全文获取类型
收费全文 | 138篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 5篇 |
地球物理 | 37篇 |
地质学 | 43篇 |
海洋学 | 14篇 |
天文学 | 15篇 |
自然地理 | 24篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 9篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 11篇 |
2008年 | 2篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 5篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1920年 | 2篇 |
排序方式: 共有148条查询结果,搜索用时 31 毫秒
51.
美国西部近8000年来树木年轮重建降雨量序列中的气候突变 总被引:1,自引:0,他引:1
1 IntroductionThe U niversity of A rizona Laboratory of Tree-Ring Research collected tree-ring sam ples from anum ber of long-lived trees, dating back thousands of years, from eight states in the w esternU nited States. H ughes and G raum lich (1996) pres… 相似文献
52.
Stephen C. Kuehn Duane G. Froese Franklin F. Foit Jr. Peter Rotheisler 《Quaternary Research》2009,71(2):201-47
The Glacier Peak tephra beds are among the most widespread and arguably some of the most important late Pleistocene chronostratigraphic markers in western North America. These beds represent a series of closely-spaced Plinian and sub-Plinian eruptions from Glacier Peak, Washington. The two most widespread beds, Glacier Peak ‘G’ and ‘B’, are reliably distinguished by their glass major and trace element abundances. These beds are also more broadly distributed than previously considered, covering at least 550,000 and 260,000 km2, respectively. A third bed, the Irvine bed, known only from southern Alberta, is similar in its major-element composition to the Glacier Peak G bed, but it shows considerable differences in trace element concentrations. The Irvine bed is likely considerably older than the G and B tephras and probably records an additional Plinian eruption, perhaps also from Glacier Peak but from a different magma than G through B. A review of the published radiocarbon ages, new ages in this study, and consideration in a Bayesian framework suggest that the widespread G and B beds are several hundred years older than widely assumed. Our revised age is about 11,600 14C yr BP or a calibrated age (at 2 sigma) of 13,710-13,410 cal yr BP. 相似文献
53.
54.
55.
In this paper, we first predict eclipses and occultations of the Galilean satellites in 1979 and find that, although circumstances are generally poor, about 75 events are observable. We have then made a special point of including 40 eclipses of J5 (Amalthea) by the Galilean satellites in the hope that both visual and far-infrared light curves can be obtained—the former giving accurate astrometric information for J5, and the latter possibly bearing on its surface stucture or composition. 相似文献
56.
This paper attempts to present a critical assessment of the evidence bearing on the possible existence of a tenth (S10) and an eleventh (S11) satellite of Saturn. For S10 we have two candidates: Themis and Janus. An inspection of the original plates dispels any possibility favoring the presence of Themis. Definitive statements concerning the other two satellites are more difficult to make, but we show quantitatively that existing observations are unable to provide unique orbits—the usual criterion for existence. However, a considerably stronger case can be made for Janus than for S11. The safest conclusion seems to be that the region between ring A and Mimas may well contain one, two, or even many satellites that should be carefully looked for during the ring-plane passages in 1979/80. 相似文献
57.
F.A. Franklin 《Icarus》1979,40(3):329-334
A principal feature of the asteroidal distribution is the rapid truncation of its population outward from ~3.4 AU. This paper presents further evidence, based on the motion and distribution of certain minor planets with large semimajor axes, that this truncation cannot be strictly the result of gravitational perturbations of the major planets even acting over times of ~109 years. The motion of other outer asteroids sets a probable upper limit of 0.081 on Jupiter's eccentricity. 相似文献
58.
59.
The interaction of Mn2+ with the surface of calcite in aqueous solutions is complex. In dilute solutions the Mn2+ is rapidly absorbed, MnCO33 nucleates on the calcite surface and then grows by a first order reaction with respect to the initial Mn2+ concentration. At higher ionic strengths in NaCl solutions, the rate of these processes is slower, but the same general pattern persists. In solutions containing Mg2+, at the concentration of seawater and in seawater, the nucleation phase of the uptake process does not appear to occur. The long-term uptake rate of Mn2+ on the surface of calcite in seawater is first order with respect to the dissolved Mn2+ concentration. The rate constant is over three orders of magnitude smaller than that found in dilute Mg2+-free solutions. A probable explanation for the slower growth rate in seawater is that MnCO3 is not nucleated on the calcite surface due to the presence of high Mg2+ concentrations. The Mg2+, through site competition, prevents enough Mn2+ from being adsorbed to reach a critical concentration for MnCO3 nucleation. This behavior is similar to that found for orthophosphate with calcite surfaces in dilute solutions and seawater. It indicates that rhodochrosite cannot nucleate in carbonate-rich recent sediments unless the Mg2+ concentration is lowered below that of seawater.Measurements of the solubility of rhodochrosite in seawater gave results from an undersaturation approach to equilibrium in excellent agreement with those found in previous studies in dilute solutions. When equilibrium was approached from supersaturation, approximately fifty times more calcium was precipitated than Mn2+. The measured solubility was over twice that determined from undersaturation. It is possible that a Mn—calcite containing 25 to 30 mol% MnCO3 formed on the rhodochrosite from the supersaturated solutions. Consequently, it is doubtful that pure rhodochrosite controls the concentration of Mn2+ even in calcium carbonate-poor marine environments. 相似文献
60.
Alves SR Severino PC Ibbotson DP da Silva AZ Lopes FR Sáenz LA Bainy AC 《Marine environmental research》2002,54(3-5):241-245
Furadan is a carbamate pesticide used widely to combat agricultural pests. However little information is available about the toxicity of furadan in aquatic macroinvertebrates. The in vivo effects of furadan were evaluated in mussels, Perna perna, and oysters, Crassostrea rhizophorae. Glutathione S-transferase (GST), catalase (CAT) and cholinesterase (ChE) activities were measured in the gills of both species exposed to furadan (100 microg/l) for 96 h. No changes were observed in GST activity in the exposed groups. CAT activity was higher (9%) in the oysters exposed to furadan. ChE activity was inhibited by 64 and 35%, respectively, in C. rhizophorae and P. perna exposed to furadan, suggesting that the former is more susceptible to the toxic effects of furadan. 相似文献