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991.
Major chemical elements and Rb, Sr, Ba abundances were measured for loess samples from Chashmanigar loess-soil sequence in
southern Tajikistan. And the degree of element loss and intensity of weathering of the samples were calculated. From these
calculations we found that the paleosol horizons of the Chashmanigar section were chemically weathered to some extent and
the weathering intensity of the soils is stronger than that of loess horizons, indicating that paleosols in southern Tajikistan
were deposited in relatively warm and humid interglacial ages. In addition, the southern Tajikistan loess deposited before
0.9Ma BP was more intensely weathered than that deposited after 0.9Ma BP, which may imply the intensification of aridity in
this area since 0.9Ma BP. 相似文献
992.
南沙群岛及其邻近海区第四纪气候演化的非线性特征 总被引:1,自引:0,他引:1
南沙群岛及其邻近海区近18.5万年以来气候与环境非线性研究表明曾发生三次明显气候转变,形成四个映射区。其中氧同位素第5期与第4期转变较明显,其次是氧同位素第6期与第5期的转变,最后是第3与第2期之间的变化,这与全球第四纪古气候研究结果是一致的,得到了氧同位素和古生物资料的进一步印证。半深海-深海海底沉积物有机质演化阶段在海进海退过程中表现出垂直分带和非线性变化。上陆坡以氧化堆积带为主,有机质供给多、但消耗迅速且水动力相对强;中陆坡为利于有机质保存的还原带;下陆坡为有机质缩合阶段,陆坡下缘-远洋为有机质沉降氧化带与沉积埋藏阶段的植烷形成带。这几个带在古气候、古海平面非线性变化中是沿海底向上或向下迁移的,其变化是非线性的。 相似文献
993.
青藏高原北部的第四纪断层运动 总被引:16,自引:0,他引:16
近10年来,通过详细考察和填图工作,对青藏高原北部的第四纪活动构造及断层运动取得了大批新资料,在最近在中法合作研究中,对东昆仑活动断裂带及邻区又进行了较深入的调查,本文以上述新资料为基础,简要讨论了青藏高原北部第四纪活断层的运动学和动力学基本特征本区重要的活动断裂可划分为下述3类,(1)大规模的弧形左旋走滑断裂带,其中包括青藏高原北部边缘的阿尔金活动断裂带,昌马活动断裂带及海原活动断裂带,中部的东 相似文献
994.
湖南第四纪地层划分及其下限 总被引:4,自引:0,他引:4
根据第四纪沉积物特征、孢粉组合、古脊椎动物、古地磁等有关资料,将湖南省区内第四系地层自老至新划分为:泪罗组、新开铺组、陈家咀组、白沙井组、马王堆组、白水江组、丁蜀组及水陆洲组等。原划为早更新世湖仙山组或伍家峪组均为上新世乃至中新世地层,并确定其第四纪下限为25MaB.P. 相似文献
995.
关于长江三角洲第四纪海侵的─孔之见 总被引:1,自引:0,他引:1
实际钻孔资料进一步揭示了长江三角洲地区(河口带区)的海陆变迁特征,在海侵范围内存有"陆岛",海侵层在平面上并非那样连续,特别是更新世的几次海侵层、经常被陆相堆积物割离,反映了对长江三角洲古地理的"现状"认识尚须深入。 相似文献
996.
甘肃玉门地区第四纪晚期构造阶地的红外释光测年 总被引:4,自引:0,他引:4
光释光(OSL)测年是近几年从热释光(TL)测年基础工起来的测定第四纪沉积物年龄的一种新技术,其原理与TL测年类似。不同的是:OSL是单色光束激发品体中储存的电离辐射能使其以光的形式释放出来。当用近红外线束作为激光光源时称之为红外释光测年。与TL测年相比,ISL测年可以不考虑残留的OSL信号,而且测量具有简便,迅速且准确等优点。本文用细颗粒红外释放技术对玉门地区的构造阶地进行了年龄测定,初步结果表 相似文献
997.
B. Gehrke K. S. Lackschewitz H. -J. Wallrabe-Adams 《International Journal of Earth Sciences》1996,85(3):525-535
Sediment samples from the Mid-Atlantic Reykjanes Ridge (59°N) were taken to get information about sediment genesis and to
identify different sources during the late Quaternary. Samples were investigated by X-ray diffraction and grain-size analyses.
