全文获取类型
收费全文 | 2890篇 |
免费 | 122篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 107篇 |
大气科学 | 339篇 |
地球物理 | 616篇 |
地质学 | 871篇 |
海洋学 | 325篇 |
天文学 | 540篇 |
综合类 | 4篇 |
自然地理 | 226篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 32篇 |
2020年 | 43篇 |
2019年 | 47篇 |
2018年 | 84篇 |
2017年 | 63篇 |
2016年 | 114篇 |
2015年 | 67篇 |
2014年 | 88篇 |
2013年 | 143篇 |
2012年 | 123篇 |
2011年 | 159篇 |
2010年 | 131篇 |
2009年 | 194篇 |
2008年 | 174篇 |
2007年 | 159篇 |
2006年 | 132篇 |
2005年 | 109篇 |
2004年 | 117篇 |
2003年 | 105篇 |
2002年 | 98篇 |
2001年 | 76篇 |
2000年 | 83篇 |
1999年 | 68篇 |
1998年 | 84篇 |
1997年 | 45篇 |
1996年 | 45篇 |
1995年 | 33篇 |
1994年 | 23篇 |
1993年 | 33篇 |
1992年 | 22篇 |
1991年 | 32篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 26篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1973年 | 8篇 |
1971年 | 7篇 |
排序方式: 共有3028条查询结果,搜索用时 234 毫秒
991.
992.
GPS-derived orbits for the GOCE satellite 总被引:5,自引:4,他引:1
Heike Bock Adrian Jäggi Ulrich Meyer Pieter Visser Jose van den IJssel Tom van Helleputte Markus Heinze Urs Hugentobler 《Journal of Geodesy》2011,85(11):807-818
The first ESA (European Space Agency) Earth explorer core mission GOCE (Gravity field and steady-state Ocean Circulation Explorer)
was launched on 17 March 2009 into a sun-synchronous dusk–dawn orbit with an exceptionally low initial altitude of about 280 km.
The onboard 12-channel dual-frequency GPS (Global Positioning System) receiver delivers 1 Hz data, which provides the basis
for precise orbit determination (POD) for such a very low orbiting satellite. As part of the European GOCE Gravity Consortium
the Astronomical Institute of the University of Bern and the Department of Earth Observation and Space Systems are responsible
for the orbit determination of the GOCE satellite within the GOCE High-level Processing Facility. Both quick-look (rapid)
and very precise orbit solutions are produced with typical latencies of 1 day and 2 weeks, respectively. This article summarizes
the special characteristics of the GOCE GPS data, presents POD results for about 2 months of data, and shows that both latency
and accuracy requirements are met. Satellite Laser Ranging validation shows that an accuracy of 4 and 7 cm is achieved for
the reduced-dynamic and kinematic Rapid Science Orbit solutions, respectively. The validation of the reduced-dynamic and kinematic
Precise Science Orbit solutions is at a level of about 2 cm. 相似文献
993.
A statistical characterization is presented of Global Positioning System (GPS) user range error as a normally distributed
random variable with non-zero mean over the length of the aircraft precision approach operation, correlated from one GPS measurement
epoch to another and from one satellite to another. This leads directly to modeling GPS error in the position domain as multivariate
normal with non-zero mean. Based on this model, a vertical composite protection level VPLc and a horizontal composite protection level HPLc are each calculated as scalar values from a univariate normal distribution displaced from the origin by the worst-case position
domain bias combination possible, given the maximum possible individual satellite bias magnitudes and the satellite geometry.
A method is then presented by which exact values—that is, values accurate to a user-defined error tolerance and consistent
with statistical assumptions—of VPLc and HPLc are obtained, and by which computationally efficient approximations may be evaluated. A statistical quadratic form under
the multivariate normal distribution is used to derive a new class of protection levels based on the probability enclosed
within a radius defined in two or more dimensions. A central Chi-square representation of this quadratic form is also presented
and is incorporated into a six-step computational procedure for the two-dimensional composite radial protection level RPLc. This procedure is extended to the spherical protection level (SPLc) and the ellipsoidal protection level (EPLc). 相似文献
994.
