全文获取类型
收费全文 | 1652篇 |
免费 | 199篇 |
国内免费 | 255篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 11篇 |
地球物理 | 331篇 |
地质学 | 902篇 |
海洋学 | 601篇 |
天文学 | 7篇 |
综合类 | 49篇 |
自然地理 | 188篇 |
出版年
2024年 | 4篇 |
2023年 | 12篇 |
2022年 | 15篇 |
2021年 | 30篇 |
2020年 | 48篇 |
2019年 | 57篇 |
2018年 | 49篇 |
2017年 | 51篇 |
2016年 | 58篇 |
2015年 | 42篇 |
2014年 | 59篇 |
2013年 | 142篇 |
2012年 | 81篇 |
2011年 | 95篇 |
2010年 | 95篇 |
2009年 | 90篇 |
2008年 | 97篇 |
2007年 | 105篇 |
2006年 | 97篇 |
2005年 | 103篇 |
2004年 | 69篇 |
2003年 | 73篇 |
2002年 | 69篇 |
2001年 | 65篇 |
2000年 | 66篇 |
1999年 | 45篇 |
1998年 | 62篇 |
1997年 | 41篇 |
1996年 | 44篇 |
1995年 | 40篇 |
1994年 | 29篇 |
1993年 | 34篇 |
1992年 | 32篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2106条查询结果,搜索用时 15 毫秒
1.
王发君 《中国海洋湖沼学报》1992,10(1):84-91
Based on a puff model . and together with the consideration of convection , dispersion and descent of suspended waste particles in marine environment , a numerical model is presented to predict the initial sedimentation of waste particles discharged from ocean outfalls in coastal waters and to compute the stable sedimentation rate in homogeneous trde current fields with water depth constant . When the time step selected is small enough , the results from this model agree well with that from the semi-analytical solution , and have sufficient precision for evaluating the impact on the environment caused by sedimentation of waste particles discharged from ocean outfalls. A numerical example is given for predicting the sedimentation of waste particles discharged in Heishijiao , Dalian . 相似文献
2.
Olga Hadz̆ija Mladen Jurac̆ić Marija Luić Maja Tonković Biserka Jeric̆ević 《Estuarine, Coastal and Shelf Science》1985,21(5):701-709
The investigation of mineral, granulometric and chemical composition of sediments of the River Krka estuary (Yugoslavia) were performed in order to elucidate the origin of the sediments and the pattern of sedimentation. Estuarine surface sediments were found to be fine-grained with a bimodal distribution. Environmental conditions in estuarine sediments favour conservation of the organic matter (anoxic conditions). The carbohydrates in the sediments were investigated to determine whether they are of terrigenous or authigenous origin. Glucose, galactose, mannose, xylose, rhamnose, glucosamine and glucuronic acid were detected in the sediments. Their mutual relationship indicates a preferentially terrigenous source of sedimented organic material in estuarine sediments. 相似文献
3.
JÜRGEN TITSCHACK CAMPBELL S. NELSON TIM BECK ANDRÉ FREIWALD ULRICH RADTKE 《Sedimentology》2008,55(6):1747-1776
Autochthonous red algal structures known as coralligène de plateau occur in the modern warm‐temperate Mediterranean Sea at water depths from 20 to 120 m, but fossil counterparts are not so well‐known. This study describes, from an uplifted coastal section at Plimiri on the island of Rhodes, a 450 m long by 10 m thick Late Pleistocene red algal reef (Coralligène Facies), interpreted as being a coralligène de plateau, and its associated deposits. The Coralligène Facies, constructed mainly by Lithophyllum and Titanoderma, sits unconformably upon the Plio‐Pleistocene Rhodes Formation and is overlain by a Maerl Facies (2 m), a Mixed Siliciclastic‐Carbonate Facies (0·2 m) and an Aeolian Sand Facies (2·5 m). The three calcareous facies, of Heterozoan character, are correlated with established members in the Lindos Acropolis Formation in the north of the island, while the aeolian facies is assigned to the new Plimiri Aeolianite Formation. The palaeoenvironmental and genetic‐stratigraphic interpretations of these mixed siliciclastic‐carbonate temperate water deposits involved consideration of certain characteristics associated with siliciclastic shelf and tropical carbonate shelf models, such as vertical grain‐size trends and the stratigraphic position of zooxanthellate coral growths. Integration of these results with electron spin resonance dates of bivalve shells indicates that the Coralligène Facies was deposited during Marine Isotope Stage 6 to 5e transgressive event (ca 135 to 120 ka), in water depths of 20 to 50 m, and the overlying Maerl Facies was deposited during regression from Marine Isotope Stage 5e to 5d (ca 120 to 110 ka), at water depths of 25 to 40 m. The capping Aeolian Sand Facies, involving dual terrestrial subunits, is interpreted as having formed during each of the glacial intervals Marine Isotope Stages 4 (71 to 59 ka) and 2 (24 to 12 ka), with soil formation during the subsequent interglacial periods of Marine Isotope Stages 3 and 1, respectively. Accumulation rates of about 0·7 mm year?1 are estimated for the Coralligène Facies and minimum accumulation rates of 0·2 mm year?1 are estimated for the Maerl Facies. The existence of older red algal reefs in the Plimiri region during at least Marine Isotope Stages 7 (245 to 186 ka) and 9 (339 to 303 ka) is inferred from the occurrence of reworked coralligène‐type lithoclasts in the basal part of the section and from the electron spin resonance ages of transported bivalve shells. 相似文献
4.
