全文获取类型
收费全文 | 2030篇 |
免费 | 69篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 42篇 |
大气科学 | 142篇 |
地球物理 | 969篇 |
地质学 | 508篇 |
海洋学 | 37篇 |
天文学 | 367篇 |
综合类 | 5篇 |
自然地理 | 37篇 |
出版年
2021年 | 24篇 |
2020年 | 27篇 |
2018年 | 54篇 |
2017年 | 66篇 |
2016年 | 94篇 |
2015年 | 77篇 |
2014年 | 88篇 |
2013年 | 100篇 |
2012年 | 41篇 |
2011年 | 55篇 |
2010年 | 79篇 |
2009年 | 65篇 |
2008年 | 55篇 |
2007年 | 54篇 |
2006年 | 37篇 |
2005年 | 22篇 |
2004年 | 30篇 |
2003年 | 35篇 |
2002年 | 36篇 |
2001年 | 24篇 |
2000年 | 28篇 |
1999年 | 20篇 |
1998年 | 32篇 |
1997年 | 21篇 |
1996年 | 40篇 |
1995年 | 24篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 31篇 |
1991年 | 26篇 |
1990年 | 31篇 |
1989年 | 26篇 |
1988年 | 31篇 |
1987年 | 25篇 |
1986年 | 34篇 |
1985年 | 19篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 34篇 |
1981年 | 25篇 |
1980年 | 22篇 |
1979年 | 37篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1975年 | 21篇 |
1974年 | 25篇 |
1973年 | 26篇 |
1972年 | 27篇 |
1971年 | 29篇 |
1970年 | 18篇 |
排序方式: 共有2107条查询结果,搜索用时 234 毫秒
41.
B. Vršnak 《Astrophysics and Space Science》1990,170(1-2):141-147
Eruptive prominences trace disruptions of magnetic arcades in which they are embedded. The stability of an arcade containing an electric current filament at its axis is discussed. The model provides criteria for the onset of the eruptive instability in terms of prominence twist and overall geometry, i.e., the parameters which could be measured directly. The evolution of the eruption is analyzed, and the dependence of the acceleration and the pitch of field-lines on the height is established. The model is compared with the observations of one eruptive prominence where the development of helical structure was followed.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
42.
Summary Climatological studies show that the Altai-Sayan lee side is one of the major cyclogenesis areas in the Northern Hemisphere. In case of the Altai-Sayan lee cyclogenesis, the surface cyclone is generated when a primary cyclone is swept north of the mountains. In the mid-troposphere, a trough develops and finally turns into a cutoff low within 48 h. The main synoptic features are similar to those of Alpine cyclogenesis. Numerical simulations are performed to assess the effect of different representation of orography on the Altai-Sayan cyclogenesis. Two experiments are performed, a step-mountain (ETA) and an envelope orography (SGM) experiment. The ETA experiment produced the cyclogenesis in a way similar to that in the analysis both at the surface and at mid-troposphere. The SGM experiment failed in the simulation of the upper cutoff low. The difference in predicted pressure between the ETA and the SGM experiment shows a dipolar structure suggesting that the blocking effect of the mountains is essential in the development of the Altai-Sayan lee cyclogenesis.With 7 Figures 相似文献
43.
Daniel H. Doctor E. Calvin Alexander Jr Metka Petrič Janja Kogovšek Janko Urbanc Sonja Lojen Willibald Stichler 《Hydrogeology Journal》2006,14(7):1171-1191
Karst aquifer components that contribute to the discharge of a water supply well in the Classical Karst (Kras) region (Italy/Slovenia) were quantitatively estimated during storm events. Results show that water released from storage within the epikarst may comprise as much as two-thirds of conduit flow in a karst aquifer following rainfall. Principal components analysis (PCA) and end-member mixing analysis (EMMA) were performed using major ion chemistry and the stable isotopes of water (δ18O, δ2H) and of dissolved inorganic carbon (δ13CDIC) to estimate mixing proportions among three sources: (1) allogenic river recharge, (2) autogenic recharge, and (3) an anthropogenic component stored within the epikarst. The sinking river most influences the chemical composition of the water-supply well under low-flow conditions; however, this proportion changes rapidly during recharge events. Autogenic recharge water, released from shallow storage in the epikarst, displaces the river water and is observed at the well within hours after the onset of precipitation. The autogenic recharge end member is the second largest component of the well chemistry, and its contribution increases with higher flow. An anthropogenic component derived from epikarstic storage also impacts the well under conditions of elevated hydraulic head, accounting for the majority of the chemical response at the well during the wettest conditions. 相似文献
44.
