全文获取类型
收费全文 | 928篇 |
免费 | 80篇 |
国内免费 | 297篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 126篇 |
地球物理 | 222篇 |
地质学 | 771篇 |
海洋学 | 92篇 |
天文学 | 8篇 |
综合类 | 23篇 |
自然地理 | 51篇 |
出版年
2024年 | 8篇 |
2023年 | 18篇 |
2022年 | 20篇 |
2021年 | 27篇 |
2020年 | 17篇 |
2019年 | 40篇 |
2018年 | 23篇 |
2017年 | 39篇 |
2016年 | 36篇 |
2015年 | 24篇 |
2014年 | 50篇 |
2013年 | 38篇 |
2012年 | 34篇 |
2011年 | 58篇 |
2010年 | 54篇 |
2009年 | 83篇 |
2008年 | 103篇 |
2007年 | 68篇 |
2006年 | 72篇 |
2005年 | 73篇 |
2004年 | 50篇 |
2003年 | 36篇 |
2002年 | 38篇 |
2001年 | 35篇 |
2000年 | 30篇 |
1999年 | 25篇 |
1998年 | 39篇 |
1997年 | 24篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 19篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 1篇 |
排序方式: 共有1305条查询结果,搜索用时 15 毫秒
991.
利用地质学、天文学、地球物理学、古生物学资料进行约束,对地球的去气作用进行研究发现:太阳系的部分冷物质,通过吸积作用形成早期地球.在碰撞动能转变的热能作用下,造成了早期地球的表面熔融.在熔融状态的高温高压作用下,构成地球表面物质的结晶水排出地表进入原始大气;在高温高压下分解的碳酸盐、硫酸盐、卤化物等产生的二氧化碳、硫化氢、二氧化硫、氯化氢、氟化氢等气体进入原始大气,和水蒸汽一道共同组成原始大气.当地球内部在重力势能和放射能的作用下继续熔融时,地球表面固化为原始岩石圈.后来,地球除表面岩石圈外,整个地球完全熔融.地球内部物质熔融形成的水和二氧化碳等气体,被岩石圈圈闭.只有当冰川形成和消融,引起造海和造陆作用,导致火山喷发和地震时,这些气体才可能排出地表.这些气体的排出,受地球内部的熔融状态、冰川形成的位置(是在海洋或是在陆地)、生物的演化、太阳光的强度等因素的综合影响. 相似文献
992.
993.
Sediment profiles of less commonly determined elements measured by Laser Ablation ICP-MS 总被引:1,自引:0,他引:1
Marvourneen K. Dolor George R. Helz William F. McDonough 《Marine pollution bulletin》2009,59(4-7):182
Anthropogenic influences on trace element profiles in dated sediments from estuaries have been often documented, with the vast majority of studies focusing on a short list of high-abundance trace elements. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) provides a new approach that minimizes sample preparation and contamination while yielding data on a much larger list of elements simultaneously. We present concentrations and enrichment factor profiles for 22 elements at a locality that is 50 km southeast of Baltimore, the principal industrial city on Chesapeake Bay. Samples representing deposition over almost the entire 20th century were obtained from two archived cores collected 20 years apart. The following elements exhibit profiles consistent with a strong anthropogenic influence, i.e. enrichment after 1920 followed by decline after ca.1980, possibly reflecting increased regulatory efforts: Mn, Co, Cu, Zn, Ag, Cd, In, Sn, Sb, Te, Tl, Pb and Bi. As expected, the redox-sensitive elements: Mo, Re and U have similar profiles to one another. Previously, the potentially hazardous elements, Ag, In, Sb, Te, Tl and Bi, have been measured only rarely in estuarine sediments and never in Chesapeake Bay. Our discovery that their profiles track those of well-known pollutants underscores a need to investigate their sources, transport and biogeochemical behavior. Several rarely determined trace elements, Ga, Ge and Nb, exhibit trendless profiles, as do the major elements, Ti and Fe. 相似文献
994.
长江口新生相形成的实验研究 总被引:2,自引:0,他引:2
证实了长江河水与长江口海水相混可形成新生相,新生相能强烈地捕集水体中的痕量元素;并首次用动态光散射技术测定了新生相的颗粒大小与分布。 相似文献
995.
于1978年采集了西藏高原26个盐湖、6条河流、10处泉水及3地盐湖区的大气降水的水样,以ZCP等离子光谱仪测定所采水样中Fe,Mn,Al,Cu,Pb,Zn,Ni,Cr等痕量金属含量,结果表明,1.盐湖水及河流、泉水和大气降水等水系中的痕量金属均高度富集,但以盐湖水的最大;盐湖水中各痕量金属富集程度不一,其顺序:Pb>Mn>Cr>Fe>Zn>Cu>Al>Ni。2.区域出露的岩性、气候、湖盆及水文等为盐湖水中富集痕量金属创造了有利条件。3.高痕量金属浓度的河流、泉水及大气降水是控制和影响盐湖水中痕量金属富集的主要的直接因素。4.盐湖水的矿化度、pH及水化学类型也影响着水中痕量金属的富集。 相似文献
996.
In order to trace their feeding habits, stable carbon and nitrogen isotope ratios (delta15N and delta13C), as well as trace metal concentrations (Zn, Cd, Fe, Cu, Se and Hg) were analysed in the tissues of five commercial shark species from the Celtic Sea: the tope shark Galeorhinus galeus, the black-mouthed catshark Galeus melastomus, the starry smooth hound Mustelus asterias, the spiny dogfish Squalus acanthias and the lesser-spotted dogfish Scyliorhinus canicula. Our results were compared to previously described stomach contents and isotopic composition of potential preys. Isotopic ratio delta15N suggested that tope sharks fed at a higher trophic level (16.7 per thousand in the muscle) than the other species, reflecting its piscivorous diet. The lower values of spiny dogfish (11.6 per thousand in the muscle) might be explained, amongst other things, by either its migratory behaviour or its preference for preys from lower trophic levels. Cd and Hg were correlated with isotopic ratios delta13C and delta15N, and were shown to be diet-related whereas Zn, Fe and Cu seemed much more linked to species-specific metabolism. Although this multidisciplinary approach is revealed as a useful tool for the study of shark ecology, the lack of known trophic fractionation suggests that isotopic data be compared to traditional diet analyses. 相似文献
997.
