全文获取类型
收费全文 | 3644篇 |
免费 | 423篇 |
国内免费 | 159篇 |
专业分类
测绘学 | 153篇 |
大气科学 | 228篇 |
地球物理 | 1678篇 |
地质学 | 1151篇 |
海洋学 | 384篇 |
天文学 | 32篇 |
综合类 | 37篇 |
自然地理 | 563篇 |
出版年
2024年 | 13篇 |
2023年 | 21篇 |
2022年 | 29篇 |
2021年 | 72篇 |
2020年 | 152篇 |
2019年 | 133篇 |
2018年 | 112篇 |
2017年 | 164篇 |
2016年 | 159篇 |
2015年 | 131篇 |
2014年 | 157篇 |
2013年 | 366篇 |
2012年 | 79篇 |
2011年 | 115篇 |
2010年 | 110篇 |
2009年 | 170篇 |
2008年 | 244篇 |
2007年 | 231篇 |
2006年 | 208篇 |
2005年 | 192篇 |
2004年 | 151篇 |
2003年 | 124篇 |
2002年 | 109篇 |
2001年 | 95篇 |
2000年 | 117篇 |
1999年 | 116篇 |
1998年 | 113篇 |
1997年 | 102篇 |
1996年 | 73篇 |
1995年 | 75篇 |
1994年 | 55篇 |
1993年 | 60篇 |
1992年 | 36篇 |
1991年 | 30篇 |
1990年 | 26篇 |
1989年 | 22篇 |
1988年 | 23篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有4226条查询结果,搜索用时 15 毫秒
51.
52.
Evaluating fishery impacts using metrics of community structure 总被引:8,自引:14,他引:8
53.
贡湖及其相关水域风生流模拟研究 总被引:9,自引:0,他引:9
在太湖风生流的数值模拟研究的基础上,设计模拟贡湖及其相关水域风生流的套网格数值模式。应用该模式研究不同风情下,梅梁湖,太湖主体湖水对贡湖的影响。 相似文献
54.
Three-dimensional modelling from single images remains an interesting topic of investigation in the research community, even though range sensors are becoming a common alternative for the generation of 3D information. The interest in single-image-based modelling is motivated by a wide spectrum of applications such as cultural heritage, civil engineering, urban planning and even criminology. In this paper a complete new production flowline is presented for modelling based on a single image. The modelling process consists of a series of familiar steps in photogrammetry and computer vision: feature extraction, vanishing point computation, camera self-calibration, 3D reconstruction and dimensional analysis. In particular, the methodology developed for single-image-based modelling takes a scientific approach combining several proven techniques with robust estimators. Finally, in order to demonstrate its capabilities, the reported examples include several real situations applied in different contexts. 相似文献
55.
A data-driven approach to local gravity field modelling using spherical radial basis functions 总被引:3,自引:0,他引:3
We propose a methodology for local gravity field modelling from gravity data using spherical radial basis functions. The methodology
comprises two steps: in step 1, gravity data (gravity anomalies and/or gravity disturbances) are used to estimate the disturbing
potential using least-squares techniques. The latter is represented as a linear combination of spherical radial basis functions
(SRBFs). A data-adaptive strategy is used to select the optimal number, location, and depths of the SRBFs using generalized
cross validation. Variance component estimation is used to determine the optimal regularization parameter and to properly
weight the different data sets. In the second step, the gravimetric height anomalies are combined with observed differences
between global positioning system (GPS) ellipsoidal heights and normal heights. The data combination is written as the solution
of a Cauchy boundary-value problem for the Laplace equation. This allows removal of the non-uniqueness of the problem of local
gravity field modelling from terrestrial gravity data. At the same time, existing systematic distortions in the gravimetric
and geometric height anomalies are also absorbed into the combination. The approach is used to compute a height reference
surface for the Netherlands. The solution is compared with NLGEO2004, the official Dutch height reference surface, which has
been computed using the same data but a Stokes-based approach with kernel modification and a geometric six-parameter “corrector
surface” to fit the gravimetric solution to the GPS-levelling points. A direct comparison of both height reference surfaces
shows an RMS difference of 0.6 cm; the maximum difference is 2.1 cm. A test at independent GPS-levelling control points, confirms
that our solution is in no way inferior to NLGEO2004. 相似文献
56.
