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991.
长江带现代地震构造应力场分布特征 总被引:1,自引:0,他引:1
根据长江带76个地震震源机制解与17个小震综合断层面解的结果统计分析,得到该带地震应力场主应力方向的优势分布。表明该带处于北东东—南东东向挤压和北北西—近南北向引张的构造应力作用之中。在力的性质上,该带水平张应力高于水平压应力,斜向压应力又高于斜向张应力,与华北地区比较,主应力方向相对向东南方向偏转,该带水平力和斜力所占比例均高于华北地区,同时讨论了该带中三个分区的现代构造应力场分布及它们的力源关系。 相似文献
992.
A substantial proportion of the glacial sediments of East Anglia, England, are chaotic and highly deformed. This has been attributed to (a) direct glaciotectonic deformation or (b) slumping of glaciomarine sediments. We show that interpretation (a) leads to a classification of subglacial glaciotectonic deposits into sites of ‘constructional deformation’, where little or no erosion of the preglacial deposits has occurred and styles of deformation are preserved moving up in the sequence, and ‘excavational deformation’, where substantial erosion of preglacial sediments has occurred and deformational styles are superimposed on each other. By using glaciological and geotechnical theory, we show that the expression of these deformational styles in East Anglia is a natural response to the stress fields imposed by the ice-sheet, and that in consequence their spatial relationships are explicable. The depth of deformation is related to the geotechnical properties of till and substrate, the stress and effective stress fields, and found to be consistent with observations. 相似文献
993.
994.
Variation in glycogen concentration, condition index (CI) and filtration activity were measured in the bivalve Macoma balthica buried in sediment and experimentally exposed to cadmium (Cd). The stress due to elevated but sub-lethal concentrations (300 ppb Cd) affected the overall fitness of the organism as all parameters monitored responded significantly. Lower concentrations tested (10, 30 and 100 ppb) only induced a significant decrease in filtration activity, which may play a protective role, enabling the organism to slow down its metabolic activity and preserving the integrity of its reserves (reflected by stable CI and glycogen levels). Hence, the various endpoints selected show different thresholds. Our results also demonstrate that under high exposure, small individuals loose proportionally more glycogen per unit of weight than larger ones, thus confirming the higher sensitivity of small individuals to metal contamination. Furthermore, exposure to intermediate concentration (30 ppb) seems to be beneficial to the small individuals as indicated by their high CI values compared to the control. These results showed thus that non-sigmoidal concentration–response relationship and sizes of individuals should be considered in monitoring programmes and risk assessment. 相似文献
995.
The statistical analysis of the source parameters of 9 earthquake sets of different types (aftershocks, scattered events, swarms) and of different seismic regions shows that the density distribution function (ddf) of the linear dimension l of a fault is represented by a negative power law, as well as the ddf of the static stress drop σ and of the scalar seismic moment Mo. It is then suggested, and tentatively verified, that also the ddf of the root mean square ground acceleration, defined as a function of l and σ, may be represented by a negative power law and that, at least in the cases examined, it scales like the ddf of σ. It is seen that the variability of the static stress drop is significant from one region to another, as is well known, but it seems remarkable also in the same seismic region (in particular in California, σ varies by several orders of magnitude) and in the different sets of events of a given region (as observed again for California). It is hypothesized that a correlation, although weak, between the stress drop and the linear dimension of a fault exists and the analyses seem not to contradict that σ may be a decreasing function of l. Finally, it is suggested that the seismicity of a region may be represented two-dimensionally as a function of the ddf of the stress drop and of the linear dimension of a fault instead of the classic b and bo values. 相似文献
996.
A rotational kinematic hardening constitutive model with the capability of predicting the behavior of soil during 3-D stress-reversals has been developed. An existing elasto-plastic constitutive model, the Single Hardening Model, utilizing isotropic hardening serves as the basic framework in these formulations. To this framework is added the capability of handling cross-anisotropic behavior as well as the kinematic hardening mechanism to capture inherent anisotropy of the sand in addition to the large stress-reversals. The model involves thirteen parameters, which can be determined from simple laboratory experiments, such as isotropic compression, drained triaxial compression and triaxial extension tests. The results from a series of true triaxial tests with large stress-reversals performed on loose cross-anisotropic Santa Monica Beach sand are employed for comparison with predictions. 相似文献
997.
On the modeling of the state dependency of granular soils 总被引:3,自引:0,他引:3
Experimental studies have revealed that principal elements of the mechanical behavior of granular soils like the angles of internal peak friction and dilatancy are highly influenced by the combined effect of soil density and mean principal effective stress. In the literature, various empirical correlations between these elements and some parameters indicating soil state have been suggested. Herein, by using two well-known empirical expressions for state dependent peak friction and dilatancy angles, proper constitutive equations are derived and implemented in a stress ratio-based bounding surface plasticity framework. It is shown that the modified model is capable of simulating sand response in either loose or dense states using a unique set of parameters. 相似文献
998.
Łukasz Gągała 《International Journal of Earth Sciences》2009,98(2):461-479
In the course of numerical experiments selected algorithms for stress tensor inversion and separation of heterogeneous populations
of calcite twins and striated faults were tested. Artificial data sets were created in a manner simulating natural processes.
They were composed of data, dynamically compatible with one or two stress tensors and chaotic “noise” imitating natural imperfections.
For calcite twins the classical inversion procedure is considered valid, with restrictions regarding a high proportion of
chaotic data, when shape ratio of the stress tensor Φ is poorly constrained. The algorithm of Etchecopar (1984 fide Tourneret and Laurent in Tectonophysics 180:287–302, 1990) devised originally for calcite twins has been modified and applied to fault/slip data, facilitating a rejection of incompatible
outliers. Two main classes of data separation procedures were tested: separation contemporary with inversion and separation
prior to inversion, utilising hierarchical clustering. The separation contemporary with inversion performs moderately but
often fails with complex calcite twin sets. The performance of hierarchical clustering is high, but only with a σ
1 orientation as a similarity criterion—the new strategy introduced in this contribution. For fault/slip data the hierarchical
clustering with the right-dihedra construction as the similarity criterion (Nemcok et al. 1999) is satisfactory. Additionally, a new approach is proposed for fault/slip data, utilising principles of the classical algorithm
for heterogeneous populations of calcite twins. Validated algorithms for striated faults were successfully applied to a natural
data set from the Holy Cross Mts (central Poland). 相似文献
999.
1000.
旧路拓宽全过程三维有限元分析 总被引:17,自引:1,他引:16
旧路拓宽是西部山区高等级公路建设中的重要课题。运用岩土工程专业软件包P laxis 3D Tunnel,对旧路拓宽进行了全过程的三维弹塑性有限元数值模拟,包括新路基的填筑,路面各结构层的铺筑及轮载最不利位置的施加等,重点分析了新旧路基不均匀沉降变形及应力分布的规律,比较了拓宽方式、新老路基土模量差异对路面变形和使用寿命的影响,并就实际施工提出了一些建议。 相似文献