全文获取类型
收费全文 | 5848篇 |
免费 | 279篇 |
国内免费 | 103篇 |
专业分类
测绘学 | 173篇 |
大气科学 | 606篇 |
地球物理 | 1672篇 |
地质学 | 2520篇 |
海洋学 | 287篇 |
天文学 | 688篇 |
综合类 | 85篇 |
自然地理 | 199篇 |
出版年
2022年 | 52篇 |
2021年 | 100篇 |
2020年 | 74篇 |
2019年 | 60篇 |
2018年 | 217篇 |
2017年 | 217篇 |
2016年 | 305篇 |
2015年 | 210篇 |
2014年 | 315篇 |
2013年 | 373篇 |
2012年 | 303篇 |
2011年 | 243篇 |
2010年 | 295篇 |
2009年 | 309篇 |
2008年 | 226篇 |
2007年 | 181篇 |
2006年 | 147篇 |
2005年 | 141篇 |
2004年 | 113篇 |
2003年 | 100篇 |
2002年 | 114篇 |
2001年 | 105篇 |
2000年 | 91篇 |
1999年 | 83篇 |
1998年 | 107篇 |
1997年 | 74篇 |
1996年 | 86篇 |
1995年 | 67篇 |
1994年 | 73篇 |
1993年 | 52篇 |
1992年 | 37篇 |
1991年 | 40篇 |
1990年 | 47篇 |
1989年 | 42篇 |
1988年 | 32篇 |
1987年 | 46篇 |
1986年 | 36篇 |
1985年 | 47篇 |
1984年 | 49篇 |
1983年 | 56篇 |
1982年 | 51篇 |
1981年 | 45篇 |
1980年 | 46篇 |
1979年 | 45篇 |
1978年 | 45篇 |
1977年 | 46篇 |
1976年 | 33篇 |
1975年 | 49篇 |
1974年 | 40篇 |
1973年 | 41篇 |
排序方式: 共有6230条查询结果,搜索用时 15 毫秒
81.
Conceptual hydrodynamic model of the Pamukkale hydrothermal field, southwestern Turkey, based on hydrochemical and isotopic data 总被引:4,自引:1,他引:4
Cüneyt Dilsiz 《Hydrogeology Journal》2006,14(4):562-572
The results of study on the hydrochemical and isotope characteristics of shallow and deep waters at Pamukkale hydrothermal
field Turkey are described in order to obtain a better understanding of the hydrological circulation. The field can be grouped
into two groundwater sub-systems; cold water springs of Ca–HCO3 type (10–12 °C), and CO2-rich thermal waters of Ca–HCO3–SO4 type (25–58 °C). The occurrence of these water types is closely related to the morphology of the region, where intense tectonism
formed horst and graben structures. Hence, two hydrogeological systems were defined: a deep geothermal system which is related
to extensive and deep circulation of meteoric water in the regional flow system, and a shallow system which is related to
local groundwater flow through sedimentary strata. The meteoric water falling at higher elevations percolates to the local
groundwater system at a shallow level and flows to the deep geothermal system. During a deep convection cycle from a recharge
to discharge area, the cold water attains heat from the asthenospheric intrusions, causing it to ascend. Variations of chemical
and isotopic composition of thermal waters result from their mixing with cool groundwater in a shallow aquifer during their
ascent to the surface.
Résumé Les résultats d'une étude portant sur les caractéristiques hydrochimiques et isotopiques de puits phréatiques et profonds situés dans le champ hydrothermal de Pamukkale, sont décrits de telle manière à éclairer le fonctionnement des circulations hydrologiques. Le champ peut étre divisé en deux sous-systèmes d'eaux souterraines, l'un avec des eaux de sources froides (10–12 °C) de type Ca–HCO3, et les eaux thermales (25–58 °C) riches en CO2 et de type Ca–HCO3–SO4. L'occurrence de ces types d'eaux est fermement liée à la morphologie de la région, oùne tectonique intense a engendré des structures en horsts et en grabens. Dés lors deux systèmes hydrogéologiques ont été définis : un système profond, qui est lié à la circulation extensive et profonde des eaux météoritiques dans le système régional d'écoulement, et un système phréatique lié aux écoulements locaux des eaux souterraines à travers les strates sédimentaires. Les eaux météoritiques aux altitudes élevées, percolent jusqu'aux systèmes locaux phréatiques, puis coulent jusqu'aux systèmes géothermaux plus profonds. Durant le cycle de convection profond des zones de recharge jusqu'aux zones de décharge, l'eau froide atteint les zones chaudes liées aux intrusions athenosphériques, provoquant la remontée. Les variations de la composition chimique et isotopique des eaux thermales résultent dans leurs mélanges avec des eaux souterraines froides dans les aquifères phréatiques durant leur remontée jusqu'à la surface.
