全文获取类型
收费全文 | 108篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 8篇 |
地球物理 | 35篇 |
地质学 | 31篇 |
海洋学 | 18篇 |
天文学 | 12篇 |
自然地理 | 13篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 8篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 11篇 |
2007年 | 5篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有119条查询结果,搜索用时 15 毫秒
1.
The morphological and velocity structures in the gaseous (HI and CO) and stellar components of two interacting systems are
examined. Both Arp 140 and Arp 104 reveal extended tidal tails in the HI. The Hα and FIR fluxes of Arp 140 yield similar SFR
of ∼ 0.8 M⊙ yr-1. In contrast the Hα flux of Arp 104 yields a SFR of ∼ 0.05 M⊙ yr-1, ∼ 20 times smaller than that obtained from the FIR flux. Spectra were used to examine the changing velocity of atomic and
molecular gas in NGC 5218 (Arp 104). The atomic and molecular gas were found to be dynamically similar with comparable velocities
and velocity widths across the galaxy; consistent with the two phases responding similarly to the interaction, or enhanced
HI to CO conversion in the centre of the galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Thermodynamic characterization of the partitioning of iron between soluble and colloidal species in the Atlantic Ocean 总被引:2,自引:1,他引:2
Recent electrochemical measurements have shown that iron (Fe) speciation in seawater is dominated by complexation with strong organic ligands throughout the water column and have provided important thermodynamic information about these compounds. Independent work has shown that iron exists in both soluble and colloidal fractions in the Atlantic Ocean. Here we have combined these approaches in samples collected from a variety of regimes within the Atlantic Ocean. We measured the partitioning of Fe between soluble (< 0.02 μm) and colloidal (0.02 to 0.4 μm) size classes and characterized the concentrations and conditional stability constants of Fe ligands within these size classes. Results suggest that equilibrium partitioning of Fe between soluble and colloidal ligands is partially responsible for the distribution of Fe between soluble and colloidal size classes. However, a significant fraction of the colloidal Fe was inert to ligand exchange as soluble Fe concentrations were generally lower than values predicted by a simple equilibrium partitioning model.In surface waters, strong ligands with conditional stability constants of 1013 relative to total inorganic Fe appeared to dominate speciation in both the soluble and colloidal fractions. In deep waters these ligands were absent, and instead we found ligands with stability constants 12–15 fold smaller that were predominantly in the soluble pool. Nevertheless, significant levels of colloidal Fe were found in these samples, which we inferred must be inert to coordination exchange. 相似文献
3.
Heidi M. Cullen Alexey Kaplan Phillip A. Arkin Peter B. deMenocal 《Climatic change》2002,55(3):315-338
Interannual to decadal variations in Middle Eastern temperature, precipitationand streamflow reflect the far-field influence of the North Atlantic Oscillation (NAO), a dominant mode of Atlantic sector climate variability. Using a new sea surface temperature (SST) based index of the NAO and availablestreamflow data from five Middle Eastern rivers, we show that the first principal component of December through March streamflow variability reflects changes in the NAO. However, Middle East rivers have two primary flooding periods.The first is rainfall-driven runoff from December through March, regulated on interannual to decadal timescales by the NAO as reflected in local precipitation and temperature.The second period, from April through June, reflects spring snowmelt and contributes in excess of 50% of annual runoff.This period, known locally as the khamsin, displays no significantNAO connections and a less direct relationship with local climatic factors, suggesting that streamflow variability during this period reflects land-cover change, possibly related to agriculture and hydropower generation, and snowmelt. 相似文献
4.
Stanislav V. Sinogeikin Jay D. Bass Bridget O'Neill Tibor Gasparik 《Physics and Chemistry of Minerals》1997,24(2):115-121
The adiabatic elastic moduli of polycrystalline En50Py50 and En80Py20 majorite-garnet solid solutions (where En=4MgSiO3, Py=Mg3Al2Si3O12) and the end-member En100 tetragonal majorite were determined at ambient conditions using Brillouin spectroscopy. The adiabatic bulk modulus, K, and
shear modulus, μ, of En50Py50 were found to be K=173.1 (20) and μ=92.3 (10) GPa, and are indistinguishable from those of the end-member pyrope, Py100. The moduli of the more majorite-rich samples are significantly lower and are virtually identical to each other (K=162.6(11)
and μ=85.7(7) for En80Py20; K=166(5) and μ=88(2) for En100). In combination with previously reported moduli for this system, we conclude that both K and μ are constant over the compositional
range from Py100 to a majorite content of about 70–80%, whereupon the moduli decrease substantially. For compositions ranging from En80Py20 to the end-member majorite, the moduli are also approximately independent of composition, but at a lower value. An alternative
model with a continuous decrease in moduli with increasing majorite content cannot be excluded, within the uncertainties of
existing measurements. The contrast in moduli between aluminous pyrope garnet and Al-free majorite are small compared with
the modulus changes accompanying the pyroxene – majorite phase transformation.
