全文获取类型
收费全文 | 1082篇 |
免费 | 21篇 |
国内免费 | 31篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 99篇 |
地球物理 | 178篇 |
地质学 | 441篇 |
海洋学 | 60篇 |
天文学 | 211篇 |
综合类 | 18篇 |
自然地理 | 114篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2018年 | 49篇 |
2017年 | 44篇 |
2016年 | 28篇 |
2015年 | 32篇 |
2014年 | 33篇 |
2013年 | 72篇 |
2012年 | 40篇 |
2011年 | 59篇 |
2010年 | 54篇 |
2009年 | 58篇 |
2008年 | 46篇 |
2007年 | 47篇 |
2006年 | 51篇 |
2005年 | 38篇 |
2004年 | 45篇 |
2003年 | 31篇 |
2002年 | 22篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 24篇 |
1995年 | 14篇 |
1994年 | 19篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1971年 | 9篇 |
排序方式: 共有1134条查询结果,搜索用时 578 毫秒
71.
Eugene Yee 《Boundary-Layer Meteorology》2001,98(3):517-527
A simple analytical model is developed for the meanupcrossing rate of plume concentration fluctuations assuming that thisprocess can be well approximated by a lognormal process. The resultingexpression requires only the specification of the in-plume fluctuationintensity and in-plume Taylor micro-time scale and, hence, does notexplicitly involve the joint probability density function of theconcentration and its derivative. The analytical model provides agood fit to some field measurements of the mean upcrossing rate ina dispersing plume. 相似文献
72.
Dust in the Wind: Long Range Transport of Dust in the Atmosphere and Its Implications for Global Public and Ecosystem Health 总被引:4,自引:0,他引:4
Movement of soil particles in atmospheres is a normal planetary process. Images of Martian dust devils (wind-spouts) and dust
storms captured by NASA's Pathfinder have demonstrated the significant role that storm activity plays in creating the red
atmospheric haze of Mars. On Earth, desert soils moving in the atmosphere are responsible for the orange hues in brilliant
sunrises and sunsets. In severe dust storm events, millions of tons of soil may be moved across great expanses of land and
ocean. An emerging scientific interest in the process of soil transport in the Earth's atmosphere is in the field of public
and ecosystem health. This article will address the benefits and the potential hazards associated with exposure to particle
fallout as clouds of desert dust traverse the globe.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
73.
R. Eugene Turner 《Estuaries and Coasts》2001,24(2):139-150
Important parameters of estuarine variability include morphology, flushing times, nutrient loading rates, and wetland: water ratios. This variability both reflects and disguises underlying relationships between the physics and biology of estuaries, which this comparative analysis seeks to reveal, using the Gulf of Mexico (GOM) estuaries as a starting point. A question used to focus this analysis is: are the GOM estuaries unique? The GOM receives the Mississippi River, a uniquely large, world-class river, which dominates the freshwater and nutrient inflows to the GOM continental shelf, whose margins include 35 major estuarine systems. These GOM estuaries have 28% and 41% of the U.S. estuarine wetlands and open water, respectively. Within the GOM, estuarine nitrogen, phosphorus, and suspended matter loading varies over 2 orders of magnitude. Anoxic estuarine events tend to occur in estuaries with relatively slow freshwater turnover and high nitrogen loading. Compared to estuaries from other regions in the U.S., the average GOM estuary is distinguished by shallower depths, faster freshwater flushing time, a higher wetland area:open water area ratio, greater fisheries yield per area wetland, lower tidal range, and higher sediment accumulation rates. The average GOM estuary often, but not always, has a flora and fauna not usually found in most other U.S. estuaries (e.g., manatees and mangroves). Coastal wetland loss in the GOM is extraordinarily high compared to other regions and is causally linked to cultural influences. Variations in nutrient loading and population density are very large among and within estuarine regions. This variation is large enough to demonstrate that there are insufficient systematic differences among these estuarine regions that precludes cross-system analyses. There are no abrupt discontinuities among regions in the fisheries yields per wetland area, tidal amplitude and vegetation range, salt marsh vertical accretion rates and organic accumulations, nitrogen retention, or wetland restoration rates. These results suggest that a comparative analysis emphasizing forcing functions, rather than geographic uniqueness, will lead to significant progress in understanding how all estuaries function, are perturbed, and even how they can be restored. 相似文献
74.
