全文获取类型
收费全文 | 5099篇 |
免费 | 1346篇 |
国内免费 | 46篇 |
专业分类
测绘学 | 107篇 |
大气科学 | 175篇 |
地球物理 | 2439篇 |
地质学 | 2256篇 |
海洋学 | 335篇 |
天文学 | 748篇 |
综合类 | 9篇 |
自然地理 | 422篇 |
出版年
2023年 | 11篇 |
2022年 | 15篇 |
2021年 | 77篇 |
2020年 | 104篇 |
2019年 | 231篇 |
2018年 | 264篇 |
2017年 | 336篇 |
2016年 | 406篇 |
2015年 | 404篇 |
2014年 | 433篇 |
2013年 | 552篇 |
2012年 | 376篇 |
2011年 | 398篇 |
2010年 | 362篇 |
2009年 | 301篇 |
2008年 | 338篇 |
2007年 | 215篇 |
2006年 | 192篇 |
2005年 | 205篇 |
2004年 | 174篇 |
2003年 | 179篇 |
2002年 | 164篇 |
2001年 | 130篇 |
2000年 | 120篇 |
1999年 | 44篇 |
1998年 | 27篇 |
1997年 | 21篇 |
1996年 | 20篇 |
1995年 | 24篇 |
1994年 | 22篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 17篇 |
1986年 | 20篇 |
1985年 | 13篇 |
1984年 | 21篇 |
1983年 | 26篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 14篇 |
1974年 | 7篇 |
1973年 | 13篇 |
排序方式: 共有6491条查询结果,搜索用时 15 毫秒
31.
Daniel Jean Stanley Harrison Sheng Douglas N. Lambert Peter A. Rona David W. McGrail J.Stacy Jenkyns 《Marine Geology》1981,40(3-4):215-235
Analyses of DSRV “Alvin” core samples on the Cape Hatteras margin indicate major textural and compositional changes at depths of about 1000 and well below 2500 m. The distribution patterns of petrologic parameters correlate well with water mass flow and suspended-sediment plumes measured on this margin by other workers. Our study also shows: (a) vigorous erosion and sediment transport at depths of less than 400 m resulting from the NE-trending Gulf Stream flow; (b) deposition, largely planktonic-rich sediment released from the Gulf Stream, on the upper- to mid-slope, to depths of about 800–1200 m; (c) winnowing, resuspension and deposition induced by periodically intensified slope currents on the mid-slope to uppermost rise, between about 1000 and 2500 m; and (d) prevailing deposition on the upper rise proper (below 2500 m), from transport by the SW-trending Western Boundary Undercurrent. Sediments moved by bottom currents have altered the composition and distribution patterns of material transported downslope by offshelf spillover; this mixing of gravity-emplaced and bottom-current-transported sediment obscures depositional boundaries. Moreover, reworking of the seafloor by benthic organisms alters physical properties and changes erodability of surficial sediments by bottom currents. Measurement of current flow above the seafloor and direct observation of the bottom are insufficient to delineate surficial sediment boundaries. Detailed petrologic analyses are needed to recognize the long-term signature of processes and define depositional provinces. 相似文献
32.
Jean Tournadre 《Marine Geodesy》2004,27(1):153-169
New rain flags based on the dual frequency capabilities of the new Jason Poseidon-2 and Envisat RA2 altimeters have been tested, developed and adopted for the operational processing of the altimeter data. Their validation conducted during the calibration/validation phases of the satellites is presented here. The Jason flag is validated by comparison with the TOPEX one, using the Tandem mission. The results show a very good agreement between the two sensors and the two rain flags The Envisat flag is validated by comparison with both Jason and TOPEX using global and collocated data sets. The results show similar performances for the three sensors. The f relations estimated during the calibration-validation period and presented here have been given to the altimeter ground processing facilities for operational use. 相似文献
33.
Toward a generic method for studying water renewal, with application to the epilimnion of Lake Tanganyika 总被引:3,自引:0,他引:3
Olivier Gourgue Eric Deleersnijder Laurent White 《Estuarine, Coastal and Shelf Science》2007,74(4):628
We present a method, based on the concept of age and residence time, to study the water renewal in a semi-enclosed domain. We split the water of this domain into different water types. The initial water is the water initially present in the semi-enclosed domain. The renewing water is defined as the water entering the domain of interest. Several renewing water types may be considered depending on their origin. We present the equations for computing the age and the residence time of a certain water type. These timescales are of use to understand the rate at which the water renewal takes place. Computing these timescales can be achieved at an acceptable extra computer cost.The above-mentioned method is applied to study the renewal of epilimnion (i.e. the surface layer) water in Lake Tanganyika. We have built a finite element reduced-gravity model modified to take into account the water exchange between the epilimnion and the hypolimnion (i.e. the bottom layer), the water supply from precipitation and incoming rivers, and the water loss from evaporation and the only outgoing river. With our water renewal diagnoses, we show that the only significant process in the renewal of epilimnion water in Lake Tanganyika is the water exchange between the epilimnion and the hypolimnion, other phenomena being negligible. 相似文献
34.
