全文获取类型
收费全文 | 4293篇 |
免费 | 159篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 172篇 |
大气科学 | 623篇 |
地球物理 | 1005篇 |
地质学 | 1748篇 |
海洋学 | 186篇 |
天文学 | 555篇 |
综合类 | 18篇 |
自然地理 | 159篇 |
出版年
2021年 | 66篇 |
2020年 | 59篇 |
2019年 | 43篇 |
2018年 | 132篇 |
2017年 | 149篇 |
2016年 | 221篇 |
2015年 | 132篇 |
2014年 | 204篇 |
2013年 | 264篇 |
2012年 | 110篇 |
2011年 | 171篇 |
2010年 | 182篇 |
2009年 | 211篇 |
2008年 | 146篇 |
2007年 | 107篇 |
2006年 | 106篇 |
2005年 | 87篇 |
2004年 | 56篇 |
2003年 | 66篇 |
2002年 | 94篇 |
2001年 | 84篇 |
2000年 | 72篇 |
1999年 | 73篇 |
1998年 | 71篇 |
1997年 | 62篇 |
1996年 | 55篇 |
1995年 | 67篇 |
1994年 | 74篇 |
1993年 | 33篇 |
1992年 | 36篇 |
1991年 | 32篇 |
1990年 | 45篇 |
1989年 | 38篇 |
1988年 | 32篇 |
1987年 | 32篇 |
1985年 | 48篇 |
1984年 | 49篇 |
1983年 | 58篇 |
1982年 | 43篇 |
1981年 | 42篇 |
1980年 | 41篇 |
1979年 | 35篇 |
1978年 | 57篇 |
1977年 | 33篇 |
1976年 | 33篇 |
1975年 | 48篇 |
1974年 | 52篇 |
1973年 | 51篇 |
1970年 | 26篇 |
1968年 | 25篇 |
排序方式: 共有4466条查询结果,搜索用时 15 毫秒
91.
Nassima Atmaoui Nina Kukowski Bernhard Stöckhert Diethard König 《International Journal of Earth Sciences》2006,95(2):225-238
Typical pull-apart structures were created in scaled clay experiments with a pure strike-slip geometry (Riedel type experiments). A clay slab represents the sedimentary cover above a strike-slip fault in the rigid basement. At an early stage of the development of the deformation zone, synthetic shear fractures (Riedel shears) within the clay slab display dilatational behaviour. With increasing basal displacement the Riedel shears rotate and open further, developing into long, narrow and deep troughs. The shear displacement and the low angle with the prescribed principal basal fault set them apart from tension gashes. At a more evolved stage, synthetic segments (Y-shears) parallel to the basal principal fault develop and accommodate progressive strike-slip deformation. The Y-shears connect the tips of adjacent troughs developed from the earlier Riedel shears, resulting in the typical rhomb-shaped structures characteristic for pull-apart basins. The Strait of Sicily rift zone, with major strike-slip systems being active from the Miocene to the Present, comprises pull-apart basins at different length scales, for which the structural record suggests development by a mechanism similar to that observed in our experiments. 相似文献
92.
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
93.
Four of the major plutons in the vicinity of the Candelaria mine (470 Mt at 0.95% Cu, 0.22 g/t Au, 3.1 g/t Ag) and a dike–sill system exposed in the Candelaria open pit have been dated with the U–Pb zircon method. The new geochronological data indicate that dacite magmatism around 123 Ma preceded the crystallization of hornblende diorite (Khd) at 118 ± 1 Ma, quartz–monzonite porphyry (Kqm) at 116.3 ± 0.4 Ma, monzodiorite (Kmd) at 115.5 ± 0.4 Ma, and tonalite (Kt) at 110.7 ± 0.4 Ma. The new ages of the plutons are consistent with field relationships regarding the relative timing of emplacement. Plutonism temporally overlaps with the iron oxide Cu–Au mineralization (Re–Os molybdenite ages at ∼115 Ma) and silicate alteration (ages mainly from 114 to 116 and 110 to 112 Ma) in the Candelaria–Punta del Cobre district. The dated dacite porphyry and hornblende diorite intrusions preceded the ore formation. A genetic link of the metallic mineralization with the quartz–monzonite porphyry and/or the monzodiorite is likely. Both of these metaluminous, shoshonitic (high-K) intrusions could have provided energy and contributed fluids, metals, and sulfur to the hydrothermal system that caused the iron oxide Cu–Au mineralization. The age of the tonalite at 110.7 Ma falls in the same range as the late alteration at 110 to 112 Ma. Tonalite emplacement may have sustained existing or driven newly developed hydrothermal cells that caused this late alteration or modified 40Ar/39Ar and K/Ar systematic in some areas. 相似文献
94.
95.
Skier-triggered avalanches are the main cause of avalanche accidents in backcountry skiing. The risk of accidents during backcountry
skiing was analysed statistically and related to factors such as elevation level, aspect, stability rating and the time of
the year. The analysis is based on a database about terrain usage and avalanche accidents from a large heli-skiing operator
in Canada, which makes it possible to study the conditional probability of accidents given the recorded pattern of terrain
usage. This study shows that the historical risk of accidentally triggering an avalanche greater than size 1 depends highly
on the stability rating, with the highest risk occurring during “poor” stability. The risk is greater at high elevations,
and it is lower during the late season than earlier on. Skier risk does not depend as much on aspect as may be indicated from
avalanche data alone. However, it is relatively high in the N–NE–E sector. These factors are not independent of each other
and therefore analyses of combined factors were also performed. Questionnaires and interviews were used to gain knowledge
about the terrain selection of professional mountain guides. These results indicate that when selecting terrain, guides first
look at the overall shape and size of the terrain, but avalanche history of terrain and inclination are also important factors.
