全文获取类型
收费全文 | 37641篇 |
免费 | 5787篇 |
国内免费 | 8528篇 |
专业分类
测绘学 | 4688篇 |
大气科学 | 6194篇 |
地球物理 | 8266篇 |
地质学 | 15393篇 |
海洋学 | 5126篇 |
天文学 | 5454篇 |
综合类 | 2428篇 |
自然地理 | 4407篇 |
出版年
2024年 | 127篇 |
2023年 | 368篇 |
2022年 | 1052篇 |
2021年 | 1241篇 |
2020年 | 1459篇 |
2019年 | 1768篇 |
2018年 | 1403篇 |
2017年 | 1645篇 |
2016年 | 1716篇 |
2015年 | 1914篇 |
2014年 | 2291篇 |
2013年 | 2490篇 |
2012年 | 2355篇 |
2011年 | 2626篇 |
2010年 | 2275篇 |
2009年 | 2849篇 |
2008年 | 2873篇 |
2007年 | 2770篇 |
2006年 | 2592篇 |
2005年 | 2266篇 |
2004年 | 1976篇 |
2003年 | 1655篇 |
2002年 | 1484篇 |
2001年 | 1269篇 |
2000年 | 1191篇 |
1999年 | 1071篇 |
1998年 | 934篇 |
1997年 | 741篇 |
1996年 | 658篇 |
1995年 | 557篇 |
1994年 | 528篇 |
1993年 | 472篇 |
1992年 | 275篇 |
1991年 | 235篇 |
1990年 | 169篇 |
1989年 | 138篇 |
1988年 | 128篇 |
1987年 | 67篇 |
1986年 | 53篇 |
1985年 | 61篇 |
1984年 | 47篇 |
1983年 | 19篇 |
1982年 | 29篇 |
1981年 | 16篇 |
1980年 | 23篇 |
1979年 | 12篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 4篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
131.
132.
133.
134.
135.
136.
137.
138.
A palaeotemperature reconstruction based on periglacial phenomena in Europe north of approximately 51 °N, is compared with high‐resolution regional climate model simulations of the marine oxygen isotope Stage 3 (Stage 3) palaeoclimate. The experiments represent Stage 3 warm (interstadial), Stage 3 cold (stadial) and Last Glacial Maximum climatic conditions. The palaeotemperature reconstruction deviates considerably for the Stage 3 cold climate experiments, with mismatches up to 11 °C for the mean annual air temperature and up to 15 °C for the winter temperature. However, in this reconstruction various factors linking climate and permafrost have not been taken into account. In particular a relatively thin snow cover and high climatic variability of the glacial climate could have influenced temperature limits for ice‐wedge growth. Based on modelling the 0 °C mean annual ground temperature proves to be an appropriate upper temperature limit. Using this limit, mismatches with the Stage 3 cold climate experiments have been reduced but still remain. We therefore assume that the Stage 3 ice wedges were generated during short (decadal time‐scale) intervals of extreme cold climate, below the mean temperatures indicated by the Stage 3 cold climate model simulations. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
139.
Ignacio Ferreras Alessandro Melchiorri Domenico Tocchini-Valentini 《Monthly notices of the Royal Astronomical Society》2003,344(1):257-261
The age of the Universe has been increasingly constrained by different techniques, such as the observations of type Ia supernovae (SNIa) at high redshift or dating the stellar populations of globular clusters. In this paper, we present a complementary approach using the colours of the brightest elliptical galaxies in clusters over a wide redshift range ( z ≲ 1) . We put new and independent bounds on the dark energy equation of state parametrized by a constant pressure-to-density ratio w Q and by a parameter (ξ) which determines the scaling between the matter and dark energy densities. We find that accurate estimates of the metallicities of the stellar populations in moderate and high-redshift cluster galaxies can pose stringent constraints on the parameters that describe dark energy. Our results are in good agreement with the analysis of dark energy models using SNIa data as a constraint. Accurate estimates of the metallicities of stellar populations in cluster galaxies at z ≲ 2 will make this approach a powerful complement to studies of cosmological parameters using high-redshift SNIa. 相似文献
140.
Short-lived asteroids in the 7/3 Kirkwood gap and their relationship to the Koronis and Eos families
A population of 23 asteroids is currently observed in a very unstable region of the main belt, the 7/3 Kirkwood gap. The small size of these bodies—with the notable exception of (677) Aaltje (∼30 km)—as well as the computation of their dynamical lifetimes (3<TD<172 Myr) shows that they cannot be on their primordial orbits, but were recently injected in the resonance. The distribution of inclinations appears to be bimodal, the two peaks being close to 2° and 10°. We argue that the resonant population is constantly being replenished by the slow leakage of asteroids from both the Koronis (I∼2°) and Eos (I∼10°) families, due to the drift of their semi-major axes, caused by the Yarkovsky effect. Assuming previously reported values for the Yarkovsky mean drift rate, we calculate the flux of family members needed to sustain the currently observed population in steady state. The number densities with respect to semi-major axis of the observed members of both families are in very good agreement with our calculations. The fact that (677) Aaltje is currently observed in the resonance is most likely an exceptional event. This asteroid should not be genetically related to any of the above families. Its size and the eccentricity of its orbit suggest that the Yarkovsky effect should have been less efficient in transporting this body to the resonance than close encounters with Ceres. 相似文献