全文获取类型
收费全文 | 116469篇 |
免费 | 2271篇 |
国内免费 | 1090篇 |
专业分类
测绘学 | 3427篇 |
大气科学 | 8924篇 |
地球物理 | 24120篇 |
地质学 | 39682篇 |
海洋学 | 9854篇 |
天文学 | 26280篇 |
综合类 | 356篇 |
自然地理 | 7187篇 |
出版年
2021年 | 833篇 |
2020年 | 983篇 |
2019年 | 1112篇 |
2018年 | 2363篇 |
2017年 | 2238篇 |
2016年 | 2999篇 |
2015年 | 1894篇 |
2014年 | 2932篇 |
2013年 | 5844篇 |
2012年 | 3082篇 |
2011年 | 4272篇 |
2010年 | 3757篇 |
2009年 | 5136篇 |
2008年 | 4533篇 |
2007年 | 4338篇 |
2006年 | 4287篇 |
2005年 | 3474篇 |
2004年 | 3518篇 |
2003年 | 3332篇 |
2002年 | 3258篇 |
2001年 | 2926篇 |
2000年 | 2838篇 |
1999年 | 2491篇 |
1998年 | 2420篇 |
1997年 | 2439篇 |
1996年 | 2115篇 |
1995年 | 2021篇 |
1994年 | 1835篇 |
1993年 | 1651篇 |
1992年 | 1518篇 |
1991年 | 1447篇 |
1990年 | 1609篇 |
1989年 | 1472篇 |
1988年 | 1313篇 |
1987年 | 1572篇 |
1986年 | 1392篇 |
1985年 | 1675篇 |
1984年 | 1982篇 |
1983年 | 1807篇 |
1982年 | 1747篇 |
1981年 | 1590篇 |
1980年 | 1412篇 |
1979年 | 1362篇 |
1978年 | 1425篇 |
1977年 | 1275篇 |
1976年 | 1197篇 |
1975年 | 1130篇 |
1974年 | 1147篇 |
1973年 | 1222篇 |
1972年 | 782篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
Walter H Pearson Stephen E Miller J.W Blaylock Bori L Olla 《Marine environmental research》1981,5(1):3-11
The ability of the blue crab, Callinectes sapidus, to detect petroleum hydrocarbons was measured with behavioural techniques. When presented with a water-soluble fraction of Prudhoe Bay crude oil, blue crabs abruptly changed antennular orientation, began rhythmic beating of the maxillipedal flagellae, and increased antennular flicking rate. The threshold concentration at which 50% of the crabs detected the water-soluble fraction was 2 × 10?6 mg/litre. The blue crab apparently can readily detect petroleum hydrocarbons at concentrations found in chronically polluted areas as well as oil spill situations. 相似文献
994.
M. Arockiasamy H. El-Tahan A.S.J. Swamidas W.E. Russell D.V. Reddy 《Ocean Engineering》1984,11(5):463-490
The paper presents an analytical and experimental study on the transient response of semisubmersibles to bergybit impact and the strength of bergybit ice to high strain-rate loadings. Two approaches have been proposed for the solution of the semisubmersible-bergybit interaction problem, one using the energy approach and the other using the conventional structural dynamics approach with initial velocity conditions. In addition the local behaviour of the impacted regions have been analysed for deformation and failure. Numerical results have been given for local behaviour of an impacted column and global behaviour of semisubmersible-bergybit system. Experimental study has been reported on the impact strength of iceberg ice at strain rates of 10−3, 10−2 and 10−1; the indentation impact strength of ice is found to be 3–4 times the unaixial compressive strength, at the same strain rate. 相似文献
995.
C.H.K. Williamson 《Applied Ocean Research》1985,7(2):97-106
The most widely used mathematical model to represent flow-induced in-line forces on structures is based on the Morison1 equation. The present paper investigates the validity of using an extension of Morison's equation for non-stationary structures, by comparing predictions with results from a simple laboratory experiment. An elastically-mounted circular cylinder is placed in the sinusoidal flow of a U-tube, and responds in-line with the flow. Cylinder forces and responses are recorded over a range of Keulegan Carpenter numbers up to 35. An equation of motion is solved simply by using relative coordinates and by employing equivalent linearisation. The linear results are compared over a wide variation of parameters with solutions using the full nonlinear equation. Thereafter experimental results are compared with linear predictions. 相似文献
996.
