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991.
I. S. Krassivskaya E. V. Sharkov N. S. Bortnikov A. V. Chistyakov N. V. Trubkin T. I. Golovanova 《Petrology》2010,18(3):263-277
Altered variolites described for the first time in the axial zone of the Mid-Atlantic Ridge are represented by rounded globules
of andesite (icelandite) composition with light trachyandesite rim embedded in a picrobasaltic matrix. The globules were transferred
with picrobasaltic melt and then floated to the surface of lava flow, while formation of leucocratic rims was presumably related
to thermodiffusion (Soret effect) in a cooling heterogeneous melt. This heterogeneous melt was formed by penetration of ascending
column of picrobasaltic magma in already existing small intracructsal magmatic chamber filled with residual icelanditetype
andesite melt and involvement of the latter into a general upward movement. The rapid ascent of the melts in the oceanic spreading
zones by means of turbulent flowing caused dispersion of the extragenous melt into small drops in a jet of picrobasaltic magma,
without their interaction. Variolites were formed during cooling of such heterogeneous lava flow. No signs of liquid immiscibility
were found in the studied variolites. 相似文献
992.
A. V. Kudymov 《Russian Journal of Pacific Geology》2010,4(6):495-501
The study of tectonic sliding surfaces (hereafter, slickensides) and striae, as well as strike-slip echelons of quartz streaks,
in the Kiselevka fault zone made it possible to reconstruct four groups of stress fields with a wide age range (from the Paleocene
to Recent). The meridional compression and latitudinal extension of the earliest stress field promoted the left-lateral displacement
along the Kiselevka fault. The fault activation in that period was accompanied by the final-phase magmatite formation in the
East Sikhote-Alin volcanoplutonic belt. In contrast, the subsequent stress field of the sublatitudinal compression and submeridional
extension changed the fault kinematics to right-lateral strike-slip ones. The origin and development of the Udyl intermontane
depression is linked to these deformations. Upthrow deformations complicated the structure of the Udyl depression, whereas
normal fault deformations produced the depression of Lake Udyl and the bays along the left bank of the Amur River. 相似文献
993.
Newly obtained petrological and geochemical data on Late Mesozoic-Cenozoic volcanic complexes in the Japan, Okhotsk, and Philippine
marginal seas of the Pacific Ocean made it possible to specify the types and characteristics of various stages of volcanism
in the seas, trace the evolutionary history of the volcanic processes, and identify the geodynamic environments in which the
deep-sea basins were formed, as well as to distinguish inherent features in the evolution of marginal seas in the continent-ocean
transition zone in the Central Asian sector of the Pacific Ocean. These features imply that the processes that formed this
zone in the region were similar. Significant differences revealed between the zones in the region were predetermined, first
of all, by the different types of the Earth’s crust that was involved in the major tectonic-magmatic processes and participated
in the generation of the magmatic melts. 相似文献
994.
Willapa Bay is a large, economically and ecologically important estuary on the Washington coast, USA for which the zooplankton
community has not previously been studied. Thus, in 2006 and 2007, six stations within Willapa Bay were sampled biweekly for
macrozooplankton, chlorophyll, and various abiotic variables to elucidate the processes underlying community composition and
dynamics. Non-metric multidimensional scaling identified water temperature and upwelling values as major factors defining
two distinct temporal communities. High densities and a community dominated by oceanic species (Calanus pacificus, Centropages abdominalis) marked the winter season, while summer (or the upwelling season) was dominated by estuarine species (Palaemonidae, Clevelandia ios). Smaller scale changes in the community were characterized by variation in chlorophyll a concentration and salinity and were marked by the presence of other taxa (Neotrypaea californiensis, Mysidae). These results point to the importance of physical processes, including the import of marine organisms and retention
of estuarine organisms, in the structuring of the macrozooplankton community in Willapa Bay. 相似文献
995.