Resumen Se describen los resultados del estudio de las características isotópicas e hidroquímicas de las aguas someras y profundas para obtener un mejor entendimiento de la circulación hidrológica del campo hidrotermal Pamukkale. El campo puede agruparse en dos sub-sistemas de agua subterránea: manantiales de agua fría del tipo Ca–HCO3 (10–12°C) y aguas termales ricas en CO2 del tipo Ca–HCO3–SO4(25–58°C). El ambiente de estos tipos de aguas se relaciona estrechamente con la morfología de la región donde el tectonismo intenso ha formado estructuras extensionales tipo graben y horst. Se definieron dos sistemas hidrogeológicos: un sistema geotermal profundo que se relaciona con la circulación profunda y extensa de agua meteórica en el sistema regional de flujo y un sistema somero el cual se relaciona con flujo local de agua subterránea a través de estratos sedimentarios. El agua meteórica que cae en altas elevaciones percola al sistema local de agua subterránea en un nivel somero y fluye hacia el sistema geotermal profundo. Durante un ciclo de convección del área de recarga hacia la zona de descarga, el agua fría se calienta a partir de los intrusivos astenosféricos lo que ocasiona que asciendan. Como resultado de la mezcla de las aguas recalentadas, con agua subterránea fría en un acuífero somero durante el ascenso hacia la superficie, se derivan variaciones en la composición química e isotópica de las aguas termales.相似文献
82.
A new earthquake catalogue for central, northern and northwestern Europe with unified Mw magnitudes, in part derived from chi-square maximum likelihood regressions, forms the basis for seismic hazard calculations
for the Lower Rhine Embayment. Uncertainties in the various input parameters are introduced, a detailed seismic zonation is
performed and a recently developed technique for maximum expected magnitude estimation is adopted and quantified. Applying
the logic tree algorithm, resulting hazard values with error estimates are obtained as fractile curves (median, 16% and 84%
fractiles and mean) plotted for pga (peak ground acceleration; median values for Cologne 0.7 and 1.2 m/s2 for probabilities of exceedence of 10% and 2%, respectively, in 50 years), 0.4 s (0.8 and 1.5 m/s2) and 1.0 s (0.3 and 0.5 m/s2) pseudoacclerations, and intensity (I0 = 6.5 and 7.2). For the ground motion parameters, rock foundation is assumed. For the area near Cologne and Aachen, maps
show the median and 84% fractile hazard for 2% probability of exceedence in 50 years based on pga (maximum median value about
1.5 m/s2), and 0.4 s (>2 m/s2) and 1.0 s (about 0.8 m/s2) pseudoaccelerations, all for rock. The pga 84% fractile map also has a maximum value above 2 m/s2 and shows similarities with the median map for 0.4 s. In all maps, the maximum values fall within the area 6.2–6.3° E and
50.8–50.9° N, i.e., east of Aachen. 相似文献
83.
84.
Sven O. Franz Lorenz Schwark Cathrin Brüchmann Burkhard Scharf Ralf Klingel Jon D. Van Alstine Namık Çagatay Umut B. Ülgen 《Journal of Paleolimnology》2006,35(4):715-736
A limnogeological reconnaissance study was carried out on Lake Iznik, located in the southeast of the Marmara region of Turkey,
involving a seismic survey and collection of short sediment cores. This lake is located on the middle branch of the North
Anatolian Fault Zone (NAFZ), a transform plate boundary between the Eurasian and Anatolian Plates. It is, therefore, tectonically
active and offers an opportunity to investigate the interplay of sedimentary and seismo-tectonic processes, as well as climate
change and human impact in the region. Short cores of the three sub-basins, maximum length of 35.5 cm, recovered non-laminated,
blackish clays and silts with varying amounts of biogenic and minerogenic (allochthonous, autochthonous) material, which documented
almost the last 80 years of deposition and environmental history. High sedimentation rates in the deeper core sections are
accompanied by changes in land use (conversion of woodland to farmland) in the northern areas of Lake Iznik, which caused
the deposition of more weathered material (high K/Na ratios) and higher contents of Mn in the lake. A tendency towards eutrophic
conditions within the last 20 years is indicated by high nutrient content (N, TOC, P), decreasing C/N-ratios, and characteristic
diatom and cladoceran associations. Also increased pollution is revealed by higher Pb, Cu, and Zn contents and increased supply
of human and animal faeces (high coprostanol content) during the last two decades. But simultaneous lower sedimentation rates
towards the core tops complicate the reconstruction of recent and past eutrophication and pollution states of Lake Iznik.
This requires an extension of the pilot study and deeper sediment cores, to recover non-anthropogenic influenced sediment
levels. 相似文献
85.
