全文获取类型
收费全文 | 66232篇 |
免费 | 1122篇 |
国内免费 | 493篇 |
专业分类
测绘学 | 1635篇 |
大气科学 | 5278篇 |
地球物理 | 13740篇 |
地质学 | 21419篇 |
海洋学 | 5725篇 |
天文学 | 15232篇 |
综合类 | 133篇 |
自然地理 | 4685篇 |
出版年
2020年 | 474篇 |
2019年 | 496篇 |
2018年 | 937篇 |
2017年 | 916篇 |
2016年 | 1363篇 |
2015年 | 1011篇 |
2014年 | 1414篇 |
2013年 | 3237篇 |
2012年 | 1490篇 |
2011年 | 2271篇 |
2010年 | 1941篇 |
2009年 | 2920篇 |
2008年 | 2660篇 |
2007年 | 2395篇 |
2006年 | 2459篇 |
2005年 | 2134篇 |
2004年 | 2234篇 |
2003年 | 2062篇 |
2002年 | 1967篇 |
2001年 | 1776篇 |
2000年 | 1749篇 |
1999年 | 1504篇 |
1998年 | 1494篇 |
1997年 | 1480篇 |
1996年 | 1273篇 |
1995年 | 1210篇 |
1994年 | 1091篇 |
1993年 | 998篇 |
1992年 | 943篇 |
1991年 | 799篇 |
1990年 | 1009篇 |
1989年 | 849篇 |
1988年 | 754篇 |
1987年 | 927篇 |
1986年 | 816篇 |
1985年 | 1020篇 |
1984年 | 1182篇 |
1983年 | 1123篇 |
1982年 | 1017篇 |
1981年 | 976篇 |
1980年 | 833篇 |
1979年 | 815篇 |
1978年 | 867篇 |
1977年 | 787篇 |
1976年 | 750篇 |
1975年 | 695篇 |
1974年 | 703篇 |
1973年 | 709篇 |
1972年 | 440篇 |
1971年 | 384篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
111.
112.
113.
114.
A canonical theory for short GPS baselines.
Part II: the ambiguity precision and correlation 总被引:1,自引:0,他引:1
P. J. G. Teunissen 《Journal of Geodesy》1997,71(7):389-401
The present contribution is the second of four parts. It considers the precision and correlation of the least-squares estimators
of the carrier phase ambiguities. It is shown how the precision and correlation of the double-differenced ambiguities as well
as of the widelane ambiguities are effected by the observation weights, by the number of satellites tracked, by the number
of observation epochs used, and by the change over time of the relative receiver-satellite geometry. Also the ability of the
widelane transformation to decorrelate and to improve the precision is investigated.
Received: 16 July 1996 / Accepted: 14 November 1996 相似文献
115.
Global assessment of the potential impacts of anthropogenically-induced climate change on vector-borne diseases suggests an increase in extent of the geographical areas susceptible to transmission of malarial Plasmodium parasites, dengue Flavivirus and Schistosoma worms. The transmission potential of the three associated vector-borne diseases studied is highly sensitive to climate changes on the periphery of the currently endemic areas and at higher altitudes within such areas. Our findings vis-à-vis the present endemic areas indicate that the increase in the epidemic potential of malaria and dengue transmission may be estimated at 12–27% and 31–47%, respectively, while in contrast, schistosomiasis transmission potential may be expected to exhibit a 11–17% decrease. 相似文献
116.
We have determined the quenched cation ordering states of five orthopyroxene crystals collected from the marginal border
group and the lower zone a and b of the Skaergaard intrusion, and modeled these data to retrieve their closure temperatures
(T
c) of Fe–Mg ordering and cooling rates. According to existing thermal models for the Skaergaard pluton, conductive cooling
dominated the high and low temperature regimes, which were separated by an intermediate temperature regime in which the cooling
was controlled primarily by convective fluid circulation. The cooling rates retrieved from the quenched cation ordering states
of the orthopyroxene crystals strictly apply to temperatures around the closure temperatures of the ordering states, ∼340–400° C, which fall at the transition from convective to the lower temperature conductive cooling. The cooling rates obtained from
the cation ordering states of orthopyroxene vary from ∼1 to 270 K/ka. These results agree well with a thermal model calculated
using an assumed average permeability of 10-12 cm2 for the pluton, but not completely with a model calculated on the basis of an average permeability of 10-13 cm2, although both values produced shifts of δ18O that are comparable to those observed in the pluton.
Received: 27 February 1995/Accepted: 20 July 1995 相似文献
117.
118.
119.
120.
Production of a molybdophore during metal-targeted dissolution of silicates by soil bacteria 总被引:1,自引:0,他引:1
Laura J. Liermann Robin L. Guynn Ariel Anbar Susan L. Brantley 《Chemical Geology》2005,220(3-4):285-302
Although many bioessential metals are scarce in natural water and rock systems, microbial secretion of high-affinity ligands for metal extraction from solid phases has only been documented for Fe. However, we have discovered that Mo is extracted from a silicate by a high-affinity ligand (a possible “molybdophore”) secreted by an N2-fixing soil bacterium. The putative molybdophore, aminochelin, is secreted as a siderophore under Fe-depleted conditions, but is also secreted under Fe-sufficient, Mo-depleted conditions. Presumably, molybdophore production facilitates uptake of Mo for use in Mo enzymes. In contrast, an Fe-requiring soil bacterium without a special Mo requirement only enhances the release of Fe from the silicate. Fractionation of Mo stable isotopes during uptake to cells may provide a “fingerprint” for the importance of chelating ligands in such systems. Many such metal-specific ligands secreted by prokaryotes for extraction of bioessential metals, their effects on Earth materials, and their possible utility in the recovery of economic metals remain to be discovered. 相似文献