全文获取类型
收费全文 | 62786篇 |
免费 | 722篇 |
国内免费 | 376篇 |
专业分类
测绘学 | 1583篇 |
大气科学 | 4444篇 |
地球物理 | 11444篇 |
地质学 | 24801篇 |
海洋学 | 5201篇 |
天文学 | 13071篇 |
综合类 | 213篇 |
自然地理 | 3127篇 |
出版年
2021年 | 402篇 |
2020年 | 402篇 |
2019年 | 454篇 |
2018年 | 3759篇 |
2017年 | 3487篇 |
2016年 | 2592篇 |
2015年 | 724篇 |
2014年 | 1030篇 |
2013年 | 2075篇 |
2012年 | 2152篇 |
2011年 | 4167篇 |
2010年 | 3885篇 |
2009年 | 4418篇 |
2008年 | 3564篇 |
2007年 | 4247篇 |
2006年 | 1629篇 |
2005年 | 1777篇 |
2004年 | 1614篇 |
2003年 | 1665篇 |
2002年 | 1434篇 |
2001年 | 1078篇 |
2000年 | 1017篇 |
1999年 | 811篇 |
1998年 | 812篇 |
1997年 | 827篇 |
1996年 | 667篇 |
1995年 | 655篇 |
1994年 | 615篇 |
1993年 | 567篇 |
1992年 | 525篇 |
1991年 | 494篇 |
1990年 | 505篇 |
1989年 | 496篇 |
1988年 | 473篇 |
1987年 | 553篇 |
1986年 | 488篇 |
1985年 | 604篇 |
1984年 | 649篇 |
1983年 | 592篇 |
1982年 | 527篇 |
1981年 | 589篇 |
1980年 | 488篇 |
1979年 | 458篇 |
1978年 | 433篇 |
1977年 | 432篇 |
1976年 | 386篇 |
1975年 | 378篇 |
1974年 | 376篇 |
1973年 | 384篇 |
1971年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
501.
Summary A geometrically simple volcano is considered, havig a spherical magma chamber of 2.5 km radius centred at 10 km depth. The Curie point isotherm is assumed to be a plane at 20 km depth, except for the spherical volume which is also non-magnetic. The stress pattern in the vicinity of the spherical chamber, due to regional stress of sufficient intensity to cause an eruptions, is used to calculate the change in magnetization which results from the piezomagnetic effect through the volume of solid rock. The consequent magnetic field anomaly at the surface is then obtaied by numerical integration of the dipole law of force over the stressed volume. For rocks of the type found on the volcanic island of St. Vincent (West Indies), this model gives a maximum local volcano-magnet c effect of about 7 gammas. 相似文献
502.
503.
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
504.
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
505.
The hydroelastic responses of a very-long floating structure (VLFS) placed behind a reverse T-shape freely floating breakwater with a built-in oscillating water column (OWC) chamber are analyzed in two dimensions. The Bernoulli–Euler beam equation is coupled with the equations of rigid and elastic motions of the breakwater and the VLFS. The interaction of waves between the floating rigid breakwater and the elastic VLFS is formulated in a consistent manner. It has been shown numerically that the structural deflections of the VLFS can be reduced significantly by a suitably designed reverse T-shape floating breakwater. 相似文献
506.
The motion and the drift force of a floating OWC (oscillating water column) wave energy device in regular waves are studied taking account of the oscillating surface-pressure due to the pressure drop across the duct of the air chamber. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine-type Green function while the outer problem with the Kelvin-type Green function. The added mass, wave damping and excitation coefficients as well as the motion and drift force of the OWC device are calculated for various values of parameter related to the pressure drop. 相似文献
507.
A sonic well log was obtained within the basement complex of the Walvis Ridge during Deep Sea Drilling Project Leg 74. The top of the basement complex is characterized by smooth acoustic reflectors. The rocks recovered within the basement complex consist of basalts with intercalated sediments. According to the log ~-50% of the upper 75 m of basement are igneous rocks and the other 50% sedimentary. Sonobuoy results indicate that the ratio of sediments to basalt increases with depth for an additional 225 m until a typical oceanic velocity structure is observed. Paleontological results suggest that the processes forming this upper 300 m of the basement complex was accomplished within a short time interval. 相似文献
508.
Surface currents influenced by a wind-driven upwelling event in San Pedro Bay moved total suspended matter (TSM) confined
to the inner shelf on 19 April 1978 seaward, so that by 27 April surface TSM had increased over the outer shelf. Near-bottom
concentrations of TSM also increased across the shelf during this time. This is explained by sediment resuspended by large
surface waves being advected from the inner shelf seaward by the mean flow after this flow had turned from southeasterly to
southerly when upwelling ceased on 26 April. These complex shelf dynamics contribute to the off-shelf transport of mud to
the slope and deep basins. 相似文献
509.
510.
A theory is outlined for time-dependent currents induced near the sea surface in deep water, away from coastal boundaries, by a variable wind stress and deep-water wave field. It is based on the theory of Weber (1983) which uses a second-order perturbation expansion of the Navier-Stokes equations in Lagrangian coordinates and includes the Coriolis effect. It uses an eddy viscosity formulation for both wave dissipation and momentum transfer within the current field: the eddy viscosity ν may be allowed to vary with depth. The wind stress may be time-varying and the wave field may vary in both space and time.For the case of a constant ν, the results agree with those of Ursell (1950), Hasselmann (1970) and Pollard (1970) in the limit ν→0, and the steady-state results agree with those of Weber. For a particular case of depth-varying ν, results (obtained from numerical simulations) are in better general agreement with observations of wind-induced surface drift than when a constant ν is used.An outline is given of the application of the theory to the case of a random sea state. There are good prospects for using output data from numerical wave prediction models to drive the equations of this near-surface current model. 相似文献