全文获取类型
收费全文 | 413篇 |
免费 | 16篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 37篇 |
地球物理 | 65篇 |
地质学 | 242篇 |
海洋学 | 25篇 |
天文学 | 41篇 |
综合类 | 4篇 |
自然地理 | 10篇 |
出版年
2020年 | 7篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 13篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 20篇 |
2009年 | 18篇 |
2008年 | 15篇 |
2007年 | 9篇 |
2006年 | 22篇 |
2005年 | 15篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1982年 | 4篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1968年 | 3篇 |
1967年 | 4篇 |
1962年 | 3篇 |
1960年 | 5篇 |
1959年 | 3篇 |
1958年 | 4篇 |
1956年 | 4篇 |
1953年 | 4篇 |
1952年 | 3篇 |
1950年 | 4篇 |
1949年 | 4篇 |
1948年 | 3篇 |
1921年 | 4篇 |
1914年 | 3篇 |
1912年 | 4篇 |
排序方式: 共有440条查询结果,搜索用时 15 毫秒
181.
182.
183.
Thomas Leipe Franz Tauber Henry Vallius Joonas Virtasalo Szymon U?cinowicz Nicole Kowalski Sven Hille Susanna Lindgren Tero Myllyvirta 《Geo-Marine Letters》2011,31(3):175-188
In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic
Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep
muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry
bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum
POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm–3) and moderate POC concentrations (4–7 mg cm–3). Furthermore, sediment mass accumulation rates (MAR), based on 210Pb and 137Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial
rates. Overall, these vary between 14 and 35 g m–2 year–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC
contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented
data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition
can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor
(morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon
cycle in this large brackish-water marginal sea. 相似文献
184.
ISO-SWS spectra of two Mira variables (R Cas and T Dra), taken at two different pulsational phases, are presented. We describe
the reduction of the data and the encountered problems. The dust features observed by ISO at different phases and with the
Low Resolution Spectrometer of IRAS are compared. We briefly discuss the results in terms of current models for the circumstellar
dust shells of AGB variables.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
185.
Lunar Laser Ranging (LLR) provides various quantities related to reference frames like Earth orientation parameters, coordinates and velocities of ground stations in the Earth-fixed frame and selenocentric coordinates of the lunar retro-reflectors. This paper presents the recent results from LLR data analysis at the Institut für Erdmessung, Leibniz Universität Hannover, based on all LLR data up to the end of 2016. The estimates of long-periodic nutation coefficients with periods between 13.6 days and 18.6 years are obtained with an accuracy in the order of 0.05–0.7 milliarcseconds (mas). Estimations of the Earth rotation phase \(\Delta \)UT are accurate at the level of 0.032 ms if more than 14 normal points per night are included. The tie between the dynamical ephemeris frame to the kinematic celestial frame is estimated from pure LLR observations by two angles and their rates with an accuracy of 0.25 and 0.02 mas per year. The estimated station coordinates and velocities are compared to the ITRF2014 solution and the geometry of the retro-reflector network with the DE430 solution. The given accuracies represent 3 times formal errors of the parameter fit. The accuracy for \(\Delta \)UT is based on the standard deviation of the estimates with respect to the reference C04 solution. 相似文献
186.
187.
Marina A. IVANOVA Natalia N. KONONKOVA Alexander N. KROT Richard C. GREENWOOD Ian A. FRANCHI Alexander B. VERCHOVSKY Mario TRIELOFF Ekaterina V. KOROCHANTSEVA Franz BRANDSTÄTTER 《Meteoritics & planetary science》2008,43(5):915-940
Abstract— Isheyevo is a metal‐rich carbonaceous chondrite that contains several lithologies with different abundances of Fe,Ni metal (7–90 vol%). The metal‐rich lithologies with 50–60 vol% of Fe,Ni metal are dominant. The metal‐rich and metal‐poor lithologies are most similar to the CBb and CH carbonaceous chondrites, respectively, providing a potential link between these chondrite groups. All lithologies experienced shock metamorphism of shock stage S4. All consist of similar components—Fe,Ni metal, chondrules, refractory inclusions (Ca, Al‐rich inclusions [CAIs] and amoeboid olivine aggregates [AOAs]), and heavily hydrated lithic clasts—but show differences in their modal abundances, chondrule sizes, and proportions of porphyritic versus non‐porphyritic chondrules. Bulk chemical and oxygen isotopic compositions are in the range of CH and CB chondrites. Bulk nitrogen isotopic composition is highly enriched in 15N (δ15N = 1122‰). The magnetic fraction is very similar to the bulk sample in terms of both nitrogen release pattern and isotopic profile; the non‐magnetic fraction contains significantly less heavy N. Carbon released at high temperatures shows a relatively heavy isotope signature. Similarly to CBb chondrites, ~20% of Fe,Ni‐metal grains in Isheyevo are chemically zoned. Similarly to CH chondrites, some metal grains are Ni‐rich (>20 wt% Ni). In contrast to CBb and CH chondrites, most metal grains are thermally decomposed into Ni‐rich and Ni‐poor phases. Similar to CH chondrites, chondrules have porphyritic and non‐porphyritic textures and ferromagnesian (type I and II), silica‐rich, and aluminum‐rich bulk compositions. Some of the layered ferromagnesian chondrules are surrounded by ferrous olivine or phyllosilicate rims. Phyllosilicates in chondrule rims are compositionally distinct from those in the hydrated lithic clasts. Similarly to CH chondrites, CAIs are dominated by the hibonite‐, grossite‐, and melilite‐rich types; AOAs are very rare. We infer that Isheyevo is a complex mixture of materials formed by different processes and under different physico‐chemical conditions. Chondrules and refractory inclusions of two populations, metal grains, and heavily hydrated clasts accreted together into the Isheyevo parent asteroid in a region of the protoplanetary disk depleted in fine‐grained dust. Such a scenario is consistent with the presence of solar wind—implanted noble gases in Isheyevo and with its comparatively old K‐Ar age. We cannot exclude that the K‐Ar system was affected by a later collisional event. The cosmic‐ray exposure (CRE) age of Isheyevo determined by cosmogenic 38Ar is ~34 Ma, similar to that of the Bencubbin (CBa) meteorite. 相似文献
188.
