全文获取类型
收费全文 | 679篇 |
免费 | 30篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 119篇 |
地球物理 | 149篇 |
地质学 | 244篇 |
海洋学 | 49篇 |
天文学 | 73篇 |
综合类 | 3篇 |
自然地理 | 42篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 24篇 |
2017年 | 30篇 |
2016年 | 37篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 40篇 |
2012年 | 34篇 |
2011年 | 37篇 |
2010年 | 44篇 |
2009年 | 41篇 |
2008年 | 36篇 |
2007年 | 32篇 |
2006年 | 23篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 11篇 |
2002年 | 24篇 |
2001年 | 18篇 |
2000年 | 5篇 |
1999年 | 21篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1984年 | 4篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1951年 | 2篇 |
1948年 | 1篇 |
排序方式: 共有711条查询结果,搜索用时 46 毫秒
601.
Two coeval stalagmites from Katerloch Cave show pronounced intervals of low δ18O values around 8.2, 9.1, and 10.0 kyr (all ages are reported before the year 2000 AD) and represent an inorganic U–Th dated climate archive from the southeast of the European Alps, a region where only very few well-dated climate records exist. The O isotope curves, providing near-annual resolution, allow a direct comparison to the Greenland ice core records, as temperature was the primary factor controlling the O isotopic composition of Katerloch speleothems.The 8.2 kyr climate anomaly lasted about one century, from 8196 to 8100 yr, with a maximum amplitude of 1.1‰ at 8175 yr. The event is characterized by a rapid onset and a more gradual demise and U–Th data as well as annual lamina counting support a rapid climate change towards cooler conditions within 10–20 yr. There is no strong evidence that the 8.2 kyr anomaly was superimposed on a pronounced longer-term cooling episode, nor do the new data support two separate cooling events within the 8.2 kyr event as reported by other studies. Our record also shows a distinct climate anomaly around 9.1 kyr, which lasted 70–110 yr and showed a maximum amplitude of 1.0‰, i.e. it had a similar duration and amplitude as the (central) 8.2 kyr event. Compared to the 8.2 kyr event, the 9.1 kyr anomaly shows a more symmetrical structure, but onset and demise still occurred within a few decades only. The different progression of the 8.2 (asymmetrical) and 9.1 kyr anomaly (symmetrical) suggests a fundamental difference in the trigger and/or the response of the climate system. Moreover, both stalagmites show evidence of a climate anomaly around 10.0 kyr, which was of comparable magnitude to the two subsequent events.Using a well constrained modern calibration between air temperature and δ18O of precipitation for the study area and cave monitoring data (confirming speleothem deposition in Katerloch reflecting cave air temperature), a maximum cooling by ca 3 °C can be inferred at 8.2 and 9.1 kyr, which is similar to other estimates, e.g., from Lake Ammersee north of the Alps. The O isotopic composition of meteoric precipitation, however, is a complex tracer of the hydrological cycle and these temperature estimates do not take into account additional effects such as changes in the source area or synoptic shifts. Apart from that, the relative thickness of the seasonally controlled lamina types in the Katerloch stalagmites remains rather constant across the intervals comprising the isotopic anomalies, i.e. the stalagmite petrography argues against major shifts in seasonality during the early Holocene climate excursions. 相似文献
602.
603.
The groundwater flow regime at great depth within the Molasse Basin (SW Germany) was studied. Data relevant for a flow model at 600–1,600 m depth are sparse in the western part of the basin. However, temperature measurements are available covering much of the area at a wide range of depths. Therefore, a thermal 3D steady-state model was set up with the aim of comparing modeled with observed subsurface temperatures. Stratigraphic information from many boreholes was also available, but only a few values of rock thermal conductivity and heat-production rate could be obtained. Some strong thermal residual anomalies were identified with respect to the purely conductive model, especially along fault zones, and within stratigraphic layers with high hydraulic conductivity. These anomalies can be explained by various advective heat-transport mechanisms, yet most explanations can be eliminated. The most plausible constellation explaining the major positive thermal anomalies of 10 Kelvin and more is a fault zone of E–W strike, intersected by an aquifer with flow parallel to the fault zone. This concept was investigated by using a simplified type model. In spite of some shortcomings, the method presented here can be used to identify temperature anomalies, and to identify possible explanations. 相似文献
604.
