全文获取类型
收费全文 | 150篇 |
免费 | 14篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 53篇 |
地球物理 | 47篇 |
地质学 | 44篇 |
海洋学 | 19篇 |
综合类 | 7篇 |
自然地理 | 16篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 4篇 |
2012年 | 4篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1986年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有187条查询结果,搜索用时 15 毫秒
91.
NI Jinren WANG Guangqian Dr. of Eng- Dept. of Geography Peking University China Dr. of Eng 《国际泥沙研究》1991,(3)
The problem of sediment concentration distribution in a vertical for channel and pipe flows is studied in this paper. Considering the variation of the vertical component of the fluctuation velocity v as an independent variable, two types of sediment concentration distribution can be derived. However, only one type of distribution is commonly quoted while the other one rarely reported. In this paper explanation for such phenomena is given and conditions for the occurrence of both types are also discussed. 相似文献
92.
Observations of the dispersion of a contaminant plume in theatmospheric boundary layer, obtained using a Lidar, are analysedin a coordinate frame relative to the instantaneous centre of massof the plume. To improve the estimates of relative dispersionstatistics, maximum entropy inversion is used to remove noise fromthe Lidar concentration profiles before carrying out the analysis.A parametric form is proposed for the probability density function(pdf) of concentration, consisting of a mixture of a betadistribution and of a generalised Pareto distribution (GPD). Thispdf allows for the possibility of a unimodal or bimodaldistribution, and is shown to give a satisfactory fit toobservations from a range of positions relative to the source. Thevariation of the fitted parameters with crossplume location isanalysed, and the maximum possible concentration is found todecrease away from the plume centre. 相似文献
93.
The primary degradation of a technical nonylphenol ethoxylate surfactant with an average chain length of 10 ethoxylate units (NPEO‐10) was studied in a flow‐through system by means of miniaturized biofilm reactors (mBFR) with bacteria from an activated sludge plant. 5 mg/L of the test compound (total EO concentration) were spiked in synthetic wastewater (SWW) and fed to the reactors continuously for 64 days. Compound removal and the formation of degradation products (DP) were monitored under both oxic and anoxic conditions. Solid‐phase extraction and RP‐HPLC with fluorescence detection were employed for sample preparation and analysis. Better removal of the parent compound was seen with the oxic reactors (50 to 70%) than with the anoxic reactors (30 to 50%). Compared to SWW organic matter, the test compound proved to be of refractory nature. The appearance of degradation products in the effluent was earlier with anoxic reactors despite their lower elimination efficiency. After extraction of biomass only minor amounts of NPEO‐10 and metabolites were found, indicating that small amounts were present in adsorbed or intracellular form. Ultimate biodegradation of NPEO‐10 and of octylphenol ethoxylates (OPEO‐9.5; average chain length of 9.5 EO units) was tested by means of manometric respirometry at a theoretical oxygen demand (ThOD) of 100 mg/L. Whereas NPEO‐10 was biodegraded by only 26%, at best, in 28 days, OPEO‐9.5 degradation amounted to (40 ± 5)%. 相似文献
94.
95.
五道梁大气气溶胶的化学组成和浓度及其季节变化 总被引:4,自引:3,他引:4
利用1993年9-10月和1994年4-5月及7-8月在青藏高原五道梁采集的大气气溶胶元素浓度资料,分析了气溶胶化学组成的总体特征和浓度及其季节变化。结果表明:五道梁低层大气中气溶胶在总体上保持自然大气的组成,以地壳土壤元素为主,由人类活动造成的污染轻微,春季的气溶胶浓度约为秋季的1.75倍,夏季可能与秋季接近,基本上反映了五道梁低层大气气溶胶浓度的季节变化特征。按元素质量深度的季节变化特征可将其 相似文献
96.
On the basis of previous study of the 1679 Sanhe-Pinggu(M8.0) earthquake,the biggest event in history ever recorded in Beijing and its adjacent area,we made a 3-D strong ground motion simulation utilizing the staggered-grid finite differences method to study the distributions of peak ground velocity with different earthquake source models in the Beijing region.In the paper,earthquake source models and a transmission medium velocity model are established and the corresponding parameters are given in accordance to the results from a related previous study.Then,using a three-dimensional finite difference computing program of near-fault strong ground motion developed by Graves,the peak ground velocity caused by a destructive earthquake in the Beijing area is simulated.In our computation model,the earthquake source is 3km in depth,and a total number of 21,679 observation points on the ground surface are figured out.The transmission medium velocity model is composed of four stratums which are the Quaternary deposit,the upper crust,the upper part of the middle crust and the lower part of the middle crust.With the minimum grid spacing of 0.15km,a total of 2.28×106 grids are generated.Using a time step of 0.02 seconds we calculated the peak ground velocity for a duration of 8 seconds.After the analysis of the simulation results,we observed some basic characteristics of near-fault strong ground motion such as the concentration effect of near-fault peak ground velocity,rupture directivity effect,hanging wall effect,and basin effect.The results from our simulation and analysis suggest that the source and transmitting medium parameters in our model are suitable and the finite difference method is applicable to estimate the distribution of strong ground motion in the study region. 相似文献
97.
