全文获取类型
收费全文 | 167篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 14篇 |
地球物理 | 32篇 |
地质学 | 56篇 |
海洋学 | 31篇 |
天文学 | 13篇 |
自然地理 | 19篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2011年 | 11篇 |
2010年 | 4篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 7篇 |
2005年 | 2篇 |
2004年 | 8篇 |
2003年 | 3篇 |
2002年 | 10篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 6篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1951年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有177条查询结果,搜索用时 15 毫秒
1.
2.
3.
Arthur C. R. Gleason Diego Lirman Dana Williams Nuno R. Gracias Brooke E. Gintert Hossein Madjidi R. Pamela Reid G. Chris Boynton Shahriar Negahdaripour Margaret Miller & Philip Kramer 《Marine Ecology》2007,28(2):254-258
Four hurricanes impacted the reefs of Florida in 2005. In this study, we evaluate the combined impacts of hurricanes Dennis, Katrina, Rita, and Wilma on a population of Acropora palmata using a newly developed video‐mosaic methodology that provides a high‐resolution, spatially accurate landscape view of the reef benthos. Storm damage to A. palmata was surprisingly limited; only 2 out of 19 colonies were removed from the study plot at Molasses Reef. The net tissue losses for those colonies that remained were only 10% and mean diameter of colonies decreased slightly from 88.4 to 79.6 cm. In contrast, the damage to the reef framework was more severe, and a large section (6 m in diameter) was dislodged, overturned, and transported to the bottom of the reef spur. The data presented here show that two‐dimensional video‐mosaic technology is well‐suited to assess the impacts of physical disturbance on coral reefs and can be used to complement existing survey methodologies. 相似文献
4.
The conditional acid dissociation constants (pKa′) of two sulfonephthalein dyes, thymol blue (TB) and m-cresol purple (mCP), were assessed throughout the estuarine salinity range (0<S<40) using a tris/tris–HCl buffer and spectrophotometric measurement. The salinity dependence of the pKa′ of both dyes was fitted to the equations (25 °C, total proton pH scale, mol kg soln−1):The estimated accuracy of pH measurements using these calculated pKa′ values is considered to be comparable to that possible with careful use of a glass electrode (±0.01 pH unit) but spectrophotometric measurements in an estuary have the significant advantage that it is not necessary to calibrate an electrode at different salinities. pH was measured in an estuary over a tidal cycle with a precision of ±0.0005 pH unit at high (S>30) salinity, and ±0.002 pH unit at low (S<5) salinity. The pH increased rapidly in the lower salinity ranges (0<S<15) but less rapidly at higher salinities. 相似文献
5.
Shane M. Ohline Malcolm R. Reid Shamus L.G. Husheer Kim I. Currie Keith A. Hunter 《Marine Chemistry》2007
Accurate measurement of seawater pH has long been sought by marine chemists (for example: [Dickson, A.G. 1993a. The measurement of sea water pH. Marine Chemistry, 44, 131–142, Dickson, A.G. 1993b. pH buffers for sea water media based on the total hydrogen ion concentration scale. Deep-Sea Research, 40, 107–118; Zhang, 1996; Tapp, M., Hunter, K.A., Currie, K. and Macaskill, B. 2000. Apparatus of continuous-flow underway spectrophotometric measurement of surface water pH. Marine Chemistry 72(2–4), 193–202; Friis, K., Koetzinger, A., Wallace, D.W.R. 2004. Spectrophotometric pH measurement in the ocean: Requirements, design and testing of an autonomous charge-coupled device detector system. Limnology and Oceanography: Methods 2, 126–136]. Recently, such attempts have taken on greater significance as anthropogenic carbon dioxide emissions may create rapidly changing oceanic pH. Spectrophotometric techniques have been accepted generally as the best for determination of seawater pH. Here we report a new technique using thymol blue as the indicator dye and fitting the entire spectrum from 400 to 900 nm rather than measuring the absorbance values at only two or three points in the spectrum. This full-spectrum modelling enables a reduction in signal to noise over other techniques. In the laboratory, we find with seawater samples a pH precision increase of five-fold “within” a sample and seven-fold “between” samples when comparing the full spectrum to the three-point method of analysis [Zhang, H., Byrne, R.H. 1996. Spectrophotometric pH measurements of surface seawater at in-situ conditions: absorbance and protonation behaviour of thymol blue. Marine Chemistry 52, 17–25]. 相似文献
6.