In the southern Pannonian Basin, the Variscan Barrovian- and overprinted Abukuma-type progressive metamorphic sequences of the South Tisia in Slavonian Mts. (SM) and Mt. Moslava)ka Gora (MG) are interlayered with orthoamphibolites. These sequences represent part of a disrupted Variscan belt that extends southeastwards of the Bohemian Massif through the Carpathians to the Caucasus. Orthoamphibolites contain hornblende (Mg-hornblende, tschermakite, pargasite, and edenite), plagioclase An48-98 (MG) and An26-35 (SM), biotite, grossular (MG) and almandine (SM) enriched garnet, diopside (MG), with accessory ilmenite, titanite, and clinozoisite. Based on major and trace element analyses and CIPW norms, these orthoamphibolites, which originally were olivine tholeiites to slightly alkalic basalts, can be correlated with tholeiites of consuming plate margins. '18O of orthoamphibolites varies from 5.8 to 7.1, the measured 87Sr/86Sr ratio from 0.70435 to 0.70665, which indicates slight continental crust contamination, and the calculated ratio from 0.70262 to 0.70535, indicating an upper mantle origin of the original basaltic melts. For associated penecontemporaneous I-type granitoids, the calculated initial 87Sr/86Sr ratio also have upper mantle values ranging between 0.70293 and 0.70368. Geochemical data for orthoamphibolites and the associated penecontemporaneous I-type granites, and the occurrence of alpine-type ultramafic bodies within the Barrovian sequence, indicate that they have many features in common with orogenic associations related to recent subduction-related settings. Some characteristic element ratios suggest back-arc basin environments and the Ce/K vs. Ce diagram suggests a pargasite-lherzolite source. Its partial melting gave primitive basaltic melts of olivine tholeiite to slight alkalic affinities that produced at first differentiated mafic rocks by olivine fractionation (future orthoamphibolites) and, afterwards, a strongly differentiated suite of I-type granitoids by amphibole fractionation. Magma emplacement and subsequent AFC processes took place in subduction environments preceding the main Variscan deformational metamorphic event during which orthoamphibolites were generated. This interpretation is compatible with geodynamic modeling of this part of the Paleotethys. 相似文献
45.
Correlation Functions of Random Media 总被引:8,自引:0,他引:8
L. Klimeš 《Pure and Applied Geophysics》2002,159(7-8):1811-1831
46.
47.
A new method is presented for the computation of the gravitational attraction of topographic masses when their height information is given on a regular grid. It is shown that the representation of the terrain relief by means of a bilinear surface not only offers a serious alternative to the polyhedra modeling, but also approaches even more smoothly the continuous reality. Inserting a bilinear approximation into the known scheme of deriving closed analytical expressions for the potential and its first-order derivatives for an arbitrarily shaped polyhedron leads to a one-dimensional integration with – apparently – no analytical solution. However, due to the high degree of smoothness of the integrand function, the numerical computation of this integral is very efficient. Numerical tests using synthetic data and a densely sampled digital terrain model in the Bavarian Alps prove that the new method is comparable to or even faster than a terrain modeling using polyhedra. 相似文献
48.
Nikola Stražičić 《GeoJournal》1996,38(4):445-453
Croatia, through its geographic position, is a Mediterranean/Adriatic and Central European/Danube state. As an Adriatic coastal state, it has a long maritime tradition, which is apparent in its well-developed shipping (2.4 million GT), the high-quality ship-building industry (among the top six in the world) and through its numerous sea ports, of which many were established in ancient times. The leading national port is Rijeka, which is at the same time an important transit port for Austria, Hungary, Slovakia and the Czech Republic.The exceptionally indented Croatian Adriatic coast with its attractive archipelagos and favorable climatic and oceanographic conditions in the coastal sea offers very advantageous conditions for comprehensive tourist utilization. This is particularly true of nautical tourism, which is complimented by a larger number of constructed and well-equipped yachting ports/marinas on the coast and islands. 相似文献
49.
The Carpatho-Balkanides and adjacent area: a sector of the Tethyan Eurasian metallogenic belt 总被引:3,自引:1,他引:3
S. Janković 《Mineralium Deposita》1997,32(5):426-433
The Tethyan Eurasian metallogenic belt (TEMB) was formed during Mesozoic and post-Mesozoic times in the area of the former
Tethyan ocean on the southern margin of Eurasia, with the Afro-Arabian and Indian plates to the south. It extends from western
Mediterranean via the Alps and southeastern Europe through the Lesser Caucasus, the Hindu Kush, and the Tibet Plateau to Burma
and SW Indonesia, linking with the West Pacific metallogenic belt. The Carpatho-Balkan region is one of the sectors of the
TEMB, characterized by some specific features. The emplacement of ore deposits is related to a definite time interval, and
to specific tectonic settings such as:
1. Late Permian-Triassic intracontinental rifting along the northern margin of Gondwanaland and/or fragments already separated.
This setting involves volcanogenic and volcano-sedimentary deposits (iron, lead/zinc, manganese, antimony, mercury, barite),
skarn deposits associated with volcano-plutonic complexes of bimodal magmatism, and low temperature carbonate-hosted lead/zinc
deposits.
2. Jurassic intraoceanic rifting – ophiolite complexes: This setting hosts major magmatic (particularly podiform chrome deposits)
and volcano-sedimentary deposits, mainly of the Cyprus type.
3. Subduction-related setting involves porphyry copper deposits, lesser skarn deposits (iron, locally Pb-Zn), massive sulphide
Cu (e.g. Bor) accompanied locally by Pb-Zn of replacement type, epithermal gold deposits, associated with calc-alkaline igneous
complexes of the Early Tertiary-Late Cretaceous, and the Neogene gold/silver and base metals deposits.
4. Post-collision continent-continent setting includes deposits of Pb-Zn, Sb, As, Au-Cu associated with volcano-plutonic complexes
of calc-alkaline affinity.
Several major Alpine metallogenic units are developed in the Carpatho-Balkanides and adjacent area, each characterized by
specific development, mineral associations, and types of ore deposits.
Received: 3 June 1996 / Accepted: 10 January 1997 相似文献
50.
A methodology for improving geopotential models has been developed. Theoretical relations have been derived converting coefficients in harmonic expansions for radial distortions due to geopotential models into geopotential Stokes coefficients. Terms of the order of 10
–10
in magnitude have been retained. 相似文献