全文获取类型
| 收费全文 | 41375篇 |
| 免费 | 6884篇 |
| 国内免费 | 8812篇 |
专业分类
| 测绘学 | 3823篇 |
| 大气科学 | 5529篇 |
| 地球物理 | 7478篇 |
| 地质学 | 21426篇 |
| 海洋学 | 5556篇 |
| 天文学 | 3484篇 |
| 综合类 | 2799篇 |
| 自然地理 | 6976篇 |
出版年
| 2024年 | 167篇 |
| 2023年 | 538篇 |
| 2022年 | 1378篇 |
| 2021年 | 1590篇 |
| 2020年 | 1512篇 |
| 2019年 | 1929篇 |
| 2018年 | 1379篇 |
| 2017年 | 1626篇 |
| 2016年 | 1656篇 |
| 2015年 | 1844篇 |
| 2014年 | 2359篇 |
| 2013年 | 2427篇 |
| 2012年 | 2494篇 |
| 2011年 | 2641篇 |
| 2010年 | 2282篇 |
| 2009年 | 2824篇 |
| 2008年 | 2754篇 |
| 2007年 | 2858篇 |
| 2006年 | 2768篇 |
| 2005年 | 2591篇 |
| 2004年 | 2260篇 |
| 2003年 | 2153篇 |
| 2002年 | 1836篇 |
| 2001年 | 1642篇 |
| 2000年 | 1645篇 |
| 1999年 | 1445篇 |
| 1998年 | 1239篇 |
| 1997年 | 945篇 |
| 1996年 | 792篇 |
| 1995年 | 667篇 |
| 1994年 | 629篇 |
| 1993年 | 520篇 |
| 1992年 | 411篇 |
| 1991年 | 331篇 |
| 1990年 | 232篇 |
| 1989年 | 181篇 |
| 1988年 | 144篇 |
| 1987年 | 86篇 |
| 1986年 | 61篇 |
| 1985年 | 51篇 |
| 1984年 | 29篇 |
| 1983年 | 32篇 |
| 1982年 | 22篇 |
| 1981年 | 17篇 |
| 1980年 | 11篇 |
| 1979年 | 6篇 |
| 1978年 | 22篇 |
| 1977年 | 6篇 |
| 1976年 | 5篇 |
| 1954年 | 7篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
91.
92.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
93.
V. Castellani S. Degl'Innocenti P. G. Prada Moroni 《Monthly notices of the Royal Astronomical Society》2001,320(1):66-72
We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy. 相似文献
94.
95.
96.
We report on a year's study of spatial and seasonal patterns of zooplankton abundance in Port Phillip and Westernport Bays, July 1982 to August 1983. These two bays, closely adjacent on the southern coast of Victoria, Australia, differ in several respects: Port Phillip is a nearly landlocked bay with a broad basin, while Westernport is an open tidal embayment with extensive mud and seagrass banks. Both bays have a resident zooplankton fauna distinct from that of Bass Strait. Although these resident communities have many species in common, patterns of abundance and dominance are quite different. We found that the holoplankton of Port Phillip was about half copepods, mostly Paracalanus indicus, with 23% Caldocera and 21% larvaceans. Westernport Bay zooplankton was dominated by Acartia tranteri, with no resident cladoceran fauna. Bass Strait species were more often found in Westernport than in Port Phillip Bay, but the resident community of Port Phillip Bay was more similar to that of Bass Strait than to that of Westernport.Although this study was undertaken in an exceptionally dry year, the available historical data show that the overall patterns found in 1982–1983 are typical for these bays. The differences in community composition probably relate to differences in depth profile, predator abundance, and suspended matter between the bays. 相似文献
97.
Sunetra Giridhar N. Kameswara Rao David L. Lambert 《Journal of Astrophysics and Astronomy》1996,17(1-2):23-40
Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines
show a radial velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission components to some CII lines present
in 1989 are almost entirely absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII] appear unchanged from 1989 to
1992 相似文献
98.
位于华南褶皱带南缘的右江盆地,其发展可分为两个不同的阶段。它的轮廓和结构,与NW向及NE向同沉积断裂关系密切。盆地内的沉积物,分别由特征不同的非补偿性和补偿性沉积相组成两个双层结构。盆地内火山活动发育,也明显的分为两个阶段。海西期,古特提斯洋的发展使哀牢山洋盆开裂,导致了右江地区在拉张应力条件下出现若干NW向裂陷带,这时的盆地具有大陆边缘裂谷特点。东吴运动后开始的印支期,区域应力条件发生变化。滨大平洋构造的发生,使盆地轮廓和结构发生明显变化,与此同时开始的哀牢山洋盆向NE方向的俯冲消减作用,使盆地在新的挤压条件下再次发生张裂和拗陷。进入了弧后盆地发展阶段。印支期末,盆地封闭。 相似文献
99.
李新生 《地球科学与环境学报》1993,(Z2)
本文首先简述了斜坡演化过程与构造运动的关系,然后阐明了滑坡的空间分布、活动周期及活动规模与构造因素的联系。在此基础上指出:构造因素是滑坡产生的基础,对滑坡分布具宏观控制作用,并与滑坡的活动周期和活动规模密切相关,是滑坡研究及其灾害预测、预防研究工作中值得重视的重要因素。 相似文献
100.