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991.
Rockfalls into forests: Analysis and simulation of rockfall trajectories — considerations with respect to mountainous forests in Switzerland 总被引:3,自引:1,他引:2
Rockfalls are a major threat to settlements and transportation routes in many places. Although the general protective effect of forests against rockfalls is currently not questioned, little is known about the ideal properties of a forest stand that provides good protection. Therefore, in this study the question was assessed of how mountainous forests may influence rockfalls of single boulders. An actual rockfall trajectory was measured, recorded, analysed and simulated with a rockfall model. Rockfalls into different forest scenarios were also modelled for the site. Results showed that the actual rockfall event can be well simulated. Furthermore, a completely forested slope reduces velocity and energy of the falling blocks much better than a sparsely forested slope. For the profile discussed in this paper, the largest effect upon falling 3 m3 blocks was obtained with a high forest containing 350 trees per ha. The results confirmed common assumptions on ideal properties of a protective forest stand against rockfalls. 相似文献
992.
Chris Kennedy Hans Ericsson P. L. R. Wong 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(1-2):119-125
A technique for modeling contaminant transport based on Markov process theory is developed. Transport is quantified by summing
the first two moments of independent random displacements and applying the central limit theorem (CLT) to obtain solute distributions
of a Gaussian nature. For non-uniform flow fields the CLT is applied in a streamfunction/equi-travel time space and transforms
are used to give concentrations in Cartesian coordinates. Simulations in uniform, radially converging and circular flow fields
show the method to be two to three orders of magnitude faster than modeling with the advection-dispersion equation, using
a control volume technique. 相似文献
993.
Hans J. Rick Silke Rick Urban Tillmann Uwe Brockmann Uwe Gärtner Claus Dürselen Jürgen Sündermann 《Estuaries and Coasts》2006,29(1):4-23
Within the KUSTOS program (Coastal Mass and Energy Fluxes-the Land-Sea Transition in the Southeastern North Sea) 28 to 36
German Bight stations were seasonally surveyed (summer 1994, spring 1995, winter 1995–1996) for light conditions, dissolved
inorganic nutrient concentrations, chlorophylla (chla), and photosynthesis versus light intensity (P:E) parameters. Combining P:E curve characteristics with irradiance, attenuation,
and chlorophyll data resulted in seasonal estimates of the spatial distribution of total primary production. These data were
used for an annual estimate of the total primary production in the Bight. In winter 1996 the water throughout the German Bight
was well mixed. Dissolved inorganic nutrient concentrations were relatively high (nitrogen [DIN], soluble reactive phosphorus
[SRP], and silicate [Si]: 23, 1, and 10 μM, respectively). Chla levels generally were low (< 2 μg l−1) with higher concentrations (4–16 μg l−1) in North Frisian coastal waters. Phytoplankton was limited by light. Total primary production averaged 0.2 g C m−2 d−1. Two surveys in April and May 1995 captured the buildup of a strong seasonal thermo-cline accompained by the development
of a typical spring diatom bloom. High nutrient levels in the mixed layer during the first survey (DIN, SRP, and Si: 46, 0.45,
and 11 μM, respectively) decreased towards the second survey (DIN, SRP, and Si: 30.5, 0.12, and 1.5 μM, respectively) and
average nutrient ratios shifted further towards highly imbalanced values (DIN:SRP: 136 in survey 1, 580 in survey 2; DIN:Si:
13.5 in survey 1, 96 in survey 2). Chla ranged from 2 to 16 μg l−1 for the first survey and rose to 12–50 μg l−1 in the second survey. Phytoplankton in nearshore areas continued to be light limited during the second survey, while data
from the stratified regions in the open German Bight indicates SRP and Si limitation. Total primary production ranged from
4.0 to 6.3 g C m−2 d−1. During summer 1994 a strong thermal stratification was present in the German Bight proper and shallow coastal areas showed
unusually warm (up to 22°C), mixed waters. Chla concentrations ranged from 2 to 18 μg l−1. P:E characteristics were relatively high despite the low nutrient regime (DIN, SRP, and Si: 2, 0.2, and 1.5 μM, respectively),
resulting in overall high total primary production values with an average of 7.7 g C m−2 d−1. Based on the seasonal primary production estimates of the described surveys a budget calculation yielded a total annual
production of 430 g C m−2 yr−1 for the German Bight. 相似文献
994.
995.
Ohne Zusammenfassung 相似文献
996.
