全文获取类型
收费全文 | 7455篇 |
免费 | 678篇 |
国内免费 | 168篇 |
专业分类
测绘学 | 292篇 |
大气科学 | 764篇 |
地球物理 | 2525篇 |
地质学 | 2985篇 |
海洋学 | 592篇 |
天文学 | 549篇 |
综合类 | 200篇 |
自然地理 | 394篇 |
出版年
2023年 | 10篇 |
2022年 | 30篇 |
2021年 | 63篇 |
2020年 | 53篇 |
2019年 | 67篇 |
2018年 | 526篇 |
2017年 | 481篇 |
2016年 | 383篇 |
2015年 | 261篇 |
2014年 | 236篇 |
2013年 | 259篇 |
2012年 | 756篇 |
2011年 | 601篇 |
2010年 | 250篇 |
2009年 | 297篇 |
2008年 | 262篇 |
2007年 | 226篇 |
2006年 | 220篇 |
2005年 | 900篇 |
2004年 | 957篇 |
2003年 | 706篇 |
2002年 | 218篇 |
2001年 | 104篇 |
2000年 | 72篇 |
1999年 | 30篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1973年 | 5篇 |
1965年 | 6篇 |
1963年 | 4篇 |
排序方式: 共有8301条查询结果,搜索用时 31 毫秒
1.
2.
3.
Emilio Donoso Ana O'Mill Diego G. Lambas 《Monthly notices of the Royal Astronomical Society》2006,369(1):479-484
We analyse a high-redshift sample (0.4 < z < 0.5) of luminous red galaxies (LRGs) extracted from the Sloan Digital Sky Survey data release 4 and their surrounding structures to explore the presence of alignment effects of these bright galaxies with neighbour objects. In order to avoid projection effects, we compute photometric redshifts for galaxies within 3 h −1 Mpc in projection of LRGs and calculate the relative angle between the LRG major axis and the direction to neighbours within 1000 km s−1 . We find a clear signal of alignment between LRG orientations and the distribution of galaxies within 1.5 h −1 Mpc. The alignment effects are present only for the red population of tracers; LRG orientation is uncorrelated to the blue population of neighbour galaxies. These results add evidence to the alignment effects between primaries and satellites detected at low redshifts. We conclude that such alignments were already present at z ∼ 0.5. 相似文献
4.
5.
Summary A model of radial drifting and oscillating dipoles to represent geomagnetic palaeosecular variations, which showed to be appropriate for the Southern Hemisphere, is evaluated for the Northern Hemisphere. After a new fitting of some involved parameters, its theoretical results are compared with the palaeomagnetic data of Lake de Bouchet (France) and the Black Sea. A time lag between the declination and inclination profiles is observed in both cases. A good cross-correlation coefficient is obtained for the declination and inclination data.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990. 相似文献
6.
An Example of Island-Arc Petrogenesis: Geochemistry and Petrology of the Southern Luzon Arc, Philippines 总被引:7,自引:1,他引:6
DEFANT MARC J.; MAURY REN? C.; RIPLEY EDWARD M.; FEIGENSON MARK D.; JACQUES DARIO 《Journal of Petrology》1991,32(3):455-500
Volcanism throughout the Luzon arc is associated with eastwardsubduction of the South China Sea floor along the Manila Trench.The southern section of the arc, the focus of this study, extendsfrom the Lingayen-Dingalan fault to the small islands just southof Luzon. Two segments appear to exist along this section ofthe arc the northern Bataan and southern Mindoro segments whichare separated by the Macolod Corridor. The volcanic rocks have typical arc phenocryst mineralogies:olivine, clinopyroxene, plagioclase, and titanomagnetite inthe most mafic rocks and clinopyroxene, plagioclase, orthopyroxene,titanomagnetite, ? amphibole in the more felsic samples. Complexzoning, sieve textures, and decoupling of incompatible traceelements suggest that processes such as assimilation have takenplace. The rocks from the study area range from basalts to rhyolitesand show typical calc-alkaline features. The rocks of the MacolodCorridor and Mindoro segment are particularly enriched in largeion lithophile elements (LILE), light rare earth elements (LREE),and radiogenic Sr compared with the Bataan segment. The datafall within the mantle array on Sr-Nd isotopic diagrams andgrade toward higher Sr and lower Nd isotopic values from northto south. A likely source for the volcanics of this study is either amid-ocean ridge basalt (MORB)-type mantle that undergoes higherdegrees of partial melting than regions involved in MORB generationor a previously depleted source. We suggest that the high fieldstrength element (HFSE) anomalies have been derived throughdifferential element partitioning during fluid transport fromthe subducted lithosphere to the mantle wedge. Continental crustal material seems to play a significant roleparticularly in the Macolod Corridor and the Mindoro segment,based on the high LILE, La/Sm ratios, radiogenic Sr isotopes,and 18O values. The Macolod Corridor and the Mindoro segmenthave undergone source contamination by crustal material fromthe North Palawan-Mindoro crustal block either during the collisionof this block with the Manila Trench or by subduction of sedimentsrich in this crustal material. A similar component has alsobeen detected in the Bataan segment but in minor amounts. Thetrace element and isotopic differences between the northernand southern sections of the arc are interpreted in terms ofvariable composition (i. e., variable amounts of a crustal componentintroduced from the Palawan-Mindoro crustal terrain) of themetasomatic fluids released into the source. 相似文献
7.
