全文获取类型
收费全文 | 384篇 |
免费 | 15篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 30篇 |
地球物理 | 100篇 |
地质学 | 195篇 |
海洋学 | 41篇 |
天文学 | 22篇 |
自然地理 | 24篇 |
出版年
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 4篇 |
2015年 | 9篇 |
2014年 | 9篇 |
2013年 | 29篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 8篇 |
2005年 | 17篇 |
2004年 | 15篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 14篇 |
1996年 | 23篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有420条查询结果,搜索用时 46 毫秒
141.
Janet S. Herman 《Engineering Geology》1989,26(4):301-317
Much of the assessment of high-level radioactive waste repositories will be accomplished through the application of geochemical models. Such models will be used to understand geochemical processes in the repository and the surrounding environment. The purpose of this paper is to review the nature of the currently available geochemical models. The kinds of calculations that a number of these models perform include aqueous speciation, mineral solubility, and mass transfer reactions. Presently, there are limitations on the success of calculation of adsorption reactions and rate-limited reactions. Ongoing development of geochemical models requires that more work be done to compile thermodynamic and kinetic data, incorporate additional geochemical processes and parameters into existing codes, and assess the accuracy of all simulations through validation studies and sensitivity analyses. 相似文献
142.
143.
Hydraulic properties of saturated and unsaturated stony soils were studied on a 3.35 m long column, 1.24 m in diameter, filled with alternating sand and boulder layers. The boulders averaged 6.2 × 15 × 20 cm in size and were laid down on their flat side. Tensiometers and a neutron probe access tube were placed in the column for measuring pressure heads and water contents, respectively. Saturated conditions were obtained by ponding the column. The resulting hydraulic conductivity K was 5.1 m/day. This value could also be calculated from the measured K for the sand alone on separate samples, using a simple equation that takes into account the void ratio of the sand alone and that of the boulder-sand mixture. Unsaturated K was determined by applying water at less than ponded infiltration rates. Resulting relations between the unsaturated K and water content or negative pressure head could also be estimated from the relation between unsaturated K and pressure head for the sand alone and the calculated saturated K of the boulder-sand mixture. The method of Millington and Quirk for calculating the relation between unsaturated K and water content also gave reasonable results. The dispersivity of the boulder-sand column was 18 times that of the sand alone. Pore velocity was accurately estimated as the Darcy velocity divided by the volumetric water content. Hydraulic properties of stony vadose zones are difficult to determine. This work shows that they can be estimated from K relations measured in the laboratory on samples of the soil between the rocks. Knowledge of hydraulic properties of vadose zones is important in predicting movement of water and pollutants to the underlying ground water. 相似文献
144.
This paper outlines the development of a multi-disciplinary strategy to focus exploration for economic kimberlites on the Ekati property. High-resolution aeromagnetic data provide an over-arching spatial and magnetostratigraphic framework for exploration and kimberlite discovery at Ekati, and hence also for this investigation. The temporal, geomagnetic, spatial and related attributes of kimberlites with variable diamond content have been constrained by judiciously augmenting the information gathered during routine exploration with detailed, laboratory-based or field-based investigations. The natural remanent magnetisation of 36 Ekati kimberlites has been correlated with their age as determined by isotopic dating techniques, and placed in the context of a well-constrained geomagnetic polarity timescale. Kimberlite magmatism occurred over the period 75 to 45 Ma, in at least five temporally discrete intrusive episodes. Based on current evidence, the older kimberlites (75 to 59 Ma) have low diamond contents and are distributed throughout the property. Younger kimberlites (56 to 45 Ma) have moderate to high diamond contents and occur in three distinct intrusive corridors with NNE to NE orientations. Economic kimberlite pipes erupted at 55.4±0.4 Ma along the A154-Lynx intrusive corridor, which is 7 km wide and oriented at 015°, and at 53.2±0.3 Ma along the Panda intrusive corridor, which is 1 km wide and oriented at 038°. The intrusion ages straddle a paleopole reversal at Chron C24n, consistent with the observation that the older economic kimberlites present as aeromagnetic “low” anomalies while the younger economic pipes are characterised as aeromagnetic “highs”. The aeromagnetic responses for these kimberlites are generally muted because they contain volcaniclastic rock types with low magnetic susceptibility. Kimberlites throughout the Ekati property carry a primary natural magnetic remanence (NRM) vector in Ti-bearing groundmass magnetite, and it dominates over vectors related to induced magnetisation. Magnetostratigraphic correlation of Ekati kimberlites may therefore present a powerful adjunct to existing exploration techniques, mainly because the diamond content of Ekati kimberlites apparently is related more to the age of eruption than to any other parameter investigated in this work. 相似文献
145.