G. Abate M. R. Massimino M. Maugeri D. Muir Wood 《Geotechnical and Geological Engineering》2010,28(1):37-59
Dynamic soil-structure interaction (DSSI) plays a fundamental role in many geotechnical and/or structural design situations,
as clearly shown by the damage which occurred during several recent earthquakes (Kobe 1995; Koaceli 1999; Chi-Chi 1999; L’Aquila
2009). For a long time civil engineering researchers have devoted increasing attention to this subject. Thanks to their efforts,
several technical regulations, such as EC8 (2003), have taken DSSI into account. However, many steps are still necessary in order to increase our knowledge regarding this
complex phenomenon, as well as to make all the results achieved known to academics and practitioners. This paper presents
the results of a shaking table test performed on a scaled physical model consisting of a 3-D steel frame resting on a bed
of sand. The experimental results are compared with the numerical ones obtained using a sophisticated elasto-plastic constitutive
model recently implemented in the FEM code utilised. The solution of geotechnical problems requires the use of appropriate
constitutive models. Many interesting constitutive models have been developed, but only a few of these have been implemented
into commercial numerical codes; which is particularly so when dynamic analyses are required. The described experimental results,
as well as the comparison between them and the numerical results, allow interesting considerations to be drawn on dynamic
soil-structure interaction and on its numerical simulation. 相似文献
996.
997.
Evangelos P. Tziritis 《Environmental Earth Sciences》2010,60(7):1381-1390
Kopaida plain is a cultivated region of Eastern Greece, with specific characteristic related with the paleogeographic evolution
and the changes in land use. The present article examines the contamination that derives from nitrates, in terms of contaminant
levels, definition of sources and spatial distribution of contaminant plume. For this purpose, 50 water samples were collected
from the karstic aquifer and analyzed for 15 parameters including major ions, trace elements, physicochemical parameters,
and stable isotopes. The assessment of the above parameter values along with the notes derived by the statistical process
revealed the existence of nitrate contamination which has been spatial defined with the aid of spatial interpolation techniques.
The correlation of NO3
− concentrations with the stable isotope values, defined the infiltration conditions and showed contaminant transport. Nitrate
values revealed the potential environmental threat for local people, as 10% of the samples exceeded the parametric value of
50 ppm and 54% of them are above 25 ppm, indicating no optimal quality conditions. The origin of nitrate contamination seems
to derive exclusively from the application of N-fertilizers, since the rest of potential sources were not verified by analytical
data and field works. 相似文献
998.
Controlling factors of loess landslides in western China 总被引:4,自引:1,他引:4
Based on detailed field data from recent geo-hazards surveys in the Loess Plateau region of western China, this study analyzes
the key factors that control loess landslides. The evolution phase of river valleys, the geological structure of slopes and
the geometry of slopes are all found to play a role in determining the occurrence, distribution and other characteristics
of loess landslides. Groundwater and vegetation also contribute to their formation. A combination of human engineering activities
and precipitation events are the principal triggering factors for the instability of loess slopes. 相似文献
999.
1000.
A sequence of mineral associations was examined in eclogitized basites of the Krasnaya Guba dike field in the Belomorian Mobile
Belt. Two morphological types of eclogite and eclogite-like rocks were recognized: (1) eclogite rocks that developed after
ferrogabbro dikes and completely replaced these dikes from contact to contact and (2) eclogite-like rocks that developed after
gabbronorites in zones of ductile deformations and shearing. According to data mineral geothermobaromety, both rock types
were formed within temperature and pressure ranges corresponding to high-pressure and high-temperature amphibolite facies
at T = 700 ± 40°C and P = 10.0 ± 0.5 kbar. The peak metamorphic parameters of the host gneisses are analogous. The decompressional stage, which is
unambiguously identified by reaction textures, occurred at 630–660°C and 7.9–8.2 kbar. As the temperature and, first of all,
pressure decreased, the SiO2 activity in the fluid systematically varied. The eclogitization of the basites took place locally in relation to fluid fluxes,
which were restricted to zones of intense deformations, at variable SiO2 activity. The rocks show evidence of two stages of post-eclogite amphibolization. Older amphibolization 1 was coeval with
the late prograde metamorphic stage (T = 650°C, P = 10–11 kbar). Younger amphibolization 2 affected eclogitized basite dikes and unaltered gabbronorites (together with their
host gneisses) over large areas. This process coincided with decompression (T = 580°C, P = 7–8 kbar) and was likely accompanied by the exhumation of deep zones of BMB to upper-middle crustal levels. 相似文献