全文获取类型
收费全文 | 5735篇 |
免费 | 273篇 |
国内免费 | 32篇 |
专业分类
测绘学 | 295篇 |
大气科学 | 376篇 |
地球物理 | 1474篇 |
地质学 | 2031篇 |
海洋学 | 477篇 |
天文学 | 1007篇 |
综合类 | 36篇 |
自然地理 | 344篇 |
出版年
2023年 | 22篇 |
2022年 | 47篇 |
2021年 | 96篇 |
2020年 | 126篇 |
2019年 | 106篇 |
2018年 | 249篇 |
2017年 | 218篇 |
2016年 | 342篇 |
2015年 | 256篇 |
2014年 | 307篇 |
2013年 | 362篇 |
2012年 | 287篇 |
2011年 | 387篇 |
2010年 | 294篇 |
2009年 | 364篇 |
2008年 | 313篇 |
2007年 | 221篇 |
2006年 | 236篇 |
2005年 | 198篇 |
2004年 | 185篇 |
2003年 | 150篇 |
2002年 | 148篇 |
2001年 | 105篇 |
2000年 | 93篇 |
1999年 | 93篇 |
1998年 | 105篇 |
1997年 | 80篇 |
1996年 | 51篇 |
1995年 | 44篇 |
1994年 | 54篇 |
1993年 | 26篇 |
1992年 | 41篇 |
1991年 | 26篇 |
1990年 | 38篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 25篇 |
1984年 | 16篇 |
1983年 | 34篇 |
1982年 | 19篇 |
1981年 | 13篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1975年 | 12篇 |
1973年 | 12篇 |
1972年 | 13篇 |
排序方式: 共有6040条查询结果,搜索用时 31 毫秒
991.
992.
Francisco Mota de Sá Mónica Amaral Ferreira Carlos Sousa Oliveira 《Bulletin of Earthquake Engineering》2016,14(7):2047-2067
Earthquakes are a permanent threat to urban environments worldwide. The communication of the related risk demands accurate damage model simulations and an interactive visualization of results. The aim of this paper is to provide a realistic problem-solving environment for earthquake discussions among decision makers, stakeholders, and the general public. QuakeIST® is an integrated earthquake simulator developed by Instituto Superior Técnico (Lisbon University), oriented towards the performance of risk calculations concerning damage propagations that use the Disruption Index concept. This software imports data stored in a GIS environment, handles different ground motion scenarios, and deals with a complex situation of different soils and vulnerabilities of various layers of civil structures (buildings, lifelines, and other urban structures). It models interdependencies between several infrastructures and between infrastructures and the urban tissue. The computer programme is very versatile, written in separate modules, allowing an experimented user to incorporate new formulations. Results can be treated with any statistical application and most common GIS commercial environments can produced their geographic visualization. Current progress and new upcoming are briefly described at the end of the paper. 相似文献
993.
994.
995.
F. J. García Navarro J. A. Amorós Ortiz-Villajos C. J. Sánchez Jiménez S. Bravo Martín-Consuegra E. Márquez Cubero Raimundo Jiménez Ballesta 《Environmental Earth Sciences》2009,59(3):603-611
The study described here involved evaluating the effects that the application of one by-product (sugar foam waste) has upon
red soils in the region of La Mancha (Central Spain). In view of the fact that this is a location where this type of soil
abounds, this technique has been a common practice for many years. The principal goal was to investigate the impact of this
approach on some of the soil properties and, secondly, on its level of fertility. As a result, this represents an investigation
into the effects that this type of waste has on some soil quality parameters. The results showed that, after the addition
of by-products over 25 years, sugar foam waste is of agricultural interest mainly due to the increase in organic matter concentration
(about 2%) and, to a lesser extent, by increases in calcium carbonate (more than 30%) and P (four times more). The soil pH
was also found to increase slightly (1.4), while the electrical conductivity almost did not change. The properties associated
with these pedological qualities therefore had a positive effect by improving nutrient availability. As a result, foams arising
from sugar industries have a positive effect on soil quality and the application of such foams to soils is beneficial since
the need to dispose this residue is also removed. 相似文献
996.
This paper aims to present the usability of an adaptive neuro fuzzy inference system (ANFIS) for the prediction swelling potential
of the compacted soils that are important materials for geotechnical purposes such as engineered barriers for municipal solid
waste, earth dams, embankment and roads. In this study the swelling potential that is also one of significant parameters for
compacted soils was modeled by ANFIS. For the training and testing of ANFIS model, data sets were collected from the tests
performed on compacted soils for different geotechnical application in Nigde. Four parameters such as coarse-grained fraction
ratio (CG), fine-grained fraction ratio (FG), plasticity index (PI) and maximum dry density (MDD) were presented to ANFIS
model as inputs. The results obtained from the ANFIS models were validated with the data sets which are not used for the training
stage. The analyses revealed that the predictions from ANFIS model are in sufficient agreement with test results. 相似文献
997.