BRUECKNER HANNES K.; VAN ROERMUND HERMAN L. M.; PEARSON NORMAN J. 《Journal of Petrology》2004,45(2):415-437
Mineralogical, isotopic, geochemical and geochronological evidencedemonstrates that the Friningen body, a garnet peridotite bodycontaining garnet pyroxenite layers in the Seve Nappe Complex(SNC) of Northern Jämtland, Sweden, represents old, certainlyProterozoic and possibly Archean, lithosphere that became incorporatedinto the Caledonian tectonic edifice during crustal subductioninto the mantle at c. 450 Ma. Both garnet peridotite and pyroxenitecontain two (M1 and M2) generations of garnet-bearing assemblagesseparated by the formation of two-pyroxene, spinel symplectitearound the M1 garnet and the crystallization of low-Cr spinel1Cin the matrix. These textures suggest initial high-pressure(HP) crystallization of garnet peridotite and pyroxenite succeededby decompression into the spinel stability field, followed byrecompression into the garnet peridotite facies. Some pyroxenitelayers appear to be characterized solely by M2 assemblages withstretched garnet as large as several centimeters. Laser ablationmicroprobeinductively coupled plasma mass spectrometryReOs analyses of single sulfide grains generally definemeaningless model ages suggesting more than one episode of Reand/or Os addition and/or loss to the body. Pentlandite grainsfrom a single polished slab of one garnet peridotite, however,define a linear array on an ReOs isochron diagram that,if interpreted as an errorchron, suggests an Archean melt extractionevent that left behind the depleted dunite and harzburgite bodiesthat characterize the SNC. Refertilization of this mantle bymelts associated with the development of the pyroxenite layersis indicated by enriched clinopyroxene SrNd isotope ratios,and by parallel large ion lithophile-enriched trace elementpatterns in clinopyroxene from pyroxenite and the immediatelyadjacent peridotite. Clinopyroxene and whole-rock model SmNdages (TDM = 1·12·2 Ga) indicate that fertilizationtook place in Proterozoic times. SmNd garnet2clinopyroxene2wholerock ± orthopyroxene2 mineral isochrons from three pyroxenitelayers define overlapping ages of 452·1 ± 7·5and 448 ± 13 Ma and 451 ± 43 Ma (2 相似文献
146.
VAN REENEN D. D.; PERCHUK L. L.; SMIT C. A.; VARLAMOV D. A.; BOSHOFF R.; HUIZENGA J. M.; GERYA T. V. 《Journal of Petrology》2004,45(7):1413-1439
The Central Zone (CZ) of the Limpopo Complex of southern Africais characterized by a complex deformational pattern dominatedby two types of fold geometries: large sheath folds and crossfolds. The sheath folds are steeply SSW-plunging closed structureswhereas the cross folds are northsouth-oriented withnear-horizontal fold axes. In the area south of Messina thiscomplexly folded terrain grades continuously towards the southinto a crustal-scale ENEWSW-trending ductile shear zonewith moderate dip towards the WSW. All sheath folds documentconsistent top-to-the-NE thrust movement of high-grade material.The timing of this shear deformational event (D2) and thus ofthe gneissic fabric (S2) is constrained (at 相似文献
147.
A series of solar brightness distributions observed over the Venus disk at several wavelengths is analyzed. A single absorption mechanism is assumed, the main localization of which is varied within the clouds, in different models. An attempt is made to retrieve all of the observations from one or more of the models. From the ultraviolet observations, models in which the absorption is highly localized give a better fit although better measurements are needed before a definite conclusion may be drawn. Isophote maps in visible light disagree with the theoretical predictions of all the models, suggesting that a second absorption mechanism (perhaps the ground) ought to be called for in this spectral region. 相似文献
148.
149.
Przemysław Herman 《Ocean Engineering》2009,36(3-4):306-312
A method for dynamics investigation and coupling detection between velocities of autonomous underwater vehicles (AUVs) is presented in this paper. The method is based on transformation of equations of motion, which are usually used for an underwater vehicle, into equations with a diagonal mass matrix. The obtained equations contain quasi-velocities and allow one to give a further insight into the AUV dynamics especially for an underactuated system. Some advantages of the proposed approach are discussed, too. An analytical example for a 3-DOF AUV shows possible application of the transformed equations. Moreover, the given approach is validated via simulation on a 6-DOF vehicle. 相似文献
150.
A palaeoecological study of the mites (Acari) from a Lateglacial deposit at Usselo (The Netherlands)
JAAP SCHELVIS BAS VAN GEEL 《Boreas: An International Journal of Quaternary Research》1989,18(3):237-243
The distribution of the remains of mites in the Lateglacial (Late Weichselian) type section at Usselo (The Netherlands) is presented. The division of the sequence into (sub-)zones, based upon combined palaeo-botanical and palaeoentomological studies, is shown, as well as the approximate age based on 14 C determinations. The present habitats of the species are in agreement with the reconstruction of the local vegetational succession Four species of mites, three oribatids and one uropodid, have not previously been recorded as subfossils. 相似文献