全文获取类型
收费全文 | 76049篇 |
免费 | 765篇 |
国内免费 | 478篇 |
专业分类
测绘学 | 1939篇 |
大气科学 | 4854篇 |
地球物理 | 14158篇 |
地质学 | 30387篇 |
海洋学 | 6298篇 |
天文学 | 16156篇 |
综合类 | 296篇 |
自然地理 | 3204篇 |
出版年
2022年 | 570篇 |
2021年 | 872篇 |
2020年 | 941篇 |
2019年 | 996篇 |
2018年 | 4199篇 |
2017年 | 3761篇 |
2016年 | 3277篇 |
2015年 | 1104篇 |
2014年 | 2028篇 |
2013年 | 3308篇 |
2012年 | 2951篇 |
2011年 | 4651篇 |
2010年 | 4067篇 |
2009年 | 4696篇 |
2008年 | 3971篇 |
2007年 | 4558篇 |
2006年 | 2691篇 |
2005年 | 1848篇 |
2004年 | 1775篇 |
2003年 | 1767篇 |
2002年 | 1633篇 |
2001年 | 1410篇 |
2000年 | 1273篇 |
1999年 | 920篇 |
1998年 | 905篇 |
1997年 | 1001篇 |
1996年 | 756篇 |
1995年 | 789篇 |
1994年 | 759篇 |
1993年 | 636篇 |
1992年 | 635篇 |
1991年 | 616篇 |
1990年 | 665篇 |
1989年 | 590篇 |
1988年 | 568篇 |
1987年 | 596篇 |
1986年 | 491篇 |
1985年 | 687篇 |
1984年 | 687篇 |
1983年 | 701篇 |
1982年 | 666篇 |
1981年 | 591篇 |
1980年 | 650篇 |
1979年 | 504篇 |
1978年 | 519篇 |
1977年 | 474篇 |
1976年 | 433篇 |
1975年 | 431篇 |
1974年 | 429篇 |
1973年 | 431篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
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
153.
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
154.
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
155.
156.
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
157.
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
158.
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
159.
R. Vílchez-Gómex G. A. Bruzual R. Pelló R. Domínguez 《Astrophysics and Space Science》2001,276(2-4):757-764
We have developed model predictions for the morphological distribution of cluster galaxies as a function of the cluster-centric
distance and the local galaxy density, using a semi-analytical code. This code allows us to obtain magnitudes and colours
for cluster galaxies at different redshifts, and thus to study in detail the evolution of the colour–magnitude relation of
specific distant clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
160.