全文获取类型
收费全文 | 1339篇 |
免费 | 72篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 56篇 |
大气科学 | 108篇 |
地球物理 | 331篇 |
地质学 | 405篇 |
海洋学 | 186篇 |
天文学 | 247篇 |
综合类 | 5篇 |
自然地理 | 87篇 |
出版年
2022年 | 8篇 |
2021年 | 18篇 |
2020年 | 22篇 |
2019年 | 16篇 |
2018年 | 36篇 |
2017年 | 34篇 |
2016年 | 51篇 |
2015年 | 35篇 |
2014年 | 50篇 |
2013年 | 91篇 |
2012年 | 39篇 |
2011年 | 67篇 |
2010年 | 56篇 |
2009年 | 81篇 |
2008年 | 58篇 |
2007年 | 61篇 |
2006年 | 72篇 |
2005年 | 37篇 |
2004年 | 40篇 |
2003年 | 40篇 |
2002年 | 27篇 |
2001年 | 23篇 |
2000年 | 22篇 |
1999年 | 20篇 |
1998年 | 23篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 23篇 |
1984年 | 35篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 11篇 |
排序方式: 共有1425条查询结果,搜索用时 15 毫秒
111.
The Willowbar, Oklahoma meteorite was found by Kendall Rhoton in December, 1971, lat 36° 44′ N.; long 102° 12′ W. It is a shocked brecciated L6 chondrite (Fa-24.3) with large black veins cutting areas of normal chondritic texture. It weighed 2.07 kg. 相似文献
112.
Tom Magna Uwe Wiechert Timothy L. Grove Alex N. Halliday 《Earth and Planetary Science Letters》2006,250(3-4):428-443
We present lithium (Li) abundances and isotope compositions for a suite of anhydrous olivine tholeiites (HAOTs) and hydrous basalt-andesitic (BA) lavas from the Mt. Shasta and Medicine Lake regions, California. The values of δ7Li vary from + 0.9‰ to + 6.4‰ and correlate inversely with distance from the trench. These data are consistent with continuous isotope fractionation of Li during dehydration of the subducted oceanic lithosphere, an interpretation corroborated by uniformly high pre-eruptive H2O contents in basaltic andesites accompanied by high Li, Rb, Sr, Ba and Pb abundances. The subduction-derived component that was added to these hydrous magmas is shown to be very similar beneath both Mt. Shasta and Medicine Lake volcanoes despite characteristically distinct Li isotope compositions in the magmas themselves. More evolved andesites and dacites from Mt. Shasta have δ7Li from + 2.8 to + 6.9‰ which is identical with the range obtained for HAOTs and BA lavas from Mt. Shasta. Therefore, Li isotopes do not provide evidence for any other crustal component admixed to Mt. Shasta andesites or dacites during magmatic differentiation and magma mixing in the crust. 相似文献
113.
Explicit formula for the geoid-quasigeoid separation 总被引:1,自引:0,他引:1
The explicit formula for the geoid-to-quasigeoid correction is derived in this paper. On comparing the geoidal height and
height anomaly, this correction is found to be a function of the mean value of gravity disturbance along the plumbline within
the topography. To evaluate the mean gravity disturbance, the gravity field of the Earth is decomposed into components generated
by masses within the geoid, topography and atmosphere. Newton’s integration is then used for the computation of topography-and
atmosphere-generated components of the mean gravity, while the combined solution for the downward continuation of gravity
anomalies and Stokes’ boundary-value problem is utilized in computing the component of mean gravity disturbance generated
by mass irregularities within the geoid. On application of this explicit formulism a theoretical accuracy of a few millimetres
can be achieved in evaluation of the geoid-to-quasigeoid correction. However, the real accuracy could be lower due to deficiencies
within the numerical methods and to errors within the input data (digital terrain and density models and gravity observations). 相似文献
114.
Dan Schafferman Alex Beharav Ella Shabelsky Zohara Yaniv 《Journal of Arid Environments》1998,40(4):431-439
Citrulus colocynthis(wild gourd) is a desert plant of the Cucurbitaceae, naturally adapted to arid environments. It was known in biblical times as a source of seed oil and its fruits were used as an efficient laxative. Accessions were collected in Israel and evaluated as a potential oil seed crop adapted to arid zones. It was found that its oil composition is similar to safflower oil, with a total of 80-85% unsaturated fatty acids. A potential yield of oil of 250-400 l ha−1was calculated. The best yield was obtained during the first 4 weeks of the 10-week maturation period. Yield potential should be estimated under desert conditions in order to evaluate the plant's economic future as a crop suitable for an arid environment. 相似文献
115.
A transient Green function due to suddenly applied line loads in an isotropic and homogeneous half-space is reported in this paper. The derivation of the half-space Green function in the Laplace and the Fourier transform spaces is first reviewed. Following an explicit inversion of the Fourier transform, the inverse Laplace transform is implemented along the contour integral on the p-complex plane in an integral form. The half-space Green function consists of full-space Green functions and a singularity-free complementary term. It can be easily incorporated into current transient boundary elements using the transient full-space Green function. Combined with finite elements, the half-space Green function can be used in a hybrid procedure to solve transient half-space problems without discretization of the free surface. Numerical results are presented to illustrate transient wave propagation in a half-space. 相似文献
116.
