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951.
We reformulate the original model of Hatchell and Bourne and Røste, Stovas and Landrø that couples fractional velocity change to subsurface strain via a fundamental constant R. The new model combines elastic compressibility of a dual‐porosity system for a sand–shale mixture with horizontal planes of inter‐granular weakness. The majority of observed R‐factor magnitudes from post‐stack 4D seismic data in both the reservoir and overburden can thus be explained. R is predicted to depend strongly on lithology and also initial strain state. The model is also extended to predict the observed angle‐dependence of time‐lapse time‐shifts from pre‐stack data. An expression for the gradient of time‐shift with incidence angle is obtained in terms of the background VP/VS, and also the ratio of tangential to normal compliances BT/BN representing loss or creation of inter‐granular coupling. If accurately estimated from data, this compliance ratio can be used as an additional parameter to assess the post‐production state of the overburden. It is concluded that whilst R remains the over‐arching parameter controlling the magnitude of time‐shifts measured from 4D seismic data, BT/BN is a subtler parameter that may also prove of future value. 相似文献
952.
This article examines the use of rocking steel braced frames for the retrofit of existing seismically deficient steel building structures. Rocking is also used to achieve superior seismic performance to reduce repair costs and disruption time after earthquakes. The study focuses on low‐rise buildings for which re‐centring is solely provided by gravity loads rather than added post‐tensioning elements. Friction energy dissipative (ED) devices are used to control drifts. The system is applied to 2‐storey and 3‐storey structures located in 2 seismically active regions of Canada. Firm ground and soft soil conditions are considered. The seismic performance of the retrofit scheme is evaluated using nonlinear dynamic analysis and ASCE 41‐13. For all structures, rocking permits to achieve immediate occupancy performance under 2% in 50 years seismic hazard if the braces and their connections at the building's top storeys are strengthened to resist amplified forces due to higher mode response. Base shears are also increased due to higher modes. Impact at column bases upon rocking induces magnified column forces and vertical response in the gravity system. Friction ED is found more effective for drift control than systems with ring springs or bars yielding in tension. Drifts are sufficiently small to achieve position retention performance for most nonstructural components. Horizontal accelerations are generally lower than predicted from ASCE 41 for regular nonrocking structures. Vertical accelerations in the gravity framing directly connected to the rocking frame are however higher than those predicted for ordinary structures. Vertical ground motions have limited effect on frame response. 相似文献
953.
Landslides - In the last three decades, a series of large landslides have occurred in the Siguas River Valley, Peru, and their causes have been attributed to irrigation input affecting the local... 相似文献
954.
Richelle M. Allen-King Rebecca L. Kiekhaefer Daniel J. Goode Paul A. Hsieh Michelle M. Lorah Thomas E. Imbrigiotta 《Ground Water Monitoring & Remediation》2022,42(2):23-34
We present a new field measurement and numerical interpretation method (combined termed “test”) to parameterize the diffusion of trichloroethene (TCE) and its biodegradation products (DPs) from the matrix of sedimentary rock. The method uses a dual-packer system to interrogate a low-permeability section of the rock matrix adjacent to a previously contaminated borehole and uses the borehole monitoring history to establish the pretest condition. TCE and its DPs are removed from the groundwater between the packers at the onset of the testing. The parameters estimated by fitting a radial diffusion model to the concentration history and borehole concentration data, also termed back diffusion, are the tortuosity factor and sorption coefficients of TCE and DPs in the rock matrix and the TCE and DP biodegradation rate coefficients in the borehole. We demonstrate the equipment design and the interpretive method using a borehole accessing the gray mudstone at a TCE contaminated site in the Newark Basin. In this test, both nonreactive (bromide) and reactive (trichlorofluoroethene) tracers are used to constrain the estimated parameters; however, the bromide tracer was not needed to estimate the parameters in this test. The parameters estimated from the field test are consistent with values measured independently in laboratory experiments using field samples of similar lithology. From the interpretation, we compute the TCE and DP concentration distributions in the rock matrix prior to the test to illustrate how the results can be used to enhance understanding of contaminant distribution in the rock matrix. 相似文献
955.