Results concerning the concentration of cadmium and lead in Mediterranean waters collected during the 2nd PHYCEMED cruise (Oct. 1983) are discussed. Sampling has been performed at seven stations in the Western Mediterranean Basin, two in the Strait of Gibraltar and the near Atlantic, two in the Sicily Strait and the Eastern Basin.In the Western Basin the observations are in fair agreement with those of PHYCEMED 1. Cadmium has a fairly homogeneous distribution vertically as well as from one station to another, with an average concentration of 8 ng l−1; while lead shows a slight but continuous decrease in concentrations with depth (from at least 50 ng l−1 in surface waters to 20 or 25 ng l−1 at depth). On the other hand, at the basin boundaries, where waters from different origins are present, vertical distributions appear very different. On the basis of calculated water budgets it can be estimated that the Mediterranean Sea discharges about 200 t y−1 of cadmium and about 250 t y−1 of lead into the Atlantic Ocean while 1000 t y−1 of lead are transferred from the Western to the Eastern Basin. 相似文献
35.
The objective in this experimental work is to evaluate the capability of several cylindrical buoys to follow and measure waves. Eleven configurations have been studied, eight among which were furnished with disks of different diameters at the waterline. The experiments took place in the test basin at ISITV. On the one hand, we have obtained a set of transfer coefficients for each frequency and each configuration in regular waves. On the other hand, we have determined the corresponding transfer functions, then we have used the latter to measure irregular waves. The time signals as measured by the buoys with and without corrections have been compared with wave gage measurements and subjected to a wave-by-wave analysis. The results allow the conclusion that the buoy with a medium size disk constitutes the best compromise. In fact, it permits the buoy to follow the free surface while minimizing parasitic motions. 相似文献
36.
37.
Combining indicator trends to assess ongoing changes in exploited fish communities: diagnostic of communities off the coasts of France 总被引:1,自引:1,他引:1
38.
The macrobenthic fauna in the large, hypersaline, shallow Keta lagoon in Ghana was sampled at 20 stations in the wet (September
2002) and dry seasons (March 2003) to elucidate the effects of abiotic factors on community patterns. The macrobenthic fauna
was low in density and species diversity and numerically dominated by bivalves and capitellid polychaetes. These organisms
appear able to withstand physical disturbance (when lagoon water levels become extremely low) and osmotic stress (when salinities
are extremely high) and tend to redistribute along environmental gradients. Parallel seasonal differences in several environmental
variables and the macrobenthic fauna indicate a highly dynamic system. Species richness and diversity were higher in the wet
season than the dry season. Salinity, percent clay, pH, and turbidity in that order were the major significant variables structuring
the macrobenthic faunal assemblage in Keta lagoon. The strong effect of seasonal salinity changes on macrobenthic faunal assemblages
may have trophic consequences for higher organisms of commercial importance, such as fishes and shorebirds, in the Keta lagoon. 相似文献
39.
Olivier Rossier Emmanuel Castella Jean-Bernard Lachavanne 《Aquatic Sciences - Research Across Boundaries》1996,58(1):1-14
The abundance of different size classes of perch and roach in the littoral zone of Lake Geneva was compared between submerged aquatic vegetation and unvegetated zones. Samples were taken with gillnets during four periods between June and October 1993. During the vegetation period (June to September), perch 9 cm and roach 10 cm were more abundant in vegetation whereas roach > 20 cm were more abundant in open water. Perch larger than 18 cm and medium roach were equally distributed in both habitats whatever the period, whereas medium perch distribution fluctuated according to the period. In October, after the decline of the vegetation, no more differences in fish distribution were observed except for small roach, which were always more abundant in the vegetated sites. 相似文献
40.
Richard Dallier Jean-Gabriel Cuby Jean Czarny Jacques Baudrand 《Experimental Astronomy》1994,3(1-4):183-184
ISIS IR is the first attempt to use fibre optics for near infrared spectroscopy (1.8m). It is a field spectrograph (2D spectroscopy), and can work at various resolving powers (up to 25000). It can be transported anywhere, and soon it will be used at CFHT with one NICMOS 3-based camera.Département d'Astrophysique Extragalactique et de Cosmologie 相似文献