全文获取类型
收费全文 | 923篇 |
免费 | 63篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 52篇 |
地球物理 | 276篇 |
地质学 | 364篇 |
海洋学 | 113篇 |
天文学 | 110篇 |
综合类 | 6篇 |
自然地理 | 65篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 31篇 |
2020年 | 22篇 |
2019年 | 25篇 |
2018年 | 35篇 |
2017年 | 40篇 |
2016年 | 61篇 |
2015年 | 33篇 |
2014年 | 51篇 |
2013年 | 54篇 |
2012年 | 37篇 |
2011年 | 62篇 |
2010年 | 54篇 |
2009年 | 66篇 |
2008年 | 62篇 |
2007年 | 38篇 |
2006年 | 38篇 |
2005年 | 45篇 |
2004年 | 36篇 |
2003年 | 20篇 |
2002年 | 26篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 16篇 |
1998年 | 22篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 10篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有1006条查询结果,搜索用时 15 毫秒
991.
Francisco Sánchez-Martos Luis Molina-Sánchez Juan Gisbert-Gallego 《Environmental Earth Sciences》2014,71(1):67-76
Water resources management in coastal wetlands requires the degree of interdependence between groundwater and terrestrial ecosystems to be known. This is especially so in semiarid areas where surface inflows are restricted, marine influence is marked and the evaporation rate is high. Thus, chemistry of surface waters is very variable in the Cerrillos-Punta Entinas wetlands system. Using classical hydrogeochemical tools, the main processes that favor a diversity of water types were described, related to: presence of salt deposits on the lagoon beds, marine origin of the water, and local influence of groundwater. All these factors make it difficult to establish what reference conditions should be used to define “good” water quality of the surface waters—as required by the Water framework directive—and to understand the influence of groundwater on these coastal wetlands. Knowledge about the influence of the different interaction of these factors on the hydrogeochemical dynamics is required for the sustainable management of this protected natural site. 相似文献
992.
The Portuguese National Ecological Reserve (NER) was created in 1983, with the aim of preserving, in certain areas, the biophysical structure necessary to maintain exploitation of natural resources and land use without jeopardizing their sustainability. For the first time, issues related to groundwater resources were addressed. Since then, this legal tool has been revised for a better integration of the new national and European legislation and new scientific and technical knowledge. In the latest NER, the concept of “strategic areas of protection and aquifer recharge (SAPAR)” was created, being now necessary to define which are the methodologies and criteria to be applied for its delimitation. This paper summarizes the strategic guidelines that were established from debates held in several meetings with land-use planners, water resources managers, specialists and other stakeholders concerning the development of harmonized definitions and criteria of NER. As a result of those contributions a report was elaborated where guidelines and criteria for the NER delimitation were defined at national level, in accordance with national legislation and other relevant sector plans. In this work, the articulation and integration of SAPAR-protected areas in Portuguese Water Act and the expected difficulties of its application at operative level are evaluated since the SAPAR are important for the control of urban sprawl and therefore to preserve groundwater resources and dependent ecosystems. A brief explanation about the Portuguese main hydrogeological features is given for a better understanding of the groundwater resources and dependent ecosystems. Finally, the key guidelines for a good NER delimitation are compiled. 相似文献
993.
Vania Bogorny Chiara Renso Artur Ribeiro de Aquino Fernando de Lucca Siqueira Luis Otavio Alvares 《Transactions in GIS》2014,18(1):66-88
Several works have been proposed in the last few years for raw trajectory data analysis, and some attempts have been made to define trajectories from a more semantic point of view. Semantic trajectory data analysis has received significant attention recently, but the formal definition of semantic trajectory, the set of aspects that should be considered to semantically enrich trajectories and a conceptual data model integrating these aspects from a broad sense is still missing. This article presents a semantic trajectory conceptual data model named CONSTAnT, which defines the most important aspects of semantic trajectories. We believe that this model will be the foundation for the design of semantic trajectory databases, where several aspects that make a trajectory “semantic” are taken into account. The proposed model includes the concepts of semantic subtrajectory, semantic points, geographical places, events, goals, environment and behavior, to create a general concept of semantic trajectory. The proposed model is the result of several years of work by the authors in an effort to add more semantics to raw trajectory data for real applications. Two application examples and different queries show the flexibility of the model for different domains. 相似文献
994.
