全文获取类型
收费全文 | 895篇 |
免费 | 41篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 60篇 |
地球物理 | 252篇 |
地质学 | 314篇 |
海洋学 | 90篇 |
天文学 | 90篇 |
综合类 | 5篇 |
自然地理 | 113篇 |
出版年
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 16篇 |
2019年 | 14篇 |
2018年 | 25篇 |
2017年 | 24篇 |
2016年 | 21篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 47篇 |
2012年 | 39篇 |
2011年 | 39篇 |
2010年 | 24篇 |
2009年 | 42篇 |
2008年 | 48篇 |
2007年 | 46篇 |
2006年 | 42篇 |
2005年 | 26篇 |
2004年 | 45篇 |
2003年 | 15篇 |
2002年 | 39篇 |
2001年 | 17篇 |
2000年 | 25篇 |
1999年 | 24篇 |
1998年 | 25篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 6篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1966年 | 3篇 |
排序方式: 共有944条查询结果,搜索用时 15 毫秒
101.
Pumping Test Analysis for a Tidally Forced Aquifer 总被引:3,自引:0,他引:3
102.
D.R. Hunter 《Precambrian Research》1974,1(4):295-326
The relationship in time and space of the elements comprising the greenstone—granitie terrane in the eastern Transvaal and Swaziland is discussed. On the evidence derived from structural analysis, metamorphic style, geochemistry, and geophysics it is concluded that sialic crust (now represented by the Ancient Gneiss Complex in Swaziland) pre-dates the Swaziland Sequence. It is postulated that the sialic crust formed as a result of partial and total melting of hydrous basaltic lithosphere under tectonically metastable conditions. Limited sedimentation and volcanism in small basins on this early crust took place during periods of quiescence, following which deformation resulted in the tectonic interslicing of the early sialic crust and the sedimentary—volcanic sequences that were metamorphosed at high temperatures and low pressure (Abukuma-type), and included limited partial melting. The protocontinental crust so formed was distended along linear zones overlying sites of mantle upwelling. Rifting resulted from the distension and was accompanied by intense volcanism typical of greenstone belts. Following mantle withdrawal sagging was initiated in the linear zone leading to sedimentation that was initially of turbidite type. As greater stability was achieved, the style of sedimentation changed and cratonic-type, Moodies Group sediments were deposited. The cyclic nature of the volcanism and sedimentation is considered to be a response to, and a reflection of, the degree of distension and of the vertical adjustments along the bounding faults. Diapiric rise of tonalitic magma produced as a result of partial melting of the early sialic crust mixing with mantle material caused the deformation of the original linear geometry. Continued depression of the amphibolite facies of the sialic crust into the zone of partial melting gave rise to potassic granitic magma that spread at higher crustal levels at interfaces of low free energy to form hood-like sheets of granite flanking the original linear rift. It is concluded that the eastern Transvaal and Swaziland area attained a crustal thickness of ± 25 km prior to 3.0 b.y. 相似文献
103.
104.
The application of a modified version of dynamic TOPMODEL for two subcatchments at Plynlimon, Wales is described. Conservative chemical mixing within mobile and immobile stores has been added to the hydrological model in an attempt to simulate observed stream chloride concentrations. The model was not fully able to simulate the observed behaviour, in particular the short‐ to medium‐term dynamics. One of the primary problems highlighted by the study was the representation of dry deposition and cloud‐droplet‐deposited chloride, which formed a significant part of the long‐term chloride mass budget. Equifinality of parameter sets inhibited the ability to determine the effective catchment mixing volumes and coefficients or the most likely partition between occult mass inputs and chloride mass inputs determined by catchment immobile‐store antecedent conditions. Some success was achieved, in as much as some aspects of the dynamic behaviour of the signal were satisfactorily simulated, although spectral analysis showed that the model could not fully reproduce the 1/f power spectra of observed stream chloride concentrations with its implications of a wide distribution of residence times for water in the catchment. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
105.
