全文获取类型
收费全文 | 706篇 |
免费 | 43篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 57篇 |
地球物理 | 248篇 |
地质学 | 242篇 |
海洋学 | 62篇 |
天文学 | 74篇 |
综合类 | 1篇 |
自然地理 | 52篇 |
出版年
2023年 | 6篇 |
2021年 | 18篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 29篇 |
2013年 | 49篇 |
2012年 | 32篇 |
2011年 | 36篇 |
2010年 | 48篇 |
2009年 | 39篇 |
2008年 | 39篇 |
2007年 | 40篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 29篇 |
2003年 | 32篇 |
2002年 | 23篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1907年 | 1篇 |
排序方式: 共有757条查询结果,搜索用时 993 毫秒
361.
A tier III, essential fish habitat analysis was used to evaluate the biochemical condition of common mummichog Fundulus heteroclitus residing in two isolated tidal salt marshes, one a relatively undisturbed polyhaline site dominated by Spartina alterniflora and the other a meso-oligohaline site dominated by an invasive variety of Phragmites australis. Stable isotopes signatures of C, N, and S in whole tissue samples of F. heteroclitus were used to compare the trophic spectrum for this species in each marsh as a function of the dominant macrophytes present
with additional contributions from phytoplankton and benthic microalgae. Allometry of wet mass and its components, water mass,
lean protein mass and lipid mass in individual fish exhibited hyperallometric patterns; and average lipid mass fell within
the range reported for most fundulids, including F. heteroclitus. Significant differences were also detected in the allocation of lipid classes to energy reserves in the form of triacylglycerols
(TAG) and free fatty acids. These reserves, especially TAG, are critical for reproduction, migration, and overwintering survival
in many taxa and were significantly lower in fish collected in the P. australis-dominated marsh. Relative to the relatively undisturbed Spartina-dominated site, we tentatively conclude that the P. australis-invaded marsh was an inferior habitat for F. heteroclitus. 相似文献
362.
New in situ techniques for the estimation of the dielectric properties and moisture content of soils
Jean-Pierre Frangi Daniel-Christian Richard Xavier Chavanne Idris Bexi Florence Sagnard Vincent Guilbert 《Comptes Rendus Geoscience》2009,341(10-11):831-845
Two original in situ HF techniques of dielectric characterization in two wide bands have been developed in order to estimate the moisture content of soils by complex impedance measurement. These techniques are based on the capacitive effect (1–20 MHz) and on the propagation of electromagnetic waves at high frequencies (0.1–4 GHz). The two measurement techniques use straight conductors that are inserted into the soil. Specific inversion algorithms were developed to estimate the apparent real permittivity of the soil versus frequency from the complex impedance. The validation of both instruments was made in the laboratory in the presence of dry and wet sands. In situ experiments were also made at high frequencies. These complementary devices should enlarge the range of usual soil moisture measurement techniques. 相似文献
363.
Anthony E. Fallick Gaston Giuliani Thomas Rigaudier Adrian J. Boyce Van Long Pham Vincent Pardieu 《Comptes Rendus Geoscience》2019,351(1):27-36
Oxygen isotope systematics for co-existing pairs of gem-spinel and calcite in marble from Vietnam and other worldwide deposits have been determined in order to characterize the O-isotope fractionation between calcite and spinel. In Vietnam, the Δ18Occ–sp (= 3.7 ± 0.1‰ for six samples from the An Phu and Cong Troi deposits) is remarkably constant. The combination of these data with those obtained on calcite–spinel pairs of Paigutan (Nepal, n = 2), Ipanko (Tanzania, n = 1), and Mogok (Myanmar, = 2) are also consistent with an overall Δ18Occ–sp of 3.6 ± 0.3‰ for all the spinel samples (n = 11). The straight line correlation δ18Occ = 0.96 δ18Osp + 4.4 is excellent despite their worldwide geographic spread. The increment method of calculating oxygen isotope fractionation gave a geologically unreasonable temperature of formation for both minerals at 1374 °C when compared to temperatures obtained by mineral assemblage equilibrium of these marble type deposits, between 610 and 750 °C. The constant Δ18Occ–sp reflects a constant temperature for this amphibolite facies assemblage, whose current best estimate is calculated at 620 ± 40 °C, but unquantified uncertainties remain. 相似文献
364.
