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681.
Carles Canet Rosa María Prol-Ledesma William L. Bandy Peter Schaaf Carlos Linares Antoni Camprubí Esperana Tauler Carlos Mortera-Gutirrez 《Marine Geology》2008,251(1-2):47-59
Marine hydrogenetically precipitated ferromanganese crusts are widespread in the Pacific Ocean. They occur as pavements coating volcanic or sedimentary hard-rock substrates, mainly on the slopes of seamounts, plateaus and hills in ocean basins and continental margins. We studied three ferromanganese crusts from one dredge haul from the Rivera Plate (western margin of Mexico), which are up to 15 mm thick and grow directly on a substrate of pillow basalt fragments. They consist of laminated, botryoidal, porous aggregates mostly of Fe and Mn oxyhydroxides and up to 10% silicates. XRD analysis showed the predominance of poorly crystallized mineral phases in the crusts that include Mn-feroxyhyte and vernadite, and an authigenic smectite-like clay. Detrital minerals probably derive from granodiorites of the eastern wall of the neighboring Middle America Trench. Scattered barite grains occur on the crust surface and suggest plume fall-out derived from hydrothermal vents, although a possible pelagic source cannot be dismissed. Ratios between major (Fe, Mn, Si) and trace (Co, Ni, Cu) elements reveal that such crusts are predominantly hydrogenetic in origin, although they show a hydrothermal influence that increases in the outer layers. Iron contents range from 16.2 to 25.2 wt.%, and manganese from 3.4 to 14.5 wt.%. The Fe/Mn ratio ranges from 1.6 to 7.0. The SiO2/Al2O3 ratio ranges from 4.3 to 6.6, indicating the presence of biogenic silica (radiolarians). The concentrations of copper (up to 383 ppm) and cobalt (up to 534 ppm) are significantly below those of the typical hydrogenetic crusts, whereas Ni (up to 1320 ppm) is about the same or slightly lower. REE normalized profiles and ΣREE values (486 to 732 ppm) match those reported for hydrogenetic crusts, but suggest a hydrothermal contribution for the later crust layers. The inferred crust growth rates using the Co-chronometer (44 and 229 mm/Myr) are higher than those reported for pure hydrogenetic crusts (mostly 1 to 6 mm/Myr), thus indicating an increasing hydrothermal influence. The highest growth rate (229 mm/Myr, corresponding to the outer crust layers) suggests a regional hydrothermal input of iron and manganese to seawater. The intensification of regional submarine hydrothermal activity began about 13,000 yr ago, and may be related to the tectonic activity in the complex junction of the Rivera, Cocos, Pacific and North America plates. 相似文献
682.
Effects of biological crust coverage on soil hydraulic properties for the Loess Plateau of China 总被引:5,自引:0,他引:5 下载免费PDF全文
Biological soil crusts (BSCs) are ubiquitous living covers that have been allowed to grow on abandoned farmlands over the Loess Plateau because the “Grain for Green” project was implemented in 1999 to control serious soil erosion. However, few studies have been conducted to quantify the effects of BSC coverage on soil hydraulic properties. This study was performed to assess the effects of BSC coverage on soil hydraulic properties, which are reflected by the soil sorptivity under an applied pressure of 0 (S 0 ) and ?3 (S 3 ) cm, saturated hydraulic conductivity (K s ), wetting front depth (WFD ), and mean pore radius (λ m ), for the Loess Plateau of China. Five classes of BSC coverage (i.e., 1–20%, 20–40%, 40–60%, 60–80%, and 80–100%) and a bare control were selected at both cyanobacteria‐ and moss‐covered sites to measure soil hydraulic properties using a disc infiltrometer under 2 consecutive pressure heads of 0 and ?3 cm, allowing the direct calculation of S 0 , S 3 , K s , and λ m . The WFD was measured onsite using a ruler immediately after the experiments of infiltration. The results indicated that both cyanobacteria and moss crusts were effective in changing the soil properties and impeding soil infiltration. The effects of moss were greater than those of cyanobacteria. Compared to those of the control, the S 0 , S 3 , K s , WFD , and λ m values of cyanobacteria‐covered soils were reduced by 13.7%, 11.0%, 13.3%, 10.6%, and 12.6% on average, and those of moss‐covered soils were reduced by 27.6%, 22.1%, 29.5%, 22.2%, and 25.9%, respectively. The relative soil sorptivity under pressures of 0 (RS 0 ) and ?3 (RS 3 ) cm, the relative saturated hydraulic conductivity (RK s ), the relative wetting front depth (RWFD ), and the relative mean pore radius (Rλ m ) decreased exponentially with coverage for both cyanobacteria‐ and moss‐covered soils. The rates of decrease in RS 0 , RS 3 , RK s , RWFD , and Rλ m of cyanobacteria were significantly slower than those of moss, especially for the coverage of 0–40%, with smaller ranges. The variations of soil hydraulic properties with BSC coverage were closely related to the change in soil clay content driven by the BSC coverage on the Loess Plateau. The results are useful for simulating the hydraulic parameters of BSC‐covered soils in arid and semiarid areas. 相似文献
683.