《China Geology》2021,4(2):256-265
The rare earth elements (REE) content of the coal in the Erlian Basin was determined by inductively coupled plasma mass spectrometry (ICP-MS), and it turns out that the REE content from different geological age shows a significant difference: The REE content of the coal in the Jurassic Alatanheli Group is from 152.05×10−6 to 1416.21×10−6, with an average value of 397.31×10−6, and the relative concentration factor shows enriched; the REE content of the coal in Early Cretaceous Baiyanhua Group is from 20.65×10−6 to 102.53×10−6, the mean value is 49.06×10−6, and the relative concentration factor shows normally. The REE distribution patterns samples in Jurassic and Cretaceous shows the difference: The REE pattern in Jurassic coal mainly manifests as H-type distribution, with the Y, Lu positive anomaly, it is speculated that the fluid carried REE ions into the coal-bearing basin, and the heavy REE gather in the coal due to the different chemical properties of each REE. The REE occurrence mode is presumed to be mainly organic. Flat type is the REE main distribution pattern in Cretaceous coal. The REE patterns in clastic rocks of the roof, parting and floor of coal seam are similar to the REE patterns in the coal and the most possible reason is that the REE main source is from the clastic rock. It showed that the coal of the Early Jurassic, especially of Amugulen coalfield has resource value. 相似文献
98.
流域水资源演化与气候变化和人类活动紧密相关,气候变化与人类活动的加剧极大地改变了流域水文循环。通过相似性和独立性分析,从CMIP5公开发布的47个气候模式中筛选出5个代表性气候模式,然后计算未来高、中、低3种不同排放情景下的气温和降水,构造符合研究区产汇流特性的水文模型,计算洞庭湖流域水资源量并分析其演化规律。结果表明:不论温室气体排放水平如何,洞庭湖流域水资源量在未来60a呈现增加态势,汛期水量增加概率加大,而在高排放情景下枯季水资源量表现为减少趋势;未来洞庭湖流域水资源的时程分配将更趋不均匀化,而温室气体的持续排放将使其变化加剧。 相似文献
99.
Changing properties of precipitation concentration in the Pearl River basin, China 总被引:16,自引:3,他引:13
Qiang Zhang Chong-yu Xu Marco Gemmer Yongqin David Chen Chunling Liu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(3):377-385
In this paper, precipitation concentrations across the Pearl River basin and the associated spatial patterns are analyzed
based on daily precipitation data of 42 rain gauging stations during the period 1960–2005. Regions characterized by the different
changing properties of precipitation concentration index (CI) are identified. The southwest and northeast parts of the Pearl
River basin are characterized by lower and decreasing precipitation CI; the northwest and south parts of the study river basin
show higher and increasing precipitation CI. Higher but decreasing precipitations CI are found in the West and East River
basin. Comparison of precipitation CI trends before and after 1990 shows that most parts of the Pearl River basin are characterized
by increasing precipitation CI after 1990. Decreasing precipitation CI after 1990 (compared to precipitation CI changes before
1990) is observed only in a few stations located in the lower Gui River and the lower Yu River. Significant increasing precipitation
CI after 1990 is detected in the West River, lower North River and upper Beipan River. These changes of precipitation CI in
the Pearl River basin are likely to be associated with the consequences of the well-evidenced global warming. These findings
can contribute to basin-scale water resource management and conservation of ecological environment in the Pearl River basin. 相似文献
100.
Based on the three Dimensional Particle Tracking Velocimetry (3D PTV) system, the characteristics of motion of particles with four different diameters were investigated under the steady flow conditions.The longitudinal average velocity profiles of these particles were in accordance with Log-law, while the vertical and transverse velocities remained very low with minimal fluctuation. The time-average velocity of particles in the bed load layer was 8.5u., close to Bagnold's assumption Un -ω. The vertical concentration distribution of particles in the suspension region agreed with the Rouse equation. When the diameter of particles was relatively large, there existed an evident concentration gradient in the bed load layer. 相似文献