全文获取类型
收费全文 | 2270篇 |
免费 | 165篇 |
国内免费 | 22篇 |
专业分类
测绘学 | 53篇 |
大气科学 | 197篇 |
地球物理 | 681篇 |
地质学 | 1005篇 |
海洋学 | 139篇 |
天文学 | 266篇 |
综合类 | 14篇 |
自然地理 | 102篇 |
出版年
2022年 | 20篇 |
2021年 | 49篇 |
2020年 | 54篇 |
2019年 | 43篇 |
2018年 | 86篇 |
2017年 | 111篇 |
2016年 | 147篇 |
2015年 | 121篇 |
2014年 | 152篇 |
2013年 | 231篇 |
2012年 | 177篇 |
2011年 | 124篇 |
2010年 | 110篇 |
2009年 | 112篇 |
2008年 | 93篇 |
2007年 | 50篇 |
2006年 | 85篇 |
2005年 | 49篇 |
2004年 | 54篇 |
2003年 | 51篇 |
2002年 | 57篇 |
2001年 | 32篇 |
2000年 | 22篇 |
1999年 | 15篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 12篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 25篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 7篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 14篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 12篇 |
1969年 | 8篇 |
1966年 | 6篇 |
排序方式: 共有2457条查询结果,搜索用时 15 毫秒
91.
92.
[Translated by the editorial staff] Simulating the precipitation regime of Northern Africa is challenging for regional climate models, particularly because of the strong spatial and temporal variability of rain events in the region. In this study we evaluate simulations conducted with two recent versions of regional climate models (RCM) developed in Canada: the CRCM5 and CanRCM4. Both are also used in the COordinated Regional Climate Downscaling EXperiment (CORDEX)-Africa. The assessment is based on the occurrence, duration, and intensity indices of daily precipitation in Maghreb during the fall and spring seasons from 1998 to 2008. We also examine the links between the North-Atlantic Oscillation (NAO) index, weather systems, and the precipitation regime over the region. During the rainy season (September to February), the CRCM5 reproduces the frequency and intensity of extreme precipitation adequately, as well as the occurrence of days with rain, while the CanRCM4 underestimates precipitation extremes. The study of links between weather systems and the precipitation regime shows that, along the Atlantic coast, precipitation (occurrence, intensity, and wet sequences) increases significantly with storm frequency in the fall. In winter, these links grow stronger going east, from the Atlantic coast to the Mediterranean coast. The negative phases of the NAO index are statistically associated with the increase in rain intensity, extremes, and accumulation along the Atlantic coast in the fall. However, the link weakens in winter over these regions and strengthens along the Mediterranean coast as the precipitation frequency rises during negative phases of the NAO. Both RCMs generally reproduce the links between the NAO and the precipitation regime well, regardless of location. 相似文献
93.
94.
Anabele Lindner Cira Souza Pitombo Samille Santos Rocha José Alberto Quintanilha 《地球空间信息科学学报》2016,19(4):245-254
Studies in transportation planning routinely use data in which location attributes are an important source of information. Thus, using spatial attributes in urban travel forecasting models seems reasonable. The main objective of this paper is to estimate transit trip production using Factorial Kriging with External Drift (FKED) through an aggregated data case study of Traffic Analysis Zones in São Paulo city, Brazil. The method consists of a sequential application of Principal Components Analysis (PCA) and Kriging with External Drift (KED). The traditional Linear Regression (LR) model was adopted with the aim of validating the proposed method. The results show that PCA summarizes and combines 23 socioeconomic variables using 4 components. The first component is introduced in KED, as secondary information, to estimate transit trip production by public transport in geographic coordinates where there is no prior knowledge of the values. Cross-validation for the FKED model presented high values of the correlation coefficient between estimated and observed values. Moreover, low error values were observed. The accuracy of the LR model was similar to FKED. However, the proposed method is able to map the transit trip production in several geographical coordinates of non-sampled values. 相似文献
95.
96.
97.
98.
