全文获取类型
收费全文 | 113858篇 |
免费 | 1912篇 |
国内免费 | 846篇 |
专业分类
测绘学 | 3063篇 |
大气科学 | 8603篇 |
地球物理 | 22804篇 |
地质学 | 40930篇 |
海洋学 | 9540篇 |
天文学 | 24666篇 |
综合类 | 350篇 |
自然地理 | 6660篇 |
出版年
2021年 | 617篇 |
2020年 | 767篇 |
2019年 | 880篇 |
2018年 | 4197篇 |
2017年 | 3964篇 |
2016年 | 3593篇 |
2015年 | 1576篇 |
2014年 | 2288篇 |
2013年 | 4667篇 |
2012年 | 3297篇 |
2011年 | 5644篇 |
2010年 | 5165篇 |
2009年 | 6430篇 |
2008年 | 5466篇 |
2007年 | 5749篇 |
2006年 | 3646篇 |
2005年 | 3366篇 |
2004年 | 3308篇 |
2003年 | 3176篇 |
2002年 | 2948篇 |
2001年 | 2496篇 |
2000年 | 2413篇 |
1999年 | 2083篇 |
1998年 | 2046篇 |
1997年 | 2056篇 |
1996年 | 1749篇 |
1995年 | 1665篇 |
1994年 | 1496篇 |
1993年 | 1379篇 |
1992年 | 1273篇 |
1991年 | 1157篇 |
1990年 | 1318篇 |
1989年 | 1206篇 |
1988年 | 1060篇 |
1987年 | 1274篇 |
1986年 | 1133篇 |
1985年 | 1381篇 |
1984年 | 1650篇 |
1983年 | 1499篇 |
1982年 | 1423篇 |
1981年 | 1344篇 |
1980年 | 1174篇 |
1979年 | 1132篇 |
1978年 | 1190篇 |
1977年 | 1066篇 |
1976年 | 1000篇 |
1975年 | 945篇 |
1974年 | 935篇 |
1973年 | 979篇 |
1972年 | 636篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
The long-wave outgoing radiation, effective cloudiness equal to the product of the total cloud amount by their optical density,
and the sea-surface temperature determined from the satellites are used to determine the annual course of the components of
external heat balance on the sea surface whose climatic anomalies, parallel with the meridional heat and water transfer in
the ocean-atmosphere system, specify the intraannual and interannual large-scale variations of weather in different regions
of the Earth. The development of these studies is connected with the progress of satellite hydrophysics because the data obtained
from the space become sufficiently exact, regular, and global. The increase in the existing data array on the external heat
balance of the oceans from ∼15–20 to 100 yr and more would promote the solution of the problem of oscillations of Earth's
climate. We present examples of coordinated numerical analysis of the heat balance of the upper (0–100 m ) layer of the Black
Sea performed on the basis of the shipborne and satellite data.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 59–75, November–December, 2007. 相似文献
995.
Isotopic variation of fishes in freshwater and estuarine zones of a large subtropical coastal lagoon
A.M. Garcia D.J. Hoeinghaus J.P. Vieira K.O. Winemiller 《Estuarine, Coastal and Shelf Science》2007,73(3-4):399-408
We used stable C and N isotope ratios of tissues from 29 fish species from a large subtropical lagoon in southern Brazil to examine spatial variability in isotopic composition and vertical trophic structure across freshwater and estuarine habitats. Nitrogen isotope ratios indicated a smooth gradation in trophic positions among species, with most fishes occupying the secondary and tertiary consumer level. Fish assemblages showed a significant shift in their carbon isotopic signatures between freshwater and estuarine sites. Depleted carbon signatures (from −24.7‰ to −17.8‰) were found in freshwater, whereas more enriched signatures (from −19.1‰ to −12.3‰) were obtained within the estuarine zone downstream. Based on our survey of the C3 and C4 plants and isotopic values for phytoplankton and benthic microalgae reported for ecosystems elsewhere, we hypothesized that the observed δ13C differences in the fish assemblage between freshwater and estuarine sites is due to a shift from assimilating organic matter ultimately derived from C3 freshwater marsh vegetation and phytoplankton at the freshwater site (δ13C ranging from −25‰ to −19‰), to C4 salt-marsh (e.g. Spartina) and widgeon grass (Ruppia maritima), benthic microalgae and marine phytoplankton at the estuarine sites (from −18‰ to −12‰). Our results suggested that fish assemblages are generally supported by autochthonous primary production. Freshwater fishes that likely were displaced downstream into the estuary during periods of high freshwater discharge had depleted δ13C values that were characteristic of the upper lagoon. These results suggest that spatial foodweb subsidies can occur within the lagoon. 相似文献
996.
