全文获取类型
收费全文 | 4100篇 |
免费 | 118篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 169篇 |
大气科学 | 577篇 |
地球物理 | 946篇 |
地质学 | 1676篇 |
海洋学 | 175篇 |
天文学 | 532篇 |
综合类 | 16篇 |
自然地理 | 139篇 |
出版年
2021年 | 65篇 |
2020年 | 56篇 |
2019年 | 38篇 |
2018年 | 129篇 |
2017年 | 145篇 |
2016年 | 214篇 |
2015年 | 125篇 |
2014年 | 194篇 |
2013年 | 238篇 |
2012年 | 92篇 |
2011年 | 154篇 |
2010年 | 169篇 |
2009年 | 203篇 |
2008年 | 135篇 |
2007年 | 113篇 |
2006年 | 106篇 |
2005年 | 78篇 |
2004年 | 53篇 |
2003年 | 60篇 |
2002年 | 85篇 |
2001年 | 78篇 |
2000年 | 68篇 |
1999年 | 69篇 |
1998年 | 67篇 |
1997年 | 59篇 |
1996年 | 49篇 |
1995年 | 66篇 |
1994年 | 73篇 |
1993年 | 32篇 |
1992年 | 31篇 |
1991年 | 33篇 |
1990年 | 42篇 |
1989年 | 38篇 |
1988年 | 29篇 |
1987年 | 31篇 |
1985年 | 42篇 |
1984年 | 43篇 |
1983年 | 57篇 |
1982年 | 40篇 |
1981年 | 41篇 |
1980年 | 38篇 |
1979年 | 28篇 |
1978年 | 55篇 |
1977年 | 30篇 |
1976年 | 31篇 |
1975年 | 44篇 |
1974年 | 52篇 |
1973年 | 50篇 |
1972年 | 27篇 |
1968年 | 25篇 |
排序方式: 共有4230条查询结果,搜索用时 15 毫秒
91.
Björn Heincke Thomas Günther Einar Dalsegg Jan Steinar Rønning Guri Venvik Ganerød Harald Elvebakk 《Journal of Applied Geophysics》2010,70(4):292-306
We present a combined 3-D geoelectric and seismic tomography study conducted on the large Åknes rockslide in western Norway. Movements on the slope are strongly influenced by water infiltration, such that the hydrogeological regime is considered as a critical factor affecting the slope stability. The aim of our combined geophysical study was to identify and visualize the main shallow tension fractures and to determine their effect on hydraulic processes by comparing the geophysical results with information from borehole logging and tracer tests. To resolve the complex subsurface conditions of the highly fractured rock mass, a three-dimensional set-up was chosen for our seismic survey. To map the water distribution within the rock mass, a pattern of nine intersecting 2-D geoelectric profiles covered the complete unstable slope. Six of them that crossed the seismic survey area were considered as a single data set in a 3-D inversion. For both methods, smoothing-constraint inversion algorithms were used, and the forward calculations and parameterizations were based on unstructured triangular meshes. A pair of parallel shallow low-velocity anomalies (< 1400 m/s) observed in the final seismic tomogram was immediately underlain by two anomalies with resistivities <13 kΩm in the resistivity tomogram. In combination with borehole logging results, the low-velocity and resistivity anomalies could be associated with the drained and water-filled part of the tension fractures, respectively. There were indications from impeller flowmeter measurements and tracer tests that such tension fractures intersected several other water-filled fractures and were responsible for distinct changes of the main groundwater flow paths. 相似文献
92.
Ohne Zusammenfassung 相似文献
93.
Female and male individuals of the same species often differ with respect to their susceptibility to toxicant stress. In the present study, sea urchins (Psammechinus miliaris) of both sexes were exposed to high (150 μg L?1) and environmentally relevant (5 μg L?1) concentrations of phenanthrene over 10 days. While food intake was significantly decreased following exposure to 150 μg L?1 phenanthrene, histological indices (lipofuscin accumulation, fibrosis, oocyte atresia), energetic status (energy charge, sum adenylates, AMP/ATP ratio) as well as ascorbate levels in the gonads showed either little or no effect upon phenanthrene exposure. However, most parameters (vitamin C, energy charge, sum adenylates, AMP/ATP ratio, ATP and ADP concentrations, lipofuscin content, fibrosis) significantly differed between male and female animals. This study illustrates the difficulties to identify toxic injury in reproductive tissue as it may be superimposed by gametogenesis and spawning of gametes. 相似文献
94.
F. A. Lopes G. Michard M. Poulin A. Roué F. Prévot D. Jézéquel E. Viollier 《Aquatic Geochemistry》2010,16(4):587-610
A reactive transport model was developed to describe seasonal variations of biogeochemical and physical processes in Lake
Aydat. The model includes physical processes such as vertical mixing, sedimentation and advection related to inflows into
the lake and biogeochemical conversion processes in the water column and in the sediment surface layer. The reactions described
in the model include primary redox reactions such as primary production, aerobic and anaerobic respiration, methanogenesis
and secondary reactions established between oxidants and reducers produced by the primary reactions. After adjusting various
kinetic constants, the model reasonably reproduced the main features of seasonal variations of dissolved oxygen and nitrate
depth profiles and pH. The reactive transport model was also used to quantify the relative importance of different biogeochemical
pathways. For instance, ferrous denitrification seems to play an important role when stratification is increasing. 相似文献
95.
96.
