全文获取类型
收费全文 | 54487篇 |
免费 | 768篇 |
国内免费 | 612篇 |
专业分类
测绘学 | 1802篇 |
大气科学 | 4108篇 |
地球物理 | 11035篇 |
地质学 | 19326篇 |
海洋学 | 4320篇 |
天文学 | 12157篇 |
综合类 | 172篇 |
自然地理 | 2947篇 |
出版年
2021年 | 385篇 |
2020年 | 404篇 |
2019年 | 436篇 |
2018年 | 1089篇 |
2017年 | 1010篇 |
2016年 | 1374篇 |
2015年 | 848篇 |
2014年 | 1327篇 |
2013年 | 2755篇 |
2012年 | 1464篇 |
2011年 | 1960篇 |
2010年 | 1625篇 |
2009年 | 2170篇 |
2008年 | 1918篇 |
2007年 | 1829篇 |
2006年 | 1883篇 |
2005年 | 1578篇 |
2004年 | 1524篇 |
2003年 | 1474篇 |
2002年 | 1460篇 |
2001年 | 1273篇 |
2000年 | 1269篇 |
1999年 | 1155篇 |
1998年 | 1095篇 |
1997年 | 1111篇 |
1996年 | 974篇 |
1995年 | 943篇 |
1994年 | 895篇 |
1993年 | 801篇 |
1992年 | 730篇 |
1991年 | 710篇 |
1990年 | 755篇 |
1989年 | 642篇 |
1988年 | 664篇 |
1987年 | 774篇 |
1986年 | 655篇 |
1985年 | 886篇 |
1984年 | 958篇 |
1983年 | 940篇 |
1982年 | 830篇 |
1981年 | 743篇 |
1980年 | 759篇 |
1979年 | 667篇 |
1978年 | 671篇 |
1977年 | 615篇 |
1976年 | 609篇 |
1975年 | 575篇 |
1974年 | 630篇 |
1973年 | 643篇 |
1972年 | 407篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
W. Fehlmann 《Aquatic Sciences - Research Across Boundaries》1931,5(1-2):130-141
Ohne Zusammenfassung 相似文献
172.
Regression surface techniques have been used on partial whole-rockchemical analyses from the Puscao pluton to establish the three-dimensionalnature of the chemical variations within this body, which wasemplaced at a depth of between 4 km and 8 km within the crust.Block diagrams produced by the computer program are consistentwith the hypothesis that during the period preceding the totalconsolidation of the magma, the pluton has undergone in situdifferentiation to give a layered structure. Statistical analysis confirms that there is a large scale variationwithin the pluton and that local variation, such as might beexpected to result from the contamination of the Puscao magmaby assimilated volcanic material, did not contribute significantlyto the overall variation. Evidence is presented which suggests that the layering withinthe Puscao pluton was disturbed as a result of the emplacementof the much later Cañhas pluton, and that this disturbancehas the form of a simple doming centred upon the site of thepresent Cañas intrusion. 相似文献
173.
Meysam Fadaee I. Anastasopoulos G. Gazetas M.K. Jafari M. Kamalian 《地震工程与工程振动(英文版)》2013,12(3):473-486
When seismic thrust faults emerge on the ground surface,they are particularly damaging to buildings,bridges and lifelines that lie on the rupture path.To protect a structure founded on a rigid raft,a thick diaphragm-type soil bentonite wall(SBW) is installed in front of and near the foundation,at sufficient depth to intercept the propagating fault rupture.Extensive numerical analyses,verified against reduced–scale(1 g) split box physical model tests,reveal that such a wall,thanks to its high deformability and low shear resistance,"absorbs" the compressive thrust of the fault and forces the rupture to deviate upwards along its length.As a consequence,the foundation is left essentially intact.The effectiveness of SBW is demonstrated to depend on the exact location of the emerging fault and the magnitude of the fault offset.When the latter is large,the unprotected foundation experiences intolerable rigid-body rotation even if the foundation structural distress is not substantial. 相似文献
174.
175.
