全文获取类型
收费全文 | 5233篇 |
免费 | 147篇 |
国内免费 | 61篇 |
专业分类
测绘学 | 125篇 |
大气科学 | 455篇 |
地球物理 | 1110篇 |
地质学 | 1757篇 |
海洋学 | 465篇 |
天文学 | 953篇 |
综合类 | 17篇 |
自然地理 | 559篇 |
出版年
2021年 | 59篇 |
2020年 | 63篇 |
2019年 | 75篇 |
2018年 | 96篇 |
2017年 | 88篇 |
2016年 | 119篇 |
2015年 | 129篇 |
2014年 | 131篇 |
2013年 | 280篇 |
2012年 | 158篇 |
2011年 | 252篇 |
2010年 | 212篇 |
2009年 | 298篇 |
2008年 | 213篇 |
2007年 | 204篇 |
2006年 | 191篇 |
2005年 | 166篇 |
2004年 | 182篇 |
2003年 | 189篇 |
2002年 | 176篇 |
2001年 | 104篇 |
2000年 | 108篇 |
1999年 | 103篇 |
1998年 | 102篇 |
1997年 | 64篇 |
1996年 | 82篇 |
1995年 | 70篇 |
1994年 | 64篇 |
1993年 | 64篇 |
1992年 | 55篇 |
1991年 | 73篇 |
1990年 | 57篇 |
1989年 | 52篇 |
1988年 | 47篇 |
1987年 | 70篇 |
1986年 | 48篇 |
1985年 | 63篇 |
1984年 | 85篇 |
1983年 | 63篇 |
1982年 | 57篇 |
1981年 | 76篇 |
1980年 | 62篇 |
1979年 | 54篇 |
1978年 | 74篇 |
1977年 | 53篇 |
1976年 | 56篇 |
1975年 | 45篇 |
1974年 | 44篇 |
1973年 | 44篇 |
1971年 | 36篇 |
排序方式: 共有5441条查询结果,搜索用时 0 毫秒
21.
Richard J. Seymour 《Ocean Engineering》1986,13(5)
A class of turbidity flows is investigated in which sediment is entrained sufficient to balance losses and an equilibrium flow is sustained. The analytical models for predicting equilibrium flow configurations are surveyed. These are found to differ by two orders of magnitude in the required flow speeds. Five field observations of self-sustaining turbidity flows are investigated as a test for the analytical models. The model of Bagnold (1962) is found to have skill in predicting all of the field observations. The significance of these flows to the reliability of pipelines, cables and other engineering structures on continental shelves is considered. Circumstantial evidence is presented that suggests that these flows may be a mechanism for offshore flows of sand from beaches during major storms. 相似文献
22.
It has been shown by Brown and Emslie (1988) that any optically thin thermal bremsstrahlung source must emit an energy spectrumL () (keV s–1 keV–1) which has the property that higher derivatives alternate in sign, i.e., (–)
j
L(j)() > 0 for allj. In this short note, we apply this test to the superhot component discussed by Linet al. (1981) in order to determine whether a strictly thermal interpretation of this component is valid. We find that all statistically significant higher derivatives do indeed have the correct sign; this strengthens the identification of this component as due to a thermal source.Presidential Young Investigator. 相似文献
23.
Mirdita Zone ophiolites and associated sediments in Albania reveal Neotethys Ocean origin 总被引:1,自引:1,他引:0
Hans-Jürgen Gawlick Wolfgang Frisch Lirim Hoxha Paulian Dumitrica Leopold Krystyn Richard Lein Sigrid Missoni Felix Schlagintweit 《International Journal of Earth Sciences》2008,97(4):865-881
The Mirdita Ophiolite Zone in Albania is associated with widespread mélanges containing components of up to nappe-size. We
dated matrix and components of the mélange by radiolarians, conodonts, and other taxa. The components consist of radiolarites,
pelagic limestones and shallow-water limestones, all of Triassic age, as well as ophiolites. Triassic radiolarite as a primary
cover of ophiolite material proves Middle Triassic onset of Mirdita ocean-floor formation. The mélange contains a turbiditic
radiolarite-rich matrix (“radiolaritic flysch”), dated as Late Bajocian to Early Oxfordian. It formed as a synorogenic sediment
during west-directed thrusting of ophiolite and sediment-cover nappes representing ocean floor and underplated fragments of
the western continental margin. The tectonic structures formed during these orogenic events (“Younger Kimmeridian or Eohellenic
Orogeny”) are sealed by Late Jurassic platform carbonates. The geological history conforms with that of the Inner Dinarides
and adjoining areas; we therefore correlate the Mirdita-Pindos Ophiolite Zone with the Vardar Zone and explain its present
position by far-distance west-directed thrusting. 相似文献
24.