Willard S. Moore 《Journal of Earth System Science》1998,107(4):343-349
The fate of dissolved material delivered to the coastal ocean depends on its reactivity and the rate at which it is mixed
offshore. To measure the rate of exchange of coastal waters, we employ two short-lived radium isotopes,223Ra and224Ra. Along the coast of South Carolina, shore-perpendicular profiles of223Ra and224Ra in surface waters show consistent gradients which may be modeled to yield eddy diffusion coefficients of 350–540 m2s−1. Coupling the exchange rate with offshore concentration gradients yields estimates of offshore fluxes of dissolved materials.
For systems in steady state, the offshore fluxes must be balanced by new inputs from rivers, groundwater, sewers or other
sources. Two tracers that show promise in evaluating groundwater input are barium and226Ra. These tracers have high relative concentrations in the fluids and low-reactivity in the coastal ocean. Applying the eddy
diffusion coefficients to the offshore gradient of226Ra concentration provides an estimate of the offshore flux of226Ra. Measuring the concentrations of226Ra in subsurface fluids provides an estimate of the fluid flux necessary to provide the226Ra. These estimates indicate that the volume of groundwater required to support these fluxes is of the order of 40% of the
surface water flow. 相似文献
117.
Moore Emerson Skinner Meixner Arens & Jernigan 《Monthly notices of the Royal Astronomical Society》1998,299(4):1209-1214
We present arcsec-resolution images at 8.2, 10.0 and 11.3 μm of the unusual young object WL 16 in Ophiuchus, which has an extended envelope of fluorescing hydrocarbon molecules. To the limit of achieved sensitivity, the faint 10.0-μm continuum has a surface-brightness distribution that is not distinguishable from those at 8.2 and 11.3 μm, where the luminosity is known to be dominated by the polycyclic aromatic hydrocarbon (PAH) emission features. We conclude that the 10-μm continuum either arises from non-equilibrium heating of small dust grains that are well mixed with the hydrocarbons or is quasi-continuous emission from the PAH particles themselves, rather than thermal equilibrium emission from macroscopic dust grains, and that there is no significant silicate absorption variation across the source. The extended hydrocarbon emission may trace a flattened, equatorial distribution of circumstellar material or arise in bipolar lobes. The former case is slightly favoured, based on currently available data, and would imply that WL 16 is a relatively evolved Herbig Ae star, the equatorial plane of which has been almost cleared of normal dust, leaving only fluorescing hydrocarbons and larger coagulated particles as a possibly transient fossil of the original circumstellar disc. 相似文献
118.
Dhanpat Rai R.G. Strickert D.A. Moore R.J. Serne 《Geochimica et cosmochimica acta》1981,45(11):2257-2265
Americium-241 concentrations in solutions contacting contaminated sediments for up to 2 yr were measured as a function of pH. Steady-state concentrations were reached within a few days. The solubility-limited Am concentration was found to decrease approximately 10-fold with one unit increase in pH. The log equilibrium constant for the solubility of Am(soil) solid was found to be ?4.12. The predictions based upon thermodynamic data suggest that Am(aq complex)+ is likely to be Am(OH)2+. Although the chemical formula of Am(soil) was not determined, it does not appear to be Am(OH)3(a).Published data on sorption coefficients of Am by different rocks, soils, and minerals were critically evaluated. Final Am solution concentrations calculated from the sorption coefficients of a variety of earth materials with several solutions agreed well with the concentrations predicted from the solubility of Am(soil) solid, indicating that the sorption coefficient data are controlled by Am precipitation. 相似文献
119.
Willard S. Moore Kenneth W. Bruland Jacqueline Michel 《Earth and Planetary Science Letters》1981,53(3):391-399
Samples from the MANOP Santa Barbara Basin sediment trap intercomparison were analyzed for the isotopes of uranium, thorium, radium, lead, and polonium. All of the traps showed approximately the same compositions and isotopic ratios, indicating that they trapped similar materials. The234Th flux via falling particles was very close to the flux predicted from the production and scavenging rates of234Th from the water column. The210Pb content of the trapped particles and the surface sediments were the same, however, the measured flux of210Pb was seven times greater than the predicted flux. Predicted and measured fluxes of228Th and210Po were similarly out of balance. To explain this apparent inconsistency, we suggest (as others have done) that the Santa Barbara Basin is an area where scavenging from the water column is intensified and where sediments deposited initially on the margins may be physically remobilized on a short time scale. These two effects increase the apparent area from which the basin derives the longer-lived isotopes but does not increase significantly the supply of the short-lived234Th. 相似文献
120.
Emergent Pleistocene sea level indicators in the northern Bahamas include: a bioerosional notch at +5.3 to 5.9 m; sea caves, notches, and marine terraces at about +4.3 m; and lithified coral rubble and reef deposits between 0 and 3 m. Thorium 230 dates of the fossil corals, which were deposited as these features were being produced, span the age range from 100 to 145 thousand years BP with a majority falling between 115 and 130 thousand years BP. The notch at about +5.6 m is interpreted to be the product of a sea level stand 125 thousand years BP, while the features at +4.3 m are believed to be formed sometime later as sea level fell from the higher position. Part of the age span is inherent in the dating technique and possible sample alteration. Another cause of the spread may be mixing of corals of different ages into a single deposit. 相似文献