Wolfgang Siebel Horst P. Hann Martin Danišík Cosmas K. Shang Christoph Berthold Johann Rohrmüller Klaus Wemmer Noreen J. Evans 《International Journal of Earth Sciences》2010,99(6):1187-1197
Movement within the Earth’s upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements
to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their
displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the
evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality,
ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal
alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological
techniques (zircon Pb-evaporation, K–Ar and Rb–Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied
to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization
age of the primary rock type (known as “Kristallgranit”) at 325 ± 7 Ma, whereas the K–Ar and Rb–Sr ages of two illite fractions
<2 μm (266–255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation
period. During this time, the “Kristallgranit” was already at or near the Earth’s surface as indicated by the sedimentary
record and thermal modelling results of apatite fission track data. (U–Th)/He thermochronology of two single fluorite grains
from a fluorite–quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization
age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by
geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling
results are consistent with the prevalence of elevated temperatures (50–80°C) in the fault zone during the Cretaceous. 相似文献
605.
Tobias F. Ertefai Verena B. Heuer Christoph Vogt Jeffrey Seewald 《Geochimica et cosmochimica acta》2010,74(21):6033-6048
Sorption of volatile hydrocarbon gases (VHCs) to marine sediments is a recognized phenomenon that has been investigated in the context of petroleum exploration. However, little is known about the biogeochemistry of sorbed methane and higher VHCs in environments that are not influenced by thermogenic processes. This study evaluated two different extraction protocols for sorbed VHCs, used high pressure equipment to investigate the sorption of methane to pure clay mineral phases, and conducted a geochemical and mineralogical survey of sediment samples from different oceanographic settings and geochemical regimes that are not significantly influenced by thermogenic gas. Extraction of sediments under alkaline conditions yielded higher concentrations of sorbed methane than the established protocol for acidic extraction. Application of alkaline extraction in the environmental survey revealed the presence of substantial amounts of sorbed methane in 374 out of 411 samples (91%). Particularly high amounts, up to 2.1 mmol kg−1 dry sediment, were recovered from methanogenic sediments. Carbon isotopic compositions of sorbed methane suggested substantial contributions from biogenic sources, both in sulfate-depleted and sulfate-reducing sediments. Carbon isotopic relationships between sorbed and dissolved methane indicate a coupling of the two pools. While our sorption experiments and extraction conditions point to an important role for clay minerals as sorbents, mineralogical analyses of marine sediments suggest that variations in mineral composition are not controlling variations in quantities of sorbed methane. We conclude that the distribution of sorbed methane in sediments is strongly influenced by in situ production. 相似文献
606.
Peter J. Vincent Peter Wilson Tom C. Lord Christoph Schnabel 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(1):24-31
Cosmogenic isotope (36Cl) surface exposure dating of four of the erratic boulders at Norber in the Yorkshire Dales National Park, northwest England, yielded mean ages of ∼22.2 ± 2.0 ka BP and ∼18.0 ± 1.6 ka BP for their emplacement. These two mean values derive from different 36Cl production rates used for exposure age calculation. The ages are uncorrected for temporal variations in production rates and may underestimate the true ages by 5-7%. The former age, although implying early deglaciation for this area of the British ice sheet, is not incompatible with minimum deglaciation ages from other contexts and locations in northwest England. However, the latter age is more consistent with the same minimum deglaciation ages and geochronological evidence for ice-free conditions in parts of the northern sector of the Irish Sea. Within uncertainties, the younger of the mean ages from Norber may indicate that boulder emplacement was associated with North Atlantic Heinrich event 1. The limited spatial (downvalley) extent of the Norber boulders implies that at the time of their deposition the ice margin was coincident with the distal margin of the erratic train. Loss of ice cover at Norber was followed by persistent stadial conditions until the abrupt opening of the Lateglacial Interstadial when large carnivorous mammals colonised the area. The 36Cl ages are between ∼3.0 ka and ∼13.0 ka older than previous estimates based on rates of limestone dissolution derived from the heights of pedestals beneath the erratics. 相似文献
607.
Soil contamination by heavy metals and organic pollutants around industrial premises is a problem in many countries around
the world. Delineating zones where pollutants exceed tolerable levels is a necessity for successfully mitigating related health
risks. Predictions of pollutants are usually required for blocks because remediation or regulatory decisions are imposed for
entire parcels. Parcel areas typically exceed the observation support, but are smaller than the survey domain. Mapping soil
pollution therefore involves a local change of support. The goal of this work is to find a simple, robust, and precise method
for predicting block means (linear predictions) and threshold exceedance by block means (nonlinear predictions) from data
observed at points that show a spatial trend. By simulations, we compared the performance of universal block kriging (UK),
Gaussian conditional simulations (CS), constrained (CK), and covariance-matching constrained kriging (CMCK), for linear and
nonlinear local change of support prediction problems. We considered Gaussian and positively skewed spatial processes with
a nonstationary mean function and various scenarios for the autocorrelated error. The linear predictions were assessed by
bias and mean square prediction error and the nonlinear predictions by bias and Peirce skill scores. 相似文献
608.
