首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   73363篇
  免费   976篇
  国内免费   611篇
测绘学   1794篇
大气科学   5278篇
地球物理   13753篇
地质学   25806篇
海洋学   6678篇
天文学   17286篇
综合类   169篇
自然地理   4186篇
  2021年   679篇
  2020年   790篇
  2019年   826篇
  2018年   1789篇
  2017年   1717篇
  2016年   2036篇
  2015年   1148篇
  2014年   2036篇
  2013年   3881篇
  2012年   2097篇
  2011年   2751篇
  2010年   2548篇
  2009年   3209篇
  2008年   2871篇
  2007年   2925篇
  2006年   2754篇
  2005年   2117篇
  2004年   2034篇
  2003年   1923篇
  2002年   1886篇
  2001年   1691篇
  2000年   1604篇
  1999年   1461篇
  1998年   1407篇
  1997年   1392篇
  1996年   1166篇
  1995年   1106篇
  1994年   1078篇
  1993年   967篇
  1992年   937篇
  1991年   893篇
  1990年   1028篇
  1989年   840篇
  1988年   815篇
  1987年   949篇
  1986年   787篇
  1985年   1080篇
  1984年   1156篇
  1983年   1118篇
  1982年   1078篇
  1981年   982篇
  1980年   903篇
  1979年   859篇
  1978年   856篇
  1977年   763篇
  1976年   726篇
  1975年   662篇
  1974年   729篇
  1973年   723篇
  1972年   462篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The influence of potassium bromide on the bands near 10 μm, 18 μm and 33 μm was calculated for any silicate. The wavelength shift, the deepening, and the broadening of the bands were calculated for different band's depths of each band. The results were applied on the investigation of an extensive catalogue of silicate spectra, which were got on the basis of the KBr pressing technique too. So it was possible to picle out those silicates from the variety of silicates, which are probable candidates for the interstellar silicate component.  相似文献   
992.
A brief review of the studies performed by Russian scientists in dynamic meteorology in 2003–2006 is presented. This review is based on the material prepared by the Commission on Dynamic Meteorology of the National Geophysical Committee of the Russian Academy of Sciences and included in the general information report of the Section of Meteorology and Atmospheric Sciences at the 24th General Assembly of the International Union of Geodesy and Geophysics.  相似文献   
993.
The studies conducted in 1991–2004 by scientists of the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, and the Karpov Institute of Physical Chemistry yielded data on the structures of the surface air layer (to a height of 20 m) and both subinversion and inversion layers (to heights of from 800 m to 1 km), where arid aerosol is transported. One of the main objectives of the 2007 experiment was to record the space-vortex structures within a layer of 30–700 m that directly provide the removal and long-range transport of fine-dispersed (<5 µm) desert aerosol. This paper describes the organization of the Khar-Gzyr 2007 experiment (Black Lands, 2007) to study the convective removal of arid aerosol from desertificated lands, and it presents some data obtained from the remote sensing of the atmospheric boundary layer with a sodar network in the course of this experiment. The sodar network, which was developed to study a spatial structure of coherent vortices, included three identical minisodars (with carrier frequencies of 3.8 kHz) located at the apices of a triangle, each side of which was about 3.5 km, and a sodar (with a carrier frequency of 1.7 kHz). The vertical profiles of the three wind-velocity components and the characteristics of air temperature fluctuations were determined. The procedure of identifying coherent vortex structures is described. The variations in the vertical and horizontal wind-velocity components and the scales characteristic of such structures are estimated.  相似文献   
994.
The proposed concept of the “marine coastal zone” (MCZ) is substantiated with considering the role of the neotectonics in the formation and evolution of the corresponding morphologic system using the Antarctic Peninsula as an example. For this purpose, the results of the immediate geologic-geomorphologic observations are correlated with an original schematic neotectonic map compiled for the region in question. It is shown that neotectonic movements are responsible for the block structure of the coastal zone representing its most stable element, which is complicated by subsequent regional exogenic coast-forming processes with the glacial one being dominant. Other aspects of the marine coastal zone influenced by neotectonics are also considered. A new (near-polar) type of the marine coastal zone is defined.  相似文献   
995.