We used transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to study magmatic crystals in the Ben
Lomond rhyolite lava dome, Taupo Volcanic Center, New Zealand. Using TEM and SEM to investigate the size distributions of
these crystals, we identified three size populations: microphenocrysts (>1.2 μm wide), microlites (>0.6 μm wide), and smaller
crystals (<0.6 μm wide) which we term "nanolites". The predominant mineral phases of the microlites and nanolites are augites,
pigeonites, and hypersthenes. The compositions and microstructures within these pyroxenes indicate disequilibrium crystallization
at approximately 850–900 °C and undercoolings as high as 300 °C from equilibrium crystallization temperatures. Complex microstructures
resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian
layer of the Ben Lomond rhyolite dome. This study demonstrates the existence of sub-micron magmatic crystals in a rhyolite
and illustrates the potential of TEM to provide unique information about the crystallization and cooling histories of glassy
volcanic rocks.
Received: May 8, 1995 / Accepted: November 27, 1995 相似文献
25.
Richard C. Adams Jeffrey M. Cohen John C. Peterson 《Astrophysics and Space Science》1996,236(2):229-256
In a previous paper Adams, Cary and Cohen (1994) presented a model of a supernova. In that paper the equations of General Relativity describing the evolution of a spherically symmetric, radiating star were solved analytically. The evolution of the star was determined by the application of boundary conditions at the center and at the edge. Due to lmitations in the presupernova model, only the very slow inward motion of an unstable, degenerate core could be considered. The solution was also limited by the need to exclude a runaway term, one that increased exponentially with time. Without the exclusion of the runaway, the luminosity would have increased without bound and the mass would have become negative.This paper presents a completely analytic solution to the equations of General Relativity describing the evolution of a Type II supernova. Professor S.E. Woosley kindly gave us data on the physical variables of a 12M
0 presupernova star. In our model the core collapses within 1 s, leaving a 1.3M
0 remnant. Shortly afterward 10.6M
0 is ejected to infinity, and 0.17M
0 is radiated away in the form of neutrinos. The distance of the edge from the center increases proportionally to the two-thirds power of the time. The luminosity decreases proportionally to the inverse four-thirds power.Although the runaway solution was modified by the exploding rather than a static envelope, it must still be excluded by adjusting initial conditions. Its character is changed from an exponential to a very large power (55) of time. The removal of a degree of freedom by this exclusion leads to physically non-sensical results such as negative luminosity. The inclusion of a term describing motion of the mantle due to neutrino interactions provides the additional degree of freedom necessary for physically reasonable results. 相似文献
26.
A microflare or a group of Ellerman bombs was found to be associated with several points of white-light enhancements. These points had similar sizes as facular points (d 0.3 arc sec). Temporal evolution of these activities is described. Origins of these activities are discussed to be deeply seated excess heating in chromospheric and photospheric levels. 相似文献
27.
Richard A. Serafin 《Celestial Mechanics and Dynamical Astronomy》1996,65(4):389-398
We deal here with the efficient starting points for Kepler's equation in the special case of nearly parabolic orbits. Our approach provides with very simple formulas that allow calculating these points on a scientific vest-pocket calculator. Moreover, srtarting with these points in the Newton's method we can calculate a root of Kepler's equation with an accuracy greater than 0.001 in 0–2 iterations. This accuracy holds for the true anomaly || 135° and |e – 1| 0.01. We explain the reason for this effect also.Dedicated to the memory of Professor G.N. Duboshin (1903–1986). 相似文献
28.
29.
Measurements made when testing an interferometric system for imaging the sodium emission indicate that, between 3 and 7.5 arc min (9 and 23RJ) from Jupiter, the observed emissions can probably be attributed to terrestrial airglow. 相似文献
30.