全文获取类型
收费全文 | 2581篇 |
免费 | 155篇 |
国内免费 | 33篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 292篇 |
地球物理 | 676篇 |
地质学 | 808篇 |
海洋学 | 218篇 |
天文学 | 356篇 |
综合类 | 6篇 |
自然地理 | 324篇 |
出版年
2024年 | 7篇 |
2022年 | 13篇 |
2021年 | 52篇 |
2020年 | 63篇 |
2019年 | 59篇 |
2018年 | 67篇 |
2017年 | 85篇 |
2016年 | 115篇 |
2015年 | 89篇 |
2014年 | 99篇 |
2013年 | 185篇 |
2012年 | 120篇 |
2011年 | 158篇 |
2010年 | 121篇 |
2009年 | 143篇 |
2008年 | 142篇 |
2007年 | 140篇 |
2006年 | 134篇 |
2005年 | 109篇 |
2004年 | 91篇 |
2003年 | 92篇 |
2002年 | 81篇 |
2001年 | 53篇 |
2000年 | 56篇 |
1999年 | 38篇 |
1998年 | 34篇 |
1997年 | 30篇 |
1996年 | 29篇 |
1995年 | 30篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 28篇 |
1988年 | 11篇 |
1987年 | 20篇 |
1986年 | 11篇 |
1985年 | 23篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 8篇 |
排序方式: 共有2769条查询结果,搜索用时 15 毫秒
91.
Ruth M. K. Plets S. Louise Callard J. Andrew G. Cooper Joseph T. Kelley Daniel F. Belknap Robin J. Edwards Antony J. Long Rory J. Quinn Derek W. T. Jackson 《第四纪科学杂志》2019,34(4-5):285-298
The interplay of eustatic and isostatic factors causes complex relative sea‐level (RSL) histories, particularly in paraglacial settings. In this context the past record of RSL is important in understanding ice‐sheet history, earth rheology and resulting glacio‐isostatic adjustment. Field data to develop sea‐level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea‐level curves. We use seismic stratigraphy, 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of Belfast Lough, Northern Ireland, and reconstruct past RSL. A typical sequence of till, glacimarine and Holocene sediments is preserved. Two sea‐level lowstands (both max. ?40 m) are recorded at c. 13.5 and 11.5k cal a bp . Each is followed by a rapid transgression and subsequent periods of RSL stability. The first transgression coincides temporally with a late stage of Meltwater Pulse 1a and the RSL stability occurred between c. 13.0 and c. 12.2k cal a bp (Younger Dryas). The second still/slowstand occurred between c. 10.3 and c. 11.5k cal a bp . Our data provide constraints on the direction and timing of RSL change during deglaciation. Application of the Depth of Closure concept adds an error term to sea‐level reconstructions based on seismic stratigraphic reconstructions. 相似文献
92.
93.
94.
Gilbert J. Price Gregory E. Webb Jian-xin Zhao Yue-xing Feng Andrew S. Murray Bernard N. Cooke Scott A. Hocknull Ian H. Sobbe 《Quaternary Science Reviews》2011,30(7-8):899-914
A key to understanding Late Pleistocene megafaunal extinction dynamics is knowledge of megafaunal ecological response(s) to long-term environmental perturbations. Strategically, that requires targeting fossil deposits that accumulated during glacial and interglacial intervals both before and after human arrival, with subsequent palaeoecological models underpinned by robust and reliable chronologies. Late Pleistocene vertebrate fossil localities from the Darling Downs, eastern Australia, provide stratigraphically-intact, abundant megafaunal sequences, which allows for testing of anthropogenic versus climate change megafauna extinction hypotheses. Each stratigraphic unit at site QML796, Kings Creek Catchment, was previously shown to have had similar sampling potential, and the basal units contain both small-sized taxa (e.g., land snails, frogs, bandicoots, rodents) and megafauna. Importantly, sequential faunal horizons show stepwise decrease in taxonomic diversity with the loss of some, but not all, megafauna in the geographically-small palaeocatchment. The purpose of this paper is to present the results of our intensive, multidisciplinary dating study of the deposits (>40 dates). Dating by means of accelerator mass spectrometry (AMS) 14C (targeting bone, freshwater molluscs, and charcoal) and thermal ionisation mass spectrometry U/Th (targeting teeth and freshwater molluscs) do not agree with each other and, in the case of AMS 14C dating, lack internal consistency. Scanning electron microscopy and rare earth element analyses demonstrate that the dated molluscs are diagenetically altered and contain aragonite cements that incorporated secondary young C, suggesting that such dates should be regarded as minimum ages. AMS 14C dated charcoals provide ages that occur out of stratigraphic order, and cluster in the upper chronological limits of the technique (~40–48 ka). Again, we suggest that such results should be regarded as suspicious and only minimum ages. Subsequent OSL and U/Th (teeth) dating provide complimentary results and demonstrate that the faunal sequences actually span ~120–83 ka, thus occurring beyond the AMS 14C dating window. Importantly, the dates suggest that the local decline in biological diversity was initiated ~75,000 years before the colonisation of humans on the continent. Collectively, the data are most parsimoniously consistent with a pre-human climate change model for local habitat change and megafauna extinction, but not with a nearly simultaneous extinction of megafauna as required by the human-induced blitzkrieg extinction hypothesis. This study demonstrates the problems inherent in dating deposits that lie near the chronological limits of the radiocarbon dating technique, and highlights the need to cross-check previously-dated archaeological and megafauna deposits within the timeframe of earliest human colonisation and latest megafaunal survival. 相似文献
95.
To achieve environmental sustainability and reduce their vulnerability to oil shocks, countries can develop new energy technologies. Technological advances reduce the cost of structural changes in the energy economy, and thus also increase the political feasibility of such changes. But what explains international variation in the form and quality of energy technology innovation? We build on previous theories and offer an integrated account: increasing oil prices reinforce existing sectoral innovation systems, both politically and economically, thus allowing public policymakers and private entrepreneurs to profitably invest in new energy technologies. We test this theoretical argument against data on public R&D expenditures and patents in the domain of renewable energy technology for industrialized countries from 1989 to 2007. We find strong support for the interactive hypothesis. Thus, we contribute to literatures on (i) domestic responses to international shocks, (ii) environmental sustainability and energy security, and (iii) the political economy of technology innovation. 相似文献
96.
97.
Esther Salazar Dorit Hammerling Xia Wang Bruno Sansó Andrew O. Finley Linda O. Mearns 《Climatic change》2016,138(1-2):55-69
We consider the problem of projecting future climate from ensembles of regional climate model (RCM) simulations using results from the North American Regional Climate Change Assessment Program (NARCCAP). To this end, we develop a hierarchical Bayesian space-time model that quantifies the discrepancies between different members of an ensemble of RCMs corresponding to present day conditions, and observational records. Discrepancies are then propagated into the future to obtain high resolution blended projections of 21st century climate. In addition to blended projections, the proposed method provides location-dependent comparisons between the different simulations by estimating the different modes of spatial variability, and using the climate model-specific coefficients of the spatial factors for comparisons. The approach has the flexibility to provide projections at customizable scales of potential interest to stakeholders while accounting for the uncertainties associated with projections at these scales based on a comprehensive statistical framework. We demonstrate the methodology with simulations from the Weather Research & Forecasting regional model (WRF) using three different boundary conditions. We use simulations for two time periods: current climate conditions, covering 1971 to 2000, and future climate conditions under the Special Report on Emissions Scenarios (SRES) A2 emissions scenario, covering 2041 to 2070. We investigate and project yearly mean summer and winter temperatures for a domain in the South West of the United States. 相似文献
98.
99.
100.