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701.
Phreatomagmatic deposits at Narbona Pass, a mid-Tertiary maar in the Navajo volcanic field (NVF), New Mexico (USA), were characterized
in order to reconstruct the evolution and dynamic conditions of the eruption. Our findings shed light on the temporal evolution
of the eruption, dominant depositional mechanisms, influence of liquid water on deposit characteristics, geometry and evolution
of the vent, efficiency of fragmentation, and the relative importance of magmatic and external volatiles. The basal deposits
form a thick (5–20 m), massive lapilli tuff to tuff-breccia deposit. This is overlain by alternating bedded sequences of symmetrical
to antidune cross-stratified tuff and lapilli tuff; and diffusely-stratified, clast-supported, reversely-graded lapilli tuffs
that pinch and swell laterally. This sequence is interpreted to reflect an initial vent-clearing phase that produced concentrated
pyroclastic density currents, followed by a pulsating eruption that produced multiple density currents with varying particle
concentrations and flow conditions to yield the well-stratified deposits. Only minor localized soft-sediment deformation was
observed, no accretionary lapilli were found, and grain accretion occurs on the lee side of dunes. This suggests that little
to no liquid water existed in the density currents during deposition. Juvenile material is dominantly present as blocky fine
ash and finely vesiculated fine to coarse lapilli pumice. This indicates that phreatomagmatic fragmentation was predominant,
but also that the magma was volatile-rich and vesiculating at the time of eruption. This is the first study to document a
significant magmatic volatile component in an NVF maar-diatreme eruption. The top of the phreatomagmatic sequence abruptly
contacts the overlying minette lava flows, indicating no gradual drying-out period between the explosive and effusive phases.
The lithology of the accidental clasts is consistent throughout the vertical pyroclastic stratigraphy, suggesting that the
diatreme eruption did not penetrate below the base of the uppermost country rock unit, a sandstone aquifer ∼360 m thick. By
comparison, other NVF diatremes several tens of kilometers away were excavated to depths of ∼1,000 m beneath the paleosurface
(e.g., Delaney PT. Ship Rock, New Mexico: the vent of a violent volcanic eruption. In: Beus SS (ed) Geological society of
America Centennial Field Guide, Rocky Mountain Section 2:411–415 (1987)). This can be accounted for by structurally controlled variations in aquifer thickness beneath different regions of the
volcanic field. Variations in accidental clast composition and bedding style around the edifice are indicative of a laterally
migrating or widening vent that encountered lateral variations in subsurface geology. We offer reasonable evidence that this
subsurface lithology controlled the availability of external water to the magma, which in turn controlled characteristics
of deposits and their distribution around the vent.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
702.
Providing reliable and accurate storm surge forecasts is important for a wide range of problems related to coastal environments. In order to adequately support decision-making processes, it also become increasingly important to be able to estimate the uncertainty associated with the storm surge forecast. The procedure commonly adopted to do this uses the results of a hydrodynamic model forced by a set of different meteorological forecasts; however, this approach requires a considerable, if not prohibitive, computational cost for real-time application. In the present paper we present two simplified methods for estimating the uncertainty affecting storm surge prediction with moderate computational effort. In the first approach we use a computationally fast, statistical tidal model instead of a hydrodynamic numerical model to estimate storm surge uncertainty. The second approach is based on the observation that the uncertainty in the sea level forecast mainly stems from the uncertainty affecting the meteorological fields; this has led to the idea to estimate forecast uncertainty via a linear combination of suitable meteorological variances, directly extracted from the meteorological fields. The proposed methods were applied to estimate the uncertainty in the storm surge forecast in the Venice Lagoon. The results clearly show that the uncertainty estimated through a linear combination of suitable meteorological variances nicely matches the one obtained using the deterministic approach and overcomes some intrinsic limitations in the use of a statistical tidal model. 相似文献
703.
An economical alternative to conventional crudes, Canadian bitumen, harvested as a semi-liquid, is diluted with condensate to make it viable to transport by pipeline to coastal areas where it would be shipped by tankers to global markets. Not much is known about the fate of diluted bitumen (dilbit) when spilled at sea. For this purpose, we conducted dilbit (Access Western Blend; AWB and Cold Lake Blend; CLB) weathering studies for 13 days in a flume tank containing seawater. After six days of weathering, droplets detached from the AWB slick and were dense enough to sink in seawater. The density of CLB also increased, but at a slower rate compared to AWB, which was attributed to the high concentration of alkylated polycyclic aromatic hydrocarbons in it, which are more resistant to weathering. An empirical, Monod-type model was introduced and was found to closely simulate the increase in oil density with time. Such a model could be used within oil spill models. 相似文献
704.
