首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   12589篇
  免费   1022篇
  国内免费   2177篇
测绘学   449篇
大气科学   341篇
地球物理   1399篇
地质学   4231篇
海洋学   2624篇
天文学   5151篇
综合类   688篇
自然地理   905篇
  2024年   46篇
  2023年   106篇
  2022年   266篇
  2021年   294篇
  2020年   342篇
  2019年   432篇
  2018年   344篇
  2017年   322篇
  2016年   357篇
  2015年   389篇
  2014年   627篇
  2013年   723篇
  2012年   694篇
  2011年   852篇
  2010年   859篇
  2009年   1140篇
  2008年   1091篇
  2007年   998篇
  2006年   919篇
  2005年   831篇
  2004年   690篇
  2003年   593篇
  2002年   462篇
  2001年   405篇
  2000年   394篇
  1999年   340篇
  1998年   242篇
  1997年   125篇
  1996年   120篇
  1995年   107篇
  1994年   129篇
  1993年   114篇
  1992年   71篇
  1991年   52篇
  1990年   45篇
  1989年   34篇
  1988年   37篇
  1987年   14篇
  1986年   26篇
  1985年   28篇
  1984年   25篇
  1983年   19篇
  1982年   20篇
  1981年   22篇
  1980年   11篇
  1979年   5篇
  1978年   6篇
  1977年   15篇
  1877年   1篇
  1875年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
93.
94.
95.
地倾斜台站数字化、模拟观测数据频率特性研究   总被引:2,自引:2,他引:0  
分析了四川、云南的部分地倾斜数字化观测与模拟观测资料的特性,从频率范围,周期10天以上的FFT谱特性,固体潮波振幅,相位特征值等方面,论述了地倾斜数字化资料较模拟记录资料的信息组成变化,并对资料的分析与应用进行了初步探讨。  相似文献   
96.
97.
1StrongtideandastronomicalconditionsPartial solar eclipse occurred 4 times in 1964, 1982 and 2000 respectively. Time interval is about 3 Saros periods (one Saros period is 18 years and 10.33~11.33 days). Total lunar eclipse occurred 2 times in 1964 and 2000 respectively and 3 times in 1982. However, there was no lunar eclipse in 1966, 1984 and 2002. It seems that they had similar astro-nomical conditions and the best was in 1982. The studies about the effect of tide on the global climate…  相似文献   
98.
99.
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   
100.
K. Tsiganis  H. Varvoglis 《Icarus》2003,166(1):131-140
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号