南海ODP1146站位烃类气体地球化学特征及其意义 总被引:5,自引:0,他引:5
ODP1146站位位于东沙群岛南部的尖峰北小型裂谷盆地内。系统的顶空气和酸解烃分析结果表明,在0~250m(海底合成深度)区间的烃类气体含量较低且变化不大,但在390~590m特别是在550~590m区间存在较明显的高烃异常。这一高烃异常可能与天然气水合物有关,是邻区天然气水合物分解后释放出的高烃流体沿层间裂隙或断层侧向迁移的结果。甲烷碳同位素的测定结果显示其δ^13C1值为-24.0‰~-37.8‰(PDB标准),结合烃类气体的分子比值C1/(C2+C3),1146站位的烃类气体应是热解气或是以热解气为主的混合气,但在中上部可能存在部分微生物气。 相似文献
998.
The chemical speciation of Cu and Zn was investigated by voltammetric titration methods in the surface waters (10 m) of the western Black Sea during an Istanbul–Sevastopol cruise conducted in November 1998. Supporting parameters (temperature (T), salinity (S), pH, alkalinity (Alk), suspended particulate matter (SPM) and dissolved and particulate 234Th) were obtained in order to distinguish hydrographic features against involvement of the metals in biogeochemical processes. In the Turkish continental slope region, the cruise track intersected a narrow vein of colder water originating on the western shelf. The core of this cold water vein was characterised by a relatively low salinity, higher specific alkalinity and higher metal (especially Cu) and metal-binding ligand concentrations.A very large portion of Cu (93–99.8%) and Zn (82–97%) was organically complexed. The degree of complexation was highest in shelf waters and lowest in the central gyre. Titration data for Cu were modelled by two classes of organic binding ligands characterised by (CL1=3–12 nM, log K1′=13.1–13.9) and (CL2=20–70 nM, log K2′=9.4–11.2). These ligands occurred mainly in the ‘dissolved’ phase, as defined by 0.4-μm filtration. The stronger Cu-binding ligand seemed to be produced in situ in response to Cu concentration, whereas the weaker Cu-binding ligand appeared to be derived from terrestrial sources and/or reducing shelf sediments. Titration results for Zn were generally represented by one class of ligands (CL1=8–23 nM, log K1′=9.4–10.2), which were almost uniformly distributed between the ‘dissolved’ (78±8%) and the particulate phase (22±8%). The concentration of these strong Zn-binding ligands showed a very good correlation with SPM (r2=0.64), which improved when the dissolved ligands alone were considered (r2=0.78). It is hypothesised that these ligands were produced in situ by the bacterial breakdown of particulate organic matter. 相似文献
999.
Distribution and contamination of trace metals in surface sediments of the East China Sea 总被引:3,自引:0,他引:3
Tien-Hsi Fang Jou-Yun Li Hui-Min Feng Hung-Yu Chen 《Marine environmental research》2009,68(4):178-187
The distributions, contamination status and annual sedimentation flux of trace metals in surface sediments of the East China Sea (ECS) were studied. Higher concentrations of the studied metals were generally found in the inner shelf and the concentrations decreased seaward. The sequences of the enrichment factor (EF) of the studied metals are Cu > Mn > Ni > Zn > Pb > Fe. The values of EF suggest that the metals contamination in the middle and outer shelves of the ECS is still minor. The annual sedimentation fluxes of trace metals in the ECS were: Fe, 3.48 × 107 t/y; Mn, 9.07 × 105 t/y; Zn, 1.08 × 105 t/y; Ni, 4.48 × 104 t/y; Pb, 4.32 × 104 t/y and Cu, 3.1 × 104 t/y, respectively. Approximately 55–70% and 10–17% of the sedimentation fluxes of trace metals were deposited in the inner shelf and the Changjiang estuarine zone. 相似文献
1000.
造成全球暖化的主要原因是温室气体的过量排放,其中CO2的贡献率达60%,贝类养殖具有碳沉积作用。依据农业部渔业局编制的《中国渔业统计年签》,以2001年到2010年的年平均产量计算贝类捕获和养殖的碳沉积能力,并评估其碳沉积潜力;计算牡蛎、蛤、扇贝与贻贝4种贝壳单位面积的碳沉积能力并与森林、珊瑚礁的碳沉积能力进行比较分析。分析表明中国近10年贝类总产量稳定在1100万t以上,并有增加的趋势,其中海水养殖贝类约占87.34%。贝类养殖和捕获总产量的碳沉积和海水养殖产量的碳沉积量分别为58.57、51.15万t/a,碳沉积能力分别相当于122.28、106.78万ha的造林,可分别减少大气CO2增加量的0.0125%、0.0109%。牡蛎、蛤、扇贝与贻贝的单位面积碳沉积速率分别为1.573、0.388、0.301、1.039t碳/(ha·a);牡蛎和贻贝高于森林的碳沉积能力0.479t碳/(ha·a);但低于珊瑚礁的碳沉积能力1.8t碳/(ha·a)。中国贝类淡、海水养殖产量可分别创造约268.4万元/a、12 711.2万元/a的碳权商机。 相似文献