全文获取类型
收费全文 | 1532篇 |
免费 | 65篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 63篇 |
大气科学 | 243篇 |
地球物理 | 385篇 |
地质学 | 537篇 |
海洋学 | 37篇 |
天文学 | 257篇 |
综合类 | 6篇 |
自然地理 | 78篇 |
出版年
2021年 | 19篇 |
2020年 | 27篇 |
2019年 | 19篇 |
2018年 | 60篇 |
2017年 | 49篇 |
2016年 | 79篇 |
2015年 | 69篇 |
2014年 | 76篇 |
2013年 | 110篇 |
2012年 | 34篇 |
2011年 | 46篇 |
2010年 | 67篇 |
2009年 | 75篇 |
2008年 | 36篇 |
2007年 | 46篇 |
2006年 | 54篇 |
2005年 | 34篇 |
2004年 | 13篇 |
2003年 | 35篇 |
2002年 | 33篇 |
2001年 | 29篇 |
2000年 | 30篇 |
1999年 | 24篇 |
1998年 | 17篇 |
1997年 | 30篇 |
1996年 | 21篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1984年 | 14篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 20篇 |
1972年 | 13篇 |
1971年 | 10篇 |
1970年 | 12篇 |
1969年 | 11篇 |
1968年 | 12篇 |
1965年 | 14篇 |
排序方式: 共有1606条查询结果,搜索用时 328 毫秒
91.
Mögliche Massnahmen zur Restaurierung des Sempachersees 总被引:1,自引:1,他引:1
R. Gächter D. Imboden H. Bührer P. Stadelmann 《Aquatic Sciences - Research Across Boundaries》1983,45(1):246-266
Since 1954 average orthophosphate and total phosphorus concentrations have increased twenty and eightfold respectively in
Lake Sempach. It is demonstrated that the lake is not in steady state with its phosphorus loading and that the net deposition
rate of phosphorus is not linearly related to the phosphorus content of the lake. This implies that linear steady state one-box
models are unsuitable to describe the phosphorus balance of this lake. Applying a nonlinear dynamic lake model we predict
that the defined water quality goals ([P] ⩽30 mg m−3, [O2 ⩾4 mg m−3]) can only be achieved within the next 15 years if the external phosphorus loading is reduced by at least 50% and simultaneously
lake-internal measures, such as hypolimnion areation or hypolimnion siphoning are carried into effect.
相似文献
92.
Superstructures in synthetic mullite, Al4+2x Si2?2x O10?x , prepared using the zone melting technique, are studied by high resolution electron microscopy (HREM), electron diffraction, and in situ energy dispersive X-ray spectroscopy. For x=0.40 composition HREM images indicate only short-range order. Near x=0.5 composition mullite has an antiphase domain structure with antiphase boundaries (APB's) oriented parallel to (100). For higher Al-content the APB's run in non-rational orientations which are slightly inclined against the {601}-planes. We propose models for the superstructures in which oxygen vacancies are arranged in channels parallel to the crystal b-axis. The models are supported by a one-to-one match between observed and computer-simulated images. An Al-rich limit of x=2/3 for mullite is deduced on the basis of stereochemical considerations. Different ordering schemes for the tetrahedral cations are believed to result in the orientation change of the APB's near x=0.5 composition. 相似文献
93.
It is shown that the annealing kinetics of fission tracks in apatite can be described by a sum of exponential decay functions. From an analysis of the temperature dependence of this annealing law it is concluded that the etchability of fission tracks is due to extended defects, i.e. systems of dislocation loops. The multiexponential annealing law is also applied to prove that the plateau correction method is basically correct, but rather as a method for determining a lower limit than the “true” fission track age. 相似文献
94.
M. Frey J. C. Hunziker E. Jäger W. B. Stern 《Contributions to Mineralogy and Petrology》1983,83(1-2):185-197
Some 150 white K-micas from the Central Alps were analysed for their polymorph and phengite content. Pre-Alpine white K-micas and those belonging to the Meso-Alpine Lepontine Metamorphic “High” show exclusively the 2M1 polymorph. The 3T structural form, on the other hand, has been found in one third of the white K-micas formed during the Alpine regional metamorphism. In most cases this trigonal structure coexists with varying amounts of the 2M1 form. The 3T distribution pattern suggests that this polymorph originated during the Eo-Alpine high-pressure/“low temperature” metamorphism. Provided this interpretation is correct, the sporadic occurrence of this polymorph within the Meso-Alpine staurolite zone may be used as a tracer for the Eo-Alpine metamorphism. The following improved correlation between the (060, 331) reflections of 2M1 white K-micas and the RM-content (= 2Fe2O3+FeO+MgO in molar proportions), based on 24 micas from granitoid rocks, is presented: d(060, 331)= 1.498+0.082 RM. The phengite content of Alpine white K-micas belonging to the assemblage muscovite-biotite-K-feldspar-quartz was estimated from RM values or derived from chemical analyses and was found to be clearly related to metamorphic grade. Phengite-rich micas were formed during the Eo-Alpine high-P/“ low-T” metamorphism while aluminous muscovite was found within the Meso-Alpine thermal high of the Lepontine gneiss area. White K-micas from areas which underwent both the Eo-Alpine and the Meso-Alpine metamorphism display variable phengite contents. Although these micas show Tertiary Rb-Sr and K-Ar ages, the variable phengite content presumably reflects conditions during the Eo-Alpine high-P/“low-T” metamorphism. This interpretation implies that the cations occupying the interlayer positions are more easily equilibrated than those in octahedral and tetrahedral structural sites. A compilation of 3T white K-mica occurrences described in the literature is given in the appendix. 相似文献
95.
