全文获取类型
收费全文 | 70419篇 |
免费 | 988篇 |
国内免费 | 443篇 |
专业分类
测绘学 | 1510篇 |
大气科学 | 4189篇 |
地球物理 | 13877篇 |
地质学 | 26356篇 |
海洋学 | 6297篇 |
天文学 | 16085篇 |
综合类 | 192篇 |
自然地理 | 3344篇 |
出版年
2022年 | 598篇 |
2021年 | 918篇 |
2020年 | 1036篇 |
2019年 | 1162篇 |
2018年 | 2440篇 |
2017年 | 2317篇 |
2016年 | 2416篇 |
2015年 | 1135篇 |
2014年 | 2230篇 |
2013年 | 3490篇 |
2012年 | 2566篇 |
2011年 | 3178篇 |
2010年 | 2808篇 |
2009年 | 3336篇 |
2008年 | 3009篇 |
2007年 | 3181篇 |
2006年 | 2884篇 |
2005年 | 2250篇 |
2004年 | 2316篇 |
2003年 | 2162篇 |
2002年 | 1636篇 |
2001年 | 1509篇 |
2000年 | 1317篇 |
1999年 | 1059篇 |
1998年 | 1081篇 |
1997年 | 1121篇 |
1996年 | 876篇 |
1995年 | 873篇 |
1994年 | 787篇 |
1993年 | 698篇 |
1992年 | 651篇 |
1991年 | 686篇 |
1990年 | 731篇 |
1989年 | 633篇 |
1988年 | 601篇 |
1987年 | 638篇 |
1986年 | 579篇 |
1985年 | 775篇 |
1984年 | 813篇 |
1983年 | 802篇 |
1982年 | 741篇 |
1981年 | 680篇 |
1980年 | 655篇 |
1979年 | 590篇 |
1978年 | 597篇 |
1977年 | 574篇 |
1976年 | 503篇 |
1975年 | 514篇 |
1974年 | 495篇 |
1973年 | 554篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
951.
The nonlinear energy transfer through the wave spectrum is studied on the basis of the previously obtained explicit equation for matrix elements of a four-wave kinetic integral. The equation describes the evolution of a system of gravity waves at the surface of a sea of finite depth with a uniform distribution of broken ice over the sea surface. Particular attention is paid to the analytical part of the algorithm of the calculation of the kinetic integral. This part differs from the standard algorithm by a set of prominent features of the dispersion relation for wave oscillations in the ice-covered water. The kinetic integral for the system under consideration is calculated, and the results are compared with the results obtained for the ice-free water. 相似文献
952.
Until recently, the ideas about the age of the Black Sea deep-water basin have been based on land geological observations in the coastal areas at the interaction periphery, underwater observations from manned submersibles, and on the data of seismic reflection and refraction studies and drilling. Formerly, the scarcity of the information led to a wide scattering of the age determinations: from the Jurassic to the Eocene. Recently, with the appearance of reliable geological and geophysical data, the range of the age estimates has been considerably reduced during the last few years, although there is no commonly accepted opinion on this issue. Therefore, the first attempt to determine the age of the Western Black Sea basin using an analysis of the anomalous magnetic field is of certain interest. The following results were obtained: the basin probably opened between 71.338 and 71.587 My B.P. (subchron C32n.1r). During the interval 68.737–71.071 My B.P. (subchron C31r), extinction of the spreading axes took place. Thus, the total duration of the Campanian-Maestrichtian phase of the opening was about 3 My (interval from 71.587 to 68.737 My B.P.). This result does not agree with the geological and geophysical data available to date. To solve this problem, collection of new geological data and further studies of the structure of the anomalous magnetic field are required. 相似文献
953.
C. Svensen D. Vili
i P. Wassmann E. Arashkevich T. Ratkova 《Estuarine, Coastal and Shelf Science》2007,71(3-4):381-390
The aim of this study was to investigate phytoplankton abundance, composition and vertical export in the highly stratified Krka estuary, Croatia. The estuary is stratified throughout the year, and an interface between fresh- and brackish water plays an important role in production and degradation of biogenic matter. Vertical export of particulate organic carbon (POC), phytoplankton carbon (PPC) and faecal pellet carbon (FPC) was studied by deploying sediment traps in the middle and lower reach of the estuary and in the adjacent coastal zone. Zooplankton faecal pellet (FP) production experiments were conducted to provide additional information on the potential contribution of FP to the total carbon flux. High suspended concentrations of POC, chlorophyll a and phytoplankton was found in the lower reaches of the Krka estuary, adjacent to a source of anthropogenic eutrophication. The fraction of organic detritus to the total POC flux was 61–69% inside the estuary but only 7% at the marine station. This indicates that the primary producers in the surface layer of the Krka estuary are decomposed in and below the interface and then settle as detritus to the bottom. Low sedimentation rates in the coastal zone outside the estuary revealed that the eutrophication does not spread out of the estuary. Mesozooplankton played a modest role in vertical flux regulation, due to their low abundance and dominance of smaller forms as well as low faecal pellet production rates. It is concluded that processes taking place at the freshwater-seawater interface are of major importance for the vertical carbon flux in the investigated area. 相似文献
954.
The mineralogy of eight gravity cores recovered between Sierra Leone and 25°W longitude has been examined in an investigation
of the provenance of the recent sediments in the eastern Equatorial Atlantic. X-ray analyses show that the principal mineral
components are calcite, quartz, feldspar, kaolinite, illite and montmorillonite. One core taken from the upper continental
slope off Freetown also contains gibbsite, a product of intense tropical weathering. Biogenic material forms the dominant
component of most sections of the cores but it is clear from the abundance of quartz, kaolinite and freshwater diatoms that
an aeolian supply of continental detritus has been important in the formation of the recent sediment cover. A significant
contribution from volcanic sources can be recognised to the west of the Sierra Leone Rise. The occurrence of calcareous turbidites
in two cores from the St. Paul's Fracture Zone and from the basin west of the Sierra Leone Rise appears to be a reflection
of recent tectonic activity. 相似文献
955.
956.
957.
Measurements of 226Ra and 210Pb in barite samples separated from different depths of a piston core from the eastern equatorial Pacific are reported. 226Ra is enriched in the barite as would be expected from the chemistries of Ra and Ba; the ratio centers around 1.5 · 1014 atoms/mole. The results suggest that barite is concentrating Ra at a rate comparable to its decay rate, viz. 5.78 · 10?3 yr?1. The gross 210Pb depletion with respect to 226Ra is indicative of 222Rn loss due to the smallness of the barite crystals. 相似文献
958.
The distribution of the colour index is considered in the region bounded by 8–11°N and 13°30–18°30W based on the results of measurements made on board vessels of the Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences (MHI) in 1977–1985. Mean values and statistical characteristics are calculated for the colour index variability over one-degree squares. A map of its multi-yearly average distribution is plotted.Translated by M. M. Trufanov. 相似文献
959.
A stochastic prognostic model of the atmospheric precipitation in the tropical area of the Atlantic Ocean is developed on the basis of a large data array. The data represent a series of monthly precipitation rates for 31 towns in the Republic of Guinea covering a period of 35–64 years as well as satellite data on the meridional displacement of the Intertropical Convergence Zone during 11 years. The model takes into account major regularities of the tropical precipitation: their impulsive periodic regime, trends, and the modulation of the stochastic component by the determined variability.Translated by Mikhai M. Trufanov. 相似文献
960.
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