全文获取类型
收费全文 | 78358篇 |
免费 | 1569篇 |
国内免费 | 916篇 |
专业分类
测绘学 | 1857篇 |
大气科学 | 5285篇 |
地球物理 | 16401篇 |
地质学 | 28756篇 |
海洋学 | 7128篇 |
天文学 | 17279篇 |
综合类 | 400篇 |
自然地理 | 3737篇 |
出版年
2022年 | 580篇 |
2021年 | 912篇 |
2020年 | 1007篇 |
2019年 | 1085篇 |
2018年 | 2789篇 |
2017年 | 2520篇 |
2016年 | 2716篇 |
2015年 | 1353篇 |
2014年 | 2339篇 |
2013年 | 3989篇 |
2012年 | 3177篇 |
2011年 | 3671篇 |
2010年 | 3046篇 |
2009年 | 3794篇 |
2008年 | 3399篇 |
2007年 | 3511篇 |
2006年 | 3193篇 |
2005年 | 3025篇 |
2004年 | 3031篇 |
2003年 | 2681篇 |
2002年 | 1956篇 |
2001年 | 1743篇 |
2000年 | 1592篇 |
1999年 | 1292篇 |
1998年 | 1232篇 |
1997年 | 1269篇 |
1996年 | 1063篇 |
1995年 | 978篇 |
1994年 | 875篇 |
1993年 | 777篇 |
1992年 | 781篇 |
1991年 | 763篇 |
1990年 | 808篇 |
1989年 | 687篇 |
1988年 | 658篇 |
1987年 | 701篇 |
1986年 | 630篇 |
1985年 | 837篇 |
1984年 | 891篇 |
1983年 | 864篇 |
1982年 | 807篇 |
1981年 | 724篇 |
1980年 | 696篇 |
1979年 | 622篇 |
1978年 | 668篇 |
1977年 | 564篇 |
1976年 | 517篇 |
1975年 | 524篇 |
1974年 | 519篇 |
1973年 | 544篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
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
162.
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
163.
A very long series of photographic observations of the comet Hale-Bopp has been made during January–April 1997 at the double
astrograph (400/2000) of the Main Astronomical Observatory (Kyiv, Ukraine). Some of the cometary photos were obtained with
two wide-band filter combinations. One of these combinations isolates C2 emission, another — the nearby dust continuum. The images were digitized by means of AMDPH-XY machine and then calibrated
following the standard procedure. After subtraction of the dust continuum the distribution of surface brightness in the C2 emission coma of comet Hale-Bopp was studied. We found an asymmetric brightness distribution both pre- and post-perihelion.
On 21.77 April 1997 a secondary brightness peak is found at the distance of 1.03 × 105 km from the nucleus. It is possible that this peak is related to the extended source of the C2 molecules.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
164.
165.
The distribution of perihelion distances of nearly periodic comets was studied using different assumptions about comet discovery probabilities. It was shown that the concentration of perihelia at small heliocentric distances cannot be explained solely by the influence of visibility conditions. 相似文献
166.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
167.
The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical 'slab window' which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment. 相似文献
168.
169.
Perspectives for the Radio-Optical Telescope 54/32/2.6 are given for scientific research in radioastronomy. Its characteristics and potential scientific fields are summarized in the frame of the present French-Armenian collaboration. A 3-phase upgrade plan including a detailed technical evaluation of the antenna is presented.Published in Astrofizika, Vol. 38, No. 4, pp. 645–648, October–December, 1995. 相似文献
170.
G. Cevolani G. Bortolotti L. Foschini C. Franceschi G. Grassi G. Trivellone A. Hajduk V. Porubčan 《Earth, Moon, and Planets》1995,68(1-3):247-255
Continuous radio-wave monitoring of the Geminid activity in December 1992 and 1993 by using a forward scatter (FS) bistatic radar over the Bologna-Lecce baseline (700 km) in Italy, reveals peculiar structural aspects of the stream in terms of signal amplitude-rate and duration-rate dependence. The observational results of the Geminid display obtained in the two consecutive years with differentiated peak levels of transmitted power, exhibit different time distributions of underdense meteors against the signal received power. Both sets of the data relative to the peak activity in December 12–14, show reflection properties of Geminids which are atypical if compared with echoes from cometary-type showers, with really high echo counts at mid-upper levels of the peak received power. An assymmetric curve of activity of the Geminids complex is evidenced, with the peak flux of smaller particles occurring earlier than that of larger ones. 相似文献