全文获取类型
收费全文 | 74021篇 |
免费 | 1133篇 |
国内免费 | 1219篇 |
专业分类
测绘学 | 1920篇 |
大气科学 | 5167篇 |
地球物理 | 14000篇 |
地质学 | 29961篇 |
海洋学 | 6210篇 |
天文学 | 15105篇 |
综合类 | 405篇 |
自然地理 | 3605篇 |
出版年
2022年 | 512篇 |
2021年 | 819篇 |
2020年 | 794篇 |
2019年 | 867篇 |
2018年 | 4037篇 |
2017年 | 3762篇 |
2016年 | 3035篇 |
2015年 | 1129篇 |
2014年 | 1688篇 |
2013年 | 2940篇 |
2012年 | 2910篇 |
2011年 | 4821篇 |
2010年 | 4304篇 |
2009年 | 4969篇 |
2008年 | 4078篇 |
2007年 | 4744篇 |
2006年 | 2617篇 |
2005年 | 2029篇 |
2004年 | 1882篇 |
2003年 | 1853篇 |
2002年 | 1694篇 |
2001年 | 1298篇 |
2000年 | 1200篇 |
1999年 | 944篇 |
1998年 | 985篇 |
1997年 | 950篇 |
1996年 | 804篇 |
1995年 | 783篇 |
1994年 | 680篇 |
1993年 | 578篇 |
1992年 | 609篇 |
1991年 | 544篇 |
1990年 | 612篇 |
1989年 | 539篇 |
1988年 | 484篇 |
1987年 | 600篇 |
1986年 | 491篇 |
1985年 | 602篇 |
1984年 | 694篇 |
1983年 | 621篇 |
1982年 | 616篇 |
1981年 | 569篇 |
1980年 | 571篇 |
1979年 | 512篇 |
1978年 | 482篇 |
1977年 | 467篇 |
1976年 | 424篇 |
1975年 | 416篇 |
1974年 | 423篇 |
1973年 | 483篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Tiago M. Alves Vasilios Lykousis Dimitris Sakellariou Stamatina Alexandri Paraskevi Nomikou 《Geo-Marine Letters》2007,27(1):41-61
Bathymetric, 9.5-kHz long-range sidescan sonar (OKEAN), seismic reflection and sediment-core data are used in the analysis
of two tectonic troughs south of Crete, Eastern Mediterranean Sea. Here, up to 1.2 s two-way travel time (TWTT) of strata
have accumulated since the Middle Miocene in association with extension in the South Aegean region. The study area comprises
>100-km- long by >25-km-wide basins filled by sediments subdivided into two seismic units: (1) an upper Unit 1 deposited in
sub-basins which follow the present-day configuration of the southern Cretan margin; (2) a basal Unit 2, more than 500 ms
(TWTT) thick, accumulated in deeper half-graben/grabens distinct from the present-day depocentres. Both units overlap a locally
stratified Unit 3 comprising the pre-Neogene core complex of Crete and Gavdos. In this work, the interpreted seismic units
are correlated with the onshore stratigraphy, demonstrating that denudation processes occurring on Crete and Gavdos in response
to major tectonic events have been responsible for high sedimentation rates along the proximal southern Cretan margin. Consequently,
topographically confined sedimentary units have been deposited south of Crete in the last 12 Ma, including turbidites and
other mass-flow deposits fed by evolving transverse and axial channel systems. Surface processes controlling facies distribution
include the direct inflow of sediment from alluvial-fan systems and incising mountain rivers onto the Cretan slope, where
significant sediment instability processes occur at present. In this setting, seismic profiles reveal eight different types
of stratigraphic contacts on basin-margin highs, and basinal areas show evidence of halokinesis and/or fluid escape. The acquired
data also show that significant changes to the margin’s configuration occurred in association with the post-Alpine tectonic
and eustatic episodes affecting the Eastern Mediterranean. 相似文献
102.
The illegal plundering of fishing stocks worldwide is masked behind a maze of corporate structures that makes discovery of the beneficiaries of such activity, difficult, if not impossible to identify. This paper outlines the problem of illegal fishing and then develops a multi-layered response to avert the veil of corporate entity being used as a means of preventing domestic States from answering the principal thematic question—who is the true beneficiary of this illegal behaviour, and who should be held responsible. 相似文献
103.