Bilal?El OuaragliEmail author Mohamed?Najib?Zaghloul Hajar?El Talibi Roberta?Somma 《Arabian Journal of Geosciences》2016,9(15):660
This work deals with sedimentological, petrographic, and structural analyses of a middle Miocene late-orogenic sedimentary cycle, denoted Oued Dayr Formation, recognized in the Rifian sector of the Maghrebian Chain (Morocco). The analyzed Formation (75 m thick) starts with 15–20 m of light colored polymict conglomerates, with minor sandstone beds, lying on the Paleozoic basement and Mesozoic cover of the Ghomaride Nappe. Facies analysis indicates a fining-upward deposition in a marine environment characterized by increasing deepening, reflecting a subsidence rate that exceeds sedimentary supply. Petrographic analysis points out that sandstones are represented by litharenites originated by erosion of recycled orogen. The conglomerates pebbles and cobbles consist of Alpine low- to high-grade metamorphic rocks as metarenites, phyllites, mylonitic quartzites, micaschists, augen gneisses deriving from the exhumed deep metamorphic basement, the overlying metasedimentary of the Sebtide Nappes and of sedimentary rocks as sandstones, jaspes, limestones, and shales deriving from the Ghomaride Nappes and their sedimentary cover. Data reveal mixed provenance indicating that the Oued Dayr Formation was fed by the Internal Nappes stack of the Maghrebian Chain. Structural analysis shows that the Oued Dayr Formation accumulated in a Thrust-Top basin, during an early extension (D0 phase), recorded by synsedimentary normal faults within middle Langhian deposits on the rear of the Internal Nappes stack. Subsequent ductile and brittle compressional (D1, D2, D3) and extensional (D4) deformation phases occurred during and/or after the stacking, exhumation, and early unroofing of Sebtide Complex coeval with the opening of the western Mediterranean back-arc basins since middle Miocene time. 相似文献
99.
Spatial distribution of crustaceans associated with shallow soft‐bottom habitats in a coral reef lagoon
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The ecology and diversity of the shallow soft‐bottom areas adjacent to coral reefs are still poorly known. To date, the few studies conducted in these habitats dealing with macroinvertebrate fauna have focused on their abundance spatial patterns at high taxonomic levels. Thus, some aspects important to evaluate the importance and vulnerability of these habitats, such as species diversity or the degree of habitat specialization, have often been overlooked. In this study we compared the crustacean assemblages present in four different habitats at Magoodhoo Island coral reef lagoon (Maldives): coral rubble, sandy areas and two different seagrass species (Thalassia hemprichii and Cymodocea sp.). Forty‐two different crustacean species belonging to 30 families and four orders were found. ‘Site’ was a significant factor in all of the statistical analyses, indicating that tropical soft‐bottom habitats can be highly heterogeneous, even at a spatial scale between tens and hundreds of meters. Although traditionally it has been considered that seagrass beds host greater species diversity and abundance of organisms than adjacent unvegetated habitats, no differences in the univariate measures of fauna (abundance of organisms, number of species and Shannon diversity) were observed among habitats. However, sandy areas, coral rubble and seagrass beds exhibited different species composition of crustacean communities. The percentage of taxa considered as potential habitat specialists was 27% and the number of species exclusively occurring in one habitat was especially high in seagrass beds. Thus, degradation of this vegetated habitat would result in a great loss of biodiversity in tropical shallow soft‐bottom habitats. 相似文献
100.
Catherine Robin Shannon Nudds Phillip MacAulay André Godin Bodo De Lange Boom Jason Bartlett 《Marine Geodesy》2016,39(2):195-222
Since the advent of Global Navigation Satellite Systems, it has been possible to perform hydrographic survey reductions through the ellipsoid, which has the potential to simplify operations and improve bathymetric products. This technique requires a spatially continuous separation surface connecting chart datum (CD) to a geodetic ellipsoid. The Canadian Hydrographic Service (CHS), with support from the Canadian Geodetic Survey, has developed a new suite of such surfaces, termed Hydrographic Vertical Separations Surfaces, or HyVSEPs, for CD and seven tidal levels. They capture the spatial variability of the tidal datum and levels between tide gauges and offshore using semiempirical models coupling observations at tide stations with relative sea-level rise estimates, dynamic ocean model solutions, satellite altimetry, and a geoid model. HyVSEPs are available for all tidal waters of Canada, covering over seven million square kilometers of ocean and more than 200,000 kilometers of shoreline. This document provides an overview of the CHS's modeling approach, tools, methods, and procedures.
The HyVSEP for CD defines the new hydrographic datum for the tidal waters of Canada. HyVSEPs for other tidal levels are fundamental for coastal studies, climate change adaptation and the definition of the Canadian shoreline and offshore boundaries. HyVSEPs for inland waters are not discussed. 相似文献