Light-induced reduction of dissolved and particulate Fe(III) has been observed to occur in the surface waters of the acidic
mine pit lake of San Telmo (143,600 m2, pH 2.8, Fetotal = 2.72 mM). This photochemical production of Fe(II) is directly related to the intensity of solar radiation and competes
with biologically catalyzed reactions (i.e., bacterial re-oxidation of Fe(II)) and physical processes (including ionic diffusion,
advection, and convection, which tend to homogenize the epilimnetic concentration of Fe(II) at every moment). Therefore, diel
cycles of Fe(II) concentration are observed at the lake surface, with minimum values of 10–20 μM Fe(II) (0.35–0.70% Fetotal) at the sunrise and sunset, and maximum values of 90 μM Fe(II) (3.2% Fetotal) at midday in August 2005. Field and experimental work conducted in San Telmo and other pit lakes of the Iberian Pyrite Belt
(IPB) (pH 2.3–3.1, Fetotal = 0.34–17 mM) indicate that the kinetics of the photoreductive reaction is zero-order and is independent of the Fe(III) concentration,
but highly dependent on the intensity of solar radiation and temperature. Experimental work conducted with natural Fe(III)
minerals (schwertmannite, goethite, and lepidocrocite) suggests that dissolved organic matter is an important factor contributing
to the photochemical production of Fe(II). The wavelengths involved in the photoreduction of Fe(III) include not only the
spectrum of UV-A radiation (315–400 nm), but also part of the photosynthetically active radiation (PAR, 400–700 nm). This
finding is of prime importance for the understanding of the photoreduction processes in the pit lakes of the IPB, because
the photo-reactive depth is not limited to the penetration depth of UV-A radiation (upper 1–10 cm of the water column depending
on the TDS content), but it is approximately equal to the penetration depth of PAR (e.g., first 4–6 m of the water column
in San Telmo on July 2007); thus, increasing the importance of photochemical processes in the hydro(bio)geochemistry of pit
lakes. 相似文献
998.
The Duna-Tisza Interfluve, Hungary has an agricultural economy but is plagued by severe problems of soil and wetland salinization despite 200 years of intensive research. The study’s objective was to determine the origin of salts and the mechanisms of salinity distribution. To this end, flow-patterns and chemistry of groundwater were evaluated in a 100 km?×?65 km area, with emphasis on the Kolon- and Kelemenszék Lakes region. The lakes are located 13 km apart and have chemically contrasting water and soil types. Two groundwater flow-domains were identified: a gravity-drive meteoric fresh water and an over-pressured deeper domain of saline water. The waters are channeled by a highly permeable gravel aquifer to the surface and may merge near Kelemenszék Lake, causing it to be saline. Kolon Lake receives meteoric groundwater only, hence its fresh chemical character. The cross-formational ascent of the deep waters, combined with the gravitational systems’ geometry and the flow-channeling effect of the near-surface rocks, explains the contrasting chemistry between lakes, and the origin and pattern of soil salinization. The scheme is proposed as a generally valid hydrogeological profile for the interfluve, and has been named the Duna-Tisza Interfluve Hydrogeological Type Section. 相似文献
999.
Integration of hydrogeological and geological data into a conceptual model is critical for site investigation programs, since this model is the basis for hydrogeological modeling and for engineering. In the Hungarian Radioactive Waste Disposal Investigation Program, several methods have been used to characterize the potential host rock (granite) at the Bátaapáti site for a repository for low and intermediate level radioactive waste. Hydrogeological data acquisition revealed some characteristic aspects of the site. One of the most important is the presence of extensive rock deformation zones (faults) with low hydraulic conductivity, which strongly reduce the direct hydraulic communication between adjacent blocks of rock (compartmentalization). This characteristic of the rock mass results in a mosaic-like distribution of rock compartments, each with an almost constant hydraulic head. Within the compartments, hydraulic tests have shown that transmissivity is strongly scale dependent: the larger the scale, the higher the measured transmissivity. The extensive highly transmissive zones cause very low hydraulic gradients within each block, thus the transport processes are strongly influenced by the low or average transmissivity zones and the rock matrix. 相似文献
1000.
David Sanz Juan José Gómez-Alday Santiago Castaño Angel Moratalla Jorge De las Heras Pedro Emilio Martínez-Alfaro 《Hydrogeology Journal》2009,17(6):1375-1391
The Mancha Oriental System (MOS) has a surface area of 7,260 km2, making it one of the largest carbonate aquifer systems in Spain. The system sustains about 1,000 km2 of irrigated crops and supplies groundwater to 275,000 inhabitants. The economic transformation brought about by the development of extensive irrigated cropland has led to a water-balance disequilibrium of about 75 million m3/year. This input–output deficit has negative consequences in the quantity and quality of the available resources, in the river–aquifer relationship, and in the associated ecosystems as well. To understand the hydrogeological behaviour of the system, it is necessary to design a conceptual model. Further, the conceptualisation of a groundwater flow system is a requirement of the European Water Framework Directive for the characterisation of groundwater bodies. The robustness of the conceptual model depends heavily on the user capability of representing the real system. In this work, a multidisciplinary approach has been used to represent the three-dimensional geological framework and the groundwater flow conceptualisation of the MOS. Data management and three-dimensional visualisation have been carried out by means of geographical information system (GIS) tools and software for contouring and three-dimensional surface mapping. 相似文献