Jeff A. K. Suva Paul E. Mariner Hans W. Meinardus Jon S. Ginn 《Ground Water Monitoring & Remediation》2003,23(1):85-92
An automated in-line analytical system has been developed to provide near real-time results for partitioning interwell tracer testing (PITT) and surfactant enhanced aquifer remediation (SEAR). The analytical methodology is based on gas chromatography (GC) with flame ionization detection and direct aqueous injection. The system was constructed from both commercially available and custom-manufactured components that are linked electronically to facilitate autonomous operation. For the field trials presented herein, the in-line GC method provided superior or comparable PITT and SEAR data compared to conventional sample collection followed by shipment and analysis at a commercial analytical laboratory. Analytical precolumns were shown to effectively safeguard the integrity of the analytical column, despite the consecutive analysis of more than 1000 samples per PITT or SEAR. Additionally, the use of the in-line GC resulted in an 85% and 74% reduction in analytical costs per PITT and SEAR, respectively. 相似文献
997.
In this study we aim at comparing turbulence parameters from field observations and model simulations under convective conditions.
The comparison is focused on the depth dependence and temporal dynamics of viscous and diffusive dissipation rates ɛ and χ.
The near-surface observations were obtained by using a quasi-free-rising profiler which measured small-scale shear and temperature
fluctuations to within the vicinity of the water surface. Convective conditions during the experiment are characterized by
low wind speeds (between 0 and 4 m s−1) and a typical heat loss of about 150 Wm−2. We applied a state-of-the-art two-equation k-ɛ turbulence model with an algebraic second-moment closure scheme. The qualitative agreement of the turbulence quantities
resulting from observations and simulations is rather good. The temporal dynamics of the temperature field is simulated correctly,
whereas in the spatial dynamics some deficiencies of the model due to its local character can be seen. It is concluded that
such models realistically reproduce convective turbulence and therefore represent a reasonable compromise between complexity
and simplicity, so that they can be used with acceptable costs in large-scale models.
Received: 31 October 2001 / Accepted: 20 September 2002
Acknowledgements The whole project was intitiated by Peter Schlittenhardt, who strongly supported the development of the observational technique
in uprising mode and encouraged us to undertake the experiment in Lake Maggiore; for which we will thank him most. Performing
the measurement campaign was only possible with the help of several colleagues from the Marine Environment Unit at the Joint
Research Centre. Thanks to all of them, but especially to Dirk van d. Linde, Ulisse Devisioni, Bjarke Rasmussen and Hartmut
Prandke. The Istituto Italiano di Idrobiologia, Verbania Pallanza, provided the boat Livia for the installation and removal
of the measurement system; thanks to the master Stefano Maurizio for his engagement. Ute Tschesche provided the data evaluation
and presentation software and Judith Challis helped to polish our English. Part of the study was␣supported by the PROVESS
project (MAS3-CT97-0159); thanks to our sponsors at the European Commission. We are further grateful to two anonymous referees
for their constructive comments.
Responsible Editor: Charitha Pattiaratchi 相似文献
998.
999.
1000.
Water solubility in pyrope to 100 kbar 总被引:14,自引:0,他引:14
The solubility and incorporation mechanism of water in natural, almost pure pyrope from Dora Maira, Western Alps was investigated.
The infrared spectrum of the natural, untreated sample (58 ppm water) shows several exceptionally sharp bands in the OH-stretching
region, including a single band at 3601.9 cm−1 and a band system with main components at 3640.5, 3650.8 and 3660.6 cm−1. High-temperature and high-pressure infrared spectra suggest that the two absorption features arise from almost free OH groups
in sites with different compressibility and thermal expansivity, with the site causing the 3601.9 cm−1 band being much stiffer. Pyrope samples were annealed in a piston-cylinder or multi-anvil apparatus for several days in the
presence of excess water, excess SiO2 and excess Al2SiO5 to determine the equilibrium solubility of water in pyrope to 100 kbar. Total solubility increases with pressure, however,
this is exclusively due to the high-frequency band system, while the intensity of the low-frequency band decreases with pressure.
At 1000 °C and the oxygen fugacity of the Ni-NiO buffer, the bulk solubility can be described by the equation c
OH
=Af
H2O
0.5exp(−PΔV/RT) with A = 0.679 ppm/bar0.5 and ΔV = 5.71 cm3/mol. This equation implies the incorporation of water in the crystal as isolated OH groups. With increasing temperature,
solubility appears to decrease with ΔH = − 14 kJ/mol. At Fe-FeO buffer conditions, solubility is 30 to 50% lower than with the Ni-NiO buffer, suggesting that the
incorporation of OH is not coupled to the reduction of Fe3+. Possibly, the 3601.9 cm−1 band is associated with the tetrahedral OH B defect and the high-frequency system with the dodecahedral OH Li defect. Based
on the experimentally established solubility model, it is estimated that garnet in a hot subducted slab will transport 170 ppm
of water into the mantle beyond the breakdown limit of amphibole. In a cold slab, 470 ppm of water can be incorporated into
garnet at the breakdown limit of phengite. These numbers imply that a significant fraction of the total water in the hydrosphere
has been recycled into the mantle since the Proterozoic.
Received: 6 January 1997 / Accepted: 27 March 1997 相似文献