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21.
Station-keeping for a translunar communication station 总被引:1,自引:0,他引:1
John V. Breakwell Ahmed A. Kamel Martin J. Ratner 《Celestial Mechanics and Dynamical Astronomy》1974,10(3):357-373
A translunar communication station is to be kept close to a nominal unstable periodic ‘Halo’ orbit, visible at all times from Earth. The analytically computed nominal orbit is not perfect, requiring an average control acceleration of about 10?6 g's for tight control. An adjustable quadratic combination of position deviation and control acceleration is minimized to provide an (adjustable) control law with period feedback gains and a periodic bias. The average control acceleration can be reduced to less than 10?8 g's with an error settling time of less than 21/2 months. The resulting limiting motion provides, in turn, an improved nominal, permitting the same low control cost with much tighter control, corresponding to settling times of the order of one day. 相似文献
22.
Amor Ben Moussa Sarra Bel Haj Salem Kamel Zouari Faycel Jelassi 《Arabian Journal of Geosciences》2017,10(20):446
The major ion hydrochemistry, sodium absorption ratio (SAR), sodium percentage, and isotopic signatures of Hammamet-Nabeul groundwaters were used to identify the processes that control the mineralization, irrigation suitability, and origin of different water bodies. This investigation highlights that groundwater mineralization is mainly influenced by water-rock interaction and pollution by the return flow of irrigation water. The comparison of groundwater quality with irrigation suitability standards proves that most parts of groundwater are unacceptable for irrigation and this long-term practice may result in a significant increase of the salinity and alkalinity in the soils. Based on isotopic signatures, the shallow aquifer groundwater samples were classified into (i) waters with depleted δ18O and δ2H contents, highlighting recharge by modern precipitation, and (ii) waters with enriched stable isotope contents, reflecting the significance of recharge by contaminated water derived from the return flow of evaporated irrigation waters. The deep-aquifer groundwater samples were also classified into (i) waters with relatively enriched isotope contents derived from modern recharge and mixed with shallow-aquifer groundwater and (ii) waters with depleted stable isotope contents reflecting a paleoclimatic origin. Tritium data permit to identify three origins of recharge, i.e., contemporaneous, post-nuclear, and pre-nuclear. Carbon-14 activities demonstrate the existence of old paleoclimatic recharge related to the Holocene and Late Pleistocene humid periods. 相似文献
23.
Groundwater salinization processes in shallow coastal aquifer of Djeffara plain of Medenine, Southeastern Tunisia 总被引:3,自引:3,他引:0
Rim Trabelsi Kamel Abid Kamel Zouari Houcine Yahyaoui 《Environmental Earth Sciences》2012,66(2):641-653
Urban and industrial development and the expansion of irrigated agriculture have led to a drastic increase in the exploitation
of groundwater resources. The over-exploitation of coastal aquifers has caused a seawater intrusion and has seriously degraded
groundwater quality. The shallow coastal aquifer of the Djeffara plain, southeastern Tunisia constitutes an example of water
resource suffering an intensive and uncontrolled pumping for irrigation. Intensive exploitation of the aquifer and climate
aridity caused a decrease in piezometric level and an increase in salinity. According to the hydrochemical data (Cl−, SO4
2−, NO3
−, HCO3
−, Br−, Ca2+, Mg2+, Na+, K+) and the stable isotope composition (oxygen-18 and deuterium content), groundwater salinization in the investigated system
is caused by three main processes: (i) salts dissolution especially in the central part of Jerba and around Medenine plain;
(ii) evaporation process; and (iii) seawater intrusion which caused the increase in salinity in the peninsula of El Jorf,
in Jerba and in the North of Ben Gardane. 相似文献
24.
Samir Kamel 《Environmental Earth Sciences》2011,63(1):189-199
The hydrodynamic groundwater data and stable isotopes of water have been used jointly for better understanding of upward leakage
and mixing processes in the Djerid aquifer system (southwestern Tunisia). The aquifer system is composed of the upper unconfined
Plio-Quaternary (PQ) aquifer, the intermediate (semi-)confined Complex Terminal (CT) aquifer and the deeper confined Continental
Intercalaire (CI) aquifer. A total of 41 groundwater samples from the CT and PQ aquifers were collected during June 2001.
The stable isotope composition of waters establishes that the CT deep groundwater (depleted as compared to present Nefta local
rainfall) is ancient water recharged during late Quaternary time. The relatively recent water in the shallow PQ aquifer is
composed of mixed water resulting from upward leakage and sporadic meteoric recharge. In order to characterize the meteoric
input signal for PQ in the study area, rainfall water samples were collected during 4 years (2000–2003) at the Nefta meteorological
station. Weighted mean values of isotopic contents with respect to rainfall amounts have been computed. Despite the short
collection period in the study area, results agree with those found in Beni Abbes (southwestern Algerian Sahara) by Fontes
on 9 years of rainfall surveillance. Stable isotopic relationships provide clear evidence of shallow PQ aquifer replenishment
by deep CT groundwater. The 18O/upward leakage rate allowed the identification of distinctive PQ waters related to CT aquifer configuration (confined in
the western part of the study area, semi-permeable in the eastern part). These trends were confirmed by the relation 18O/TDS. The isotope balance model indicated a contribution of up to 75% of the deep CT groundwater to the upper PQ aquifer
in the western study area, between Nefta and Hazoua. 相似文献
25.