M. S. Kirkgz 《Ocean Engineering》1995,22(1)
The results of laboratory experiments on the maximum and bottom impact pressures from waves breaking directly on vertical and sloping faced coastal structures are presented. Direct wave breaking on a wall is classified as early, late, and perfect breaking. Although the present study is aimed at dealing with the type of impact resulting from the perfect breaking, to some extent the occurrence of early and late breaking are unavoidable. The wave impact pressures, therefore, have a random nature of variation from impact-to-impact under the same conditions. The maximum and bottom impact pressures on walls are treated statistically. The effects of the wall angle and foreshore slope on these two quantities are examined. The results show that for practical applications, the still-water level can be taken as the acting place for the maximum impact pressure on the wall. Simultaneous impact pressure distribution below and above still-water level may be approximated as parabolic and linear, respectively. Finally, using a wall deflection criterion, a water depth region in front of the wall is defined, where the breaking wave forces may reach a critical level. 相似文献
97.
The seaweeds Fucus vesiculosus, Fucus serratus, Ascophyllum nodosum and Cladophora glomerata and crustaceans of the Idothea and Gammarus families have proven to be excellent bioindicators for radioactive corrosion products released from a nuclear power plant into the marine environment. These bioindicators have been used to map the spatial and temporal distribution of the released radioactivity. The activity has been followed up to 150 km from the power plant, and the decrease in activity concentration C(z) in the bioindicators with distance z can be expressed by a power function C(z) = α. z?1·4 where α is a constant.The variation with time of activity concentration very well reflects the amount of activity discharged from the power plant, with surprisingly good resolution in time.The bioindicators exhibit different uptake patterns of the radionuclides detected, and variations from summer to winter for the crustaceans Idothea, when compared to Fucus, has been found. 相似文献
98.
From the laboratory experiments and field studies it has been shown that when a wave breaks directly on a vertical wall, impact pressures of high magnitude and short duration, are produced. Despite the recent advances made in collecting data on impact pressure histories and their spatial distributions, analyses on the structural behaviour of the walls loaded by the impact forces do not seem adequate. In the present study the theoretical analysis of the response characteristics of a caisson plate, having different aspect ratios, under the wave impact loading is investigated. Numerical results for the dynamic values of moments and transverse displacements are obtained by the method of finite elements. Some prerequisite experimental data for wave breaking and resulting impact pressures are provided. The static results for moments and deflections are also computed for comparing them with the dynamic values. The dynamic results are found significantly greater than the static values. The ratio between the dynamic and static values is called “Dynamic magnification factor” that varies with plate aspect ratio. Based on this factor a procedure is proposed which may have practical consequences in the design of caisson plates. 相似文献
99.
Jörn Thiede Stephanie Pfirman Hans-Werner Schenke Wolfgang Reil 《Marine Geophysical Researches》1990,12(3):197-214
The sea floor of Fram Strait, the over 2500 m deep passage between the Arctic Ocean and the Norwegian-Greenland Sea, is part of a complex transform zone between the Knipovich mid-oceanic ridge of the Norwegian-Greenland Sea and the Nansen-Gakkel Ridge of the Arctic Ocean. Because linear magnetic anomalies formed by sea-floor spreading have not been found, the precise location of the boundary between the Eurasian and the North American plate is unknown in this region. Systematic surveying of Fram Strait with SEABEAM and high resolution seismic profiling began in 1984 and continued in 1985 and 1987, providing detailed morphology of the Fram Strait sea floor and permitting better definition of its morphotectonics. The 1984 survey presented in this paper provided a complete set of bathymetric data from the southernmost section of the Svalbard Transform, including the Molloy Fracture Zone, connecting the Knipovich Ridge to the Molloy Ridge; and the Molloy Deep, a nodal basin formed at the intersection of the Molloy Transform Fault and the Molloy Ridge. This nodal basin has a revised maximum depth of 5607 m water depth at 79°8.5N and 2°47E. 相似文献
100.
In the polymetamorphic Austroalpine Matsch Unit (European Eastern Alps) Cretaceous upper greenschist facies metamorphism overprinted Variscan and Permian magmatic and metamorphic assemblages. Mineral compositional and (micro-)structural data of metapelites and metapegmatites document different mechanisms of interrelated deformation and (re-)equilibration during Cretaceous overprinting: i) Microfractures in relic garnet represented pathways for material transport, and thus established material exchange between intragranular domains and the matrix. Major element equilibration by fast diffusion along microfractures contrasts with limited volume diffusion in adjacent host garnet. ii) Syn-tectonic breakdown of staurolite initially to paragonite, then chloritoid allows correlating reaction progress with the formation of different fracture sets. iii) Syn-tectonic mineral growth with shape-preferred orientation in foliation domains contrasts with radial growth in microlithons and strain shadows of the mylonitic foliation. iv) Syn-tectonic unmixing of pre-existing oligoclase (an14–16) produced fine-grained aggregates of two supposedly coexisting plagioclase-phases (an3–6 and an20–25) in strain shadows of the oligoclase-clasts. v) Pre-existing deformation-induced heterogeneities in the spatial distribution of phases and their preferred orientation influence the kinetics of phase equilibration. Understanding the mechanisms of the mutual interrelation between deformation and phase equilibration is a prerequisite for deducing PT-constraints from strained metamorphic rocks. New garnet—whole rock Sm-Nd data from metapegmatites indicate their emplacement at 263–280 Ma and provide an important age constraint on the interrelated deformation and re-equilibration processes. 相似文献