全文获取类型
| 收费全文 | 7561篇 |
| 免费 | 1406篇 |
| 国内免费 | 1593篇 |
专业分类
| 测绘学 | 103篇 |
| 大气科学 | 564篇 |
| 地球物理 | 1006篇 |
| 地质学 | 5096篇 |
| 海洋学 | 464篇 |
| 天文学 | 2327篇 |
| 综合类 | 346篇 |
| 自然地理 | 654篇 |
出版年
| 2024年 | 24篇 |
| 2023年 | 79篇 |
| 2022年 | 193篇 |
| 2021年 | 189篇 |
| 2020年 | 198篇 |
| 2019年 | 230篇 |
| 2018年 | 208篇 |
| 2017年 | 236篇 |
| 2016年 | 227篇 |
| 2015年 | 265篇 |
| 2014年 | 341篇 |
| 2013年 | 338篇 |
| 2012年 | 412篇 |
| 2011年 | 383篇 |
| 2010年 | 313篇 |
| 2009年 | 617篇 |
| 2008年 | 540篇 |
| 2007年 | 685篇 |
| 2006年 | 626篇 |
| 2005年 | 560篇 |
| 2004年 | 525篇 |
| 2003年 | 487篇 |
| 2002年 | 445篇 |
| 2001年 | 373篇 |
| 2000年 | 344篇 |
| 1999年 | 312篇 |
| 1998年 | 315篇 |
| 1997年 | 189篇 |
| 1996年 | 135篇 |
| 1995年 | 150篇 |
| 1994年 | 133篇 |
| 1993年 | 116篇 |
| 1992年 | 96篇 |
| 1991年 | 64篇 |
| 1990年 | 53篇 |
| 1989年 | 63篇 |
| 1988年 | 38篇 |
| 1987年 | 22篇 |
| 1986年 | 16篇 |
| 1985年 | 5篇 |
| 1984年 | 6篇 |
| 1983年 | 1篇 |
| 1982年 | 1篇 |
| 1981年 | 1篇 |
| 1980年 | 1篇 |
| 1979年 | 1篇 |
| 1978年 | 1篇 |
| 1977年 | 1篇 |
| 1954年 | 2篇 |
排序方式： 共有10000条查询结果，搜索用时 234 毫秒
41.
42.
S. C. Trager Guy Worthey S. M. Faber Alan Dressler 《Monthly notices of the Royal Astronomical Society》2005,362(1):2-8
We present numerical investigations into the formation of massive stars from turbulent cores of density structure ρ∝ r −1.5 . The results of five hydrodynamical simulations are described, following the collapse of the core, fragmentation and the formation of small clusters of protostars. We generate two different initial turbulent velocity fields corresponding to power-law spectra P ∝ k −4 and P ∝ k −3.5 , and we apply two different initial core radii. Calculations are included for both completely isothermal collapse, and a non-isothermal equation of state above a critical density (10−14 g cm−3 ) . Our calculations reveal the preference of fragmentation over monolithic star formation in turbulent cores. Fragmentation was prevalent in all the isothermal cases. Although disc fragmentation was largely suppressed in the non-isothermal runs due to the small dynamic range between the initial density and the critical density, our results show that some fragmentation still persisted. This is inconsistent with previous suggestions that turbulent cores result in the formation of a single massive star. We conclude that turbulence cannot be measured as an isotropic pressure term. 相似文献
43.
44.
45.
46.
47.
48.
Summary. A residual map of the total magnetic field (above 25 000 nT base) is presented for a portion of the central crystalline shield area of Nigeria and overlapping small portions of the Chad basin and the Benue rift (8°30'−12° 00'lat, and 7°−10°30' long). The map (based on a dataset digitized from recently released aeromagnetic sheets of Nigeria) leads to four results. (1) A magnetic boundary, evident on the map, separates the Younger Granite complexes into two groups. The groups are petrologically different, and the boundary may be a fault line with uplift to the south. (2) South of the boundary the map is dominated by a system of sub-parallel anomalies striking NE–SW, possibly representing major tectonic trends, and a set of fractures through which the Younger Granite complexes were intruded. The trend of the system parallels the Benue rift and lineaments in the oceanic crust off West Africa. (3) Negative magnetic anomalies lie over most of the known ring complexes, and over some suspected buried ring complexes and other intrusions. (4) 2½-and 3-D modelling shows that the larger complexes extend to 12 km depth, and the smaller ones to 6 km. They have nearly vertical sides, and magnetization contrasts range from 0.3 to 0.5 A m−1 . 相似文献
49.
陈刘组为新建立的岩石地层单位，代表广西早三叠世盆地滨岸相带沉积类型。层型剖面位于贵港市陈刘村附近。层型定义指位于龙潭组与板纳组之间的沉积序列，岩性为灰绿、紫红色泥岩、粉砂细砂岩夹少量火山岩及碳酸盐岩，含菊石、双壳类、牙形石等化石，厚３５９ｍ。 相似文献
50.
熊耳群为玄武粗安岩-英安流纹岩组合,大红口组为粗面岩组合,属B类的过渡型拉斑玄武岩浆系列,具以太华群为岩浆房的壳幔混染型成因;秦岭群和宽坪群为变拉斑玄武岩建造,属A类拉斑玄武岩浆系列,具幔源型成因;二郎坪群和丹凤群属细碧岩-石英角斑岩建造,C类石英角斑岩浆系列与A类拉斑玄武岩浆系列共存,具壳幔双层混合型成因。 相似文献