The clay mineral assemblages in sediments of the Reykjanes Ridge reflect paleoceanographic changes during the late Quaternary.
Holocene sediments are characterized by high contents of smectite, mainly of less developed crystallinity. In the spatial
distribution of clay minerals high smectite concentrations on the eastern flank and slightly decreasing concentrations on
the western flank of the Reykjanes Ridge indicate the action of bottom-water transport. The smectite originates mainly from
the volcanogenous Icelandic shelf and reflects the influence of Iceland-Scotland Overflow Water (ISOW). Stratigraphic variability
in the clay mineral composition reflects predominantly the influence of different sources, resulting from oceanographic and
glacial transport processes. During glacial time sediment transport is due mainly to input by icebergs. Increasing amounts
of illite, chlorite, and kaolinite characterize ice-rafted sediments of the “Heinrich layers”. In these sediments smectite
crystallinity is well developed. In contrast, several other ice-rafted layers contain smectite with low crystallographic order,
similar to smectites of Holocene age. The icelandic source was proved by distinct amounts of basaltic glass in the coarse-grained
sediment. At approximately 55 ka increasing amounts of chlorite and kaolinite suggest an enhanced influx of warm North Atlantic
surface waters. This hypothesis is supported by a high carbonate shell production at this time. Relative low concentrations
and the well-developed crystallinity of smectite minerals characterize the Last Glacial Maximum (LGM; 18–16 ka), indicating
a reduced supply of fine icelandic material. Shortly after the LGM, at the beginning of termination IA, a distinct increase
in fine-grained quartz (<2μm) and smectite are visible, which are proposed to reflect a supply of fine-grained ice-rafted
material. At 13 ka linear increasing smectite concentrations of lower crystallographic order indicate increasing supply of
fine-grained material from Iceland, linked to reinitiation of bottom currents of the ISOW. Full reinitiation is indicated
at around 10 ka, where a strong increase in smectite of low crystallographic order is detected. 相似文献
998.
Groundwater recharge estimation using chloride,stable isotopes and tritium profiles in the sands of northwestern Senegal 总被引:2,自引:0,他引:2
A study of environmental chloride, deuterium, oxygen-18, and tritium in deep sand profiles (35 m) has been carried out in order to estimate their relative value for measuring average groundwater recharge. The investigation was located at a 0.1-km2 site in Quaternary sands near the northwestern coast of Senegal in a zone of rainfed agriculture. By using a steady-state model for duplicate unsaturated zone chloride profiles, the long-term average recharge at the site was estimated to be 30 mm yr–1 or around 10% of the average precipitation (290 mm). The chloride concentration of adjacent shallow groundwater was relatively uniform and comparable to the unsaturated zone average, while the spatial variability in the depth distribution of Cl– in the unsaturated zone was considerable. Stable isotope (deuterium and oxygen-18) data show that there is some isotopic enrichment due to direct evaporation through the soil surface. The degree of heavy isotope enrichment is proportional to the extent of evaporative loss and there is good correspondance with the chloride enrichment. Nevertheless, stable isotopes cannot be used quantitatively to estimate the recharge. The excellent preservation of the peak in thermonuclear tritium in precipitation in the unsaturated zone at depths between 12 and 20 m enables an estimated annual recharge of 24 mm yr–1 in this area to be calculated, using the piston flow model. Agreement therefore between Cl and3H as tools for recharge measurement is reasonable over the site. 相似文献
999.
1000.
周口店地区第四纪哺乳动物群的演化与环境变迁探讨 总被引:2,自引:0,他引:2
讨论了Alilepusannectens、HypolagusbrachypusLepussp.、Sciurotamiaspraecox、AllocricetusteilhardiCricetinusvarians、Hyperacriusyenshanensis、Allophaiomyscf.pliocaenicus、Proedromyscf.bedfordi、Chardinomysnihewanicus、Muscf.musculus和Apodemusdominans的地史分布。根据哺乳动物群的分析与对比,得出第18地点为早更新世早期,第12地点、东洞地点为早更新世中期,第9地点、西洞地点为早更新世晚期,第13地点为早更新世末期至中更新世初期,第1、2、5、6、11、10、21、23及上店洞地点为中更新世,新洞为中更新世晚期至晚更新世早期,东岭子洞为晚更新世,山顶洞为晚更新世晚期。还讨论了周口店地区一些主要第四纪哺乳动物群的生态类型特点,第四纪的气候波动及生态环境变迁。 相似文献