Combined subsidence and thermal 1D modelling was performed on six well-sections located in the north-western Mid-Polish Trough/Swell
in the eastern part of the Central European Basin system. The modelling allowed constraining quantitatively both the Mesozoic
subsidence and the magnitude of the Late Cretaceous–Paleocene inversion and erosion. The latter most probably reached 2,400 m
in the Mid-Polish Swell area. The modelled Upper Cretaceous thickness did not exceed 500 m, and probably corresponded to 200–300 m
in the swell area as compared with more than 2,000 m in the adjacent non-inverted part of the basin. Such Upper Cretaceous
thickness pattern implies early onset of inversion processes, probably in the Late Turonian or Coniacian. Our modelling, coupled
with previous results of stratigraphic and seismic studies, demonstrates that the relatively low sedimentation rates in the
inverted part of the basin during the Late Cretaceous were the net result of several discrete pulses of non-deposition and/or
erosion that were progressively more pronounced towards the trough axis. The last phase of inversion started in the Late Maastrichtian
and was responsible for the total amount of erosion, which removed also the reduced Upper Cretaceous deposits. According to
our modelling results, a Late Cretaceous heat-flow regime which is similar to the present-day conditions (about 50 mW/m2) was responsible for the observed organic maturity of the Permian-Mesozoic rocks. This conclusion does not affect the possibility
of Late Carboniferous–Permian and Late Permian–Early Triassic thermal events. 相似文献
57.
The Glueckstadt Graben of the North-German Basin: new insights into the structure from 3D and 2D gravity analyses 总被引:1,自引:0,他引:1
Tamara Yegorova Yuriy Maystrenko Ulf Bayer Magdalena Scheck-Wenderoth 《International Journal of Earth Sciences》2008,97(5):915-930
The structure of the Glueckstadt Graben has been investigated by use of 3D gravity backstripping technique and by 2D gravity
and magnetic modelling. Subtracting the gravity effects of the Meso-Cenozoic sediments together with Permian salt reveals
a positive residual anomaly within the Glueckstadt Graben. This anomaly includes two local maxima over the Westholstein and
Eastholstein Troughs. The 2D gravity models point to the presence of a high-density body within the lower crust of the Glueckstadt
Graben. In addition, the results of 2D magnetic modelling indicate that the central part of the high-density body is overlain
by an area with high susceptibility. Most probable, the formation of this high-density body is a result of complex poly-phase
tectonic history of the study area. Finally, the results of gravity modelling indicate that Permian salt is not homogeneous.
3D gravity analysis and, especially, 2D gravity modelling have distinguished the differences in degree of salt saturation
in salt-rich bodies, and elucidate the proportion of Rotliegend salt. 相似文献
58.
New basis for the constitutive modelling of aggregated soils 总被引:1,自引:1,他引:0
Natural and compacted soils are usually characterized by aggregation of particles. The mechanical behaviour of these materials
depends on soil structure. The oedometric compression tests performed on aggregated samples presented here showed that these
materials exhibit a yield limit depending not only on stress history and stress state but also on soil structure. Evidence
is provided using the neutron tomography technique. These results revealed that soil structure modification occurs together
with plastic deformations. The experimental results are used to propose a new state parameter to quantify the soil structure.
Based on pore-scale experimental observations, an evolution law for this parameter is proposed as a function of associated
plastic strains. Considering both soil fabric and inter-particle bonding effects, a new yield limit depending on stress state,
stress history and soil structure is introduced for the aggregated soils. Accordingly, a new constitutive framework consistent
with strain hardening plasticity is proposed to consider soil structure effects in the modelling of aggregated soils. 相似文献
59.
Changing grading of soil: effect on critical states 总被引:6,自引:3,他引:3
Examples of situations are presented where the grading of a soil changes during its lifetime either by crushing of particles
leading to an increase of fine material or by slow transport of fine particles with seepage leading to a decrease of fine
material. Such grading changes influence the basic constitutive properties of the soil, in particular properties such as critical
states which are dependent on the available range of densities of packing. Discrete element modelling is used to show the
dependence of critical state conditions on grading and the way in which the particle assembly seeks out new critical state
conditions as the grading changes. 相似文献
60.
青藏高原东南缘是研究构造、地貌演化和气候变化相互作用的理想场所,前人研究主要揭示了晚始新世—早中新世和晚中新世以来的快速剥蚀事件,缺乏晚白垩世—早新生代时期地貌演化过程的研究。次林错花岗岩已有的低温热年代学数据覆盖了整个新生代时期,为探索该区域新生代早期的剥露演化历史提供了重要资料。该岩体新生代早期冷却事件是岩浆冷却单一作用的结果,还是受快速剥蚀作用的影响,目前仍然存疑,需要定量研究。因此,本文结合已有的岩石地化和年代学数据,对次林错花岗岩开展了锆石饱和温度和一维岩浆冷却模拟研究。锆石饱和温度计算结果表明次林错花岗岩的岩浆结晶温度介于647~705℃之间,属低温花岗岩。一维岩浆冷却模拟结果显示岩体侵位时的最小围岩温度为160~120℃,对应深度约为3. 7~5. 0 km。结合锆石和磷灰石(U- Th)/He年代学数据,本文认为该岩体在晚白垩世—早新生代时期(67~40 Ma)经历了一期剥蚀量至少为2 km的快速剥蚀事件。已发表成果的综合分析表明,此次快速剥露事件可能是整个青藏高原地区广泛存在的构造剥蚀事件,新特提斯洋的俯冲闭合与印亚板块的初始碰撞可能是触发此次大规模区域剥蚀的主要原因 相似文献