Vegetation of two San Francisco Bay, California, U.S.A. tidal marshes was examined to determine the effects of recirculation ditches designed to eliminate mosquito-breeding. Salicornia virginica L. biomass and production in Petaluma Marsh and plant species composition in Suisun Marsh were measured with respect to distance from ditches and natural channels. In Petaluma Marsh, both annual above-ground production estimates and infrared aerial photographs indicated that S. virginica growth rates were higher near ditches than in the open marsh. In the floristically diverse, less saline Suisun Marsh, there was a displacement of the more salt tolerant S. virginica by the less tolerant Juncus balticus Willd. and a significantly greater number of species near the ditches. Results in both marshes are correlated with low groundwater salinities near ditches and suggest that tidal circulation within ditches locally ameliorates extremes in soil conditions. 相似文献
365.
366.
Vincent J. Abreu 《Planetary and Space Science》1985,33(9):1049-1055
The theoretical development of a technique to recover velocities measured with a Fabry-Perot interferometer in the presence of scattered light is presented. Simulations are carried out which show that the inversion is effective in recovering actual velocities, especially in instances when the observed brightness is dominated by scattered light. 相似文献
367.
368.
GIS-based hydrogeological databases and groundwater modelling 总被引:4,自引:2,他引:2
Radu Gogu Guy Carabin Vincent Hallet Valerie Peters Alain Dassargues 《Hydrogeology Journal》2001,9(6):555-569
Reliability and validity of groundwater analysis strongly depend on the availability of large volumes of high-quality data.
Putting all data into a coherent and logical structure supported by a computing environment helps ensure validity and availability
and provides a powerful tool for hydrogeological studies. A hydrogeological geographic information system (GIS) database that
offers facilities for groundwater-vulnerability analysis and hydrogeological modelling has been designed in Belgium for the
Walloon region. Data from five river basins, chosen for their contrasting hydrogeological characteristics, have been included
in the database, and a set of applications that have been developed now allow further advances. Interest is growing in the
potential for integrating GIS technology and groundwater simulation models. A "loose-coupling" tool was created between the
spatial-database scheme and the groundwater numerical model interface GMS (Groundwater Modelling System). Following time and
spatial queries, the hydrogeological data stored in the database can be easily used within different groundwater numerical
models.
Electronic Publication 相似文献
369.
Michael?BizimisEmail author Vincent?J.?M.?Salters J.?Barry?Dawson 《Contributions to Mineralogy and Petrology》2003,145(3):281-300
Hf, Zr and Ti in carbonatites primarily reside in their non-carbonate fraction while the carbonate fraction dominates the Nd and Sr elemental budget of the whole rock. A detailed investigation of the Hf, Nd and Sr isotopic compositions shows frequent isotopic disequilibrium between the carbonate and non-carbonate fractions. We suggest that the trace element and isotopic composition of the carbonate fraction better represents that of the carbonatite magma, which in turn better reflects the composition of the carbonatitic source. Experimental partitioning data between carbonatite melt and peridotitic mineralogy suggest that the Lu/Hf ratio of the carbonatite source will be equal to or greater than the Lu/Hf ratio of the carbonatite. This, combined with the Hf isotope systematics of carbonatites, suggests that, if carbonatites are primary mantle melts, then their sources must be short-lived features in the mantle (maximum age of 10–30 Ma), otherwise they would develop extremely radiogenic Hf compositions. Alternatively, if carbonatites are products of extreme crystal fractionation or liquid immiscibility then the lack of radiogenic initial Hf isotope compositions also suggests that their sources do not have long-lived Hf depletions. We present a model in which the carbonatite source is created in the sublithospheric mantle by the crystallization of earlier carbonatitic melts from a mantle plume. This new source melts shortly after its formation by the excess heat provided by the approaching hotter center of the plume and/or the subsequent ascending silicate melts. This model explains the HIMU-EMI isotope characteristics of the East African carbonatites, their high LREE/HREE ratios as well as the rarity of carbonatites in the oceanic lithosphere. 相似文献
370.
Radu?Constantin?GoguEmail author Vincent?Hallet Alain?Dassargues 《Environmental Geology》2003,44(8):881-892
Five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared. The test area was a slightly karstified district in the Condroz region of Belgium. The basin covers about 65 km2 and the karst aquifer provides a water-supply of about 28,000 m3d-1. The methods tested were: EPIK (Doerfliger et al. 1999), DRASTIC (Aller et al. 1987), 'German method' (von Hoyer and Söfner 1998), GOD (Foster 1987) and ISIS (Civita and De Regibus 1995). The results are compared and critically examined. From the analysis, it seems that reducing the number of parameters is unsatisfactory, due to the variety of geological conditions. The various methods produce very different results at any given site. As only physically-based methods can be checked for their reliability, it is clear that future vulnerability mapping techniques must incorporate such methods. 相似文献