全文获取类型
收费全文 | 135篇 |
免费 | 13篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 17篇 |
地球物理 | 30篇 |
地质学 | 60篇 |
海洋学 | 23篇 |
天文学 | 8篇 |
综合类 | 4篇 |
自然地理 | 8篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 14篇 |
2013年 | 7篇 |
2012年 | 10篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 4篇 |
2005年 | 9篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有159条查询结果,搜索用时 296 毫秒
81.
怀柔应急水源地是北京第一个建成的特大型应急备用水源地,经过数年的开采后,应急水源地水位大幅度下降,地下水漏斗面积不断扩大。PSInSAR技术在监测地面沉降方面具有很大的优势,本文利用PSInSAR技术和2003年—2009年间28幅Enviast卫星的ASAR影像监测怀柔应急水源地地区地面沉降情况,试验结果表明该地区平均沉降量为8mm/a。通过该地区地面沉降状况和地下水漏斗发展趋势之间的对比,发现地面沉降范围和地下水漏斗有较大的空间一致性,平面分布趋势整体上由南西—北东向北西—南东转变。 相似文献
82.
Observations and Large-Eddy Simulations of Entrainment in the Sheared Sahelian Boundary Layer 总被引:1,自引:1,他引:0
Guylaine Canut Fleur Couvreux Marie Lothon David Pino Frédérique Saïd 《Boundary-Layer Meteorology》2012,142(1):79-101
At the top of the planetary boundary layer, the entrainment of air, which incorporates dry and warm air from the free troposphere
into the boundary layer, is a key process for exchanges with the free troposphere since it controls the growth of the boundary
layer. Here, we focus on the semi-arid boundary layer where the entrainment process is analyzed using aircraft observations
collected during the African Monsoon Multidisciplinary Analysis experiment and large-eddy simulations. The role of the entrainment
is specifically enhanced in this region where very large gradients at the planetary boundary-layer top can be found due to
the presence of the moist, cold monsoon flow on which the dry, warm Harmattan flow is superimposed. A first large-eddy simulation
is designed based on aircraft observations of 5 June 2006 during the transition period between dry conditions and the active
monsoon phase. The simulation reproduces the boundary-layer development and dynamics observed on this day. From this specific
case, sensitivity tests are carried out to cover a range of conditions observed during seven other flights made in the same
transition period in order to describe the entrainment processes in detail. The combination of large-eddy simulations and
observations allows us to test the parametrization of entrainment in a mixed-layer model with zero-order and first-order approximations
for the entrainment zone. The latter representation of the entrainment zone gives a better fit with the conditions encountered
in the Sahelian boundary layer during the transition period because large entrainment thicknesses are observed. The sensitivity
study also provides an opportunity to highlight the contribution of shear stress and scalar jumps at the top of the boundary
layer in the entrainment process, and to test a relevant parametrization published in the recent literature for a mixed-layer
model. 相似文献
83.
The involvement of local people in protected area management a key factor in the sustainable and efficient protection of wildlife,
and an economically preferable approach for the effective everyday care and protection of the environment. This paper aims
to explore the community participation and protected area management challenges faced by national park authorities in developing
countries, through a case study of the Pelister National Park in the Republic of Macedonia. The paper focuses on the multiple
social, economic and political expressions of flexibility in national park management at the local scale. These examinations
are based on field research in Pelister, executed in the summer of 2006, and involving 20 in-depth interviews with local policy-makers,
nature protection experts and local inhabitants, as well as a questionnaire survey of 140 residents of three villages in and
around the park (Nizhepole, Malovishta and Brajchino). 相似文献
84.
Estimation of colored dissolved organic matter and salinity fields in case 2 waters using SeaWiFS: Examples from Florida Bay and Florida Shelf 总被引:1,自引:0,他引:1
E. J. D’Sa C. Hu F. E. Muller-Karger K. L. Carder 《Journal of Earth System Science》2002,111(3):197-207
Estimates of water quality variables such as chlorophylla concentration (Chl), colored dissolved organic matter (CDOM), or salinity from satellite sensors are of great interest to
resource managers monitoring coastal regions such as the Florida Bay and the Florida Shelf. However, accurate estimates of
these variables using standard ocean color algorithms have been difficult due to the complex nature of the light field in
these environments. In this study, we process SeaWiFS satellite data using two recently developed algorithms; one for atmospheric
correction and the other a semianalytic bio-optical algorithm and compare the results with standard SeaWiFS algorithms. Overall,
the two algorithms produced more realistic estimates of Chl and CDOM distributions in Florida Shelf and Bay waters. Estimates
of surface salinity were obtained from the CDOM absorption field assuming a conservative mixing behavior of these waters.
A comparison of SeaWiFS-derived Chl and CDOM absorption with field measurements in the Florida Bay indicated that although
well correlated, CDOM was underestimated, while Chl was overestimated. Bottom reflectance appeared to affect these estimates
at the shallow central Bay stations during the winter. These results demonstrate the need for new bio-optical algorithms or
tuning of the parameters used in the bio-optical algorithm for local conditions encountered in the Bay. 相似文献
85.
