全文获取类型
收费全文 | 6131篇 |
免费 | 78篇 |
国内免费 | 164篇 |
专业分类
测绘学 | 44篇 |
大气科学 | 1055篇 |
地球物理 | 1390篇 |
地质学 | 3512篇 |
海洋学 | 67篇 |
天文学 | 158篇 |
综合类 | 43篇 |
自然地理 | 104篇 |
出版年
2013年 | 70篇 |
2011年 | 66篇 |
2010年 | 57篇 |
2009年 | 74篇 |
2006年 | 90篇 |
2005年 | 99篇 |
2004年 | 127篇 |
2003年 | 73篇 |
1999年 | 46篇 |
1997年 | 48篇 |
1996年 | 84篇 |
1995年 | 49篇 |
1994年 | 51篇 |
1993年 | 69篇 |
1992年 | 159篇 |
1991年 | 160篇 |
1990年 | 143篇 |
1989年 | 146篇 |
1988年 | 138篇 |
1987年 | 176篇 |
1986年 | 129篇 |
1985年 | 118篇 |
1984年 | 153篇 |
1983年 | 168篇 |
1982年 | 185篇 |
1981年 | 183篇 |
1980年 | 152篇 |
1979年 | 189篇 |
1978年 | 162篇 |
1977年 | 154篇 |
1976年 | 119篇 |
1975年 | 139篇 |
1974年 | 125篇 |
1973年 | 141篇 |
1972年 | 129篇 |
1971年 | 137篇 |
1970年 | 144篇 |
1969年 | 100篇 |
1968年 | 130篇 |
1967年 | 123篇 |
1966年 | 85篇 |
1965年 | 96篇 |
1964年 | 100篇 |
1963年 | 44篇 |
1962年 | 92篇 |
1960年 | 105篇 |
1954年 | 67篇 |
1952年 | 49篇 |
1950年 | 61篇 |
1949年 | 44篇 |
排序方式: 共有6373条查询结果,搜索用时 15 毫秒
1.
2.
Xue-Fei Chen Zhan-Wen HanNational Astronomical Observatories Yunnan Observatory Chinese Academy of Sciences. Kunming Graduate School of the Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(1):65-76
We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the 相似文献
3.
4.
The dunes in estuary of Tumen River in China lie to the area between the Jiushaping and Fangchuan in the left bank of Tumen River (Fig.1). The dis-tance is about 15~20 km between the dunes and the coast. It ranges from China to D. P. R. Korea and Russia. The range of the height of dunes is about 15~20 m and the width is 100~200 m. By the re-connaissance, we protracted 9 section planes of the dunes and collected 40 sand samples of the dunes, and identified the sedimentary environment … 相似文献
5.
Based on the Intensive Field Campaign(IFC-1)data of Boreal Ecosystem-Atmosphere Study(BOREAS).a three-dimensional meso-β scale model is used to simulate the effect of boreal forests onthe lower atmosphere.A fine horizontal resolution of 2 km×2 km is used in order to distinguish thevegetative heterogeneity in the boreal region.A total of 20×25 grid points cover the entire sub-modeling area in BOREAS' South Study Area(SSA).The ecosystem types and their coverage ineach grid square are extracted from the North American Land Cover Characteristics Data Base(NALCCD)generated by the U.S.Geographical Survey(USGS)and the University of Nebraska-Lincoln(UNL).The topography of the study area is taken from the Digital Elevation Map(DEM)of USGS.The model outputs include the components of the energy balance budget within the canopyand at the ground.the turbulence parameters in the atmospheric boundary layer and the wind.temperature and humidity profiles extending up to a height of 1500 m.In addition to the fine timeand spatial step,the unique feature of the present model is the incorporation of both dynamic andbiological effects of the Boreal forest into the model parameterization scheme.The model resultscompare favorably with BOREAS' IFC-1 data in 1994 when the forest was in the luxuriant growingperiod. 相似文献
6.
7.
8.
9.
10.
Dr M. J. Wooller D. L. Swain K. J. Ficken A. D. Q. Agnew F. A. Street-Perrott G. Eglinton 《第四纪科学杂志》2003,18(1):3-15
Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755‐cm‐long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon‐isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the C4 photosynthetic pathway was greater during the Late Pleistocene than in the Holocene. Pollen data show that grasses were a major constituent of the vegetation throughout the Late Pleistocene and Holocene. The proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum (LGM). Grass cuticles confirm evidence that C4 grass taxa were present at the LGM and that the majority followed the cold‐tolerant NADP‐MEC4 subpathway. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献