Shallow Miocene basaltic magma reservoirs in the Bahia de Los Angeles basin, Baja California, Mexico
Luis A. Delgado-Argote Juan García-Abdeslem 《Journal of Volcanology and Geothermal Research》1999,88(1-2)
The basement in the Bahía de Los Angeles basin consists of Paleozoic metamorphic rocks and Cretaceous granitoids. The Neogene stratigraphy overlying the basement is formed, from the base to the top, by andesitic lava flows and plugs, sandstone and conglomeratic horizons, and Miocene pyroclastic flow units and basaltic flows. Basaltic dikes also intrude the whole section. To further define its structure, a detailed gravimetric survey was conducted across the basin about 1 km north of the Sierra Las Flores. In spite of the rough and lineal topography along the foothills of the Sierra La Libertad, we found no evidence for large-scale faulting. Gravity data indicates that the basin has a maximum depth of 120 m in the Valle Las Tinajas and averages 75 m along the gravimetric profile. High density bodies below the northern part of the Sierra Las Flores and Valle Las Tinajas are interpreted to be part of basaltic dikes. The intrusive body located north of the Sierra Las Flores is 2.5 km wide and its top is about 500 m deep. The lava flows of the top of the Sierra Las Flores, together with the distribution of basaltic activity north of this sierra, suggests that this intrusive body continues for 20 km along a NNW-trending strike. Between the sierras Las Flores and Las Animas, a 0.5-km-wide, 300-m-thick intrusive body is interpreted at a depth of about 100 m. This dike could be part of the basaltic activity of the Cerro Las Tinajas and the small mounds along the foothills of western Sierra Las Animas. The observed local normal faulting in the basin is inferred to be mostly associated with the emplacement of the shallow magma reservoirs below Las Flores and Las Tinajas. 相似文献
995.
996.
Rafael Pérez-López José Miguel Nieto Israel López-Coto Juan Luis Aguado Juan Pedro Bolívar María Santisteban 《Applied Geochemistry》2010
The dynamics of trace elements from phosphate rock ore to the environment in a phosphoric acid plant located in SW Spain and the impact of phosphogypsum wastes were investigated through total digestion and BCR-sequential extraction. Based on total concentration, element transfer factors as criteria for examining the potential environmental risk of waste with respect to ore rock were calculated, and it was observed that most trace elements are only transferred into phosphogypsum at rates of 2–12%. However, based on those concentrations that are likely to be most readily mobile in the environment, phosphogypsum acts as a higher emission source of contaminants than the original rock. About 100 million tonnes of phosphogypsum are stack-piled in a dump of 1200 ha over salt-marshes of an estuary formed by the confluence of the Tinto and Odiel rivers. Phosphogypsum has been applied, at the recommended rate of 20–25 t/ha since 1978–2001, to improve fertility and reduce Na saturation in agricultural soils of the Guadalquivir river valley (140 km2). Phosphogypsum capacity as a source of mobile contaminants in three environmental scenarios (water leaching, exposure to oxidising and reducing conditions) was quantified by combining sequential extraction and waste mass. The amounts of mobile contaminants that could be released for every tonne of phosphogypsum are approximately 7 × 102 g Sr, 1.1 × 102 g Fe, 55 g Y, 30 g Ce, 12 g Cr, 11 g Ti, 5 g Zn, 4 g each of Cu and Pb, 3 g each of V and Cd, 2 g each of As and Ni and 1 g U. Multiplying these amounts by 100 Mt and 20–25 t/ha, it is possible to calculate risk assessments of phosphogypsum for both estuarine zones, e.g. in a hypothetical stack collapse and waste spilling, and agricultural soils, respectively. 相似文献
997.
