全文获取类型
收费全文 | 87712篇 |
免费 | 2162篇 |
国内免费 | 1815篇 |
专业分类
测绘学 | 2412篇 |
大气科学 | 7055篇 |
地球物理 | 17048篇 |
地质学 | 34160篇 |
海洋学 | 7416篇 |
天文学 | 17603篇 |
综合类 | 848篇 |
自然地理 | 5147篇 |
出版年
2022年 | 508篇 |
2021年 | 795篇 |
2020年 | 774篇 |
2019年 | 896篇 |
2018年 | 4243篇 |
2017年 | 3927篇 |
2016年 | 3260篇 |
2015年 | 1332篇 |
2014年 | 1803篇 |
2013年 | 3395篇 |
2012年 | 2920篇 |
2011年 | 5043篇 |
2010年 | 4685篇 |
2009年 | 5443篇 |
2008年 | 4484篇 |
2007年 | 5134篇 |
2006年 | 2600篇 |
2005年 | 2588篇 |
2004年 | 2439篇 |
2003年 | 2450篇 |
2002年 | 2246篇 |
2001年 | 1904篇 |
2000年 | 1764篇 |
1999年 | 1558篇 |
1998年 | 1531篇 |
1997年 | 1462篇 |
1996年 | 1186篇 |
1995年 | 1172篇 |
1994年 | 1057篇 |
1993年 | 971篇 |
1992年 | 898篇 |
1991年 | 809篇 |
1990年 | 825篇 |
1989年 | 784篇 |
1988年 | 713篇 |
1987年 | 839篇 |
1986年 | 725篇 |
1985年 | 914篇 |
1984年 | 987篇 |
1983年 | 919篇 |
1982年 | 821篇 |
1981年 | 861篇 |
1980年 | 753篇 |
1979年 | 726篇 |
1978年 | 705篇 |
1977年 | 668篇 |
1976年 | 614篇 |
1975年 | 615篇 |
1974年 | 566篇 |
1973年 | 590篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
A. G. Matul T. A. Khusid V. V. Mukhina M. P. Chekhovskaya S. A. Safarova 《Oceanology》2007,47(1):80-90
The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600–1100 years B.P.) and the Little Ice Age (~100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ~5100–6200 years B.P. 相似文献
994.
995.
Spatio-temporal variability of small copepods (especially Oithona plumifera) in shallow nearshore waters off the south coast of South Africa 总被引:1,自引:0,他引:1
Francesca Porri Christopher D. McQuaid William P. Froneman 《Estuarine, Coastal and Shelf Science》2007,72(4):711-720
Although small copepods are one of the main dietary sources for many commercially important fish, their role in the pelagic trophic dynamics has traditionally been underestimated due to the methodology commonly used in plankton sampling. Temporal variation in abundance of adults and nauplii of small copepods (particularly Oithona plumifera) in nearshore waters on the south coast of South Africa was investigated fortnightly over 14 months at site (km) and location (100 m) scales. Sampling was within <500 m of the shore, where depth was ca. 10 m, using vertical hauls of an 80-μm mesh plankton net from 1 m above the seabed to the surface. Twenty-seven adult copepod taxa were recorded, but Oithona spp. was consistently the most abundant. Taxon richness was 7–19 on each sampling occasion. There was strong temporal variation (Oithona varied between 0 and 2300 m−3), but much of this was short-term variability (e.g. between consecutive sampling sessions), with no seasonality or other long-term discernable patterns. There were periods of consistently low numbers, but very high numbers often followed samples with low abundances. Nor was there spatial structure at the location scale, though numbers differed between sites. Despite considerable variability at the location scale within sites, Kenton consistently showed higher densities than High Rocks. Separate analyses, with Bonferroni adjustment, showed that this difference was significant on eight out of 21 occasions for Oithona, six for other pelagic copepods and three for nauplii. This suggests that hydrodynamics favour aggregation of plankton at Kenton. A high degree of short-term variability, with a tendency for aggregation of small zooplankton at certain sites has implications for both pelagic processes and food-web links between the benthic and pelagic environments. 相似文献
996.