Water tanks as traditional rainwater harvesting systems for agriculture are widely distributed in South India. They have a strong impact on hydrological processes, affecting streamflow in rivers as well as evapotranspiration. This study aims at an accurate representation of water harvesting systems in a hydrologic model to improve model performance and assessment of the catchment water balance. To this end, spatio-temporal variations of water bodies between the years 2016 and 2018 and the months of January and May 2017 were derived from Sentinel-2 satellite data to parameterize the water tanks (reservoir) parameters in the Soil and Water Assessment Tool (SWAT+) model of the Adyar basin, Chennai, India. Approximately 16% of the basin is covered by water tanks. The initial model performance was evaluated for two model setups, with and without water tanks. The best model run was selected with a multi-metric approach comparing observed and modelled monthly streamflow for 5000 model runs. The final model evaluation was carried out by comparing estimated water body areas by the model and remote sensing observations for January to May 2017. The results showed that representing water tanks in the hydrologic model led to an improvement in the representation of the seasonal variations of streamflow for the whole simulation period (2004–2018). The model performance was classified as good and very good for the calibration (2004–2011) and validation (2012–2018) periods as NSE varies between 0.67 and 0.85, KGE varies between 0.65 and 0.72, PBIAS varies between −24.1 and −23.6, and RSR varies between 0.57 and 0.39. The best fit was shown for the high and middle flow segments of the hydrograph where the coefficient of determination (R2) ranges from 0.81 to 0.97 and 0.75 to 0.81, respectively. The monthly variation of water body areas in 2017 estimated by the hydrologic model was consistent with changes observed in remote sensing surveys. In summary, the water tank parametrization using remote sensing techniques enhanced the hydrologic model's efficiency and applicability for future studies. 相似文献
705.
706.
贝壳堤的形成与风暴沉积——以广东台山长湾贝壳堤为例 总被引:3,自引:0,他引:3
台山市西南部沿海有一条由典型风暴潮沉积堆积形成,出露高度远高于现代风暴潮增水面的贝壳堤.根据贝壳堤出露的横向与纵向剖面以及横剖面上的3个钻孔的形成年代、沉积特征的分析表明风暴潮在贝壳堤发育过程中的不同阶段具有不同的侵蚀与堆积作用;贝壳堤风暴沉积也具有丘状层理、切割充填结构等典型的风暴沉积特征,但贝壳堤风暴沉积与浅海陆架上的风暴沉积在沉积过程、堆积层位、保存条件等方面具有明显的差异.长湾贝壳堤是由多次风暴加积而成,形成贝壳堤的风暴增水高度接近或高于历史最高记录.形成贝壳堤的风暴沉积堆积于平均海面之上,所以增 相似文献
707.
708.
基于ADICRC-SWAN耦合模式,文章模拟了山东半岛1985— 2017年的61场风暴潮过程,研究了佳益、明波、富瀚3个海洋牧场的增水与有效波高的分布特征。通过分析3个海洋牧场的风暴增水与有效波高的年极值序列得出,台风风暴潮发生次数最多,但强度没有明显的规律;温带气旋频率最低,但引起的平均增水较高。寒潮引起的风暴潮主要在明波海洋牧场形成高增水,同时在佳益海洋牧场形成大浪。以年极值序列为基础,利用Gumbel极值分布计算了出3个海洋牧场的百年一遇增水与有效波高,增水在明波最高,在佳益最低,而有效波高则相反。进一步考虑波高与增水的联合概率分布,佳益海洋牧场的百年一遇有效波高在增水为50 cm时降低至6.5~7.1 m,在增水150 cm的情况再降至3.9~4.6 m;富瀚海洋牧场的波高在50 cm增水条件下降幅比较明显,在水位增加到150 cm时变化不大,都在2.6~3.2 m;明波海洋牧场在增水为0,50 cm和150 cm时的波高在1.9~2.8 m,与考虑单变量极值情况差别不大。模拟结果对海洋牧场的风暴潮防灾减灾工作有一定参考价值。 相似文献
709.
710.
胶州湾风暴潮增水重现值的长期预测 总被引:1,自引:0,他引:1
以胶州湾30 a风暴潮过程的极值增水值为统计序列,按照年、季、月等不同时段,分别抽样极值增水样本,提出泊松最大熵分布,采用年极值法和过阈法对增水重现值进行长期预测,统计分析结果对于胶州湾防潮减灾有参考作用,其随机分析方法对于遭受风暴潮影响的海岸区域有借鉴意义。 相似文献