Marcos García-Arias Luis Guillermo Corretgé Antonio Castro 《Mineralogy and Petrology》2010,99(3-4):153-164
Melting experiments on a gneissic protolith using the diamond trap technique produced an accumulation of crystals of biotite in the boundary of the diamond trap. Several hypotheses can be inferred to explain this feature, but textural evidence and calculations of the settling and drag velocities of the crystals suggest a model of extraction of melt due to a pressure gradient inside the capsule as the most likely origin of this biotite layer. This biotite layer and the trapped melt resemble the melanosome and leucosome, respectively, of stromatic metatexite migmatites. The melt extraction model developed is similar to the “filter pressing” model for migmatite formation. The diamond trap technique is a suitable method to develop migmatites experimentally. 相似文献
998.
Uranium minerals from the San Marcos District, Chihuahua, Mexico 总被引:1,自引:0,他引:1
Manuel Reyes-Cortés Luis Fuentes-Cobas Enrique Torres-Moye Hilda Esparza-Ponce María Elena Montero-Cabrera 《Mineralogy and Petrology》2010,99(1-2):121-132
The mineralogy of the two uranium deposits (Victorino and San Marcos I) of Sierra San Marcos, located 30 km northwest of Chihuahua City, Mexico, was studied by optical microscopy, powder X-ray diffraction with Rietveld analysis, scanning electron microscopy with energy dispersive X-ray analysis, inductively coupled plasma spectrometry, and gamma spectrometry. At the San Marcos I deposit, uranophane Ca(UO2)2Si2O7·6(H2O) (the dominant mineral at both deposits) and metatyuyamunite Ca(UO2)(V2O8)·3(H2O) were observed. Uranophane, uraninite (UO2+x), masuyite Pb(UO2)3O3(OH)·3(H2O), and becquerelite Ca(UO2)6O4(OH)6 ·(8H2O) are present at the Victorino deposit. Field observations, coupled with analytical data, suggest the following sequence of mineralization: (1) deposition of uraninite, (2) alteration of uraninite to masuyite, (3) deposition of uranophane, (4) micro-fracturing, (5) calcite deposition in the micro-fractures, and (6) formation of becquerelite. The investigated deposits were formed by high-to low-temperature hydrothermal activity during post-orogenic evolution of Sierra San Marcos. The secondary mineralization occurred through a combination of hydrothermal and supergene alteration events. Becquerelite was formed in situ by reaction of uraninite with geothermal carbonated solutions, which led to almost complete dissolution of the precursor uraninite. The Victorino deposit represents the second known occurrence of becquerelite in Mexico, the other being the uranium deposits at Peña Blanca in Chihuahua State. 相似文献
999.
Sylvia Bonilla Daniel Conde Luis Aubriot María del Carmen Pérez 《Estuaries and Coasts》2005,28(6):884-895
A survey was carried out to investigate the relationship of phytoplankton biovolume, structure, and species life strategies
with major abiotic factors in a subtropical choked coastal lagoon (34°33′S, 54°22′W) naturally connecting with the Atlantic
Ocean several times a year. Marine and limnetic influence areas were sampled on a monthly basis during two periods, one of
low rainfall and high conductivity (August 1996 to February 1998) and a second period with the opposite tendency (December
1998 to March 2000). Photosynthetically active radiation availability was high and reached the bottom (>1% of the incident
light), while dissolved inorganic nitrogen (0.6–18.4 μM), soluble reactive phosphorus (<0.3–2.7 μM), and reactive silica (5–386
μM) were highly variable. Life strategies were identified in the phytoplankton as a function of morphology. C-strategists,
invasive planktonic and epipelic species of small size, and R-strategists, mixing-dependent species of medium size, characterized
this permanently mixed system. High frequency of exchange with the ocean prevented high biomass accumulation. Phytoplankton
biomass was lower in the second period of high rainfall (2.3 and 1.1 mm3 1−1 for period 1 and 2 respectively). A canonical correspondence analysis showed that conductivity, nitrogen, phosphorus, and
silica were the main environmental variables explaining phytoplankton species composition patterns. During the first period,
Bacillariophyceae (mostly pennate species) and the potentially toxicPrococentrum minimum were dominant; during the second period a higher contribution of flagellates (Cryptophyceae, Euglenophyceae, Prasinophyceae,
and flagellates <7 μm) was found. Differences of phytoplankton biomass, main taxonomic groups, and strategies were found between
periods but not between limnic and marine areas, suggesting that hydrological dynamic is more relevant than seasonal and spatial
differences. 相似文献
1000.