The representative concentration pathways: an overview 总被引:20,自引:4,他引:16
Detlef P. van Vuuren Jae Edmonds Mikiko Kainuma Keywan Riahi Allison Thomson Kathy Hibbard George C. Hurtt Tom Kram Volker Krey Jean-Francois Lamarque Toshihiko Masui Malte Meinshausen Nebojsa Nakicenovic Steven J. Smith Steven K. Rose 《Climatic change》2011,109(1-2):5-31
This paper summarizes the development process and main characteristics of the Representative Concentration Pathways (RCPs), a set of four new pathways developed for the climate modeling community as a basis for long-term and near-term modeling experiments. The four RCPs together span the range of year 2100 radiative forcing values found in the open literature, i.e. from 2.6 to 8.5 W/m2. The RCPs are the product of an innovative collaboration between integrated assessment modelers, climate modelers, terrestrial ecosystem modelers and emission inventory experts. The resulting product forms a comprehensive data set with high spatial and sectoral resolutions for the period extending to 2100. Land use and emissions of air pollutants and greenhouse gases are reported mostly at a 0.5?×?0.5 degree spatial resolution, with air pollutants also provided per sector (for well-mixed gases, a coarser resolution is used). The underlying integrated assessment model outputs for land use, atmospheric emissions and concentration data were harmonized across models and scenarios to ensure consistency with historical observations while preserving individual scenario trends. For most variables, the RCPs cover a wide range of the existing literature. The RCPs are supplemented with extensions (Extended Concentration Pathways, ECPs), which allow climate modeling experiments through the year 2300. The RCPs are an important development in climate research and provide a potential foundation for further research and assessment, including emissions mitigation and impact analysis. 相似文献
995.
Detlef P. van Vuuren Elke Stehfest Michel G. J. den Elzen Tom Kram Jasper van Vliet Sebastiaan Deetman Morna Isaac Kees Klein Goldewijk Andries Hof Angelica Mendoza Beltran Rineke Oostenrijk Bas van Ruijven 《Climatic change》2011,109(1-2):95-116
The RCP2.6 emission and concentration pathway is representative of the literature on mitigation scenarios aiming to limit the increase of global mean temperature to 2°C. These scenarios form the low end of the scenario literature in terms of emissions and radiative forcing. They often show negative emissions from energy use in the second half of the 21st century. The RCP2.6 scenario is shown to be technically feasible in the IMAGE integrated assessment modeling framework from a medium emission baseline scenario, assuming full participation of all countries. Cumulative emissions of greenhouse gases from 2010 to 2100 need to be reduced by 70% compared to a baseline scenario, requiring substantial changes in energy use and emissions of non-CO2 gases. These measures (specifically the use of bio-energy and reforestation measures) also have clear consequences for global land use. Based on the RCP2.6 scenario, recommendations for further research on low emission scenarios have been formulated. These include the response of the climate system to a radiative forcing peak, the ability of society to achieve the required emission reduction rates given political and social inertia and the possibilities to further reduce emissions of non-CO2 gases. 相似文献
996.
Malte Meinshausen S. J. Smith K. Calvin J. S. Daniel M. L. T. Kainuma J-F. Lamarque K. Matsumoto S. A. Montzka S. C. B. Raper K. Riahi A. Thomson G. J. M. Velders D.P. P. van Vuuren 《Climatic change》2011,109(1-2):213-241
We present the greenhouse gas concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs). These projections include all major anthropogenic greenhouse gases and are a result of a multi-year effort to produce new scenarios for climate change research. We combine a suite of atmospheric concentration observations and emissions estimates for greenhouse gases (GHGs) through the historical period (1750?C2005) with harmonized emissions projected by four different Integrated Assessment Models for 2005?C2100. As concentrations are somewhat dependent on the future climate itself (due to climate feedbacks in the carbon and other gas cycles), we emulate median response characteristics of models assessed in the IPCC Fourth Assessment Report using the reduced-complexity carbon cycle climate model MAGICC6. Projected ??best-estimate?? global-mean surface temperature increases (using inter alia a climate sensitivity of 3°C) range from 1.5°C by 2100 for the lowest of the four RCPs, called both RCP3-PD and RCP2.6, to 4.5°C for the highest one, RCP8.5, relative to pre-industrial levels. Beyond 2100, we present the ECPs that are simple extensions of the RCPs, based on the assumption of either smoothly stabilizing concentrations or constant emissions: For example, the lower RCP2.6 pathway represents a strong mitigation scenario and is extended by assuming constant emissions after 2100 (including net negative CO2 emissions), leading to CO2 concentrations returning to 360 ppm by 2300. We also present the GHG concentrations for one supplementary extension, which illustrates the stringent emissions implications of attempting to go back to ECP4.5 concentration levels by 2250 after emissions during the 21st century followed the higher RCP6 scenario. Corresponding radiative forcing values are presented for the RCP and ECPs. 相似文献
997.
