全文获取类型
收费全文 | 1289篇 |
免费 | 42篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 61篇 |
大气科学 | 100篇 |
地球物理 | 270篇 |
地质学 | 420篇 |
海洋学 | 90篇 |
天文学 | 250篇 |
综合类 | 5篇 |
自然地理 | 143篇 |
出版年
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 29篇 |
2017年 | 29篇 |
2016年 | 31篇 |
2015年 | 19篇 |
2014年 | 24篇 |
2013年 | 74篇 |
2012年 | 47篇 |
2011年 | 50篇 |
2010年 | 48篇 |
2009年 | 59篇 |
2008年 | 59篇 |
2007年 | 56篇 |
2006年 | 41篇 |
2005年 | 42篇 |
2004年 | 34篇 |
2003年 | 38篇 |
2002年 | 37篇 |
2001年 | 23篇 |
2000年 | 41篇 |
1999年 | 22篇 |
1998年 | 22篇 |
1997年 | 20篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 13篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 23篇 |
1989年 | 16篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 22篇 |
1983年 | 26篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1972年 | 19篇 |
1971年 | 12篇 |
1969年 | 7篇 |
排序方式: 共有1339条查询结果,搜索用时 31 毫秒
461.
Climate and weather are important for tourism and leisure as they impact on destination attractiveness and subsequent visitation. Through an archive analysis of media articles and a content analysis of Regional Tourism Organisation (RTO) websites, this paper explores perceived deficiencies in the currently available climate and weather information for tourists in New Zealand. While media reports focused on concern by many RTOs over the poor regional images generated by inaccurate and poorly presented climate and weather data, the RTO websites were found to contain limited climate and weather information. There is considerable potential for RTOs to improve in this respect. 相似文献
462.
J.R. Wilson B.R. Broitman J.E. Caselle D.E. Wendt 《Estuarine, Coastal and Shelf Science》2008,79(3):483-490
Recruitment of pelagic larval fishes to the nearshore environment is dependent on a suite of biological and physical processes operating at many spatial and temporal scales. Nearshore circulation processes associated with coastal upwelling are widely upheld as major determinants of year class strength for many rockfishes (Sebastes spp.), but the mechanism by which these processes drive recruitment is largely unknown. We used Standard Monitoring Units for the Recruitment of Fishes (SMURFs) to monitor recruitment of two rockfish complexes (Sebastes spp.) and cabezon (Scorpaenichthys marmoratus) from March to September of 2004 and 2005 at 3 sites along the central California coast. We examined the relationship between recruitment of these fishes and measurements of oceanographic variability associated with upwelling dynamics, including in situ water temperature, AVHRR sea surface temperature, the Bakun upwelling index, and an index of alongshore surface water transport. We found that rockfish comprising the KCGB complex (Sebastes atrovirens, Sebastes caurinus, Sebastes carnatus, Sebastes chrysomelas) recruit during early summer, while fishes of the BYO complex (Sebastes melanops, Sebastes flavidus, Sebastes serranoides), as well as cabezon recruit during late summer. Our results provide limited support for an association between the arrival of juvenile pelagic rockfish and cabezon to the nearshore environment and physical processes related to upwelling and relaxation. Beyond the limitations of our bimonthly sampling scheme, the lack of a clear pattern may be related to the near absence of upwelling–relaxation cycles along this stretch of coast during these two study periods. Moreover, the settlement and recruitment of nearshore fishes may be closely tied to processes occurring earlier in the larval stage. 相似文献
463.
464.
P. R. Wilson 《Solar physics》1988,117(2):205-215
The presentations and discussions which took place during the second meeting of the Solar Cycle Workshop are summarized under the headings: sunspot minimum, the extended cycle, the large-scale photospheric motions, the large-scale magnetic fields and the polar reversal, the small-scale fields, global cyclic phenomena and the fundamental processes. The progress achieved so far is assessed and the directions for future observational and theoretical work are suggested. 相似文献
465.