Kmar Ben İsmail-Lattrache Kamel Boukhalfa Pratul Kumar Saraswati Mohamed Soussi Luigi Jovane 《Geodinamica Acta》2013,26(1-2):94-121
The orthophragminids in lower Bartonian Reineche Limestone member, a fossiliferous shallow-marine unit exposed in Cap Bon peninsula in Tunisia, are represented by 17 species assigned to Discocyclinidae Galloway 1928 and Orbitoclypeidae Brönnimann 1946. These taxa, associated with nummulitids and alveolinids, belong to the lineages of Discocyclina Gümbel 1870, Nemkovella, 1987, Orbitoclypeus Silvestri 1907, and Asterocyclina Gümbel 1870, described for the first time from north Africa lying at the southern margin of Tethyan ocean during Paleogene. We identified Nemkovella evae, previously not recorded in upper Lutetian/lower Bartonian and younger Eocene deposits of northern Tethyan platforms, and erected a new subspecies, N. evae reinechensis n. ssp. A comparison of Reineche orthophraminids, assigned to orthophragmines zone (OZ) 12 and shallow benthic zone (SBZ 17), to the well-described coeval assemblages at northern Tethyan platforms in Italy, Hungary, Turkey, and to those in Kutch Basin in the Indian subcontinent suggests that some species are confined to certain paleogeographic domains. Orbitoclypeus haynesi, the only orbitoclypeid and the most abundant orthophragminid in lower Bartonian deposits in Kutch, appears to be the most common orbitoclypeid in Reineche Limestone. In Europe, this species is not known and is replaced by Orbitoclypeus varians, the most common orbitoclypeid in middle Eocene of central Europe. Both species occur in varying proportions in marine successions in Turkey. Asterocyclina sireli, identified so far only in Turkey, occurs in Reineche Limestone and in lower Bartonian deposits in Kutch. This species is recorded for the first time in the Indian subcontinent. Relying on present study, as well as our recent studies in Kutch Basin, we conclude that the generic and specific diversity of orthophragminids decreases eastward from the peri-Mediterranean region to Indian subcontinent and to the western Pacific. 相似文献
26.
R. Yavari S. J. Ahmadi F. Farkhondehru V. Gholipoor L. Kamel 《International Journal of Environmental Science and Technology》2014,11(4):1073-1080
A new organic/inorganic composite based on polyacrylonitrile and stannic molybdophosphate (PAN–SMP) as an adsorbent was synthesized under various conditions. The physicochemical properties of this material were specified by elemental analysis, scanning electron microscopy, infrared spectroscopy and thermogravimetry studies. The synthesized material was found to be stable in demineralized water, in dilute acids, under gamma radiation up to the total radiated of 100 kGy doses and in high temperature up to 500 °C. Ion exchange capacity of the synthesized composite and its distribution coefficient (K d) for several metal ions were determined. The results showed that PAN–SMP has a great affinity toward some metal ions such as Tl+, Sr2+, Ba2+, UO2 2+ and La4+. Based on the determined K d values, two binary quantitative separations of metal ions (Cr6+ from Cu2+ and Pb2+ from Cu2+) have been achieved on columns of this ion exchanger. The ability of PAN–SMP to decontaminate low-level liquid waste was also investigated. 相似文献
27.
We establish the solution of the ninth order — in masses — canonical J-S equations of motion by Hori-Lie technique — i.e., by expressing the initial Poincaré canonical variables as functions of the new variables through the Hori-Lie canonical transformation. Terms of order higher than 9 in the masses are neglected. 相似文献
28.
We expand both parts, the principal and indirect, of the Hamiltonian function up to the third order in the masses for the four major planets Jupiter-Saturn-Uranus-Neptune. Accordingly we write down the secular terms ofF
1,F
2,F
3 and the critical terms ofF
1,F
2 in terms of the canonical variables of H. Poincaré neglecting powers higher than the second inH, K, P, Q. 相似文献
29.
Osman M. Kamel 《Earth, Moon, and Planets》1992,58(1):97-103
Motivated by the recent proposals of A. Abian, we investigate in this paper the second order perturbations up to the second degree in eccentricity-inclination of a new model of our solar system after the landing of Mars or Ceres on the Earth. The theory is established through the HoriLie technique and in terms of Jacobi coordinates and Poincare canonical variables. 相似文献
30.
We expand the planetary Hamiltonian function with its two parts, the principal and the indirect, up to the seventh order in the planetary masses. We adopt the Jacobi-Radau system of origins. The expansiion is valid for any number of planets. 相似文献