全文获取类型
收费全文 | 60504篇 |
免费 | 5088篇 |
国内免费 | 6614篇 |
专业分类
测绘学 | 2107篇 |
大气科学 | 8312篇 |
地球物理 | 13014篇 |
地质学 | 28506篇 |
海洋学 | 5165篇 |
天文学 | 7566篇 |
综合类 | 3202篇 |
自然地理 | 4334篇 |
出版年
2024年 | 73篇 |
2023年 | 423篇 |
2022年 | 1154篇 |
2021年 | 1281篇 |
2020年 | 1103篇 |
2019年 | 1255篇 |
2018年 | 4876篇 |
2017年 | 4543篇 |
2016年 | 3569篇 |
2015年 | 1550篇 |
2014年 | 1957篇 |
2013年 | 2034篇 |
2012年 | 2845篇 |
2011年 | 4737篇 |
2010年 | 4589篇 |
2009年 | 4715篇 |
2008年 | 3912篇 |
2007年 | 4529篇 |
2006年 | 1539篇 |
2005年 | 1775篇 |
2004年 | 1508篇 |
2003年 | 1608篇 |
2002年 | 1276篇 |
2001年 | 994篇 |
2000年 | 1217篇 |
1999年 | 1613篇 |
1998年 | 1340篇 |
1997年 | 1333篇 |
1996年 | 1207篇 |
1995年 | 1045篇 |
1994年 | 955篇 |
1993年 | 834篇 |
1992年 | 647篇 |
1991年 | 554篇 |
1990年 | 421篇 |
1989年 | 411篇 |
1988年 | 357篇 |
1987年 | 307篇 |
1986年 | 255篇 |
1985年 | 206篇 |
1984年 | 179篇 |
1983年 | 162篇 |
1982年 | 183篇 |
1981年 | 167篇 |
1980年 | 131篇 |
1979年 | 113篇 |
1977年 | 72篇 |
1976年 | 78篇 |
1975年 | 60篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
21.
A spectacular change in the lower corona on the south-west limb has been found in solar images taken by the Yohkoh soft X-ray telescope. The event is characterized by a large topological change in magnetic field and a large intensity decrease observed after the X1. 1/1B flare on 9 November, 1991. A coronal mass ejection (CME) was observed by the Mark III K-coronameter (MK3) at the HAO/Mauna Loa Observatory. Both the MK3 (white-light) and soft X-ray observations showed that one leg of this CME was located above the flare site. An interplanetary shock associated with this event was observed by Pioneer Venus Orbiter, and, possibly, by IMP-8.Also Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, U.S.A. 相似文献
22.
E. C. Hopewell M. J. Barlow J. E. Drew Y. C. Unruh Q. A. Parker M. J. Pierce P. A. Crowther C. Knigge S. Phillipps A. A. Zijlstra 《Monthly notices of the Royal Astronomical Society》2005,363(3):857-866
We report the discovery of five massive Wolf–Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission-line stars in the Anglo-Australian Observatory United Kingdom Schmidt Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195–6775 Å spectra of the stars are presented and discussed. A WC9 class is assigned to all five stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near-infrared (NIR) excesses characteristic of hot dust emission (as seen in the great majority of known WC9 stars), we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to seven. Reddenings and distances for all five stars are estimated. 相似文献
23.
24.
张希然 《云南地理环境研究》1990,2(1):72-81
粤东海岸东起闽粤交界的大埕湾,西迄深圳市的大鹏湾,岸线曲折,港湾较多,河溪人海泥沙在潮间带及紧邻5m 等深线以内形成大片海涂,土壤类型多样,以泥质和沙泥质土壤为主;除河口湾的土壤含盐量低外,其余较高;土壤有机质含量中等,钾素较丰富,磷素较低。因地处亚热带南缘,光、热和水资源条件较好,且多数海湾有深入内地的小海湾和潮沟,甚适合发展海水养殖与晒盐,韩江口的义丰河和海门龟头海大闸外等滩地尚有围垦价值。多处海湾潮滩沙土适合作海滨浴场,也有小片滩地红树林适合旅游观赏。 相似文献
25.
B. A. Ivanov 《Solar System Research》2005,39(5):381-409
Multi-ring impact basins have been found on the surfaces of almost all planetary bodies in the Solar system with solid crusts. The details of their formation mechanism are still unclear. We present results of our numerical modeling of the formation of the largest known terrestrial impact craters. The geological and geophysical data on these structures accumulated over many decades are used to place constraints on the parameters of available numerical models with a dual purpose: (i) to choose parameters in available mechanical models for the crustal response of planetary bodies to a large impact and (ii) to use numerical modeling to refine the possible range of original diameters and the morphology of partially eroded terrestrial craters. We present numerical modeling results for the Vredefort, Sudbury, Chicxulub, and Popigai impact craters and compare these results with available geological and geophysical information. 相似文献
26.
Histological study on the ontogeny of the lymphoid organs, kidney, thymus and spleen of Japanese flounder, Paralichthys olivaceus, from hatching to 40 d was carried out. The pronephric kidney duct appeared early in hatching although the primordial haemopoietic
stem cells were observed within a week after hatching. The spleen was first seen after 8d of hatching. The thymus appeared
after 15d, situated near the pronephric kidney. Small lymphoid cells appeared during the later phase of the post-larval stage
in the sequence of thymus, kidney and spleen. During the 40d of observations, there were no distinct inner or outer zones
in thymus and no red or white pulp in spleen. These results suggest that the nonspecific defense immune system plays a very
important role in the early larval stage of Japanese flounder. 相似文献
27.
本文论述了珠穆朗玛峯地区土壤中稀土元素的含量,以及它们在土壤中的分布模式,并发现土壤中稀土元素的含量水平在很大程度上受土壤母质的制约。 相似文献
28.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem. 相似文献
29.
30.