全文获取类型
收费全文 | 2405篇 |
免费 | 118篇 |
国内免费 | 24篇 |
专业分类
测绘学 | 100篇 |
大气科学 | 169篇 |
地球物理 | 878篇 |
地质学 | 776篇 |
海洋学 | 155篇 |
天文学 | 305篇 |
综合类 | 11篇 |
自然地理 | 153篇 |
出版年
2021年 | 26篇 |
2020年 | 57篇 |
2019年 | 39篇 |
2018年 | 65篇 |
2017年 | 58篇 |
2016年 | 109篇 |
2015年 | 86篇 |
2014年 | 97篇 |
2013年 | 142篇 |
2012年 | 93篇 |
2011年 | 126篇 |
2010年 | 111篇 |
2009年 | 127篇 |
2008年 | 108篇 |
2007年 | 75篇 |
2006年 | 79篇 |
2005年 | 54篇 |
2004年 | 44篇 |
2003年 | 56篇 |
2002年 | 37篇 |
2001年 | 54篇 |
2000年 | 37篇 |
1999年 | 43篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 27篇 |
1993年 | 17篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 30篇 |
1988年 | 26篇 |
1987年 | 27篇 |
1986年 | 35篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 35篇 |
1982年 | 33篇 |
1981年 | 30篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 24篇 |
1975年 | 22篇 |
1973年 | 24篇 |
1972年 | 16篇 |
1971年 | 18篇 |
排序方式: 共有2547条查询结果,搜索用时 15 毫秒
411.
Tatiana F. Maria Jan Vanaverbeke Ruth Gingold André M. Esteves Ann Vanreusel 《Marine Ecology》2013,34(2):207-217
Lately, across‐shore zonation has been found to be more important in structuring the nematode community of a tropical macrotidal sandy beach than microhabitat heterogeneity. To evaluate whether this zonation pattern applies to a temperate beach, a macrotidal ridge‐and‐runnels sandy beach in the North Sea was studied. We investigated whether a similar zonation occurs in sandbar and runnel microhabitats, and whether the runnels harbour a different community from the subtidal. Our results indicate that nematode communities from runnel and sandbar habitats are significantly different. In addition, horizontal zonation patterns for nematode communities differ between both habitats. Nematode assemblages from sandbars are divided to lower, middle and upper beach while upper and middle runnels cluster together. The subtidal and upper runnels showed dissimilar nematode assemblages, although runnels showed the same dominant species (Daptonema normandicum), which increases its abundance towards the upper runnels. This study illustrates the importance of microhabitat heterogeneity, which resulted in different zonation patterns across the sandy beach examined. The divergent zonation between sandbars and runnels in the macrotidal temperate sandy beach, compared with the pattern observed for a subtropical sandy beach with similar morphodynamics, indicates that generalizations about nematode distribution patterns should be made with caution. 相似文献
412.
The membrane interface probe (MIP) is widely used to characterize the subsurface distribution of volatile organic compounds (VOCs). One problem that arises during MIP application is that disproportionately high MIP signals are obtained after passing source zones which contain mobile or residual phases. This serious problem occurs because of a carry-over effect, in particular caused by compound-specific retention times in the conventional unheated transfer line, commonly used during such an investigation. The objective of this study was to perform a qualitative methodical field evaluation of the carry-over effect of a conventional MIP system with a conventional unheated transfer line. This was achieved by coupling a mobile mass spectrometer to the MIP device. Results obtained were then further compared with those achieved using a laser induced fluorescence (LIF) system. Because of this coupling, time- and depth-dependent signals for different substances became known. Field evaluation data obtained showed complex superpositions of compounds with MIP system results. As a result of this superposition, MIP signals from the saturated zone beneath the source zone (zone with free and/or residual phase) are blurred and are therefore not representative of particular depths. However, utilizing multidirectional probing alongside conventional MIP probing (forwards and backwards), it was possible to detect the upper and lower phase boundary of the source zone. These MIP results correlated excellently with the LIF results. An important conclusion that can be drawn from the field investigation is that coupling a mobile mass spectrometer to the MIP system enables advanced MIP signal interpretation to be successfully achieved. 相似文献
413.
Global set of trajectories of satellite-tracked Lagrangian drifters is used to study the dynamics of marine debris. A probabilistic model is developed to eliminate the bias in spatial distribution of drifter data due to heterogeneous deployments. Model experiments, simulating long-term evolution of initially homogeneous drifter array, reveal five main sites of drifter aggregation, located in the subtropics and maintained by converging Ekman currents. The paper characterizes the geography and structure of the collection regions and discusses factors that determine their dynamics. A new scale R(c)=(4k/|D|)(?) is introduced to characterize tracer distribution under competing effects of horizontal divergence D and diffusion k. Existence and locations of all five accumulation zones have been recently confirmed by direct measurements of microplastic at the sea surface. 相似文献
414.
Tijmen Jan Moser 《Studia Geophysica et Geodaetica》2012,56(2):411-432
The ray-Born approximation is a very useful tool for forward modeling of scattered waves. The fact that ray-Born modeling underlies most seismic migration techniques, and therefore shares their assumptions, is a justification in itself to consider it for forward modeling. The ray-Born approximation does not make an explicit distinction between specular reflections and nonspecular diffractions. It therefore allows the modeling of diffractions from structural discontinuities such as edges and tips, as well as caustic diffractions. In the simplest implementation ray-Born seismograms are multiple-free. Ray-Born modeling can be orders of magnitude faster than finite-difference modeling, both in two-and three dimensions. 相似文献
415.