Zhao Jiagang Li Shufeng Farnsworth Alexander Valdes Paul J. Reichgelt Tammo Chen Linlin Zhou Zhekun Su Tao 《中国科学:地球科学(英文版)》2022,65(7):1339-1352
Science China Earth Sciences - The growth of the Qinghai-Tibetan Plateau (QTP) during the Cenozoic drove dramatic climate and environmental change in this region. However, there has been limited... 相似文献
956.
Afroosa M. Rohith B. Paul Arya Durand Fabien Bourdallé-Badie Romain Joseph Sudheer Prerna S. Shenoi S. S. C. 《Ocean Dynamics》2022,72(7):523-538
Ocean Dynamics - An intraseasonal see-saw has been observed in the Indo-Pacific barotropic sea level anomaly during boreal winters. This see-saw carries a significant amount of energy and is... 相似文献
957.
Paul Gonez Hung Nguyên HuuPhuong Ta Hoa Gaël ClémentPhilippe Janvier 《Journal of Asian Earth Sciences》2012,43(1):51-63
Several outcrops of the Late Silurian and Devonian of the Ngoc Vung Series, northern Vietnam, yielded plant remains. The Late Silurian localities delivered the earliest known flora of the South China block. Although the fossils are fragmentary, they complement our knowledge about the global composition of the flora. The major components of the flora are plants with dichotomous habit and terminal bivalvate sporangia, which are close relatives to zosterophylls, and zosterophylls. Plants with possible euphyllophyte affinities and bryophytes are occasionally present. This floral composition is similar to that of the rich, younger South China block assemblages from the Posongchong and Xujiachong Formations of China, considered Pragian in age. The South China block flora is therefore likely to have been dominated by zosterophylls and pre-zosterophylls at least from the Late Silurian to the Pragian (i.e. a 20 million years long period). It also strengthens the hypothesis that more derived plants were present on eastern Gondwana earlier that elsewhere, in the first steps of tracheophyte evolution. The Devonian localities of the Ngoc Vung Series delivered a thick fibrous stem fragment and a basal euphyllophyte. These latter plant remains provide some stratigraphic data. The large stem fragment is consistent with an Eifelian age for the Duong Dong Formation (part of the Ngoc Vung Series), as suggested by the brachiopod fauna. The accompanying basal euphyllophyte displays a combination of characters (axes 3-4 mm wide and lateral branchings) that is also consistent with an Eifelian age, but possibly more characteristic of the Emsian flora. It is therefore suggested that the stratigraphic range of the Duong Dong Formation might be extended down to the Emsian. 相似文献
958.
Jie Xu Patricia M. Glibert Hongbin Liu Kedong Yin Xiangcheng Yuan Mianrun Chen Paul J. Harrison 《Estuaries and Coasts》2012,35(2):559-571
Phytoplankton uptake rates of ammonium (NH4 +), nitrate (NO3 −), and urea were measured at various depths (light levels) in Hong Kong waters during the summer of 2008 using 15N tracer techniques in order to determine which form of nitrogen (N) supported algal growth. Four regions were sampled, two differentially impacted by Pearl River discharge, one impacted by Hong Kong sewage discharge, and a site beyond these influences. Spatial differences in nutrient concentrations, ratios, and phytoplankton biomass were large. Dissolved nutrient ratios suggested phosphorus (P) limitation throughout the region, largely driven by high N loading from the Pearl River in summer. NH4 + and urea made up generally ≥50% of the total N taken up and the f ratio averaged 0.26. Even at the river-impacted site where concentrations of NO3 − were >20 μM N, NH4 + comprised >60% of the total N uptake. Inhibition experiments demonstrated that NO3 − uptake rates were reduced by 40% when NH4 + was >5 μM N. The relationship between the total specific uptake rates of N (sum of all measured substrates, V, per hour) and the chlorophyll a-specific rates (micromolars of N per microgram of Chl a per hour) varied spatially with phytoplankton biomass. Highest uptake rates and biomass were observed in southern waters, suggesting that P limitation and other factors (i.e., flushing rate) controlled production inshore and that the unincorporated N (mainly NO3 −) was transported offshore. These results suggest that, at the beginning of summer, inshore algal blooms are fueled primarily by NH4 + and urea, rather than NO3 −, from the Pearl River discharge. When NH4 + and urea are depleted, then NO3 − is taken up and can increase the magnitude of the bloom. 相似文献
959.