The Kachchh Basin and the Jaisalmer Basin are two neighboring Mesozoic sedimentary basins at the western margin of the Indian
craton. The Jurassic succession of the Kachchh Basin is more complete and more fossiliferous than that of the Jaisalmer Basin.
Consequently, intrabasinal correlation of the sedimentary units has been possible in the Kachchh Basin, but not in the Jaisalmer
Basin. However, some marker beds existing in the Kachchh Basin can be recognized also in the Jaisalmer Basin. Ammonite evidence
shows that they are time-equivalent. The following four units form marker intervals in both basins: (1) the pebbly rudstone
unit with Isastrea bernardiana and Leptosphinctes of the Kaladongar Formation (Kachchh Basin) and the Isastrea bernardiana-bearing rudstone of the Jaisalmer Formation (Jaisalmer Basin) both represent transgressive systems tract deposits dated as
Late Bajocian; (2) bioturbated micrites with anomalodesmatan bivalves within the Goradongar Yellow Flagstone Member (Kachchh
Basin) and bioturbated units in the Fort Member (Jaisalmer Basin) represent maximum flooding zone deposits of the Middle to
Late Bathonian; (3) trough-crossbedded, sandy pack- to grainstones of the Raimalro Limestone Member (Kachchh Basin) and the
basal limestone-sandstone unit of the Kuldhar section of the Jaisalmer Formation (Jaisalmer Basin) correspond to Late Bathonain
transgressive systems tract deposits; and (4) ferruginous ooid-bearing carbonates with hardgrounds of the Dhosa Oolite member
(Kachchh Basin) and the middle part of the Jajiya Member (Jaisalmer Basin) are Oxfordian transgressive systems tract deposits.
The fact that in both basins similar biofacies prevailed during certain time intervals demonstrates a common control of their
depositional history. As the two basins represent different tectonic settings, the most likely controlling factors were the
relative sea-level changes produced by eustatic processes, a common subsidence history of the northwestern margin of the Indian
craton, and the paleoclimate. 相似文献
189.
柴达木盆地北缘晚中生代—新生代构造应力场——来自构造节理分析的证据 总被引:2,自引:1,他引:1
柴达木盆地的构造演化,尤其是中、新生代的构造演化历史及其影响程度一直存在争议。在冷湖0号、冷湖4号、鄂博梁、结绿素等剖面开展了野外构造节理测量,应用地层恢复技术,分析了柴北缘晚中生代—新生代构造应力场的演化过程。结果表明:晚侏罗世之后,柴北缘主要受东西方向的挤压,这与区域上的研究结果一致;早白垩世北西—南东向的挤压应力可能再次影响了侏罗系;晚白垩世受南北挤压应力的影响,地层隆升遭受剥蚀;始新世下干柴沟期至上新世狮子沟期,柴北缘处于弱活动时期,接受稳定沉积;上新统狮子沟组沉积之后,由于阿尔金山的隆升,盆地北缘主体受北西—南东向应力的影响,涉及地层包括上干柴沟组、下油砂山组和上油砂山组;早、中更新世七个泉期之后,受南北向构造应力场的强烈影响,在狮子沟组、上油砂山组和下油砂山组中都有其分量,较老地层的地表露头中也有记录,这期构造运动对柴北缘油气运聚具有破坏和二次成藏的作用。因此,围绕柴北缘其他地质剖面开展更进一步的构造节理测量和分析工作,对油气资源勘探具有指导意义。 相似文献
190.