Pleistocene sediments and soils exposed at Stebbing in central Essex, England are described, analysed and interpreted. The sand and gravel units above Eocene London Clay and Upper Pliocene Red Crag are shown to be a high level member of the Kesgrave Formation, with a surface immediately beneath that of the Westland Green Gravels, which are tentatively assigned to the Pre-Pastonian ‘a’ Stage of the British Quaternary succession. The rubified, argillic soil developed in the surface of these fluvial deposits is a composite of the Valley Farm and Barham Soils and displays micromorphological evidence of several phases of clay illuviation, gleying and clay coating disruption. Originally truncated and buried beneath Anglian gelifluction deposits, cover sand and till, the soil has been exhumed in most places by subsequent erosion. The full succession, however, is preserved within large gulls that formed by periglacial cambering prior to this erosion. More recent loess incorporation and pedogenesis have modified the exhumed soil and the materials within the gulls. 相似文献
106.
Colin K. Ballantyne 《第四纪科学杂志》2007,22(4):343-359
Geomorphological mapping of northern Arran provides evidence for two advances of locally nourished glaciers, the younger being attributable to the Loch Lomond Stade (LLS) of ca. 12.9–11.5 k yr BP, primarily through the mutually exclusive relationship between glacial limits and Lateglacial periglacial features. The age of the earlier advance is unknown. Inferred LLS glacier cover comprised two small icefields and eight small corrie or valley glaciers and totalled 11.1 km2. ELAs reconstructed using area–altitude balance ratio methods range from 268 m to 631 m for individual glaciers, with an area‐weighted mean ELA of 371 m. ELAs of individual glaciers are strongly related to snow‐contributing areas. The area‐weighted mean ELA is consistent with a north–south decline in LLS ELAs along the west coast of Great Britain. This decline has an average latitudinal gradient of 70 m 100 km?1, equivalent to a mean southwards ablation‐season temperature increase of ca. 0.42°C 100 km?1. Mean June–August temperatures at the regional climatic ELA, estimated from chironomid assemblages in SE Scotland, lay between 5.7 ± 0.1°C and 4.1 ± 0.2°C. Empirical relationships between temperature and precipitation at modern glacier ELAs indicate equivalent mean annual precipitation at the ELA lay between 2002 ± 490 mm and 2615 ± 449 mm. These figures suggest that stadial precipitation on Arran fell within a range between +8% and ?33% of present mean annual precipitation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
107.
Li Zhai Blair J.W. Greenan John Hunter Thomas S. James Guoqi Han Phillip MacAulay 《大气与海洋》2015,53(5):476-490
AbstractSea-level allowances at 22 tide-gauge sites along the east coast of Canada are determined based on projections of regional sea-level rise for the Representative Concentration Pathway 8.5 (RCP8.5) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) and on the statistics of historical tides and storm surges (storm tides). The allowances, which may be used for coastal infrastructure planning, increase with time during the twenty-first century through a combination of mean sea-level rise and the increased uncertainty of future projections with time. The allowances show significant spatial variation, mainly a consequence of strong regionally varying relative sea-level change as a result of glacial isostatic adjustment (GIA). A methodology is described for replacement of the GIA component of the AR5 projection with global positioning system (GPS) measurements of vertical crustal motion; this significantly decreases allowances in regions where the uncertainty of the GIA models is large. For RCP8.5 with GPS data incorporated and for the 1995–2100 period, the sea-level allowances range from about 0.5?m along the north shore of the Gulf of St. Lawrence to more than 1?m along the coast of Nova Scotia and southern Newfoundland. 相似文献
108.
Colin R. McInnes 《Celestial Mechanics and Dynamical Astronomy》2011,110(3):199-215
This paper investigates new families of displaced, highly non-Keplerian orbits in the two-body problem and artificial equilibria
in the circular restricted three-body problem. The families of orbits presented extend prior work by using periodic impulses
to generate displaced orbits rather than continuous thrust. The new displaced orbits comprise a sequence of individual Keplerian
arcs whose intersection is continuous in position, with discontinuities in velocity removed using impulses. For frequent impulses
the new families of orbits approximate continuous thrust non-Keplerian orbits found in previous studies. To generate approximations
to artificial equilibria in the circular restricted three-body problem, periodic impulses are used to generate a sequence
of connected three-body arcs which begin and terminate at a fixed position in the rotating frame of reference. Again, these
families of orbits reduce to the families of artificial equilibria found using continuous thrust. 相似文献
109.
