全文获取类型
收费全文 | 4768篇 |
免费 | 669篇 |
国内免费 | 889篇 |
专业分类
测绘学 | 234篇 |
大气科学 | 781篇 |
地球物理 | 1930篇 |
地质学 | 1790篇 |
海洋学 | 425篇 |
天文学 | 635篇 |
综合类 | 228篇 |
自然地理 | 303篇 |
出版年
2023年 | 61篇 |
2022年 | 139篇 |
2021年 | 172篇 |
2020年 | 161篇 |
2019年 | 146篇 |
2018年 | 182篇 |
2017年 | 204篇 |
2016年 | 228篇 |
2015年 | 222篇 |
2014年 | 228篇 |
2013年 | 249篇 |
2012年 | 177篇 |
2011年 | 220篇 |
2010年 | 219篇 |
2009年 | 196篇 |
2008年 | 177篇 |
2007年 | 175篇 |
2006年 | 151篇 |
2005年 | 136篇 |
2004年 | 134篇 |
2003年 | 163篇 |
2002年 | 180篇 |
2001年 | 182篇 |
2000年 | 136篇 |
1999年 | 153篇 |
1998年 | 116篇 |
1997年 | 135篇 |
1996年 | 130篇 |
1995年 | 97篇 |
1994年 | 113篇 |
1993年 | 84篇 |
1992年 | 82篇 |
1991年 | 59篇 |
1990年 | 56篇 |
1989年 | 61篇 |
1988年 | 65篇 |
1987年 | 56篇 |
1986年 | 49篇 |
1985年 | 34篇 |
1984年 | 49篇 |
1983年 | 42篇 |
1982年 | 42篇 |
1981年 | 36篇 |
1979年 | 44篇 |
1978年 | 36篇 |
1977年 | 34篇 |
1975年 | 34篇 |
1973年 | 38篇 |
1972年 | 33篇 |
1971年 | 38篇 |
排序方式: 共有6326条查询结果,搜索用时 78 毫秒
21.
Mass heterogeneities and convection in the earth's mantle inferred from gravity and core-mantle boundary irregularities 总被引:1,自引:0,他引:1
Mass heterogeneities in the earth's mantle are retrieved from the gravity data and the topography of the core-mantle boundary as well as the topography of the earth's surface. A mantle circulation induced by the heterogeneities is modelled by solving the Stokes problem for incompressible Newtonian fluid. The derived models of mantle motions correlate well with the plate tectonics and point at a close relation between the surface tectonic activity and the processes in the vicinity of the core-mantle boundary. 相似文献
22.
Vladmír Skalský 《Astrophysics and Space Science》1991,181(2):313-322
The Friedmannian model of the Universe with ultra-relativistic equation of statep=–1/3 withk=0 is nondecelerative, i.e., it expands with the constant velocityv=c during the whole expanding phase of evolution of the Universe. The ultrastable nondecelerative model is the only model of the Universe which fulfills all conditions resulting from the quantum-mechanical and relativistic analysis of the Universe. 相似文献
23.
Jan Palouš 《Astrophysics and Space Science》1986,128(1):151-156
The relation between molecular clouds, star clusters, and the stellar component of the galactic disk is investigated. According to Elmegreen (1985) bound stellar systems, e.g., open star clusters, can be formed from molecular cloud of mass 104
M
. A close encounter with a giant molecular cloud or massive black hole disrupts such stellar systems and forms superclusters. This explains why some open star clusters are so mass-deficient. Unbound stellar systems, e.g., expanding OB associations, are formed from molecular clouds of mass 105
M
. When disruptive O-type stars appear the star formation is halted and the cloud is destroyed. An example of the relict of GMC disruption in the solar vicinity is Gould's belt. The velocity dispersion-versus-age relation is also investigated and explained as a consequence of gravitational scattering of stars on GMC, or massive black holes, or as due to recurrent transient spirals.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986. 相似文献
24.
25.
The analytic construction of the direct periodic orbits in the circular 3-body problem is given in explicit form to the linear terms in . It is shown to be in good agreement with the numerically found orbits for large values of . 相似文献
26.
On the coronograph spectrophotographic records taken on 31.372 UT, August 1979, some faint emission features were found which can be ascribed to Siii and Niii. These emissions were obviously a transient phenomena which were detected only 10 hr after the supposed fall of Comet 1979 XI in the Sun's photosphere. It cannot be excluded that the appearance of Si and Ni lines was triggered by the evaporation of dust particles with a high abundance of heavier elements in the solar corona. This assumption is also supported by intensity distribution of the Fex coronal line around the Sun's limb. The maximum coincide with the position angle of the projected path of the comet. 相似文献
27.
The largest karst cave discovered in a tunnel during motorway construction in Slovenia’s Classical Karst (Kras) 总被引:1,自引:0,他引:1
Karst researchers of the Karst Research Institute ZRC SAZU are regularly consulted during the planning of Slovenia’s motorways
and invited to observe and monitor construction in the karst areas. More than 350 caves have been discovered in the course
of building 60 km of new motorways over the past decade. Access to the most important caves is preserved by concrete tubes
closed with metal covers at the roadside. The largest cave system in a tunnel, named LC-S647, is almost entirely preserved.
The protection of this cave will serve as a good example for the preservation of natural heritage in the future. Construction
work for the motorway uncovered a high degree of karstification. In particular, the discovery of this cave in the Kastelec
tunnel LC-S647 showed the existence of a major cave system in the geological and speleological past. A number of unconnected
passages have also been found. Caves discovered during highway construction have brought new knowledge about the cavernosity
and the geological history of this part of the karst. 相似文献
28.
Huijun Jin Zhi Wei Shaoling Wang Qihao Yu Lanzhi Lü Qingbai Wu Yanjun Ji 《Engineering Geology》2008,101(3-4):96-109
The Qinghai–Tibet Highway and Railway (the Corridor) across the Qinghai–Tibet Plateau traverses 670 km of permafrost and seasonally frozen-ground in the interior of the Plateau, which is sensitive to climatic and anthropogenic environmental changes. The frozen-ground conditions for engineering geology along the Corridor is complicated by the variability in the near-surface lithology, and the mosaic presence of warm permafrost and talik in a periglacial environment. Differential settlement is the major frost-effect problem encountered over permafrost areas. The traditional classification of frozen ground based on the areal distribution of permafrost is too generalized for engineering purposes and a more refined classification is necessary for engineering design and construction. A proposed classification of 51 zones, sub-zones, and sections of frozen ground has been widely adopted for the design and construction of foundations in the portion of the Corridor studied. The mean annual ground temperature (MAGT), near-surface soil types and moisture content, and active faults and topography are most commonly the primary controlling factors in this classification. However, other factors, such as local microreliefs, drainage conditions, and snow and vegetation covers also exert important influences on the features of frozen ground. About 60% of the total length of the Corridor studied possesses reasonably good frozen-ground conditions, which do not need special mitigative measures for frost hazards. However, other sections, such as warm and ice-rich or -saturated permafrost, particularly in the sections in wetlands, ground improvement measures such as elevated land bridges and passive or proactive cooling techniques need to be applied to ensure the long-term stability of thermally unstable, thick permafrost subsoils, and/or refill with non-frost-susceptible soils. Due to the long-history of the construction and management of the Corridor by various government departments, adverse impacts of construction and operation on the permafrost environment have been resulted. It is recommended that an integrated, executable plan for the routing of major construction projects within this transportation corridor be established and long-term monitoring networks installed for evaluating and mitigating the impact from anthropogenic and climatic changes in frozen-ground conditions. 相似文献
29.
30.