全文获取类型
收费全文 | 93篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 10篇 |
地球物理 | 31篇 |
地质学 | 35篇 |
海洋学 | 6篇 |
天文学 | 9篇 |
综合类 | 1篇 |
自然地理 | 8篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2010年 | 4篇 |
2009年 | 8篇 |
2008年 | 7篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1997年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有101条查询结果,搜索用时 31 毫秒
1.
Armando L. Brinca 《Planetary and Space Science》1977,25(9):879-885
Analysis of the modifications introduced in a turbulent whistler noise spectrum with the injection of a coherent whistler leads to a nonlinear dispersion equation for the stochastic modes. These modes are submitted to real frequency shifts and corrections to their growth rates which are in qualitative agreement with observations made in the Siple Station VLF wave injection experiment showing the creation of noise-free bands when CW whistler modes are transmitted. 相似文献
2.
3.
4.
This paper reports improvements to algorithms for the simulation of 3-D hydraulic fracturing with the Generalized Finite Element Method (GFEM). Three optimizations are presented and analyzed. First, an improved initial guess based on solving a 3-D elastic problem with the pressure from the previous step is shown to decrease the number of Newton iterations and increase robustness. Second, an improved methodology to find the time step that leads to fracture propagation is proposed and shown to decrease significantly the number of iterations. Third, reduced computational cost is observed by properly recycling the linear part of the coupled stiffness matrix. Two representative examples are used to analyze these improvements. Additionally, a methodology to include the leak-off term is presented and verified against asymptotic analytical solutions. Conservation of mass is shown to be well satisfied in all examples. 相似文献
5.
6.
Stephen Foster Antonio Pulido-Bosch Ángela Vallejos Luis Molina Armando Llop Alan M. MacDonald 《Hydrogeology Journal》2018,26(8):2781-2791
Intensive irrigated agriculture substantially modifies the hydrological cycle and often has major environmental impacts. The article focuses upon a specific concern—the tendency for progressive long-term increases in the salinity of groundwater recharge derived from irrigated permeable soils and replenishment of unconfined aquifers in more arid regions. This process has received only scant attention in the water-resource literature and has not been considered by agricultural science. This work makes an original contribution by analysing, from scientific principles, how the salinisation of groundwater recharge arises and identifies the factors affecting its severity. If not proactively managed, the process eventually will impact irrigation waterwell salinity, the productivity of agriculture itself, and can even lead to land abandonment. The types of management measure required for mitigation are discussed through three detailed case histories of areas with high-value groundwater-irrigated agriculture (in Spain, Argentina and Pakistan), which provide a long-term perspective on the evolution of the problem over various decades. 相似文献
7.
Pietro Catania Luigi Badalucco Vito Armando Laudicina Mariangela Vallone 《Environmental Earth Sciences》2018,77(9):348
Tillage, especially in semiarid Mediterranean environment, enhances the mineralization process of soil organic matter (SOM) and, in turn, decreases aggregate stability. Furthermore, continuous tillage leads to the formation of plough pan beneath the tilled layer. In the present study, we investigated the effect of an innovative self-propelled machine (spading machine, SM) for shallow tillage on SOM, water stable aggregates (WSA) and soil penetration resistance (PR). Such effects were compared to those of chisel plough (CP), rotary tiller (RT) and no tillage (NT). Each tilling method was applied up to a depth of 15 cm, whereas in NT only a brush cutter was used for weed control. Soil analyses were performed at the start of the experiment (March 2009, T0), in April 2010 (T1), May 2012 (T3), and June 2014 (T5) at both 0–15 and 15–30 cm. Compared to T0, soil PR increased with time in all the treatments and generally followed the order SM?<?RT?<?CP?<?NT. In soil tilled with the SM, soil PR never exceeded 2.5 MPa that was demonstrated to be a critical value for root elongation, and no evidence of the formation of plough pan beneath the tilled layer was observed. SOC as well as water content and WSA were higher in SM compared with CP and RT. In conclusion, the spading machine was proved to be more efficient in lowering the soil PR and in avoiding the formation of the plough pan. Furthermore, SM increased SOC and WSA. 相似文献
8.
The Patia Valley situated between the Western and Central Cordilleras of the southwest Colombian Andes contains two areas in which Mesozoic basic and ultrabasic rocks crop out in abundance. Late Cretaceous Diabase Group pillow basalts which make up much of the Western Cordillera are at least 81 ± 5 Ma in the E1 Tambo-E1 Peñol area. 105-97 Ma hornblende and whole-rock dates from the ophiolitic Los Azules complex indicate an Albian age of formation, although many dates are lower (65-62 Ma) owing the low-grade ocean-floor metamorphism. The metamorphic age distribution here supports an end of Cretaceous emplacement for the complex rather than the Early-Mid Cretaceous emplacement suggested for North Colombian ophiolites similarly aligned along the Romeral fault system. Tertiary dacites intruding the Low Azules complex are 36-15 Ma. 相似文献
9.
Belowground production of roots and rhizomes in the top 20 cm of soil was 2.2 kg m?2 yr?1 based on a maximum minus minimum estimation procedure in a giant cordgrass (Spartina cynosuroides (L.) Roth) marsh in Mississippi. Approximately 1.9 kg m?2 (86%) of this production occurred in late spring-summer and 0.3 kg m?2 in late fall. This estimate ignores any production below 20 cm depth and is thus an underestimate. Production values increased to 4.0 kg m?2 yr?1 using Smalley’s technique and accounting for decomposition. Aboveground tissues (leaves and stems) were depleted in nitrogen in July which corresponded to peaks in both above- and belowground biomass. The low root/shoot ratio (2.6) on this marsh does not suggest that growth is nutrient limited. Indeed, total productivity (above- and belowground) for this marsh was high (between 4.4 and 6.2 kg m?2 yr?1). 相似文献
10.
To control vertical movements in the Orinoco Oil Belt, a high-precision levelling network was installed in an area of about 100 km2. Links to the National Geodetic Network were established.
A total of 190 BMs with deep pile foundations is already installed and the first measurement campaign was concluded. The accuracies obtained are those of first-order levelling works. 相似文献