Techniques to measure grain-size distributions of loamy sediments: a comparative study of ten instruments for wet analysis 总被引:2,自引:0,他引:2
DIRK GOOSSENS 《Sedimentology》2008,55(1):65-96
Ten instruments for measuring the grain‐size distribution of loamy sediments in water were tested in a comparative study. Instruments tested were: the Malvern Mastersizer S, the Coulter LS 200, the Fritsch Analysette 22 (version C), the Horiba Partica LA‐950, the Sedigraph 5100, the Atterberg cylinder, the Coulter Multisizer 3, the CIS‐100, the EyeTech and the image analysis software Histolab. The first four instruments use laser diffraction. The Sedigraph and Atterberg cylinder are based on sedimentation. The Coulter Multisizer 3 uses impedance measurements and the last three instruments use optical techniques. Grain‐size analyses were carried out on four sediments with median grain diameters of approximately 35, 30, 12 and 9 μm, respectively, and with no particles >90 μm. The laser diffraction instruments produced the best results for the various criteria considered in this study, followed by the Coulter Multisizer 3 (electrical sensing zone technique), the sedimentation techniques and the optical methods. However, the study also showed that there is no such thing as an ‘ideal’ method because techniques may score differently according to the criterion tested. An appropriate evaluation thus requires that various criteria be considered. Issues to be taken into account are: type of sediment, quantity of sediment available, speed of measurement, complexity of the measurement protocol, processing of the data, reproducibility of the results and the specific aims of the study undertaken. 相似文献
5.
Lake Sapanca in NW Turkey is a fault originated freshwater basin fed by seasonally variable flows of 15 streams. Considerations of lake–river interaction, supported by statistical measures of 47 bottom samples, suggest that sediment transport and deposition within the lake is controlled by two types of human constructed structures in addition to natural factors: (1) the dykes constructed in the front of streams, which feed the lake by strong flows, to prevent the filling of lakebed by coarse-grained sediments; (2) the constructed regulator on the outflowing Çarksuyu stream results in a higher sedimentation rate of clay-sized material on the NE corner of the lake, which is extraordinary in the shelf environment. 相似文献
6.
B. B. Kochnev 《Stratigraphy and Geological Correlation》2008,16(1):20-30
A model of sedimentation settings is elaborated for siliciclastic deposits of the Vendian Vanavara Formation, the Katanga saddle, inner areas of the Siberian platform. Four lithologic complexes are distinguished in the formation. The lower complex is composed of proluvial continental deposits exemplifying a dejection cone of ephemeral streams. Its eroded surface is overlain by second complex largely represented by sandstones of coastal zone, which grade upward into siltstones and shales of deeper sedimentation settings (third complex). Sea transgression advanced in northeastern direction. The fourth complex resting with scouring on the third one was deposited in settings of a spacious shallow-water sea zone: in a tidal flat, sand shoals and islands. Sedimentological data are used to correlate more precisely the Vendian siliciclastic deposits of the Katanga saddle and northeastern Nepa-Botuoba anteclise, and to verify subdivision of the Vanavara Formation into subformations and character of its boundary with the overlying Oskoba Formation. 相似文献
7.
Praxedes Muñoz Javier Sellanes Carina Lange Maritza Palma 《Progress in Oceanography》2007,75(3):586-602
We estimated monthly fluxes of 210Pb in shelf sediments beneath a high productivity area off central-southern Chile (36°S) during 1 year (September 2002-August 2003). Sediment cores were obtained using a multiple corer and were analyzed mainly for 210Pb, total pigments, and macrofauna abundance. The 210Pb inventories and fluxes were estimated for surface sediments (0-5 cm) and bioturbation coefficients were inferred using chlorophyll-a (reactive) profiles. In general, 210Pb content was inversely correlated with phytodetritus fluxes. High photosynthetic pigment contents in surface sediments were consistently associated with lower 210Pb contents. Macrofaunal activity responded to oxygen and organic matter supplies at the sediment surface, generally concentrated in the first centimeters, but particularly so during months of high organic matter fluxes and deficient bottom water oxygen conditions. At this study site, several processes involved in the 210Pb surface distribution make it difficult to accurately estimate ages at the surface. We postulate that the organic fluxes promote changes in the faunal activity, which, in combination with sediment resuspension and water circulation over the shelf, produce seasonal variations in the 210Pb inventories. 相似文献
8.
9.
Abstract. The consequences of the following episodic phenomena for the pelagic-benthic coupling in the Nordic Seas are illustrated: (1) Advection of water masses between fjords and shelf environments, (2) freshwater run-off and vertical stability, (3) dynamics of the marginal ice zone in the central and northern Barents Sea and the Polar Ocean, (4) drift patterns of sinking particles along the North Norwegian coast, (5) advection of zooplankton into subarctic fjords and the southern Barents Sea, zooplankton overwintering and composition, and (6) transport of organic particulate matter from the Barents Sea shelf. It is shown that physical processes in the north-eastern North Atlantic and Polar Ocean can be strongly variable on time scales of days to decades. They have a significant influence on the dynamics of pelagic-benthic coupling. The physical oceanography influences the vertical and horizontal particle flux not only directly (mixing, advection, up- and down-welling), but also indirectly through its impact on the biota (for example radiation, wind, ice cover, freshwater run-off and overwintering, advection and retention of zooplankton). Understanding pelagic-benthic coupling at high latitudes depends even more on a best possible understanding of the physical oceanography and the time scales involved than elsewhere. 相似文献
10.
试论东海陆架盆地的基底构造演化和盆地形成机制 总被引:4,自引:0,他引:4
本文主要根据东海陆架盆地和周边的地质、地球物理资料,分析盆地的基底岩性特征、结构特征。认为东海陆架盆地的基底除元古界片麻岩外,还分布有一定范围的中生界及古生界。基底构造特征是纵向上多层次,横向上不均一,南北有别,东西分带。构造演化上经历了张、合、压、扭等复杂过程。 相似文献