全文获取类型
收费全文 | 1903篇 |
免费 | 71篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 47篇 |
大气科学 | 126篇 |
地球物理 | 542篇 |
地质学 | 614篇 |
海洋学 | 210篇 |
天文学 | 306篇 |
综合类 | 6篇 |
自然地理 | 141篇 |
出版年
2021年 | 20篇 |
2020年 | 26篇 |
2019年 | 27篇 |
2018年 | 45篇 |
2017年 | 33篇 |
2016年 | 59篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 86篇 |
2012年 | 50篇 |
2011年 | 67篇 |
2010年 | 82篇 |
2009年 | 84篇 |
2008年 | 73篇 |
2007年 | 94篇 |
2006年 | 68篇 |
2005年 | 63篇 |
2004年 | 65篇 |
2003年 | 60篇 |
2002年 | 50篇 |
2001年 | 30篇 |
2000年 | 39篇 |
1999年 | 30篇 |
1998年 | 32篇 |
1997年 | 29篇 |
1996年 | 30篇 |
1995年 | 34篇 |
1994年 | 33篇 |
1993年 | 14篇 |
1992年 | 32篇 |
1991年 | 32篇 |
1990年 | 42篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 32篇 |
1984年 | 40篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 32篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 16篇 |
1972年 | 12篇 |
排序方式: 共有1992条查询结果,搜索用时 31 毫秒
371.
372.
373.
Charles A. Stock Michael A. Alexander Nicholas A. Bond Keith M. Brander William W.L. Cheung Enrique N. Curchitser Thomas L. Delworth John P. Dunne Stephen M. Griffies Melissa A. Haltuch Jonathan A. Hare Anne B. Hollowed Patrick Lehodey Simon A. Levin Jason S. Link Kenneth A. Rose Ryan R. Rykaczewski Jorge L. Sarmiento Ronald J. Stouffer Franklin B. Schwing Francisco E. Werner 《Progress in Oceanography》2011,88(1-4):1-27
The study of climate impacts on Living Marine Resources (LMRs) has increased rapidly in recent years with the availability of climate model simulations contributed to the assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Collaboration between climate and LMR scientists and shared understanding of critical challenges for such applications are essential for developing robust projections of climate impacts on LMRs. This paper assesses present approaches for generating projections of climate impacts on LMRs using IPCC-class climate models, recommends practices that should be followed for these applications, and identifies priority developments that could improve current projections. Understanding of the climate system and its representation within climate models has progressed to a point where many climate model outputs can now be used effectively to make LMR projections. However, uncertainty in climate model projections (particularly biases and inter-model spread at regional to local scales), coarse climate model resolution, and the uncertainty and potential complexity of the mechanisms underlying the response of LMRs to climate limit the robustness and precision of LMR projections. A variety of techniques including the analysis of multi-model ensembles, bias corrections, and statistical and dynamical downscaling can ameliorate some limitations, though the assumptions underlying these approaches and the sensitivity of results to their application must be assessed for each application. Developments in LMR science that could improve current projections of climate impacts on LMRs include improved understanding of the multi-scale mechanisms that link climate and LMRs and better representations of these mechanisms within more holistic LMR models. These developments require a strong baseline of field and laboratory observations including long time series and measurements over the broad range of spatial and temporal scales over which LMRs and climate interact. Priority developments for IPCC-class climate models include improved model accuracy (particularly at regional and local scales), inter-annual to decadal-scale predictions, and the continued development of earth system models capable of simulating the evolution of both the physical climate system and biosphere. Efforts to address these issues should occur in parallel and be informed by the continued application of existing climate and LMR models. 相似文献
374.
Charles C. Wall Bradley J. Peterson Christopher J. Gobler 《Estuaries and Coasts》2011,34(6):1262-1277
While many coastal ecosystems previously supported high densities of seagrass and abundant bivalves, the impacts of overfishing,
eutrophication, harmful algal blooms, and habitat loss have collectively contributed to the decline of these important resources.
Despite improvements in wastewater treatment in some watersheds and subsequent reduced nutrient loading to neighboring estuaries,
seagrass and bivalve populations in these locations have generally not recovered. We performed three mesocosm experiments
to simultaneously examine the contrasting effects of nutrient loading and historic suspension-feeding bivalve densities on
the growth of eelgrass (Zostera marina), juvenile bivalves (northern quahogs, Mercenaria mercenaria; eastern oysters, Crassostrea virginica; and bay scallops, Argopecten irradians), and juvenile planktivorous fish (sheepshead minnow, Cyprinodon variegatus). High nutrient loading rates led to significantly higher phytoplankton (chlorophyll a) levels in all experiments, significantly increased growth of juvenile bivalves relative to controls with lower nutrient
loading rates in two experiments, and significantly reduced the growth of eelgrass in one experiment. The filtration provided
by adult suspension feeders (M. mercenaria and C. virginica) significantly decreased phytoplankton levels in all experiments, significantly increased light penetration and the growth
of eelgrass in one experiment, and significantly decreased the growth of juvenile bivalves and fish in two experiments, all
relative to controls with no filtration from adult suspension feeders. These results demonstrate that an appropriate level
of nutrient loading can have a positive effect on some estuarine resources and that bivalve filtration can mediate the effects
of nutrient loading to the benefit or detriment of different estuarine resources. Future ecosystem-based approaches will need
to simultaneously account for anthropogenic nutrient loading and bivalve restoration to successfully manage estuarine resources. 相似文献
375.