Miriam Dühnforth Andreas G. N. Bergner Martin H. Trauth 《Journal of Paleolimnology》2006,36(3):281-294
The Nakuru-Elmenteita basin in the Central Kenya Rift, contains two shallow, alkaline lakes, Lake Nakuru (1770 m above sea level) and Lake Elmenteita (1786 m). Ancient shorelines and lake sediments at 1940 m suggest that these two lakes formed a single large and deep lake as a result of a wetter climate during the early Holocene. Here, we used a hydrological model to compare the precipitation–evaporation balance during the early Holocene to today. Assuming that the Nakuru-Elmenteita basin was hydrologically closed, as it is today, the most likely climate scenario includes a 45% increase in mean-annual precipitation, a 0.5°C decrease in air temperature, and an increase of 9% in cloud coverage from the modern values. Compared to the modeling results from other East African lake basins, this dramatic increase in precipitation seems to be unrealistic. Therefore, we propose a significant flow of water from the early Holocene Lake Naivasha in the south towards the Nakuru-Elmenteita basin to compensate the extremely negative hydrological budget of this basin. Since we did not find any field evidence for a surface connection, as often proposed during the last 70 years, the hydrological deficit of the Nakuru-Elmenteita basin could have also been compensated by a subsurface water exchange. 相似文献
86.
In the Sandıklı (Afyon) region, western Taurides, the Late Proterozoic rocks of the Sandıklı basement complex are composed of low-grade meta-sedimentary rocks (Güvercinoluk Formation) intruded by felsic rocks (Kestel Cayı Porphyroid Suite, KCPS). The KCPS is a deformed and highly sheared, dome-shaped rhyolitic body with a granitic core. Quartz porphyry dikes intrude both the slightly metamorphic igneous and the sedimentary rocks of the basement complex. Both the quartz porphyries and rhyolites were converted into mylonites with relict igneous textures. Geochemical data show that these felsic igneous rocks are subalkaline and mainly granitic in composition with SiO2 >72 wt% and Al2O3 >11.5 wt%. The chondrite-normalized incompatible trace element patterns are characterized by distinct negative Rb, Nb, Sr, P, Ti, and Eu with enrichment in Th, U, La, Ce, Nd, Sm, and Zr. The REE patterns of the felsic rocks indicate a strong enrichment in LREE but display slightly flat HREE patterns. According to geochemical characteristics and petrogenetic modeling, extrusive and intrusive rocks of the KCPS were probably derived from an upper continental crustal source (partial melting of granites/felsic rocks) by 18–20% fractional melting plus 18–20% Rayleigh fractional crystallization, which seems to be the most effective igneous process during the crystallization of the KCPS. Single zircon age data from the granitoids and fossils from the disconformably overlying sedimentary successions indicate that the metamorphism and the igneous event in the Taurides are related to the Cadomian orogeny. Based on the geological, geochemical and petrogenetic correlation of the post-collisional granitoids it is further suggested that the Tauride belt in western central Turkey was in a similar tectonic setting to the Gondwanan terranes in North Africa (Younger Granitoids) and southern Europe (Spain, France, Bohemia, Brno Massifs) during the Late Cadomian period. 相似文献
87.
The formation of colloids during the weathering of phyllite was investigated by exposing ground phyllite to Milli-Q water. Secondary mineral colloids of 101–102 nm were detected in significant concentrations. At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, manganese oxyhydroxides, aluminosilicates, amorphous Al(OH)3 and gibbsite with possible additions of iron silicates and␣iron-alumino silicates. The colloids were stable over longer periods of time (at least several weeks), even in the presence of suspended ground rock. Direct formation of iron-containing secondary mineral colloids at the rock–water interface by the weathering of rock material is an alternative to the well-known mechanism of iron colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine waste rock piles. Colloids produced by this mechanism, too, can influence the transport of contaminants such as actinides because these colloids have a large specific surface area and a high sorption affinity. 相似文献
88.
The devastating 1999 Marmara and Düzce earthquakes led to a significant increase in the earthquake studies in Turkey in geological,
engineering and financial aspects. Extreme Value Theory (EVT) has a range of applications from stock market changes to natural
disasters like floods and hurricanes. Here EVT is fitted to the ordinary and earthquake reinsurance claims of Turkey. 相似文献
89.
90.
A debris flow originating from the Alcamayo River on 10th April 2004 destroyed a part of the town of Aguas Calientes, resulting
in 11 victims, and with serious affects to the tourist flow to the Machupicchu inka citadel. On the same day, as well as in
January and March 2004, other similar phenomena occurred on the Cedrobamba and Leonchayoq Rivers, affecting the railway and
an electrical tower, and disrupting the train service. 相似文献