Avriel Venis L. Cirineo Akira Imai Ryohei Takahashi Redempta P. Baluda Noel C. Oliveros Victor B. Maglambayan Roy Ronald C. Luis Maria Lourdes M. Faustino Jacky Almadin 《Resource Geology》2021,71(1):1-40
The Southwest prospect is located at the southwestern periphery of the Sto. Tomas II porphyry copper–gold deposit in the Baguio District, northwestern Luzon, Philippines. The Southwest prospect hosts a copper‐gold mineralization related to a complex of porphyry intrusions, breccia facies, and overlapping porphyry‐type veinlets emplaced within the basement Pugo metavolcanics rocks and conglomerates of the Zigzag Formation. The occurrences of porphyry‐type veinlets and potassic alteration hosted in the complex are thought to be indications of the presence of blind porphyry deposits within the Sto. Tomas II vicinity. The complex is composed of at least four broadly mineralogically similar dioritic intrusive rocks that vary in texture and alteration type and intensity. These intrusions were accompanied with at least five breccia facies that were formed by the explosive brecciation, induced by the magmatic–hydrothermal processes and phreatomagmatic activities during the emplacement of the various intrusions. Hydrothermal alteration assemblages consisting of potassic, chlorite–magnetite, propylitic and sericite–chlorite alteration, and contemporaneous veinlet types were developed on the host rocks. Elevated copper and gold grades correspond to (a) chalcopyrite–bornite assemblage in the potassic alteration in the syn‐mineralization early‐mineralization diorite (EMD) and contemporaneous veinlets and (b) chalcopyrite‐rich mineralization associated with the chalcopyrite–magnetite–chlorite–actinolite±sericite veinlets contemporaneous with the chlorite–magnetite alteration. Erratic remarkable concentrations of gold were also present in the late‐mineralization Late Diorite (LD). High XMg of calcic amphiboles (>0.60) in the intrusive rocks indicate that the magmas have been oxidizing since the early stages of crystallization, while a gap in the composition of Al between the rim and the cores of the calcic amphiboles in the EMD and LD indicate decompression at some point during the crystallization of these intrusive rocks. Fluid inclusion microthermometry suggests the trapping of immiscible fluids that formed the potassic alteration, associated ore mineralization, and sheeted quartz veinlets. The corresponding formation conditions of the shallower and deeper quartz veinlets were estimated at pressures of 50 and 30 MPa and temperatures of 554 and 436°C at depths of 1.9 and 1.1 km. Temperature data from the chlorite indicate that the chalcopyrite‐rich mineralization associated with the chlorite–magnetite alteration was formed at a much lower temperature (ca. 290°C) than the potassic alteration. Evidence from the vein offsetting matrix suggests multiple intrusions within the EMD, despite the K‐Ar ages of the potassic alteration in EMD and hornblende in the LD of about the same age at 3.5 ± 0.3 Ma. The K‐Ar age of the potassic alteration was likely to be thermally reset as a result of the overprinting hydrothermal alteration. The constrained K‐Ar ages also indicate earlier formed intrusive rocks in the Southwest prospect, possibly coeval to the earliest “dark diorite” intrusion in the Sto. Tomas II deposit. In addition, the range of δ34S of sulfide minerals from +1.8‰ to +5.1‰ in the Southwest prospect closely overlaps with the rest of the porphyry copper and epithermal deposits in the Sto. Tomas II deposit and its vicinity. This indicates that the sulfides may have formed from a homogeneous source of the porphyry copper deposits and epithermal deposits in the Sto. Tomas II orebody and its vicinity. The evidence presented in this work proves that the porphyry copper‐type veinlets and the adjacent potassic alteration in the Southwest prospect are formed earlier and at a shallower level in contrast with the other porphyry deposits in the Baguio District. 相似文献