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101.
A new reassembly of the continents around the North Atlantic Ocean is presented. The first criterion used for this reassembly is the identification of the structural framework related to the opening which consists of marginal fracture zones generated by offsets of the Rift. The Africa—North America, Eurasia—Greenland, Greenland—North America and Eurasia—North America adjustments are successively discussed. It is argued that the adjustments are best made at the 3000-meters isobath between Africa and North America and at the 2000-meters isobath for the younger rifts. The difference is attributed to subsidence and modification of continental margins with time. The importance of the Late Paleozoic tectonic phase in determining the subsequent pattern of Mesozoic rifting is emphasized. 相似文献
102.
Sérgio P. Ávila Patrícia Madeira C. Marques da Silva Mário Cachão Bernard Landau Rui Quartau A. M. de Frias Martins 《第四纪科学杂志》2008,23(8):777-785
The Pleistocene (Eemian) outcrops of Lagoinhas and Prainha, located at Santa Maria Island (Azores), were investigated and their fossil mollusc content reported. These studies revealed that the last glaciation affected two groups of molluscs: the ‘warm‐guest’ gastropods with West African or Caribbean affinities (e.g. Conus spp., Cantharus variegatus, Bulla amygdala, Trachypollia nodulosa) and shallow bivalve species mainly associated with sandy habitats (Ensis minor, Lucinella divaricata, and probably Laevicardium crassum). In this paper we focus on this group of bivalves, which has since locally disappeared from the Azores. We relate the local disappearance of these bivalves in the Azores with the lack of sand in the shelf. The specific characteristics of the Santa Maria shelf combined with the sea‐level drop during the Weichselian prevented deposition of the lowstand deposits and permitted erosion of the previous ones, leaving the shelf without a sediment cover. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
103.
Evaluating infiltration losses in a Mediterranean wetland: Las Tablas de Daimiel National Park,Spain
Las Tablas de Daimiel National Park is a series of wetlands which naturally originated from groundwater discharges from the Mancha Occidental aquifer, Spain. Despite the relatively large size of this aquifer, 30 years of intensive groundwater pumping have significantly depleted the water table. As a result, wetlands only remain functional due to artificial inflows. Infiltration loss is therefore a key parameter to evaluate how much water is needed to maintain ecosystem functionality. Although yearly infiltration estimates existed prior to this work, these did not take into account key parameters such as the temporal evolution of the flooded area. This paper presents a more concrete estimate of the average infiltration losses. Infiltration is calculated as the closure term of daily water balances during a period of time where all other elements were known to an acceptable accuracy. A validation mechanism is provided to check the potential utility of the calculated infiltration in wetland management practices. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
104.
M. Martínez G. Márquez F.J. Alejandre J.J. Del Río A. Hurtado 《Journal of South American Earth Sciences》2009,27(2-3):211-218
The aim of this research work is a geochemical, mineralogical, and textural characterization of spontaneously smouldered coal-derived products in northwestern Venezuela (Cerro Pelado Formation, some 10 km from Pedregal city). Several solid samples were collected from this formation, six of unweathering coal, an other six of resulting unmelted rocks forming on a surface coal bed, and the last four of mineralizations found accumulating around gas vents. The fresh coal and the unmelted material were analysed by scanning electron microscopy, X-ray diffraction, and proximate techniques. Products such as magnetite and chabazite-K were identified in the alteration rocks. Likewise, both materials were also studied in order to determine the mobilization of 17 elements into the environment; such elements were analysed through inductively coupled plasma atomic emission spectroscopy on extracts obtained by a sequential extraction method: each sample was firstly extracted with MilliQ water and then the resultant residue was washed. This and the subsequently resulting residues are extracted according to the mentioned procedure by using, respectively, ammonium acetate, chlorhydric acid, peroxide and chlorhydric acid, nitric acid and fluorhydric acid, and nitric acid. The studied elements are classified as highly mobile (Na, Ni, ...), nearly immobile (Ti, P) and partially mobile (Mg, Fe, K, ...). In regards to mineralizations around fumaroles associated with smoldering coal seams, Fourier-transform infrared spectroscopy and X-ray diffraction analyses have revealed the presence of salammoniac, mascagnite and other solid combustion compounds formed by reaction of gas emitted from coal oxidation, in addition to previously non-reported sulfur-rich by-products associated with gas fissures, particularly ammonium thiosulfate, a phase first obtained only synthetically in the laboratory. Another objective of the research was to collect and analyse gases escaping from surficial vents. Relatively high concentrations of several aromatic compounds were detected in the gas collected at the studied coal outcrop, as well as aliphatic hydrocarbons including ethane, propane, butanes, among others. High contents of carbon monoxide, methane and carbon dioxide were also measured for gas samples. 相似文献
105.
Diego F. Torres Shu Zhang Olaf Reimer Xavier Barcons Amalia Corral Valentí Bosch-Ramon Josep M. Paredes Gustavo E. Romero Jin Qu Werner Collmar Volker Schönfelder Yousaf Butt 《Astrophysics and Space Science》2007,309(1-4):17-21
The COMPTEL unidentified source GRO J 1411-64 was observed by INTEGRAL and XMM-Newton in 2005. The Circinus Galaxy is the
only source detected within the 4σ location error of GRO J1411-64, but in here excluded as the possible counterpart. At soft X-rays, 22 reliable and statistically
significant sources (likelihood >10) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932,
is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the
COMPTEL source position uncertainty make an association hard to quantify and thus risky. At the best location of the source,
detections at hard X-rays show only upper limits, which, together with MeV results obtained by COMPTEL suggest the existence
of a peak in power output located somewhere between 300–700 keV for the so-called low state. Such a spectrum resembles those
in blazars or microquasars, and might suggest at work by the models accordingly. However, an analysis using a microquasar
model consisting on a magnetized conical jet filled with relativistic electrons, shows that it is hard to comply with all
observational constrains. This fact and the non-detection at hard X-rays introduce an a-posteriori question mark upon the
physical reality of this source, what is discussed here. 相似文献
106.
107.
CL de Moor SJ Johnston A Brandão RA Rademeyer JP Glazer LB Furman 《African Journal of Marine Science》2015,37(3):285-311
The waters off South Africa's coastline boast a rich mix of commercially fished species. Quantitative assessments of these marine resources have developed from simple methods first applied in the 1970s, to models that encompass a wide range of methodologies. The more valuable resources have undergone regular assessments in recent decades, with frequencies closely related to the management approach employed for each fishery. Many of these assessments form the operating models used to simulation-test candidate management procedures. This paper provides a comprehensive review of the assessments of 11 of the most important fisheries resources in South Africa. Some assessments use simple biomass dynamics models, whereas others are a hybrid of age- and length-based models, each designed to model the specific characteristics of the resource and fishery concerned. Many of the assessments have been disaggregated by species/stock and/or area as related multispecies/stock/ distribution hypotheses have arisen. This paper explores the similarities and differences in the data available and the methods applied. The review indicates that, whereas the status of three of these resources cannot be estimated reliably at present, the status of six resources is considered to be reasonable to good, whereas that of abalone Haliotis midae and West Coast rock lobster Jasus lalandii remains poor. 相似文献
108.
Spijker Jeroen Recaño Joaquín Martínez Sandra Carioli Alessandra 《Journal of Geographical Systems》2021,23(2):161-207
Journal of Geographical Systems - Colombia is undergoing major changes in mortality patterns. National- and department-level cause-specific analyses have previously been carried out, but very... 相似文献
109.
110.