It is widely believed that successful colonization of ecosystems by non-native species will have catastrophic consequences
for the recipient system. Within the Mobile–Tensaw Delta, AL, exotic Eurasian milfoil (Myriophyllum spicatum) has been reported to trigger degradation of ecosystem structure and function. We evaluated the impacts of structurally complex
milfoil on food web structure and predator-prey interactions via comparisons with two native grasses, structurally simple
wild celery (Vallisneria americana) and the more complex water stargrass (Heteranthera dubia). While significant differences were not detected in the faunal compositions of milfoil and stargrass habitats, significant
differences between milfoil and wild celery were found. Laboratory experiments showed that rainwater killifish, a key contributor
to these differences, preferred milfoil over wild celery, but did not occupy milfoil more than stargrass. Subsequent experiments
indicated that survivorship was drastically lower in wild celery. Though many of the documented impacts of Eurasian milfoil
have been cast as detrimental, shelter-seeking organisms may perceive milfoil in the same way as other complex native species. 相似文献
376.
This article 1) examines the policy context that created a demand for biogeographic information, 2) describes early national and regional experiences in applying biogeographic classifications, 3) extracts lessons about their usefulness, 4) introduces a broad-scale biogeographic classification for the open ocean and deep seabed called the Global Open Ocean and Deep Seabed (GOODS) biogeographic classification and explains its relevance in this policy context. In so doing it highlights potential uses of biogeographic classifications for the open ocean and deep seabed: these include ecosystem-based management approaches, marine spatial planning and identification of representative networks of MPAs. It also discusses approaches for dealing with problems of uncertainty and connectivity. The article concludes with recommendations for the further development of the GOODS and finer-scale biogeographic classifications. 相似文献
377.
Meagan E. Ankney Clark M. Johnson Charles R. Bacon Brian L. Beard Brian R. Jicha 《Contributions to Mineralogy and Petrology》2013,166(2):563-585
Uranium-series isotope ratios determined for 35 volcanic rocks and 4 glass separates erupted from ~36 to 4.8 ka at Mt. Mazama, Crater Lake, Oregon, identify both 230Th-excess and 238U-excess components. U–Th isotope compositions cover a wide range, exceeding those previously measured for the Cascade arc. Age-corrected (230Th/232Th) and (238U/232Th) activity ratios range from 1.113 to 1.464 and from 0.878 to 1.572 (44.4 % 230Th-excess to 8.8 % 238U-excess), respectively. The most distinctive aspect of the data set is the contrast in U–Th isotope ratios between low and high Sr (LSr, HSr) components that have been previously identified in products of the 7.7 ka caldera-forming climactic eruption and preclimactic rhyodacite lavas. The LSr component exclusively contains 238U-excess, but the HSr component, as well as more primitive lavas, are marked by 230Th-excess. 230Th-excesses such as those recorded at Mt. Mazama are commonly observed in the Cascades. Melting models suggest that high 230Th-excesses observed in the more primitive lavas evolved through mixing of a mantle melt with a partial melt of a mafic lower crustal composition that contained garnet in the residuum that was produced through dehydration melting of amphibolite that was initially garnet free. Dehydration melting in the lower crust offers a solution to the “hot-slab paradox” of the Cascades, where low volatile contents are predicted due to high slab temperatures, yet higher water contents than expected have been documented in erupted lavas. The 238U-excess observed at Mt. Mazama is rare in Cascade lavas, but occurs in more than half of the samples analyzed in this study. Traditionally, 238U-excess in arc magmas is interpreted to reflect slab fluid fluxing. Indeed, 238U-excess in arcs is common and likely masks 230Th-excess resulting from lower crustal interaction. Isotopic and trace element data, however, suggest a relatively minor role for slab fluid fluxing in the Cascades. We propose that 238U-excess reflects melting and assimilation of young, hydrothermally altered upper crust. The processes related to generating 238U-excess are likely important features at Mt. Mazama that accompanied development of a large-scale silicic magma chamber that led to the caldera-forming eruption. 相似文献
378.