A special issue on the RCPs 总被引:2,自引:1,他引:1
998.
Yanina L. Romero J. Bessembinder N. C. van de Giesen F. H. M. van de Ven 《Climatic change》2011,106(3):393-405
The Royal Netherlands Meteorological Institute (KNMI) has published the KNMI’06 climate scenarios in 2006. These scenarios
give the possible states of the climate in The Netherlands for the next century. Projections of changes in precipitation were
made for a time scale of 1 day. The urban drainage sector is, however, more interested in projections on shorter time scales.
Specifically, time scales of 1 h or less. The aim of this research is to provide projections of precipitation at these shorter
time scales based on the available daily scenarios. This involves an analysis of climate variables and their relations to
precipitation at different time scales. On the basis of this analysis, one can determine a numeric factor to translate daily
projections into shorter time scale projections. 相似文献
999.
Exploring high-end scenarios for local sea level rise to develop flood protection strategies for a low-lying delta—the Netherlands as an example 总被引:4,自引:1,他引:3
Caroline A. Katsman A. Sterl J. J. Beersma H. W. van den Brink J. A. Church W. Hazeleger R. E. Kopp D. Kroon J. Kwadijk R. Lammersen J. Lowe M. Oppenheimer H. -P. Plag J. Ridley H. von Storch D. G. Vaughan P. Vellinga L. L. A. Vermeersen R. S. W. van de Wal R. Weisse 《Climatic change》2011,109(3-4):617-645
Sea level rise, especially combined with possible changes in storm surges and increased river discharge resulting from climate change, poses a major threat in low-lying river deltas. In this study we focus on a specific example of such a delta: the Netherlands. To evaluate whether the country’s flood protection strategy is capable of coping with future climate conditions, an assessment of low-probability/high-impact scenarios is conducted, focusing mainly on sea level rise. We develop a plausible high-end scenario of 0.55 to 1.15 m global mean sea level rise, and 0.40 to 1.05 m rise on the coast of the Netherlands by 2100 (excluding land subsidence), and more than three times these local values by 2200. Together with projections for changes in storm surge height and peak river discharge, these scenarios depict a complex, enhanced flood risk for the Dutch delta. 相似文献
1000.
V. Palastanga G. van der Schrier S. L. Weber T. Kleinen K. R. Briffa T. J. Osborn 《Climate Dynamics》2011,36(5-6):973-987
The role of a reduction in the Atlantic meridional overturning and that of a persistently negative North Atlantic Oscillation in explaining the coldness of the European Little Ice Age (LIA) has been assessed in two sets of numerical experiments. These experiments are performed using an intermediate complexity climate model and a full complexity GCM. The reduction in the Meridional Overturning Circulation (MOC) of ca. 25% is triggered by a conventional fresh-water hosing set-up. A persistently negative NAO winter circulation, at NAO-index value ?0.5, is imposed using recently developed data-assimilation techniques applicable on paleoclimatic timescales. The hosing experiments lead to a reduction in oceanic meridional heat transport and cooler sea-surface temperatures. Next to a direct cooling effect on European climate, the change in ocean surface temperatures feedback on the atmospheric circulation modifying European climate significantly. The data-assimilation experiments showed a reduction of winter temperatures over parts of Europe, but there is little persistence into the summer season. The output of all model experiments are compared to reconstructions of winter and summer temperature based on the available temperature data for the LIA period. This demonstrates that the hypothesis of a persistently negative NAO as an explanation for the European LIA does not hold. The hosing experiments do not clearly support the hypothesis that a reduction in the MOC is the primary driver of LIA climate change. However, a reduction in the Atlantic overturning might have been a cause of the European LIA climate, depending on whether there is a strong enough feedback on the atmospheric circulation. 相似文献