全文获取类型
收费全文 | 313篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 25篇 |
地球物理 | 54篇 |
地质学 | 83篇 |
海洋学 | 45篇 |
天文学 | 87篇 |
自然地理 | 21篇 |
出版年
2021年 | 3篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 17篇 |
2012年 | 12篇 |
2011年 | 18篇 |
2010年 | 13篇 |
2009年 | 24篇 |
2008年 | 20篇 |
2007年 | 7篇 |
2006年 | 17篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有318条查询结果,搜索用时 93 毫秒
311.
Tjaša Kanduč Fausto Grassa Jennifer McIntosh Vekoslava Stibilj Marija Ulrich-Supovec Ivan Supovec Sergej Jamnikar 《Hydrogeology Journal》2014,22(4):971-984
The geochemical and isotopic composition of surface waters and groundwater in the Velenje Basin, Slovenia, was investigated seasonally to determine the relationship between major aquifers and surface waters, water–rock reactions, relative ages of groundwater, and biogeochemical processes. Groundwater in the Triassic aquifer is dominated by HCO3 –, Ca2+, Mg2+ and δ13CDIC indicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has δ18O and δD values that plot near surface waters on the local and global meteoric water lines, and detectable tritium, likely reflecting recent (<50 years) recharge. In contrast, groundwater in the Pliocene aquifers is enriched in Mg2+, Na+, Ca2+, K+, and Si, and has high alkalinity and δ13CDIC values, with low SO4 2– and NO3 – concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and Mg-rich clay minerals. Pliocene aquifer waters are also depleted in 18O and 2H, and have 3H concentrations near the detection limit, suggesting these waters are older, had a different recharge source, and have not mixed extensively with groundwater in the Triassic aquifer. 相似文献
312.
Lirong Zhong Kirk Cantrell Alex Mitroshkov Jesse Shewell 《Environmental Earth Sciences》2014,71(9):4261-4272
Supercritical CO2 (scCO2) is a good solvent for organic compounds such as benzene, toluene, ethyl-benzene, and xylene (BTEX), phenols, and polycyclic aromatic hydrocarbons (PAHs). Monitoring results from geological carbon sequestration (GCS) field tests have shown that organic compounds are mobilized following CO2 injection. Such results have raised concerns regarding the potential for groundwater contamination by toxic organic compounds mobilized during GCS. Knowledge of the mobilization mechanism of organic compounds and their transport and fate in the subsurface is essential for assessing risks associated with GCS. Extraction tests using scCO2 and methylene chloride (CH2Cl2) were conducted to study the mobilization of volatile organic compounds (VOCs, including BTEX), the PAH naphthalene, and n-alkanes by scCO2 from representative reservoir rock and caprock obtained from depleted oil reservoirs and coal from an enhanced coal-bed methane recovery site. Results showed that the extent of mobilization for the organic compounds was a function of the source rock. In fate and transport sand column experiments, moisture content was found to have an important influence on the transport of the organic compounds. In dry sand columns the majority of the compounds were retained in the column except benzene and toluene. In wet sand columns the mobility of the BTEX was much higher than that of naphthalene. Based upon the results determined for the reservoir rock, caprock, and coal samples studied here, the risk to aquifers from contamination by organic compounds appears to be relatively low; however, further work is necessary to fully evaluate the risks. 相似文献
313.
Samantha Kirk Ioannis Haranas Ioannis Gkigkitzis 《Astrophysics and Space Science》2013,344(2):313-320
In this paper, we consider a satellite orbiting in a Manev gravitational potential under the influence of an atmospheric drag force that varies with the square of velocity. Using an exponential atmosphere that varies with the orbital altitude of the satellite, we examine a circular orbit scenario. In particular, we derive expressions for the change in satellite radial distance as a function of the drag force parameters and obtain numerical results. The Manev potential is an alternative to the Newtonian potential that has a wide variety of applications, in astronomy, astrophysics, space dynamics, classical physics, mechanics, and even atomic physics. 相似文献
314.
Ioannis Gkigkitzis Ioannis Haranas Samantha Kirk 《Astrophysics and Space Science》2013,346(2):553-557
In this study, we have investigated the geometrical and physical properties of stationary axisymmetric solutions. The expressions for the axial-vector and the gravitational energy and momentum densities are obtained in the context of teleparallel equivalent of general relativity. The obtained results are compared with that obtained previously in the context of Møller’s tetrad theory of gravitation. We discussed special cases of these solutions. 相似文献
315.
