全文获取类型
收费全文 | 2892篇 |
免费 | 49篇 |
国内免费 | 50篇 |
专业分类
测绘学 | 71篇 |
大气科学 | 355篇 |
地球物理 | 599篇 |
地质学 | 989篇 |
海洋学 | 152篇 |
天文学 | 677篇 |
综合类 | 15篇 |
自然地理 | 133篇 |
出版年
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 49篇 |
2017年 | 41篇 |
2016年 | 60篇 |
2015年 | 35篇 |
2014年 | 63篇 |
2013年 | 107篇 |
2012年 | 82篇 |
2011年 | 115篇 |
2010年 | 89篇 |
2009年 | 121篇 |
2008年 | 133篇 |
2007年 | 115篇 |
2006年 | 93篇 |
2005年 | 119篇 |
2004年 | 98篇 |
2003年 | 82篇 |
2002年 | 94篇 |
2001年 | 80篇 |
2000年 | 80篇 |
1999年 | 90篇 |
1998年 | 89篇 |
1997年 | 73篇 |
1996年 | 70篇 |
1995年 | 69篇 |
1994年 | 51篇 |
1993年 | 51篇 |
1992年 | 47篇 |
1991年 | 56篇 |
1990年 | 44篇 |
1989年 | 43篇 |
1988年 | 21篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1984年 | 51篇 |
1983年 | 33篇 |
1982年 | 38篇 |
1981年 | 42篇 |
1980年 | 39篇 |
1979年 | 33篇 |
1978年 | 32篇 |
1977年 | 20篇 |
1976年 | 26篇 |
1975年 | 15篇 |
1974年 | 30篇 |
1973年 | 17篇 |
1971年 | 22篇 |
排序方式: 共有2991条查询结果,搜索用时 15 毫秒
961.
962.
Salt weathering in deserts 总被引:1,自引:0,他引:1
963.
964.
965.
Wolf U. Reimold Christian Koeberl Cedric Wright Iain McDonald 《Meteoritics & planetary science》2001,36(5):747-749
Abstract— Gorter and Glikson (2000) proposed that the Fohn‐1 structure in the Timor Sea north of Australia probably is an impact structure. Examination of their evidence reveals that it is almost impossible to confirm any of their conclusions, as the authors do not provide sufficient detail of their experimental methods. Problems with the presentation of both seismic and geochemical data cast further doubt on their conclusions. Absence of evidence for shock metamorphism and non‐chondritic siderophile element patterns in the few samples analysed make it likely that Fohn‐1 is neither a probable, nor even a possible, impact structure. 相似文献
966.
This work evaluates objective functions for multiresponse non-linear modeling using computersimulations.Tests are performed under a variety of signal-to-noise ratios and noise variance-covariancestructures.The standard error of prediction for the model parameters,computed from 50 trials,is usedfor performance comparisons.The full rank and rank-deficient problems are considered.For the fullrank problem one model was investigated,a first-order two-step consecutive reaction model,and twoobjective functions were considered,the total sum of squares and the determinant criterion.Nodistinction could be made between the two objective functions for this model.For the rank-deficient case two models were investigated,a first-order two-step consecutive reactionas in the full rank case,and a pH titration model described by the Henderson-Hasselbalch equation.Three objective functions were investigated for the rank-deficient case,the total sum of squares,aweighted total sum of squares and the determinant criterion.The total sum of squares was found toperform poorly under all conditions tested compared to the weighted total sum of squares and thedeterminant criterion.The determinant criterion was found to perform much better than the other twocriteria when the data have a combination of a low signal-to-noise ratio and high variance-covariancenoise structure. 相似文献
967.
B. G. Lottermoser U. Schütz J. Boenecke R. Oberhänsli B. Zolitschka J. F. W. Negendank 《Environmental Geology》1997,31(3-4):236-247
The accumulation of heavy metals and trace elements has been investigated in a well laminated sequence of Holocene and late
Pleistocene lake sediments composed of diatomaceous gyttja, tuff and silt and clay sediments. Varve chronology of the annually
deposited gyttja yielded a continuous high-resolution time sequence and allowed the absolute age dating of the sediment.
Fluxes of elements remained largely uniform from the late Pleistocene into the Holocene (12 867–2 364 VT years ago; VT: varve
time, years before 1950). Higher trace element and heavy metal fluxes occur from 2 322 to 862 VT years ago and reached their
maxima in the uppermost sediments (<845 VT years ago). These increasing element fluxes correlate with increasing inputs of
clastic material. The changing accumulation rates are the result of elevated soil erosion in the lake catchment caused by
human settlement, deforestation and agricultural activities. Thus disturbances of the natural geochemical cycles of the Holzmaar
region have occurred since the beginning of the Iron Age and especially since the beginning of the Middle Ages.
Received: 29 May 1996 · Accepted: 19 August 1996 相似文献
968.
ColomboC.G.Tassinari JoseM.U.Munha WilsonTeixeira TeresaPalacios AllenP.Nutman CesarSosaS. AdjairP.Santos BrunoO.Calado 《《幕》》2004,27(1):3-12
SHRIMP U/Pb-zircon data and Nd mean crustal residence ages indicate that the lmataca Complex developed from an Archean (≥3.2Ga) continental protolith which has undergone considerable isotopic disturbance plus and juvenile accretion during late-Archean (-2.8Ga) times. Transamazonian granulites experienced peak metamorphic conditions of 750-800℃, 6-8kbar with associated transpressive thrusting and tectonic imbrication. Geochronology on zircon, pyroxene and garnet constrains the timing of peak metamorphism at 1.98-2.05Ga. Diffusion modeling of Fe-Mg exchange between biotite inclusions and host garnet yields (near metamorphic peak) cooling rates of 50-100℃/Ma, with petrological cooling rates being generally consistent with cooling rates determined from geochronology. Combining the retrograde P-T path with cooling rates suggests that after the metamorphic peak, large portions of the lmataca Complex were exhumed from 30 to 17km at a rate of 7-2km/Ma.After this, exhumation rates progressively decreased as the rocks approached the surface. Rapid overall upliftlerosion had ceased when the rocks passed below 600-550℃ at 2.01-1.96 Ga ago. Observed variations in mineral cooling ages are interpreted as to reflect episodic differential tectonic exhumation within major fault systems. Inferred (maximum) ages of fault re-activation generally coincide with major continental accretion events in the Amazonian Craton and reflect long-term thermal evolution of the lmataca terrane, as conditioned by variable response to continued continental convergence during the Proterozoic. 相似文献
969.
U. R. Rao K. Kasturirangan D. P. Sharma A. K. Jain U. B. Jayanthi 《Astrophysics and Space Science》1976,42(1):193-199
The paper presents the results of the investigation on the short term X-ray emission characteristics of Cyg X-1 in the 20–150 keV range. The observations were made with balloon-borne oriented scintillation telescope and the flights were conducted from Hyderabad, India. The source was tracked over a duration of 1 hr that enabled detailed observations with time resolution of the order of 1 min. Fluctuations in the intensity of Cyg X-1 with time scales of the order of minutes have been detected besides short-term flare-like enhancements. The spectral characteristics of the flare emission features are discussed and their relationship to the phase of the binary is examined.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
970.