全文获取类型
收费全文 | 602篇 |
免费 | 106篇 |
国内免费 | 135篇 |
专业分类
测绘学 | 34篇 |
大气科学 | 78篇 |
地球物理 | 115篇 |
地质学 | 344篇 |
海洋学 | 96篇 |
天文学 | 34篇 |
综合类 | 67篇 |
自然地理 | 75篇 |
出版年
2024年 | 2篇 |
2023年 | 15篇 |
2022年 | 41篇 |
2021年 | 36篇 |
2020年 | 27篇 |
2019年 | 45篇 |
2018年 | 43篇 |
2017年 | 30篇 |
2016年 | 38篇 |
2015年 | 41篇 |
2014年 | 45篇 |
2013年 | 47篇 |
2012年 | 39篇 |
2011年 | 26篇 |
2010年 | 29篇 |
2009年 | 32篇 |
2008年 | 25篇 |
2007年 | 35篇 |
2006年 | 26篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 18篇 |
2001年 | 24篇 |
2000年 | 16篇 |
1999年 | 24篇 |
1998年 | 19篇 |
1997年 | 15篇 |
1996年 | 18篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有843条查询结果,搜索用时 31 毫秒
61.
If the upstream boundary conditions are prescribed based on the incident wave only, the time-dependent numerical models cannot effectively simulate the wave field when the physical or spurious reflected waves become significant. This paper describes carefully an approach to specifying the incident wave boundary conditions combined with a set sponge layer to absorb the reflected waves towards the incident boundary. Incorporated into a time-dependent numerical model, whose governing equations are the Boussinesq-type ones, the effectiveness of the approach is studied in detail. The general boundary conditions, describing the down-wave boundary conditions are also generalized to the case of random waves. The numerical model is in detail examined. The test cases include both the normal one-dimensional incident regular or random waves and the two-dimensional oblique incident regular waves. The calculated results show that the present approach is effective on damping the reflected waves towards the incident wave boundary. 相似文献
63.
64.
Journal of Oceanology and Limnology - We present observations from deployments of turbulent microstructure instrument and CTD package in the northern South China Sea from April to May 2010. From... 相似文献
65.
WANG Qingsong YU Qingyang 《世界地质(英文版)》2014,17(3):170-175
The excavation for the municipal tunnel will disturb the soil around the tunnel, and the deformation and subsidence of the earth surface always take place, which may lead to instability and even collapse for the building above the tunnel. At the same time the deformation and subsidence of the earth surface affect the normal use of underground municipal pipelines, and may cause the road sudden collapse, leading to significantly traffic accidents. The authors did a research by simulating for the excavation of municipal tunnel and designed the related supporting plan, and put forward some suggestions and measures for the design and construction of urban tunnel. 相似文献
66.
老工业区产业结构转型与用地结构转型互动机制及优化路径——以上海市宝山区为例 总被引:1,自引:0,他引:1
尝试理清老工业区产业结构转型与用地结构转型内涵,提出其转型效率的函数表达,分析二者间的互动关系;并运用改进的动态变化度及偏离系数,对上海市宝山区进行实证研究。结果表明:(1)宝山区产业结构与用地结构变化度逐渐增加,工业和第三产业动态度分别由1996年的2.48%和5.36%上升至2012年的4.75%和5.51%,用地结构动态度由11.16%上升至13.53%;(2)宝山区三次产业结构总体趋于优化,但产业内部并未优化,仍以重化工业和传统服务业为主导;(3)宝山区用地结构与产业结构不协调并处于加剧的状态。老工业区产业结构与用地结构存在较强的互动关系,改进的动态变化度及偏离系数方法为老工业区产业结构转型与用地结构转型问题提供了一种研究思路。提出宝山区产业结构转型与用地结构转型的优化路径。 相似文献
67.
68.
琼东南盆地深水区断层垂向输导及成藏模式 总被引:2,自引:1,他引:1
In the Qiongdongnan Basin, faults are well developed.Based on the drilling results, the traps controlled two or more faults are oil-rich. However, when only one fault cut through the sand body, there is no sign for hy-drocarbon accumulation in the sandstone. In terms of this phenomenon, the principle of reservoir-forming controlled by fault terrace is proposed, i.e., when the single fault activates, because of the incompressibility of pore water, the resistance of pore and the direction of buoyancy, it is impossible for hydrocarbon to ac-cumulate in sandstone. But when there are two or more faults, one of the faults acts as the spillway so the hydrocarbon could fill in the pore of sandstone through other faults. In total five gas bearing structures and four failure traps are considered, as examples to demonstrate our findings. According to this theory, it is well-advised that south steep slope zone of Baodao-Changchang Depression, south gentle slope zone of Lingshui Depression, north steep slope zone of Lingshui Depression, and north steep slope zone of Baodao Depression are the most favorable step-fault zones, which are the main exploration direction in next stage. 相似文献
69.
A. H. Khan J. Q. Shang R. Alam 《International Journal of Environmental Science and Technology》2014,11(7):1989-1998
A sample preparation method of total sulphur measurement of reactive mine tailings was optimized. The total sulphur was measured by inductively coupled plasma optical emission spectroscopy, and ultrasound technique was used for sample digestion. The optimization process was adopted by a combined approach of experimental design and response surface methodology. The digestion time, temperature and acid-oxidant combination (i.e. effect of H2O2 with a fixed amount of acid mixture) were investigated. A two-level and three-factor (23) full factorial design of experiment was applied to identify the most significant factors, and a central composite design was used to optimize the digestion procedure. KZK-1, a sericite schist, was selected as the certified reference material. The optimum methodology at 95 % confidence level (P < 0.05) was identified to be 10 min of digestion at 77 °C, with a solution of 1 ml HNO3:1 ml HCl:1.35 ml H2O2. This combination resulted in 100 % sulphur recovery. The investigated method was verified by X-ray diffraction analysis. The optimum digestion level was applied to a reactive mine tailings, which achieved satisfactory results with a percentage relative standard deviation < 3 %. 相似文献
70.
Large amounts of groundwater are discharged during underground mining operations. As a result, the drawdown of groundwater, known as aquifer dewatering, is common in mining areas. Because of variability in permeability between different media in mines, mine drainage occurs primarily as non-continuous flow. However, calculations of mine water yield are usually made based on the continuous flow theory, and therefore often produce erroneous results. This study predicts the water yield of a mine using the module MODFLOW and incorporating the non-continuous flow theory into the calculation. Using this method, the predicted water yield of a mine was approximately 50 % lower than that predicted using the continuous flow theory. The model also demonstrates that the rate of mine drainage varies over time; there is initially a decrease in the rate of drainage which gradually approaches a constant value. Double level flow occurs when there is non-continuous flow in continuous media, which can effectively minimize the influence of mine drainage on upper aquifers and relieve the conflict between groundwater supply and drainage in the mining area. 相似文献