全文获取类型
收费全文 | 142篇 |
免费 | 19篇 |
国内免费 | 31篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 46篇 |
地球物理 | 32篇 |
地质学 | 49篇 |
海洋学 | 35篇 |
天文学 | 2篇 |
综合类 | 13篇 |
自然地理 | 6篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 14篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 10篇 |
2012年 | 13篇 |
2011年 | 9篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1941年 | 1篇 |
排序方式: 共有192条查询结果,搜索用时 15 毫秒
61.
APPLICATION OF A SPLITTING FRACTURE MODEL TO THE SIMULATION OF ROCK INDENTATION SUBSURFACE FRACTURES
A two-dimensional fracture model based on micro-fracture mechanics is applied to the Hertzian indentation stress field to simulate subsurface fractures in an axi-symmetrical plane. The simulation of fracture development reveals quantitatively the effects of loading force, mechanical properties of the rocks, and original micro cracks on the formation of subsurface fractures. The distribution patterns of the subsurface fractures are determined by the magnitudes and trajectories of the indentation stresses. Lateral confinement prohibits the fracture development. Simulations of the subsurface fractures in granite and marble are in good agreement with the indentation experiments. © 1997 by John Wiley & Sons, Ltd. 相似文献
62.
On Newton-like methods for solving nonlinear equations 总被引:1,自引:0,他引:1
KOU Jisheng LIU Dingyou LI Yitian HE Julin 《地球空间信息科学学报》2006,9(1):76-78
Introduction Manymethodsforsolvingnonlinearequations aredescribedindetail[1,2].TheNewtonmethod fortheapproximationofarootofnonlinear equationf(x)=0isanimportantandbasic method,whichconvergesquadratically.The Newtonmethodanditsdeformationsarefocused onallt… 相似文献
63.
64.
AbstractAn experimental study of the performance of concrete pipe piles during installation under different penetration speeds and static load tests on the piles in sand is presented. The applied jacking force, the amount of pile penetration, length of soil plug formed and ultimate bearing capacity were measured during the model tests. The results showed that the concrete pipe piles were partially plugged and the behavior of the soil plug was significantly affected by the penetration speed. The lower the penetration speed, the larger the soil plug formed which in turn leads to a greater ultimate bearing capacity. The size of soil plug can be evaluated by the m value defined as the ratio of the volume of the soil plug to that of the penetrated pile wall. The relationship between the m value and the penetration speeds can be used to estimate the amount of soil plug and the depth of penetration for an open-ended concrete pipe pile jacked into sand. 相似文献
65.
The Qinling Mountains is not only the geographical boundary between North and South China,but also the boundary between subtropical and warm temperate zones.It plays an important role in the geo-ecological pattern of China.However,there is controversy about the specific location of this geographical boundary in academic community due to the complexity,transition and heterogeneity of the transitional zone,as well as the differences in the delimitation indicators and research purposes.To further reveal the characteristics of the North-South transitional zone and clarify the specific location of the geo-ecological boundary between North and South China,combined with SRTM topographic data,temperature and precipitation data,Pinus massoniana forest and Pinus tabulaeformis forest,which represent subtropical coniferous forest in South China and temperate coniferous forest in North China respectively,were chosen to analyze their spatial distributions in the Qinling-Daba Mountains and the climatic conditions at their boundary with the climatic indexes of annual precipitation,the coldest month(January) average temperature,the warmest month(July) average temperature and the annual average temperature.The results show that:(1) Pinus massoniana and Pinus tabulaeformis forests and the climate indicators of their boundary can be used as one of the vegetation-climate indexes for the delimitation of subtropical and warm temperate zones.The boundary between the subtropical coniferous forest(Pinus massoniana forest) and temperate coniferous forest(Pinus tabulaeformis forest) is located along the south slope of Funiu Mountain to the north edge of Hanzhong Basin(the south slope of Qinling Mountains) at an altitude of 1000–1200 m,where the climatic indictors are stable:the annual precipitation is about 750–1000 mm,the annual average temperature is about 12–14℃,the coldest monthly average temperature is 0–4℃,and the warmest monthly average temperature is about 22–26℃.(2) It can be more scientifically to delimitate the boundary of subtropical and warm temperate zones in China by comprehensively considering the vegetation-climate indicators.Additionally,the boundary between subtropical and warm temperate zones in Qinling-Daba Mountains should be a transitional zone consisting of the boundaries of coniferous forests,broad-leaved forests and shrubs between subtropical and warm temperate zones.The results provide a scientific basis for the selection of delimitation index of subtropical and warm temperate zones. 相似文献
66.
67.
北京天竺晚上新世以来植被演替与气候变迁 总被引:4,自引:2,他引:4
研究了北京天竺TZ01钻孔岩心孢粉样品239块,孢粉组合反映了北京天竺晚上新世以来(约3.580 Ma BP)植被演替和气候变迁大致经历了10个发展阶段:(1) 3.580~3.050 Ma BP:以针叶林植被为主,气候寒冷偏湿;(2) 3.050~2.555 Ma BP:植被为落叶阔叶和常绿阔叶混交林-草原类型,该阶段开始升温,但气候较为温暖湿润;(3)2.555~2.300 Ma BP:植被为温凉偏干的疏林草原,湿度开始下降;(4) 2.300~1770 Ma BP:植被类型仍为疏林草原,该阶段温度上升,但幅度并不大,湿度基本不变,气候温凉干爽;(5) 1.770~1.070 Ma BP:植被类型为针阔混交林-草原,气候温暖湿润;(6) 1.070~0.922 Ma BP:植被演替为较暖湿略干的针阔混交林-草原;(7)0.922~0.800 Ma BP:植被为较寒冷干燥的疏林草原,温度降低,降水减少;(8) 0.800~0.650 Ma BP:植被为温暖偏干的以松为主的疏林草原,温度有所上升,但湿度变化较小;(9)0.650~0.160 Ma BP:植被为温凉湿润的针阔叶混交林-草原;(10) 0.160 Ma BP至今:植被以针阔叶混交林-草原为主,前期气候冷湿,后期较为温暖湿润。 相似文献
68.
69.
将大肠杆菌 O157:H7培养于低温贫养条件下 ,以涂布平板法 (PC)和最大近似值法(MPN)检测可培养细菌数 ,95~ 115d后表明可培养菌数下降为零。吖啶橙荧光显微镜直接计数法(AODC)检测细菌总数 ,表明细菌总数始终变化不大 ,而活菌直接镜检计数 (DVC)检测到的活菌数保持在 10 6个 / m L。实验证明了大肠杆菌 O157:H7在一定的条件下可进入活的非可培养状态(VBNC)。 相似文献
70.
Leilei Kou Xiaoqing Wang Maosheng Xiang 《Journal of the Indian Society of Remote Sensing》2014,42(1):1-12
Circular SAR imaging on the geosynchronous orbit is an innovative SAR imaging mode, which can perform high resolution three-dimensional (3D) imaging with continuous observations for a large area. However, for geosynchronous satellites the orbit is severely disturbed by perturbing effects, and the orbit error will be an important factor influencing the SAR imaging on the geosynchronous orbit. In this paper, the effects of the orbit error on performances of 3D geosynchronous circular SAR (GEOCSAR) imaging are analyzed. The error model is firstly made, and then the orbit error propagating into the distance from the radar to the target (range) is derived. Furthermore, the effects of different components of the range error on the quality of focused SAR signals are deduced, based on the 3D GEOCSAR signal model with time-domain correlation algorithm. The analyses and simulations will quantify and verify the required accuracies of GEOCSAR orbit estimation for ensuring the 3D imaging quality. 相似文献