全文获取类型
收费全文 | 325篇 |
免费 | 15篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 7篇 |
地球物理 | 58篇 |
地质学 | 245篇 |
海洋学 | 22篇 |
天文学 | 6篇 |
综合类 | 5篇 |
自然地理 | 7篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2012年 | 9篇 |
2011年 | 12篇 |
2010年 | 9篇 |
2009年 | 15篇 |
2008年 | 24篇 |
2007年 | 54篇 |
2006年 | 32篇 |
2005年 | 15篇 |
2004年 | 28篇 |
2003年 | 22篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1980年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有356条查询结果,搜索用时 15 毫秒
81.
大连海港常采用高黏粒吹填土作为吹淤造陆工程土料,但高黏粒吹填土的黏粒含量大,真空预压处理地基时竖向排水体四周常常被黏粒淤堵,延误工程进度。为深入研究该类吹填土工程地质特性,基于室内物理模型采用80 kPa真空预压技术处理高黏粒吹填土,针对淤堵难题进行分析。通过测试土体的物理化学参数,建立含水率、易溶盐总量、钠离子含量、酸碱度、阳离子交换量、有机质含量等物理化学指标的特征分布曲线。结果表明:80 kPa真空预压处理的高黏粒吹填土含水率与易溶盐总量、酸碱度等化学指标呈反比;竖向排水体四周吹填土的易溶盐含量较大,有机质含量高;阳离子交换量与酸碱度呈正比。同时物化指标在排水板四周富集的现象反映80 kPa真空预压处理的高黏性吹填土固结状况,同时建议真空预压处理过程中采用分级真空预压方法,改进高黏粒吹填土地基处理,以降低淤堵状况。 相似文献
82.
目前,尽管针对不良地质生态状况出现的危险和风险的预报及评价问题的各种观点进行了多次研究,但是制定绘制风险和危险图的唯一途径及形成统一的方法问题远远未得到解决。这是许多原因造成的,其中一个主要原因是基本概念的解释不统一(风险、危险、脆弱性、保护性等等)。毫无疑问,仔 相似文献
83.
84.
金刚石的研究将推动超硬矿物材料学,宝石矿物材料学,半导体材料科学甚至纳米材料科学等的发展,本综述了金刚石中的N、H、O、B及过渡金属等杂质元素,近年来金刚石的合成及优化处理的开发成果,探讨了有关的研究方法,为宝石级金刚石材料的系统化研究提供了较为详尽的资料。 相似文献
85.
Fillmann G Watson GM Francioni E Readman JW Depledge MH 《Marine environmental research》2002,54(3-5):823-828
Urine and haemolymph can be repeatedly sampled from crabs with no (or limited) damage to the organism. Their analysis offers a measure of the animals' exposure to biologically available contaminants. Shore crabs (Carcinus maenas) were exposed to the PAHs phenanthrene and pyrene at concentrations ranging from 20 to 200 microg l(-1). After 48 h, urine and haemolymph samples were taken and analysed using ELISA and UV-fluorescence spectrophotometry. High correlations were recorded between the two sets of results from the urine analyses (r2 = 0.83 for phenanthrene and r2 = 0.88 for pyrene). Contaminant concentrations were much lower in haemolymph than in the urine. Analyses of urine taken from crabs collected from clean and contaminated sites confirm the suitability of these analyses for environmentally exposed organisms. Again, a good correlation was recorded between the ELISA and spectrofluorimetric analysis (r2 = 0.83). In this instance, difficulties were experienced with haemolymph analyses owing to a lack of sensitivity. 相似文献
86.