The flow field generated by a Rankine body moving under a free surface in afinite-depth water is calculated by potential theory. Velocity field generated by a source located at the origin is calculated first by using highly efficient and adaptive quadratures of the QUADPACK library. This solution is used for generating the flow around a Rankine body by locating a source and an equal strength sink along the body axis. Results agree well with the existing literature. 相似文献
104.
Data collected in three Californian estuaries indicate that hypersaline conditions exist during the dry summers typical of a Mediterranean climate. The generalised seasonal and longitudinal hydrographic structures are described and explained. It is argued that this seasonal hypersalinity is common and that it represents a major class of estuaries. The observed accumulation of salt indicates surprisingly long residence times in small basins which have free exchange with the ocean. This semi-isolation of the inner basin leads to a large build-up or severe depletion of nutrients, pollutants and plankton in these systems. Of concern are the trends to increase pollutant loading in the same systems that are experiencing an increase in residence times owing to freshwater extraction in the watershed. 相似文献
105.
Andrew R. Bowie Eric P. Achterberg Peter L. Croot Hein J.W. de Baar Patrick Laan James W. Moffett Simon Ussher Paul J. Worsfold 《Marine Chemistry》2006
The first large-scale international intercomparison of analytical methods for the determination of dissolved iron in seawater was carried out between October 2000 and December 2002. The exercise was conducted as a rigorously “blind” comparison of 7 analytical techniques by 24 international laboratories. The comparison was based on a large volume (700 L), filtered surface seawater sample collected from the South Atlantic Ocean (the “IRONAGES” sample), which was acidified, mixed and bottled at sea. Two 1-L sample bottles were sent to each participant. Integrity and blindness were achieved by having the experiment designed and carried out by a small team, and overseen by an independent data manager. Storage, homogeneity and time-series stability experiments conducted over 2.5 years showed that inter-bottle variability of the IRONAGES sample was good (< 7%), although there was a decrease in iron concentration in the bottles over time (0.8–0.5 nM) before a stable value was observed. This raises questions over the suitability of sample acidification and storage. 相似文献
106.
This environmental overview of Eckernförde Bay (northern Germany) summarizes the results of previous studies relevant to the Office of Naval Research's Coastal Benthic Boundary Layer (CBBL) Baltic field exercise conducted during 1993–1994. Significant environmental characteristics include the following: (1) surface sediment distribution is related to water depth, dictated primarily by hydrodynamic reworking of older glacial deposits; (2) the origin and characteristics of small-scale sedimentary structures depend on storm-generated waves and currents; (3) the proximity of the sea surface and sediment —water interface results in a pelagic—benthic coupling that drives biogeochemical processes and produces organicrich, acoustically turbid sediments; and (4) the bay floor is complicated topographically by pockmarks and manmade sedimentary structures. 相似文献
107.
We consider the problem of stable development of natural economical complexes from the viewpoint of basic balances in an ecological
economical system. We construct a basic dynamical model of the complex capable of predicting various scenarios of the industrial
development, consumption of natural resources, and pollution of the environment and propose a mechanism of control over the
process of development by introducing rent payments for the use of natural resources and ecological fines for the pollution
of the environment. The efficiency of the applied model is demonstrated by analysing the process of control over the concentration
of biological resources in marine media as an example. We describe the results of numerical experiments performed to show
the possibility of creation of the information technology of control over marine bioresources.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
108.
Environmental concern for the deep-sea ecosystem is increasing as contaminants, originating from anthropogenic activities, have been detected in deep-sea biota. However, little is known on the xenobiotics metabolising capability of deep-sea fauna. In this study, the deep-sea amphipod Eurythenes gryllus was selected as sentinel species to measure the total oxyradical scavenging capacity (TOSC). Individuals of E. gryllus were sampled at 2000 m depth in the Arctic Ocean. The TOSC assay was measured on the cytosolic fraction and the soluble fraction (3 kDa) of the digestive gland and on the cell-free haemolymph toward peroxyl, hydroxyl and peroxynitrite radicals according to the method of Winston et al. [Free Radical Biology and Medicine 24 (3) (1998) 480] and Regoli and Winston [Toxicology and Applied Pharmacology 156 (1999) 96]. These results provide the first baseline data set for total antioxidant capacity in a deep-sea amphipod. 相似文献
109.
110.