central Taiwan and parts of eastern Taiwan. Approximately 10 000 Chi‐chi earthquake‐induced landslides and 6000 Toraji typhoon‐related mass movements were delineated in an area of 2400 km2 using Satellite Pour l’Observation de la Terre (SPOT; French earth resource satellite) images. The landslide distribution could be closely related to the distribution of peak ground acceleration registered during the Chi‐chi earthquake. The study area was composed of Tertiary sedimentary and metamorphic rocks, whose age and induration increased eastward. The earthquake‐induced landslides were mostly distributed in the region between the Chelungpu Fault and the Lishan Fault to the east, whereas they were few in the region east of the Lishan Fault. The Toraji typhoon in 2001 severely damaged both regions that had been shattered by the Chi‐chi earthquake in 1999. The occurrence of earthquake‐induced landslides can be correlated with epicentral distance, and their occurrence has more influence from the rock type than from the ground motion. 相似文献