全文获取类型
收费全文 | 1587篇 |
免费 | 64篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 128篇 |
地球物理 | 443篇 |
地质学 | 493篇 |
海洋学 | 127篇 |
天文学 | 310篇 |
综合类 | 1篇 |
自然地理 | 137篇 |
出版年
2021年 | 29篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 50篇 |
2017年 | 38篇 |
2016年 | 68篇 |
2015年 | 39篇 |
2014年 | 46篇 |
2013年 | 94篇 |
2012年 | 69篇 |
2011年 | 91篇 |
2010年 | 66篇 |
2009年 | 103篇 |
2008年 | 85篇 |
2007年 | 67篇 |
2006年 | 67篇 |
2005年 | 72篇 |
2004年 | 51篇 |
2003年 | 47篇 |
2002年 | 55篇 |
2001年 | 34篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 30篇 |
1997年 | 18篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 7篇 |
1971年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有1670条查询结果,搜索用时 15 毫秒
51.
52.
Summary An overview of economics and design consideration for explosive overburden casting is given and the criteria for the successful application of this technique are discussed. These criteria are: blast design, economic considerations and environmental considerations. Explosive overburden casting may effect considerable cost savings if the market for increased production is available. However, if a fixed sales constraint exists the economic benefits of explosive overburden casting may be marginal and an extensive economic analysis is warranted. 相似文献
53.
Relationships among bottom-water dissolved oxygen (DO), vertical stratification, and the factors responsible for stratification-destratification in this shallow, low tidal-energy estuary were studied using a 15-yr set of biweekly measurements, along with some recent continuous-monitoring data. Hypoxia develops only when there is both vertical water-column stratification and warm water temperature (>15°C). In July, 75% of the DO readings were <5 mg 1?1, and one-third were <1 mg 1?1. Severe hypoxia occurs more frequently in the upper half of the estuary than near the mouth. Both the time series data and correlation analysis results indicate that stratification events and DO levels are tightly coupled with variations in freshwater discharge and wind stress. Stratification can form or disappear in a matter of hours, and episodes lasting from one to several days seem to be common. Estimated summertime respiration rates in the water and sediments are sufficient to produce hypoxia if the water is mixed only every 6–12 d. There has been no trend toward lower bottom water DO in the Pamlico River Estuary over the past 15 yr. *** DIRECT SUPPORT *** A01BY059 00002 相似文献
54.
This paper is a pedagogical introduction to avalanche models of solar flares, including a comprehensive review of recent modeling
efforts and directions. This class of flare model is built on a recent paradigm in statistical physics, known as self-organized
criticality. The basic idea is that flares are the result of an ‘avalanche’ of small-scale magnetic reconnection events cascading
through a highly stressed coronal magnetic structure, driven to a critical state by random photospheric motions of its magnetic
footpoints. Such models thus provide a natural and convenient computational framework to examine Parker's hypothesis of coronal
heating by nanoflares.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013301521745 相似文献
55.
Chigurupati Murali & Scott Tremaine 《Monthly notices of the Royal Astronomical Society》1998,296(3):749-762
We determine the response of a self-similar isothermal stellar system to small adiabatic gravitational perturbations. For odd spherical harmonics the response is identical to the response of the analogous isothermal fluid system. For even spherical harmonics the response can be regarded as an infinite series of wavetrains in log r , implying alternating compression and rarefaction in equal logarithmic radius intervals. Partly because of the oscillatory nature of the solutions, tidal fields from external sources are not strongly amplified by an intervening isothermal stellar system, except at radii ≲10−3.5 times the satellite radius; at some radii the stellar system can even screen the external tidal field in a manner analogous to Debye screening. As Weinberg has pointed out, individual resonances in a stellar system can strongly amplify external tidal fields over a limited radial range, but we cannot address this possibility because we examine only adiabatic perturbations. We also discuss the application of our method to the halo response caused by the slow growth of an embedded thin disc. 相似文献
56.
57.
58.
59.
Phillip H. Larson Ronald I. Dorn R. Evan Palmer Zack Bowles Emma Harrison Scott Kelley 《自然地理学》2014,35(5):369-389
The Sonoran Desert portion of the Basin and Range physiographic province contains a number of streams that now flow across once-closed basins. We explore here the research questions of if and how granitic rock pediments respond to the transition from rimming endorheic basins to bordering through-flowing streams. Granitic rock pediments of the northern Usery and eastern McDowell Mountains once graded to the closed Miocene–Pliocene Pemberton basin that occupied the present-day location of the confluence of the Salt and Verde Rivers. The process of lake overflow, which integrated these rivers, first aggraded fill terraces that, in turn, caused aggradation of a mantle of transported grus on bedrock pediments. Subsequent episodic incision of the Salt and Verde rivers lowered the base level; this led to the development of erosional features such as rolling topography of a degrading pediment mantle; exposure of the former piedmont angle and its associated zones of enhanced bedrock decay and regolith carbonate; and exposure of spheroidally weathered bedrock and emerging tors, some of which experienced 20th century erosion. The granitic pediments of the former Pemberton Basin, which now transport grus to the Salt and Verde rivers, have actively adjusted to aggradational and degradational events associated with drainage integration and do not appear to be inherited from an ancient wet climatic interval. 相似文献
60.
R. M. Hueckstaedt S. H. Batha M. M. Balkey N. D. Delamater J. R. Fincke R. L. Holmes N. E. Lanier G. R. Magelssen J. M. Scott J. M. Taccetti C. J. Horsfield K. W. Parker S. D. Rothman 《Astrophysics and Space Science》2005,298(1-2):255-259
Observations of the interstellar medium reveal a dynamic realm permeated by shocks. These shocks are generated on a large
range of scales by galactic rotation, supernovae, stellar winds, and other processes. Whenever a shock encounters a density
interface, Richtmyer-Meshkov instabilities may develop. Perturbations along the interface grow, leading to structure formation
and material mixing. An understanding of the evolution of Richtmyer-Meshkov instabilities is essential for understanding galactic
structure, molecular cloud morphology, and the early stages of star formation. An ongoing experimental campaign studies Richtmyer-Meshkov
mixing in a convergent, compressible, miscible plasma at the Omega laser facility. Cylindrical targets, consisting of a low
density foam core and an aluminum shell covered by an epoxy ablator, are directly driven by fifty laser beams. The aluminum
shell is machined to produce different perturbation spectra. Surface types include unperturbed (smooth), single-mode sinusoids,
multi-mode (rough), and multi-mode with particular modes accentuated (specified-rough). Experimental results are compared
to theory and numerical simulations. 相似文献