Heather Katherine Handley Colin G. Macpherson Jon P. Davidson 《Contributions to Mineralogy and Petrology》2010,159(6):885-908
The Gede Volcanic Complex (GVC) of the Sunda island arc (West Java, Indonesia) consists of multiple volcanic centres and eruptive
groups with complex magmatic histories. We present new petrological, mineralogical, whole-rock major and trace element and
Sr–O isotopic data to provide constraints on the relative importance of fractional crystallisation and magma mixing in petrogenesis,
as well as on the role and nature of the arc crust. Banded juvenile scoria from Young and Old Gede provide unequivocal evidence
for the (late-stage) interaction of distinct magmas at Gede volcano. However, the relatively small-degree compositional zoning
observed in plagioclase phenocrysts of all eruptive groups (up to ~20 mol% An) may be attributed to physical changes in magma
properties (e.g. P, T, and PH2O) rather than changes in melt composition. Major element and trace element variations within each eruptive series are inconsistent
with magmatic evolution through simple mixing processes. Instead, mixing of variably fractionated magma batches is suggested
to account for the significant scatter in some element variation diagrams. No correlation is observed between textural complexity
and/or mineral disequilibrium and whole-rock geochemistry. REE data and geochemical modelling indicate that fractional crystallisation
involving amphibole in the mid- to lower crust, and fractionation of plagioclase, clinopyroxene, Fe–Ti oxide ± olivine ± orthopyroxene
provide strong control on the geochemical evolution of GVC rocks. Two-pyroxene geothermobarometry provides pre-eruption crystallisation
temperatures of 891–1,046°C and pressures of 3.4–6.5 kbar, equivalent to ~13–24 km depth beneath the volcanoes (mid- to lower
crust). Low, mantle-like clinopyroxene δ18O values of GVC lavas and poor correlation of Sr isotope ratios with indices of differentiation precludes significant assimilation
of isotopically distinct crust during magmatic differentiation. Therefore, we suggest that the geochemical character of the
moderately thick West Javan arc crust is relatively immature compared to typical continental crust. Trace element ratios and
strontium isotopes show that the magmatic source composition of the older geographical units, Gegerbentang and Older Quaternary,
is distinct from the other GVC groups. 相似文献
110.
The prairie pothole region (PPR) in the north-central United States and south-central Canada constitutes the most important waterfowl breeding area in North America. Projected long-term changes in precipitation and temperature may alter the drivers of waterfowl abundance: wetland availability and emergent vegetation cover. Previous studies have focused on isolated wetland dynamics, but the implications of changing precipitation on managed, river-fed wetlands have not been addressed. Using a structured decision making (SDM) approach, we derived optimal water management actions for 20 years at four river-fed National Wildlife Refuges (NWRs) in North and South Dakota under contrasting increasing/decreasing (+/?0.4 %/year) inflow scenarios derived from empirical trends. Refuge pool depth is manipulated by control structures. Optimal management involves setting control structure heights that have the highest probability of providing a desired mix of waterfowl habitat, given refuge capacities and inflows. We found optimal seasonal control structure heights for each refuge were essentially the same under increasing and decreasing inflow trends of 0.4 %/year over the next 20 years. Results suggest managed pools in the NWRs receive large inflows relative to their capacities. Hence, water availability does not constrain management; pool bathymetry and management tactics can be greater constraints on attaining management objectives than climate-mediated inflow. We present time-dependent optimal seasonal control structure heights for each refuge, which are resilient to the non-stationary precipitation scenarios we examined. Managers can use this information to provide a desired mixture of wildlife habitats, and to re-assess management objectives in reserves where pool bathymetry prevents attaining the currently stated objectives. 相似文献