Finally, remarks in avalanche reports were analysed, and common human factors identified. 相似文献
96.
Summary ?Microclimatological data obtained during a field experiment in the nongrowing winter period were used to study the microclimatologically
stable night conditions of a 200 × 150 m miscanthus (Miscanthus cv. giganteus) stand and compared to open field conditions. The microclimatological pattern within the miscanthus canopy
was characterized by long-wave radiative cooling of the plant stand and by an established temperature inversion within the
canopy at calm nights. The results show that there are significant differences in air temperature and energy balance components
between the open field and the miscanthus field during calm and clear nights. In general, net radiation difference during
the cold and calm nights was relatively constant and about 20 W m−2 less negative in miscanthus (because of lower surface temperatures) than at the open field. Air temperature differences also
remained fairly constant and were up to 3 °C lower than at the open field (at the height of 1 m). Through thermal inversion
cold air accumulated in the lower parts of the canopy as shown by the vertical air temperature profiles. They showed a greater
amplitude within the diurnal cycle in the miscanthus stand than in the open field. Through the onset of wind, temperature
profiles changed rapidly and differences diminished. Vertical katabatic air drainage into the canopy layers was estimated
indirectly by using the energy balance approach. It was calculated from the significant energy balance closure gap and showed
a mean air exchange rate of up to 22 m3 m−2 h−1, related to a stand volume of 1 m2 area and 4 m height, during the mostly calm and clear nights, depending on the canopy net radiation and turbulent heat exchange
forced by slight wind spells. Quantitative uncertainties in calculated cold air drainage which are introduced by the measurement
method and certain assumptions in the calculations, were considered in a sensitivity analysis. In spite of these uncertainties
evidence of katabatic cold air flow is given.
Received July 29, 1999; revised June 11, 2001; accepted March 14, 2002 相似文献
97.
Anders Moberg Hans Bergström Josefin Ruiz Krigsman Ola Svanered 《Climatic change》2002,53(1-3):171-212
Daily meteorological observations have been made at the old astronomical observatory in Stockholm since 1754. Complete daily mean series of air temperature and sea level pressure are reconstructed from the observational data for 1756–1998. The temperature and pressure series arereconstructed and homogenized with the aid of metadata, statistical tests and comparisons with data from other stations. Comparisons with independently reconstructed daily series for nearby Uppsala (1722–1998) show that the quality of thedaily Stockholm data is good, although the reliability is lower before the mid-19th century. The daily temperature data show that the colder winter mean temperatures of the late 18th to early 19th centuries were connected with a particularly high frequency of very cold winter days. The warmer summers of the same period are more connected with a general shift of the temperature distribution towards higher temperatures than in the late 20th century. 相似文献
98.
Ulrich Lange Michael Bröcker Klaus Mezger Jerzy Don 《International Journal of Earth Sciences》2002,91(6):1005-1016
Amphibolite-facies orthogneisses of the Orlica-vnienik dome in the West Sudetes (Poland) show a local continuous transition from weakly deformed augen gneisses to finely laminated mylonites. Field evidence indicates that ductile shearing developed pre- or syntectonically to a migmatization event. Bulk-rock compositions of variably deformed samples yield no indications for deformation- and/or fluid-enhanced element mobility and redistribution. 87Rb-86Sr geochronology (biotite, phengite, whole rock) places time constraints on the deformation process and the post-orogenic cooling history. Phengite- and biotite-whole-rock pairs yield Rb-Sr ages of 340 to 334 Ma and 335 to 294 Ma, respectively, independent of the degree of deformation. The weighted mean of phengite-whole-rock pairs indicates an age of 337.4DŽ.3 Ma. Combining most of the biotite-whole-rock data yields a weighted mean age of 328.6dž.4 Ma. Because of their different closure temperatures for the Rb-Sr system, these differences are interpreted to date cooling after a thermal event. Direct dating of the deformation is not possible, but the cooling history record defines a minimum age for the development of ductile shearing and the last migmatization event. These time constraints provide evidence for the initiation of crustal collapse during or immediately following peak metamorphic conditions. The results of this study further document the importance of Variscan metamorphism in the Orlica-vnienik dome. 相似文献
99.
100.
Abundance and distribution of PGE and Au in the island-arc mantle: implications for sub-arc metasomatism 总被引:5,自引:0,他引:5
Ultramafic xenoliths from a veined mantle wedge beneath the Kamchatka arc have non-chondritic, fractionated chondrite-normalized platinum-group element (PGE) patterns. Depleted (e.g., low bulk-rock Al2O3 and CaO contents) mantle harzburgites show clear enrichment in the Pd group relative to the Ir group PGEs and, in most samples, Pt relative to Rh and Pd. These PGE signatures most likely reflect multi-stage melting which selectively concentrates Pt in Pt–Fe alloys while strongly depleting the sub-arc mantle wedge in incompatible elements. Elevated gold concentrations and enrichment of strongly incompatible enrichment (e.g., Ba and Th) in some harzburgites suggest a late-stage metasomatism by slab-derived, saline hydrous fluids. Positive Pt, Pd, and Au anomalies coupled with Ir depletions in heavily metasomatized pyroxenite xenoliths probably reflect the relative mobility of the Pd and Ir groups (especially Os) during sub-arc metasomatism which is consistent with Os systematics in arc mantle nodules. Positive correlations between Pt, Pd, and Au and various incompatible elements (Hf, U, Ta, and Sr) also suggest that both slab-derived hydrous fluids and siliceous melts were involved in the sub-arc mantle metasomatism beneath the Kamchatka arc. 相似文献