Clay mineralogy and whole-rock stable isotopes (δ18O and δ13C) of Upper Cretaceous marly sediments on the Basque-Cantabrian Basin have been integrated to determine the main effects of diagenesis, palaeoclimate and tectono-sedimentary factors in sections belonging to deep- (Barrika) and platform-marine (Isla de Castro, Villamartín and Olazagutía) settings.The mean values for the clay assemblages and δ18O exhibit notable differences among the sections, partially explainable by the influence of diagenesis. The Barrika sediments, with more diagenetically advanced illite-smectite (I-S) mixed-layer (R1, 70% illite), authigenic chlorite, and low δ18O (−4.05‰ PDB), experienced higher diagenetic grade than Isla de Castro and Olazagutía, which have R0 I-S (20% illite) and heavier δ18O. Villamartín was also affected by higher diagenesis than Isla de Castro and Olazagutía, given the occurrence of R1 I-S (60% illite) and low δ18O (−4.11‰ PDB). However, the absence of other clays in Villamartín (e.g. authigenic chlorite) is indicative of less diagenetic grade than Barrika. These results show the useful integration of clay mineralogy and stable isotopes to detect different diagenetic grades in distinct marine successions of the same basin.Despite being influenced by diagenesis, the clay mineralogy partially preserves its inherited signature. This allows detection of major contents of I-S and mica, and minor kaolinite, interpreted as indicative of warm palaeoclimatic conditions. High kaolinite content in Villamartín and absence of kaolinite in Isla de Castro, though, are considered to be a product of neither diagenesis nor palaeoclimatic influences. Instead, tectono-sedimentary causes, related to unsuitable conditions for clay formation and transport from the local source areas, contributed to original clay differences. The inferred effects of diagenesis, palaeoclimate and tectono-sedimentary factors make this work important to show the potentially great variety of controls on the clay mineralogy of marine sections, which are often uncritically treated in studies concerning the Late Cretaceous. 相似文献
8.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献
9.
Jos M. Marques Paula M. Carreira Maria Rosrio Carvalho Maria J. Matias Fraser E. Goff Maria J. Basto Rui C. Graa Luís Aires-Barros Luís Rocha 《Applied Geochemistry》2008,23(12):3278-3289
This paper reviews the geochemical, isotopic (2H, 18O, 13C, 3H and 14C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO3 type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ2H and δ18O suggest a common meteoric origin and that the Mg–HCO3 type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO3 to Mg–HCO3 waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO2 (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of 14C and 13C values, which is in agreement with the 3H concentrations being below the detection limit. 相似文献
10.
Vittorio Zanon Fátima Viveiros Catarina Silva Ana Rita Hipólito Teresa Ferreira 《Natural Hazards》2008,45(1):19-31
A detailed study was carried out on a piece of land that had been struck by lightning during the violent rainstorm that raged
over the Island of S?o Miguel (Azores Archipelago) in late October 2006. Temperature and gas measurements (CO2, CO, H2S and CH4) were performed in four study trenches, dug in an area of ∼3 m2, where an underground fire had been initiated by the impact with a lightning stroke, followed by the emission of a column
of gases and smoke. The soil under study was originally a well-pedogenized about 80 cm thick bed, made of volcanic clayey
to silty tephra fallouts and contained 5.5–9.7% of organic matter. The underground fire was monitored for one week and revealed a peak release of
404 ppm CO and 3.4% CO2 originating from a horizon located about 45 cm under the soil surface. Measurements of temperature, performed one week after
the impact, indicated a maximum value of 326°C inside the soil, while 516.5°C were measured on the surface of a lava block
interred about 20 cm under the surface. Subsequently, a stratigraphic and sedimentologic study proved the role of the grain-size
of the soil and of the organic matter content of the different horizons of the impact area, in determining the ratio between
anoxic/oxidised combustion conditions and in the progress of the process itself. It was also noticed that combustion was not
total all over in the soil bed and that the process had slightly migrated toward SW during the observation period. The combustion
process went on for about ten days, in spite of several other violent rainstorms, until it was artificially extinguished through
the excavations made to obtain study trenches. This particular circumstance evidenced the potential natural hazard represented
by this kind of atmospheric event, especially in a land where the volcanic nature of the soil may easily mislead inexperienced
observers and, consequently, delay proper action. 相似文献