Karen L. Hunter Dewayne A. Fox Lori M. Brown Kenneth W. Able 《Estuaries and Coasts》2006,29(3):487-498
Modification of brackish marshes by nonindigenousPhragmites australis has occurred across a broad geographical area in eastern North America. Among its effects on marsh processes,Phragmites may be increasingly unfavorable to marsh surface fishes as its invasion progresses within an estuary. We assessed the effect
of thePhragmites invasion on resident marsh surface fishes by examining the population response ofFundulus heteroclitus (mummichog, 5–48 mm TL) andF. luciae (spotfin killifish, 5–41 mm TL) to four distinct invasion stages in three estuaries of the U.S. mid Atlantic region (New
Jersey, Delaware, and Maryland). We documented precipitous declines in mean catch per unit effort ofF. heteroclitus in pit traps from natural marsh (51.6), through initial (33.8), early (12.3), and late invasion stages (2.4) across all sites.
A similar pattern was documented forF. luciae, with mean catch per unit effort in pit traps declining from natural marsh (48.9), through initial (39.1), early (9.3), and
late invasion stages (2.7). Population structure of both species also changed somewhat across invasion stages such that we
collected a narrower size range of individuals of both species from late invasion stages. Patterns suggest that as thePhragmites invasion progresses, there is a decline in habitat function for larval and juvenileF. heteroclitus and an increased risk of extirpation ofF. luciae from brackish marshes along the east coast of the U.S. 相似文献
7.
Uranium co-precipitation with iron oxide minerals 总被引:2,自引:0,他引:2
Martine C. DuffJessica Urbanik Coughlin Douglas B. Hunter 《Geochimica et cosmochimica acta》2002,66(20):3533-3547
In oxidizing environments, the toxic and radioactive element uranium (U) is most soluble and mobile in the hexavalent oxidation state. Sorption of U(VI) on Fe-oxides minerals (such as hematite [α-Fe2O3] and goethite [α-FeOOH]) and occlusion of U(VI) by Fe-oxide coatings are processes that can retard U transport in environments. In aged U-contaminated geologic materials, the transport and the biological availability of U toward reduction may be limited by coprecipitation with Fe-oxide minerals. These processes also affect the biological availability of U(VI) species toward reduction and precipitation as the less soluble U(IV) species by metal-reducing bacteria.To examine the dynamics of interactions between U(VI) and Fe oxides during crystallization, Fe-oxide phases (containing 0.5 to 5.4 mol% U/(U + Fe)) were synthesized by means of solutions of U(VI) and Fe(III). Wet chemical (digestions and chemical extractions) and spectroscopic techniques were used to characterize the synthesized Fe oxide coprecipitates after rinsing in deionized water. Leaching the high mol% U solids with concentrated carbonate solution (for sorbed and solid-phase U(VI) species) typically removed most of the U, leaving, on average, about 0.6 mol% U. Oxalate leaching of solids with low mol% U contents (about 1 mol% U or less) indicated that almost all of the Fe in these solids was crystalline and that most of the U was associated with these crystalline Fe oxides. X-ray diffraction and Fourier-transform infrared (FT-IR) spectroscopic studies indicate that hematite formation is preferred over that of goethite when the amount of U in the Fe-oxides exceeds 1 mol% U (∼4 wt% U). FT-IR and room temperature continuous wave luminescence spectroscopic studies with unleached U/Fe solids indicate a relationship between the mol% U in the Fe oxide and the intensity or existence of the spectra features that can be assigned to UO22+ species (such as the IR