全文获取类型
收费全文 | 1719篇 |
免费 | 102篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 46篇 |
大气科学 | 121篇 |
地球物理 | 455篇 |
地质学 | 700篇 |
海洋学 | 226篇 |
天文学 | 157篇 |
综合类 | 12篇 |
自然地理 | 114篇 |
出版年
2023年 | 6篇 |
2022年 | 20篇 |
2021年 | 38篇 |
2020年 | 35篇 |
2019年 | 40篇 |
2018年 | 67篇 |
2017年 | 80篇 |
2016年 | 96篇 |
2015年 | 83篇 |
2014年 | 88篇 |
2013年 | 105篇 |
2012年 | 93篇 |
2011年 | 129篇 |
2010年 | 98篇 |
2009年 | 125篇 |
2008年 | 107篇 |
2007年 | 87篇 |
2006年 | 73篇 |
2005年 | 57篇 |
2004年 | 69篇 |
2003年 | 48篇 |
2002年 | 31篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 12篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有1831条查询结果,搜索用时 15 毫秒
201.
ABSTRACTThe continuous submission and scaling-up of Nationally Determined Contributions (NDCs) constitutes a key feature of the Paris Agreement. In their NDCs, states propose governance mechanisms for implementation of climate action, in turn distinguishing appropriate roles for the state in climate governance. Clarity on Parties’ suggested roles for the state makes explicit assumptions on the premise of climate policy, in turn contributing to enhanced transparency in negotiations on the scaling-up of NDCs. This also speaks to ongoing debates on roles for the state in climate governance literature. This article identifies the governance mechanisms proposed by states in their NDCs and the roles for the state envisioned by those governance mechanisms, and also examines how cross-national patterns of roles for the state break or converge with conventional patterns of international politics. The analysis shows that states propose a plurality of roles, which to different extents may be complementary or conflictual. We conclude that income, region, and the Annexes under the United Nations Framework Convention on Climate Change (UNFCCC) are important for understanding suggested roles for the state, but that there are nuances to be further explored. We argue that this paper has three key findings: i) a majority of states rely on market mechanisms to implement their NDCs while rules on implementation and assessment of market mechanisms are still an outstanding issue in the negotiations, meaning that resolving this issue will be essential; ii) the process for evaluating and assessing qualitative governance mechanisms needs to be specified; and iii) increased awareness of differing views on the state’s roles makes explicit different perspectives on what constitutes an ambitious and legitimate contribution to combating climate change.Key policy insights
A majority of states (> 75%) envision the state as regulator (creating and strengthening legislation), market facilitator (creating and maintaining market structures), or facilitator (creating more favourable material conditions for climate-friendly behaviour).
Greater awareness of differing views on roles for the state can increase understanding of different perspectives on ambition and legitimacy of contributions, in turn facilitating trust in negotiations.
A distinction between substantive and procedural qualitative governance mechanisms and their function and interaction would facilitate the stocktaking dialogues.
202.
Anna Losiak Eva Maria Wild Leonard Michlmayr Christian Koeberl 《Meteoritics & planetary science》2014,49(3):394-411
Rocks from drill cores LB‐07A (crater fill) and LB‐08A (central uplift) into the Bosumtwi impact crater, Ghana, were analyzed for the presence of the cosmogenic radionuclide 10Be. The aim of the study was to determine the extent to which target rocks of various depths were mixed during the formation of the crater‐filling breccia, and also to detect meteoric water infiltration within the impactite layer. 10Be abundances above background were found in two (out of 24) samples from the LB‐07A core, and in none of five samples from the LB‐08A core. After excluding other possible explanations for an elevated 10Be signal, we conclude that it is most probably due to a preimpact origin of those clasts from target rocks close to the surface. Our results suggest that in‐crater breccias were well mixed during the impact cratering process. In addition, the lack of a 10Be signal within the rocks located very close to the lake sediment–impactite boundary suggests that infiltration of meteoric water below the postimpact crater floor was limited. This may suggest that the infiltration of the meteoric water within the crater takes place not through the aerial pore‐space, but rather through a localized system of fractures. 相似文献
203.