The time evolution of a two-dimensional line thermal-a turbulent flow produced by an initial element with signifi-cant buoyancy released in a large water body, is numerically studied with the two-equation k - e model for turbulence closure. The numerical results show that the thermal is characterized by a vortex pair flow and a kidney shaped concentra-tion structure with double peak maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless time around 10. There are two regions in the flow field of a line thermal: a mixing region where the concentration of tracer fluid is high and the flow is turbulent and rotational with a pair of vortex eyes, and an ambient region where the concentration is zero and the flow is potential and well-described by a model of doublet with strength very close to those given by early experimental and analytical studies. The added virtual mass coeffi-cient of the thermal motion is found to be approximat 相似文献
997.
On October 3 and 4, 1986, DSRVAlvin dives encountered a strong current at 2,300 m in South Wilmington Canyon. The current, estimated at 1 knot, transported surficial
sediment and constructed and modified bedforms. It appears to have been constant in its direction of flow from 30 to 40°.
The observed current was probably a burst of fast flow in a region of slow average currents in the Deep Western Boundary Undercurrent.
Such episodic events may have a greater influence on the stratigraphic record than the temporally longer more tranquil flow
conditions. 相似文献
998.
Tilapia is a common fish species inhabiting inland waters and estuarine regions in Hong Kong and Southeast Asia, and useful for bio-monitoring of metal pollution. Metallothionein (MT) gene expression in fish tissues has been useful to sub-lethal risk assessment as biomarker of exposure to metal ions in fishes inhabiting metal contaminated area. To investigate metal inductions of Tilapia MT gene expression in vivo, Tilapias were injected with different concentrations of heavy metals and tissues were then removed for quantitative PCR assay using mimic PCR methods. All of the metal ions tested (Cu(2+), Cd(2+), Hg(2+), Ni(2+), Pb(2+) and Zn(2+)) were able to induce hepatic MT mRNA levels. Renal MT mRNA levels of Cd(2+) and Zn(2+) treated fish was not induced with significant fold induction, however MT mRNA levels in gills were sensitive to the administrations of these metal ions. These data indicated that Tilapia MT mRNA levels in gills and liver are sensitive biomarker of exposure to various metal ions. 相似文献
999.
M.J. Tucker 《Ocean Engineering》1982,9(3):259-270
The vertical response of spar buoys to waves is examined. The response is the product of a rather complex wave forcing function and the resonant response of the buoy. With compound spar buoys (that is, consisting of more than one section of different diameters) the forcing function has a zero at a frequency which is usually close to the resonant frequency, but which can be arranged to be somewhat higher with beneficial effects on the response. Only the effects of pressure and inertia are considered, since this paper is mainly concerned to clarify some specific general principles and it is difficult to include the effects of drag, which are complex. 相似文献
1000.
Investigations of short term acute exposure of bay scallops, Argopecten irradians and two scallop predators, the oyster drill Urosalpinx cinerea and the common starfish Asterias forbesi, to oil, dispersant, and oil-dispersant mixtures (Kuwait Crude Oil and Corexit 9527) suggested that predator and prey have different lethal susceptibilities. Scallops were most sensitive to dispersant and dispersant mixed with oil, starfish were only sensitive to dispersant while the oyster drill seemed unaffected even though all were exposed to dilutions of identically prepared stock solutions. Scallops were least susceptible during winter months and most susceptible at summer temperatures. Treatment had less effect on predators than on scallops at summer temperatures. Sublethal concentrations of dispersant and oil-dispersant mixtures diminished the behavioural ability of scallops to recognise drills and starfish. The degree of effect increased with temperature. Predator detection of prey at the same concentrations was more complex. The feeding response or posturing reflex of starfish was significantly slowed by all treatments. In contrast, drills were unaffected in their recognition of scallop effluent in a choice chamber after treatment. 相似文献