全文获取类型
收费全文 | 76488篇 |
免费 | 741篇 |
国内免费 | 528篇 |
专业分类
测绘学 | 1923篇 |
大气科学 | 4761篇 |
地球物理 | 14538篇 |
地质学 | 30785篇 |
海洋学 | 6222篇 |
天文学 | 16066篇 |
综合类 | 276篇 |
自然地理 | 3186篇 |
出版年
2022年 | 526篇 |
2021年 | 812篇 |
2020年 | 886篇 |
2019年 | 947篇 |
2018年 | 4124篇 |
2017年 | 3682篇 |
2016年 | 3153篇 |
2015年 | 998篇 |
2014年 | 1829篇 |
2013年 | 3171篇 |
2012年 | 2795篇 |
2011年 | 4510篇 |
2010年 | 4006篇 |
2009年 | 4554篇 |
2008年 | 3896篇 |
2007年 | 4478篇 |
2006年 | 2536篇 |
2005年 | 1812篇 |
2004年 | 1749篇 |
2003年 | 1782篇 |
2002年 | 1631篇 |
2001年 | 1334篇 |
2000年 | 1235篇 |
1999年 | 947篇 |
1998年 | 952篇 |
1997年 | 999篇 |
1996年 | 781篇 |
1995年 | 800篇 |
1994年 | 754篇 |
1993年 | 677篇 |
1992年 | 651篇 |
1991年 | 606篇 |
1990年 | 697篇 |
1989年 | 556篇 |
1988年 | 584篇 |
1987年 | 624篇 |
1986年 | 510篇 |
1985年 | 769篇 |
1984年 | 811篇 |
1983年 | 808篇 |
1982年 | 679篇 |
1981年 | 671篇 |
1980年 | 704篇 |
1979年 | 578篇 |
1978年 | 621篇 |
1977年 | 540篇 |
1976年 | 546篇 |
1975年 | 515篇 |
1974年 | 542篇 |
1973年 | 560篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The problem of monitoring of the mesoscale variability of hydrophysical fields in the shelf zone is considered. The usefulness of the data available in regional information centres is discussed. The possibility of monitoring the dynamics of the oceanic fields in the tropical Atlantic encompassing separate observation sites is demonstrated using the oceanographic databank of the scientific research centre (CERESCOR) in Conakry-Rogbane as an example. The results of assimilation of the hydrophysical survey data derived on the shelf in a telescopic model of the region are given.Translated by Mikhail M. Trufanov. 相似文献
993.
The Three Kings Ridge has been described as a remnant arc or an east-facing arc on the western side of the South Fiji Basin
under which symmetric South Fiji Basin magnetic anomaly lineations have been lost. We find evidence of neither arc-trench
morphology on the eastern flank of the ridge nor collision tectonism within the adjacent South Fiji Basin that might have
obliterated it. We believe there is room for the missing magnetic lineations within the South Fiji Basin and we recognize
the distinctive island-arc morphology characteristic of a west-facing arc on the western flank of the Three Kings Ridge. Our
interpretation requires that arc volcanism postdated formation of much of the South Fiji Basin and that oceanic lithosphere
from the adjacent Norfolk Basin must have been subducted beneath the west-facing Three Kings Arc. 相似文献
994.
Dorrik A. V. Stow 《Geo-Marine Letters》1983,3(2-4):217-222
The Brae oilfield reservoir in the North Sea comprises Upper Jurassic resedimented conglomerates and sandstones interbedded with organic-rich silstone and mudstone thin-bedded turbidites. The system represents a series of small overlapping fans that form a thick (300 m) slope-apron accumulation of sediments deposited in a narrow (<10 km wide) belt along an active fault zone. The complex lateral and vertical distribution of facies was due mainly to variable tectonic activity, and partly also to sediment supply and sea-level changes. 相似文献
995.