J. Acosta E. Uchupi A. Muñoz P. Herranz C. Palomo M. Ballesteros 《Marine Geophysical Researches》2003,24(1-2):1-40
In this paper we discuss the results of a swath bathymetric investigation of the Canary archipelago offshore area. These new
data indicate that volcanism is pervasive throughout the seafloor in the region, much more that would be suggested by the
islands. We have mapped tens of volcanic edifices between Fuerteventura and Gran Canaria and offshore Tenerife, La Gomera,
El Hierro and La Palma. Volcanic flows are present between Tenerife and La Gomera and salic necks dominate the eastern insular
slope of La Gomera. This bathymetry also supports land geologic studies that indicate that the oceanic archipelago has acquired
its present morphology in part by mass wasting, a consequence of the collapse of the volcanic edifices. In the younger islands,
Tenerife, La Palma and El Hierro, the Quaternary (1.2 to 0.15 Ma) debris avalanches are readily recognizable and can be traced
offshore for distances measured in tens of km. Off the older islands, Lanzarote, Fuerteventura, Gran Canaria and La Gomera
(<20 to 3.5 Ma), the avalanches have been obscured by subsequent turbidity current deposition and erosion as well as hemipelagic
processes. The failure offshore western Lanzarote is in the form of a ramp at the base of the insular slope bound on the seaward
side by a scarp. Its size and the lack of evidence of rotation along its landwards side precludes the possibility that it
is a slump. It probably represents a slide whose outer scarp is caused by break-up of the slide. Mounds on the ramp’s surface
may represent post-displacement volcanic structures or exotic blocks transported to their present locations by the slide.
The failures offshore Fuerteventura are so large that, although they occurred in the Miocene-Pliocene, exotic blocks displaced
from upslope are still recognizable in the insular margin morphology. The Canary Island insular margin appears to be a creation
of Miocene-Pliocene mass wasting and more recent turbidity current deposition and erosion, and hemilepagic deposition. Failures
offshore La Gomera are due to debris flows and/or turbidity currents. These events have obscured earlier mass wasting events.
An erratum to this article is available at . 相似文献
997.
Three outdoor plastic tanks were filled with North Sea water. The water was filtered free of algae and inoculated with the diatom Thalassiosira rotula. Under nearly natural nutrient supply an exponential plankton growth occurred with realistic cell concentrations. The flexible tanks (3–4 m3, 4–5 m deep) were exposed in the German Bight at a station in the outer harbour of Helgoland. The concentration changes of dissolved free amino acids (DFAA) were determined. The direct determination method applied permitted an analysis in picomole range without loss and with good reproducibility. The preliminary concentration of DFAA amounted to 0.2 μmol dm−3 in all three cultures, increasing during the development of T. rotula to 0.9–1.3 μmol dm−3 and decreasing in the stationary phase back again to smaller values. A high degree of temporal variation in DFAA was observed in all three cultures. In spite of these rapid changes in concentration, a good parallel development could be shown for all cultures, which extended as far as the spectra of the amino acids. Relationships between DFAA and other parameters of the culture-systems were examined. 相似文献
998.
999.
1000.
Bioerosion by chemosynthetic biological communities on Holocene submarine slide scars 总被引:1,自引:0,他引:1
Geomorphic, stratigraphic, and faunal observations of submarine slide scars that occur along the flanks of Monterey Canyon in 2.0–2.5 km water depths were made to identify the processes that continue to alter the surface of a submarine landslide scar after the initial slope failure. Deep-sea chemosynthetic biological communities and small caves are common on the sediment-free surfaces of the slide scars, especially along the headwall. The chemosynthetic organisms observed on slide scars in Monterey Canyon undergo a faunal succession based in part on their ability to maintain their access to the redox boundaries in the sediment on which they depend on as an energy source. By burrowing into the seafloor, these organisms are able to follow the retreating redox boundaries as geochemical re-equilibration occurs on the sole of the slide. As these organisms dig into the seafloor on the footwall, they often generate small caves and weaken the remaining seafloor. While chemosynthetic biological communities are typically used as indicators of fluid flow, these communities may be supported by methane and hydrogen sulfide that are diffusing out of the fresh seafloor exposed at the sole of the slide by the slope failure event. If so, these chemosynthetic biological communities may simply mark sites of recent seafloor exhumation, and are not reliable fluid seepage indicators. 相似文献