Stephan Schulz Rike Becker Juan Carlos Richard-Cerda Muhammad Usman Tim aus der Beek Ralf Merz Christoph Schüth 《水文研究》2021,35(3):e14077
Information on water balance components such as evapotranspiration and groundwater recharge are crucial for water management. Due to differences in physical conditions, but also due to limited budgets, there is not one universal best practice, but a wide range of different methods with specific advantages and disadvantages. In this study, we propose an approach to quantify actual evapotranspiration, groundwater recharge and water inflow, i.e. precipitation and irrigation, that considers the specific conditions of irrigated agriculture in warm, arid environments. This approach does not require direct measurements of precipitation or irrigation quantities and is therefore suitable for sites with an uncertain data basis. For this purpose, we combine soil moisture and energy balance monitoring, remote sensing data analysis and numerical modelling using Hydrus. Energy balance data and routine weather data serve to estimate ET0. Surface reflectance data from satellite images (Sentinel-2) are used to derive leaf area indices, which help to partition ET0 into energy limited evaporation and transpiration. Subsequently, first approximations of water inflow are derived based on observed soil moisture changes. These inflow estimates are used in a series of forward simulations that produce initial estimates of drainage and ETact, which in turn help improve the estimate of water inflow. Finally, the improved inflow estimates are incorporated into the model and then a parameter optimization is performed using the observed soil moisture as the reference figure. Forward simulations with calibrated soil parameters result in final estimates for ETact and groundwater recharge. The presented method is applied to an agricultural test site with a crop rotation of cotton and wheat in Punjab, Pakistan. The final model results, with an RMSE of 2.2% in volumetric water content, suggest a cumulative ETact and groundwater recharge of 769 and 297 mm over a period of 281 days, respectively. The total estimated water inflow accounts for 946 mm, of which 77% originates from irrigation. 相似文献
609.
High-Resolution Fibre-Optic Temperature Sensing: A New Tool to Study the Two-Dimensional Structure of Atmospheric Surface-Layer Flow 总被引:1,自引:0,他引:1
Christoph K. Thomas Adam M. Kennedy John S. Selker Ayla Moretti Martin H. Schroth Alexander R. Smoot Nicholas B. Tufillaro Matthias J. Zeeman 《Boundary-Layer Meteorology》2012,142(2):177-192
We present a novel approach based on fibre-optic distributed temperature sensing (DTS) to measure the two-dimensional thermal
structure of the surface layer at high resolution (0.25 m, ≈0.5 Hz). Air temperature observations obtained from a vertically-oriented
fibre-optics array of approximate dimensions 8 m × 8 m and sonic anemometer data from two levels were collected over a short
grass field located in the flat bottom of a wide valley with moderate surface heterogeneity. The objectives of the study were
to evaluate the potential of the DTS technique to study small-scale processes in the surface layer over a wide range of atmospheric
stability, and to analyze the space–time dynamics of transient cold-air pools in the calm boundary layer. The time response
and precision of the fibre-based temperatures were adequate to resolve individual sub-metre sized turbulent and non-turbulent
structures, of time scales of seconds, in the convective, neutral, and stable surface layer. Meaningful sensible heat fluxes
were computed using the eddy-covariance technique when combined with vertical wind observations. We present a framework that
determines the optimal environmental conditions for applying the fibre-optics technique in the surface layer and identifies
areas for potentially significant improvements of the DTS performance. The top of the transient cold-air pool was highly non-stationary
indicating a superposition of perturbations of different time and length scales. Vertical eddy scales in the strongly stratified
transient cold-air pool derived from the DTS data agreed well with the buoyancy length scale computed using the vertical velocity
variance and the Brunt–Vaisala frequency, while scales for weak stratification disagreed. The high-resolution DTS technique
opens a new window into spatially sampling geophysical fluid flows including turbulent energy exchange. 相似文献
610.
We consider the Sitnikov problem; from the equations of motion we derive the approximate Hamiltonian flow. Then, we introduce
suitable action–angle variables in order to construct a high order normal form of the Hamiltonian. We introduce Birkhoff Cartesian
coordinates near the elliptic orbit and we analyze the behavior of the remainder of the normal form. Finally, we derive a
kind of local stability estimate in the vicinity of the periodic orbit for exponentially long times using the normal form
up to 40th order in Cartesian coordinates. 相似文献