We describe contemporaneous changes in environmental quality and social deprivation in English local authority districts over four decades, using secondary source GIS modelled data on environmentally intrusive development. The distribution of this development is described with respect to the Townsend material deprivation score, corroborated against the Breadline Britain index. Spatial patterns of environmental intrusion and material deprivation change markedly over the period, although a clear environmental inequality remains throughout. However, it is not the most deprived who experience the greatest decline in their environmental quality, as most of the increase in environmental intrusion occurs in those districts whose population were amongst the most affluent in the early 1960s. We note that the environmental justice implications of these observations are dependent upon conceptions of justice held, and reflect on the challenge of testing, through empirical longitudinal analysis, the notion that environmental sustainability and social justice are incompatible. 相似文献
960.
Madhuparna Paul Jyotisankar Ray C. Manikyamba Sohini Ganguly M. Rajanikanta Singh Saraswati Pachal Debaleena Sarkar 《Geological Journal》2021,56(1):102-129
Precambrian mafic magmatism is an important global episode which played a significant role in the crustal evolution. In India, Singhbhum Craton being the oldest craton, witnessed significant occurrences of Precambrian geological activity, marked by several episodes of volcanism, plutonism, sedimentation spanning from Palaeoarchean to Mesoproterozoic age. Here we present petrological and geochemical characteristics of Precambrian mafic volcanic rocks (occurring in western Iron Ore Group (IOG), Singhbhum Craton, eastern India) to evaluate their petrogenetic aspects, tectonic setting, and magma generation. The mafic volcanic rocks are porphyritic in nature with the phenocrysts of plagioclase and groundmass composed of clinopyroxene, plagioclase, ilmenite, and volcanic glass. These rocks are mostly tholeiitic, sometimes with a transitional behaviour towards calc-alkaline nature and display basalt-basaltic andesite affinity. These mafic volcanic rocks also preserve geochemical signatures (high Nb/U, Nb/La, [Nb/Th]pm ratios) in support of Nb-enriched basalts and are classified as Nb-enriched basalts (NEB; Nb > 7 ppm) and high-Nb basalts (HNB; Nb > 20 ppm) on the basis of Nb concentrations and mantle normalized Nb/La ratios (>0.5). The NEBs and HNBs are marked by lesser magnitude of negative Nb anomalies with high (Nb/Th)pm, (Nb/La)pm, and Nb/U ratios as compared to normal arc basalts. Several major element oxides, trace elements, and selected element ratios (like SiO2, CaO/Al2O3, Y, V/Cr, Zr/Nb, and ∑REE) show systematic variations with MgO which suggests role of magmatic fractionation. Chondrite-normalized REE patterns for NEB and HNB rocks exhibit uniform LREE enrichment with distinct Eu negative anomalies while primitive mantle-normalized incompatible trace element patterns reflect enrichment in LILE and LREE with prominent Nb-Ta anomalies. Different HFSE ratios corroborate a subduction related setting for magma generation formed by ∼10%–20% melting in the domain of garnet lherzolite. Relative enrichment of LILE and LREE with depleted HFSE characteristics attest a garnet-bearing mantle source and melt extraction with garnet in the residue. Geochemical signatures suggest that the genesis of NEB and HNB is attributable to slab-melting and wedge hybridization processes during matured stages of subduction. Selected incompatible trace element ratios for the studied mafic volcanic rocks invoke an enriched (EM1-EM2 type) mantle source and unequivocally suggest effects of continental crustal assimilation of the parent magma. Liquid immiscibility has played an important role as a differentiation mechanism leading to presence of high and low FeO types. The IOG mafic volcanic rocks preserve distinct geochemical signatures of matured stage of subduction, slab melting, crustal contamination and magma generation at an Archean ocean–continent convergent margin setting. 相似文献