96.
We investigate the formation process and pathways of deep water masses in a coupled ice–ocean model of the Arctic and North
Atlantic Oceans. The intent is to determine the relative roles of these water masses from the different source regions (Arctic
Ocean, Nordic Seas, and Subpolar Atlantic) in the meridional overturning circulation. The model exhibits significant decadal
variability in the deep western boundary current and the overturning circulation. We use detailed diagnostics to understand
the process of water mass formation in the model and the resulting effects on the North Atlantic overturning circulation.
Particular emphasis is given to the multiple sources of North Atlantic Deep Water, the dominant deep water masses of the world
ocean. The correct balance of Labrador Sea, Greenland Sea and Norwegian Sea sources is difficult to achieve in climate models,
owing to small-scale sinking and convection processes. The global overturning circulation is described as a function of potential
temperature and salinity, which more clearly signifies dynamical processes and clarifies resolution problems inherent to the
high latitude oceans. We find that fluxes of deep water masses through various passages in the model are higher than observed
estimates. Despite the excessive volume flux, the Nordic Seas overflow waters are diluted by strong mixing and enter the Labrador
Sea at a lighter density. Through strong subpolar convection, these waters along with other North Atlantic water masses are
converted into the densest waters [similar density to Antarctic Bottom Water (AABW)] in the North Atlantic. We describe the
diminished role of salinity in the Labrador Sea, where a shortage of buoyant surface water (or excess of high salinity water)
leads to overly strong convection. The result is that the Atlantic overturning circulation in the model is very sensitive
to the surface heat flux in the Labrador Sea and hence is correlated with the North Atlantic Oscillation. As strong subpolar
convection is found in other models, we discuss broader implications. 相似文献
97.
S. I. Demidova M. A. Nazarov C. A. Lorenz G. Kurat F. Brandstätter Th. Ntaflos 《Petrology》2007,15(4):386-407
The paper presents the first analyses of major and trace elements in 19 lunar meteorites newly found in Oman. These and literature data were used to assay the composition of highland, mare, and transitional (highland-mare interface) regions of the lunar surface. The databank used in the research comprises data on 44 meteorites weighing 11 kg in total, which likely represent 26 individual falls. Our data demonstrate that the lunar highland crust should be richer in Ca and Al but poorer in mafic and incompatible elements than it was thought based on studying lunar samples and the first orbital data. The Ir concentration in the highland crust and the analysis of lunar crater population suggest that most lunar impactites were formed by a single major impact event, which predetermined the geochemical characteristics of these rocks. Lunar mare regions should be dominated by low-Ti basalts, which are, however, enriched in LREEs compared to those sampled by lunar missions. The typical material of mare-highland interface zones can contain KREEP and magnesian VLT basalts. The composition of the lunar highland crust deduced from the chemistry of lunar meteorites does not contradict the model of the lunar magma ocean, but the average composition of lunar mare meteorites is inconsistent with this concept and suggests assimilation of KREEP material by basaltic magmas. The newly obtained evaluations of the composition of the highland crust confirm that the Moon can be enriched in refractory elements and depleted in volatile and siderophile elements. 相似文献
98.
99.
A model for estimating the value of sampling programs and the optimal number of samples for contaminated soil 总被引:1,自引:0,他引:1
Pär-Erik Back 《Environmental Geology》2007,52(3):573-585
A model is presented for estimating the value of information of sampling programs for contaminated soil. The purpose is to calculate the optimal number of samples when the objective is to estimate the mean concentration. A Bayesian risk–cost–benefit decision analysis framework is applied and the approach is design-based. The model explicitly includes sample uncertainty at a complexity level that can be applied to practical contaminated land problems with limited amount of data. Prior information about the contamination level is modelled by probability density functions. The value of information is expressed in monetary terms. The most cost-effective sampling program is the one with the highest expected net value. The model was applied to a contaminated scrap yard in Göteborg, Sweden, contaminated by metals. The optimal number of samples was determined to be in the range of 16–18 for a remediation unit of 100 m2. Sensitivity analysis indicates that the perspective of the decision-maker is important, and that the cost of failure and the future land use are the most important factors to consider. The model can also be applied for other sampling problems, for example, sampling and testing of wastes to meet landfill waste acceptance procedures. 相似文献
100.
Manfred Baer Nicolas Deichmann Jochen Braunmiller John Clinton Stephan Husen Donat Fäh Domenico Giardini Philipp Kästli Urs Kradolfer Stefan Wiemer 《Swiss Journal of Geoscience》2007,100(3):517-528
This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during
2006. During this period, 572 earthquakes and 91 quarry blasts were detected and located in the region under consideration.
Of these earthquakes, two occurred in conjunction with the construction of the new Gotthard railway tunnel and 165 were induced
artificially by the stimulation of a proposed geothermal reservoir beneath the city of Basel. With 20 events with M
L
≥ 2.5, five of which were artificially induced, the seismic activity in the year 2006 was far below the average over the
previous 31 years. Nevertheless, six events were felt by the public, most prominently the strongest of the induced Basel events
(M
L
3.4), which caused some non-structural building damage. Noteworthy are also the two earthquakes near Cortaillod (M
L
3.2), on the shore of Lake Neuchatel, and in Val Mora (M
L
3.5), between the Engadin and Val Müstair, as well as the 42 aftershocks of the M
L
4.9 Vallorcine earthquake, between Martigny and Chamonix, of September 2005.
Editorial handling: Stefan Bucher 相似文献