In recent years, considerable amount of effort has been made to design earthquake resistant offshore structures in seismic active areas. In order to achieve this objective, all components of a typical structure should function properly to dissipate seismically-induced energy within the members. Among components of an offshore installation, braces are of significant importance as they contribute substantially to total energy dissipation of the structure. Buckling in compression and yielding in tension assist the process of energy absorption. Nevertheless, the functionality of braces is dependent upon their joints where joint-cans are included to avoid any brittle fracture and unpredicted failure mechanisms.In this paper, special attention is being paid to energy dissipation of jacket type offshore platforms with two different pile–leg interactions. A case study representing an offshore platform is studied both analytically and experimentally. Analytical models are validated step by step based on available experimental tests and observations on individual members. Several parameters such as cyclic behavior, maximum bearing load and most importantly energy dissipation of two different 2D frames are investigated. Results provide promising insights into design and fabrication of fixed platforms with different pile–leg interactions.  相似文献   
996.
With concerns mounting over the UK’s energy future and the effects of climate change, it will soon become paramount that all viable sources of renewable energy are fully exploited. This study has examined the scope for reliable and fully predictable tidal electricity generation from the conjunctive operation of 5 major estuary barrages on the West Coast of the UK in an attempt to establish the potential scale of the extractable resources. Two levels of investigation have been undertaken: simple 0-D (‘two-tank’) modelling of barrage energy generation under different operational modes, using the hydraulic characteristics of turbine performance; and 2-D modelling of tidal hydrodynamics over a wide sea area in a computational grid incorporating the barrages with turbines and sluices. It has been demonstrated that more than 33TWh per year of electricity should be attainable, from 22GW of installed capacity, this representing close to 10% of present UK demand.  相似文献   
997.
998.
Yves Morel  Leif N. Thomas   《Ocean Modelling》2009,27(3-4):185-197
In this article, the authors study the influence of a constant wind on the displacement of a vortex. The well known Ekman current develops in the surface layer and is responsible for a transport perpendicular to the wind: the Ekman drift.An additional process is, however, evidenced, whose importance is as strong as the Ekman drift. There indeed exists a curl of the wind-driven acceleration along isopycnic surfaces when they are spatially variable (they enter and leave the depth where the wind stress acts), which generates potential vorticity anomalies. This diabatic effect is shown to generate potential vorticity anomalies which acts on the propagation of vortical waves and non linear vortices.It is shown that this effect drastically reduces the effect of the Ekman drift for linear waves and surface intensified vortices, while extending its effect to subsurface vortices. It also generates along wind propagation, whose sign depends on the vortex characteristics.  相似文献   
999.
1000.
The present study investigates the potential of readily available and easily accessible global data sets to understand regional/local level interactions in wetland systems. The biogeographical zones of India were used a base-frame to select three sites. The study well fits the interests of National Wetland Committee of India to investigate and document fundamental information on wetland extent/distribution. The national partnership with SACON represents this interest. SACON commenced the inland wetland inventory module at national scale using geospatial data, although the provincial scale analysis is underway. In addition, the global irrigated area mapping (GIAM-IWMI) project generated multi-scalar spatial outputs for irrigated/rain-fed areas. With the existing information base, a multi-level geospatial analysis using Arc GIS algorithmic modelling was used to derive comprehensive appraisal of wetland systems complementing the data from GIAM and SACON. It was observed that the overlap between the two layers was 58 percent for Gujarat and 10 percent in Tamil Nadu. In Krishna basin the wetland’s cover 1.04 million hectare excluding the rice agro-ecosystem. The difference in the biogeography of the case sites governs the gradient of information derived from both data layers. Additionally, the global lakes and wetlands database (GLWD) database added thematic information on coastal wetlands. In summary we describe the cross-scaling the global data layers to compliment the regional/national level monitoring assignments.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号