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排序方式: 共有343条查询结果,搜索用时 15 毫秒
1.
2.
Hydrodynamic implications of large offshore mussel farms 总被引:2,自引:0,他引:2
Plew D.R. Stevens C.L. Spigel R.H. Hartstein N.D. 《Oceanic Engineering, IEEE Journal of》2005,30(1):95-108
3.
F. Moseley J.C. Cuttell E.W. Lange D. Stevens J.R. Warbrick 《Journal of Structural Geology》1981,3(3):237-251
The Pre-Betic is the most northerly of the Alpine zones forming the Betic Cordilleras of southern Spain. It consists of strongly folded and faulted Mesozoic and Tertiary rocks, the oldest of which are ferruginous and gypsiferous Triassic mudstones, followed by a predominantly carbonate facies of Cretaceous, Palaeogene and Miocene age. Although this sequence is interrupted by a number of minor unconformities, the major structures were formed during the middle or late Miocene. The highly incompetent Triassic rocks are the most strongly deformed, and form diapiric intrusions discordant to regional structural trends in the younger rocks. The latter are essentially of two facies: massive competent limestones which are deformed by relatively simple folds of large wavelength, and highly incompetent marl-limestone interbeds with complex disharmonic folds and crush belts. Faults include low-angle and high-angle thrusts, gravity slides and wrench faults. The regional tectonic strike is ENE to NE, but the diapiric intrusions mostly follow WNW and N directions. These intrusions have pushed the younger rocks aside, the result being polyphase structures of several trends.Less intense post-Miocene tectonics are mostly associated with continued diapirism and have resulted in the folding and tilting of the late Miocene to Quaternary elastic sediments. 相似文献
4.
Zsuzsanna Balogh-Brunstad C. Kent Keller Forrest Stevens Bernard T. Bormann 《Geochimica et cosmochimica acta》2008,72(11):2601-2618
Ectomycorrhiza-forming fungi (EMF) alter the nutrient-acquisition capabilities of vascular plants, and may play an important role in mineral weathering and the partitioning of products of weathering in soils under nutrient-limited conditions. In this study, we isolated the weathering function of Suillus tomentosus in liquid-cultures with biotite micas incubated at room temperature. We hypothesized that the fungus would accelerate weathering by hyphal attachment to biotite surfaces and transmission of nutrient cations via direct exchange into the fungal biomass. We combined a mass-balance approach with scanning electron microscopy (SEM) and atomic force microscopy (AFM) to estimate weathering rates and study dissolution features on biotite surfaces. Weathering of biotite flakes was about 2-3 orders of magnitude faster in shaken liquid-cultures with fungus compared to shaken controls without fungus, but with added inorganic acids. Adding fungus in nonshaken cultures caused a higher dissolution rate than in inorganic pH controls without fungus, but it was not significantly faster than organic pH controls without fungus. The K+, Mg2+ and Fe2+ from biotite were preferentially partitioned into fungal biomass in the shaken cultures, while in the nonshaken cultures, K+ and Mg2+ was lost from biomass and Fe2+ bioaccumulated much less. Fungal hyphae attached to biotite surfaces, but no significant surface changes were detected by SEM. When cultures were shaken, the AFM images of basal planes appeared to be rougher and had abundant dissolution channels, but such channel development was minor in nonshaken conditions. Even under shaken conditions the channels only accounted for only 1/100 of the total dissolution rate of 2.7 × 10−10 mol of biotite m−2 s−1. The results suggest that fungal weathering predominantly occurred not by attachment and direct transfer of nutrients via hyphae, but because of the acidification of the bulk liquid by organic acids, fungal respiration (CO2), and complexation of cations which accelerated dissolution of biotite. Results further suggest that both carbohydrate source (abundant here) and a host with which nutrients are exchanged (missing here) may be required for EMF to exert an important weathering effect in soils. Unsaturated conditions and physical dispersal of nutrient-rich minerals in soils may also confer a benefit for hyphal growth and attachment, and promote the attachment-mediated weathering which has been observed elsewhere on soil mineral surfaces. 相似文献
5.