Laura Sandri Gill Jolly Jan Lindsay Tracy Howe Warner Marzocchi 《Bulletin of Volcanology》2012,74(3):705-723
By using BET_VH, we propose a quantitative probabilistic hazard assessment for base surge impact in Auckland, New Zealand.
Base surges resulting from phreatomagmatic eruptions are among the most dangerous phenomena likely to be associated with the
initial phase of a future eruption in the Auckland Volcanic Field. The assessment is done both in the long-term and in a specific
short-term case study, i.e. the simulated pre-eruptive unrest episode during Exercise Ruaumoko, a national civil defence exercise.
The most important factors to account for are the uncertainties in the vent location (expected for a volcanic field) and in
the run-out distance of base surges. Here, we propose a statistical model of base surge run-out distance based on deposits
from past eruptions in Auckland and in analogous volcanoes. We then combine our hazard assessment with an analysis of the
costs and benefits of evacuating people (on a 1 × 1-km cell grid). In addition to stressing the practical importance of a
cost-benefit analysis in creating a bridge between volcanologists and decision makers, our study highlights some important
points. First, in the Exercise Ruaumoko application, the evacuation call seems to be required as soon as the unrest phase
is clear; additionally, the evacuation area is much larger than what is recommended in the current contingency plan. Secondly,
the evacuation area changes in size with time, due to a reduction in the uncertainty in the vent location and increase in
the probability of eruption. It is the tradeoff between these two factors that dictates which cells must be evacuated, and
when, thus determining the ultimate size and shape of the area to be evacuated. 相似文献
416.
417.
Audun Libak Rolf Mjelde Henk Keers Jan Inge Faleide Yoshio Murai 《Marine Geophysical Researches》2012,33(2):185-207
This paper describes results from a geophysical study in the Vestbakken Volcanic Province, located on the central parts of the western Barents Sea continental margin, and adjacent oceanic crust in the Norwegian-Greenland Sea. The results are derived mainly from interpretation and modeling of multichannel seismic, ocean bottom seismometer and land station data along a regional seismic profile. The resulting model shows oceanic crust in the western parts of the profile. This crust is buried by a thick Cenozoic sedimentary package. Low velocities in the bottom of this package indicate overpressure. The igneous oceanic crust shows an average thickness of 7.2 km with the thinnest crust (5–6 km) in the southwest and the thickest crust (8–9 km) close to the continent-ocean boundary (COB). The thick oceanic crust is probably related to high mantle temperatures formed by brittle weakening and shear heating along a shear system prior to continental breakup. The COB is interpreted in the central parts of the profile where the velocity structure and Bouguer anomalies change significantly. East of the COB Moho depths increase while the vertical velocity gradient decreases. Below the assumed center for Early Eocene volcanic activity the model shows increased velocities in the crust. These increased crustal velocities are interpreted to represent Early Eocene mafic feeder dykes. East of the zone of volcanoes velocities in the crust decrease and sedimentary velocities are observed at depths of more than 10 km. The amount of crustal intrusions is much lower in this area than farther west. East of the Kn?legga Fault crystalline basement velocities are brought close to the seabed. This fault marks the eastern limit of thick Cenozoic and Mesozoic packages on central parts of the western Barents Sea continental margin. 相似文献
418.
Raúl Prellezo Paolo AccadiaJesper L. Andersen Bo S. AndersenErik Buisman Alyson LittleJ. Rasmus Nielsen Jan Jaap PoosJeff Powell Christine Röckmann 《Marine Policy》2012,36(2):423-431
The lessons learned from a review of thirteen existing European bio-economic models used in the evaluation of EU policies are presented. How these models compare and differ in terms of their biological and economic components, the integration between the components, which indicators are selected and how they are used, are described and analysed. The article concludes that the multitude of construction differences reflects the necessity of adapting the modelling approach to answer different questions. Since real life questions in fisheries are so diverse, answering them requires a diversity of models. 相似文献
419.
Large-scale, low-gradient ancient landslides estimated at 5.4–18.9 km2 in area and 0.2–1.2 km3 in volume have been studied in the northern hilly periphery of the Crimean Mountains (Ukraine). They originated on slopes along wide water gaps of rivers (Belbek, Kacha, Alma and Biyuk–Karasu) crossing the cuestas of the northern foothills. The slopes generally consist of slightly northward tilting Miocene (mainly Sarmatian) limestones overlying weak, clay-rich Lower Neogene–Palaeogene substratum with a significant content of smectite. Although the region is characterised by the least active contemporary morphodynamics within the Crimean Mountains, the landslides which were studied are of the same size or even larger than various types of landslides occupying active geomorphic domains of the highest mountain range in the southernmost part of the peninsula. The landslides are generally a spreading type, but the sliding mechanics were probably very complex, involving toppling, rotational slides, gravitational folding and translational block slides. All the landslides which were studied are located in the vicinity of regional faults and three of them have headscarps aligned along faults. A common feature is also a location close (within several km) to the Mesozoic suture zone which is the most important tectonic feature in the northern periphery of the Crimean Orogene. This suture was formerly classified as aseismic; however, evidence of strong, low-frequency palaeoearthquakes was collected during the last decade within both the Mesozoic suture and the low-lying northern part of the Crimean Peninsula. Radiocarbon dating of deposits associated with the landslides has revealed at least two phases of increased landslide-activity during the Late Glacial chronozone and Holocene epoch. The main landslide phase presumably took place at some time between the Late Glacial and Atlantic chronozones. Minor reactivation of landslide toes occurred during the Subatlantic chronozone and some of them have been active up to recent times. The first major landslide phase was possibly triggered by an earthquake, whereas late Holocene activity can be attributed both to seismic and hydroclimatic factors. 相似文献