On the radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas 总被引:1,自引:0,他引:1
The radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas of finite depth is investigated. The analytical expressions for the radiated and diffracted potentials are derived as infinite series by use of the method of separation of variables. The unknown coefficients in the series are determined by the eigenfunction expansion matching method. The expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are given and verified by the boundary element method. Using the present analytical solution, the hydrodynamic influences of the angle of incidence, the submergence, the width and the thickness of the structure on the wave forces, hydrodynamic coefficients, and reflection and transmission coefficients are discussed in detail. 相似文献
997.
We collected surface water along the 142nd E meridian from Tasmania to Antarctica in December 1999. We measured temperature,
salinity and total chlorophyll a; additionally, we collected suspended particle size fractions and used fluorometric analysis to determine the quantity of
chlorophyll a in each of four cell size classes: picoplankton (<3 μm), two nanoplankton fractions (3–10 μm and 10–20 μm) and microplankton
(> 20 μm). Changes in temperature and salinity show that we crossed 6 water masses separated by 5 fronts. We found low abundance
(<0.2 mg m−3) of chlorophyll in all size classes, with the exception of higher values near the continent (0.2 to 0.4 mg m−3). Lowest chlorophyll values (<0.1 mg m−3) were found in the Polar Frontal Zone (51° to 54°S). Microplankton made up the largest portion of total chlorophyll throughout
most of the region. We conclude that biomass of all phytoplankton fractions, especially pico-and nanoplankton, was constrained
by limiting factors, most probably iron, throughout the region and that ecosystem dynamics within a zone are not circumpolar
but are regionalized within sectors. 相似文献
998.
S. D. Nikolaev 《Oceanology》2006,46(4):513-525
The objective of this study was to present details of the evolution of the thermal field of the ocean during the last Cenozoic glacial megacycle. The main causes of the phenomena observed are discussed based on the generalization of original data accumulated during many years and numerous publications. It is shown that, in the Eocene and Early Oligocene, the climatic conditions in the World Ocean were uniform and featured no evident zonal differences, the meridional temperature gradients were low, and the mean global temperature was close to the present-day value. Starting from the Late Oligocene and throughout the entire Neogene, the meridional contrasts in the temperature and hydrological conditions have increased, and, in the Late Pliocene, the climatic pattern resembled the present-day situation. The general tendency in the climate changes since the Eocene until the Pliocene consisted of its latitudinal differentiation and growing contrasts rather than of general climate cooling. In the Pleistocene, with the onset of the glaciation in the Northern Hemisphere, the character of the temperature field changed and variations in the mean global temperature values began to dominate. The factors that result from the climate changes observed are discussed and the causes are shown that lead to the differences between the author’s data and the existing concepts. 相似文献
999.
Interannual variability in Nordic seas primary production 总被引:1,自引:0,他引:1
1000.
AbstractShallow water bathymetry has proved to be a challenging task for remote sensing applications. In this work, Green-Wavelength Terrestrial Laser Scanning (GWTLS) is employed to survey nearshore bathymetry under clear atmospheric and water conditions. First, the obtained seabed points were corrected for refraction and then geo-registration, and filtering processes were exerted to obtain an accurate bathymetric surface. Terrain analysis was performed with respect to a reference surface derived from classical surveying techniques. The overall analysis has shown that the best results stem from 35° to 50° incident angles, whereas for angles higher than 65° measurements are not acceptable, although for the same angle in front and close to the instrument accuracy is considered acceptable due to the high laser power. Also, high resolution micro-topography, shallower than 1?m water depth, was managed to be captured. Systematic experimental approaches are expected to improve the GWTLS technique to detect bathymetry, which is anticipated to assist in mapping very shallow foreshore, tidal, and deltaic environments, to contribute conceptual into developing hybrid observation systems for coastal monitoring, and also to be applied in various maritime applications. 相似文献