The metallogenic mapping program of the Geological Survey, Department of Mines, New South Wales has two aims, to provide an inventory of information on all known mineral deposits in New South Wales, and to enable the recognition and delineation of metallogenic districts and provinces. Each deposit is described on a standardized data sheet. Selected information is symbolized on a coloured geological or tectonic background map at a scale of 1:250 000. This scale is considered to be suitable for locating deposits in the field and at the same time gives an impression of the regional distribution of deposits. The tectonic map is constructed using a plate tectonic model. Each map is accompanied by interpretative notes which are not of standard form but in which one of three approaches may be adopted: an interpretation according to the geological association, the delineating of groupings of deposits in structural zones, and the recognition of metallogenic units based on a plate tectonic model. In many, but not all cases, mineral districts were first delineated before the above approaches were adopted. The New South Wales Geological Survey's metallogenic maps may be used to develop concepts in ore genesis, and prognostic concepts for exploration. They assist in understanding the relationships between tectonic process and the concentration of ore minerals. They are valuable in land use and resource management studies. 相似文献
6.
Government policies intended to reduce flood losses can increase the potential for catastrophe by stimulating development
inside the floodplain, a phenomenon referred to as the “safe development paradox.” New Urbanist design has the potential to
both exacerbate and alleviate flood risks. Because they are built at relatively high densities, New Urbanist developments
can exacerbate risk by placing more people and property in harm’s way. Conversely, New Urbanist design features theoretically
better enable designers of New Urbanist developments to avoid floodplain portions of project sites than designers of conventional
subdivisions. Using a sample of New Urbanist developments in the US that contain floodplain portions within their boundaries,
this paper focuses on whether and why these developments locate built structures inside the floodplain. The authors find that
roughly 30% of the developments locate structures inside the floodplain, and that the odds of locating structures inside the
floodplain increase with the proportion of the project site located inside the floodplain and decrease with the presence of
government policies that prohibit residential development in the floodplain. The authors also identify confusion among government
planners regarding the distinction between pre and postconstruction floodplain boundaries. A subset of New Urbanist developments
is found to have built structures located outside the postconstruction floodplain boundary, but inside the preconstruction
floodplain boundary. This finding is cited as an example of the “safe development paradox” in action. The authors recommend
changes in New Urbanist design codes and local government floodplain management to increasingly direct new development away
from the floodplain. 相似文献
7.
R. Soria R. P. Fender D. C. Hannikainen A. M. Read I. R. Stevens 《Monthly notices of the Royal Astronomical Society》2006,368(4):1527-1539
We studied the radio source associated with the ultraluminous X-ray source in NGC 5408 ( L X ≈ 1040 erg s−1 ) . The radio spectrum is steep (index ≈−1 ), consistent with optically thin synchrotron emission, not with flat-spectrum core emission. Its flux density (≈0.28 mJy at 4.8 GHz, at a distance of 4.8 Mpc) was the same in the March 2000 and December 2004 observations, suggesting steady emission rather than a transient outburst. However, it is orders of magnitude higher than expected from steady jets in stellar-mass microquasar. Based on its radio flux and spectral index, we suggest that the radio source is either an unusually bright supernova remnant, or, more likely, a radio lobe powered by a jet from the black hole (BH). Moreover, there is speculative evidence that the source is marginally resolved with a radius ∼30 pc. A faint H ii region of similar size appears to coincide with the radio and X-ray sources, but its ionization mechanism remains unclear. Using a self-similar solution for the expansion of a jet-powered electron–positron plasma bubble, in the minimum-energy approximation, we show that the observed flux and (speculative) size are consistent with an average jet power ≈ 7 × 1038 erg s−1 ∼ 0.1 L X ∼ 0.1 L Edd , an age ≈105 yr, a current velocity of expansion ≈80 km s−1 . We briefly discuss the importance of this source as a key to understand the balance between luminosity and jet power in accreting BHs. 相似文献
8.
Water surface profiles and horizontal and vertical water particle velocity components have been measured to investigate the properties of intermediate depth waves generated in the laboratory. The data has been compared with linear wave theory. It was found that linear theory predicted the attenuation of velocity field with depth successfully and that it overestimates both components of velocity slightly. 相似文献
9.
Rodney L. Stevens 《Geo-Marine Letters》1991,11(3-4):162-165
Quartz and feldspar extracts, obtained by chemical dissolution of the clay minerals, provide insight into the inorganic flocculation
and mineralogical influences upon the texture of fine-grained glaciomarine deposits. Glacial comminution in higher latitudes
explains the relatively high contents of quartz and feldspars. Quartz and feldspar are better sorted and were apparently less
influenced by flocculation than were phyllosilicates, except for particles less than approximately 16 μm, which are poorly
sorted due to their inclusion in flocs. The 16-μm boundary is suggested to be useful for approximately separating fines that
are usually involved in flocculation and coarse silt and larger grains that are less influenced. 相似文献
10.