电解二氧化锰废渣中的重金属元素在雨水淋滤下,通过地表径流对下游水生态系统及农业生态系统造成不同程度的环境污染和安全隐患,因此,准确测定电解二氧化锰废渣浸出液中的重金属元素含量具有重要的现实意义。电解二氧化锰废渣浸出液中的重金属元素含量通常很低,采用原子吸收光谱法、电感耦合等离子体发射光谱法测定,检出限通常难以满足测定要求。采用电感耦合等离子体质谱法(ICP-MS)测定,消除复杂质谱干扰面临挑战。本文采用电感耦合等离子体串联质谱(ICP-MS/MS)测定电解二氧化锰废渣浸出液中的重金属元素含量。电解二氧化锰废渣中6种重金属元素Cr、Ni、As、Cd、Hg、Pb经硫酸和硝酸混合酸浸出后直接采用ICP-MS/MS进行测定,利用串联质谱的O_2反应模式消除分析过程中Cr、Ni、As、Cd受到的质谱干扰,通过考察不同分析模式下~(52)Cr、~(60)Ni、~(75)As、~(111)Cd的背景等效浓度(BEC),评价质谱干扰对分析结果的影响。结果表明:在MS/MS模式下选择O_2为反应气,采用质量转移法和原位质量法可以消除~(52)Cr、~(60)Ni、~(75)As、~(111)Cd的所有质谱干扰。Cr、Ni、As、Cd、Hg、Pb检出限分别为3.06、9.31、3.50、2.72、2.03、1.89ng/L,加标回收率在95.6%~106.2%之间,相对标准偏差(RSD)≤3.9%。所建立的方法已应用于电解二氧化锰废渣浸出液中重金属元素的测定。 相似文献
684.
针对深海探测过程中对海底富钴结壳厚度变化曲线测绘的要求,基于超声波测厚原理和B样条曲线拟合算法,结合"蛟龙号"载人潜水器的位置信息设计了深海富钴结壳厚度测绘系统。首先利用超声探头获取富钴结壳测量点表面和底部基岩的两次回波信息,通过测量渡越时间计算结壳的厚度值;将测点厚度值与"蛟龙号"载人潜水器的传感器数据融合,根据测点间的位置间隔,通过基于轮廓关键点的B样条曲线拟合绘制航行过程中的结壳厚度变化曲线。模拟实验结果表明,测绘系统可以采集测点的结壳厚度,厚度计算误差约5.6%,B样条曲线拟合能有效绘制结壳的厚度变化,误差小于10%,拟合曲线与结壳截面的纹路相符。 相似文献
685.
元素活动态测量的分析方法 总被引:5,自引:1,他引:4
发展了元素活动态各相中11 种以上元素的分析方法,讨论了提取操作和分析、测定中的关键 相似文献
686.
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688.
Chemical and enzymatic reagents have been employed to determine available concentrations of Fe, Mn, Cu and Zn in contaminated estuarine sediment. Gastric and intestinal enzymes (pepsin, pH 2, and trypsin, pH 7·6, respectively) removed significantly more metal than was water-soluble or exchangeable (by seawater or ammonium acetate), while gastro-intestinal fluid of the demersal teleost, Pleuronectes platessa L. (plaice), employed to operationally define a bioavailable fraction of contaminants, generally solubilized more metal than the model enzymes. Manganese was considerably more available than Fe under these conditions and it is suggested that the principal mechanism of contaminant release is via surface complexation and reductive solubilization of Mn oxides, a process which is enhanced under conditions of low pH. Of the chemical reagents tested, acetic acid best represents the fraction of Mn (as well as Cu and Zn) which is available under gastro-intestinal conditions, suggesting that the reducing tendency of acetate is similar to that of the ligands encountered in the natural digestive environment. Although the precise enzymatic and non-enzymatic composition of plaice gastro-intestinal fluid may be different to that encountered in more representative, filter-feeding or burrowing organisms, a general implication of this study is that contaminants associated with Mn oxides are significantly more bioavailable than those associated with Fe oxides, and that contaminant bioavailability may be largely dictated by the oxidic composition of contaminated sediment. 相似文献
689.
690.