全文获取类型
收费全文 | 57711篇 |
免费 | 920篇 |
国内免费 | 1159篇 |
专业分类
测绘学 | 2225篇 |
大气科学 | 4486篇 |
地球物理 | 12042篇 |
地质学 | 23453篇 |
海洋学 | 3740篇 |
天文学 | 8526篇 |
综合类 | 2227篇 |
自然地理 | 3091篇 |
出版年
2021年 | 369篇 |
2020年 | 400篇 |
2019年 | 376篇 |
2018年 | 5491篇 |
2017年 | 4776篇 |
2016年 | 3615篇 |
2015年 | 929篇 |
2014年 | 1133篇 |
2013年 | 1894篇 |
2012年 | 2125篇 |
2011年 | 3985篇 |
2010年 | 3184篇 |
2009年 | 3758篇 |
2008年 | 3139篇 |
2007年 | 3542篇 |
2006年 | 1339篇 |
2005年 | 1142篇 |
2004年 | 1327篇 |
2003年 | 1264篇 |
2002年 | 1078篇 |
2001年 | 837篇 |
2000年 | 836篇 |
1999年 | 614篇 |
1998年 | 619篇 |
1997年 | 662篇 |
1996年 | 509篇 |
1995年 | 536篇 |
1994年 | 545篇 |
1993年 | 426篇 |
1992年 | 429篇 |
1991年 | 398篇 |
1990年 | 423篇 |
1989年 | 384篇 |
1988年 | 380篇 |
1987年 | 400篇 |
1986年 | 367篇 |
1985年 | 466篇 |
1984年 | 450篇 |
1983年 | 487篇 |
1982年 | 464篇 |
1981年 | 425篇 |
1980年 | 460篇 |
1979年 | 362篇 |
1978年 | 349篇 |
1977年 | 333篇 |
1976年 | 300篇 |
1975年 | 303篇 |
1974年 | 299篇 |
1973年 | 296篇 |
1971年 | 209篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
P. B. Tissera R. Domínguez-Tenreiro C. Scannapieco A. Sáiz 《Monthly notices of the Royal Astronomical Society》2002,333(2):327-338
We use cosmological smooth particle hydrodynamical (SPH) simulations to study the effects of mergers in the star formation history of galactic objects in hierarchical clustering scenarios. We find that during some merger events, gaseous discs can experience two starbursts: the first one during the orbital decay phase, owing to gas inflows driven as the satellite approaches, and the second one when the two baryonic clumps collide. A trend for these first induced starbursts to be more efficient at transforming the gas into stars is also found. We detect that systems that do not experience early gas inflows have well-formed stellar bulges and more concentrated potential wells, which seem to be responsible for preventing further gas inward transport triggered by tidal forces. The potential wells concentrate owing to the accumulation of baryons in the central regions and of dark matter as the result of the pulling in by baryons. The coupled evolution of the dark matter and baryons would lead to an evolutionary sequence during which systems with shallower total potential wells suffer early gas inflows during the orbital decay phase that help to feed their central mass concentration, pulling in dark matter and contributing to build up more stable systems. Within this scenario, starbursts triggered by early gas inflows are more likely to occur at early stages of evolution of the systems and to be an important contributor to the formation of stellar bulges. Our results constitute the first proof that bulges can form as the product of collapse, collisions and secular evolution in a cosmological framework, and they are consistent with a rejuvenation of the stellar population in bulges at intermediate z with, at least, 50 per cent of the stars (in SCDM) being formed at high z . 相似文献
112.
113.
We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of
these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite
spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that
huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline
silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation
with stellar age only is apparent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
114.
B. D. F. Methley 《The Photogrammetric Record》1994,14(83):793-803
A case is made for the development of an inexpensive and portable data capturing unit which could be used with existing mirror stereoscopes and which could provide an accuracy sufficient for most digital map databases. The results of simulation experiments to test the accuracy of the system are presented. 相似文献
115.
Evaluation of Fluorobenzoate Tracers in Surface Soils 总被引:2,自引:0,他引:2
Dan B. Jaynes 《Ground water》1994,32(4):532-538
116.
117.
118.
119.
J.C. Vega Beltrán W.W. Zeilinger A. Pizzella E.M. Corsini F. Bertola J.G. Funes J.E. Beckman 《Astrophysics and Space Science》2001,276(2-4):1201-1210
In this paper we present the kinematics of the gas and/or the stars of a sample of 20 disc galaxies. We investigate whether there is any relation between the kinematics of the gas and stars and the classical morphological type of the galaxies in the sample. We deduce that, in most of the late-type spirals we have studied, the stars and the ionized gas are moving with virtually circular velocity, except when the spectroscopic slit crosses a bar region. On the other hand, we found in the central parts of early-type disc galaxies a wider variety of different behaviour of stars and gas. We find many possible factors that complicate the classification of the kinematical properties of the galaxies by their morphological type: the presence of counter-rotations (star vs. stars or star vs. gas), misalignment between the different kinematic components present in the galaxy, the presence of a bar structure and its orientation with respect to the line of nodes of the galaxy, and interactions and mergers or external accretion processes are some of the problems we find in the study of the kinematics of a galaxy. 相似文献
120.
Ken Ebisawa Aya Kubota Tsunefumi Mizuno Piotr Życki 《Astrophysics and Space Science》2001,276(1):11-14
The Ultra-luminous Compact X-ray Sources (ULXs)in nearby spiral galaxies and the Galactic super-luminaljet sources sharethe common spectral characteristic that they haveextremely high disk temperatures which cannot be explainedin the framework of the standard accretion disk modelin the Schwarzschild metric. We have calculated an extreme Kerr disk model to examine if the Kerr disk model can instead explain the observed `too hot' accretion disk spectra.We found that the Kerr disk spectrum becomes significantly hardercompared to the Schwarzschild disk only when the disk is highlyinclined.For super-luminal jet sources, which are known to beinclined systems, the Kerr disk model may thuswork if we choose proper values for the black hole angular momentum. For the ULXs, however, the Kerr disk interpretation will be problematic,as is is highly unlikely that their accretion disks are preferentiallyinclined. 相似文献