Wei Lin Michel Faure Yan Chen Wenbin Ji Fei Wang Lin Wu Nicolas Charles Jun Wang Qingchen Wang 《Gondwana Research》2013,23(1):54-77
With a cratonic nucleus, the North China Craton (NCC) experienced a complex tectonic evolution with multiphase compressional and extensional events during Mesozoic times. Along the northern part of the NCC, the Yinshan–Yanshan fold and thrust belt was a typical intraplate orogen. Jurassic and Cretaceous continental sedimentation, magmatism, widespread intraplate characterize the Yinshan–Yanshan orogenic belt. The geodynamic significance of these tectonic events is still in dispute. In the western part of the Liaoning province, the Yiwulüshan massif crops out at the eastern end of the Yinshan–Yanshan orogenic belt. The Yiwulüshan massif presents an elliptical domal shape with a NE–SW striking long axis. The structural evolution of this massif brings new insights for the understanding of the Mesozoic plutonic–tectonic history of the NCC. A multidisciplinary study involving structural geology, geochronology, Anisotropy of Magnetic Susceptibility (AMS) and gravity modeling have been carried out. The presentation of the new results splits into two parts. Part I (this paper) deals with field and laboratory structural observations, and presents the main geochronological results. The AMS, gravity modeling data will be provided in a companion paper (Part II). The early compressional deformation (D1) corresponds to a Late Jurassic to Early Cretaceous southward thrusting. The subsequent deformation is related to the Early Cretaceous exhumation of the Yiwulüshan massif. A detailed structural analysis allows us to distinguish several deformation events (D2, D3, and D4). The Cretaceous extensional structures, such as syntectonic plutons bounded by ductile normal faults, metamorphic core complexes, and half-graben basins are recognized in many places in East Asia. These new data from the Yiwulüshan massif constitute a link between Transbaikalia, Mongolia, North China and South China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region. 相似文献
379.
Clues from Current High CO2 Environments on the Effects of Ocean Acidification on CaCO3 Preservation
Andreas J. Andersson Nicholas R. Bates Marlene A. Jeffries Kyra Freeman Charles Davidson Shaun Stringer Evan Betzler Fred T. Mackenzie 《Aquatic Geochemistry》2013,19(5-6):353-369
Acidification of surface seawater owing to anthropogenic activities has raised serious concerns on its consequences for marine calcifying organisms and ecosystems. To acquire knowledge concerning the future consequences of ocean acidification (OA), researchers have relied on incubation experiments with organisms exposed to future seawater conditions, numerical models, evidence from the geological record, and recently, observations from aquatic environments exposed to naturally high CO2 and low pH, e.g., owing to volcanic CO2 vents, upwelling, and groundwater input. In the present study, we briefly evaluate the distribution of dissolved CO2–carbonic acid parameters at (1) two locations in the Pacific and the Atlantic Ocean as a function of depth, (2) a mangrove environment in Bermuda, (3) a seasonally stratified body of water in a semi-enclosed sound in Bermuda, and (4) in temporarily isolated tide pools in Southern California. We demonstrate that current in situ conditions of seawater pCO2, pH, and CaCO3 saturation state (Ω) in these environments are similar or even exceed the anticipated changes to these parameters in the open ocean over the next century as a result of OA. The observed differences between the Pacific and Atlantic Oceans with respect to seawater CO2–carbonic acid chemistry, preservation of CaCO3 minerals, and the occurrence and distribution of deep-sea marine calcifiers, support the hypothesized negative effects of OA on the production and preservation of CaCO3 in surface seawater. Clues provided from shallow near-shore environments in Bermuda and Southern California support these predictions, but also highlight that many marine calcifiers already experience relatively high seawater pCO2 and low pH conditions. 相似文献
380.
Field Test Research on Embankment Supported by Plastic Tube Cast-in-place Concrete Piles 总被引:1,自引:1,他引:0
Yonghui Chen Changguang Qi Hongyue Xu Charles W. W. Ng 《Geotechnical and Geological Engineering》2013,31(4):1359-1368
The plastic tube cast-in-place concrete pile (TC pile) with a small diameter consists of pre-driven plastic tube filled with concrete. Based on the case of TC pile-reinforced embankment on soft ground, and according to the monitoring data of the TC pile-reinforced embankment system, the treatment effect and reinforcement characteristics for this system were analyzed. The field monitoring results indicates that the critical height of embankment is about 1.1 times the pile net spacing, and the small-spacing arranged TC piles can be applied to low embankment engineering; the load share rate can reflect the degree of soil arching more better and steadily and exceeds 70 % at the end of monitoring period; the settlements of pile cap and soil between piles mainly occurs in the embankment construction period; the different settlement between pile cap and soil approaches the maximum and then reduces gradually when the embankment height is about 2.2 times the pile net spacing. The variation of layered settlement and pore water pressure illustrates that the embankment settlement is mainly caused by the compression of soils within pile length, which is about 90 % of the total settlement; the influence depth of pore water pressure is about 1/3 pile length. 相似文献