全文获取类型
收费全文 | 28442篇 |
免费 | 2894篇 |
国内免费 | 2393篇 |
专业分类
测绘学 | 1760篇 |
大气科学 | 3527篇 |
地球物理 | 5875篇 |
地质学 | 14142篇 |
海洋学 | 1831篇 |
天文学 | 1787篇 |
综合类 | 2587篇 |
自然地理 | 2220篇 |
出版年
2025年 | 8篇 |
2024年 | 227篇 |
2023年 | 257篇 |
2022年 | 485篇 |
2021年 | 527篇 |
2020年 | 517篇 |
2019年 | 546篇 |
2018年 | 4208篇 |
2017年 | 3630篇 |
2016年 | 2597篇 |
2015年 | 684篇 |
2014年 | 687篇 |
2013年 | 577篇 |
2012年 | 1308篇 |
2011年 | 2765篇 |
2010年 | 2080篇 |
2009年 | 2316篇 |
2008年 | 1990篇 |
2007年 | 2339篇 |
2006年 | 464篇 |
2005年 | 483篇 |
2004年 | 592篇 |
2003年 | 589篇 |
2002年 | 504篇 |
2001年 | 323篇 |
2000年 | 342篇 |
1999年 | 378篇 |
1998年 | 312篇 |
1997年 | 295篇 |
1996年 | 251篇 |
1995年 | 216篇 |
1994年 | 224篇 |
1993年 | 181篇 |
1992年 | 154篇 |
1991年 | 116篇 |
1990年 | 91篇 |
1989年 | 74篇 |
1988年 | 85篇 |
1987年 | 47篇 |
1986年 | 41篇 |
1985年 | 37篇 |
1984年 | 31篇 |
1983年 | 29篇 |
1982年 | 33篇 |
1981年 | 41篇 |
1980年 | 22篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1958年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Marianne Holmer Núria Marbà Morgane Lamote Carlos M. Duarte 《Estuaries and Coasts》2009,32(3):456-466
Species of the macroalgae Caulerpa sp. are increasingly being observed in meadows of the endemic Mediterranean seagrass Posidonia oceanica, and in particular Caulerpa taxifolia, has been considered as an invasive species leading to seagrass decline. Studies have so far failed to reveal the underlying
mechanisms of the success of the macroalgae, and here, we examine how biogeochemical changes of the environment associated
to indigenous (Caulerpa prolifera) and non-indigenous (Caulerpa racemosa and C. taxifolia) species affect the habitat of P. oceanica. Two of the species (C. prolifera and C. racemosa) affect the sediment biogeochemical conditions by increasing organic matter pools, microbial activity, and sulfide pools
of the sediments, and limited effects were found for C. taxifolia. Biomass of the macroalgae contributed to the extent of impacts, and high sulfide invasion into the seagrasses and regression
of the meadow were pronounced at the location with the highest Caulerpa biomass. This suggests that Caulerpa invasion contributes to seagrass decline probably because Caulerpa thrives better than the seagrasses in the modified environment. 相似文献
22.
Do diatoms in the Swiss Alps reflect the length of ice-cover? 总被引:11,自引:0,他引:11
23.
24.
The SWOT Mission and Its Capabilities for Land Hydrology 总被引:2,自引:0,他引:2
Sylvain Biancamaria Dennis P. Lettenmaier Tamlin M. Pavelsky 《Surveys in Geophysics》2016,37(2):307-337
25.
Identification of the Main Control Factors and Failure Modes for the Failure of Baiyuzui Landslide Control Project 总被引:1,自引:0,他引:1
Du Yi Yan Echuan Gao Xu Mwizerwa Schadrack Yuan Liwei Zhao Song 《Geotechnical and Geological Engineering》2021,39(5):3499-3516
Geotechnical and Geological Engineering - The failure of landslide control project presents a deformation that continues to develop along the crack system, and the continuous failure of mechanical... 相似文献
26.
27.
Anil Misra Lance A. Roberts Steven M. Levorson 《Geotechnical and Geological Engineering》2007,25(1):65-77
Load displacement analysis of drilled shafts can be accomplished by utilizing the “t-z” method, which models soil resistance
along the length and tip of the drilled shaft as a series of springs. For non-linear soil springs, the governing differential
equation that describes the soil-structure interaction may be discretized into a set of algebraic equations based upon finite
difference methods. This system of algebraic equations may be solved to determine the load–displacement behavior of the drilled
shaft when subjected to compression or pullout. By combining the finite difference method with Monte Carlo simulation techniques, a probabilistic load–displacement analysis can be conducted. The probabilistic analysis is advantageous
compared to standard factor of safety design because uncertainties with the shaft–soil interface and tip properties can be
independently quantified. This paper presents a reliability analysis of drilled shaft behavior by combining the finite difference
technique for analyzing non-linear load–displacement behavior with Monte Carlo simulation method. As a result we develop probabilistic relationships for drilled shaft design for both total stress (undrained)
and effective stress (drained) parameters. The results are presented in the form of factor of safety or resistance factors
suitable for serviceability design of drilled shafts. 相似文献
28.
Fluid exchange across the sediment–water interface in a sandy open continental shelf setting was studied using heat as a tracer. Summertime tidal oscillation of cross-shelf thermal fronts on the South Atlantic Bight provided a sufficient signal at the sediment–water interface to trace the advective and conductive transport of heat into and out of the seabed, indicating rapid flushing of ocean water through the upper 10–40 cm of the sandy seafloor. A newly developed transport model was applied to the in situ temperature data set to estimate the extent to which heat was transported by advection rather than conduction. Heat transported by shallow 3-D porewater flow processes was accounted for in the model by using a dispersion term, the depth and intensity of which reflected the depth and intensity of shallow flushing. Similar to the results of past studies in shallower and more energetic nearshore settings, transport of heat was greater when higher near-bed velocities and shear stresses occurred over a rippled bed. However, boundary layer processes by themselves were insufficient to promote non-conductive heat transport. Advective heat transport only occurred when both larger boundary layer stresses and thermal instabilities within the porespace were present. The latter process is dependent on shelf-scale heating and cooling of bottom water associated with upwelling events that are not coupled to local-scale boundary layer processes. 相似文献
29.
30.
Because the flexible net barrier is a gradually developed open-type debris-flow counter-measure, there are still uncertainties in its design criterion. By using several small-scale experimental flume model tests, the dynamical evolution properties of debris flows controlled by large and small mesh-sized (equal to D90 and D50, respectively) flexible net barriers are studied, including the debris flow behaviors, segregation, and permeability of sediments, as well as the energy absorption rates and potential overtopping occurring when debris flows impact the small mesh-sized one. Experimental results reveal that (a) two sediment deposition patterns are observed depending on variations in debris flow textures and mesh sizes; (b) the aggregation against flexible net barriers is dominated by flow dynamics; (c) the segregation and permeable functions of the barrier are determined by the mesh size, concentration, and flow dynamics; and (d) the smaller mesh-sized flexible net barrier tends to be more efficient in restraining more turbulent debris flows and can absorb greater rate of kinematic energy, and finally, the great kinematic energy dissipation that occurs when secondary debris flows interact with the post-deposits in front of the small mesh-sized flexible net barrier is believed to cause the failure of overtopping phenomenon. The mesh size is concluded to be the decisive parameter that should be associated with debris flow textures to design the control functions of flexible net barriers. 相似文献