ten Hallers-Tjabbes CC Wegener JW Van Hattum B Kemp JF ten Hallers E Reitsemae TJ Boon JP 《Marine environmental research》2003,55(3):203-233
The presence and the development of imposex were investigated in the common whelk (Buccinum undatum) and the red whelk (Neptunea antiqua) from the open North Sea and the Skagerrak. Imposex development was related to levels of organotins in snails and in the fine fractions (< 63 microm) of the sediments they inhabit. The sampling locations were classified according to three levels of traffic densities of ships of > or = 100 gt per day passing within 15 Nautical miles of the sampling station, shipping levels being: high (> 10 ships day(-1)), intermediate (5--10 ships day(-1)), and low (< 5 ships day(-1)). Sampling stations were also classified according to presence or absence of a vertically stratified water column. In the snails the body levels of the butyltin metabolites MBT and DBT and the parent phenyltin compound TPT, were higher than those of TBT and PT metabolites. In the sediment, the parent compounds and the mono-substituted metabolites MBT and MPT were present in the highest concentrations. The highest body levels of all organotin compounds and the highest imposex indices for the common whelk were found at those locations in the Southern Bight and the German Bight that had a high shipping density as well as a homogeneously mixed water column during the whole year. At these locations sediment levels of organotins were also higher than at other sites. In contrast, the body levels of organotins were low and imposex was sometimes even completely absent in snails from stratified deep-water stations in the Skagerrak, despite a very high shipping density in the entrance area of the Baltic. In sediments from stratified locations with low or intermediate shipping densities, organotin compounds were below or close to their respective limits of detection. These stations were located in areas with a stratified water column during the whole year. The results can be explained by postulating a much higher resistance for dissolved organotins to migrate through a pycnocline. Organotins could only transgress through a pycnocline when adsorbed to settling particles that manage to transgress the boundary between layers. N. antiqua could only be obtained in sufficient numbers from deeper water stations, which almost all had a stratified water column. At stations where both snail species were obtained and imposex was present, the imposex index was higher in the red whelk. Hence N. antiqua seems to be the more sensitive species of the two. In the red whelk, imposex development increased with shipping density too, though in the smaller samples the trend was not significant. Average biota-sediment accumulation factors (BSAFs; normalised for lipid content in snails and TOC content in the fraction < 63 microm in sediments) for Buccinum ranged from 0.4 to 1.0 for butyltins and were similar to literature values reported for TBT in other marine species. Higher average BSAF values were found for phenyltins 1.5 (MPT) to 17 (TPT). The high values for TPT match the ranges expected from equilibrium partitioning concepts of persistent hydrophobic compounds. The ratio of live snails to the total number of live snails plus empty shells ranged between 2.5 and 93%. This parameter might be a useful indicator to compare past and present densities of populations of both species in different areas of the North Sea. 相似文献
88.
89.
前言
在所有城市和近郊辖区,均设有用于储集城市污水沉淀物(OCB)的过滤场。城市污水沉淀物是地下水的污染源,其主要污染物是:尿素分解时产生的铵以及腐殖族的有机物。当地下水水位高出城市污水沉淀物的底面时,在大面积过滤场下形成厌氧条件。 相似文献
90.
An exact, closed‐form analytical solution is derived for one‐dimensional (1D), coupled, steady‐state advection‐dispersion equations with sequential first‐order degradation of three dissolved species in groundwater. Dimensionless and mathematical analyses are used to examine the sensitivity of longitudinal dispersivity in the parent and daughter analytical solutions. The results indicate that the relative error decreases to less than 15% for the 1D advection‐dominated and advection‐dispersion analytical solutions of the parent and daughter when the Damköhler number of the parent decreases to less than 1 (slow degradation rate) and the Peclet number increases to greater than 6 (advection‐dominated). To estimate first‐order daughter product rate constants in advection‐dominated zones, 1D, two‐dimensional (2D), and three‐dimensional (3D) steady‐state analytical solutions with zero longitudinal dispersivity are also derived for three first‐order sequentially degrading compounds. The closed form of these exact analytical solutions has the advantage of having (1) no numerical integration or evaluation of complex‐valued error function arguments, (2) computational efficiency compared to problems with long times to reach steady state, and (3) minimal effort for incorporation into spreadsheets. These multispecies analytical solutions indicate that BIOCHLOR produces accurate results for 1D steady‐state, applications with longitudinal dispersion. Although BIOCHLOR is inaccurate in multidimensional applications with longitudinal dispersion, these multidimensional multispecies analytical solutions indicate that BIOCHLOR produces accurate steady‐state results when the longitudinal dispersion is zero. As an application, the 1D advection‐dominated analytical solution is applied to estimate field‐scale rate constants of 0.81, 0.74, and 0.69/year for trichloroethene, cis‐1,2‐dichloroethene, and vinyl chloride, respectively, at the Harris Palm Bay, FL, CERCLA site. 相似文献