全文获取类型
收费全文 | 6820篇 |
免费 | 1216篇 |
国内免费 | 1583篇 |
专业分类
测绘学 | 491篇 |
大气科学 | 1902篇 |
地球物理 | 1466篇 |
地质学 | 2945篇 |
海洋学 | 1008篇 |
天文学 | 874篇 |
综合类 | 354篇 |
自然地理 | 579篇 |
出版年
2024年 | 27篇 |
2023年 | 47篇 |
2022年 | 158篇 |
2021年 | 202篇 |
2020年 | 217篇 |
2019年 | 286篇 |
2018年 | 206篇 |
2017年 | 255篇 |
2016年 | 236篇 |
2015年 | 280篇 |
2014年 | 349篇 |
2013年 | 375篇 |
2012年 | 322篇 |
2011年 | 346篇 |
2010年 | 320篇 |
2009年 | 498篇 |
2008年 | 469篇 |
2007年 | 559篇 |
2006年 | 481篇 |
2005年 | 481篇 |
2004年 | 442篇 |
2003年 | 356篇 |
2002年 | 329篇 |
2001年 | 303篇 |
2000年 | 298篇 |
1999年 | 274篇 |
1998年 | 261篇 |
1997年 | 195篇 |
1996年 | 201篇 |
1995年 | 143篇 |
1994年 | 154篇 |
1993年 | 118篇 |
1992年 | 111篇 |
1991年 | 88篇 |
1990年 | 52篇 |
1989年 | 43篇 |
1988年 | 45篇 |
1987年 | 27篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 14篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有9619条查询结果,搜索用时 171 毫秒
31.
32.
介绍了近年来河外H2O超脉泽的主要观测结果。H2O超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在 Serfert 2星系或低电离核区。至今为止,已有20个星系探测到H2O超脉泽。脉泽辐射的各向同性光度为10~6000L⊙。所有超脉泽星系显示出核的活动,显然,脉泽是由核活动所产生的射电和X射线光子或激波来抽运的。H2O超脉泽倾向存在于高倾斜度的星系,这使得沿视线上的分子柱密度增高,产生足够大的放大光深。最有可能产生H2O超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。 相似文献
33.
L. I. Matveenko 《Astronomy Letters》2001,27(11):686-690
The core (injector) and the jet (relativistic plasma outflow) of AGN objects are surrounded by an ionized medium, an H II region observed in emission lines. The synchrotron radiation from the core and the jet is observed through a thin screen that cocoons the structure under consideration. The screen transparency depends on wavelength and distance from the injector. We consider the objects 3C 345 and 1803+784 whose core emission at decimeter wavelengths is absorption by more than 25 dB. The visible bright compact component is the bright nearby portion of the jet that extends outside the dense part of the screen. We explore the possibility of measuring the screen transparency from absorption in Hα recombination lines with different quantum numbers at centimeter wavelengths. 相似文献
34.
35.
I.A. Crawford 《Astrophysics and Space Science》2003,285(3-4):661-675
I review the recent discoveries of variable interstellar absorption lines, widely taken to imply the existence of very small
scale(10–100 AU) structure in the interstellar medium. Possible origins of this structure are discussed, and attention is
drawn to the fact that most known examples seem to be associated with interstellar shells and bubbles of various kinds. On
the other hand, in at least one case (κ Velorum),the variation appears to occur in the supposedly quiescent cold neutral medium,
consistent with earlier studies of small scale structure in atomic hydrogen probed at radio wavelengths. Further work is urgently
required to determine the prevalence, mode of formation, and the physical and chemical state of these enigmatic structures.
Only then will their implications for our wider understanding of the interstellar medium become apparent.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
36.
37.
1IntroductionOne of the key factors related to basin geody-namics is deep process controlling formation and evolution of sedimentary basin. Depth and tempera-ture of asthenosphere,existence of mantle plume,occurrence of mantle melting,and amounts of melts under depressurization during thinning of lithosphere are controlling factors influenced formation and characteristics of extensional basin directly (Li,1994). Rifting is probably governed by frictional forces exerted on the base of litho… 相似文献
38.
M. T. Murphy S. J. Curran J. K. Webb 《Monthly notices of the Royal Astronomical Society》2003,342(3):830-836
We describe initial results of a search for redshifted molecular absorption towards four millimetre-loud, optically faint quasars. A wide frequency bandwidth of up to 23 GHz per quasar was scanned using the Swedish–ESO Submillimetre Telescope at La Silla. Using a search list of commonly detected molecules, we obtained nearly complete redshift coverage up to z abs = 5 . The sensitivity of our data is adequate to have revealed absorption systems with characteristics similar to those seen in the four known redshifted millimetre-band absorption systems, but none were found. Our frequency-scan technique nevertheless demonstrates the value of wide-band correlator instruments for searches such as these. We suggest that a somewhat larger sample of similar observations should lead to the discovery of new millimetre-band absorption systems. 相似文献
39.
40.