asymmetric υ3 stretch for O = U = O for uranyl). These spectral features were undetectable in carbonate- or oxalate-leached solids, suggesting solid phase and sorbed U(VI)O22+ species are extracted by the leach solutions. Uranium L3-edge x-ray absorption spectroscopic (XAFS) analyses of the unleached U-Fe oxide solids with less than 1 mol% U reveal that U(VI) exists with four O atoms at radial distances of 2.19 and 2.36 Å and second shell Fe at a radial distance at 3.19 Å.Because of the large ionic radius of UO22+ (∼1.8 Å) relative to that of Fe3+ (0.65 Å), the UO22+ ion is unlikely to be incorporated in the place of Fe in Fe(III)-oxide structures. Solid-phase U(VI) can exist as the uranyl [U(VI)O22+] species with two axial U-O double bonds and four or more equatorial U-O bonds or as the uranate species (such as γ-UO3) without axial U-O bonds. Our findings indicate U6+ (with ionic radii of 0.72 to 0.8 Å, depending on the coordination environment) is incorporated in the Fe oxides as uranate (without axial O atoms) until a point of saturation is reached. Beyond this excess in U concentration, precipitating U(VI) forms discrete crystalline uranyl phases that resemble the uranyl oxide hydrate schoepite [UO2(OH)2·2H2O]. Molecular modeling studies reveal that U6+ species could bond with O atoms from distorted Fe octahedra in the hematite structure with an environment that is consistent with the results of the XAFS. The results provide compelling evidence of U incorporation within the hematite structure. 相似文献
8.
1957-1996台风对中国降水的影响 总被引:15,自引:0,他引:15
台风活动中国气候的重要特点之一,它能带来大量降水并造成严重的财产损失。在一些地区,台风降水甚至可以在总降水量中占很大比例。本文目的是研究那些对中国产生影响的台风并重点关注台风对中国降水的影响。文中涉及四个方面的工作。首先,研究了影响中国台风的频率,结果表明台风影响的主要季节为5-11月,尤其以7-9月频繁;在过去40年中影响台风的频率没有明显的变化趋势。第二,对台站台风降水的气候特征分析结果显示,海南和东南沿海地区受台风的影响最大,而且长江以南大部地区每年都受到台风的影响;另外,影响区域大部分地区的台风降水在过去40年中表现出下降的趋势,但是只有东北地区南部这种趋势是显著的。第三,对台风个例的分析表明,个例降水总量和影响面积之间存在着显著的线性关系。最后,对台风造成的中国范围降水总量进行了分析,初步结果显示台风降水总量在1957-1996年间显著减少。 相似文献
9.
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
10.
The diurnal cycle of the tropospheric zenith total delay (ZTD) is one of the most obvious signals for the various physical
processes relating to climate change on a short time scale. However, the observation of such ZTD oscillations on a global
scale with traditional techniques (e.g. radiosondes) is restricted due to limitations in spatial and temporal resolution.
Nowadays, the International GNSS Service (IGS) provides an important data source for investigating the diurnal and semidiurnal
cycles of ZTD and related climatic signals. In this paper, 10 years of ZTD data from 1997 to 2007 with a 2-hour temporal resolution
are derived from global positioning system (GPS) observations taken at 151 globally distributed IGS reference stations. These
time series are used to investigate diurnal and semidiurnal oscillations. Significant diurnal and semidiurnal oscillations
of ZTD are found for all GPS stations used in this study. The diurnal cycles (24 hours period) have amplitudes between 0.2
and 10.9 mm with an uncertainty of about 0.5 mm and the semidiurnal cycles (12 h period) have amplitudes between 0.1 and 4.3 mm
with an uncertainty of about 0.2 mm. The larger amplitudes of the diurnal and semidiurnal ZTD cycles are observed in the low-latitude
equatorial areas. The peak times of the diurnal cycles spread over the whole day, while the peak value of the semidiurnal
cycles occurs typically about local noon. These GPS-derived diurnal and semidiurnal ZTD signals are similar with the surface
pressure tides derived from surface synoptic pressure observations, indicating that atmospheric tides are the main driver
of the diurnal and semidiurnal ZTD variations. 相似文献