全文获取类型
收费全文 | 439篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 44篇 |
地球物理 | 100篇 |
地质学 | 164篇 |
海洋学 | 27篇 |
天文学 | 67篇 |
综合类 | 1篇 |
自然地理 | 41篇 |
出版年
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 15篇 |
2009年 | 24篇 |
2008年 | 17篇 |
2007年 | 22篇 |
2006年 | 13篇 |
2005年 | 16篇 |
2004年 | 9篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1969年 | 4篇 |
排序方式: 共有449条查询结果,搜索用时 431 毫秒
121.
Consideration of the history of Holocene climate in the Rocky Mountains indicates that the over-all trend during the past 2500 yr has been toward increasing warmth, interrupted by cooler times of minor advances of cirque glaciers. Comparison of Holocene climatic history with the record of past interglacials in the region suggests that the present interglacial is not complete and that the climate may become first warmer and subsequently wetter before it is completed. Correlation of the timing of the regional glacial-interglacial record for the past 140,000 yr with the record of major sea level changes and with the calculated changes in the earth's insolation suggest that the present interglacial may be completed within a few millenia and that it may be followed by a significant cooling of the climate. 相似文献
122.
Numerical simulations of the thermal evolution of carbonaceous chondrite parent bodies indicate a period of several million years during which convective motion of water could occur. The present study considers variations of permeability, radiogenic heating, and body radius. The model accounts for the radial variation of gravity within the body, melting of ice, freezing of liquid water, and variable water properties and incorporates a realistic equation of state for water. Some regions of a parent body experience no pore water flow while other regions experience hundreds of pore volumes of liquid water flow. The spatial heterogeneity in pore water flow reflects the convective pattern in the body. Hydrothermal alteration of minerals inside the parent body will accordingly vary greatly with location in the body, and one parent body could be the source of chemically diverse meteorites. 相似文献
123.
124.
Christopher J. Davis Michael D. Smith & Gerald H. Moriarty-Schieven 《Monthly notices of the Royal Astronomical Society》1998,299(3):825-833
Near-infrared images in H2 line emission and submillimetre maps in CO J = 3–2 emission illustrate the remarkable association between a molecular bow shock and the redshifted molecular outflow lobe in W75N. The flow lobe fits perfectly into the wake of the bow, as one would expect if the lobe represented swept-up gas. Indeed, these observations strongly support the 'bow shock' entrainment scenario for molecular outflows driven by young stars. The characteristics of the bow shock and CO outflow lobe are compared with those of numerical simulations of jet-driven flows. These models successfully reproduce the bulge and limb-brightening in the CO outflow, although the model H2 bow exhibits more structure extending back along the flow axis. We also find that the size of the flow, the high mass fraction in the flow at low outflow velocities (low γ values) and the high CO/H2 luminosity ratio indicate that the system is evolved. We also predict a correlation, in evolved systems, between outflow age and the CO/H2 luminosity ratio. 相似文献
125.
Jason H. Curtis Mark Brenner David A. Hodell Richard A. Balser Gerald A. Islebe Henry Hooghiemstra 《Journal of Paleolimnology》1998,19(2):139-159
We used multiple variables in a sediment core from Lake Peten-Itza, Peten, Guatemala, to infer Holocene climate change and human influence on the regional environment. Multiple proxies including pollen, stable isotope geochemistry, elemental composition, and magnetic susceptibility in samples from the same core allow differentiation of natural versus anthropogenic environmental changes. Core chronology is based on AMS 14C measurement of terrestrial wood and charcoal and thus avoids the vagaries of hard-water-lake error. During the earliest Holocene, prior to 9000 14C yr BP, the coring site was not covered by water and all proxies suggest that climatic conditions were relatively dry. Water covered the coring site by 9000 14C yr BP, coinciding with filling of other lakes in Peten and farther north on the Yucatan Peninsula. During the early Holocene (9000 to 6800 14C yr BP), pollen data suggest moist conditions, but high 18O values are indicative of relatively high E/P. This apparent discrepancy may be due to a greater fractional loss of the lake's water budget to evaporation during the early stages of lake filling. Nonetheless, conditions were moist enough to support semi-deciduous lowland forest. Decrease in 18O values and associated change in ostracod species at 6800 14C yr BP suggest a transition to even moister conditions. Decline in lowland forest taxa beginning 5780 14C yr BP may indicate early human disturbance. By 2800 14C yr BP, Maya impact on the environment is documented by accelerated forest clearance and associated soil erosion. Multiple proxies indicate forest recovery and soil stabilization beginning 1100 to 1000 14C yr BP, following the collapse of Classic Maya civilization. 相似文献
126.
The characteristics of the mid-latitude Pacific cyclones that produce precipitation over California are investigated statistically to determine their role in governing precipitation receipt. From all cyclones occurring over the Pacific Ocean from December through March and between 1965–1990 inclusive, we identify a subset of cyclones likely to produce precipitation over California. The characteristics analyzed are track, frequency, duration, speed, central pressure, and proximity. These are related to monthly precipitation for the entire period and are also used to explain the difference in precipitation received during the earlier (wet) and latter (dry) halves of the 1980s. Results indicate that the winter cyclones responsible for precipitation over California originate in the southeast quadrant of the region influenced by the Aleutian Low and decay south of the Gulf of Alaska. The extent of cyclonic activity over the east Pacific Ocean near California diminished during the dry period. There were fewer cyclones, they were significantly weaker, and they traveled along a more meridional track during the dry period. 相似文献
127.
Remediating Ground Water with Zero-Valent Metals: Chemical Considerations in Barrier Design 总被引:2,自引:0,他引:2
Paul G. Tratnyek Timothy L. Johnson Michelle M. Scherer Gerald R. Eykholt 《Ground Water Monitoring & Remediation》1997,17(4):108-114
To gain perspective and insight into the performance of permeable reactive barriers containing granular iron metal, it is useful to compare the degradation kinetics of individual chlorinated solvents over a range of operating conditions. Pseudo first-order disappearance rate constants normalized to iron surface area concentration (kSA ) recently have been reported for this purpose. This paper presents the results of further exploratory data analysis showing the extent to which variation in kSA is due to initial halocarbon concentration, iron type, and other factors. To aid in preliminary design calculations, representative values of kSA and a reactive transport model have been used to calculate the minimum barrier width needed for different ground water flow velocities and degrees of halocarbon conversion. Complete dechlorination of all degradation intermediates requires a wider treatment zone, but the effect is not simply additive because degradation occurs by sequential and parallel reaction pathways. 相似文献
128.
Gerald Young 《GeoJournal》1988,16(2):237-239
IGU-Reports
IGU commission on geographical education 相似文献129.
Gerald Young 《GeoJournal》1988,17(3):435-436
IGU Reports
IGU commission on geographical educationNewsletter 16 (abridged by GeoJournal) 相似文献130.