W.J. Van Sciver 《Ocean Engineering》1973,2(5):223-229
The angular field observable in water by an observer in air depends on the configuration of the air-water interface. When the interface is a plane, the absolute limit to observable field is about
from the normal to the interface. A practical limit, because of lateral chromatic aberration is considerably less, approximately 30°. A conventionally used configuration in research submersibles, is a polymethyl methacrylate port with inner and outer surfaces parallel. This has the same optical limitations as the plane air-water interface. It is shown that if the inner and outer surfaces are not required to be parallel to each other, there are solutions which permit extending the observable field to nearly a full hemisphere with acceptably small distortion and lateral chromatic aberration. 相似文献
996.
997.
Two genetically different types of authigenic carbonate mounds are studied: those within an active hydrothermal field related to serpentinite protrusions in the zone of intersection of a transform fracture zone and the Mid-Atlantic Ridge, and those in an active field of methane seepings in the Dnieper canyon of the Black sea. The general geochemical conditions under which authigenic carbonate formation occurs in the two fields considered were found. They include the presence of reduced H2S, H2, and CH4 gases at the absence of free oxygen; the high alkalinity of the waters participating in the carbonate formation; the similarity of the textural and structural features of authigenic aragonite, which represents the initial mineral of the carbonate matter of the mounds; the paragenesis of aragonite with sulfide minerals; and the close relation of carbonate mounds with communities of sulfate-reducing and methane-oxidizing microorganisms. A new mechanism of formation of hydrothermal authigenic carbonates is suggested; it implies their microbial sulfate reduction over the hydrogen of the fluid in the subsurface zone (biosphere) of mixing between the hydrothermal solution and the adjacent seawater. 相似文献
998.
999.
Quasi-biennial variations in vertical profiles of ozone, temperature, air pressure, and zonal and meridional wind velocities are analyzed from ozonesonde data obtained at the western European stations of Lindenberg, Hohenpeissenberg, and Payerne. The effect of quasi-biennial variations manifests itself variously in different variables and is nonuniform in altitude. The period of quasi-biennial variations is not constant, and the values of the mean period group mainly around 2 and 2.5 years. As in the North American region, the effects of quasi-biennial variations in different parameters of the stratosphere and troposphere over western Europe are due to a combination of the effects of the quasi-biennial oscillation (QBO) in the equatorial stratosphere, the El Niño-Southern Oscillation (ENSO), and the North Atlantic Oscillation (NAO). The observed 2.5-year variations in stratospheric ozone are related to the equatorial QBO to a larger extent in comparison with variations in other variables. It seems likely that a determining influence on variations in stratospheric wind and temperature is exerted by the ENSO. Variations in tropospheric and stratospheric parameters with a mean period of about 2 years are due to the ENSO and NAO effects. 相似文献
1000.
The accumulation of cadmium from seawater by the blue crab, Callinectes sapidus, was studied as a function of metal concentration and exposure time, with special emphasis on cadmium-binding proteins. Cadmium was found, in decreasing order of magnitude, in gills, digestive gland and hemolymph. When exposed to 0·5 ppm cadmium for 2–24h, virtually all of the cadmium in the cytosolic fraction of the gill was associated with a low molecular weight (LMW) cadmium-binding protein (MW 8000). However, after 48h of exposure only 50% of the cadmium in the cytosol was bound to this protein. The rest wasfound to be associated with proteins of a molecular weight of 300 000 and 60 000. This pattern of cadmium distribution did not change over a 12-day depuration period. Similar results were obtained upon exposure to 0·1 ppm cadmium. The pattern of cadmium accumulation in the cytosolic fraction of the digestive gland was in marked contrast to that observed for the gill. Initially, the cadmium was distributed over three low molecular weight fractions. During depuration the distribution of cadmium changed and all of the metal became bound to a low molecular weight protein (MW 9000). The cadmium concentrations in the gill and digestive gland remained essentially constant during depuration (12 days). The LMW cadmium-binding proteins were purified by a combination of gelpermeation and ion-exchange chromatography. Their molecular weight, spectral properties and amino acid composition are characteristic of the vertebrate metallothioneins. During exposure to cadmium the metal rapidly appeared in the hemolymph, mainly associated with hemocyanin. During depuration cadmium was transferred from the hemolymph to the digestive gland, demonstrating that hemocyanin acts as a carrier in trace metal transport. 相似文献