Douglas A. Simons Paola Amico Dietrich Baade Sam Barden Randall Campbell Gert Finger Kirk Gilmore Roland Gredel Paul Hickson Steve Howell Norbert Hubin Andreas Kaufer Ralf Kohley Philip MacQueen Sergej Markelov Mike Merrill Satoshi Miyazaki Hidehiko Nakaya Darragh O'Donoghue Tino Oliva Andrea Richichi Derrick Salmon Ricardo Schmidt Hongjun Su Simon Tulloch Maria Luisa García Vargas R. Mark Wagner Olivier Wiecha Binxun Ye 《Experimental Astronomy》2005,19(1-3):15-44
Results of a survey of instrumentation and detector systems, either currently deployed or planned for use at telescopes larger than 3.5 m, in ground based observatories world-wide, are presented. This survey revealed a number of instrumentation design trends at optical, near, and mid-infrared wavelengths. Some of the most prominent trends include the development of vastly larger optical detector systems (> 109 pixels) than anything built to date, and the frequent use of mosaics of near-infrared detectors – something that was quite rare only a decade ago in astronomy. Some future science applications for detectors are then explored, in an attempt to build a bridge between current detectors and what will be needed to support the research ambitions of astronomers in the future. 相似文献
204.
205.
Josep Maria Trigo-Rodriguez Jeremie Vaubaillon José Luís Ortiz Alberto Castro-Tirado Jordi Llorca Esko Lyytinen Martin Jelínek Antonio de Ugarte Postigo Pablo Santos Sanz Francisco J. Aceituno Castro Albert Sánchez Caso Antonio Bernal González Juan Pastor Erades Francisco Ocaña 《Earth, Moon, and Planets》2005,97(3-4):269-278
Jupiter and Saturn produce important gravitational impulses on meteoroids released by comet 109P/Swift-Tuttle. The meteoroids from this comet once released follow retrograde orbits that during their periodic approaches to these planets (within 1.6 and 0.9 A.U., respectively) are impulsed gaining orbital energy. This perturbation effect is translated into a net inward shift in the node of the perturbed meteoroids. Such geometry with Jupiter occurred in 2004 over a meteoroid trail ejected by this comet during the 1862 A.D. return of the comet to perihelion. In order to study the predicted outburst produced by one-revolution meteoroids, the Spanish Photographic Meteor Network (SPMN) performed an extensive campaign. As a part of this observational effort here are presented 10 accurate meteoroid orbits. We discuss their origin by comparing them with the theoretical orbital elements of the dust trails intercepting the Earth during the 2004 Perseid return. 相似文献
206.
207.
A study of the green corona rotation rate, during the period 1970–1974, confirms that the differential rotation degree varies systematically through a solar cycle and that the corona rotates in an almost rigid manner before sunspot minimum. During the first two years, 1970–1971, the differential rotation degree, characteristic of high solar activity periods is detected. While during the years of declining activity, 1972–1974, a drastic decrease of the differential rotation degree occurs and the green corona rotates almost rigidly, as the coronal holes observed in the same period. These conclusions are valid only for the rotation of coronal features with lifetime of at least one solar rotation. 相似文献
208.
209.
Spline surfaces are interpolated for top of the Dundee Limestone of the central Michigan Basin, USA. The requirement of gridded data render spline functions inappropriate tools for representing many types of geological mapped data. Comparisons are drawn with maps for the same Michigan data based on trend surfaces and spatial filtering. 相似文献
210.
The stable isotope compositions of organic carbon and nitrogen, the contents of organic carbon and nitrogen and C/N ratios for two cores recovered from the Empakai Crater at water depths of 11 and 20 m are used to document climatic changes in northern Tanzania. Eight 14C AMS dates determined on total organic matter (OM) indicate that the sedimentation rate in this lake is about 30 cm/ka for the late Pleistocene to early Holocene period. There are differences in the δ13C values of organic carbon between the two cores, which may be a result of differences in location from the present shoreline and of different water depths. In the deeper-water core the δ13C values show a general downcore decrease to the base of the core with a sharp change to lower values of about 4‰ at a depth of 100 cm (8.7 ka). The general trend of downcore decrease in 13C values can be attributed either to a systematic decrease in the relative proportion of C4 type of OM, owing to an increase in precipitation and change in vegetation cover from grassland to forest, or to utilization of isotopically enriched carbon during photosynthesis. The δ15N values show a general downcore increase with again a sharp change of about 5‰ to lower values at about 8.7 ka. A sharp change of about 5‰ and 4‰ to more depleted values at a depth of 100 cm of both 15N and 13C, respectively, suggests either hiatus or abrupt change in climatic condition from wetter conditions to drier conditions. There is enhanced preservation of OM in the lake as depicted by high mean values of organic carbon and nitrogen at both sites. 相似文献