P. R. Wilson 《Solar physics》1986,106(1):1-28
Recent observations concerning the growth and decay of photospheric magnetic flux present a challenge to the conventional picture of the photosphere as a passive medium through which flux tubes emerge inertly. Rather, they suggest the possibility that interactions between the magnetic flux and the photospheric velocity fields may give rise to changes in the observed surface flux.In this paper the physics of flux changes are reviewed and the various terms in the hydromagnetic equation which give rise to the growth and decay of magnetic flux are examined. Several kinematic models for field changes are examined and it is shown that new flux loops may be generated by suitable oscillatory velocity fields near the boundaries of existing magnetic structures, thus increasing the gross flux through the photosphere. It is suggested that this mechanism may account for the appearance of moving magnetic features (knots of opposite polarities) at the boundaries of decaying sunspots.Other models are discussed and a tentative explanation of the apparently unbalanced growth of opposite polarities is given in terms of a current-sheet model. 相似文献
466.
A moment method with three stream division of the radiation field was suggested by Wilson, Wan and Sen (1980) for solving radiative transfer problems in stationary, non-grey extended shells surrounding a central star. Use was made of the generalised Eddington relations as the closure conditions of the moment equations. In the present paper the same method has been utilised to study the radiative transfer problems in a non-grey, expanding gaseous spherical shells surrounding a central star. The transfer equation has been set in comoving frame in spherical geometry. The radiation and material quantities, angles and frequencies have been expressed in comoving frame. The mean intensity, flux and K-integrals have been calculated for extensive atmospheres in the presence of different velocity fields. 相似文献
467.
A prominent feature of Titan's atmosphere is a thick haze region that acts as the end product of hydrocarbon and nitrile chemistry. Using a one-dimensional photochemical model, an investigation into the chemical mechanisms responsible for the formation of this haze region is conducted. The model derives profiles for Titan's atmospheric constituents that are consistent with observations. Included is an updated benzene profile that matches more closely with—recent ISO observations (Icarus 161 (2003) 383), replacing the profile given in the benzene study of Wilson et al. (J. Geophys. Res. 108 (2003) 5014). Using these profiles, pathways from polyynes, aromatics, and nitriles are considered, as well as possible copolymerization among the pathways. The model demonstrates that the growth of polycyclic aromatic hydrocarbons throughout the lower stratosphere plays an important role in furnishing the main haze layer, with nitriles playing a secondary role. The peak chemical production of haze layer ranges from 140 to 300 km peaking at an altitude of 220 km, with a production rate of 3.2×10−14 gcm−2 s−1. Possible mechanisms for polymerization and copolymerization and suggestions for further kinetic study are discussed, along with the implications for the distribution of haze in Titan's atmosphere. 相似文献
468.
The shape of the sunspot cycle 总被引:5,自引:0,他引:5
The temporal behavior of a sunspot cycle, as described by the International sunspot numbers, can be represented by a simple
function with four parameters: starting time, amplitude, rise time, and asymmetry. Of these, the parameter that governs the
asymmetry between the rise to maximum and the fall to minimum is found to vary little from cycle to cycle and can be fixed
at a single value for all cycles. A close relationship is found between rise time and amplitude which allows for a representation
of each cycle by a function containing only two parameters: the starting time and the amplitude. These parameters are determined
for the previous 22 sunspot cycles and examined for any predictable behavior. A weak correlation is found between the amplitude
of a cycle and the length of the previous cycle. This allows for an estimate of the amplitude accurate to within about 30%
right at the start of the cycle. As the cycle progresses, the amplitude can be better determined to within 20% at 30 months
and to within 10% at 42 months into the cycle, thereby providing a good prediction both for the timing and size of sunspot
maximum and for the behavior of the remaining 7–12 years of the cycle.
The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
469.
Elaine M. Sadler Roberto Ricci Ronald D. Ekers J. A. Ekers Paul J. Hancock Carole A. Jackson Michael J. Kesteven Tara Murphy Chris Phillips Robert F. Reinfrank Lister Staveley-Smith Ravi Subrahmanyan Mark A. Walker Warwick E. Wilson Gianfranco De Zotti 《Monthly notices of the Royal Astronomical Society》2006,371(2):898-914
470.