Received August 16, 1995 /Revised, accepted January 12, 1996 相似文献
5.
High-resolution historical records from Pettaquamscutt River basin sediments: 2. Pb isotopes reveal a potential new stratigraphic marker 总被引:2,自引:0,他引:2
Ana Lúcia Lima Bridget A. Bergquist Matthew K. Reuer Francis O. Dudas Timothy I. Eglinton 《Geochimica et cosmochimica acta》2005,69(7):1813-1824
A high-resolution record of Pb deposition in Rhode Island over the past 250 yr was constructed using a sediment core from the anoxic Pettaquamscutt River basin. The sedimentary Pb concentration record shows the well-described maximum associated with leaded gasoline usage in the United States. Diminished Pb variability during recorded periods of local industrial activity (1735 to 1847) supports the greater importance of regional atmospheric lead transport vs. local inputs. The Pb isotopic composition at this site shows a clear maximum in anthropogenic 206Pb/207Pb in the mid-1800s. Similar peaks have also been observed in sediments from Chesapeake Bay and the Great Lakes, suggesting a common source. Possible causes for this event include mining and smelting of Pb ores in the Upper Mississippi Valley district, which accounted for almost all Pb production in the United States in that period. The timing of this event can provide an important stratigraphic marker for sediments deposited in the past 200 yr in the Northeastern United States. The downcore profile of anthropogenic 206Pb/207Pb provides a classic example of how changes in the mixture of ores for production of tetraethyl lead caused a regional-scale shift in the sedimentary record, and suggests that coal could have played a secondary role in Pb emissions after 1920. 相似文献
6.
7.
Groundwater recharge in natural dune systems and agricultural ecosystems in the Thar Desert region, Rajasthan, India 总被引:2,自引:1,他引:1
Bridget R. Scanlon Abhijit Mukherjee John Gates Robert C. Reedy Amarendra K. Sinha 《Hydrogeology Journal》2010,18(4):959-972
Water and nutrient availability for crop production are critical issues in (semi)arid regions. Unsaturated-zone Cl tracer data and nutrient (NO3 and PO4) concentrations were used to quantify recharge rates using the Cl mass balance approach and nutrient availability in the Thar Desert, Rajasthan, India. Soil cores were collected in dune/interdune settings in the arid Thar Desert (near Jaisalmer) and in rain-fed (nonirrigated) and irrigated cropland in the semiarid desert margin (near Jaipur). Recharge rates were also simulated using unsaturated zone modeling. Recharge rates in sparsely vegetated dune/interdune settings in the Jaisalmer study area are 2.7–5.6 mm/year (2–3% of precipitation, 165 mm/year). In contrast, recharge rates in rain-fed agriculture in the Jaipur study area are 61–94 mm/year (10–16% of precipitation, 600 mm/year). Minimum recharge rates under current freshwater irrigated sites are 50–120 mm/year (8–20% of precipitation). Nitrate concentrations are low at most sites. Similarity in recharge rates based on SO4 with those based on Cl is attributed to a meteoric origin of SO4 and generally conservative chemical behavior in these sandy soils. Modeling results increased confidence in tracer-based recharge estimates. Recharge rates under rain-fed agriculture indicate that irrigation of 20–40% of cultivated land with 300 mm/year should be sustainable. 相似文献
8.
9.
10.
Trace element distribution during the reproductive cycle of female and male spiny and Pacific scallops, with implications for biomonitoring 总被引:1,自引:0,他引:1
Trace element concentrations and contents in gills, gonad, kidneys, mantle, muscle and remainder during the reproductive cycle of female and male spiny and Pacific scallops, from the Strait of Georgia, BC, Canada, were quantified by using ICPMS. The elements investigated were chromium, manganese, iron, cobalt, nickel, selenium, molybdenum, cadmium, tin and mercury. For all ten elements, the tissue distribution was to some extent influenced by species, sex and reproductive status. The implications of the present study in relation to the design of biomonitoring programmes are: (1) care should be taken to ensure an equal/constant sex composition when making interannual comparisons of pooled samples. Preferably the sexes should be monitored separately. (2) the practice of obtaining pooled samples in the interspawn phase is applicable only to monitoring long-term trends in contaminant levels, while the reproductive status should be heeded when studying short-term changes. (3) the present study confirms that direct temporal or spatial comparisons of absolute accumulated element concentrations are only valid intraspecifically. 相似文献