深层碳酸盐岩岩溶风化壳溶洞型油气藏地震波场的理论研究 总被引:1,自引:0,他引:1
碳酸盐岩洞缝型油气藏是我国乃至世界的重要油气藏类型之一,属典型的复杂非均匀介质。其中,岩溶洞穴型油气藏是最容易发现的。为了解决这类储层的勘探开发及预测问题,需要从理论上对它们的地震波场进行研究。我们利用随机介质模型和非均匀介质弹性波动方程计算了不同高度和宽度的充满流体藏层的合成地震剖面。结果表明当绕射波偏移为珠子状的同相轴时即使远小于四分之一波长的溶洞在常规带宽的地震剖面上也是可分辨的,绕射波是溶洞高度和宽度的函数。我们引入一个宽度-振幅因子。可以用这个宽度-振幅因子从对无限宽溶洞计算的绕射波计算有限宽度的溶洞的绕射振幅。 相似文献
86.
87.
Although marine lagoons are ubiquitous features along coastal margins, studies investigating the dynamics of metal, organic
matter, and nutrient concentrations in such systems are rare. Here we present a comprehensive examination of the temporal
and spatial gradients in dissolved trace metals (Ag, Cd, Cu, Mn, Pb), organic and inorganic nutrients (POC, PON, DOC, N03
−, NH4
+, H4SiO4, PO4
−3, and urea), and algal biomass in a lagoon estuary, Great South Bay (GSB), New York, USA. While this estuary has experienced
a series of environmental problems during recent decades (urbanization, loss of fisheries, harmful algal blooms), root causes
are largely unknown, in part because levels of bioactive substances, such as trace metals, have never been measured. Sampling
was undertaken within multiple estuarine, riverine, and groundwater sites during spring, summer, and fall. Trace metal tracers
(e.g., Ag, Mn) and statistical analyses were used to differentiate the influences of natural and anthropogenic processes on
the chemical composition of the lagoon. Our analyses revealed three clusters of biogeochemical constituents that behaved similarly
in GSB: constituents under strong biological control such as POC, PON, DOC and chlorophyll,a; elements indicative of benthic remobilization processes such as Mn, Cd, and Cu; and constituents strongly influence by anthropogenic
processes such as Ag, Pb, PO4
−3, NO3
−, and NH4
+. Although GSB is surrounded by a densely populated watershed (c. 1 million people), it does not appear to be significantly
contaminated by trace metals compared to other urban estuaries. Levels of DOC (up to 760 μM) in GSB were well correlated with
phytoplankton biomass and exceeded at least 98% of values reported in similar mid Atlantic estuaries at the same salinities.
These high levels of DOC are likely to be an important source of carbon export to the coastal ocean and likely promote mixotrophic
harmful algal blooms in this system. 相似文献
88.
Hydrogeological characteristics of some deep siphonal springs in Serbia and Montenegro karst 总被引:1,自引:0,他引:1
Saša Milanovic 《Environmental Geology》2007,51(5):755-759
In terms of hydrogeological, engineering-geological, and hydrotechnical tapping in karst in relation to ground waters, karst
channels, springs and ponors, speleodiving is the only research method which enables direct observation, studying and exact
geological mapping of karst channels and caverns. Data collected during speleodiving research contribute considerably to the
analysis of karst evolution process in the given region, which is very important in evaluating the depth of karstification
and determining the main direction of the groundwater flow. In the past 30 years in Serbia and Montenegro, speleodivers have
investigated over 40 siphonal springs, active cave channels and ponors, of which more than 20 are proof of deep siphonal circulation
in karstic aquifers. The karstic springs are the most interesting phenomenon from a hydrogeological view point, and their
investigations need particular attention. Most of significant karstic springs are on the rims of erosion basins—perimeters
of karst poljes, river valleys, sea coasts and contact areas between karst aquifers and hydrogeological barriers. General
characteristics of the spring regime are the direct correlation between precipitation and spring discharge. Moreover, the
hydrogeological regime of these springs also depends on the size of the catchment area, karstic aquifer retardation capacity,
total porosity, as well as lithological and structural characteristics. 相似文献
89.
目前对钙质土压缩特性的研究主要集中在钙质细砂,而实际工程中广泛存在钙质粗粒料,因此对钙质粗粒料压缩特性开展研究具有重要意义。通过颗粒强度测定仪和全自动大型固结仪对钙质土进行了单颗粒破碎试验和一维压缩试验,研究了颗粒粒径和相对密度对钙质粗粒料的颗粒强度和压缩特性的影响。单颗粒试验结果表明,钙质砂单颗粒的特征应力随着颗粒相对密度的增大而增大;单颗粒的破碎强度具有明显的尺寸效应,可利用单颗粒的特征应力进行标准化,且服从Weibull分布。压缩试验结果表明,单一粒径试样破碎后的分形维数随颗粒粒径的增大而增大;试样的Hardin破碎率与塑性功的关系为幂函数关系;在本次试验条件下,单一粒径试样的屈服应力与单颗粒的特征应力存在近似线性关系。 相似文献
90.
Acta Geotechnica - For islands in marine environments, groundwater levels vary due to the influence of tides. As a result, the external environment of backfilled carbonate sands on islands... 相似文献