M. S. Kirk K. S. Balasubramaniam J. Jackiewicz B. J. McNamara R. T. J. McAteer 《Solar physics》2013,283(1):97-111
We present a new automated algorithm to identify, track, and characterize small-scale brightening associated with solar eruptive phenomena observed in Hα. The temporal, spatially localized changes in chromospheric intensities can be separated into two categories: flare ribbons and sequential chromospheric brightenings (SCBs). Within each category of brightening we determine the smallest resolvable locus of pixels, a kernel, and track the temporal evolution of the position and intensity of each kernel. This tracking is accomplished by isolating the eruptive features, identifying kernels, and linking detections between frames into trajectories of kernels. We fully characterize the evolving intensity and morphology of the flare ribbons by observing the tracked flare kernels in aggregate. With the location of SCB and flare kernels identified, they can easily be overlaid on complementary data sets to extract Doppler velocities and magnetic-field intensities underlying the kernels. This algorithm is adaptable to any dataset to identify and track solar features. 相似文献
316.
The paper presents investigations of wave climate, tidal inlet hydraulics, and sand sediment bypassing at the entrance to Westport Harbour, South Island, New Zealand. The results complement and extend those of studies of bar morphologies and sediment characteristics already published. Longshore transport of about 1 × 106 m3/year is directed in a net eastward fashion across the inlet because of an in‐built misalignment of the harbour training walls. Approximately 90% of the drift is bypassed, and has been since 1921, by deflection and splitting of the main sediment streams through the inner and outer bars and a transverse channel aoross the entrance. The outer bar appears to be the submarine, downdrift extension of Carters Breach and river load appears to contribute an order of magnitude less sediment to the complex than annual littoral drift. River sediments and littoral drift are mixed off the harbour and a declining proportion over time is recirculated to cause progradation of North Beach. The tidal compartment contributes little to scour of the entrance because of the predominance of bar bypassing. Contrary to the recommendations of several past studies, it is argued that improvements in navigation depths at West‐port are more likely to be obtained through modification of the littoral drift system than they are from tidal compartment enlargement. 相似文献
317.
R. M. Kirk 《新西兰海洋与淡水研究杂志》2013,47(2):358-375
Abstract On shingle beaches, changes in foreshore elevation and sediment distribution landward of the break point are produced largely by variations in the uprush and backwash of waves. However, very little is known about the forces active in this zone. A field instrument system which senses and records some of the parameters thought to influence beach erosion and deposition in this zone has been constructed. The equipment is also suitable for the investigation of a number of other shore and nearshore processes including erosion on sandy and rocky shores, and flow processes affecting littoral biological communities. In the swash zone two sensing heads, a dynamometer and a depth recorder, sense variations in uprush and backwash velocities, energies, discharges, and depths of flow. Both devices are electromechanical and are coupled to a recording unit on land by PVC‐insulated cable. The dynamometer (two force plates mounted back‐to‐back on a compression spring and coupled to variable resistances) has been calibrated, statically and in a flume, to obtain velocity determinations accurate to within 10 cm . sec?1 of true flow speed. Average swash zone velocities lie between 100 and 300 cm . sec?1. A parallel‐wire resistance gauge mounted an a stilling tube records flow depths. As water level rises and falls in the tube it alters resistance in a control circuit. The land unit, amplifiers and a strip‐chart recorder, receives the output from the dynamometer and flow depth gauge. The recorder is equipped with a trip‐pen so that analysis of wave periods or other variables is possible in the field. With poles at known spacings across the shore and the trip‐pen records, velocity distributions across the swash zone can be obtained. Measurements of velocity made near the bed with the dynamometer can then be related to the local surface velocity profile. Problems with the instrument system include inability to record velocities at several points simultaneously, and unreliable records of backwash parameters with low breakers on shingle beaches because of the small volume of flow and rapid percolation of water into the beach face. 相似文献
318.
Dennis Finn Kirk L. Clawson Roger G. Carter Jason D. Rich Chris Biltoft Martin Leach 《Boundary-Layer Meteorology》2010,136(3):431-456
Concentration variability in the fast-response tracer dataset for continuous, near-surface, point source releases in the urban
core from the Joint Urban 2003 field study is analyzed. Concentration variability for conditionally and unconditionally sampled
time series is characterized by probability densities, concentration fluctuation intensity, skewness, and kurtosis. Significant
day-night differences in plume dispersion are observed. Relative to daytime, nighttime plumes were more likely to have reduced
concentration fluctuation intensities, higher normalized surface concentrations, suppressed vertical mixing, and a greater
prevalence of Gaussian-like distributions rather than log-normal or mixed mode distributions. This was in spite of the similar
stability and turbulence conditions in the urban core for day and night. The potential roles of flow meander and thermal stability
in explaining these differences are examined. Probability densities of concentration are found to be a strong function of
fluctuation intensity. There are few differences in probability densities between day and night when classified by fluctuation
intensity. There are no appreciable differences between conditional and unconditional probability densities and only small
differences between conditional and unconditional sampling statistics relative to the larger differences usually observed
in more homogeneous settings. Fluctuation intensity, skewness, and kurtosis are higher for the daytime experiments, and closer
to the source, but show little difference between conditional and unconditional results over most of their range of values.
The log-normal distribution provides a better overall fit to a broader range of the dataset than the exponential or clipped-normal
distributions. 相似文献