全文获取类型
收费全文 | 7771篇 |
免费 | 522篇 |
国内免费 | 310篇 |
专业分类
测绘学 | 293篇 |
大气科学 | 738篇 |
地球物理 | 1902篇 |
地质学 | 2849篇 |
海洋学 | 650篇 |
天文学 | 1223篇 |
综合类 | 156篇 |
自然地理 | 792篇 |
出版年
2023年 | 35篇 |
2022年 | 72篇 |
2021年 | 123篇 |
2020年 | 131篇 |
2019年 | 174篇 |
2018年 | 237篇 |
2017年 | 217篇 |
2016年 | 311篇 |
2015年 | 240篇 |
2014年 | 278篇 |
2013年 | 482篇 |
2012年 | 330篇 |
2011年 | 413篇 |
2010年 | 367篇 |
2009年 | 448篇 |
2008年 | 395篇 |
2007年 | 339篇 |
2006年 | 323篇 |
2005年 | 296篇 |
2004年 | 295篇 |
2003年 | 261篇 |
2002年 | 300篇 |
2001年 | 186篇 |
2000年 | 212篇 |
1999年 | 161篇 |
1998年 | 158篇 |
1997年 | 118篇 |
1996年 | 126篇 |
1995年 | 124篇 |
1994年 | 125篇 |
1993年 | 97篇 |
1992年 | 109篇 |
1991年 | 84篇 |
1990年 | 66篇 |
1989年 | 61篇 |
1988年 | 71篇 |
1987年 | 61篇 |
1986年 | 59篇 |
1985年 | 67篇 |
1984年 | 67篇 |
1983年 | 77篇 |
1982年 | 57篇 |
1981年 | 68篇 |
1980年 | 55篇 |
1979年 | 65篇 |
1978年 | 52篇 |
1977年 | 34篇 |
1976年 | 28篇 |
1974年 | 26篇 |
1973年 | 30篇 |
排序方式: 共有8603条查询结果,搜索用时 31 毫秒
931.
Christopher P. Burgess Michael A. Taylor Tannecia Stephenson Arpita Mandal Leiska Powell 《Natural Hazards》2015,78(1):231-256
Floods account for more than half of the global hydrometeorological risks. Severe floods cause significant economic shocks and loss of lives, particularly for developing countries such as Jamaica. There is need for more information on the present and projected flood risks to justify macro-scale planning for climate change adaptation and facilitate the decision-making processes. In this study, a catalogue of 198 flood events occurring between 1678 and 2010 is compiled for Jamaica and used to examine the climatology, occurrence, trends, causes and duration of the island’s severe events. The annual flood risk is estimated to be a loss of life rate of 4 persons and estimated annual damage of USD96.3 million per annum in 2010 values and approximately 0.84 % of GDP per annum. Macro-scale models for flood risks (deaths and damages) are also developed using data from the flood catalogue and maximum precipitation at the town and parish level. The models examine the relationship between flood risks (death and damages) and extreme rainfall depths and intensities. Future climate risks of loss of lives and damages are predicted to increase 11 and 9 %, respectively, to 4.4 persons and USD105.2 million per annum. 相似文献
932.
933.
934.
Changes in bedrock channel morphology driven by displacement rate increase during normal fault interaction and linkage
下载免费PDF全文
![点击此处可从《Basin Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We attribute changes in the morphology of relay ramp channels (increased slope and decreased width) to variations in displacement rate on ramp‐adjacent normal faults. We map the faults and fluvial channels associated with four sites in different stages of fault interaction and linkage on the Volcanic Tableland, a Late Pleistocene ash‐flow tuff in east‐central California. Because these channels are inactive today, we estimate downstream changes in channel width and depth using HEC‐RAS, a one‐dimensional open channel flow model. Our results show that channel slope must be greater than about 0.05 before there are substantial decreases in width or substantial increases in depth. Displacement rate increases during interaction between en echelon segments results in the increases in channel slope and decreases in channel width. Moreover, our data show that these changes begin to occur during the very early stages of fault interaction, well before the fault geometry would indicate ongoing or imminent linkage. 相似文献
935.
Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamic triaxial tests with multi-stage cyclic loading process. The relationship between dynamic shear stress and dynamic shear strain of frozen soil of subgrade under train loading and the influence of freezing temperatures on dynamic constitutive relation, dynamic shear modulus and damping ratio are observed in this study. Test results show that the dynamic constitutive relations of the frozen soils with different freezing temperatures comply with the hyperbolic model, in which model parameters a and b decrease with increasing freezing temperature. The dynamic shear modulus of the frozen soils decreases with increasing dynamic shear strains initially, followed by a relatively smooth attenuation tendency, whereas increases with decreasing freezing temperatures. The damping ratios decrease with decreasing freezing temperatures. Two linear functions are defined to express the linear relationships between dynamic shear modulus (damping ratio) and freezing temperature, respectively, in which corresponding linear coefficients are obtained through multiple regression analysis of test data. 相似文献
936.
937.
938.
The Reliability of Assigned Values from the GeoPT Proficiency Testing Programme from an Evaluation of Data for Six Test Materials that have been Characterised as Certified Reference Materials
下载免费PDF全文
![点击此处可从《Geostandards and Geoanalytical Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Philip J. Potts Michael Thompson Peter C. Webb 《Geostandards and Geoanalytical Research》2015,39(4):407-417
Assigned values derived from the GeoPT proficiency testing programme were compared with certified values for six certified reference materials that have been used as test materials in the GeoPT programme. Statistical analysis showed that there were few significant differences between these sets of data and that these differences had no significant impact on the GeoPT assessment when fitness‐for‐purpose criteria were taken into account. 相似文献
939.
Thomas Kenkmann Abdulkader M. Afifi Simon A. Stewart Michael H. Poelchau Douglas J. Cook Allen S. Neville 《Meteoritics & planetary science》2015,50(11):1925-1940
Here we present the first proof of an impact origin for the Saqqar circular structure in northwestern Saudi Arabia (Neville et al. 2014 ), with an apparent diameter of 34 km, centered at 29°35′N, 38°42′E. The structure is formed in Cambrian–Devonian siliciclastics and is unconformably overlain by undeformed Cretaceous and Paleogene sediments. The age of impact is not well constrained and lies somewhere between 410 and 70 Ma. The subsurface structure is constrained by 2‐D reflection seismic profiles and six drilled wells. First‐order structural features are a central uplift that rises approximately 2 km above regional datums, surrounded by a ring syncline. The crater rim is defined by circumferential normal faults. The central uplift and ring syncline correspond to a Bouguer gravity high and an annular ring‐like low, respectively. The wells were drilled within the central uplift, the deepest among them exceed 2 km depth. Sandstone core samples from these wells show abundant indicators of a shock metamorphic overprint. Planar deformation features (PDFs) were measured with orientations along (0001), {103}, and less frequently along {101} and {104}. Planar fractures (PFs) predominantly occur along (0001) and {101}, and are locally associated with feather features (FFs). In addition, some shocked feldspar grains and strongly deformed mica flakes were found. The recorded shock pressure ranges between 5 and 15 GPa. The preserved level of shock and the absence of an allochthonous crater fill suggest that Saqqar was eroded by 1–2 km between the Devonian and Maastrichtian. The documentation of unequivocal shock features proves the formation of the Saqqar structure by a hypervelocity impact event. 相似文献
940.
Ensemble standardization constraints on the influence of the tree growth trends in dendroclimatology
Shi Feng Yang Bao Linderholm Hans W. Seftigen Kristina Yang Fengmei Yin Qiuzhen Shao Xuemei Guo Zhengtang 《Climate Dynamics》2020,54(7):3387-3404
Climate Dynamics - Tree growth trends can affect the interpretation of the response of tree-ring proxies (especially tree-ring width) to climate in the low-frequency band, which in turn may limit... 相似文献