On three-dimensionality of shelterbelt structure and its influences on shelter effects 总被引:5,自引:0,他引:5
Natural shelterbelts, unlike planar barriers, have a certain width, within which interactions among wind speed, drag force and pressure perturbations create a net sheltering effect. The variations of flow, drag force, permeability, and pressure perturbation for shelterbelts of different widths and different horizontal structures are numerically studied, and their influences on shelter efficiency are discussed. Comparisons are made of fourteen medium-dense shelterbelts, with the same overall leaf-area, that differ only in width or horizontal distribution of leaf-area density. The simulated results are consistent with both field observations and wind-tunnel measurements.The simulations demonstrate that the total drag force of the entire shelterbelt varies little with changes in width and structure. The results also show that shelter distance and the overall average wind speed reduction decrease only by 15–18% as width increases by a factor of 100, and changes even less for different internal structure. However, width greatly affects the location of minimum wind speed, pressure perturbation, and the permeability of shelterbelts. Horizontal changes of wind speed inside the uniform shelterbelts have four different patterns, which depend on shelterbelt width and height. The absolute pressure perturbation significantly decreases with increasing width. A possible cause of the insensitivity of shelter efficiency to width and internal inhomogeneous structure is the compensation between the effects of permeability and pressure perturbation on shelter efficiency. 相似文献
75.
76.
77.
78.
Eugene I. Smith 《Earth, Moon, and Planets》1973,6(1-2):3-31
Over 300 previously unrecognized volcanic domes were identified on Lunar Orbiter photographs using the following criteria:
(1) the recognition of land forms on the Moon similar in morphology to terrestrial volcanic domes, (2) structural control,
(3) geomorphic discordance, and (4) the recognition of land forms modified by dome-like swellings. Many terrestrial volcanic
domes are similar in morphology to lunar domes. This analogy suggests that some lunar hills are in fact extrusive volcanic
domes. Many of the domes identified in this paper seem to be related to basins and craters, and with the exception of local
tectonic grid control few domes are related to any observable Moon-wide pattern. Domes are not uniquely found on maria. Dome
formation probably spans a wide range of lunar time and activity in areas where domes are located may be continuing to the
present as revealed by the close correlation of dome distribution with the distribution of lunar transient events. The overall
morphology of a lunar dome is a poor indicator of the composition of the rock that forms the dome.
Contribution No. 33 Planetary Geology Group, University of New Mexico. 相似文献
79.
Eugene Rabe 《Celestial Mechanics and Dynamical Astronomy》1973,8(2):177-179
As previously shown (Rabe, 1970), two classes of small periodic librations exist, in the plane, elliptic restricted problem, for an infinite sequence of easily specified oscillation frequenciesZ
j
. The present paper considers the dependence ofZ on the eccentricitye of the primary motion, in addition to its dependence on the mass parameter , and determines the resulting relations between ande, for any given periodic frequencyZ
j
. These relationships are obtained from the conditionD (Z
j
,, e)=0, where the basic determinantD has been expanded up to terms of orderZ
20, 5, ande
4.Presented at the Conference on Celestial Mechanics, Oberwolfach, Germany, August 27–September 2, 1972. 相似文献
80.
Variation in surface turbulence and the gas transfer velocity over a tidal cycle in a macro-tidal estuary 总被引:2,自引:0,他引:2
Christopher?J.?ZappaEmail author Peter?A.?Raymond Eugene?A.?Terray Wade?R.?McGillis 《Estuaries and Coasts》2003,26(6):1401-1415
The gradient flux technique, which measures the gas transfer velocity (k), and new observational techniques that probe turbulence in the aqueous surface boundary layers were conducted over a tidal
cycle in the Plum Island Sound, Massachusetts. Efforts were aimed at testing new methods in an estuarine system and to determine
if turbulence created by tidal velocity can be responsible for the short-term variability ink. Measurements were made during a low wind day, at a site with tidal excursions of 2.7 m and a range in tidal velocity of
nearly 1 m s−1. Estimates ofk using the gradient flux technique were made simultaneously with the Controlled Flux Technique (CFT), infrared imagery, and
high-resolution turbulence measurements, which measure the surface renewal rate, turbulent scales, and the turbulent dissipation
rate, respectively. All measurements were conducted from a small mobile catamaran that minimizes air- and water-side flow
distortions. Infrared imagery showed considerable variability in the turbulent scales that affect air-water gas exchange.
These measurements were consistent with variation in the surface renewal rate (range 0.02 to 2 s−1), the turbulent dissipation rate (range 10−7 to 10−5 W kg−1), andk (range 2.2 to 12.0 cm hr−1). During this low wind day, all variables were shown to correlate with tidal speed. Taken collectively our results indicate
the promise of these methods for determining short-term variability in gas transfer and near surface turbulence in estuaries
and demonstrate that turbulent transport associated with tidal velocity is a potentially important factor with respect to
gas exchange in coastal systems. 相似文献