Observed polarization ellipses for fundamental-mode surface waves observed at a digital station in Hawaii deviate from those expected for isotropic models of crust and mantle structure for that region. The anomalous motion occurs as rotations of the ellipse about all three axes in a cartesian corrdinate system. The largest and most consistent deviations occur as anomalous slopes of the ellipse about the horizontal axis transverse to the direction of propagation.The observed orientations and magnitudes of these angles can be explained by models of the upper mantle which contain olivine for which thea-axis dips significantly from the horizontal and which includes a sufficiently thick sedimentary layer (1 km) and a thicker than normal oceanic crust (15 km). The ellipses are also generally inclined from great circle paths about the vertical axis and are tilted about the axis aligned with the propagation direction. Both angles are small and difficult to measure, but the inclination angles are consistent with a model of the upper mantle in which thea-axis of olivine is preferentially oriented in an east-west direction. 相似文献
176.
Possible orbits for the motion of a region in the gravitational field of the central body of the galaxy NGC 4151 are presented.
The region is manifest through its line emission, observed in the red wing of the Hα, Pβ, and other broad lines. We carried out a computer selection of all Keplerian orbits for which the measured radial velocities
of the emission-line region could be observed. We used radial-velocity data obtained by us at the Fesenkov Astrophysical Institute,
as well as data from the literature. The computation results can be used to determine the mass range for the central body
of NGC 4151 that provides the best agreement with the observational data: (61–65)× 106
M
⊙. Suitably designed monitoring of active galactic nuclei can be used to verify these results, and to carry out similar analyses
for other Seyfert galaxies. 相似文献
177.
Time lapse movies acquired with the Sacramento Peak Observatory 6-in filter coronagraph very infrequently show dramatic transient events. Many of these events (at 1.04 < r/r
< 1.20) are correlated with H activity at the limb, especially with large surges and eruptive prominences. Metric or centrimetric radio bursts are found associated with certain types of 5303 coronal events. The heights to which such disturbances will propagate can often be estimated from the green line movie data. We report the results of a study of all the examples of such transients observed during the last 16 years. 相似文献
178.
K. Schneider-Carius 《Pure and Applied Geophysics》1949,15(3-4):236-241
Ohne Zusammenfassung 相似文献
179.
Gisela Björse Richard H. W. Bradshaw Daniel B. Michelson 《Journal of Paleolimnology》1996,16(1):67-78
A method was developed to construct maps of former forest types based on regional pollen data in southern Sweden. The considered species were Alnus, Betula, Carpinus, Corylus, Fagus, Fraxinus, Juniperus, Picea, Pinus, Populus, Quercus, Salix, Tilia and Ulmus. A network of 37 regional pollen sites with high data quality from lakes and peat deposits were selected from Sweden south of 60 ° N. Pollen percentage values were calculated and converted into estimates of tree composition. For controlling the reliability of the reconstruction, the estimates from the core-tops were compared with present day forest inventory data, and local pollen diagrams were compared with the regional pollen diagrams. An inverse distance weighted interpolation algorithm was used to generate maps for each tree species distribution at 2000 BP, 1500 BP, 1000 BP, 500 BP and 0 BP. A supervised classification routine was implemented to generate nine different forest types common to the five studied time intervals. The maps show that the amounts and patterns of distribution of the species and the forest types have varied in a significant but systematic manner through time. The changes are due to human activities, migrational patterns and changes in climate. These maps will be of value as a basis for future landscape planning, forestry and conservation of biodiversity.This is the 20th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers. 相似文献
180.
There is a need to bridge theory and practice for incorporating parameter uncertainty in geostatistical simulation modeling workflows. Simulation workflows are a standard practice in natural resource and recovery modeling, but the incorporation of multivariate parameter uncertainty into those workflows is challenging. However, the objectives can be met without considerable extra effort and programming. The sampling distributions of statistics comprise the core theoretical notion with the addition of the spatial degrees of freedom to account for the redundancy in the spatially correlated data. Prior parameter uncertainty is estimated from multivariate spatial resampling. Simulation-based transfer of prior parameter uncertainty results in posterior distributions which are updated by data conditioning and the model domain extents and configuration. The results are theoretically tractable and practical to achieve, providing realistic assessments of uncertainty by accounting for large-scale parameter uncertainty, which is often the most important component impacting a project. A simulation-based multivariate workflow demonstrates joint modeling of intrinsic shale properties and uncertainty in estimated ultimate recovery in a shale gas project. The multivariate workflow accounts for joint prior parameter uncertainty given the current well locations and results in posterior estimates on global distributions of all modeled properties. This is achieved by transferring the joint prior parameter uncertainty through conditional simulations. 相似文献